Bump packages for open value release

Add unknown ranges and open object values
Bump packages for range refinement release
2026-08-14 08:03:25 +09:00 · 2026-08-14 08:00:22 +09:00 · 2026-08-14 06:29:48 +09:00 · 2026-08-14 06:26:15 +09:00 · 2026-08-13 19:53:38 +09:00 · 2026-08-13 19:45:04 +09:00
154 changed files with 36294 additions and 3659 deletions
@@ -3,3 +3,9 @@
 /.env
 /.yoi
 /result
+node_modules
+/dist
+site/decodal-site/dist
+
+# Astro
+site/decodal-site/.astro
@@ -12,25 +12,221 @@ dependencies = [
 ]

 [[package]]
-name = "decodal"
-version = "0.1.0"
+name = "bitflags"
+version = "1.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a"
+
+[[package]]
+name = "bumpalo"
+version = "3.20.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "72f5acc6cb2ba439de613abc23857ec3d78374d8ed5ac84e9d11336e87da8649"
+
+[[package]]
+name = "cfg-if"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9330f8b2ff13f34540b44e946ef35111825727b38d33286ef986142615121801"
+
+[[package]]
+name = "crossbeam-channel"
+version = "0.5.16"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d85363c37faeca707aef026efa9f3b34d077bce547e48f770770625c6013679e"
 dependencies = [
- "decodal-core",
+ "crossbeam-utils",
 ]

 [[package]]
-name = "decodal-core"
-version = "0.1.0"
+name = "crossbeam-utils"
+version = "0.8.22"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "61803da095bee82a81bb1a452ecc25d3b2f1416d1897eb86430c6159ef717c17"
+
+[[package]]
+name = "decodal"
+version = "0.4.0"
 dependencies = [
+ "decodal-derive",
 "regex",
 ]

+[[package]]
+name = "decodal-cli"
+version = "0.4.0"
+dependencies = [
+ "decodal",
+]
+
+[[package]]
+name = "decodal-derive"
+version = "0.2.0"
+dependencies = [
+ "decodal",
+ "proc-macro2",
+ "quote",
+ "syn 2.0.117",
+]
+
+[[package]]
+name = "decodal-language-service"
+version = "0.4.0"
+dependencies = [
+ "decodal",
+]
+
+[[package]]
+name = "decodal-language-tools"
+version = "0.4.0"
+dependencies = [
+ "decodal",
+ "serde_json",
+ "wasm-bindgen",
+]
+
+[[package]]
+name = "decodal-lsp"
+version = "0.4.0"
+dependencies = [
+ "decodal",
+ "decodal-language-service",
+ "decodal-language-tools",
+ "lsp-server",
+ "lsp-types",
+ "serde_json",
+]
+
+[[package]]
+name = "decodal-wasm"
+version = "0.4.0"
+dependencies = [
+ "decodal",
+ "decodal-language-service",
+ "js-sys",
+ "serde-wasm-bindgen",
+ "serde_json",
+ "wasm-bindgen",
+]
+
+[[package]]
+name = "fluent-uri"
+version = "0.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "17c704e9dbe1ddd863da1e6ff3567795087b1eb201ce80d8fa81162e1516500d"
+dependencies = [
+ "bitflags",
+]
+
+[[package]]
+name = "futures-core"
+version = "0.3.34"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "92d699e522242e69e3003b94ecc1f960f3a5e015aa7c5d7486e65ad01dd94f5e"
+
+[[package]]
+name = "futures-task"
+version = "0.3.34"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cd417de3d1d015fc3bfd2b1ea46dfc7bab72ef86f1cc7cc9c78e728b34a6d1fd"
+
+[[package]]
+name = "futures-util"
+version = "0.3.34"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0d50a92467f8ba5dd6e3ee5d4bd04d73ab2e4e1c44474a0674821dfce14b79bc"
+dependencies = [
+ "futures-core",
+ "futures-task",
+ "pin-project-lite",
+ "slab",
+]
+
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+version = "1.0.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8f42a60cbdf9a97f5d2305f08a87dc4e09308d1276d28c869c684d7777685682"
+
+[[package]]
+name = "js-sys"
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "03d04c30968dffe80775bd4d7fb676131cd04a1fb46d2686dbffbaec2d9dfd31"
+dependencies = [
+ "cfg-if",
+ "futures-util",
+ "wasm-bindgen",
+]
+
+[[package]]
+name = "log"
+version = "0.4.33"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0ceec5bc11778974d1bcb055b18002eba7f4b3518b6a0081b3af5f21666da9ad"
+
+[[package]]
+name = "lsp-server"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3ee25a31f2e571e426eef2896179450cafc7e2f5be00d8a93b1c2d21c0ff7656"
+dependencies = [
+ "crossbeam-channel",
+ "log",
+ "serde",
+ "serde_derive",
+ "serde_json",
+]
+
+[[package]]
+name = "lsp-types"
+version = "0.97.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "53353550a17c04ac46c585feb189c2db82154fc84b79c7a66c96c2c644f66071"
+dependencies = [
+ "bitflags",
+ "fluent-uri",
+ "serde",
+ "serde_json",
+ "serde_repr",
+]
+
 [[package]]
 name = "memchr"
 version = "2.8.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "88904434abc2901f197fe8cc55f0445e7ded921dba5911dad2e2b39b48e663c4"

+[[package]]
+name = "once_cell"
+version = "1.21.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9f7c3e4beb33f85d45ae3e3a1792185706c8e16d043238c593331cc7cd313b50"
+
+[[package]]
+name = "pin-project-lite"
+version = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a89322df9ebe1c1578d689c92318e070967d1042b512afbe49518723f4e6d5cd"
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.106"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8fd00f0bb2e90d81d1044c2b32617f68fcb9fa3bb7640c23e9c748e53fb30934"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.45"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "41f2619966050689382d2b44f664f4bc593e129785a36d6ee376ddf37259b924"
+dependencies = [
+ "proc-macro2",
+]
+
 [[package]]
 name = "regex"
 version = "1.12.4"
@@ -59,3 +255,159 @@ name = "regex-syntax"
 version = "0.8.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d6f6ff9a378485b298a5286656da665ba74413d36db0979633275d2e708145d4"
+
+[[package]]
+name = "rustversion"
+version = "1.0.22"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b39cdef0fa800fc44525c84ccb54a029961a8215f9619753635a9c0d2538d46d"
+
+[[package]]
+name = "serde"
+version = "1.0.228"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9a8e94ea7f378bd32cbbd37198a4a91436180c5bb472411e48b5ec2e2124ae9e"
+dependencies = [
+ "serde_core",
+ "serde_derive",
+]
+
+[[package]]
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+version = "0.6.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8302e169f0eddcc139c70f139d19d6467353af16f9fce27e8c30158036a1e16b"
+dependencies = [
+ "js-sys",
+ "serde",
+ "wasm-bindgen",
+]
+
+[[package]]
+name = "serde_core"
+version = "1.0.228"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "41d385c7d4ca58e59fc732af25c3983b67ac852c1a25000afe1175de458b67ad"
+dependencies = [
+ "serde_derive",
+]
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d540f220d3187173da220f885ab66608367b6574e925011a9353e4badda91d79"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.117",
+]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e8014e44b4736ed0538adeecded0fce2a272f22dc9578a7eb6b2d9993c74cfb9"
+dependencies = [
+ "itoa",
+ "memchr",
+ "serde",
+ "serde_core",
+ "zmij",
+]
+
+[[package]]
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+version = "0.1.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8d3b1629de253c70a0508c3899572da79ca359fdab27c7920ff00406df418906"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 3.0.3",
+]
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+ "quote",
+ "unicode-ident",
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+dependencies = [
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+ "cfg-if",
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+
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@@ -2,12 +2,23 @@
 members = [
  "crates/decodal-core",
  "crates/decodal-cli",
+  "crates/decodal-wasm",
+  "crates/decodal-derive",
+  "crates/decodal-language-tools",
+  "crates/decodal-language-service",
+  "crates/decodal-lsp",
 ]
-resolver = "3"
+exclude = ["editors/tree-sitter-decodal"]
+resolver = "2"

-[profile.release]
-opt-level = "z"
-lto = true
-codegen-units = 1
-strip = true
-panic = "abort"
+[workspace.package]
+version = "0.4.0"
+edition = "2024"
+rust-version = "1.85"
+license = "MIT OR Apache-2.0"
+repository = "https://gitea.hareworks.net/Hare/Decodal"
+readme = "README.md"
+
+[workspace.dependencies]
+serde_json = "1"
+wasm-bindgen = "0.2"
@@ -0,0 +1,173 @@
+                              Apache License
+                        Version 2.0, January 2004
+                     http://www.apache.org/licenses/
+
+TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+1. Definitions.
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+   "You" (or "Your") shall mean an individual or Legal Entity
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+   the conditions stated in this License.
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+5. Submission of Contributions. Unless You explicitly state otherwise,
+   any Contribution intentionally submitted for inclusion in the Work
+   by You to the Licensor shall be under the terms and conditions of
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+6. Trademarks. This License does not grant permission to use the trade
+   names, trademarks, service marks, or product names of the Licensor,
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+8. Limitation of Liability. In no event and under no legal theory,
+   whether in tort (including negligence), contract, or otherwise,
+   unless required by applicable law (such as deliberate and grossly
+   negligent acts) or agreed to in writing, shall any Contributor be
+   liable to You for damages, including any direct, indirect, special,
+   incidental, or consequential damages of any character arising as a
+   result of this License or out of the use or inability to use the
+   Work (including but not limited to damages for loss of goodwill,
+   work stoppage, computer failure or malfunction, or any and all
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+   has been advised of the possibility of such damages.
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+9. Accepting Warranty or Additional Liability. While redistributing
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+   of your accepting any such warranty or additional liability.
+
+END OF TERMS AND CONDITIONS
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Decodal contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
@@ -0,0 +1,109 @@
+# Decodal
+
+Decodal is a small deterministic DSL for describing, composing, validating, and materializing structured data.
+
+It is designed around a lightweight Rust library:
+
+- host-supplied source and structured-value imports through `ImportLoader`
+- shared host environments for production and semantic editor tooling
+- no filesystem access in the library core
+- concrete and abstract values with constraints and defaults
+- asymmetric range refinement with `narrower as wider`
+- homogeneous associative-array schemas with `{...valueSchema}` and object rest constraints
+- the safe top range `Unknown`, which remains abstract until refined, defaulted, or supplied concretely
+- deterministic expression evaluation
+- optional regex support behind a Cargo feature
+- browser playground support through WebAssembly
+
+## Library crate
+
+Embedded hosts should depend on `decodal` and provide imports with an `ImportLoader`.
+
+```toml
+[dependencies]
+decodal = "0.4.0"
+```
+
+## Derive support
+
+For embedded Rust applications, Decodal can generate a schema and typed decoder from a Rust struct with the `derive` feature.
+Map fields marked with `#[decodal(rest)]` receive additional object fields; `BTreeMap<String, Data>` corresponds to `...Unknown`.
+
+```toml
+[dependencies]
+decodal = { version = "0.4.0", features = ["derive"] }
+```
+
+```rust
+use decodal::{Decodal, DecodalDecode, DecodalSchema, Engine};
+
+#[derive(Decodal)]
+struct Service {
+    name: String,
+    #[decodal(gt = 443, default = 8443)]
+    port: i64,
+    #[decodal(rename = "feature.enable", default = true)]
+    feature_enabled: bool,
+}
+```
+
+The derive implements:
+
+- `DecodalSchema`, which produces a `Value` range for `Engine::bind_global`
+- `DecodalDecode`, which converts materialized `Data` into the Rust struct
+
+## CLI
+
+A standalone CLI is kept in this repository as the `decodal-cli` workspace package.
+It builds a `decodal` binary, but it is not the primary crates.io package.
+
+Run a Decodal file from the repository:
+
+```sh
+cargo run -q -p decodal-cli -- examples/advanced/main.dcdl
+```
+
+Enable optional regex support when needed:
+
+```sh
+cargo run -q -p decodal-cli --features regex -- examples/regex/main.dcdl
+```
+
+## Language server
+
+The `decodal-language-service` crate provides transport-independent evaluation and completion, while `decodal-lsp` exposes it through the Language Server Protocol with live semantic diagnostics and document formatting.
+Its library API accepts the same host environment used for production evaluation, so application-defined globals and structured import routing remain available in the editor.
+
+```toml
+[dependencies]
+decodal = "0.4.0"
+decodal-language-service = "0.4.0"
+decodal-lsp = "0.4.0"
+```
+
+Run the default filesystem-backed server from the repository:
+
+```sh
+cargo run -q -p decodal-lsp
+```
+
+Embedded applications can implement `decodal_lsp::LspEnvironment` for their existing `HostEnvironment` and construct it from the `InitializeParams` passed to `decodal_lsp::run_stdio`.
+
+## Web playground
+
+The static documentation site and browser playground live under:
+
+```text
+site/decodal-site/
+```
+
+Browser hosts can use `decodal-wasm`. Its `DecodalLanguageService` accepts JavaScript-owned `globals`, `loadImport`, and `completeImport` callbacks; filesystem and virtual-project policy remain outside the package.
+
+## License
+
+Licensed under either of:
+
+- Apache License, Version 2.0
+- MIT license
+
+at your option.
@@ -0,0 +1,62 @@
+# Releasing Decodal
+
+Run all commands from the repository root. Publishing requires Cargo, npm, and JSR credentials; validation does not.
+
+## Versions
+
+- `decodal-derive`: `0.2.0`
+- Other published Rust crates: `0.4.0`
+- `decodal-wasm` npm/JSR package: `0.3.0`
+- `decodal-codemirror`: `0.3.0`
+
+The npm packages advertise the repository's dual `MIT OR Apache-2.0` license.
+JSR metadata uses the single `MIT` identifier required by its publisher; both license files remain included in every package.
+
+## Validate
+
+```sh
+cargo fmt --check
+cargo test --workspace
+cargo test -p decodal --no-default-features
+cargo clippy --workspace --all-targets -- -D warnings
+cargo clippy -p decodal-wasm --target wasm32-unknown-unknown -- -D warnings
+cargo clippy -p decodal-language-tools --target wasm32-unknown-unknown -- -D warnings
+npm --prefix site/decodal-site run build:wasm
+npm --prefix packages/decodal-codemirror test
+npm --prefix site/decodal-site test
+npm --prefix site/decodal-site run build
+deno check packages/decodal-wasm/mod.ts
+npm pack --dry-run ./packages/decodal-wasm
+deno publish --dry-run --config packages/decodal-wasm/jsr.json
+npm pack --dry-run ./packages/decodal-codemirror
+deno publish --dry-run --config packages/decodal-codemirror/jsr.json
+```
+
+## Publish Rust crates
+
+Publish in dependency order. Wait for each crate to become available in the crates.io index before continuing.
+Run the corresponding command with `--dry-run` immediately before each real publish.
+
+```sh
+cargo publish -p decodal-derive
+cargo publish -p decodal
+cargo publish -p decodal-language-service
+cargo publish -p decodal-language-tools
+cargo publish -p decodal-lsp
+```
+
+`decodal-cli` and the Rust `decodal-wasm` wrapper remain repository-only packages.
+
+## Publish JavaScript packages
+
+The WASM build regenerates and normalizes both committed npm/JSR packages before publishing.
+
+```sh
+npm --prefix site/decodal-site run build:wasm
+npm publish ./packages/decodal-wasm
+deno publish --config packages/decodal-wasm/jsr.json
+npm publish ./packages/decodal-codemirror
+deno publish --config packages/decodal-codemirror/jsr.json
+```
+
+After both registries accept the release, tag the release commit and update the deployed site.
@@ -1,11 +1,23 @@
 [package]
+name = "decodal-cli"
+version.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+repository.workspace = true
+readme.workspace = true
+description = "Command-line interface for the Decodal data description language."
+keywords = ["decodal", "dsl", "config", "cli"]
+categories = ["command-line-utilities", "config"]
+publish = false
+
+[[bin]]
 name = "decodal"
-version = "0.1.0"
-edition = "2024"
+path = "src/main.rs"

 [features]
 default = []
-regex = ["decodal-core/regex"]
+regex = ["decodal/regex"]

 [dependencies]
-decodal-core = { path = "../decodal-core" }
+decodal = { version = "0.4.0", path = "../decodal-core" }
@@ -4,19 +4,28 @@ use std::{
    process::ExitCode,
 };

-use decodal_core::{Data, Diagnostic, DiagnosticKind, Engine, LoadedSource, SourceLoader, Span};
+use decodal::{
+    Data, Diagnostic, DiagnosticKind, Engine, ImportLoader, LoadedImport, SourceId, Span,
+    format_diagnostic_with,
+};
+
+struct SourceInput {
+    key: String,
+    name: String,
+    source: String,
+}

 fn main() -> ExitCode {
    match run() {
        Ok(()) => ExitCode::SUCCESS,
        Err(error) => {
-            print_diagnostic(&error);
+            eprintln!("{error}");
            ExitCode::FAILURE
        }
    }
 }

-fn run() -> Result<(), Diagnostic> {
+fn run() -> Result<(), String> {
    let mut args = env::args().skip(1);
    let first = args.next().unwrap_or_else(|| String::from("--help"));
    match first.as_str() {
@@ -25,7 +34,7 @@ fn run() -> Result<(), Diagnostic> {
            Ok(())
        }
        "--version" | "-V" => {
-            println!("Decodal {}", decodal_core::version());
+            println!("Decodal {}", decodal::version());
            Ok(())
        }
        "check" => {
@@ -51,15 +60,22 @@ fn run() -> Result<(), Diagnostic> {
    }
 }

-fn materialize_path(path: &str) -> Result<Data, Diagnostic> {
-    let root = read_root_source(path)?;
+fn materialize_path(path: &str) -> Result<Data, String> {
+    let root = read_root_source(path).map_err(format_raw_diagnostic)?;
+    let root_name = root.name.clone();
    let mut engine = Engine::new(FsLoader);
-    let module = engine.add_root_source(root.key, root.name, &root.source)?;
-    let value = engine.eval_module(module)?;
-    engine.materialize(&value)
+    let module = engine
+        .add_root_source(root.key, root.name, &root.source)
+        .map_err(|error| format_diagnostic_with_root(&error, &root_name))?;
+    let value = engine
+        .eval_module(module)
+        .map_err(|error| engine.format_diagnostic(&error))?;
+    engine
+        .materialize(&value)
+        .map_err(|error| engine.format_diagnostic(&error))
 }

-fn read_root_source(path: &str) -> Result<LoadedSource, Diagnostic> {
+fn read_root_source(path: &str) -> Result<SourceInput, Diagnostic> {
    if path == "-" {
        use std::io::Read;
        let mut source = String::new();
@@ -72,7 +88,7 @@ fn read_root_source(path: &str) -> Result<LoadedSource, Diagnostic> {
                    format!("failed to read stdin: {error}"),
                )
            })?;
-        Ok(LoadedSource {
+        Ok(SourceInput {
            key: String::from("<stdin>"),
            name: String::from("<stdin>"),
            source,
@@ -85,12 +101,12 @@ fn read_root_source(path: &str) -> Result<LoadedSource, Diagnostic> {
 #[derive(Debug, Clone, Copy)]
 struct FsLoader;

-impl SourceLoader for FsLoader {
+impl ImportLoader for FsLoader {
    fn load(
        &mut self,
        current_key: Option<&str>,
        specifier: &str,
-    ) -> Result<LoadedSource, Diagnostic> {
+    ) -> Result<LoadedImport, Diagnostic> {
        let path = Path::new(specifier);
        let path = if path.is_absolute() {
            PathBuf::from(path)
@@ -102,11 +118,11 @@ impl SourceLoader for FsLoader {
        } else {
            PathBuf::from(path)
        };
-        load_path(&path)
+        load_path(&path).map(|source| LoadedImport::source(source.key, source.name, source.source))
    }
 }

-fn load_path(path: &Path) -> Result<LoadedSource, Diagnostic> {
+fn load_path(path: &Path) -> Result<SourceInput, Diagnostic> {
    let canonical = path.canonicalize().map_err(|error| {
        Diagnostic::new(
            DiagnosticKind::Import,
@@ -122,7 +138,7 @@ fn load_path(path: &Path) -> Result<LoadedSource, Diagnostic> {
        )
    })?;
    let key = canonical.to_string_lossy().into_owned();
-    Ok(LoadedSource {
+    Ok(SourceInput {
        name: key.clone(),
        key,
        source,
@@ -139,15 +155,12 @@ fn print_help() {
    println!("  decodal -                  Read DCDL source from stdin");
 }

-fn print_diagnostic(error: &Diagnostic) {
-    eprintln!(
-        "error[{kind:?}] {source}:{start}..{end}: {message}",
-        kind = error.kind,
-        source = error.span.source.0,
-        start = error.span.start,
-        end = error.span.end,
-        message = error.message,
-    );
+fn format_diagnostic_with_root(error: &Diagnostic, root_name: &str) -> String {
+    format_diagnostic_with(error, |source| (source == SourceId(0)).then_some(root_name))
+}
+
+fn format_raw_diagnostic(error: Diagnostic) -> String {
+    format_diagnostic_with(&error, |_| None)
 }

 fn print_data(data: &Data, indent: usize) {
@@ -1,12 +1,21 @@
 [package]
-name = "decodal-core"
-version = "0.1.0"
-edition = "2024"
+name = "decodal"
+version.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+repository.workspace = true
+readme.workspace = true
+description = "Parser, evaluator, and embedding API for the Decodal data description language."
+keywords = ["decodal", "dsl", "config", "schema"]
+categories = ["config", "parser-implementations"]

 [features]
 default = ["std"]
 std = []
+derive = ["dep:decodal-derive"]
 regex = ["std", "dep:regex"]

 [dependencies]
+decodal-derive = { version = "0.2.0", path = "../decodal-derive", optional = true }
 regex = { version = "1.10", default-features = false, features = ["std", "unicode-perl"], optional = true }
@@ -1,14 +1,14 @@
-use decodal_core::{Data, EmptyLoader, Engine, HostValue};
+use decodal::{Data, EmptyLoader, Engine, Value};

-fn main() -> decodal_core::Result<()> {
+fn main() -> decodal::Result<()> {
    let mut engine = Engine::new(EmptyLoader);

    engine.bind_global(
        "Service",
-        HostValue::object([
-            ("name", HostValue::string_type()),
-            ("port", HostValue::int_type().gt(443).default_int(8443)?),
-            ("enabled", HostValue::bool_type().default_bool(true)?),
+        Value::object([
+            ("name", Value::string_type()),
+            ("port", Value::int_type().gt(443).default_int(8443)?),
+            ("enabled", Value::bool_type().default_bool(true)?),
        ]),
    )?;

@@ -0,0 +1,85 @@
+use decodal::{Data, Diagnostic, DiagnosticKind, Engine, ImportLoader, LoadedImport, Span, Value};
+
+const POST: &str = r#"---
+title: Hello
+draft: false
+---
+# Hello
+
+This body stays as Markdown.
+"#;
+
+struct ContentLoader;
+
+impl ImportLoader for ContentLoader {
+    fn load(
+        &mut self,
+        _current_key: Option<&str>,
+        specifier: &str,
+    ) -> decodal::Result<LoadedImport> {
+        if specifier != "./post.md" {
+            return Err(Diagnostic::new(
+                DiagnosticKind::Import,
+                Span::default(),
+                format!("unknown content import `{specifier}`"),
+            ));
+        }
+        Ok(LoadedImport::value(
+            "content/post.md",
+            parse_markdown(POST)?,
+        ))
+    }
+}
+
+fn parse_markdown(source: &str) -> decodal::Result<Value> {
+    let source = source.strip_prefix("---\n").ok_or_else(frontmatter_error)?;
+    let (frontmatter, body) = source.split_once("\n---\n").ok_or_else(frontmatter_error)?;
+    let mut fields = Vec::new();
+    for line in frontmatter.lines() {
+        let (name, value) = line.split_once(':').ok_or_else(frontmatter_error)?;
+        let value = match value.trim() {
+            "true" => Value::bool(true),
+            "false" => Value::bool(false),
+            value => Value::string(value),
+        };
+        fields.push((name.trim(), value));
+    }
+    Ok(Value::object([
+        ("frontmatter", Value::object(fields)),
+        ("body", Value::string(body)),
+    ]))
+}
+
+fn frontmatter_error() -> Diagnostic {
+    Diagnostic::new(
+        DiagnosticKind::Import,
+        Span::default(),
+        "invalid Markdown frontmatter",
+    )
+}
+
+fn main() -> decodal::Result<()> {
+    let mut engine = Engine::new(ContentLoader);
+    let module = engine.add_root_source(
+        "main.dcdl",
+        "main.dcdl",
+        r#"
+        let post = import "./post.md";
+        in {
+            title = post.frontmatter.title;
+            draft = post.frontmatter.draft;
+            body = post.body;
+        }
+        "#,
+    )?;
+    let value = engine.eval_module(module)?;
+    let data = engine.materialize(&value)?;
+
+    let Data::Object(fields) = data else {
+        panic!("expected imported Markdown to produce an object")
+    };
+    assert_eq!(fields[0].value, Data::String(String::from("Hello")));
+    assert_eq!(fields[1].value, Data::Bool(false));
+    assert!(matches!(fields[2].value, Data::String(_)));
+    Ok(())
+}
@@ -48,8 +48,17 @@ pub struct SpannedExpr {
 pub enum Expr {
    Literal(Literal),
    Ident(String),
-    Object(Vec<Field>),
+    Object {
+        fields: Vec<Field>,
+        rest: Option<ObjectRest>,
+    },
    Array(Vec<ExprId>),
+    ArrayConstraint {
+        item: ExprId,
+    },
+    MapConstraint {
+        value: ExprId,
+    },
    Let {
        bindings: Vec<Field>,
        body: ExprId,
@@ -67,10 +76,21 @@ pub enum Expr {
        params: Vec<Param>,
        body: ExprId,
    },
+    /// An explicitly parenthesized expression.
+    ///
+    /// Keeping this node preserves the delimiters and their trivia for source
+    /// tools while evaluation remains equivalent to evaluating `expr`.
+    Parenthesized {
+        expr: ExprId,
+    },
    Match {
        scrutinee: ExprId,
        arms: Vec<MatchArm>,
    },
+    Unary {
+        op: UnaryOp,
+        expr: ExprId,
+    },
    Binary {
        op: BinaryOp,
        lhs: ExprId,
@@ -80,6 +100,10 @@ pub enum Expr {
        base: ExprId,
        fallback: ExprId,
    },
+    As {
+        narrower: ExprId,
+        wider: ExprId,
+    },
    CompareConstraint {
        op: CompareOp,
        value: ExprId,
@@ -95,6 +119,12 @@ pub struct Field {
    pub span: Span,
 }

+#[derive(Debug, Clone, PartialEq)]
+pub struct ObjectRest {
+    pub value: ExprId,
+    pub span: Span,
+}
+
 #[derive(Debug, Clone, PartialEq)]
 pub struct Param {
    pub name: String,
@@ -117,8 +147,27 @@ pub enum Literal {
    Bool(bool),
 }

+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum UnaryOp {
+    Neg,
+    Not,
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum BinaryOp {
+    Add,
+    Sub,
+    Mul,
+    Div,
+    Concat,
+    Equal,
+    NotEqual,
+    Greater,
+    GreaterEqual,
+    Less,
+    LessEqual,
+    LogicalAnd,
+    LogicalOr,
    And,
    Patch,
 }
@@ -3,103 +3,240 @@ use alloc::{string::String, vec::Vec};
 use crate::{
    Diagnostic, DiagnosticKind, Span,
    ast::CompareOp,
-    runtime::{Constraint, LiteralValue, PrimitiveType},
+    runtime::{Constraint, ConstraintEntry, LiteralValue, PrimitiveType},
 };

 pub fn normalize_constraints(
-    constraints: Vec<Constraint>,
+    constraints: Vec<ConstraintEntry>,
    span: Span,
-) -> crate::Result<Vec<Constraint>> {
-    let mut primitive = None;
-    let mut lower: Option<Bound> = None;
-    let mut upper: Option<Bound> = None;
+) -> crate::Result<Vec<ConstraintEntry>> {
+    let mut primitive: Option<(PrimitiveType, Span)> = None;
+    let mut array_span: Option<Span> = None;
+    let mut map_span: Option<Span> = None;
+    let mut lower: Option<(Bound, Span)> = None;
+    let mut upper: Option<(Bound, Span)> = None;
    let mut rest = Vec::new();

-    for constraint in constraints {
-        match constraint {
+    for entry in constraints {
+        match entry.constraint {
+            Constraint::Unknown => rest.push(ConstraintEntry {
+                constraint: Constraint::Unknown,
+                span: entry.span,
+            }),
            Constraint::Type(next) => match primitive {
-                Some(current) if current != next => {
+                Some((current, current_span)) if current != next => {
                    return Err(Diagnostic::new(
                        DiagnosticKind::Conflict,
                        span,
                        "primitive type constraints conflict",
-                    ));
+                    )
+                    .with_label(current_span, "first primitive constraint")
+                    .with_label(entry.span, "conflicting primitive constraint"));
                }
                Some(_) => {}
-                None => primitive = Some(next),
+                None => primitive = Some((next, entry.span)),
            },
            Constraint::Compare(op, value) => {
                let number = Number::from_literal(&value).ok_or_else(|| {
                    Diagnostic::new(
                        DiagnosticKind::TypeMismatch,
-                        span,
+                        entry.span,
                        "comparison constraints require numeric literals",
                    )
                })?;
                match op {
-                    CompareOp::Gt => merge_lower(&mut lower, Bound::new(number, false)),
-                    CompareOp::Gte => merge_lower(&mut lower, Bound::new(number, true)),
-                    CompareOp::Lt => merge_upper(&mut upper, Bound::new(number, false)),
-                    CompareOp::Lte => merge_upper(&mut upper, Bound::new(number, true)),
+                    CompareOp::Gt => {
+                        merge_lower(&mut lower, (Bound::new(number, false), entry.span))
+                    }
+                    CompareOp::Gte => {
+                        merge_lower(&mut lower, (Bound::new(number, true), entry.span))
+                    }
+                    CompareOp::Lt => {
+                        merge_upper(&mut upper, (Bound::new(number, false), entry.span))
+                    }
+                    CompareOp::Lte => {
+                        merge_upper(&mut upper, (Bound::new(number, true), entry.span))
+                    }
                    CompareOp::Eq => {
-                        merge_lower(&mut lower, Bound::new(number, true));
-                        merge_upper(&mut upper, Bound::new(number, true));
+                        merge_lower(&mut lower, (Bound::new(number, true), entry.span));
+                        merge_upper(&mut upper, (Bound::new(number, true), entry.span));
                    }
                }
            }
-            Constraint::Regex(pattern) => rest.push(Constraint::Regex(pattern)),
-            Constraint::BuiltinPredicate(name) => rest.push(Constraint::BuiltinPredicate(name)),
+            Constraint::Regex(pattern) => rest.push(ConstraintEntry {
+                constraint: Constraint::Regex(pattern),
+                span: entry.span,
+            }),
+            Constraint::ArrayItems(item) => {
+                array_span.get_or_insert(entry.span);
+                rest.push(ConstraintEntry {
+                    constraint: Constraint::ArrayItems(item),
+                    span: entry.span,
+                });
+            }
+            Constraint::MapValues(value) => {
+                map_span.get_or_insert(entry.span);
+                rest.push(ConstraintEntry {
+                    constraint: Constraint::MapValues(value),
+                    span: entry.span,
+                });
+            }
+            Constraint::BuiltinPredicate(name) => rest.push(ConstraintEntry {
+                constraint: Constraint::BuiltinPredicate(name),
+                span: entry.span,
+            }),
        }
    }

-    if matches!(primitive, Some(PrimitiveType::String | PrimitiveType::Bool))
+    if let (Some((_, primitive_span)), Some(array_span)) = (primitive, array_span) {
+        return Err(Diagnostic::new(
+            DiagnosticKind::Conflict,
+            span,
+            "array element constraints conflict with primitive type constraints",
+        )
+        .with_label(primitive_span, "primitive type constraint")
+        .with_label(array_span, "array element constraint"));
+    }
+
+    if let (Some((_, primitive_span)), Some(map_span)) = (primitive, map_span) {
+        return Err(Diagnostic::new(
+            DiagnosticKind::Conflict,
+            span,
+            "map value constraints conflict with primitive type constraints",
+        )
+        .with_label(primitive_span, "primitive constraint")
+        .with_label(map_span, "map value constraint"));
+    }
+
+    if let (Some(array_span), Some(map_span)) = (array_span, map_span) {
+        return Err(Diagnostic::new(
+            DiagnosticKind::Conflict,
+            span,
+            "array and map constraints conflict",
+        )
+        .with_label(array_span, "array element constraint")
+        .with_label(map_span, "map value constraint"));
+    }
+
+    if let Some(array_span) = array_span
        && (lower.is_some() || upper.is_some())
    {
-        return Err(Diagnostic::new(
+        let mut diagnostic = Diagnostic::new(
+            DiagnosticKind::Conflict,
+            span,
+            "numeric comparison constraints conflict with array element constraints",
+        )
+        .with_label(array_span, "array element constraint");
+        if let Some((_, lower_span)) = lower {
+            diagnostic = diagnostic.with_label(lower_span, "numeric comparison constraint");
+        }
+        if let Some((_, upper_span)) = upper {
+            diagnostic = diagnostic.with_label(upper_span, "numeric comparison constraint");
+        }
+        return Err(diagnostic);
+    }
+
+    if let Some(map_span) = map_span
+        && (lower.is_some() || upper.is_some())
+    {
+        let mut diagnostic = Diagnostic::new(
+            DiagnosticKind::Conflict,
+            span,
+            "numeric comparison constraints conflict with map value constraints",
+        )
+        .with_label(map_span, "map value constraint");
+        if let Some((_, lower_span)) = lower {
+            diagnostic = diagnostic.with_label(lower_span, "numeric comparison constraint");
+        }
+        if let Some((_, upper_span)) = upper {
+            diagnostic = diagnostic.with_label(upper_span, "numeric comparison constraint");
+        }
+        return Err(diagnostic);
+    }
+
+    if matches!(
+        primitive,
+        Some((PrimitiveType::String | PrimitiveType::Bool, _))
+    ) && (lower.is_some() || upper.is_some())
+    {
+        let mut diagnostic = Diagnostic::new(
            DiagnosticKind::Conflict,
            span,
            "numeric comparison constraints conflict with non-numeric primitive type",
-        ));
+        );
+        if let Some((_, primitive_span)) = primitive {
+            diagnostic = diagnostic.with_label(primitive_span, "non-numeric primitive constraint");
+        }
+        if let Some((_, lower_span)) = lower {
+            diagnostic = diagnostic.with_label(lower_span, "numeric comparison constraint");
+        }
+        if let Some((_, upper_span)) = upper {
+            diagnostic = diagnostic.with_label(upper_span, "numeric comparison constraint");
+        }
+        return Err(diagnostic);
    }

-    if primitive == Some(PrimitiveType::Int)
+    if matches!(primitive, Some((PrimitiveType::Int, _)))
        && lower
            .iter()
            .chain(upper.iter())
-            .any(|bound| !matches!(bound.number, Number::Int(_)))
+            .any(|(bound, _)| !matches!(bound.number, Number::Int(_)))
    {
-        return Err(Diagnostic::new(
+        let mut diagnostic = Diagnostic::new(
            DiagnosticKind::Conflict,
            span,
            "Int comparison constraints must use integer literals",
-        ));
+        );
+        if let Some((_, primitive_span)) = primitive {
+            diagnostic = diagnostic.with_label(primitive_span, "Int primitive constraint");
+        }
+        if let Some((bound, bound_span)) = lower {
+            if !matches!(bound.number, Number::Int(_)) {
+                diagnostic = diagnostic.with_label(bound_span, "non-integer comparison constraint");
+            }
+        }
+        if let Some((bound, bound_span)) = upper {
+            if !matches!(bound.number, Number::Int(_)) {
+                diagnostic = diagnostic.with_label(bound_span, "non-integer comparison constraint");
+            }
+        }
+        return Err(diagnostic);
    }

    ensure_bounds_non_empty(primitive, lower, upper, span)?;

    let mut normalized = Vec::new();
-    if let Some(primitive) = primitive {
-        normalized.push(Constraint::Type(primitive));
+    if let Some((primitive, primitive_span)) = primitive {
+        normalized.push(ConstraintEntry {
+            constraint: Constraint::Type(primitive),
+            span: primitive_span,
+        });
    }
-    if let Some(lower) = lower {
-        normalized.push(Constraint::Compare(
-            if lower.inclusive {
-                CompareOp::Gte
-            } else {
-                CompareOp::Gt
-            },
-            lower.number.into_literal(),
-        ));
+    if let Some((lower, lower_span)) = lower {
+        normalized.push(ConstraintEntry {
+            constraint: Constraint::Compare(
+                if lower.inclusive {
+                    CompareOp::Gte
+                } else {
+                    CompareOp::Gt
+                },
+                lower.number.into_literal(),
+            ),
+            span: lower_span,
+        });
    }
-    if let Some(upper) = upper {
-        normalized.push(Constraint::Compare(
-            if upper.inclusive {
-                CompareOp::Lte
-            } else {
-                CompareOp::Lt
-            },
-            upper.number.into_literal(),
-        ));
+    if let Some((upper, upper_span)) = upper {
+        normalized.push(ConstraintEntry {
+            constraint: Constraint::Compare(
+                if upper.inclusive {
+                    CompareOp::Lte
+                } else {
+                    CompareOp::Lt
+                },
+                upper.number.into_literal(),
+            ),
+            span: upper_span,
+        });
    }
    normalized.extend(rest);
    Ok(normalized)
@@ -147,18 +284,22 @@ impl Number {
    }
 }

-fn merge_lower(current: &mut Option<Bound>, next: Bound) {
+fn merge_lower(current: &mut Option<(Bound, Span)>, next: (Bound, Span)) {
    match current {
        None => *current = Some(next),
-        Some(current_bound) if is_stricter_lower(next, *current_bound) => *current_bound = next,
+        Some((current_bound, _)) if is_stricter_lower(next.0, *current_bound) => {
+            *current = Some(next)
+        }
        Some(_) => {}
    }
 }

-fn merge_upper(current: &mut Option<Bound>, next: Bound) {
+fn merge_upper(current: &mut Option<(Bound, Span)>, next: (Bound, Span)) {
    match current {
        None => *current = Some(next),
-        Some(current_bound) if is_stricter_upper(next, *current_bound) => *current_bound = next,
+        Some((current_bound, _)) if is_stricter_upper(next.0, *current_bound) => {
+            *current = Some(next)
+        }
        Some(_) => {}
    }
 }
@@ -178,28 +319,32 @@ fn is_stricter_upper(next: Bound, current: Bound) -> bool {
 }

 fn ensure_bounds_non_empty(
-    primitive: Option<PrimitiveType>,
-    lower: Option<Bound>,
-    upper: Option<Bound>,
+    primitive: Option<(PrimitiveType, Span)>,
+    lower: Option<(Bound, Span)>,
+    upper: Option<(Bound, Span)>,
    span: Span,
 ) -> crate::Result<()> {
-    if primitive == Some(PrimitiveType::Int) {
-        let min = lower.map(int_lower_bound).unwrap_or(i128::from(i64::MIN));
-        let max = upper.map(int_upper_bound).unwrap_or(i128::from(i64::MAX));
+    if matches!(primitive, Some((PrimitiveType::Int, _))) {
+        let min = lower
+            .map(|(bound, _)| int_lower_bound(bound))
+            .unwrap_or(i128::from(i64::MIN));
+        let max = upper
+            .map(|(bound, _)| int_upper_bound(bound))
+            .unwrap_or(i128::from(i64::MAX));
        if min > max {
-            return Err(empty_numeric_bounds(span));
+            return Err(empty_numeric_bounds(span, lower, upper));
        }
        return Ok(());
    }

-    if let (Some(lower), Some(upper)) = (lower, upper) {
-        let lower_value = lower.number.as_f64();
-        let upper_value = upper.number.as_f64();
+    if let (Some((lower_bound, _)), Some((upper_bound, _))) = (lower, upper) {
+        let lower_value = lower_bound.number.as_f64();
+        let upper_value = upper_bound.number.as_f64();
        if lower_value > upper_value {
-            return Err(empty_numeric_bounds(span));
+            return Err(empty_numeric_bounds(span, lower, upper));
        }
-        if lower_value == upper_value && !(lower.inclusive && upper.inclusive) {
-            return Err(empty_numeric_bounds(span));
+        if lower_value == upper_value && !(lower_bound.inclusive && upper_bound.inclusive) {
+            return Err(empty_numeric_bounds(span, lower, upper));
        }
    }
    Ok(())
@@ -227,12 +372,23 @@ fn int_upper_bound(bound: Bound) -> i128 {
    }
 }

-fn empty_numeric_bounds(span: Span) -> Diagnostic {
-    Diagnostic::new(
+fn empty_numeric_bounds(
+    span: Span,
+    lower: Option<(Bound, Span)>,
+    upper: Option<(Bound, Span)>,
+) -> Diagnostic {
+    let mut diagnostic = Diagnostic::new(
        DiagnosticKind::Conflict,
        span,
        String::from("numeric comparison constraints have an empty intersection"),
-    )
+    );
+    if let Some((_, lower_span)) = lower {
+        diagnostic = diagnostic.with_label(lower_span, "lower bound constraint");
+    }
+    if let Some((_, upper_span)) = upper {
+        diagnostic = diagnostic.with_label(upper_span, "upper bound constraint");
+    }
+    diagnostic
 }

 #[cfg(test)]
@@ -240,13 +396,20 @@ mod tests {
    use super::*;
    use crate::runtime::LiteralValue;

+    fn entry(constraint: Constraint) -> ConstraintEntry {
+        ConstraintEntry {
+            constraint,
+            span: Span::default(),
+        }
+    }
+
    #[test]
    fn detects_primitive_conflict() {
        assert!(
            normalize_constraints(
                alloc::vec![
-                    Constraint::Type(PrimitiveType::Int),
-                    Constraint::Type(PrimitiveType::String),
+                    entry(Constraint::Type(PrimitiveType::Int)),
+                    entry(Constraint::Type(PrimitiveType::String)),
                ],
                Span::default(),
            )
@@ -259,9 +422,9 @@ mod tests {
        assert!(
            normalize_constraints(
                alloc::vec![
-                    Constraint::Type(PrimitiveType::Int),
-                    Constraint::Compare(CompareOp::Gt, LiteralValue::Int(10)),
-                    Constraint::Compare(CompareOp::Lt, LiteralValue::Int(11)),
+                    entry(Constraint::Type(PrimitiveType::Int)),
+                    entry(Constraint::Compare(CompareOp::Gt, LiteralValue::Int(10))),
+                    entry(Constraint::Compare(CompareOp::Lt, LiteralValue::Int(5))),
                ],
                Span::default(),
            )
@@ -270,15 +433,16 @@ mod tests {
    }

    #[test]
-    fn keeps_regex_constraints_without_intersection_check() {
-        let constraints = normalize_constraints(
-            alloc::vec![
-                Constraint::Regex(String::from("^a$")),
-                Constraint::Regex(String::from("^b$")),
-            ],
-            Span::default(),
-        )
-        .unwrap();
-        assert_eq!(constraints.len(), 2);
+    fn detects_non_integer_int_bound() {
+        assert!(
+            normalize_constraints(
+                alloc::vec![
+                    entry(Constraint::Type(PrimitiveType::Int)),
+                    entry(Constraint::Compare(CompareOp::Gt, LiteralValue::Float(1.5))),
+                ],
+                Span::default(),
+            )
+            .is_err()
+        );
    }
 }
@@ -1,4 +1,4 @@
-use alloc::string::String;
+use alloc::{string::String, vec::Vec};

 use crate::span::Span;

@@ -9,6 +9,14 @@ pub struct Diagnostic {
    pub kind: DiagnosticKind,
    pub span: Span,
    pub message: String,
+    pub labels: Vec<DiagnosticLabel>,
+    pub notes: Vec<String>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct DiagnosticLabel {
+    pub span: Span,
+    pub message: String,
 }

 impl Diagnostic {
@@ -17,12 +25,27 @@ impl Diagnostic {
            kind,
            span,
            message: message.into(),
+            labels: Vec::new(),
+            notes: Vec::new(),
        }
    }

    pub fn syntax(span: Span, message: impl Into<String>) -> Self {
        Self::new(DiagnosticKind::Syntax, span, message)
    }
+
+    pub fn with_label(mut self, span: Span, message: impl Into<String>) -> Self {
+        self.labels.push(DiagnosticLabel {
+            span,
+            message: message.into(),
+        });
+        self
+    }
+
+    pub fn with_note(mut self, message: impl Into<String>) -> Self {
+        self.notes.push(message.into());
+        self
+    }
 }

 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -1,164 +0,0 @@
-use alloc::{boxed::Box, string::String, vec::Vec};
-
-use crate::runtime::{Constraint, LiteralValue, PrimitiveType};
-use crate::{CompareOp, Diagnostic, DiagnosticKind, Result, Span};
-
-#[derive(Debug, Clone, PartialEq)]
-pub enum HostValue {
-    String(String),
-    Int(i64),
-    Float(f64),
-    Bool(bool),
-    Array(Vec<HostValue>),
-    Object(Vec<HostField>),
-    Abstract {
-        constraints: Vec<Constraint>,
-        default: Option<Box<HostValue>>,
-    },
-}
-
-#[derive(Debug, Clone, PartialEq)]
-pub struct HostField {
-    pub name: String,
-    pub value: HostValue,
-}
-
-impl HostValue {
-    pub fn string(value: impl Into<String>) -> Self {
-        Self::String(value.into())
-    }
-
-    pub fn int(value: i64) -> Self {
-        Self::Int(value)
-    }
-
-    pub fn float(value: f64) -> Self {
-        Self::Float(value)
-    }
-
-    pub fn bool(value: bool) -> Self {
-        Self::Bool(value)
-    }
-
-    pub fn array<I>(items: I) -> Self
-    where
-        I: IntoIterator<Item = HostValue>,
-    {
-        Self::Array(items.into_iter().collect())
-    }
-
-    pub fn object<I, N>(fields: I) -> Self
-    where
-        I: IntoIterator<Item = (N, HostValue)>,
-        N: Into<String>,
-    {
-        Self::Object(
-            fields
-                .into_iter()
-                .map(|(name, value)| HostField {
-                    name: name.into(),
-                    value,
-                })
-                .collect(),
-        )
-    }
-
-    pub fn string_type() -> Self {
-        Self::abstract_with_constraint(Constraint::Type(PrimitiveType::String))
-    }
-
-    pub fn int_type() -> Self {
-        Self::abstract_with_constraint(Constraint::Type(PrimitiveType::Int))
-    }
-
-    pub fn float_type() -> Self {
-        Self::abstract_with_constraint(Constraint::Type(PrimitiveType::Float))
-    }
-
-    pub fn bool_type() -> Self {
-        Self::abstract_with_constraint(Constraint::Type(PrimitiveType::Bool))
-    }
-
-    pub fn builtin_predicate(name: impl Into<String>) -> Self {
-        Self::abstract_with_constraint(Constraint::BuiltinPredicate(name.into()))
-    }
-
-    pub fn abstract_with_constraint(constraint: Constraint) -> Self {
-        Self::Abstract {
-            constraints: alloc::vec![constraint],
-            default: None,
-        }
-    }
-
-    pub fn with_constraint(mut self, constraint: Constraint) -> Self {
-        match &mut self {
-            Self::Abstract { constraints, .. } => constraints.push(constraint),
-            _ => {
-                self = Self::Abstract {
-                    constraints: alloc::vec![constraint],
-                    default: Some(Box::new(self)),
-                };
-            }
-        }
-        self
-    }
-
-    pub fn gt(self, value: i64) -> Self {
-        self.with_constraint(Constraint::Compare(CompareOp::Gt, LiteralValue::Int(value)))
-    }
-
-    pub fn gte(self, value: i64) -> Self {
-        self.with_constraint(Constraint::Compare(
-            CompareOp::Gte,
-            LiteralValue::Int(value),
-        ))
-    }
-
-    pub fn lt(self, value: i64) -> Self {
-        self.with_constraint(Constraint::Compare(CompareOp::Lt, LiteralValue::Int(value)))
-    }
-
-    pub fn lte(self, value: i64) -> Self {
-        self.with_constraint(Constraint::Compare(
-            CompareOp::Lte,
-            LiteralValue::Int(value),
-        ))
-    }
-
-    pub fn default(self, value: HostValue) -> Result<Self> {
-        match self {
-            Self::Abstract {
-                constraints,
-                default: None,
-            } => Ok(Self::Abstract {
-                constraints,
-                default: Some(Box::new(value)),
-            }),
-            Self::Abstract { .. } => Err(Diagnostic::new(
-                DiagnosticKind::DefaultConflict,
-                Span::default(),
-                "host value already has a default",
-            )),
-            concrete => Ok(Self::Abstract {
-                constraints: Vec::new(),
-                default: Some(Box::new(concrete)),
-            }),
-        }
-    }
-
-    pub fn default_string(self, value: impl Into<String>) -> Result<Self> {
-        self.default(Self::string(value))
-    }
-
-    pub fn default_int(self, value: i64) -> Result<Self> {
-        self.default(Self::int(value))
-    }
-
-    pub fn default_float(self, value: f64) -> Result<Self> {
-        self.default(Self::float(value))
-    }
-
-    pub fn default_bool(self, value: bool) -> Result<Self> {
-        self.default(Self::bool(value))
-    }
-}
@@ -0,0 +1,34 @@
+use crate::{Engine, ImportLoader, Result};
+
+/// Host-owned configuration shared by runtime and language tooling.
+///
+/// Implementations create the import loader and install global bindings on a
+/// fresh engine. Calling [`HostEnvironment::create_engine`] therefore gives
+/// every consumer the same Decodal execution environment.
+pub trait HostEnvironment {
+    type Loader: ImportLoader;
+
+    fn create_loader(&self) -> Self::Loader;
+
+    fn configure_engine(&self, _engine: &mut Engine<Self::Loader>) -> Result<()> {
+        Ok(())
+    }
+
+    fn create_engine(&self) -> Result<Engine<Self::Loader>> {
+        let mut engine = Engine::new(self.create_loader());
+        self.configure_engine(&mut engine)?;
+        Ok(engine)
+    }
+}
+
+impl<T: HostEnvironment + ?Sized> HostEnvironment for &T {
+    type Loader = T::Loader;
+
+    fn create_loader(&self) -> Self::Loader {
+        T::create_loader(*self)
+    }
+
+    fn configure_engine(&self, engine: &mut Engine<Self::Loader>) -> Result<()> {
+        T::configure_engine(*self, engine)
+    }
+}
@@ -22,6 +22,7 @@ pub enum TokenKind {
    Match,
    Import,
    Default,
+    As,
    Underscore,
    LBrace,
    RBrace,
@@ -32,18 +33,45 @@ pub enum TokenKind {
    Semicolon,
    Comma,
    Dot,
+    Ellipsis,
    Colon,
    Equal,
+    EqualEqual,
+    Bang,
+    BangEqual,
    Arrow,
    Amp,
+    AmpAmp,
+    PipePipe,
+    Plus,
+    PlusPlus,
+    Minus,
+    Star,
+    Slash,
    SlashSlash,
    Gt,
    Gte,
    Lt,
    Lte,
+    /// A line comment, including its leading `#` and excluding its newline.
+    Comment,
    Eof,
 }

+/// Tokenizes source while retaining comments and source spans for tooling.
+///
+/// Whitespace remains available through the gaps between adjacent token spans,
+/// making this a lossless syntax view when paired with the original source.
+pub fn tokenize_source(source: &str) -> Result<Vec<Token>> {
+    tokenize_source_with_source_id(SourceId(0), source)
+}
+
+/// Tokenizes source with a caller-provided source identifier while retaining
+/// comments and source spans for tooling.
+pub fn tokenize_source_with_source_id(source_id: SourceId, source: &str) -> Result<Vec<Token>> {
+    Lexer::with_source_id(source_id, source).tokenize_with_comments()
+}
+
 pub struct Lexer<'a> {
    source_id: SourceId,
    source: &'a str,
@@ -52,6 +80,7 @@ pub struct Lexer<'a> {
 }

 impl<'a> Lexer<'a> {
+    #[cfg(test)]
    pub fn new(source: &'a str) -> Self {
        Self::with_source_id(SourceId(0), source)
    }
@@ -66,10 +95,30 @@ impl<'a> Lexer<'a> {
    }

    pub fn tokenize(mut self) -> Result<Vec<Token>> {
+        self.tokenize_impl(false)
+    }
+
+    fn tokenize_with_comments(mut self) -> Result<Vec<Token>> {
+        self.tokenize_impl(true)
+    }
+
+    fn tokenize_impl(&mut self, include_comments: bool) -> Result<Vec<Token>> {
        let mut tokens = Vec::new();
+        let mut previous = None;
        loop {
-            let token = self.next_token()?;
+            self.skip_whitespace();
+            if self.peek() == Some(b'#') {
+                let comment = self.lex_comment();
+                if include_comments {
+                    tokens.push(comment);
+                }
+                continue;
+            }
+            let token = self.next_non_ws_token(previous.as_ref())?;
            let is_eof = token.kind == TokenKind::Eof;
+            if !is_eof {
+                previous = Some(token.kind.clone());
+            }
            tokens.push(token);
            if is_eof {
                return Ok(tokens);
@@ -77,8 +126,7 @@ impl<'a> Lexer<'a> {
        }
    }

-    fn next_token(&mut self) -> Result<Token> {
-        self.skip_ws_and_comments();
+    fn next_non_ws_token(&mut self, previous: Option<&TokenKind>) -> Result<Token> {
        let start = self.pos;
        let Some(ch) = self.peek() else {
            return Ok(Token {
@@ -122,7 +170,18 @@ impl<'a> Lexer<'a> {
            }
            b'.' => {
                self.pos += 1;
-                TokenKind::Dot
+                if self.consume(b'.') {
+                    if self.consume(b'.') {
+                        TokenKind::Ellipsis
+                    } else {
+                        return Err(Diagnostic::syntax(
+                            self.span(start, self.pos),
+                            "expected third '.' in ellipsis",
+                        ));
+                    }
+                } else {
+                    TokenKind::Dot
+                }
            }
            b':' => {
                self.pos += 1;
@@ -134,16 +193,57 @@ impl<'a> Lexer<'a> {
            }
            b'&' => {
                self.pos += 1;
-                TokenKind::Amp
+                if self.consume(b'&') {
+                    TokenKind::AmpAmp
+                } else {
+                    TokenKind::Amp
+                }
+            }
+            b'|' => {
+                self.pos += 1;
+                if self.consume(b'|') {
+                    TokenKind::PipePipe
+                } else {
+                    return Err(Diagnostic::syntax(
+                        self.span(start, self.pos),
+                        "expected '|' after '|'",
+                    ));
+                }
+            }
+            b'+' => {
+                self.pos += 1;
+                if self.consume(b'+') {
+                    TokenKind::PlusPlus
+                } else {
+                    TokenKind::Plus
+                }
+            }
+            b'-' => {
+                self.pos += 1;
+                TokenKind::Minus
+            }
+            b'*' => {
+                self.pos += 1;
+                TokenKind::Star
            }
            b'=' => {
                self.pos += 1;
                if self.consume(b'>') {
                    TokenKind::Arrow
+                } else if self.consume(b'=') {
+                    TokenKind::EqualEqual
                } else {
                    TokenKind::Equal
                }
            }
+            b'!' => {
+                self.pos += 1;
+                if self.consume(b'=') {
+                    TokenKind::BangEqual
+                } else {
+                    TokenKind::Bang
+                }
+            }
            b'>' => {
                self.pos += 1;
                if self.consume(b'=') {
@@ -164,6 +264,8 @@ impl<'a> Lexer<'a> {
                self.pos += 1;
                if self.consume(b'/') {
                    TokenKind::SlashSlash
+                } else if previous.is_some_and(token_can_end_expr) {
+                    TokenKind::Slash
                } else {
                    self.lex_regex(start)?
                }
@@ -185,21 +287,23 @@ impl<'a> Lexer<'a> {
        })
    }

-    fn skip_ws_and_comments(&mut self) {
-        loop {
-            while matches!(self.peek(), Some(b' ' | b'\t' | b'\r' | b'\n')) {
-                self.pos += 1;
+    fn skip_whitespace(&mut self) {
+        while matches!(self.peek(), Some(b' ' | b'\t' | b'\r' | b'\n')) {
+            self.pos += 1;
+        }
+    }
+
+    fn lex_comment(&mut self) -> Token {
+        let start = self.pos;
+        while let Some(c) = self.peek() {
+            if c == b'\n' {
+                break;
            }
-            if self.peek() == Some(b'#') {
-                while let Some(c) = self.peek() {
-                    self.pos += 1;
-                    if c == b'\n' {
-                        break;
-                    }
-                }
-                continue;
-            }
-            break;
+            self.pos += 1;
+        }
+        Token {
+            kind: TokenKind::Comment,
+            span: self.span(start, self.pos),
        }
    }

@@ -303,6 +407,7 @@ impl<'a> Lexer<'a> {
            "match" => TokenKind::Match,
            "import" => TokenKind::Import,
            "default" => TokenKind::Default,
+            "as" => TokenKind::As,
            _ => TokenKind::Ident(String::from(text)),
        }
    }
@@ -341,6 +446,23 @@ fn is_ident_continue(c: u8) -> bool {
    c.is_ascii_alphanumeric() || c == b'_'
 }

+fn token_can_end_expr(kind: &TokenKind) -> bool {
+    matches!(
+        kind,
+        TokenKind::Ident(_)
+            | TokenKind::Int(_)
+            | TokenKind::Float(_)
+            | TokenKind::String(_)
+            | TokenKind::Regex(_)
+            | TokenKind::True
+            | TokenKind::False
+            | TokenKind::Underscore
+            | TokenKind::RBrace
+            | TokenKind::RBracket
+            | TokenKind::RParen
+    )
+}
+
 #[cfg(test)]
 mod tests {
    use super::*;
@@ -353,4 +475,39 @@ mod tests {
        assert_eq!(tokens[3].kind, TokenKind::Amp);
        assert_eq!(tokens[4].kind, TokenKind::Gte);
    }
+
+    #[test]
+    fn tokenizes_array_constraint_ellipsis() {
+        let tokens = Lexer::new("[...String]").tokenize().unwrap();
+        assert_eq!(tokens[0].kind, TokenKind::LBracket);
+        assert_eq!(tokens[1].kind, TokenKind::Ellipsis);
+        assert!(matches!(tokens[2].kind, TokenKind::Ident(_)));
+        assert_eq!(tokens[3].kind, TokenKind::RBracket);
+    }
+
+    #[test]
+    fn tooling_tokens_retain_comments_and_whitespace_gaps() {
+        let source = "value = 1; # trailing\n\n# leading\nnext = 2;";
+        let tokens = tokenize_source(source).unwrap();
+        let comments = tokens
+            .iter()
+            .filter(|token| token.kind == TokenKind::Comment)
+            .collect::<Vec<_>>();
+        assert_eq!(comments.len(), 2);
+        assert_eq!(
+            &source[comments[0].span.start as usize..comments[0].span.end as usize],
+            "# trailing"
+        );
+        assert!(
+            source[comments[0].span.end as usize..comments[1].span.start as usize].contains("\n\n")
+        );
+
+        let source_id = SourceId(7);
+        let identified = tokenize_source_with_source_id(source_id, "# comment").unwrap();
+        assert!(
+            identified
+                .iter()
+                .all(|token| token.span.source == source_id)
+        );
+    }
 }
@@ -5,24 +5,36 @@ extern crate alloc;
 pub mod ast;
 pub mod constraints;
 pub mod diagnostic;
-pub mod embedding;
+pub mod environment;
 pub mod eval;
-pub mod lexer;
+mod lexer;
 pub mod module;
 pub mod parser;
 pub mod runtime;
 pub mod span;
+pub mod typed;
+pub mod value;

-pub use ast::{Ast, BinaryOp, CompareOp, Expr, ExprId, Field, Literal, Param};
+pub use ast::{Ast, BinaryOp, CompareOp, Expr, ExprId, Field, Literal, ObjectRest, Param};
 pub use constraints::normalize_constraints;
+#[cfg(feature = "derive")]
+pub use decodal_derive::Decodal;
 pub use diagnostic::{Diagnostic, DiagnosticKind, Result};
-pub use embedding::{HostField, HostValue};
-pub use eval::Engine;
-pub use lexer::{Lexer, Token, TokenKind};
-pub use module::{EmptyLoader, LoadedSource, Module, SourceLoader};
+pub use environment::HostEnvironment;
+pub use eval::{Engine, format_diagnostic_with};
+pub use lexer::{
+    Token as SyntaxToken, TokenKind as SyntaxTokenKind, tokenize_source,
+    tokenize_source_with_source_id,
+};
+pub use module::{EmptyLoader, ImportCandidate, ImportLoader, LoadedImport, Module};
 pub use parser::{ParseOutput, Parser, SourceForm, parse_source, parse_source_with_source_id};
-pub use runtime::{Constraint, Data, ExprRef, LiteralValue, ModuleId, PrimitiveType, RuntimeValue};
+pub use runtime::{Constraint, Data, ExprRef, LiteralValue, ModuleId, PrimitiveType};
 pub use span::{SourceId, Span};
+pub use typed::{
+    DecodalDecode, DecodalRest, DecodalSchema, DecodeError, DecodeResult, IntoValue, data_at_path,
+    decode_path, prefix_decode_error,
+};
+pub use value::{Value, ValueField};

 pub fn version() -> &'static str {
    env!("CARGO_PKG_VERSION")
@@ -1,7 +1,7 @@
-use alloc::string::String;
+use alloc::{string::String, vec::Vec};

 use crate::{
-    Ast, ExprId, SourceForm, SourceId,
+    Ast, ExprId, SourceForm, SourceId, Value,
    runtime::{EnvId, ThunkId},
 };

@@ -17,22 +17,84 @@ pub struct Module {
    pub root_thunk: ThunkId,
 }

+/// Content resolved by an [`ImportLoader`].
 #[derive(Debug, Clone)]
-pub struct LoadedSource {
-    pub key: String,
-    pub name: String,
-    pub source: String,
+pub enum LoadedImport {
+    Source {
+        key: String,
+        name: String,
+        source: String,
+    },
+    Value {
+        key: String,
+        value: Value,
+    },
 }

-pub trait SourceLoader {
-    fn load(&mut self, current_key: Option<&str>, specifier: &str) -> crate::Result<LoadedSource>;
+/// An import specifier offered by host-owned language tooling.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ImportCandidate {
+    pub specifier: String,
+    pub detail: Option<String>,
+}
+
+impl ImportCandidate {
+    pub fn new(specifier: impl Into<String>) -> Self {
+        Self {
+            specifier: specifier.into(),
+            detail: None,
+        }
+    }
+
+    pub fn with_detail(mut self, detail: impl Into<String>) -> Self {
+        self.detail = Some(detail.into());
+        self
+    }
+}
+
+impl LoadedImport {
+    pub fn source(
+        key: impl Into<String>,
+        name: impl Into<String>,
+        source: impl Into<String>,
+    ) -> Self {
+        Self::Source {
+            key: key.into(),
+            name: name.into(),
+            source: source.into(),
+        }
+    }
+
+    pub fn value(key: impl Into<String>, value: Value) -> Self {
+        Self::Value {
+            key: key.into(),
+            value,
+        }
+    }
+}
+
+pub trait ImportLoader {
+    fn load(&mut self, current_key: Option<&str>, specifier: &str) -> crate::Result<LoadedImport>;
+
+    /// Returns host-resolvable import specifiers matching an unfinished prefix.
+    ///
+    /// Runtime-only loaders may keep the default implementation. Hosts that
+    /// provide an editor should implement this from the same namespace used by
+    /// [`ImportLoader::load`].
+    fn complete_import(
+        &mut self,
+        _current_key: Option<&str>,
+        _prefix: &str,
+    ) -> crate::Result<Vec<ImportCandidate>> {
+        Ok(Vec::new())
+    }
 }

 #[derive(Debug, Clone, Copy, Default)]
 pub struct EmptyLoader;

-impl SourceLoader for EmptyLoader {
-    fn load(&mut self, _current_key: Option<&str>, specifier: &str) -> crate::Result<LoadedSource> {
+impl ImportLoader for EmptyLoader {
+    fn load(&mut self, _current_key: Option<&str>, specifier: &str) -> crate::Result<LoadedImport> {
        Err(crate::Diagnostic::new(
            crate::DiagnosticKind::Import,
            crate::Span::default(),
@@ -2,7 +2,10 @@ use alloc::{string::String, vec::Vec};

 use crate::{
    SourceId, Span,
-    ast::{Ast, BinaryOp, CompareOp, Expr, ExprId, Field, Literal, MatchArm, Param},
+    ast::{
+        Ast, BinaryOp, CompareOp, Expr, ExprId, Field, Literal, MatchArm, ObjectRest, Param,
+        UnaryOp,
+    },
    diagnostic::{Diagnostic, Result},
    lexer::{Lexer, Token, TokenKind},
 };
@@ -38,7 +41,10 @@ pub struct Parser {
 impl Parser {
    pub fn new(tokens: Vec<Token>) -> Self {
        Self {
-            tokens,
+            tokens: tokens
+                .into_iter()
+                .filter(|token| token.kind != TokenKind::Comment)
+                .collect(),
            pos: 0,
            ast: Ast::new(),
        }
@@ -56,7 +62,7 @@ impl Parser {
                })
                .unwrap_or_else(|| self.peek().span);
            (
-                self.ast.push(Expr::Object(fields), span),
+                self.ast.push(Expr::Object { fields, rest: None }, span),
                SourceForm::Fields,
            )
        } else {
@@ -115,6 +121,110 @@ impl Parser {
            let rhs = self.parse_expr(r_bp)?;
            let span = self.ast.span(lhs).join(self.ast.span(rhs)).join(op_span);
            lhs = match kind {
+                InfixKind::Add => self.ast.push(
+                    Expr::Binary {
+                        op: BinaryOp::Add,
+                        lhs,
+                        rhs,
+                    },
+                    span,
+                ),
+                InfixKind::Sub => self.ast.push(
+                    Expr::Binary {
+                        op: BinaryOp::Sub,
+                        lhs,
+                        rhs,
+                    },
+                    span,
+                ),
+                InfixKind::Mul => self.ast.push(
+                    Expr::Binary {
+                        op: BinaryOp::Mul,
+                        lhs,
+                        rhs,
+                    },
+                    span,
+                ),
+                InfixKind::Div => self.ast.push(
+                    Expr::Binary {
+                        op: BinaryOp::Div,
+                        lhs,
+                        rhs,
+                    },
+                    span,
+                ),
+                InfixKind::Concat => self.ast.push(
+                    Expr::Binary {
+                        op: BinaryOp::Concat,
+                        lhs,
+                        rhs,
+                    },
+                    span,
+                ),
+                InfixKind::Equal => self.ast.push(
+                    Expr::Binary {
+                        op: BinaryOp::Equal,
+                        lhs,
+                        rhs,
+                    },
+                    span,
+                ),
+                InfixKind::NotEqual => self.ast.push(
+                    Expr::Binary {
+                        op: BinaryOp::NotEqual,
+                        lhs,
+                        rhs,
+                    },
+                    span,
+                ),
+                InfixKind::Greater => self.ast.push(
+                    Expr::Binary {
+                        op: BinaryOp::Greater,
+                        lhs,
+                        rhs,
+                    },
+                    span,
+                ),
+                InfixKind::GreaterEqual => self.ast.push(
+                    Expr::Binary {
+                        op: BinaryOp::GreaterEqual,
+                        lhs,
+                        rhs,
+                    },
+                    span,
+                ),
+                InfixKind::Less => self.ast.push(
+                    Expr::Binary {
+                        op: BinaryOp::Less,
+                        lhs,
+                        rhs,
+                    },
+                    span,
+                ),
+                InfixKind::LessEqual => self.ast.push(
+                    Expr::Binary {
+                        op: BinaryOp::LessEqual,
+                        lhs,
+                        rhs,
+                    },
+                    span,
+                ),
+                InfixKind::LogicalAnd => self.ast.push(
+                    Expr::Binary {
+                        op: BinaryOp::LogicalAnd,
+                        lhs,
+                        rhs,
+                    },
+                    span,
+                ),
+                InfixKind::LogicalOr => self.ast.push(
+                    Expr::Binary {
+                        op: BinaryOp::LogicalOr,
+                        lhs,
+                        rhs,
+                    },
+                    span,
+                ),
                InfixKind::And => self.ast.push(
                    Expr::Binary {
                        op: BinaryOp::And,
@@ -138,6 +248,13 @@ impl Parser {
                    },
                    span,
                ),
+                InfixKind::As => self.ast.push(
+                    Expr::As {
+                        narrower: lhs,
+                        wider: rhs,
+                    },
+                    span,
+                ),
            };
        }

@@ -173,6 +290,28 @@ impl Parser {
            TokenKind::Let => self.parse_let(token.span),
            TokenKind::Match => self.parse_match(token.span),
            TokenKind::Import => self.parse_import(token.span),
+            TokenKind::Minus => {
+                let expr = self.parse_expr(17)?;
+                let span = token.span.join(self.ast.span(expr));
+                Ok(self.ast.push(
+                    Expr::Unary {
+                        op: UnaryOp::Neg,
+                        expr,
+                    },
+                    span,
+                ))
+            }
+            TokenKind::Bang => {
+                let expr = self.parse_expr(17)?;
+                let span = token.span.join(self.ast.span(expr));
+                Ok(self.ast.push(
+                    Expr::Unary {
+                        op: UnaryOp::Not,
+                        expr,
+                    },
+                    span,
+                ))
+            }
            TokenKind::Gt | TokenKind::Gte | TokenKind::Lt | TokenKind::Lte => {
                let op = match token.kind {
                    TokenKind::Gt => CompareOp::Gt,
@@ -181,7 +320,7 @@ impl Parser {
                    TokenKind::Lte => CompareOp::Lte,
                    _ => unreachable!(),
                };
-                let value = self.parse_expr(8)?;
+                let value = self.parse_expr(12)?;
                let span = token.span.join(self.ast.span(value));
                Ok(self.ast.push(Expr::CompareConstraint { op, value }, span))
            }
@@ -190,28 +329,64 @@ impl Parser {
    }

    fn parse_object_after_lbrace(&mut self, start_span: Span) -> Result<ExprId> {
+        if self.consume_kind(&TokenKind::Ellipsis).is_some() {
+            let value = self.parse_expr(0)?;
+            self.expect_kind(
+                &TokenKind::RBrace,
+                "expected '}' after map value constraint",
+            )?;
+            let span = start_span.join(self.previous_span());
+            return Ok(self.ast.push(Expr::MapConstraint { value }, span));
+        }
+
        let mut fields = Vec::new();
        if self.consume_kind(&TokenKind::RBrace).is_some() {
-            return Ok(self
-                .ast
-                .push(Expr::Object(fields), start_span.join(self.previous_span())));
+            return Ok(self.ast.push(
+                Expr::Object { fields, rest: None },
+                start_span.join(self.previous_span()),
+            ));
        }
+        let mut rest = None;
        loop {
            fields.push(self.parse_field()?);
            if self.consume_kind(&TokenKind::Semicolon).is_some() {
                if self.consume_kind(&TokenKind::RBrace).is_some() {
                    break;
                }
+                if let Some(ellipsis) = self.consume_kind(&TokenKind::Ellipsis) {
+                    let value = self.parse_expr(0)?;
+                    rest = Some(ObjectRest {
+                        value,
+                        span: ellipsis.join(self.ast.span(value)),
+                    });
+                    let _ = self.consume_kind(&TokenKind::Semicolon);
+                    self.expect_kind(
+                        &TokenKind::RBrace,
+                        "expected '}' after object rest constraint",
+                    )?;
+                    break;
+                }
                continue;
            }
            self.expect_kind(&TokenKind::RBrace, "expected ';' or '}' after object field")?;
            break;
        }
        let span = start_span.join(self.previous_span());
-        Ok(self.ast.push(Expr::Object(fields), span))
+        Ok(self.ast.push(Expr::Object { fields, rest }, span))
    }

    fn parse_array_after_lbracket(&mut self, start_span: Span) -> Result<ExprId> {
+        if self.consume_kind(&TokenKind::Ellipsis).is_some() {
+            let item = self.parse_expr(0)?;
+            let _ = self.consume_kind(&TokenKind::Comma);
+            self.expect_kind(
+                &TokenKind::RBracket,
+                "expected ']' after array element constraint",
+            )?;
+            let span = start_span.join(self.previous_span());
+            return Ok(self.ast.push(Expr::ArrayConstraint { item }, span));
+        }
+
        let mut items = Vec::new();
        if self.consume_kind(&TokenKind::RBracket).is_some() {
            return Ok(self
@@ -243,8 +418,9 @@ impl Parser {
        }

        let expr = self.parse_expr(0)?;
-        self.expect_kind(&TokenKind::RParen, "expected ')' after expression")?;
-        Ok(expr)
+        let end_span = self.expect_kind(&TokenKind::RParen, "expected ')' after expression")?;
+        let span = start_span.join(end_span);
+        Ok(self.ast.push(Expr::Parenthesized { expr }, span))
    }

    fn parse_params_after_lparen(&mut self) -> Result<Vec<Param>> {
@@ -403,9 +579,23 @@ impl Parser {

    fn peek_infix(&self) -> Option<(InfixKind, u8, u8)> {
        match self.peek_kind() {
+            TokenKind::As => Some((InfixKind::As, 0, 1)),
            TokenKind::Default => Some((InfixKind::Default, 1, 2)),
            TokenKind::SlashSlash => Some((InfixKind::Patch, 3, 4)),
            TokenKind::Amp => Some((InfixKind::And, 5, 6)),
+            TokenKind::PipePipe => Some((InfixKind::LogicalOr, 7, 8)),
+            TokenKind::AmpAmp => Some((InfixKind::LogicalAnd, 9, 10)),
+            TokenKind::EqualEqual => Some((InfixKind::Equal, 11, 12)),
+            TokenKind::BangEqual => Some((InfixKind::NotEqual, 11, 12)),
+            TokenKind::Gt => Some((InfixKind::Greater, 11, 12)),
+            TokenKind::Gte => Some((InfixKind::GreaterEqual, 11, 12)),
+            TokenKind::Lt => Some((InfixKind::Less, 11, 12)),
+            TokenKind::Lte => Some((InfixKind::LessEqual, 11, 12)),
+            TokenKind::PlusPlus => Some((InfixKind::Concat, 12, 13)),
+            TokenKind::Plus => Some((InfixKind::Add, 13, 14)),
+            TokenKind::Minus => Some((InfixKind::Sub, 13, 14)),
+            TokenKind::Star => Some((InfixKind::Mul, 15, 16)),
+            TokenKind::Slash => Some((InfixKind::Div, 15, 16)),
            _ => None,
        }
    }
@@ -498,6 +688,20 @@ impl Parser {

 #[derive(Debug, Clone, Copy)]
 enum InfixKind {
+    As,
+    Add,
+    Sub,
+    Mul,
+    Div,
+    Concat,
+    Equal,
+    NotEqual,
+    Greater,
+    GreaterEqual,
+    Less,
+    LessEqual,
+    LogicalAnd,
+    LogicalOr,
    And,
    Patch,
    Default,
@@ -511,15 +715,79 @@ mod tests {
    #[test]
    fn parses_top_level_fields_as_object() {
        let parsed = parse_source("port = Int & >= 1 default 8080;").unwrap();
-        assert!(matches!(parsed.ast.get(parsed.root).expr, Expr::Object(_)));
+        assert!(matches!(
+            parsed.ast.get(parsed.root).expr,
+            Expr::Object { .. }
+        ));
    }

    #[test]
    fn parses_object_dot_field() {
        let parsed = parse_source("{ feature.enable = false; }").unwrap();
-        let Expr::Object(fields) = &parsed.ast.get(parsed.root).expr else {
+        let Expr::Object { fields, .. } = &parsed.ast.get(parsed.root).expr else {
            panic!()
        };
        assert_eq!(fields[0].path, ["feature", "enable"]);
    }
+
+    #[test]
+    fn parses_array_constraint() {
+        let parsed = parse_source("[...(String & /^api-/)]").unwrap();
+        let Expr::ArrayConstraint { item } = parsed.ast.get(parsed.root).expr else {
+            panic!()
+        };
+        let Expr::Parenthesized { expr } = parsed.ast.get(item).expr else {
+            panic!()
+        };
+        assert!(matches!(parsed.ast.get(expr).expr, Expr::Binary { .. }));
+        assert_eq!(parsed.ast.span(item), Span::new(SourceId(0), 4, 22));
+    }
+
+    #[test]
+    fn parser_accepts_the_public_lossless_token_stream() {
+        let tokens = crate::tokenize_source("value = (# note\n 1);").unwrap();
+        let parsed = Parser::new(tokens).parse().unwrap();
+        let Expr::Object { fields, .. } = &parsed.ast.get(parsed.root).expr else {
+            panic!()
+        };
+        assert!(matches!(
+            parsed.ast.get(fields[0].value).expr,
+            Expr::Parenthesized { .. }
+        ));
+    }
+
+    #[test]
+    fn rejects_array_constraint_without_element_constraint() {
+        assert!(parse_source("[...]").is_err());
+    }
+
+    #[test]
+    fn parses_map_constraint() {
+        let parsed = parse_source("{...String}").unwrap();
+        let Expr::MapConstraint { value } = parsed.ast.get(parsed.root).expr else {
+            panic!()
+        };
+        assert!(matches!(parsed.ast.get(value).expr, Expr::Ident(_)));
+    }
+
+    #[test]
+    fn parses_object_rest_constraint_after_named_fields() {
+        let parsed = parse_source("{ hoge = Int; fuga = String; ...Unknown }").unwrap();
+        let Expr::Object { fields, rest } = &parsed.ast.get(parsed.root).expr else {
+            panic!()
+        };
+        assert_eq!(fields.len(), 2);
+        let rest = rest.as_ref().expect("object has a rest constraint");
+        assert!(matches!(parsed.ast.get(rest.value).expr, Expr::Ident(_)));
+    }
+
+    #[test]
+    fn parses_as_below_composition() {
+        let parsed = parse_source("value & override as Schema").unwrap();
+        let Expr::As { narrower, wider } = parsed.ast.get(parsed.root).expr else {
+            panic!()
+        };
+        assert!(matches!(parsed.ast.get(narrower).expr, Expr::Binary { .. }));
+        assert!(matches!(parsed.ast.get(wider).expr, Expr::Ident(_)));
+    }
 }
@@ -1,6 +1,6 @@
 use alloc::{string::String, vec::Vec};

-use crate::{ExprId, ast::CompareOp};
+use crate::{ExprId, Span, ast::CompareOp};

 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct ModuleId(pub u32);
@@ -11,6 +11,9 @@ pub struct ExprRef {
    pub expr: ExprId,
 }

+/// Evaluator-owned representation of a lazy concrete value or unresolved range.
+///
+/// Embedders normally construct [`crate::Value`] and consume [`Data`] instead.
 #[derive(Debug, Clone, PartialEq)]
 pub enum RuntimeValue {
    Concrete(ConcreteValue),
@@ -31,12 +34,20 @@ pub enum ConcreteValue {
 #[derive(Debug, Clone, PartialEq)]
 pub struct ObjectValue {
    pub fields: Vec<ObjectField>,
+    pub rest: Option<ObjectRest>,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct ObjectRest {
+    pub value: ThunkId,
+    pub span: Span,
 }

 #[derive(Debug, Clone, PartialEq)]
 pub struct ObjectField {
    pub name: String,
    pub value: ThunkId,
+    pub span: Span,
 }

 #[derive(Debug, Clone, PartialEq)]
@@ -54,13 +65,22 @@ pub struct FunctionParam {

 #[derive(Debug, Clone, PartialEq)]
 pub struct AbstractValue {
-    pub constraints: Vec<Constraint>,
+    pub constraints: Vec<ConstraintEntry>,
    pub default: Option<ThunkId>,
 }

+#[derive(Debug, Clone, PartialEq)]
+pub struct ConstraintEntry {
+    pub constraint: Constraint,
+    pub span: Span,
+}
+
 #[derive(Debug, Clone, PartialEq)]
 pub enum Constraint {
+    Unknown,
    Type(PrimitiveType),
+    ArrayItems(ThunkId),
+    MapValues(ThunkId),
    Compare(CompareOp, LiteralValue),
    Regex(String),
    BuiltinPredicate(String),
@@ -82,6 +102,7 @@ pub enum LiteralValue {
    Bool(bool),
 }

+/// Fully materialized Decodal data.
 #[derive(Debug, Clone, PartialEq)]
 pub enum Data {
    String(String),
@@ -108,6 +129,7 @@ pub struct EnvId(pub u32);
 pub struct Thunk {
    pub kind: ThunkKind,
    pub state: ThunkState,
+    pub span: Span,
 }

 #[derive(Debug, Clone)]
@@ -0,0 +1,445 @@
+use alloc::{collections::BTreeMap, format, string::String, vec::Vec};
+
+use crate::{Data, Value, runtime::DataField};
+
+pub trait DecodalSchema {
+    fn decodal_schema() -> Value;
+}
+
+pub trait DecodalDecode: Sized {
+    fn decodal_decode(data: &Data) -> DecodeResult<Self>;
+}
+
+pub trait IntoValue {
+    fn into_value(self) -> Value;
+}
+
+/// A map-like receiver for fields not named by a derived struct schema.
+pub trait DecodalRest: Sized {
+    fn decodal_rest_schema() -> Value;
+
+    fn decodal_decode_rest(data: &Data, known_fields: &[&str]) -> DecodeResult<Self>;
+}
+
+pub type DecodeResult<T> = core::result::Result<T, DecodeError>;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct DecodeError {
+    pub path: String,
+    pub message: String,
+}
+
+impl DecodeError {
+    pub fn new(path: impl Into<String>, message: impl Into<String>) -> Self {
+        Self {
+            path: path.into(),
+            message: message.into(),
+        }
+    }
+
+    pub fn at_type(path: &str, expected: &'static str) -> Self {
+        Self::new(path, format!("expected {expected}"))
+    }
+}
+
+impl core::fmt::Display for DecodeError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        if self.path.is_empty() {
+            write!(f, "{}", self.message)
+        } else {
+            write!(f, "{}: {}", self.path, self.message)
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for DecodeError {}
+
+pub fn decode_path<T: DecodalDecode>(data: &Data, path: &str) -> DecodeResult<T> {
+    let value = data_at_path(data, path).ok_or_else(|| DecodeError::new(path, "missing field"))?;
+    T::decodal_decode(value).map_err(|error| prefix_error(path, error))
+}
+
+pub fn data_at_path<'a>(data: &'a Data, path: &str) -> Option<&'a Data> {
+    let mut current = data;
+    for part in path.split('.') {
+        if part.is_empty() {
+            return None;
+        }
+        let Data::Object(fields) = current else {
+            return None;
+        };
+        current = &fields.iter().find(|field| field.name == part)?.value;
+    }
+    Some(current)
+}
+
+pub fn prefix_decode_error(path: &str, error: DecodeError) -> DecodeError {
+    prefix_error(path, error)
+}
+
+fn prefix_error(path: &str, mut error: DecodeError) -> DecodeError {
+    if error.path.is_empty() {
+        error.path = String::from(path);
+    } else if !path.is_empty() {
+        error.path = format!("{path}.{}", error.path);
+    }
+    error
+}
+
+impl DecodalSchema for Data {
+    fn decodal_schema() -> Value {
+        Value::unknown()
+    }
+}
+
+impl DecodalDecode for Data {
+    fn decodal_decode(data: &Data) -> DecodeResult<Self> {
+        Ok(data.clone())
+    }
+}
+
+impl IntoValue for Data {
+    fn into_value(self) -> Value {
+        match self {
+            Data::String(value) => Value::string(value),
+            Data::Int(value) => Value::int(value),
+            Data::Float(value) => Value::float(value),
+            Data::Bool(value) => Value::bool(value),
+            Data::Array(items) => Value::array(items.into_iter().map(IntoValue::into_value)),
+            Data::Object(fields) => Value::object(
+                fields
+                    .into_iter()
+                    .map(|field| (field.name, field.value.into_value())),
+            ),
+        }
+    }
+}
+
+impl DecodalSchema for String {
+    fn decodal_schema() -> Value {
+        Value::string_type()
+    }
+}
+
+impl DecodalDecode for String {
+    fn decodal_decode(data: &Data) -> DecodeResult<Self> {
+        match data {
+            Data::String(value) => Ok(value.clone()),
+            _ => Err(DecodeError::at_type("", "String")),
+        }
+    }
+}
+
+impl IntoValue for String {
+    fn into_value(self) -> Value {
+        Value::string(self)
+    }
+}
+
+impl IntoValue for &str {
+    fn into_value(self) -> Value {
+        Value::string(self)
+    }
+}
+
+macro_rules! impl_int_decode {
+    ($($ty:ty),* $(,)?) => {
+        $(
+            impl DecodalSchema for $ty {
+                fn decodal_schema() -> Value {
+                    Value::int_type()
+                }
+            }
+
+            impl DecodalDecode for $ty {
+                fn decodal_decode(data: &Data) -> DecodeResult<Self> {
+                    match data {
+                        Data::Int(value) => <$ty>::try_from(*value)
+                            .map_err(|_| DecodeError::new("", "integer value is out of range")),
+                        _ => Err(DecodeError::at_type("", "Int")),
+                    }
+                }
+            }
+
+            impl IntoValue for $ty {
+                fn into_value(self) -> Value {
+                    Value::int(self as i64)
+                }
+            }
+        )*
+    };
+}
+
+impl_int_decode!(i8, i16, i32, i64, u8, u16, u32);
+
+impl DecodalSchema for f64 {
+    fn decodal_schema() -> Value {
+        Value::float_type()
+    }
+}
+
+impl DecodalDecode for f64 {
+    fn decodal_decode(data: &Data) -> DecodeResult<Self> {
+        match data {
+            Data::Float(value) => Ok(*value),
+            Data::Int(value) => Ok(*value as f64),
+            _ => Err(DecodeError::at_type("", "Float")),
+        }
+    }
+}
+
+impl IntoValue for f64 {
+    fn into_value(self) -> Value {
+        Value::float(self)
+    }
+}
+
+impl DecodalSchema for f32 {
+    fn decodal_schema() -> Value {
+        Value::float_type()
+    }
+}
+
+impl DecodalDecode for f32 {
+    fn decodal_decode(data: &Data) -> DecodeResult<Self> {
+        f64::decodal_decode(data).map(|value| value as f32)
+    }
+}
+
+impl IntoValue for f32 {
+    fn into_value(self) -> Value {
+        Value::float(f64::from(self))
+    }
+}
+
+impl DecodalSchema for bool {
+    fn decodal_schema() -> Value {
+        Value::bool_type()
+    }
+}
+
+impl DecodalDecode for bool {
+    fn decodal_decode(data: &Data) -> DecodeResult<Self> {
+        match data {
+            Data::Bool(value) => Ok(*value),
+            _ => Err(DecodeError::at_type("", "Bool")),
+        }
+    }
+}
+
+impl IntoValue for bool {
+    fn into_value(self) -> Value {
+        Value::bool(self)
+    }
+}
+
+impl<T: DecodalSchema> DecodalSchema for Vec<T> {
+    fn decodal_schema() -> Value {
+        Value::array_of(T::decodal_schema())
+    }
+}
+
+impl<T: DecodalDecode> DecodalDecode for Vec<T> {
+    fn decodal_decode(data: &Data) -> DecodeResult<Self> {
+        match data {
+            Data::Array(items) => items
+                .iter()
+                .enumerate()
+                .map(|(index, item)| {
+                    T::decodal_decode(item)
+                        .map_err(|error| prefix_error(&format!("[{index}]"), error))
+                })
+                .collect(),
+            _ => Err(DecodeError::at_type("", "Array")),
+        }
+    }
+}
+
+impl<T: IntoValue> IntoValue for Vec<T> {
+    fn into_value(self) -> Value {
+        Value::array(self.into_iter().map(IntoValue::into_value))
+    }
+}
+
+impl<T: DecodalSchema> DecodalSchema for BTreeMap<String, T> {
+    fn decodal_schema() -> Value {
+        Value::map_of(T::decodal_schema())
+    }
+}
+
+impl<T: DecodalDecode> DecodalDecode for BTreeMap<String, T> {
+    fn decodal_decode(data: &Data) -> DecodeResult<Self> {
+        match data {
+            Data::Object(fields) => fields
+                .iter()
+                .map(|field| {
+                    T::decodal_decode(&field.value)
+                        .map(|value| (field.name.clone(), value))
+                        .map_err(|error| prefix_error(&field.name, error))
+                })
+                .collect(),
+            _ => Err(DecodeError::at_type("", "Object")),
+        }
+    }
+}
+
+impl<T: IntoValue> IntoValue for BTreeMap<String, T> {
+    fn into_value(self) -> Value {
+        Value::object(
+            self.into_iter()
+                .map(|(name, value)| (name, value.into_value())),
+        )
+    }
+}
+
+impl<T: DecodalSchema + DecodalDecode> DecodalRest for BTreeMap<String, T> {
+    fn decodal_rest_schema() -> Value {
+        T::decodal_schema()
+    }
+
+    fn decodal_decode_rest(data: &Data, known_fields: &[&str]) -> DecodeResult<Self> {
+        let Data::Object(fields) = data else {
+            return Err(DecodeError::at_type("", "Object"));
+        };
+        fields
+            .iter()
+            .filter(|field| !known_fields.contains(&field.name.as_str()))
+            .map(decode_rest_field::<T>)
+            .collect()
+    }
+}
+
+#[cfg(feature = "std")]
+impl<T: DecodalSchema> DecodalSchema for std::collections::HashMap<String, T> {
+    fn decodal_schema() -> Value {
+        Value::map_of(T::decodal_schema())
+    }
+}
+
+#[cfg(feature = "std")]
+impl<T: DecodalDecode> DecodalDecode for std::collections::HashMap<String, T> {
+    fn decodal_decode(data: &Data) -> DecodeResult<Self> {
+        match data {
+            Data::Object(fields) => fields
+                .iter()
+                .map(|field| {
+                    T::decodal_decode(&field.value)
+                        .map(|value| (field.name.clone(), value))
+                        .map_err(|error| prefix_error(&field.name, error))
+                })
+                .collect(),
+            _ => Err(DecodeError::at_type("", "Object")),
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl<T: IntoValue> IntoValue for std::collections::HashMap<String, T> {
+    fn into_value(self) -> Value {
+        let mut fields: Vec<_> = self
+            .into_iter()
+            .map(|(name, value)| (name, value.into_value()))
+            .collect();
+        fields.sort_by(|left, right| left.0.cmp(&right.0));
+        Value::object(fields)
+    }
+}
+
+#[cfg(feature = "std")]
+impl<T: DecodalSchema + DecodalDecode> DecodalRest for std::collections::HashMap<String, T> {
+    fn decodal_rest_schema() -> Value {
+        T::decodal_schema()
+    }
+
+    fn decodal_decode_rest(data: &Data, known_fields: &[&str]) -> DecodeResult<Self> {
+        let Data::Object(fields) = data else {
+            return Err(DecodeError::at_type("", "Object"));
+        };
+        fields
+            .iter()
+            .filter(|field| !known_fields.contains(&field.name.as_str()))
+            .map(decode_rest_field::<T>)
+            .collect()
+    }
+}
+
+fn decode_rest_field<T: DecodalDecode>(field: &DataField) -> DecodeResult<(String, T)> {
+    T::decodal_decode(&field.value)
+        .map(|value| (field.name.clone(), value))
+        .map_err(|error| prefix_error(&field.name, error))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::runtime::{Constraint, DataField, PrimitiveType};
+
+    #[test]
+    fn string_maps_expose_map_schemas_and_decode_objects() {
+        assert!(matches!(
+            BTreeMap::<String, i64>::decodal_schema(),
+            Value::MapRange { value, .. }
+                if matches!(
+                    *value,
+                    Value::Range { ref constraints, .. }
+                        if constraints == &[Constraint::Type(PrimitiveType::Int)]
+                )
+        ));
+
+        let data = Data::Object(alloc::vec![DataField {
+            name: String::from("api"),
+            value: Data::Int(8080),
+        }]);
+        let decoded = BTreeMap::<String, i64>::decodal_decode(&data).unwrap();
+        assert_eq!(decoded.get("api"), Some(&8080));
+    }
+
+    #[test]
+    fn data_is_the_unknown_schema_and_round_trips_values() {
+        assert!(matches!(
+            Data::decodal_schema(),
+            Value::Range { ref constraints, .. }
+                if constraints == &[Constraint::Unknown]
+        ));
+
+        let data = Data::Object(alloc::vec![DataField {
+            name: String::from("nested"),
+            value: Data::Array(alloc::vec![Data::Bool(true), Data::Int(2)]),
+        }]);
+        assert_eq!(Data::decodal_decode(&data).unwrap(), data);
+        assert!(matches!(data.into_value(), Value::Object { .. }));
+    }
+
+    #[test]
+    fn rest_maps_decode_only_fields_outside_the_known_domain() {
+        let data = Data::Object(alloc::vec![
+            DataField {
+                name: String::from("name"),
+                value: Data::String(String::from("api")),
+            },
+            DataField {
+                name: String::from("priority"),
+                value: Data::Int(3),
+            },
+        ]);
+        let decoded = BTreeMap::<String, Data>::decodal_decode_rest(&data, &["name"]).unwrap();
+        assert_eq!(decoded.len(), 1);
+        assert_eq!(decoded.get("priority"), Some(&Data::Int(3)));
+    }
+
+    #[cfg(feature = "std")]
+    #[test]
+    fn hash_maps_can_receive_rest_fields() {
+        let data = Data::Object(alloc::vec![DataField {
+            name: String::from("region"),
+            value: Data::String(String::from("ap-northeast-1")),
+        }]);
+        let decoded =
+            std::collections::HashMap::<String, String>::decodal_decode_rest(&data, &[]).unwrap();
+        assert_eq!(
+            decoded.get("region").map(String::as_str),
+            Some("ap-northeast-1")
+        );
+    }
+}
@@ -0,0 +1,333 @@
+use alloc::{boxed::Box, string::String, vec::Vec};
+
+use crate::runtime::{Constraint, LiteralValue, PrimitiveType};
+use crate::{CompareOp, Diagnostic, DiagnosticKind, Result, Span};
+
+/// A Decodal value supplied through the embedding API.
+///
+/// Unlike [`crate::Data`], a `Value` may contain unresolved ranges and
+/// defaults. The evaluator converts it into its lazy runtime representation
+/// when it is bound as a global or returned from an import loader.
+#[derive(Debug, Clone, PartialEq)]
+pub enum Value {
+    String(String),
+    Int(i64),
+    Float(f64),
+    Bool(bool),
+    Array(Vec<Value>),
+    ArrayRange {
+        item: Box<Value>,
+        constraints: Vec<Constraint>,
+        default: Option<Box<Value>>,
+    },
+    MapRange {
+        value: Box<Value>,
+        constraints: Vec<Constraint>,
+        default: Option<Box<Value>>,
+    },
+    Object {
+        fields: Vec<ValueField>,
+        rest: Option<Box<Value>>,
+    },
+    Range {
+        constraints: Vec<Constraint>,
+        default: Option<Box<Value>>,
+    },
+}
+
+/// A named field in a [`Value::Object`].
+#[derive(Debug, Clone, PartialEq)]
+pub struct ValueField {
+    pub name: String,
+    pub value: Value,
+}
+
+impl Value {
+    pub fn string(value: impl Into<String>) -> Self {
+        Self::String(value.into())
+    }
+
+    pub fn int(value: i64) -> Self {
+        Self::Int(value)
+    }
+
+    pub fn float(value: f64) -> Self {
+        Self::Float(value)
+    }
+
+    pub fn bool(value: bool) -> Self {
+        Self::Bool(value)
+    }
+
+    pub fn array<I>(items: I) -> Self
+    where
+        I: IntoIterator<Item = Value>,
+    {
+        Self::Array(items.into_iter().collect())
+    }
+
+    pub fn object<I, N>(fields: I) -> Self
+    where
+        I: IntoIterator<Item = (N, Value)>,
+        N: Into<String>,
+    {
+        Self::Object {
+            fields: fields
+                .into_iter()
+                .map(|(name, value)| ValueField {
+                    name: name.into(),
+                    value,
+                })
+                .collect(),
+            rest: None,
+        }
+    }
+
+    pub fn object_from_paths<I, N>(fields: I) -> Self
+    where
+        I: IntoIterator<Item = (N, Value)>,
+        N: Into<String>,
+    {
+        let mut root = Vec::new();
+        for (path, value) in fields {
+            insert_path(&mut root, &path.into(), value);
+        }
+        Self::Object {
+            fields: root,
+            rest: None,
+        }
+    }
+
+    pub fn object_from_paths_with_rest<I, N>(fields: I, rest: Value) -> Self
+    where
+        I: IntoIterator<Item = (N, Value)>,
+        N: Into<String>,
+    {
+        let mut root = Vec::new();
+        for (path, value) in fields {
+            insert_path(&mut root, &path.into(), value);
+        }
+        Self::Object {
+            fields: root,
+            rest: Some(Box::new(rest)),
+        }
+    }
+
+    pub fn object_with_rest<I, N>(fields: I, rest: Value) -> Self
+    where
+        I: IntoIterator<Item = (N, Value)>,
+        N: Into<String>,
+    {
+        Self::Object {
+            fields: fields
+                .into_iter()
+                .map(|(name, value)| ValueField {
+                    name: name.into(),
+                    value,
+                })
+                .collect(),
+            rest: Some(Box::new(rest)),
+        }
+    }
+
+    pub fn unknown() -> Self {
+        Self::range_with_constraint(Constraint::Unknown)
+    }
+
+    pub fn string_type() -> Self {
+        Self::range_with_constraint(Constraint::Type(PrimitiveType::String))
+    }
+
+    pub fn int_type() -> Self {
+        Self::range_with_constraint(Constraint::Type(PrimitiveType::Int))
+    }
+
+    pub fn float_type() -> Self {
+        Self::range_with_constraint(Constraint::Type(PrimitiveType::Float))
+    }
+
+    pub fn bool_type() -> Self {
+        Self::range_with_constraint(Constraint::Type(PrimitiveType::Bool))
+    }
+
+    pub fn array_of(item: Value) -> Self {
+        Self::ArrayRange {
+            item: Box::new(item),
+            constraints: Vec::new(),
+            default: None,
+        }
+    }
+
+    pub fn map_of(value: Value) -> Self {
+        Self::MapRange {
+            value: Box::new(value),
+            constraints: Vec::new(),
+            default: None,
+        }
+    }
+
+    pub fn builtin_predicate(name: impl Into<String>) -> Self {
+        Self::range_with_constraint(Constraint::BuiltinPredicate(name.into()))
+    }
+
+    pub fn range_with_constraint(constraint: Constraint) -> Self {
+        Self::Range {
+            constraints: alloc::vec![constraint],
+            default: None,
+        }
+    }
+
+    pub fn with_constraint(mut self, constraint: Constraint) -> Self {
+        match &mut self {
+            Self::Range { constraints, .. } => constraints.push(constraint),
+            Self::ArrayRange { constraints, .. } | Self::MapRange { constraints, .. } => {
+                constraints.push(constraint)
+            }
+            _ => {
+                self = Self::Range {
+                    constraints: alloc::vec![constraint],
+                    default: Some(Box::new(self)),
+                };
+            }
+        }
+        self
+    }
+
+    pub fn gt(self, value: i64) -> Self {
+        self.with_constraint(Constraint::Compare(CompareOp::Gt, LiteralValue::Int(value)))
+    }
+
+    pub fn gte(self, value: i64) -> Self {
+        self.with_constraint(Constraint::Compare(
+            CompareOp::Gte,
+            LiteralValue::Int(value),
+        ))
+    }
+
+    pub fn lt(self, value: i64) -> Self {
+        self.with_constraint(Constraint::Compare(CompareOp::Lt, LiteralValue::Int(value)))
+    }
+
+    pub fn lte(self, value: i64) -> Self {
+        self.with_constraint(Constraint::Compare(
+            CompareOp::Lte,
+            LiteralValue::Int(value),
+        ))
+    }
+
+    pub fn default(self, value: Value) -> Result<Self> {
+        match self {
+            Self::ArrayRange {
+                item,
+                constraints,
+                default: None,
+            } => Ok(Self::ArrayRange {
+                item,
+                constraints,
+                default: Some(Box::new(value)),
+            }),
+            Self::ArrayRange {
+                default: Some(_), ..
+            } => Err(Diagnostic::new(
+                DiagnosticKind::DefaultConflict,
+                Span::default(),
+                "value already has a default",
+            )),
+            Self::MapRange {
+                value: map_value,
+                constraints,
+                default: None,
+            } => Ok(Self::MapRange {
+                value: map_value,
+                constraints,
+                default: Some(Box::new(value)),
+            }),
+            Self::MapRange {
+                default: Some(_), ..
+            } => Err(Diagnostic::new(
+                DiagnosticKind::DefaultConflict,
+                Span::default(),
+                "value already has a default",
+            )),
+            Self::Range {
+                constraints,
+                default: None,
+            } => Ok(Self::Range {
+                constraints,
+                default: Some(Box::new(value)),
+            }),
+            Self::Range { .. } => Err(Diagnostic::new(
+                DiagnosticKind::DefaultConflict,
+                Span::default(),
+                "value already has a default",
+            )),
+            concrete => Ok(Self::Range {
+                constraints: Vec::new(),
+                default: Some(Box::new(concrete)),
+            }),
+        }
+    }
+
+    pub fn default_string(self, value: impl Into<String>) -> Result<Self> {
+        self.default(Self::string(value))
+    }
+
+    pub fn default_int(self, value: i64) -> Result<Self> {
+        self.default(Self::int(value))
+    }
+
+    pub fn default_float(self, value: f64) -> Result<Self> {
+        self.default(Self::float(value))
+    }
+
+    pub fn default_bool(self, value: bool) -> Result<Self> {
+        self.default(Self::bool(value))
+    }
+}
+
+impl ValueField {
+    pub fn new(name: impl Into<String>, value: Value) -> Self {
+        Self {
+            name: name.into(),
+            value,
+        }
+    }
+}
+
+fn insert_path(fields: &mut Vec<ValueField>, path: &str, value: Value) {
+    let mut parts = path.splitn(2, '.');
+    let Some(head) = parts.next().filter(|part| !part.is_empty()) else {
+        return;
+    };
+    if let Some(tail) = parts.next() {
+        if let Some(field) = fields.iter_mut().find(|field| field.name == head) {
+            if let Value::Object {
+                fields: children, ..
+            } = &mut field.value
+            {
+                insert_path(children, tail, value);
+            } else {
+                let mut children = Vec::new();
+                insert_path(&mut children, tail, value);
+                field.value = Value::Object {
+                    fields: children,
+                    rest: None,
+                };
+            }
+        } else {
+            let mut children = Vec::new();
+            insert_path(&mut children, tail, value);
+            fields.push(ValueField::new(
+                head,
+                Value::Object {
+                    fields: children,
+                    rest: None,
+                },
+            ));
+        }
+    } else if let Some(field) = fields.iter_mut().find(|field| field.name == head) {
+        field.value = value;
+    } else {
+        fields.push(ValueField::new(head, value));
+    }
+}
@@ -0,0 +1,22 @@
+[package]
+name = "decodal-derive"
+version = "0.2.0"
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+repository.workspace = true
+readme.workspace = true
+description = "Derive macro for generating Decodal schemas and typed decoders from Rust structs."
+keywords = ["decodal", "derive", "proc-macro", "schema"]
+categories = ["config", "development-tools::procedural-macro-helpers"]
+
+[lib]
+proc-macro = true
+
+[dependencies]
+proc-macro2 = "1"
+quote = "1"
+syn = { version = "2", features = ["full"] }
+
+[dev-dependencies]
+decodal = { path = "../decodal-core" }
@@ -0,0 +1,313 @@
+use proc_macro::TokenStream;
+use proc_macro2::TokenStream as TokenStream2;
+use quote::{format_ident, quote};
+use syn::{
+    Data, DeriveInput, Expr, Fields, LitStr, Result, Type, parse_macro_input, spanned::Spanned,
+};
+
+#[proc_macro_derive(Decodal, attributes(decodal))]
+pub fn derive_decodal(input: TokenStream) -> TokenStream {
+    match expand_decodal(parse_macro_input!(input as DeriveInput)) {
+        Ok(tokens) => tokens.into(),
+        Err(error) => error.to_compile_error().into(),
+    }
+}
+
+fn expand_decodal(input: DeriveInput) -> Result<TokenStream2> {
+    let name = input.ident;
+    let fields = match input.data {
+        Data::Struct(data) => match data.fields {
+            Fields::Named(fields) => fields.named,
+            _ => {
+                return Err(syn::Error::new(
+                    data.struct_token.span(),
+                    "Decodal derive supports structs with named fields only",
+                ));
+            }
+        },
+        _ => {
+            return Err(syn::Error::new(
+                name.span(),
+                "Decodal derive supports structs only",
+            ));
+        }
+    };
+
+    let mut schema_fields = Vec::new();
+    let mut decode_fields = Vec::new();
+    let mut known_field_roots = Vec::new();
+    let mut rest_field = None;
+
+    for field in fields {
+        let ident = field.ident.expect("named field");
+        let ty = field.ty;
+        let attrs = FieldAttrs::from_attrs(&field.attrs, &ident.to_string())?;
+
+        if attrs.rest {
+            if attrs.rename_explicit || attrs.default.is_some() || !attrs.constraints.is_empty() {
+                return Err(syn::Error::new(
+                    ident.span(),
+                    "`rest` cannot be combined with rename, default, or field constraints",
+                ));
+            }
+            if rest_field.is_some() {
+                return Err(syn::Error::new(
+                    ident.span(),
+                    "Decodal derive supports only one `rest` field",
+                ));
+            }
+            rest_field = Some((ident, ty));
+            continue;
+        }
+
+        let path = attrs.rename.clone();
+        known_field_roots.push(
+            path.split('.')
+                .next()
+                .expect("field paths are non-empty")
+                .to_owned(),
+        );
+        let schema_value = schema_expr(&ty, &attrs)?;
+        let decode_value = decode_expr(&ty, &path, &attrs);
+
+        schema_fields.push(quote! {
+            (#path, { #schema_value })
+        });
+        decode_fields.push(quote! {
+            #ident: #decode_value
+        });
+    }
+
+    if let Some((ident, ty)) = &rest_field {
+        decode_fields.push(quote! {
+            #ident: <#ty as ::decodal::DecodalRest>::decodal_decode_rest(
+                data,
+                &[#(#known_field_roots),*],
+            )?
+        });
+    }
+
+    let schema_entries = if schema_fields.is_empty() {
+        quote! { ::core::iter::empty::<(&'static str, ::decodal::Value)>() }
+    } else {
+        quote! { [#(#schema_fields),*] }
+    };
+
+    let build_schema = if let Some((_, ty)) = &rest_field {
+        quote! {
+            ::decodal::Value::object_from_paths_with_rest(
+                #schema_entries,
+                <#ty as ::decodal::DecodalRest>::decodal_rest_schema(),
+            )
+        }
+    } else {
+        quote! {
+            ::decodal::Value::object_from_paths(#schema_entries)
+        }
+    };
+
+    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
+
+    Ok(quote! {
+        impl #impl_generics ::decodal::DecodalSchema for #name #ty_generics #where_clause {
+            fn decodal_schema() -> ::decodal::Value {
+                #build_schema
+            }
+        }
+
+        impl #impl_generics ::decodal::DecodalDecode for #name #ty_generics #where_clause {
+            fn decodal_decode(data: &::decodal::Data) -> ::decodal::DecodeResult<Self> {
+                Ok(Self {
+                    #(#decode_fields),*
+                })
+            }
+        }
+    })
+}
+
+#[derive(Default)]
+struct FieldAttrs {
+    rename: String,
+    rename_explicit: bool,
+    rest: bool,
+    default: Option<DefaultAttr>,
+    constraints: Vec<ConstraintAttr>,
+}
+
+impl FieldAttrs {
+    fn from_attrs(attrs: &[syn::Attribute], fallback_name: &str) -> Result<Self> {
+        let mut output = Self {
+            rename: fallback_name.to_string(),
+            ..Self::default()
+        };
+
+        for attr in attrs {
+            if !attr.path().is_ident("decodal") {
+                continue;
+            }
+            attr.parse_nested_meta(|meta| {
+                if meta.path.is_ident("rename") {
+                    let value: LitStr = meta.value()?.parse()?;
+                    output.rename = value.value();
+                    output.rename_explicit = true;
+                    return Ok(());
+                }
+                if meta.path.is_ident("rest") {
+                    if meta.input.peek(syn::Token![=]) || meta.input.peek(syn::token::Paren) {
+                        return Err(meta.error("`rest` does not accept a value"));
+                    }
+                    output.rest = true;
+                    return Ok(());
+                }
+                if meta.path.is_ident("default") {
+                    if meta.input.peek(syn::Token![=]) {
+                        let expr: Expr = meta.value()?.parse()?;
+                        output.default = Some(DefaultAttr::Expr(expr));
+                    } else {
+                        output.default = Some(DefaultAttr::Default);
+                    }
+                    return Ok(());
+                }
+                if let Some(kind) = ConstraintKind::from_path(&meta.path) {
+                    let expr: Expr = meta.value()?.parse()?;
+                    output.constraints.push(ConstraintAttr { kind, expr });
+                    return Ok(());
+                }
+                Err(meta.error("unsupported decodal attribute"))
+            })?;
+        }
+
+        Ok(output)
+    }
+}
+
+enum DefaultAttr {
+    Default,
+    Expr(Expr),
+}
+
+struct ConstraintAttr {
+    kind: ConstraintKind,
+    expr: Expr,
+}
+
+#[derive(Clone, Copy)]
+enum ConstraintKind {
+    Gt,
+    Gte,
+    Lt,
+    Lte,
+}
+
+impl ConstraintKind {
+    fn from_path(path: &syn::Path) -> Option<Self> {
+        if path.is_ident("gt") {
+            Some(Self::Gt)
+        } else if path.is_ident("gte") {
+            Some(Self::Gte)
+        } else if path.is_ident("lt") {
+            Some(Self::Lt)
+        } else if path.is_ident("lte") {
+            Some(Self::Lte)
+        } else {
+            None
+        }
+    }
+
+    fn method(self) -> syn::Ident {
+        match self {
+            Self::Gt => format_ident!("gt"),
+            Self::Gte => format_ident!("gte"),
+            Self::Lt => format_ident!("lt"),
+            Self::Lte => format_ident!("lte"),
+        }
+    }
+}
+
+fn schema_expr(ty: &Type, attrs: &FieldAttrs) -> Result<TokenStream2> {
+    let mut tokens = quote! {
+        let mut schema = <#ty as ::decodal::DecodalSchema>::decodal_schema();
+    };
+
+    for constraint in &attrs.constraints {
+        let method = constraint.kind.method();
+        let expr = &constraint.expr;
+        tokens.extend(quote! {
+            schema = schema.#method(#expr);
+        });
+    }
+
+    if let Some(default) = &attrs.default {
+        let default_expr = match default {
+            DefaultAttr::Default => quote! { <#ty as ::core::default::Default>::default() },
+            DefaultAttr::Expr(expr) => quote! { (#expr) },
+        };
+        tokens.extend(quote! {
+            schema = schema
+                .default(::decodal::IntoValue::into_value(#default_expr))
+                .expect("Decodal derive generated a valid default");
+        });
+    }
+
+    tokens.extend(quote! { schema });
+    Ok(tokens)
+}
+
+fn decode_expr(ty: &Type, path: &str, attrs: &FieldAttrs) -> TokenStream2 {
+    let missing = if let Some(default) = &attrs.default {
+        match default {
+            DefaultAttr::Default => quote! { <#ty as ::core::default::Default>::default() },
+            DefaultAttr::Expr(expr) => quote! { ::core::convert::Into::into(#expr) },
+        }
+    } else {
+        quote! { return Err(::decodal::DecodeError::new(#path, "missing field")); }
+    };
+
+    quote! {
+        if let Some(value) = ::decodal::data_at_path(data, #path) {
+            <#ty as ::decodal::DecodalDecode>::decodal_decode(value)
+                .map_err(|error| ::decodal::prefix_decode_error(#path, error))?
+        } else {
+            #missing
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn rejects_multiple_rest_fields() {
+        let input: DeriveInput = syn::parse_quote! {
+            struct Invalid {
+                #[decodal(rest)]
+                first: std::collections::BTreeMap<String, String>,
+                #[decodal(rest)]
+                second: std::collections::BTreeMap<String, String>,
+            }
+        };
+        assert!(
+            expand_decodal(input)
+                .unwrap_err()
+                .to_string()
+                .contains("only one `rest` field")
+        );
+    }
+
+    #[test]
+    fn rejects_rest_field_modifiers() {
+        let input: DeriveInput = syn::parse_quote! {
+            struct Invalid {
+                #[decodal(rest, default)]
+                extra: std::collections::BTreeMap<String, String>,
+            }
+        };
+        assert!(
+            expand_decodal(input)
+                .unwrap_err()
+                .to_string()
+                .contains("cannot be combined")
+        );
+    }
+}
@@ -0,0 +1,268 @@
+use std::collections::BTreeMap;
+
+use decodal::{Constraint, Data, DecodalDecode, DecodalSchema, EmptyLoader, Engine, Value};
+use decodal_derive::Decodal;
+
+#[derive(Debug, PartialEq, Decodal)]
+struct Service {
+    name: String,
+    #[decodal(gt = 443, default = 8443)]
+    port: i64,
+    #[decodal(default = true, rename = "feature.enable")]
+    feature_enabled: bool,
+    #[decodal(default)]
+    tags: Vec<String>,
+}
+
+#[derive(Debug, PartialEq, Decodal)]
+struct Worker {
+    name: String,
+    #[decodal(default = true)]
+    enabled: bool,
+}
+
+#[derive(Debug, PartialEq, Decodal)]
+struct Fleet {
+    workers: Vec<Worker>,
+}
+
+#[derive(Debug, PartialEq, Decodal)]
+struct OpenConfig {
+    name: String,
+    #[decodal(default = true, rename = "feature.enabled")]
+    enabled: bool,
+    #[decodal(rest)]
+    extra: BTreeMap<String, Data>,
+}
+
+#[derive(Debug, PartialEq, Decodal)]
+struct StringLabels {
+    name: String,
+    #[decodal(rest)]
+    labels: BTreeMap<String, String>,
+}
+
+#[derive(Debug, PartialEq, Decodal)]
+struct OpenBag {
+    #[decodal(rest)]
+    values: BTreeMap<String, Data>,
+}
+
+#[test]
+fn derives_schema_and_decode() {
+    let mut engine = Engine::new(EmptyLoader);
+    engine
+        .bind_global("Service", Service::decodal_schema())
+        .unwrap();
+    let module = engine
+        .add_root_source(
+            "test",
+            "test",
+            r#"
+            Service & {
+              name = "api";
+              port = 9443;
+              feature.enable = false;
+              tags = ["web", "prod"];
+            }
+            "#,
+        )
+        .unwrap();
+    let value = engine.eval_module(module).unwrap();
+    let data = engine.materialize(&value).unwrap();
+    let service = Service::decodal_decode(&data).unwrap();
+    assert_eq!(
+        service,
+        Service {
+            name: "api".into(),
+            port: 9443,
+            feature_enabled: false,
+            tags: vec!["web".into(), "prod".into()],
+        }
+    );
+}
+
+#[test]
+fn defaults_are_available_in_schema() {
+    let mut engine = Engine::new(EmptyLoader);
+    engine
+        .bind_global("Service", Service::decodal_schema())
+        .unwrap();
+    let module = engine
+        .add_root_source(
+            "test",
+            "test",
+            r#"
+            Service & {
+              name = "api";
+            }
+            "#,
+        )
+        .unwrap();
+    let value = engine.eval_module(module).unwrap();
+    let data = engine.materialize(&value).unwrap();
+    let service = Service::decodal_decode(&data).unwrap();
+    assert_eq!(service.port, 8443);
+    assert!(service.feature_enabled);
+    assert!(service.tags.is_empty());
+}
+
+#[test]
+fn decode_reports_field_path() {
+    let data = Data::Object(vec![]);
+    let error = Service::decodal_decode(&data).unwrap_err();
+    assert_eq!(error.path, "name");
+}
+
+#[test]
+fn vec_schema_rejects_invalid_element_before_decode() {
+    let mut engine = Engine::new(EmptyLoader);
+    engine
+        .bind_global("Service", Service::decodal_schema())
+        .unwrap();
+    let module = engine
+        .add_root_source(
+            "test",
+            "test",
+            r#"
+            Service & {
+              name = "api";
+              port = 9443;
+              tags = ["web", 1];
+            }
+            "#,
+        )
+        .unwrap();
+    let error = engine.eval_module(module).unwrap_err();
+    assert!(
+        error
+            .labels
+            .iter()
+            .any(|label| label.message.contains("array element [1]"))
+    );
+}
+
+#[test]
+fn vec_schema_applies_nested_struct_defaults() {
+    let mut engine = Engine::new(EmptyLoader);
+    engine
+        .bind_global("Fleet", Fleet::decodal_schema())
+        .unwrap();
+    let module = engine
+        .add_root_source(
+            "test",
+            "test",
+            r#"
+            Fleet & {
+              workers = [{ name = "api"; }];
+            }
+            "#,
+        )
+        .unwrap();
+    let value = engine.eval_module(module).unwrap();
+    let data = engine.materialize(&value).unwrap();
+    let fleet = Fleet::decodal_decode(&data).unwrap();
+    assert_eq!(
+        fleet,
+        Fleet {
+            workers: vec![Worker {
+                name: "api".into(),
+                enabled: true,
+            }],
+        }
+    );
+}
+
+#[test]
+fn rest_map_opens_the_derived_object_and_collects_additional_fields() {
+    let schema = OpenConfig::decodal_schema();
+    let Value::Object {
+        fields,
+        rest: Some(rest),
+    } = schema
+    else {
+        panic!("derived schema should have an object rest range")
+    };
+    assert_eq!(fields.len(), 2);
+    assert!(matches!(
+        *rest,
+        Value::Range { ref constraints, .. }
+            if constraints == &[Constraint::Unknown]
+    ));
+
+    let mut engine = Engine::new(EmptyLoader);
+    engine
+        .bind_global("OpenConfig", OpenConfig::decodal_schema())
+        .unwrap();
+    let module = engine
+        .add_root_source(
+            "test",
+            "test",
+            r#"
+            {
+              name = "api";
+              plugin = { name = "cache"; };
+              retries = 3;
+            } as OpenConfig
+            "#,
+        )
+        .unwrap();
+    let value = engine.eval_module(module).unwrap();
+    let data = engine.materialize(&value).unwrap();
+    let config = OpenConfig::decodal_decode(&data).unwrap();
+
+    assert_eq!(config.name, "api");
+    assert!(config.enabled);
+    assert_eq!(config.extra.get("retries"), Some(&Data::Int(3)));
+    assert!(matches!(config.extra.get("plugin"), Some(Data::Object(_))));
+    assert!(!config.extra.contains_key("name"));
+    assert!(!config.extra.contains_key("feature"));
+}
+
+#[test]
+fn typed_rest_map_constrains_each_additional_field() {
+    let mut engine = Engine::new(EmptyLoader);
+    engine
+        .bind_global("StringLabels", StringLabels::decodal_schema())
+        .unwrap();
+    let module = engine
+        .add_root_source(
+            "test",
+            "test",
+            r#"{ name = "service"; region = "ap-northeast-1"; tier = "edge"; } as StringLabels"#,
+        )
+        .unwrap();
+    let value = engine.eval_module(module).unwrap();
+    let data = engine.materialize(&value).unwrap();
+    let labels = StringLabels::decodal_decode(&data).unwrap();
+    assert_eq!(labels.labels.get("region"), Some(&"ap-northeast-1".into()));
+    assert_eq!(labels.labels.get("tier"), Some(&"edge".into()));
+
+    let module = engine
+        .add_root_source(
+            "invalid",
+            "invalid",
+            r#"{ name = "service"; priority = 1; } as StringLabels"#,
+        )
+        .unwrap();
+    assert!(engine.eval_module(module).is_err());
+}
+
+#[test]
+fn rest_only_struct_collects_every_field() {
+    let schema = OpenBag::decodal_schema();
+    assert!(matches!(
+        schema,
+        Value::Object {
+            ref fields,
+            rest: Some(_),
+        } if fields.is_empty()
+    ));
+
+    let data = Data::Object(vec![decodal::runtime::DataField {
+        name: "answer".into(),
+        value: Data::Int(42),
+    }]);
+    let bag = OpenBag::decodal_decode(&data).unwrap();
+    assert_eq!(bag.values.get("answer"), Some(&Data::Int(42)));
+}
@@ -0,0 +1,14 @@
+[package]
+name = "decodal-language-service"
+version.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+repository.workspace = true
+readme.workspace = true
+description = "Host-configurable semantic language service for Decodal."
+keywords = ["decodal", "lsp", "language-server", "editor"]
+categories = ["development-tools", "text-editors"]
+
+[dependencies]
+decodal = { version = "0.4.0", path = "../decodal-core" }
@@ -0,0 +1,913 @@
+use std::collections::{BTreeMap, HashMap};
+
+use decodal::{
+    Engine, HostEnvironment, ImportLoader, LoadedImport, Result, Value, runtime::RuntimeValue,
+};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum CompletionKind {
+    Keyword,
+    Constant,
+    Type,
+    Variable,
+    Namespace,
+    Property,
+    File,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct CompletionItem {
+    pub label: String,
+    pub kind: CompletionKind,
+    pub detail: Option<String>,
+    pub priority: i32,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct CompletionResult {
+    /// UTF-8 byte offset at which the unfinished token starts.
+    pub from: usize,
+    pub items: Vec<CompletionItem>,
+}
+
+#[derive(Debug, Clone, Default, PartialEq, Eq)]
+struct FieldTree(BTreeMap<String, FieldTree>);
+
+impl FieldTree {
+    fn new() -> Self {
+        Self::default()
+    }
+
+    fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+
+    fn insert(&mut self, name: String, fields: FieldTree) {
+        self.0.insert(name, fields);
+    }
+
+    fn get(&self, name: &str) -> Option<&FieldTree> {
+        self.0.get(name)
+    }
+
+    fn remove(&mut self, name: &str) -> Option<FieldTree> {
+        self.0.remove(name)
+    }
+}
+
+impl IntoIterator for FieldTree {
+    type Item = (String, FieldTree);
+    type IntoIter = std::collections::btree_map::IntoIter<String, FieldTree>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.0.into_iter()
+    }
+}
+
+impl FromIterator<(String, FieldTree)> for FieldTree {
+    fn from_iter<T: IntoIterator<Item = (String, FieldTree)>>(iter: T) -> Self {
+        Self(iter.into_iter().collect())
+    }
+}
+
+pub(crate) fn complete<E: HostEnvironment>(
+    environment: &E,
+    key: &str,
+    source: &str,
+    position: usize,
+    explicit: bool,
+) -> Result<Option<CompletionResult>> {
+    let position = floor_char_boundary(source, position.min(source.len()));
+    if let Some((from, prefix)) = unfinished_import(source, position) {
+        let mut loader = environment.create_loader();
+        let items = loader
+            .complete_import(Some(key), prefix)?
+            .into_iter()
+            .map(|candidate| CompletionItem {
+                label: candidate.specifier,
+                kind: CompletionKind::File,
+                detail: candidate.detail,
+                priority: 30,
+            })
+            .collect();
+        return Ok(Some(CompletionResult {
+            from,
+            items: unique_items(items),
+        }));
+    }
+
+    if in_string_or_comment(source, position) {
+        return Ok(None);
+    }
+
+    let tokens = tokenize(source);
+    let local_fields = collect_fields(&tokens);
+    let imports = collect_import_bindings(&tokens);
+    let globals = collect_globals(environment)?;
+
+    if let Some((from, path)) = member_path(source, position) {
+        let mut parts = path.split('.');
+        let Some(root) = parts.next() else {
+            return Ok(None);
+        };
+        let mut fields;
+        let detail;
+        if let Some(specifier) = imports.get(root) {
+            let mut loader = environment.create_loader();
+            let loaded = loader.load(Some(key), specifier)?;
+            detail = match &loaded {
+                LoadedImport::Source { name, .. } => name.clone(),
+                LoadedImport::Value { key, .. } => key.clone(),
+            };
+            fields = match loaded {
+                LoadedImport::Source { source, .. } => collect_fields(&tokenize(&source)),
+                LoadedImport::Value { value, .. } => fields_from_value(&value),
+            };
+        } else if let Some(local) = local_fields.get(root) {
+            fields = local.clone();
+            detail = String::from("local value");
+        } else if let Some(global) = globals.get(root) {
+            fields = global.clone();
+            detail = String::from("host global");
+        } else {
+            return Ok(None);
+        }
+
+        for part in parts {
+            let Some(nested) = fields.remove(part) else {
+                return Ok(None);
+            };
+            fields = nested;
+        }
+        let items = fields
+            .into_iter()
+            .map(|(label, children)| CompletionItem {
+                label,
+                kind: if children.is_empty() {
+                    CompletionKind::Property
+                } else {
+                    CompletionKind::Namespace
+                },
+                detail: Some(detail.clone()),
+                priority: 30,
+            })
+            .collect();
+        return Ok(Some(CompletionResult {
+            from,
+            items: unique_items(items),
+        }));
+    }
+
+    let word_from = word_start(source, position);
+    if word_from == position && !explicit {
+        return Ok(None);
+    }
+
+    let mut items = builtin_items();
+    for (label, children) in local_fields {
+        items.push(CompletionItem {
+            label,
+            kind: if children.is_empty() {
+                CompletionKind::Variable
+            } else {
+                CompletionKind::Namespace
+            },
+            detail: Some(if children.is_empty() {
+                String::from("local value")
+            } else {
+                String::from("local object")
+            }),
+            priority: 20,
+        });
+    }
+    for label in collect_parameters(&tokens) {
+        items.push(CompletionItem {
+            label,
+            kind: CompletionKind::Variable,
+            detail: Some(String::from("parameter")),
+            priority: 20,
+        });
+    }
+    for (label, specifier) in imports {
+        items.push(CompletionItem {
+            label,
+            kind: CompletionKind::Namespace,
+            detail: Some(specifier),
+            priority: 30,
+        });
+    }
+    for (label, children) in globals {
+        items.push(CompletionItem {
+            label,
+            kind: if children.is_empty() {
+                CompletionKind::Variable
+            } else {
+                CompletionKind::Namespace
+            },
+            detail: Some(String::from("host global")),
+            priority: 40,
+        });
+    }
+
+    Ok(Some(CompletionResult {
+        from: word_from,
+        items: unique_items(items),
+    }))
+}
+
+fn builtin_items() -> Vec<CompletionItem> {
+    [
+        ("let", CompletionKind::Keyword, "local bindings", 5),
+        ("in", CompletionKind::Keyword, "let body", 0),
+        ("match", CompletionKind::Keyword, "pattern matching", 5),
+        ("import", CompletionKind::Keyword, "load a module", 5),
+        ("default", CompletionKind::Keyword, "fallback value", 0),
+        ("as", CompletionKind::Keyword, "refine narrower as wider", 0),
+        ("true", CompletionKind::Constant, "Bool", 0),
+        ("false", CompletionKind::Constant, "Bool", 0),
+        ("String", CompletionKind::Type, "string constraint", 5),
+        ("Int", CompletionKind::Type, "integer constraint", 5),
+        ("Float", CompletionKind::Type, "float constraint", 5),
+        ("Bool", CompletionKind::Type, "boolean constraint", 5),
+        ("Unknown", CompletionKind::Type, "unknown top range", 5),
+    ]
+    .into_iter()
+    .map(|(label, kind, detail, priority)| CompletionItem {
+        label: label.into(),
+        kind,
+        detail: Some(detail.into()),
+        priority,
+    })
+    .collect()
+}
+
+fn collect_globals<E: HostEnvironment>(environment: &E) -> Result<FieldTree> {
+    let mut engine = environment.create_engine()?;
+    let mut fields = FieldTree::new();
+    for (name, value) in engine.global_values()? {
+        fields.insert(name, fields_from_runtime(&mut engine, &value, 0)?);
+    }
+    Ok(fields)
+}
+
+fn fields_from_runtime<L: ImportLoader>(
+    engine: &mut Engine<L>,
+    value: &RuntimeValue,
+    depth: usize,
+) -> Result<FieldTree> {
+    if depth >= 32 {
+        return Ok(FieldTree::new());
+    }
+    let Some(fields) = engine.value_fields(value)? else {
+        return Ok(FieldTree::new());
+    };
+    let mut tree = FieldTree::new();
+    for (name, value) in fields {
+        tree.insert(name, fields_from_runtime(engine, &value, depth + 1)?);
+    }
+    Ok(tree)
+}
+
+fn fields_from_value(value: &Value) -> FieldTree {
+    match value {
+        Value::Object { fields, .. } => fields
+            .iter()
+            .map(|field| (field.name.clone(), fields_from_value(&field.value)))
+            .collect(),
+        Value::ArrayRange {
+            default: Some(value),
+            ..
+        }
+        | Value::MapRange {
+            default: Some(value),
+            ..
+        }
+        | Value::Range {
+            default: Some(value),
+            ..
+        } => fields_from_value(value),
+        _ => FieldTree::new(),
+    }
+}
+
+fn unique_items(items: Vec<CompletionItem>) -> Vec<CompletionItem> {
+    let mut unique = HashMap::<String, CompletionItem>::new();
+    let mut order = Vec::new();
+    for item in items {
+        if !unique.contains_key(&item.label) {
+            order.push(item.label.clone());
+        }
+        let replace = unique
+            .get(&item.label)
+            .is_none_or(|previous| item.priority > previous.priority);
+        if replace {
+            unique.insert(item.label.clone(), item);
+        }
+    }
+    order
+        .into_iter()
+        .filter_map(|label| unique.remove(&label))
+        .collect()
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+enum TokenKind {
+    Identifier(String),
+    String(String),
+    Symbol(char),
+    Arrow,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+struct Token {
+    kind: TokenKind,
+}
+
+fn tokenize(source: &str) -> Vec<Token> {
+    let bytes = source.as_bytes();
+    let mut tokens = Vec::new();
+    let mut index = 0;
+    while index < bytes.len() {
+        match bytes[index] {
+            b' ' | b'\t' | b'\r' | b'\n' => index += 1,
+            b'#' => {
+                while index < bytes.len() && bytes[index] != b'\n' {
+                    index += 1;
+                }
+            }
+            b'"' => {
+                index += 1;
+                let start = index;
+                let mut escaped = false;
+                while index < bytes.len() {
+                    let byte = bytes[index];
+                    if escaped {
+                        escaped = false;
+                    } else if byte == b'\\' {
+                        escaped = true;
+                    } else if byte == b'"' || byte == b'\n' {
+                        break;
+                    }
+                    index += 1;
+                }
+                let value = unescape_string(&source[start..index]);
+                index = index.saturating_add(1);
+                tokens.push(Token {
+                    kind: TokenKind::String(value),
+                });
+            }
+            byte if is_identifier_start(byte) => {
+                let start = index;
+                index += 1;
+                while index < bytes.len() && is_identifier_continue(bytes[index]) {
+                    index += 1;
+                }
+                tokens.push(Token {
+                    kind: TokenKind::Identifier(source[start..index].into()),
+                });
+            }
+            b'=' if bytes.get(index + 1) == Some(&b'>') => {
+                tokens.push(Token {
+                    kind: TokenKind::Arrow,
+                });
+                index += 2;
+            }
+            byte => {
+                tokens.push(Token {
+                    kind: TokenKind::Symbol(byte as char),
+                });
+                index += 1;
+            }
+        }
+    }
+    tokens
+}
+
+fn unescape_string(value: &str) -> String {
+    let mut chars = value.chars();
+    let mut unescaped = String::new();
+    while let Some(ch) = chars.next() {
+        if ch != '\\' {
+            unescaped.push(ch);
+            continue;
+        }
+        let Some(escaped) = chars.next() else {
+            unescaped.push('\\');
+            break;
+        };
+        unescaped.push(match escaped {
+            'n' => '\n',
+            'r' => '\r',
+            't' => '\t',
+            escaped => escaped,
+        });
+    }
+    unescaped
+}
+
+fn collect_fields(tokens: &[Token]) -> FieldTree {
+    let mut fields = FieldTree::new();
+    collect_fields_in(tokens, 0, tokens.len(), &mut fields);
+    fields
+}
+
+fn collect_fields_in(tokens: &[Token], start: usize, end: usize, fields: &mut FieldTree) {
+    let mut index = start;
+    while index < end {
+        let Some((path, equals)) = field_definition_at(tokens, index, end) else {
+            index += 1;
+            continue;
+        };
+        let value_start = equals + 1;
+        let value_end = definition_end(tokens, value_start, end);
+        let mut nested = &mut *fields;
+        for part in path {
+            nested = nested.0.entry(part).or_default();
+        }
+        collect_fields_in(tokens, value_start, value_end, nested);
+        index = value_end.saturating_add(1);
+    }
+}
+
+fn field_definition_at(tokens: &[Token], start: usize, end: usize) -> Option<(Vec<String>, usize)> {
+    let TokenKind::Identifier(first) = &tokens.get(start)?.kind else {
+        return None;
+    };
+    let mut path = vec![first.clone()];
+    let mut index = start + 1;
+    while index + 1 < end
+        && matches!(tokens[index].kind, TokenKind::Symbol('.'))
+        && matches!(tokens[index + 1].kind, TokenKind::Identifier(_))
+    {
+        let TokenKind::Identifier(part) = &tokens[index + 1].kind else {
+            unreachable!()
+        };
+        path.push(part.clone());
+        index += 2;
+    }
+    matches!(
+        tokens.get(index).map(|token| &token.kind),
+        Some(TokenKind::Symbol('='))
+    )
+    .then_some((path, index))
+}
+
+fn definition_end(tokens: &[Token], start: usize, end: usize) -> usize {
+    let mut delimiters = Vec::new();
+    for (index, token) in tokens.iter().enumerate().take(end).skip(start) {
+        match token.kind {
+            TokenKind::Symbol('(' | '[' | '{') => delimiters.push(token.kind.clone()),
+            TokenKind::Symbol(')') if matches!(delimiters.last(), Some(TokenKind::Symbol('('))) => {
+                delimiters.pop();
+            }
+            TokenKind::Symbol(']') if matches!(delimiters.last(), Some(TokenKind::Symbol('['))) => {
+                delimiters.pop();
+            }
+            TokenKind::Symbol('}') if matches!(delimiters.last(), Some(TokenKind::Symbol('{'))) => {
+                delimiters.pop();
+            }
+            TokenKind::Symbol(';') if delimiters.is_empty() => return index,
+            _ => {}
+        }
+    }
+    end
+}
+
+fn collect_import_bindings(tokens: &[Token]) -> BTreeMap<String, String> {
+    let mut imports = BTreeMap::new();
+    for window in tokens.windows(4) {
+        let (
+            TokenKind::Identifier(binding),
+            TokenKind::Symbol('='),
+            TokenKind::Identifier(keyword),
+            TokenKind::String(specifier),
+        ) = (
+            &window[0].kind,
+            &window[1].kind,
+            &window[2].kind,
+            &window[3].kind,
+        )
+        else {
+            continue;
+        };
+        if keyword == "import" {
+            imports.insert(binding.clone(), specifier.clone());
+        }
+    }
+    imports
+}
+
+fn collect_parameters(tokens: &[Token]) -> Vec<String> {
+    let mut parameters = Vec::new();
+    for (close, token) in tokens.iter().enumerate() {
+        if !matches!(token.kind, TokenKind::Symbol(')'))
+            || !matches!(
+                tokens.get(close + 1).map(|token| &token.kind),
+                Some(TokenKind::Arrow)
+            )
+        {
+            continue;
+        }
+        let Some(open) = matching_open_paren(tokens, close) else {
+            continue;
+        };
+        let mut depth = 0usize;
+        let mut segment_start = true;
+        for token in &tokens[open + 1..close] {
+            match &token.kind {
+                TokenKind::Symbol('(' | '[' | '{') => depth += 1,
+                TokenKind::Symbol(')' | ']' | '}') => depth = depth.saturating_sub(1),
+                TokenKind::Symbol(',') if depth == 0 => segment_start = true,
+                TokenKind::Identifier(name) if depth == 0 && segment_start => {
+                    parameters.push(name.clone());
+                    segment_start = false;
+                }
+                _ => {}
+            }
+        }
+    }
+    parameters
+}
+
+fn matching_open_paren(tokens: &[Token], close: usize) -> Option<usize> {
+    let mut depth = 0usize;
+    for index in (0..close).rev() {
+        match tokens[index].kind {
+            TokenKind::Symbol(')') => depth += 1,
+            TokenKind::Symbol('(') if depth == 0 => return Some(index),
+            TokenKind::Symbol('(') => depth -= 1,
+            _ => {}
+        }
+    }
+    None
+}
+
+fn unfinished_import(source: &str, position: usize) -> Option<(usize, &str)> {
+    let bytes = source.as_bytes();
+    let mut index = 0usize;
+    let mut previous_word = None;
+    while index < position {
+        match bytes[index] {
+            b' ' | b'\t' | b'\r' | b'\n' => index += 1,
+            b'#' => {
+                while index < position && bytes[index] != b'\n' {
+                    index += 1;
+                }
+                previous_word = None;
+            }
+            b'"' => {
+                let from = index + 1;
+                index += 1;
+                let mut escaped = false;
+                while index < position {
+                    let byte = bytes[index];
+                    if escaped {
+                        escaped = false;
+                    } else if byte == b'\\' {
+                        escaped = true;
+                    } else if byte == b'"' || byte == b'\n' {
+                        break;
+                    }
+                    index += 1;
+                }
+                if index == position && previous_word == Some("import") {
+                    return Some((from, &source[from..position]));
+                }
+                index = index.saturating_add(1);
+                previous_word = None;
+            }
+            byte if is_identifier_start(byte) => {
+                let start = index;
+                index += 1;
+                while index < position && is_identifier_continue(bytes[index]) {
+                    index += 1;
+                }
+                previous_word = Some(&source[start..index]);
+            }
+            _ => {
+                index += 1;
+                previous_word = None;
+            }
+        }
+    }
+    None
+}
+
+fn in_string_or_comment(source: &str, position: usize) -> bool {
+    let bytes = source.as_bytes();
+    let mut index = 0usize;
+    while index < position {
+        match bytes[index] {
+            b'#' => {
+                while index < position && bytes[index] != b'\n' {
+                    index += 1;
+                }
+                if index == position {
+                    return true;
+                }
+            }
+            b'"' => {
+                index += 1;
+                let mut escaped = false;
+                while index < position {
+                    let byte = bytes[index];
+                    if escaped {
+                        escaped = false;
+                    } else if byte == b'\\' {
+                        escaped = true;
+                    } else if byte == b'"' || byte == b'\n' {
+                        break;
+                    }
+                    index += 1;
+                }
+                if index == position {
+                    return true;
+                }
+                index = index.saturating_add(1);
+            }
+            _ => index += 1,
+        }
+    }
+    false
+}
+
+fn member_path(source: &str, position: usize) -> Option<(usize, &str)> {
+    let bytes = source.as_bytes();
+    let from = word_start(source, position);
+    if from == 0 || bytes[from - 1] != b'.' {
+        return None;
+    }
+    let mut base_start = from - 1;
+    while base_start > 0 {
+        let byte = bytes[base_start - 1];
+        if is_identifier_continue(byte) || byte == b'.' {
+            base_start -= 1;
+        } else {
+            break;
+        }
+    }
+    let base = &source[base_start..from - 1];
+    (!base.is_empty()
+        && base
+            .split('.')
+            .all(|part| !part.is_empty() && is_identifier(part)))
+    .then_some((from, base))
+}
+
+fn word_start(source: &str, position: usize) -> usize {
+    let bytes = source.as_bytes();
+    let mut from = position;
+    while from > 0 && is_identifier_continue(bytes[from - 1]) {
+        from -= 1;
+    }
+    from
+}
+
+fn is_identifier(value: &str) -> bool {
+    let bytes = value.as_bytes();
+    bytes.first().is_some_and(|byte| is_identifier_start(*byte))
+        && bytes[1..].iter().all(|byte| is_identifier_continue(*byte))
+}
+
+fn is_identifier_start(byte: u8) -> bool {
+    byte.is_ascii_alphabetic() || byte == b'_'
+}
+
+fn is_identifier_continue(byte: u8) -> bool {
+    is_identifier_start(byte) || byte.is_ascii_digit()
+}
+
+fn floor_char_boundary(source: &str, mut position: usize) -> usize {
+    while !source.is_char_boundary(position) {
+        position -= 1;
+    }
+    position
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::BTreeMap;
+
+    use decodal::{
+        Diagnostic, DiagnosticKind, EmptyLoader, ImportCandidate, LoadedImport, Span, Value,
+    };
+
+    use super::*;
+
+    #[derive(Clone, Default)]
+    struct TestEnvironment {
+        files: BTreeMap<String, String>,
+    }
+
+    #[derive(Clone, Default)]
+    struct TestLoader {
+        files: BTreeMap<String, String>,
+    }
+
+    impl ImportLoader for TestLoader {
+        fn load(&mut self, _current_key: Option<&str>, specifier: &str) -> Result<LoadedImport> {
+            if specifier == "./post.md" {
+                return Ok(LoadedImport::value(
+                    "post.md",
+                    Value::object([
+                        (
+                            "frontmatter",
+                            Value::object([
+                                ("title", Value::string("Hello")),
+                                ("draft", Value::bool(false)),
+                            ]),
+                        ),
+                        ("body", Value::string("# Hello")),
+                    ]),
+                ));
+            }
+            let key = resolve_virtual("main.dcdl", specifier);
+            let Some(source) = self.files.get(&key) else {
+                return Err(Diagnostic::new(
+                    DiagnosticKind::Import,
+                    Span::default(),
+                    "unknown import",
+                ));
+            };
+            Ok(LoadedImport::source(key.clone(), key, source))
+        }
+
+        fn complete_import(
+            &mut self,
+            _current_key: Option<&str>,
+            prefix: &str,
+        ) -> Result<Vec<ImportCandidate>> {
+            Ok(self
+                .files
+                .keys()
+                .map(|path| format!("./{path}"))
+                .filter(|path| path.starts_with(prefix))
+                .map(ImportCandidate::new)
+                .collect())
+        }
+    }
+
+    impl HostEnvironment for TestEnvironment {
+        type Loader = TestLoader;
+
+        fn create_loader(&self) -> Self::Loader {
+            TestLoader {
+                files: self.files.clone(),
+            }
+        }
+
+        fn configure_engine(&self, engine: &mut Engine<Self::Loader>) -> Result<()> {
+            engine.bind_global(
+                "App",
+                Value::object([(
+                    "config",
+                    Value::object([("enabled", Value::bool_type()), ("port", Value::int_type())]),
+                )]),
+            )?;
+            Ok(())
+        }
+    }
+
+    fn environment() -> TestEnvironment {
+        TestEnvironment {
+            files: BTreeMap::from([
+                (
+                    "schemas/service.dcdl".into(),
+                    "Service = { name = String; resources = { cpu = Int; }; };".into(),
+                ),
+                (
+                    "env/production.dcdl".into(),
+                    "capacity = { cpu = 2000; };".into(),
+                ),
+                (
+                    "資料/service.dcdl".into(),
+                    "Service = { label = String; };".into(),
+                ),
+            ]),
+        }
+    }
+
+    fn labels(result: CompletionResult) -> Vec<String> {
+        result.items.into_iter().map(|item| item.label).collect()
+    }
+
+    #[test]
+    fn completes_import_paths_from_the_host_loader() {
+        let source = "schema = import \"./sch";
+        let result = complete(&environment(), "main.dcdl", source, source.len(), false)
+            .unwrap()
+            .unwrap();
+        assert_eq!(result.from, source.len() - 5);
+        assert!(labels(result).contains(&"./schemas/service.dcdl".into()));
+    }
+
+    #[test]
+    fn completes_nested_fields_from_imported_source() {
+        let source = "let schema = import \"./schemas/service.dcdl\"; in schema.Service.";
+        let result = complete(&environment(), "main.dcdl", source, source.len(), false)
+            .unwrap()
+            .unwrap();
+        assert_eq!(labels(result), ["name", "resources"]);
+    }
+
+    #[test]
+    fn completes_structured_host_imports() {
+        let source = "let post = import \"./post.md\"; in post.frontmatter.";
+        let result = complete(&environment(), "main.dcdl", source, source.len(), false)
+            .unwrap()
+            .unwrap();
+        assert_eq!(labels(result), ["draft", "title"]);
+    }
+
+    #[test]
+    fn preserves_unicode_import_specifiers() {
+        let source = "let schema = import \"./資料/service.dcdl\"; in schema.Service.";
+        let result = complete(&environment(), "main.dcdl", source, source.len(), false)
+            .unwrap()
+            .unwrap();
+        assert_eq!(labels(result), ["label"]);
+    }
+
+    #[test]
+    fn completes_host_globals_from_the_evaluation_environment() {
+        let source = "App.config.";
+        let result = complete(&environment(), "main.dcdl", source, source.len(), false)
+            .unwrap()
+            .unwrap();
+        assert_eq!(labels(result), ["enabled", "port"]);
+    }
+
+    #[test]
+    fn completes_language_locals_parameters_and_partial_members() {
+        let source = "let service = { port = 8080; }; in (value: Int) => service.po";
+        let result = complete(&environment(), "main.dcdl", source, source.len(), false)
+            .unwrap()
+            .unwrap();
+        assert_eq!(result.from, source.len() - 2);
+        assert_eq!(labels(result), ["port"]);
+
+        let source = "let service = { port = 8080; }; in (value: Int) => val";
+        let result = complete(&environment(), "main.dcdl", source, source.len(), false)
+            .unwrap()
+            .unwrap();
+        let labels = labels(result);
+        assert!(labels.contains(&"String".into()));
+        assert!(labels.contains(&"Unknown".into()));
+        assert!(labels.contains(&"service".into()));
+        assert!(labels.contains(&"value".into()));
+        assert!(labels.contains(&"App".into()));
+    }
+
+    #[test]
+    fn suppresses_completions_in_strings_and_comments() {
+        let string = "value = \"hello world\"";
+        assert!(
+            complete(&environment(), "main.dcdl", string, string.len() - 1, false)
+                .unwrap()
+                .is_none()
+        );
+        let comment = "value = true; # hello";
+        assert!(
+            complete(&environment(), "main.dcdl", comment, comment.len(), false)
+                .unwrap()
+                .is_none()
+        );
+    }
+
+    #[test]
+    fn empty_environment_remains_supported() {
+        let result = complete(&EmptyEnvironment, "main.dcdl", "Str", 3, false)
+            .unwrap()
+            .unwrap();
+        assert!(labels(result).contains(&"String".into()));
+        let result = complete(&EmptyEnvironment, "main.dcdl", "Unk", 3, false)
+            .unwrap()
+            .unwrap();
+        assert!(labels(result).contains(&"Unknown".into()));
+    }
+
+    struct EmptyEnvironment;
+
+    impl HostEnvironment for EmptyEnvironment {
+        type Loader = EmptyLoader;
+
+        fn create_loader(&self) -> Self::Loader {
+            EmptyLoader
+        }
+    }
+
+    fn resolve_virtual(current: &str, specifier: &str) -> String {
+        let mut parts = current.split('/').collect::<Vec<_>>();
+        parts.pop();
+        for part in specifier.split('/') {
+            match part {
+                "" | "." => {}
+                ".." => {
+                    parts.pop();
+                }
+                part => parts.push(part),
+            }
+        }
+        parts.join("/")
+    }
+}
@@ -0,0 +1,204 @@
+use decodal::{Data, Diagnostic, HostEnvironment, Result};
+
+mod completion;
+
+pub use completion::{CompletionItem, CompletionKind, CompletionResult};
+
+/// Semantic tooling backed by the same host environment as production.
+pub struct LanguageService<E> {
+    environment: E,
+}
+
+impl<E> LanguageService<E> {
+    pub fn new(environment: E) -> Self {
+        Self { environment }
+    }
+
+    pub fn environment(&self) -> &E {
+        &self.environment
+    }
+
+    pub fn environment_mut(&mut self) -> &mut E {
+        &mut self.environment
+    }
+
+    pub fn into_environment(self) -> E {
+        self.environment
+    }
+}
+
+impl<E: HostEnvironment> LanguageService<E> {
+    /// Runs the production parse, evaluation, and materialization pipeline.
+    pub fn evaluate(
+        &self,
+        key: impl Into<String>,
+        name: impl Into<String>,
+        source: &str,
+    ) -> Result<Data> {
+        let mut engine = self.environment.create_engine()?;
+        let module = engine.add_root_source(key, name, source)?;
+        let value = engine.eval_module(module)?;
+        engine.materialize(&value)
+    }
+
+    /// Evaluates a document and exposes failures in an editor-friendly form.
+    ///
+    /// The evaluator currently stops at the first failure, so an invalid
+    /// analysis contains one diagnostic. The collection leaves room for a
+    /// future diagnostic-accumulation pass without changing this API.
+    pub fn analyze(
+        &self,
+        key: impl Into<String>,
+        name: impl Into<String>,
+        source: &str,
+    ) -> SemanticAnalysis {
+        match self.evaluate(key, name, source) {
+            Ok(data) => SemanticAnalysis {
+                data: Some(data),
+                diagnostics: Vec::new(),
+            },
+            Err(diagnostic) => SemanticAnalysis {
+                data: None,
+                diagnostics: vec![diagnostic],
+            },
+        }
+    }
+
+    /// Completes the document using the same host globals and import loader as
+    /// production evaluation.
+    pub fn complete(
+        &self,
+        key: impl AsRef<str>,
+        source: &str,
+        position: usize,
+        explicit: bool,
+    ) -> Result<Option<CompletionResult>> {
+        completion::complete(&self.environment, key.as_ref(), source, position, explicit)
+    }
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct SemanticAnalysis {
+    pub data: Option<Data>,
+    pub diagnostics: Vec<Diagnostic>,
+}
+
+impl SemanticAnalysis {
+    pub fn is_valid(&self) -> bool {
+        self.diagnostics.is_empty()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use decodal::{
+        Data, Diagnostic, DiagnosticKind, Engine, ImportLoader, LoadedImport, Span, Value,
+    };
+
+    use super::*;
+
+    const ROOT: &str = r#"Post & import "./post.md""#;
+
+    struct ContentEnvironment {
+        draft: Value,
+    }
+
+    struct ContentLoader {
+        draft: Value,
+    }
+
+    impl ImportLoader for ContentLoader {
+        fn load(
+            &mut self,
+            _current_key: Option<&str>,
+            specifier: &str,
+        ) -> decodal::Result<LoadedImport> {
+            if specifier != "./post.md" {
+                return Err(Diagnostic::new(
+                    DiagnosticKind::Import,
+                    Span::default(),
+                    "unknown content import",
+                ));
+            }
+            Ok(LoadedImport::value(
+                "content/post.md",
+                Value::object([
+                    (
+                        "frontmatter",
+                        Value::object([
+                            ("title", Value::string("Hello")),
+                            ("draft", self.draft.clone()),
+                        ]),
+                    ),
+                    ("body", Value::string("# Hello")),
+                ]),
+            ))
+        }
+    }
+
+    impl HostEnvironment for ContentEnvironment {
+        type Loader = ContentLoader;
+
+        fn create_loader(&self) -> Self::Loader {
+            ContentLoader {
+                draft: self.draft.clone(),
+            }
+        }
+
+        fn configure_engine(&self, engine: &mut Engine<Self::Loader>) -> decodal::Result<()> {
+            engine.bind_global(
+                "Post",
+                Value::object([
+                    (
+                        "frontmatter",
+                        Value::object([
+                            ("title", Value::string_type()),
+                            ("draft", Value::bool_type()),
+                        ]),
+                    ),
+                    ("body", Value::string_type()),
+                ]),
+            )?;
+            Ok(())
+        }
+    }
+
+    fn evaluate_direct(environment: &ContentEnvironment) -> decodal::Result<Data> {
+        let mut engine = environment.create_engine()?;
+        let module = engine.add_root_source("main.dcdl", "main.dcdl", ROOT)?;
+        let value = engine.eval_module(module)?;
+        engine.materialize(&value)
+    }
+
+    #[test]
+    fn injected_environment_matches_direct_evaluation() {
+        let environment = ContentEnvironment {
+            draft: Value::bool(false),
+        };
+        let direct = evaluate_direct(&environment).unwrap();
+        let service = LanguageService::new(&environment);
+        let analysis = service.analyze("main.dcdl", "main.dcdl", ROOT);
+
+        assert!(analysis.is_valid());
+        assert_eq!(analysis.data, Some(direct));
+    }
+
+    #[test]
+    fn injected_environment_preserves_import_diagnostics() {
+        let service = LanguageService::new(ContentEnvironment {
+            draft: Value::string("maybe"),
+        });
+        let analysis = service.analyze("main.dcdl", "main.dcdl", ROOT);
+
+        assert!(!analysis.is_valid());
+        assert_eq!(analysis.data, None);
+        assert_eq!(
+            analysis.diagnostics[0].message,
+            "expected Bool, found String"
+        );
+        assert_eq!(
+            analysis.diagnostics[0].notes,
+            ["imported `content/post.md` at `frontmatter.draft` supplied a value of type String"]
+        );
+    }
+}
@@ -0,0 +1,22 @@
+[package]
+name = "decodal-language-tools"
+version.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+repository.workspace = true
+readme.workspace = true
+description = "Source-level language tooling for Decodal."
+keywords = ["decodal", "formatter", "lsp", "language-tools"]
+categories = ["development-tools", "text-processing"]
+
+[lib]
+crate-type = ["cdylib", "rlib"]
+
+[dependencies]
+decodal = { version = "0.4.0", path = "../decodal-core" }
+serde_json.workspace = true
+wasm-bindgen.workspace = true
+
+[package.metadata.wasm-pack.profile.release]
+wasm-opt = false
@@ -0,0 +1,838 @@
+use std::{error::Error, fmt};
+
+use decodal::{
+    Ast, BinaryOp, CompareOp, Expr, ExprId, Field, ObjectRest, Param, SourceForm, Span,
+    SyntaxToken, SyntaxTokenKind,
+    ast::{MatchArm, UnaryOp},
+    parse_source, tokenize_source,
+};
+use wasm_bindgen::prelude::*;
+
+const INDENT: usize = 4;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct FormatError {
+    message: String,
+}
+
+impl FormatError {
+    fn new(message: impl Into<String>) -> Self {
+        Self {
+            message: message.into(),
+        }
+    }
+
+    pub fn message(&self) -> &str {
+        &self.message
+    }
+}
+
+impl fmt::Display for FormatError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.message)
+    }
+}
+
+impl Error for FormatError {}
+
+/// Formats a complete Decodal source with the canonical parser and syntax tokens.
+///
+/// Native and WebAssembly callers execute this exact implementation. Comments
+/// are recovered from the lossless token stream while expression structure and
+/// precedence come from the same AST used by evaluation.
+pub fn format_source(source: &str) -> Result<String, FormatError> {
+    let parsed = parse_source(source)
+        .map_err(|diagnostic| FormatError::new(format!("parse error: {}", diagnostic.message)))?;
+    let tokens = tokenize_source(source)
+        .map_err(|diagnostic| FormatError::new(format!("lex error: {}", diagnostic.message)))?;
+    Ok(Formatter::new(source, &parsed.ast, tokens).format(parsed.root, parsed.source_form))
+}
+
+#[wasm_bindgen(js_name = formatSource)]
+pub fn format_source_json(source: &str) -> String {
+    match format_source(source) {
+        Ok(formatted) => serde_json::json!({ "ok": true, "source": formatted }).to_string(),
+        Err(error) => serde_json::json!({ "ok": false, "error": error.message() }).to_string(),
+    }
+}
+
+struct Formatter<'a> {
+    source: &'a str,
+    ast: &'a Ast,
+    tokens: Vec<SyntaxToken>,
+    comments: Vec<Span>,
+}
+
+impl<'a> Formatter<'a> {
+    fn new(source: &'a str, ast: &'a Ast, tokens: Vec<SyntaxToken>) -> Self {
+        let comments = tokens
+            .iter()
+            .filter(|token| token.kind == SyntaxTokenKind::Comment)
+            .map(|token| token.span)
+            .collect();
+        Self {
+            source,
+            ast,
+            tokens,
+            comments,
+        }
+    }
+
+    fn format(&self, root: ExprId, source_form: SourceForm) -> String {
+        let mut out = String::new();
+        if source_form == SourceForm::Fields {
+            let Expr::Object { fields, .. } = &self.ast.get(root).expr else {
+                unreachable!("field-form sources parse to an object")
+            };
+            self.write_field_list(&mut out, fields, 0, self.source.len(), 0);
+        } else {
+            let span = self.ast.span(root);
+            self.write_between(&mut out, 0, span.start as usize, None, 0);
+            self.write_expr(&mut out, root, 0, 0);
+            self.write_between(
+                &mut out,
+                span.end as usize,
+                self.source.len(),
+                Some(span.end as usize),
+                0,
+            );
+        }
+        trim_trailing_whitespace(&mut out);
+        out.push('\n');
+        out
+    }
+
+    fn write_field_list(
+        &self,
+        out: &mut String,
+        fields: &[Field],
+        start: usize,
+        end: usize,
+        indent: usize,
+    ) {
+        let mut cursor = start;
+        let mut previous_end = None;
+        for field in fields {
+            let field_start = field.span.start as usize;
+            self.write_between(out, cursor, field_start, previous_end, indent);
+            write_indent(out, indent);
+            self.write_field(out, field, indent);
+            out.push(';');
+            cursor = field.span.end as usize;
+            previous_end = Some(cursor);
+        }
+        self.write_between(out, cursor, end, previous_end, indent);
+    }
+
+    fn write_field(&self, out: &mut String, field: &Field, indent: usize) {
+        let value_start = self.ast.span(field.value).start as usize;
+        if self.has_comment_between(field.span.start as usize, value_start) {
+            out.push_str(self.raw(field.span));
+            return;
+        }
+        for (index, part) in field.path.iter().enumerate() {
+            if index > 0 {
+                out.push('.');
+            }
+            out.push_str(part);
+        }
+        out.push_str(" = ");
+        self.write_expr(out, field.value, indent, 0);
+    }
+
+    fn write_expr(&self, out: &mut String, id: ExprId, indent: usize, parent_prec: u8) {
+        let node = self.ast.get(id);
+        if self.has_comment(node.span)
+            && !matches!(
+                node.expr,
+                Expr::Object { .. } | Expr::Array(_) | Expr::Let { .. } | Expr::Match { .. }
+            )
+        {
+            out.push_str(self.raw(node.span));
+            return;
+        }
+
+        let precedence = self.precedence(id);
+        let parenthesize = precedence < parent_prec;
+        if parenthesize {
+            out.push('(');
+        }
+
+        match &node.expr {
+            Expr::Literal(_) | Expr::Ident(_) | Expr::RegexConstraint(_) | Expr::Wildcard => {
+                out.push_str(self.raw(node.span));
+            }
+            Expr::Object { fields, rest } => {
+                self.write_object(out, node.span, fields, rest.as_ref(), indent)
+            }
+            Expr::Array(items) => self.write_array(out, node.span, items, indent),
+            Expr::ArrayConstraint { item } => {
+                out.push_str("[...");
+                self.write_expr(out, *item, indent, 0);
+                out.push(']');
+            }
+            Expr::MapConstraint { value } => {
+                out.push_str("{...");
+                self.write_expr(out, *value, indent, 0);
+                out.push('}');
+            }
+            Expr::Let { bindings, body } => self.write_let(out, node.span, bindings, *body, indent),
+            Expr::Import(_) => {
+                out.push_str("import ");
+                let raw = self.raw(node.span);
+                out.push_str(raw.strip_prefix("import").unwrap_or(raw).trim());
+            }
+            Expr::Path { base, field } => {
+                self.write_expr(out, *base, indent, precedence);
+                out.push('.');
+                out.push_str(field);
+            }
+            Expr::Call { callee, args } => {
+                self.write_expr(out, *callee, indent, precedence);
+                out.push('(');
+                for (index, argument) in args.iter().enumerate() {
+                    if index > 0 {
+                        out.push_str(", ");
+                    }
+                    self.write_expr(out, *argument, indent, 0);
+                }
+                out.push(')');
+            }
+            Expr::Function { params, body } => self.write_function(out, params, *body, indent),
+            Expr::Parenthesized { expr } => {
+                out.push('(');
+                self.write_expr(out, *expr, indent, 0);
+                out.push(')');
+            }
+            Expr::Match { scrutinee, arms } => {
+                self.write_match(out, node.span, *scrutinee, arms, indent)
+            }
+            Expr::Unary { op, expr } => {
+                out.push_str(match op {
+                    UnaryOp::Neg => "-",
+                    UnaryOp::Not => "!",
+                });
+                self.write_expr(out, *expr, indent, precedence);
+            }
+            Expr::Binary { op, lhs, rhs } => {
+                self.write_expr(out, *lhs, indent, precedence);
+                out.push(' ');
+                out.push_str(binary_operator(*op));
+                out.push(' ');
+                self.write_expr(out, *rhs, indent, precedence + 1);
+            }
+            Expr::Default { base, fallback } => {
+                self.write_expr(out, *base, indent, precedence);
+                out.push_str(" default ");
+                self.write_expr(out, *fallback, indent, precedence + 1);
+            }
+            Expr::As { narrower, wider } => {
+                self.write_expr(out, *narrower, indent, precedence);
+                out.push_str(" as ");
+                self.write_expr(out, *wider, indent, precedence + 1);
+            }
+            Expr::CompareConstraint { op, value } => {
+                out.push_str(compare_operator(*op));
+                out.push(' ');
+                self.write_expr(out, *value, indent, precedence);
+            }
+        }
+
+        if parenthesize {
+            out.push(')');
+        }
+    }
+
+    fn write_object(
+        &self,
+        out: &mut String,
+        span: Span,
+        fields: &[Field],
+        rest: Option<&ObjectRest>,
+        indent: usize,
+    ) {
+        let (start, end) =
+            self.delimited_range(span, SyntaxTokenKind::LBrace, SyntaxTokenKind::RBrace);
+        if fields.is_empty() && rest.is_none() && !self.has_comment_between(start, end) {
+            out.push_str("{}");
+            return;
+        }
+        out.push_str("{\n");
+        let field_end = rest.map_or(end, |rest| rest.span.start as usize);
+        self.write_field_list(out, fields, start, field_end, indent + INDENT);
+        if let Some(rest) = rest {
+            write_indent(out, indent + INDENT);
+            out.push_str("...");
+            let value_start = self.ast.span(rest.value).start as usize;
+            let ellipsis = self
+                .tokens_between(rest.span.start as usize, value_start)
+                .find(|token| token.kind == SyntaxTokenKind::Ellipsis)
+                .expect("parsed object rest constraints contain `...`");
+            if self.has_comment_between(ellipsis.span.end as usize, value_start) {
+                self.write_between(
+                    out,
+                    ellipsis.span.end as usize,
+                    value_start,
+                    Some(ellipsis.span.end as usize),
+                    indent + INDENT,
+                );
+                write_indent(out, indent + INDENT);
+            }
+            self.write_expr(out, rest.value, indent + INDENT, 0);
+            self.write_between(
+                out,
+                rest.span.end as usize,
+                end,
+                Some(rest.span.end as usize),
+                indent + INDENT,
+            );
+        }
+        write_indent(out, indent);
+        out.push('}');
+    }
+
+    fn write_array(&self, out: &mut String, span: Span, items: &[ExprId], indent: usize) {
+        let (start, end) =
+            self.delimited_range(span, SyntaxTokenKind::LBracket, SyntaxTokenKind::RBracket);
+        if items.is_empty() && !self.has_comment_between(start, end) {
+            out.push_str("[]");
+            return;
+        }
+        let inline = !self.has_comment_between(start, end)
+            && items.iter().all(|item| self.is_inline_expr(*item));
+        if inline {
+            out.push('[');
+            for (index, item) in items.iter().enumerate() {
+                if index > 0 {
+                    out.push_str(", ");
+                }
+                self.write_expr(out, *item, indent, 0);
+            }
+            out.push(']');
+            return;
+        }
+
+        out.push_str("[\n");
+        let mut cursor = start;
+        let mut previous_end = None;
+        for item in items {
+            let item_span = self.ast.span(*item);
+            self.write_between(
+                out,
+                cursor,
+                item_span.start as usize,
+                previous_end,
+                indent + INDENT,
+            );
+            write_indent(out, indent + INDENT);
+            self.write_expr(out, *item, indent + INDENT, 0);
+            out.push(',');
+            cursor = item_span.end as usize;
+            previous_end = Some(cursor);
+        }
+        self.write_between(out, cursor, end, previous_end, indent + INDENT);
+        write_indent(out, indent);
+        out.push(']');
+    }
+
+    fn write_let(
+        &self,
+        out: &mut String,
+        span: Span,
+        bindings: &[Field],
+        body: ExprId,
+        indent: usize,
+    ) {
+        let body_span = self.ast.span(body);
+        let in_token = self
+            .tokens_between(span.start as usize, body_span.start as usize)
+            .rev()
+            .find(|token| token.kind == SyntaxTokenKind::In)
+            .expect("parsed let expressions contain `in`");
+        let let_token = self
+            .tokens_between(span.start as usize, span.end as usize)
+            .find(|token| token.kind == SyntaxTokenKind::Let)
+            .expect("parsed let expressions contain `let`");
+
+        out.push_str("let\n");
+        self.write_field_list(
+            out,
+            bindings,
+            let_token.span.end as usize,
+            in_token.span.start as usize,
+            indent + INDENT,
+        );
+        write_indent(out, indent);
+        out.push_str("in");
+        self.write_between(
+            out,
+            in_token.span.end as usize,
+            body_span.start as usize,
+            Some(in_token.span.end as usize),
+            indent + INDENT,
+        );
+        write_indent(out, indent + INDENT);
+        self.write_expr(out, body, indent + INDENT, 0);
+    }
+
+    fn write_function(&self, out: &mut String, params: &[Param], body: ExprId, indent: usize) {
+        out.push('(');
+        for (index, parameter) in params.iter().enumerate() {
+            if index > 0 {
+                out.push_str(", ");
+            }
+            out.push_str(&parameter.name);
+            if let Some(constraint) = parameter.constraint {
+                out.push_str(": ");
+                self.write_expr(out, constraint, indent, 0);
+            }
+        }
+        out.push_str(") =>");
+        if self.is_inline_expr(body) {
+            out.push(' ');
+            self.write_expr(out, body, indent, 0);
+        } else {
+            out.push('\n');
+            write_indent(out, indent + INDENT);
+            self.write_expr(out, body, indent + INDENT, 0);
+        }
+    }
+
+    fn write_match(
+        &self,
+        out: &mut String,
+        span: Span,
+        scrutinee: ExprId,
+        arms: &[MatchArm],
+        indent: usize,
+    ) {
+        out.push_str("match ");
+        self.write_expr(out, scrutinee, indent, 0);
+        let scrutinee_end = self.ast.span(scrutinee).end as usize;
+        let open = self
+            .tokens_between(scrutinee_end, span.end as usize)
+            .find(|token| token.kind == SyntaxTokenKind::LBrace)
+            .expect("parsed match expressions contain `{`");
+        let close = self
+            .tokens_between(open.span.end as usize, span.end as usize)
+            .rev()
+            .find(|token| token.kind == SyntaxTokenKind::RBrace)
+            .expect("parsed match expressions contain `}`");
+        let start = open.span.end as usize;
+        let end = close.span.start as usize;
+        if self.has_comment_between(scrutinee_end, open.span.start as usize) {
+            self.write_between(
+                out,
+                scrutinee_end,
+                open.span.start as usize,
+                Some(scrutinee_end),
+                indent,
+            );
+            write_indent(out, indent);
+            out.push('{');
+        } else {
+            out.push_str(" {");
+        }
+        if arms.is_empty() && !self.has_comment_between(start, end) {
+            out.push('}');
+            return;
+        }
+
+        out.push('\n');
+        let mut cursor = start;
+        let mut previous_end = None;
+        for arm in arms {
+            self.write_between(
+                out,
+                cursor,
+                arm.span.start as usize,
+                previous_end,
+                indent + INDENT,
+            );
+            write_indent(out, indent + INDENT);
+            if self.has_comment_between(
+                self.ast.span(arm.pattern).end as usize,
+                self.ast.span(arm.body).start as usize,
+            ) {
+                out.push_str(self.raw(arm.span));
+            } else {
+                self.write_expr(out, arm.pattern, indent + INDENT, 0);
+                out.push_str(": ");
+                self.write_expr(out, arm.body, indent + INDENT, 0);
+            }
+            out.push(';');
+            cursor = arm.span.end as usize;
+            previous_end = Some(cursor);
+        }
+        self.write_between(out, cursor, end, previous_end, indent + INDENT);
+        write_indent(out, indent);
+        out.push('}');
+    }
+
+    fn write_between(
+        &self,
+        out: &mut String,
+        start: usize,
+        end: usize,
+        previous_end: Option<usize>,
+        indent: usize,
+    ) {
+        let mut cursor = start.min(end);
+        for comment in self.comments_between(start, end) {
+            let comment_start = comment.start as usize;
+            let trailing = previous_end.is_some_and(|previous| {
+                !out.ends_with('\n') && self.same_line(previous, comment_start)
+            });
+            if trailing {
+                out.push(' ');
+                out.push_str(self.raw(*comment));
+                out.push('\n');
+            } else {
+                ensure_line_break(out);
+                if self.has_blank_line(cursor, comment_start) {
+                    ensure_blank_line(out);
+                }
+                write_indent(out, indent);
+                out.push_str(self.raw(*comment));
+                out.push('\n');
+            }
+            cursor = comment.end as usize;
+        }
+        if previous_end.is_some() {
+            ensure_line_break(out);
+        }
+        if self.has_blank_line(cursor, end) {
+            ensure_blank_line(out);
+        }
+    }
+
+    fn precedence(&self, id: ExprId) -> u8 {
+        match &self.ast.get(id).expr {
+            Expr::As { .. } => 0,
+            Expr::Default { .. } => 1,
+            Expr::Binary { op, .. } => match op {
+                BinaryOp::Patch => 3,
+                BinaryOp::And => 5,
+                BinaryOp::LogicalOr => 7,
+                BinaryOp::LogicalAnd => 9,
+                BinaryOp::Equal
+                | BinaryOp::NotEqual
+                | BinaryOp::Greater
+                | BinaryOp::GreaterEqual
+                | BinaryOp::Less
+                | BinaryOp::LessEqual => 11,
+                BinaryOp::Concat => 12,
+                BinaryOp::Add | BinaryOp::Sub => 13,
+                BinaryOp::Mul | BinaryOp::Div => 15,
+            },
+            Expr::Unary { .. } | Expr::CompareConstraint { .. } => 17,
+            Expr::Call { .. } | Expr::Path { .. } => 19,
+            Expr::Parenthesized { .. } => 20,
+            _ => 20,
+        }
+    }
+
+    fn is_inline_expr(&self, id: ExprId) -> bool {
+        let node = self.ast.get(id);
+        if self.has_comment(node.span) {
+            return false;
+        }
+        match &node.expr {
+            Expr::Literal(_)
+            | Expr::Ident(_)
+            | Expr::RegexConstraint(_)
+            | Expr::Wildcard
+            | Expr::Import(_)
+            | Expr::CompareConstraint { .. } => true,
+            Expr::Path { base, .. } => self.is_inline_expr(*base),
+            Expr::Call { callee, args } => {
+                self.is_inline_expr(*callee)
+                    && args.iter().all(|argument| self.is_inline_expr(*argument))
+            }
+            Expr::Unary { expr, .. } => self.is_inline_expr(*expr),
+            Expr::Binary { lhs, rhs, .. } => self.is_inline_expr(*lhs) && self.is_inline_expr(*rhs),
+            Expr::Default { base, fallback } => {
+                self.is_inline_expr(*base) && self.is_inline_expr(*fallback)
+            }
+            Expr::Array(items) => items.iter().all(|item| self.is_inline_expr(*item)),
+            Expr::ArrayConstraint { item } => self.is_inline_expr(*item),
+            Expr::MapConstraint { value } => self.is_inline_expr(*value),
+            Expr::Parenthesized { expr } => self.is_inline_expr(*expr),
+            Expr::As { narrower, wider } => {
+                self.is_inline_expr(*narrower) && self.is_inline_expr(*wider)
+            }
+            Expr::Object { .. } | Expr::Let { .. } | Expr::Function { .. } | Expr::Match { .. } => {
+                false
+            }
+        }
+    }
+
+    fn delimited_range(
+        &self,
+        span: Span,
+        open_kind: SyntaxTokenKind,
+        close_kind: SyntaxTokenKind,
+    ) -> (usize, usize) {
+        let open = self
+            .tokens_between(span.start as usize, span.end as usize)
+            .find(|token| same_kind(&token.kind, &open_kind))
+            .expect("parsed delimited expressions contain an opening token");
+        let close = self
+            .tokens_between(open.span.end as usize, span.end as usize)
+            .rev()
+            .find(|token| same_kind(&token.kind, &close_kind))
+            .expect("parsed delimited expressions contain a closing token");
+        (open.span.end as usize, close.span.start as usize)
+    }
+
+    fn tokens_between(
+        &self,
+        start: usize,
+        end: usize,
+    ) -> impl DoubleEndedIterator<Item = &SyntaxToken> {
+        self.tokens.iter().filter(move |token| {
+            token.span.start as usize >= start && token.span.end as usize <= end
+        })
+    }
+
+    fn comments_between(&self, start: usize, end: usize) -> impl Iterator<Item = &Span> {
+        self.comments
+            .iter()
+            .filter(move |comment| comment.start as usize >= start && comment.end as usize <= end)
+    }
+
+    fn has_comment(&self, span: Span) -> bool {
+        self.has_comment_between(span.start as usize, span.end as usize)
+    }
+
+    fn has_comment_between(&self, start: usize, end: usize) -> bool {
+        self.comments_between(start, end).next().is_some()
+    }
+
+    fn same_line(&self, start: usize, end: usize) -> bool {
+        !self.slice(start, end).contains('\n')
+    }
+
+    fn has_blank_line(&self, start: usize, end: usize) -> bool {
+        self.slice(start, end)
+            .bytes()
+            .filter(|byte| *byte == b'\n')
+            .count()
+            >= 2
+    }
+
+    fn raw(&self, span: Span) -> &'a str {
+        self.slice(span.start as usize, span.end as usize).trim()
+    }
+
+    fn slice(&self, start: usize, end: usize) -> &'a str {
+        &self.source[start.min(self.source.len())..end.min(self.source.len())]
+    }
+}
+
+fn binary_operator(operator: BinaryOp) -> &'static str {
+    match operator {
+        BinaryOp::Add => "+",
+        BinaryOp::Sub => "-",
+        BinaryOp::Mul => "*",
+        BinaryOp::Div => "/",
+        BinaryOp::Concat => "++",
+        BinaryOp::Equal => "==",
+        BinaryOp::NotEqual => "!=",
+        BinaryOp::Greater => ">",
+        BinaryOp::GreaterEqual => ">=",
+        BinaryOp::Less => "<",
+        BinaryOp::LessEqual => "<=",
+        BinaryOp::LogicalAnd => "&&",
+        BinaryOp::LogicalOr => "||",
+        BinaryOp::And => "&",
+        BinaryOp::Patch => "//",
+    }
+}
+
+fn compare_operator(operator: CompareOp) -> &'static str {
+    match operator {
+        CompareOp::Gt => ">",
+        CompareOp::Gte => ">=",
+        CompareOp::Lt => "<",
+        CompareOp::Lte => "<=",
+        CompareOp::Eq => "==",
+    }
+}
+
+fn same_kind(left: &SyntaxTokenKind, right: &SyntaxTokenKind) -> bool {
+    core::mem::discriminant(left) == core::mem::discriminant(right)
+}
+
+fn write_indent(out: &mut String, indent: usize) {
+    out.extend(core::iter::repeat_n(' ', indent));
+}
+
+fn ensure_line_break(out: &mut String) {
+    if !out.is_empty() && !out.ends_with('\n') {
+        out.push('\n');
+    }
+}
+
+fn ensure_blank_line(out: &mut String) {
+    if !out.is_empty() && !out.ends_with("\n\n") {
+        ensure_line_break(out);
+        out.push('\n');
+    }
+}
+
+fn trim_trailing_whitespace(out: &mut String) {
+    while out.ends_with(char::is_whitespace) {
+        out.pop();
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn formats_fields_and_preserves_comments() {
+        let source =
+            "Server={\n# host\nhost=String default \"localhost\"; # trailing\n\nport=Int&>0;\n};";
+        let formatted = format_source(source).unwrap();
+        assert_eq!(
+            formatted,
+            "Server = {\n    # host\n    host = String default \"localhost\"; # trailing\n\n    port = Int & > 0;\n};\n"
+        );
+    }
+
+    #[test]
+    fn formats_arrays_and_match_comments() {
+        let source = "result=match x{# c\n_: [1,{a=2;}];};";
+        let formatted = format_source(source).unwrap();
+        assert_eq!(
+            formatted,
+            "result = match x {\n    # c\n    _: [\n        1,\n        {\n            a = 2;\n        },\n    ];\n};\n"
+        );
+    }
+
+    #[test]
+    fn formats_array_constraints() {
+        let source = "tags=[...String];ports=[...(Int&>=1)];";
+        let formatted = format_source(source).unwrap();
+        assert_eq!(
+            formatted,
+            "tags = [...String];\nports = [...(Int & >= 1)];\n"
+        );
+    }
+
+    #[test]
+    fn formats_map_constraints_and_range_ascription() {
+        let source =
+            "config={service={port=8080;};}as{service={port=Int;};};labels={a=1;b=2;}as{...Int};";
+        let formatted = format_source(source).unwrap();
+        assert_eq!(
+            formatted,
+            "config = {\n    service = {\n        port = 8080;\n    };\n} as {\n    service = {\n        port = Int;\n    };\n};\nlabels = {\n    a = 1;\n    b = 2;\n} as {...Int};\n"
+        );
+        assert_eq!(format_source(&formatted).unwrap(), formatted);
+    }
+
+    #[test]
+    fn formats_let_functions_and_precedence_from_the_canonical_ast() {
+        let source = "value=let x=1+2*3;in(a:Int)=>{result=(x+a)*2;};";
+        let formatted = format_source(source).unwrap();
+        assert_eq!(
+            formatted,
+            "value = let\n    x = 1 + 2 * 3;\nin\n    (a: Int) =>\n        {\n            result = (x + a) * 2;\n        };\n"
+        );
+    }
+
+    #[test]
+    fn formats_unknown_and_object_rest_constraints() {
+        let source =
+            "value={hoge=Int;fuga=String;# remaining fields\n...# unconstrained\nUnknown};";
+        let formatted = format_source(source).unwrap();
+        assert_eq!(
+            formatted,
+            "value = {\n    hoge = Int;\n    fuga = String; # remaining fields\n    ... # unconstrained\n    Unknown\n};\n"
+        );
+    }
+
+    #[test]
+    fn preserves_regex_and_escaped_strings() {
+        let source = r#"value={pattern=/^api\/.+$/;text="a\n\"b";};"#;
+        let formatted = format_source(source).unwrap();
+        assert!(formatted.contains(r#"pattern = /^api\/.+$/;"#));
+        assert!(formatted.contains(r#"text = "a\n\"b";"#));
+    }
+
+    #[test]
+    fn preserves_comments_inside_grouping_and_between_structural_tokens() {
+        let source = "value = (# grouped\n 1 + 2); result = match x # before brace\n { _ # before body\n : value; };";
+        let formatted = format_source(source).unwrap();
+        assert!(formatted.contains("(# grouped\n 1 + 2)"));
+        assert!(formatted.contains("match x # before brace\n{"));
+        assert!(formatted.contains("_ # before body\n : value;"));
+        assert_eq!(format_source(&formatted).unwrap(), formatted);
+    }
+
+    #[test]
+    fn wasm_export_returns_the_same_formatter_result() {
+        let source = "value={a=1;};";
+        let expected = format_source(source).unwrap();
+        let output: serde_json::Value = serde_json::from_str(&format_source_json(source)).unwrap();
+        assert_eq!(output["source"], expected);
+    }
+
+    #[test]
+    fn formats_all_repository_examples_idempotently() {
+        let examples = [
+            (
+                "advanced/main",
+                include_str!("../../../examples/advanced/main.dcdl"),
+            ),
+            (
+                "advanced/profiles",
+                include_str!("../../../examples/advanced/profiles.dcdl"),
+            ),
+            (
+                "advanced/schema",
+                include_str!("../../../examples/advanced/schema.dcdl"),
+            ),
+            (
+                "arithmetic",
+                include_str!("../../../examples/arithmetic.dcdl"),
+            ),
+            (
+                "array-concat",
+                include_str!("../../../examples/array-concat.dcdl"),
+            ),
+            (
+                "array-constraint",
+                include_str!("../../../examples/array-constraint.dcdl"),
+            ),
+            ("basic", include_str!("../../../examples/basic.dcdl")),
+            (
+                "import/main",
+                include_str!("../../../examples/import/main.dcdl"),
+            ),
+            (
+                "import/schema",
+                include_str!("../../../examples/import/schema.dcdl"),
+            ),
+            ("logical", include_str!("../../../examples/logical.dcdl")),
+            (
+                "map-ascription",
+                include_str!("../../../examples/map-ascription.dcdl"),
+            ),
+            (
+                "regex/main",
+                include_str!("../../../examples/regex/main.dcdl"),
+            ),
+        ];
+        for (name, source) in examples {
+            let once = format_source(source).unwrap_or_else(|error| panic!("{name}: {error}"));
+            let twice = format_source(&once).unwrap_or_else(|error| {
+                panic!("{name} reformatted to invalid source: {error}\n{once}")
+            });
+            assert_eq!(once, twice, "{name}");
+        }
+    }
+}
@@ -0,0 +1,19 @@
+[package]
+name = "decodal-lsp"
+version.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+repository.workspace = true
+readme.workspace = true
+description = "Language Server Protocol implementation for Decodal."
+keywords = ["decodal", "lsp", "language-server", "editor"]
+categories = ["development-tools", "text-editors"]
+
+[dependencies]
+decodal = { version = "0.4.0", path = "../decodal-core" }
+decodal-language-service = { version = "0.4.0", path = "../decodal-language-service" }
+decodal-language-tools = { version = "0.4.0", path = "../decodal-language-tools" }
+lsp-server = "0.10"
+lsp-types = "0.97"
+serde_json.workspace = true
@@ -0,0 +1,11 @@
+use std::process::ExitCode;
+
+fn main() -> ExitCode {
+    match decodal_lsp::run_stdio(|_| Ok(decodal_lsp::FileSystemEnvironment::default())) {
+        Ok(()) => ExitCode::SUCCESS,
+        Err(error) => {
+            eprintln!("decodal-lsp failed: {error}");
+            ExitCode::FAILURE
+        }
+    }
+}
@@ -0,0 +1,28 @@
+[package]
+name = "decodal-wasm"
+version.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+repository.workspace = true
+readme.workspace = true
+description = "Host-configurable Decodal evaluator and language service for JavaScript runtimes."
+keywords = ["decodal", "wasm", "dsl", "config"]
+categories = ["wasm", "config"]
+publish = false
+
+[lib]
+crate-type = ["cdylib", "rlib"]
+
+[dependencies]
+decodal = { version = "0.4.0", path = "../decodal-core" }
+decodal-language-service = { version = "0.4.0", path = "../decodal-language-service" }
+serde_json.workspace = true
+wasm-bindgen.workspace = true
+
+[target.'cfg(target_arch = "wasm32")'.dependencies]
+js-sys = "0.3"
+serde-wasm-bindgen = "0.6"
+
+[package.metadata.wasm-pack.profile.release]
+wasm-opt = false
@@ -0,0 +1,263 @@
+#[cfg(target_arch = "wasm32")]
+use decodal::HostEnvironment;
+use decodal::{Data, EmptyLoader, Engine, SourceId, format_diagnostic_with};
+#[cfg(target_arch = "wasm32")]
+use decodal_language_service::{CompletionKind, LanguageService};
+use wasm_bindgen::prelude::*;
+
+#[cfg(any(target_arch = "wasm32", test))]
+mod value;
+#[cfg(target_arch = "wasm32")]
+mod web_environment;
+
+#[cfg(target_arch = "wasm32")]
+use web_environment::JsEnvironment;
+
+/// Evaluates one standalone Decodal source with no host globals or imports.
+#[wasm_bindgen]
+pub fn evaluate(source: &str) -> String {
+    encode_result(evaluate_inner(source))
+}
+
+/// A browser-facing language service configured entirely by its JavaScript host.
+///
+/// The host owns globals, import loading, and import completion. This keeps
+/// filesystem, network, and virtual-project policy outside the WASM package.
+#[cfg(target_arch = "wasm32")]
+#[wasm_bindgen(js_name = DecodalLanguageService)]
+pub struct WebLanguageService {
+    environment: JsEnvironment,
+}
+
+#[cfg(target_arch = "wasm32")]
+#[wasm_bindgen(js_class = DecodalLanguageService)]
+impl WebLanguageService {
+    #[wasm_bindgen(constructor)]
+    pub fn new(options: JsValue) -> Result<WebLanguageService, JsValue> {
+        Ok(Self {
+            environment: JsEnvironment::from_options(options)?,
+        })
+    }
+
+    /// Evaluates a source using the injected globals and import loader.
+    pub fn evaluate(&self, key: &str, name: &str, source: &str) -> String {
+        encode_result(evaluate_with_environment(
+            &self.environment,
+            key,
+            name,
+            source,
+        ))
+    }
+
+    /// Completes a source using the same injected environment as evaluation.
+    ///
+    /// Positions and returned ranges are UTF-16 offsets, matching browser
+    /// editors and the Language Server Protocol.
+    pub fn complete(&self, key: &str, source: &str, position: usize, explicit: bool) -> String {
+        encode_completion(&self.environment, key, source, position, explicit)
+    }
+}
+
+fn encode_result(result: Result<String, String>) -> String {
+    match result {
+        Ok(output) => serde_json::json!({ "ok": true, "output": output }).to_string(),
+        Err(error) => serde_json::json!({ "ok": false, "error": error }).to_string(),
+    }
+}
+
+fn evaluate_inner(source: &str) -> Result<String, String> {
+    let mut engine = Engine::new(EmptyLoader);
+    let module = match engine.add_root_source("playground", "playground", source) {
+        Ok(module) => module,
+        Err(error) => return Err(format_diagnostic_with_root(&error, "playground")),
+    };
+    let value = match engine.eval_module(module) {
+        Ok(value) => value,
+        Err(error) => return Err(engine.format_diagnostic(&error)),
+    };
+    let data = match engine.materialize(&value) {
+        Ok(data) => data,
+        Err(error) => return Err(engine.format_diagnostic(&error)),
+    };
+    Ok(format_data(&data, 0))
+}
+
+#[cfg(target_arch = "wasm32")]
+fn evaluate_with_environment(
+    environment: &JsEnvironment,
+    key: &str,
+    name: &str,
+    source: &str,
+) -> Result<String, String> {
+    let mut engine = environment
+        .create_engine()
+        .map_err(|diagnostic| diagnostic.message)?;
+    let module = match engine.add_root_source(key, name, source) {
+        Ok(module) => module,
+        Err(diagnostic) => return Err(engine.format_diagnostic(&diagnostic)),
+    };
+    let value = match engine.eval_module(module) {
+        Ok(value) => value,
+        Err(diagnostic) => return Err(engine.format_diagnostic(&diagnostic)),
+    };
+    let data = match engine.materialize(&value) {
+        Ok(data) => data,
+        Err(diagnostic) => return Err(engine.format_diagnostic(&diagnostic)),
+    };
+    Ok(format_data(&data, 0))
+}
+
+#[cfg(target_arch = "wasm32")]
+fn encode_completion(
+    environment: &JsEnvironment,
+    key: &str,
+    source: &str,
+    position: usize,
+    explicit: bool,
+) -> String {
+    let byte_position = utf16_offset_to_byte(source, position);
+    let service = LanguageService::new(environment);
+    let completion = match service.complete(key, source, byte_position, explicit) {
+        Ok(completion) => completion,
+        Err(diagnostic) => {
+            return serde_json::json!({
+                "ok": false,
+                "error": diagnostic.message,
+            })
+            .to_string();
+        }
+    };
+    let completion = completion.map(|completion| {
+        let from = byte_offset_to_utf16(source, completion.from);
+        let options = completion
+            .items
+            .into_iter()
+            .map(|item| {
+                serde_json::json!({
+                    "label": item.label,
+                    "kind": completion_kind_name(item.kind),
+                    "detail": item.detail,
+                    "priority": item.priority,
+                })
+            })
+            .collect::<Vec<_>>();
+        serde_json::json!({ "from": from, "options": options })
+    });
+    serde_json::json!({ "ok": true, "completion": completion }).to_string()
+}
+
+#[cfg(target_arch = "wasm32")]
+fn completion_kind_name(kind: CompletionKind) -> &'static str {
+    match kind {
+        CompletionKind::Keyword => "keyword",
+        CompletionKind::Constant => "constant",
+        CompletionKind::Type => "type",
+        CompletionKind::Variable => "variable",
+        CompletionKind::Namespace => "namespace",
+        CompletionKind::Property => "property",
+        CompletionKind::File => "file",
+    }
+}
+
+#[cfg(any(target_arch = "wasm32", test))]
+fn utf16_offset_to_byte(source: &str, offset: usize) -> usize {
+    let mut utf16 = 0usize;
+    for (byte, ch) in source.char_indices() {
+        if utf16 >= offset {
+            return byte;
+        }
+        let next = utf16 + ch.len_utf16();
+        if next > offset {
+            return byte;
+        }
+        utf16 = next;
+    }
+    source.len()
+}
+
+#[cfg(any(target_arch = "wasm32", test))]
+fn byte_offset_to_utf16(source: &str, mut offset: usize) -> usize {
+    offset = offset.min(source.len());
+    while !source.is_char_boundary(offset) {
+        offset = offset.saturating_sub(1);
+    }
+    source[..offset].encode_utf16().count()
+}
+
+fn format_diagnostic_with_root(diagnostic: &decodal::Diagnostic, root_name: &str) -> String {
+    format_diagnostic_with(diagnostic, |source| {
+        (source == SourceId(0)).then_some(root_name)
+    })
+}
+
+fn format_data(data: &Data, indent: usize) -> String {
+    match data {
+        Data::String(value) => json_string(value),
+        Data::Int(value) => value.to_string(),
+        Data::Float(value) => value.to_string(),
+        Data::Bool(value) => value.to_string(),
+        Data::Array(items) => {
+            if items.is_empty() {
+                return String::from("[]");
+            }
+            let mut out = String::from("[\n");
+            for (index, item) in items.iter().enumerate() {
+                out.push_str(&" ".repeat(indent + 2));
+                out.push_str(&format_data(item, indent + 2));
+                if index + 1 != items.len() {
+                    out.push(',');
+                }
+                out.push('\n');
+            }
+            out.push_str(&" ".repeat(indent));
+            out.push(']');
+            out
+        }
+        Data::Object(fields) => {
+            if fields.is_empty() {
+                return String::from("{}");
+            }
+            let mut out = String::from("{\n");
+            for (index, field) in fields.iter().enumerate() {
+                out.push_str(&" ".repeat(indent + 2));
+                out.push_str(&json_string(&field.name));
+                out.push_str(": ");
+                out.push_str(&format_data(&field.value, indent + 2));
+                if index + 1 != fields.len() {
+                    out.push(',');
+                }
+                out.push('\n');
+            }
+            out.push_str(&" ".repeat(indent));
+            out.push('}');
+            out
+        }
+    }
+}
+
+fn json_string(value: &str) -> String {
+    serde_json::to_string(value).expect("strings are always JSON-serializable")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{byte_offset_to_utf16, evaluate_inner, utf16_offset_to_byte};
+
+    #[test]
+    fn evaluates_standalone_sources() {
+        assert_eq!(
+            evaluate_inner("value = 1;").unwrap(),
+            "{\n  \"value\": 1\n}"
+        );
+    }
+
+    #[test]
+    fn converts_web_utf16_offsets() {
+        let source = "a😀β";
+        assert_eq!(utf16_offset_to_byte(source, 0), 0);
+        assert_eq!(utf16_offset_to_byte(source, 1), 1);
+        assert_eq!(utf16_offset_to_byte(source, 3), 5);
+        assert_eq!(byte_offset_to_utf16(source, 5), 3);
+        assert_eq!(byte_offset_to_utf16(source, source.len()), 4);
+    }
+}
@@ -0,0 +1,320 @@
+use decodal::{CompareOp, Constraint, LiteralValue, PrimitiveType, Value};
+use serde_json::{Map, Value as JsonValue};
+
+pub(crate) fn from_json(value: &JsonValue) -> Result<Value, String> {
+    match value {
+        JsonValue::Null => Err(String::from("null is not a Decodal value")),
+        JsonValue::Bool(value) => Ok(Value::bool(*value)),
+        JsonValue::Number(value) => number(value),
+        JsonValue::String(value) => Ok(Value::string(value)),
+        JsonValue::Array(items) => items
+            .iter()
+            .enumerate()
+            .map(|(index, value)| {
+                from_json(value).map_err(|error| format!("array item {index}: {error}"))
+            })
+            .collect::<Result<Vec<_>, _>>()
+            .map(Value::array),
+        JsonValue::Object(fields) => object(fields),
+    }
+}
+
+fn number(value: &serde_json::Number) -> Result<Value, String> {
+    if let Some(value) = value.as_i64() {
+        return Ok(Value::int(value));
+    }
+    if let Some(value) = value.as_u64() {
+        return i64::try_from(value)
+            .map(Value::int)
+            .map_err(|_| String::from("integer value is outside the signed 64-bit range"));
+    }
+    value
+        .as_f64()
+        .filter(|value| value.is_finite())
+        .map(Value::float)
+        .ok_or_else(|| String::from("invalid numeric value"))
+}
+
+fn object(fields: &Map<String, JsonValue>) -> Result<Value, String> {
+    let Some(descriptor) = fields.get("$decodal") else {
+        return fields
+            .iter()
+            .map(|(name, value)| {
+                from_json(value)
+                    .map(|value| (name.clone(), value))
+                    .map_err(|error| format!("field `{name}`: {error}"))
+            })
+            .collect::<Result<Vec<_>, _>>()
+            .map(Value::object);
+    };
+
+    let descriptor = descriptor
+        .as_str()
+        .ok_or_else(|| String::from("`$decodal` must be a descriptor name"))?;
+    let constraints = parse_constraints(fields.get("constraints"))?;
+    let default = fields
+        .get("default")
+        .map(from_json)
+        .transpose()?
+        .map(Box::new);
+
+    match descriptor {
+        "Unknown" => {
+            let mut all_constraints = vec![Constraint::Unknown];
+            all_constraints.extend(constraints);
+            Ok(Value::Range {
+                constraints: all_constraints,
+                default,
+            })
+        }
+        "String" | "Int" | "Float" | "Bool" => {
+            let primitive = match descriptor {
+                "String" => PrimitiveType::String,
+                "Int" => PrimitiveType::Int,
+                "Float" => PrimitiveType::Float,
+                "Bool" => PrimitiveType::Bool,
+                _ => unreachable!(),
+            };
+            let mut all_constraints = vec![Constraint::Type(primitive)];
+            all_constraints.extend(constraints);
+            Ok(Value::Range {
+                constraints: all_constraints,
+                default,
+            })
+        }
+        "Array" => {
+            let item = fields
+                .get("item")
+                .ok_or_else(|| String::from("Array descriptor requires `item`"))?;
+            Ok(Value::ArrayRange {
+                item: Box::new(from_json(item)?),
+                constraints,
+                default,
+            })
+        }
+        "Map" => {
+            let value = fields
+                .get("value")
+                .ok_or_else(|| String::from("Map descriptor requires `value`"))?;
+            Ok(Value::MapRange {
+                value: Box::new(from_json(value)?),
+                constraints,
+                default,
+            })
+        }
+        "Object" => {
+            if !constraints.is_empty() {
+                return Err(String::from(
+                    "Object descriptor does not accept `constraints`; constrain its fields or rest range",
+                ));
+            }
+            if default.is_some() {
+                return Err(String::from(
+                    "Object descriptor does not accept `default`; place defaults on its fields",
+                ));
+            }
+            let object_fields = fields
+                .get("fields")
+                .and_then(JsonValue::as_object)
+                .ok_or_else(|| String::from("Object descriptor requires object `fields`"))?;
+            let value_fields = object_fields
+                .iter()
+                .map(|(name, value)| {
+                    from_json(value)
+                        .map(|value| (name.clone(), value))
+                        .map_err(|error| format!("field `{name}`: {error}"))
+                })
+                .collect::<Result<Vec<_>, _>>()?;
+            let rest = fields
+                .get("rest")
+                .ok_or_else(|| String::from("Object descriptor requires `rest`"))?;
+            Ok(Value::object_with_rest(value_fields, from_json(rest)?))
+        }
+        "Range" => Ok(Value::Range {
+            constraints,
+            default,
+        }),
+        name => Err(format!("unknown Decodal value descriptor `{name}`")),
+    }
+}
+
+fn parse_constraints(value: Option<&JsonValue>) -> Result<Vec<Constraint>, String> {
+    let Some(value) = value else {
+        return Ok(Vec::new());
+    };
+    let items = value
+        .as_array()
+        .ok_or_else(|| String::from("`constraints` must be an array"))?;
+    items
+        .iter()
+        .enumerate()
+        .map(|(index, value)| {
+            parse_constraint(value).map_err(|error| format!("constraint {index}: {error}"))
+        })
+        .collect()
+}
+
+fn parse_constraint(value: &JsonValue) -> Result<Constraint, String> {
+    let fields = value
+        .as_object()
+        .ok_or_else(|| String::from("constraint must be an object"))?;
+    let kind = required_string(fields, "kind")?;
+    match kind {
+        "unknown" => Ok(Constraint::Unknown),
+        "type" => match required_string(fields, "value")? {
+            "String" => Ok(Constraint::Type(PrimitiveType::String)),
+            "Int" => Ok(Constraint::Type(PrimitiveType::Int)),
+            "Float" => Ok(Constraint::Type(PrimitiveType::Float)),
+            "Bool" => Ok(Constraint::Type(PrimitiveType::Bool)),
+            value => Err(format!("unknown primitive type `{value}`")),
+        },
+        "compare" => {
+            let operation = match required_string(fields, "op")? {
+                ">" => CompareOp::Gt,
+                ">=" => CompareOp::Gte,
+                "<" => CompareOp::Lt,
+                "<=" => CompareOp::Lte,
+                operation => return Err(format!("unknown comparison operator `{operation}`")),
+            };
+            let value = fields
+                .get("value")
+                .ok_or_else(|| String::from("compare constraint requires `value`"))?;
+            Ok(Constraint::Compare(operation, literal(value)?))
+        }
+        "regex" => Ok(Constraint::Regex(
+            required_string(fields, "value")?.to_owned(),
+        )),
+        "predicate" => Ok(Constraint::BuiltinPredicate(
+            required_string(fields, "value")?.to_owned(),
+        )),
+        kind => Err(format!("unknown constraint kind `{kind}`")),
+    }
+}
+
+fn literal(value: &JsonValue) -> Result<LiteralValue, String> {
+    match value {
+        JsonValue::String(value) => Ok(LiteralValue::String(value.clone())),
+        JsonValue::Bool(value) => Ok(LiteralValue::Bool(*value)),
+        JsonValue::Number(value) => match number(value)? {
+            Value::Int(value) => Ok(LiteralValue::Int(value)),
+            Value::Float(value) => Ok(LiteralValue::Float(value)),
+            _ => unreachable!(),
+        },
+        _ => Err(String::from("comparison value must be a primitive literal")),
+    }
+}
+
+fn required_string<'a>(fields: &'a Map<String, JsonValue>, name: &str) -> Result<&'a str, String> {
+    fields
+        .get(name)
+        .and_then(JsonValue::as_str)
+        .ok_or_else(|| format!("constraint requires string `{name}`"))
+}
+
+#[cfg(test)]
+mod tests {
+    use decodal::{Constraint, LiteralValue, PrimitiveType, Value};
+
+    use super::from_json;
+
+    #[test]
+    fn converts_plain_js_shaped_values() {
+        let value = serde_json::json!({
+            "frontmatter": { "draft": false },
+            "body": "# Hello",
+        });
+        assert_eq!(
+            from_json(&value).unwrap(),
+            Value::object([
+                ("body", Value::string("# Hello")),
+                (
+                    "frontmatter",
+                    Value::object([("draft", Value::bool(false))]),
+                ),
+            ])
+        );
+    }
+
+    #[test]
+    fn converts_schema_descriptors() {
+        let value = serde_json::json!({
+            "$decodal": "Array",
+            "item": {
+                "$decodal": "Int",
+                "constraints": [{ "kind": "compare", "op": ">", "value": 0 }],
+            },
+            "default": [1, 2],
+        });
+        assert_eq!(
+            from_json(&value).unwrap(),
+            Value::ArrayRange {
+                item: Box::new(Value::Range {
+                    constraints: vec![
+                        Constraint::Type(PrimitiveType::Int),
+                        Constraint::Compare(decodal::CompareOp::Gt, LiteralValue::Int(0)),
+                    ],
+                    default: None,
+                }),
+                constraints: Vec::new(),
+                default: Some(Box::new(Value::array([Value::int(1), Value::int(2),]))),
+            }
+        );
+    }
+
+    #[test]
+    fn converts_map_schema_descriptors() {
+        let value = serde_json::json!({
+            "$decodal": "Map",
+            "value": { "$decodal": "Bool" },
+            "default": {},
+        });
+        assert_eq!(
+            from_json(&value).unwrap(),
+            Value::MapRange {
+                value: Box::new(Value::bool_type()),
+                constraints: Vec::new(),
+                default: Some(Box::new(Value::object([] as [(&str, Value); 0]))),
+            }
+        );
+    }
+
+    #[test]
+    fn converts_unknown_and_open_object_descriptors() {
+        let value = serde_json::json!({
+            "$decodal": "Object",
+            "fields": {
+                "name": { "$decodal": "String" },
+            },
+            "rest": { "$decodal": "Unknown" },
+        });
+        assert_eq!(
+            from_json(&value).unwrap(),
+            Value::object_with_rest([("name", Value::string_type())], Value::unknown(),)
+        );
+    }
+
+    #[test]
+    fn converts_general_range_descriptors() {
+        let value = serde_json::json!({
+            "$decodal": "Range",
+            "constraints": [{ "kind": "predicate", "value": "available" }],
+            "default": true,
+        });
+        assert_eq!(
+            from_json(&value).unwrap(),
+            Value::Range {
+                constraints: vec![Constraint::BuiltinPredicate("available".into())],
+                default: Some(Box::new(Value::bool(true))),
+            }
+        );
+    }
+
+    #[test]
+    fn rejects_null_values() {
+        assert!(
+            from_json(&serde_json::Value::Null)
+                .unwrap_err()
+                .contains("null")
+        );
+    }
+}
@@ -0,0 +1,209 @@
+use std::collections::BTreeMap;
+
+use decodal::{
+    Diagnostic, DiagnosticKind, Engine, HostEnvironment, ImportCandidate, ImportLoader,
+    LoadedImport, Span, Value as DecodalValue,
+};
+use js_sys::{Function, Reflect};
+use serde_json::Value;
+use wasm_bindgen::{JsCast, JsValue};
+
+use crate::value;
+
+pub(crate) struct JsEnvironment {
+    globals: BTreeMap<String, DecodalValue>,
+    load_import: Option<Function>,
+    complete_import: Option<Function>,
+}
+
+impl JsEnvironment {
+    pub(crate) fn from_options(options: JsValue) -> Result<Self, JsValue> {
+        if !options.is_null() && !options.is_undefined() && !options.is_object() {
+            return Err(JsValue::from_str(
+                "DecodalLanguageService options must be an object",
+            ));
+        }
+
+        let globals = property(&options, "globals")?;
+        let globals = if globals.is_null() || globals.is_undefined() {
+            BTreeMap::new()
+        } else {
+            let globals: Value = serde_wasm_bindgen::from_value(globals).map_err(|error| {
+                JsValue::from_str(&format!("failed to read `globals`: {error}"))
+            })?;
+            let globals = globals.as_object().ok_or_else(|| {
+                JsValue::from_str("DecodalLanguageService `globals` must be an object")
+            })?;
+            globals
+                .iter()
+                .map(|(name, value)| {
+                    value::from_json(value)
+                        .map(|value| (name.clone(), value))
+                        .map_err(|error| {
+                            JsValue::from_str(&format!("invalid global `{name}`: {error}"))
+                        })
+                })
+                .collect::<Result<BTreeMap<_, _>, _>>()?
+        };
+
+        Ok(Self {
+            globals,
+            load_import: optional_function(&options, "loadImport")?,
+            complete_import: optional_function(&options, "completeImport")?,
+        })
+    }
+}
+
+impl HostEnvironment for JsEnvironment {
+    type Loader = JsLoader;
+
+    fn create_loader(&self) -> Self::Loader {
+        JsLoader {
+            load_import: self.load_import.clone(),
+            complete_import: self.complete_import.clone(),
+        }
+    }
+
+    fn configure_engine(&self, engine: &mut Engine<Self::Loader>) -> decodal::Result<()> {
+        for (name, value) in &self.globals {
+            engine.bind_global(name, value.clone())?;
+        }
+        Ok(())
+    }
+}
+
+pub(crate) struct JsLoader {
+    load_import: Option<Function>,
+    complete_import: Option<Function>,
+}
+
+impl ImportLoader for JsLoader {
+    fn load(
+        &mut self,
+        current_key: Option<&str>,
+        specifier: &str,
+    ) -> decodal::Result<LoadedImport> {
+        let callback = self.load_import.as_ref().ok_or_else(|| {
+            import_error(format!(
+                "no JavaScript `loadImport` callback is configured for `{specifier}`"
+            ))
+        })?;
+        let current_key = current_key.map(JsValue::from_str).unwrap_or(JsValue::NULL);
+        let specifier = JsValue::from_str(specifier);
+        let loaded = callback
+            .call2(&JsValue::UNDEFINED, &current_key, &specifier)
+            .map_err(|error| import_error(js_error_message(error)))?;
+        let loaded: Value = serde_wasm_bindgen::from_value(loaded)
+            .map_err(|error| import_error(format!("invalid `loadImport` result: {error}")))?;
+        loaded_import(&loaded).map_err(import_error)
+    }
+
+    fn complete_import(
+        &mut self,
+        current_key: Option<&str>,
+        prefix: &str,
+    ) -> decodal::Result<Vec<ImportCandidate>> {
+        let Some(callback) = &self.complete_import else {
+            return Ok(Vec::new());
+        };
+        let current_key = current_key.map(JsValue::from_str).unwrap_or(JsValue::NULL);
+        let prefix = JsValue::from_str(prefix);
+        let candidates = callback
+            .call2(&JsValue::UNDEFINED, &current_key, &prefix)
+            .map_err(|error| import_error(js_error_message(error)))?;
+        let candidates: Value = serde_wasm_bindgen::from_value(candidates)
+            .map_err(|error| import_error(format!("invalid `completeImport` result: {error}")))?;
+        import_candidates(&candidates).map_err(import_error)
+    }
+}
+
+fn loaded_import(value: &Value) -> Result<LoadedImport, String> {
+    let fields = value
+        .as_object()
+        .ok_or_else(|| String::from("`loadImport` must return an object"))?;
+    let kind = string_field(fields, "kind")?;
+    let key = string_field(fields, "key")?;
+    match kind {
+        "source" => {
+            let source = string_field(fields, "source")?;
+            let name = fields.get("name").and_then(Value::as_str).unwrap_or(key);
+            Ok(LoadedImport::source(key, name, source))
+        }
+        "value" => {
+            let value = fields
+                .get("value")
+                .ok_or_else(|| String::from("value import requires `value`"))?;
+            let value = value::from_json(value)
+                .map_err(|error| format!("invalid imported value: {error}"))?;
+            Ok(LoadedImport::value(key, value))
+        }
+        kind => Err(format!("unknown `loadImport` result kind `{kind}`")),
+    }
+}
+
+fn import_candidates(value: &Value) -> Result<Vec<ImportCandidate>, String> {
+    value
+        .as_array()
+        .ok_or_else(|| String::from("`completeImport` must return an array"))?
+        .iter()
+        .enumerate()
+        .map(|(index, value)| match value {
+            Value::String(specifier) => Ok(ImportCandidate::new(specifier)),
+            Value::Object(fields) => {
+                let mut candidate = ImportCandidate::new(string_field(fields, "specifier")?);
+                if let Some(detail) = fields.get("detail") {
+                    let detail = detail.as_str().ok_or_else(|| {
+                        format!("import candidate {index} `detail` must be a string")
+                    })?;
+                    candidate = candidate.with_detail(detail);
+                }
+                Ok(candidate)
+            }
+            _ => Err(format!(
+                "import candidate {index} must be a string or object"
+            )),
+        })
+        .collect()
+}
+
+fn string_field<'a>(
+    fields: &'a serde_json::Map<String, Value>,
+    name: &str,
+) -> Result<&'a str, String> {
+    fields
+        .get(name)
+        .and_then(Value::as_str)
+        .ok_or_else(|| format!("`loadImport` result requires string `{name}`"))
+}
+
+fn property(options: &JsValue, name: &str) -> Result<JsValue, JsValue> {
+    if options.is_null() || options.is_undefined() {
+        return Ok(JsValue::UNDEFINED);
+    }
+    Reflect::get(options, &JsValue::from_str(name))
+}
+
+fn optional_function(options: &JsValue, name: &str) -> Result<Option<Function>, JsValue> {
+    let value = property(options, name)?;
+    if value.is_null() || value.is_undefined() {
+        return Ok(None);
+    }
+    value
+        .dyn_into::<Function>()
+        .map(Some)
+        .map_err(|_| JsValue::from_str(&format!("`{name}` must be a function")))
+}
+
+fn js_error_message(value: JsValue) -> String {
+    if let Some(message) = value.as_string() {
+        return message;
+    }
+    Reflect::get(&value, &JsValue::from_str("message"))
+        .ok()
+        .and_then(|message| message.as_string())
+        .unwrap_or_else(|| String::from("JavaScript import callback failed"))
+}
+
+fn import_error(message: impl Into<String>) -> Diagnostic {
+    Diagnostic::new(DiagnosticKind::Import, Span::default(), message)
+}
@@ -4,11 +4,13 @@ pkgs.mkShell {
    cargo
    clippy
    git
+    lld
    nodejs
    nixfmt
    rustc
    rustfmt
    tree-sitter
+    wasm-pack
  ];

  shellHook = ''
@@ -0,0 +1,140 @@
+# Components
+
+Decodal is split into a small runtime core and separate syntax tooling components.
+The public surface is intentionally organized by use case: execute Decodal with Rust or WebAssembly, edit Decodal on the Web with Lezer and CodeMirror, and integrate Decodal into general-purpose editors with Tree-sitter.
+
+## Runtime components
+
+### Rust crate
+
+The `decodal` crate is the primary Rust runtime and embedding API.
+It owns parsing, evaluation, materialization, diagnostics, host-provided values, and schema/decode traits.
+Rust applications should use this crate when they want to load Decodal source, evaluate it, or embed Decodal into a host program.
+
+Important paths:
+
+```text
+crates/decodal-core/
+crates/decodal-derive/
+```
+
+`decodal-derive` provides optional derive macros for Rust struct integration.
+It is a companion to the runtime crate rather than an editor or syntax-highlighting component.
+
+### WebAssembly package
+
+`decodal-wasm` exposes the runtime to browsers.
+The documentation site playground uses it to evaluate Decodal entirely in the browser.
+
+Important paths:
+
+```text
+crates/decodal-wasm/
+packages/decodal-wasm/
+```
+
+The npm package is `decodal-wasm`.
+The JSR package is `@hare/decodal-wasm`.
+
+The generated files in `packages/decodal-wasm/` are committed so the site can build without requiring every consumer to run `wasm-pack` first.
+The WebAssembly package is for execution, not syntax highlighting.
+
+## Language tools
+
+Semantic editor integration lives in the host-configurable language service crate.
+It depends only on the runtime and accepts the same `HostEnvironment` implementation used by a production application.
+The LSP crate adapts that service to the Language Server Protocol over stdin/stdout.
+It provides full document synchronization, semantic diagnostics, and whole-document formatting.
+A host-specific LSP binary injects its loader and global schema configuration without reimplementing evaluation rules.
+
+Important paths:
+
+```text
+crates/decodal-language-service/
+crates/decodal-lsp/
+```
+
+The default `decodal-lsp` binary reads Decodal imports from the filesystem.
+Embedded hosts can call its library entry point with a custom `LspEnvironment` to reuse structured imports and to make unsaved external documents, such as Markdown, visible to the loader.
+
+Source formatting lives in a separate Rust language tools crate.
+It uses the canonical Decodal AST together with the runtime lexer's lossless syntax tokens, so native LSP and WebAssembly callers execute the same formatter implementation.
+
+This component is responsible for operations that must preserve source text details such as comments and whitespace.
+It is used by the CodeMirror package's bundled formatter WebAssembly and can also be used by an LSP adapter for formatting.
+It does not depend on Tree-sitter or Lezer.
+
+Important paths:
+
+```text
+crates/decodal-language-tools/
+```
+
+The current language tools crate exposes the formatter.
+
+## Web editor components
+
+The Web playground editor uses CodeMirror 6 with a generated Lezer parser.
+Lezer provides syntax highlighting, folding, indentation, and editor syntax tree behavior. The browser formatter command calls the canonical Rust formatter compiled to WebAssembly.
+
+Important paths:
+
+```text
+editors/lezer-decodal/decodal.grammar
+packages/decodal-codemirror/src/decodal.js
+packages/decodal-codemirror/src/decodal-parser.js
+packages/decodal-codemirror/src/decodal-parser.terms.js
+packages/decodal-codemirror/src/format.js
+packages/decodal-codemirror/wasm/
+```
+
+The npm package is `decodal-codemirror`.
+The JSR package is `@hare/decodal-codemirror`.
+
+The Lezer grammar is derived from the canonical grammar documentation, but it is not a literal copy of the EBNF.
+Precedence and token conflict handling are represented in the Lezer grammar in the form CodeMirror needs.
+
+## General editor components
+
+Tree-sitter is the portable editor-integration grammar.
+Editors such as Zed, Neovim, Helix, and Emacs should consume this component when they need Decodal parsing or highlighting outside the Web playground.
+
+Important paths:
+
+```text
+editors/tree-sitter-decodal/grammar.js
+editors/tree-sitter-decodal/queries/highlights.scm
+editors/tree-sitter-decodal/queries/locals.scm
+editors/tree-sitter-decodal/src/
+```
+
+The generated parser sources under `editors/tree-sitter-decodal/src/` are committed so editor integrations can consume the grammar without regenerating it first.
+
+## Canonical grammar
+
+The human-readable grammar lives in:
+
+```text
+doc/manual/souce/language/grammar.md
+```
+
+This EBNF is the language-level reference.
+The Rust parser, Lezer grammar, and Tree-sitter grammar should be kept aligned with it, but each implementation may encode precedence and recovery behavior in the form required by its parser generator or runtime.
+
+## Syntax token API
+
+The `decodal` crate exposes `tokenize_source`, `tokenize_source_with_source_id`, `SyntaxToken`, and `SyntaxTokenKind` for source-preserving tooling.
+Comments have explicit tokens, while whitespace is represented by gaps between token spans and can be recovered from the original source.
+The evaluator parser and formatter therefore share one lexical definition without making Tree-sitter an upstream dependency.
+
+Consumers should otherwise use the component matching their environment:
+
+- Rust execution and embedding: `decodal`
+- Browser execution: `decodal-wasm`
+- Web formatting and editor syntax: canonical formatter / CodeMirror / Lezer
+- Semantic editor analysis: `decodal-language-service`
+- Language Server Protocol integration: `decodal-lsp`
+- Rust formatting: `decodal-language-tools`
+- General editor syntax: Tree-sitter
+
+Tree-sitter and Lezer remain downstream editor grammars and are not dependencies of the runtime formatter.
@@ -1,6 +1,6 @@
 # Composition and Materialization

-`&`、`//`、`default`、materialize は、runtime value の variant に基づいて処理する。
+`&`、`//`、`as`、`default`、materialize は、runtime value の variant に基づいて処理する。

 ## `&`

@@ -59,8 +59,9 @@ Config = MyConfig & {

 ## default の合成

-初期方針では、`&` による異なる default 同士の合成は conflict とする。
-同じ default は同一候補として扱ってよい。
+`&` で片方だけが default を持つ場合、その default を保持する。
+同じ thunk 由来の default 同士は同一 default として保持する。
+異なる default 同士は conflict とする。

 ```text
 merge_default(None, None) -> None
@@ -88,7 +89,24 @@ patch(a: RuntimeValue, b: RuntimeValue) -> RuntimeValue
 - 配列、scalar、function は右辺置換とする。

 `//` は制約を保持するための演算子ではない。
-制約を満たす具体化には `&` を使う。
+対称な制約合成には `&` を使い、左辺が右辺より狭いことを確認しながら合成する場合は `as` を使う。
+
+## `as`
+
+`as` は narrower と wider の向きを固定した範囲包含確認と合成である。
+
+```text
+apply_as(narrower: RuntimeValue, wider: RuntimeValue)
+  -> RuntimeValue | Diagnostic
+```
+
+abstract / abstract では、左辺 constraints が右辺 constraints を包含することを確認し、左辺を結果にする。
+concrete / abstract では、concrete value が右辺 constraints を満たすことを確認する。
+
+object / object では右辺を field domain とする。左辺にしかない field は診断し、両側にある field は再帰的に `apply_as` し、右辺にしかない field は thunk を force せずそのまま結果へ残す。
+この扱いは default の有無に依存しない。default は包含判定の根拠でも `as` の補完値でもなく、後の materialize だけが選択する。
+
+`ArrayItems(wider)` は concrete array の全要素を、`MapValues(wider)` は concrete object の全 field value を同じ関数で絞り込む。

 ## materialize

@@ -117,3 +135,9 @@ Abstract { constraints, default: None }

 materialize は default を採用する唯一の段階である。
 通常評価中に明示値が得られた場合、default は採用されない。
+
+## Diagnostic context
+
+Composition and materialization keep source spans for object fields, constraints, defaults, and thunks where possible.
+When a conflict occurs, the diagnostic should identify the operation span and related participant spans, such as the left field, right field, constraint, or default value.
+For object materialization errors, diagnostics also include the field path being processed when known.
@@ -10,10 +10,22 @@ Diagnostic {
  kind: DiagnosticKind
  span: Span
  message: String
-  notes: Vec<Note>
+  labels: Vec<DiagnosticLabel>
+  notes: Vec<String>
+}
+
+DiagnosticLabel {
+  span: Span
+  message: String
 }
 ```

+`span` は primary location を示す。
+表示時には `Span.source` を source id のまま出すのではなく、可能な限り file path や virtual file name に解決する。
+`labels` は同じ error に関係する追加 location を示す。
+`notes` は source location を持たない semantic context を示す。
+合成や materialize の失敗では、衝突した constraint、value、default、または処理中 field path を label に含める。
+
 代表的な diagnostic kind:

 - syntax error
@@ -27,6 +39,9 @@ Diagnostic {
 - match failure
 - materialization failure

+Structured imports use semantic provenance rather than synthetic source spans.
+Constraint failures report the imported value's stable key and logical field or array path alongside the source span of the Decodal constraint that rejected it.
+
 ## エラーは値ではない

 評価失敗は `RuntimeValue` ではなく `Diagnostic` を返す。
@@ -38,6 +53,18 @@ Result<RuntimeValue, Diagnostic>

 これにより、制約違反、未定義識別子、循環依存、import 失敗などが通常値として流れることを避ける。

+## 合成と materialize の diagnostic
+
+合成や materialize の失敗は、以下を示す。
+
+1. どの段階で失敗したか: composition、patch、materialization
+2. どの field path を処理中だったか
+3. どの constraint、value、default が衝突したか
+4. なぜ合成または materialize できないか
+
+例えば default が constraint を満たさない場合は、constraint の位置と default value の位置の両方を label として持つ。
+object field の合成で concrete value が衝突する場合は、左辺 field と右辺 field の位置を label として持つ。
+
 ## `try / catch` は core に入れない

 汎用 `try / catch` は core に入れない。
@@ -47,21 +74,6 @@ fallback は有限で明示的な仕組みに限定する。

 - `default`: 未指定値の fallback。
 - `match`: 有限 pattern に基づく分岐。
- optional import: ファイル不存在など、限定された失敗だけを fallback 可能にする候補。
- optional field access: field 不在だけを fallback 可能にする候補。
- union / tagged schema: 複数 schema の選択を明示的に表す将来候補。

-## optional fallback の扱い
-
-optional import や optional field access を導入する場合も、捕捉できる失敗は限定する。
-
-例として optional import は、ファイル不存在だけを fallback 可能にし、parse error や import 先の制約違反は diagnostic として報告する方がよい。
-
-```text
-optional import:
-  file not found -> fallback
-  parse error    -> diagnostic
-  eval error     -> diagnostic
-```
-
-この方針により、fallback は通常の値選択として扱い、エラー内容に依存した実行時分岐は避ける。
+`Unknown` は明示的に書く最上位のabstract rangeであり、評価エラーを包む値ではない。
+field 不在や未解決 identifier は `Unknown` へ変換せず、diagnostic として報告する。
@@ -1,7 +1,7 @@
 # Embedding API

 Decodal core can be embedded without giving the core crate access to a filesystem.
-The host supplies imported sources through `SourceLoader` and may also provide global bindings through the host prelude API.
+The host supplies imports through `ImportLoader` and may also provide global bindings through the host prelude API.

 ## Host prelude

@@ -17,23 +17,23 @@ let / function env
 ```

 Module top-level bindings shadow prelude bindings.
-Primitive type names such as `String`, `Int`, `Float`, and `Bool` are handled before environment lookup, so they are reserved and cannot be shadowed by host bindings.
+Primitive type names such as `String`, `Int`, `Float`, and `Bool`, plus the top range `Unknown`, are handled before environment lookup, so they are reserved and cannot be shadowed by host bindings.

 ## Global bindings

 The host can bind values before adding or evaluating user sources.

 ```rust
-use decodal_core::{EmptyLoader, Engine, HostValue};
+use decodal::{EmptyLoader, Engine, Value};

 let mut engine = Engine::new(EmptyLoader);

 engine.bind_global(
    "Service",
-    HostValue::object([
-        ("name", HostValue::string_type()),
-        ("port", HostValue::int_type().gt(443).default_int(8443)?),
-        ("enabled", HostValue::bool_type().default_bool(true)?),
+    Value::object([
+        ("name", Value::string_type()),
+        ("port", Value::int_type().gt(443).default_int(8443)?),
+        ("enabled", Value::bool_type().default_bool(true)?),
    ]),
 )?;
 ```
@@ -41,38 +41,55 @@ engine.bind_global(
 A user source can then refer to `Service` without importing it.

 ```dcdl
-Service & {
+{
  name = "api";
  port = 9443;
-}
+} as Service
 ```

-## HostValue
+## Value

-`HostValue` is the public builder-facing value representation for embedding.
+`Value` is the public builder-facing value representation for embedding.
 It keeps host code from constructing internal `ThunkId` or `ObjectValue` values directly.

 ```text
-HostValue =
+Value =
  String
  Int
  Float
  Bool
-  Array(Vec<HostValue>)
-  Object(Vec<HostField>)
-  Abstract { constraints, default }
+  Array(Vec<Value>)
+  ArrayRange { item, constraints, default }
+  MapRange { value, constraints, default }
+  Object { fields, rest: Option<Value> }
+  Range { constraints, default }
 ```

-When a host value is bound, the engine internalizes it into `RuntimeValue` and allocates value thunks for object fields, array items, and defaults.
+When a value is bound by the host, the engine internalizes it into `RuntimeValue` and allocates value thunks for object fields, array items, and defaults.

-## Abstract host objects
+`Value::array_of(item)` builds an array constraint with a required element schema.
+There is no `Value` constructor for an unconstrained abstract array.

-A host-provided schema object is represented as a concrete object structure whose fields may contain abstract values.
+`Value::map_of(value)` builds a map constraint whose arbitrary object field values must satisfy `value`.
+`BTreeMap<String, T>` and, with `std`, `HashMap<String, T>` implement `DecodalSchema`, `DecodalDecode`, and `IntoValue` using this representation.
+
+`Value::unknown()` builds the top abstract range. `Value::object_with_rest(fields, rest)` builds an object with named fields and a range for all remaining fields.

 ```rust
-HostValue::object([
-    ("name", HostValue::string_type()),
-    ("port", HostValue::int_type().gt(443).default_int(8443)?),
+Value::object_with_rest(
+    [("enabled", Value::bool_type().default_bool(true)?)],
+    Value::unknown(),
+)
+```
+
+## Objects containing ranges
+
+A host-provided schema object is represented as a concrete object structure whose fields may contain ranges.
+
+```rust
+Value::object([
+    ("name", Value::string_type()),
+    ("port", Value::int_type().gt(443).default_int(8443)?),
 ])
 ```

@@ -87,11 +104,155 @@ Concrete(Object {

 This matches the runtime model used for Decodal source-defined schema objects.

-## SourceLoader and prelude together
+## Typed Rust integration

-`SourceLoader` and host prelude bindings are independent mechanisms.
+Hosts can enable the `derive` feature on `decodal` to keep a Rust struct, the Decodal schema, and the decoded result in sync.
+The derive implements two traits from the `decodal` crate:

- Use `SourceLoader` when user sources should explicitly import host-provided modules.
+- `DecodalSchema`: builds a `Value` schema that can be passed to `Engine::bind_global`.
+- `DecodalDecode`: decodes materialized `Data` back into the Rust type.
+
+An explicitly marked map field can receive the open portion of an object.
+
+```rust
+use std::collections::BTreeMap;
+use decodal::{Data, Decodal};
+
+#[derive(Decodal)]
+struct OpenConfig {
+    enabled: bool,
+
+    #[decodal(rest)]
+    extra: BTreeMap<String, Data>,
+}
+```
+
+The schema generated for `extra` is `...Unknown`. A typed receiver such as `BTreeMap<String, String>` generates `...String` instead. During decode, named top-level fields are excluded and all remaining fields are collected into the map.
+
+Only one `#[decodal(rest)]` field is allowed. It must implement `DecodalRest`; the core provides implementations for `BTreeMap<String, T>` and, with `std`, `HashMap<String, T>`. `rename`, `default`, and field constraints cannot be combined with `rest`. Without a rest receiver, a derived struct remains a closed object range.
+
+```rust
+use decodal::{Decodal, DecodalDecode, DecodalSchema, EmptyLoader, Engine};
+
+#[derive(Decodal)]
+struct Service {
+    name: String,
+
+    #[decodal(gt = 443, default = 8443)]
+    port: i64,
+
+    #[decodal(rename = "feature.enable", default = true)]
+    feature_enabled: bool,
+}
+
+let mut engine = Engine::new(EmptyLoader);
+engine.bind_global("Service", Service::decodal_schema())?;
+
+let value = engine.eval_module(module)?;
+let data = engine.materialize(&value)?;
+let service = Service::decodal_decode(&data)?;
+```
+
+Supported field attributes are intentionally small:
+
+- `rename = "path.to.field"`
+- `default`
+- `default = value`
+- numeric constraints: `gt`, `gte`, `lt`, `lte`
+
+The derive does not add host callbacks or reflection.
+It only generates schema construction and typed decoding code.
+
+## ImportLoader and prelude together
+
+`ImportLoader` and host prelude bindings are independent mechanisms.
+
+- Use `ImportLoader` when user sources should explicitly import host-provided sources or values.
 - Use prelude bindings when host-provided schemas or constants should be globally available.

 Both mechanisms share the same runtime evaluator, thunk model, and materialization rules.
+
+## Shared host environment
+
+An embedded application can implement `HostEnvironment` to keep loader creation and global binding setup in one place.
+Both production evaluation and semantic editor tooling create their engines from this environment, preventing the editor from drifting onto a separate validation path.
+
+```rust
+use decodal::{Engine, HostEnvironment};
+
+struct AppEnvironment;
+
+impl HostEnvironment for AppEnvironment {
+    type Loader = ContentLoader;
+
+    fn create_loader(&self) -> Self::Loader {
+        ContentLoader::new()
+    }
+
+    fn configure_engine(
+        &self,
+        engine: &mut Engine<Self::Loader>,
+    ) -> decodal::Result<()> {
+        engine.bind_global("Site", site_schema())?;
+        Ok(())
+    }
+}
+
+let environment = AppEnvironment;
+let mut engine = environment.create_engine()?;
+```
+
+The semantic service accepts the same environment by value:
+
+```rust
+use decodal_language_service::LanguageService;
+
+let service = LanguageService::new(&environment);
+let analysis = service.analyze("site.dcdl", "site.dcdl", source);
+```
+
+Each analysis uses a fresh engine and runs the normal parse, evaluate, and materialize pipeline.
+An environment may create loaders backed by shared filesystem, database, or editor-overlay state when repeated analysis needs a current workspace snapshot.
+
+The LSP adapter constructs that environment after receiving the client's initialization parameters:
+
+```rust
+use decodal_lsp::{LspEnvironment, run_stdio};
+
+impl LspEnvironment for AppEnvironment {}
+
+run_stdio(|initialize| {
+    let _ = initialize;
+    Ok(AppEnvironment)
+})?;
+```
+
+`LspEnvironment` adds document lifecycle hooks on top of `HostEnvironment`.
+A `run_stdio` environment factory always receives the client's `InitializeParams`; the host decides whether to use its workspace folders, initialization options, and capabilities or ignore them.
+A host that keeps unsaved buffers in shared state can update them from `open_document`, `change_document`, and `close_document`; every subsequent diagnostic pass creates the normal import loader from that updated environment.
+Synchronized non-Decodal documents are passed through these hooks but are not evaluated as Decodal roots, so a loader can parse an unsaved Markdown file into `Value` and immediately revalidate the open Decodal documents that import it.
+
+## Structured imports
+
+`ImportLoader::load` returns either `LoadedImport::Source` or `LoadedImport::Value`.
+The value variant carries a `Value`, allowing a host to parse non-Decodal resources such as Markdown into an application-specific structure.
+
+```text
+import "./post.md"
+  -> host parses content
+  -> LoadedImport::Value {
+       key: "content/post.md",
+       value: { frontmatter: {...}, body: "..." }
+     }
+  -> Engine internalizes Value
+  -> normal composition and materialization
+```
+
+The core does not select content types or bundle Markdown/frontmatter parsers.
+The loader owns path resolution, media or extension dispatch, parsing rules, and parse diagnostics.
+The stable loader key is also used to cache structured imports.
+
+When a structured value fails a Decodal constraint, the diagnostic keeps the Decodal constraint span and identifies the imported value by its stable key and logical value path, such as `content/post.md` and `frontmatter.draft`.
+`Value` does not need source spans: syntax diagnostics for the external format remain the loader's responsibility, while cross-value validation reports semantic provenance.
+
+`load` is the single import hook: loaders dispatch by extension, media type, or another host-defined rule and return the appropriate variant directly.
@@ -16,13 +16,17 @@ demand-driven evaluation
  ├─ load imported module on demand
  ├─ evaluate expression
  ├─ compose `&`
-  └─ patch `//`
+  ├─ patch `//`
+  └─ validate `as`
  ↓
 materialize
  ↓
 data / diagnostics
 ```

+Production applications and semantic language services can construct this pipeline through the same host-defined `HostEnvironment`.
+The environment creates the `ImportLoader` and installs host globals before the root module is registered.
+
 ## lexer / parser

 lexer / parser は source を AST に変換する。
@@ -66,14 +70,16 @@ ModuleRegistry:
 処理系は、まず root module を parse / desugar して registry に登録する。
 import 先 module は、この段階で全て読み込む必要はない。

-import expression が評価されたとき、処理系は `SourceLoader` に現在の module key と import specifier を渡す。
-loader は module key、表示名、source text を返す。
-module registry は key が未登録なら対象 module を parse / desugar して登録する。
-登録された module は module root thunk を持つ。
-同じ module が複数回 import された場合は、同じ `ModuleId` を返す。
+import expression が評価されたとき、処理系は `ImportLoader::load` に現在の module key と import specifier を渡す。
+loader は module key、表示名、および DCDL source text または構造化済み `Value` を返す。
+DCDL source の場合、module registry は key が未登録なら対象 module を parse / desugar して登録する。
+登録された source module は module root thunk を持つ。
+構造化値の場合、host が返した `Value` を runtime value に internalize した root thunk を key でキャッシュする。
+同じ key が複数回 import された場合は、同じ source module または structured root thunk を使う。

-つまり import は module を即時評価しない。
+つまり source import は module を即時評価しない。
 module を読み込み、module root を thunk として登録するだけにする。
+structured import も root value を thunk として保持し、object field や array item の既存 thunk model を利用する。

 AST の `ExprId` は module-local である。
 そのため runtime が保持する式参照は `ExprRef { module, expr }` として module-qualified にする。
@@ -100,9 +106,16 @@ eval(A // B):
  a = eval(A)
  b = eval(B)
  patch(a, b)
+
+eval(A as S):
+  narrower = eval(A)
+  wider = eval(S)
+  apply_as(narrower, wider)
 ```

-`&` は制約を保った合成を行い、`//` は右辺優先の deep patch を行う。
+`&` は制約を保った対称な合成を行い、`//` は右辺優先の deep patch を行う。
+`as` は左辺が右辺より狭いことを再帰的に確認する。左辺で絞られた部分は左辺を使い、右辺だけの部分は abstract のまま保持する。
+default は `as` では選択せず、materialize まで遅延する。
 詳細は [Composition and Materialization](./composition-and-materialization.md) に置く。

 ## resolver / binder
@@ -135,7 +148,7 @@ resolver / binder を追加すると、以下を早期に診断しやすくな
 - import path の一部静的解決
 - span 付き diagnostic の精度向上

-ただし、Decodal の制約検証は独立した type checking pass ではなく、`&` の合成時や materialize 時に行う。
+ただし、Decodal の制約検証は独立した type checking pass ではなく、`&` の合成時、`as` の適用時、materialize 時に行う。

 ## materialize

@@ -1,10 +1,44 @@
 # Features

-Decodal keeps the embedded core small by making heavy functionality opt-in.
+Decodal は embedded use と小さい runtime を優先する。
+言語機能を追加するときは、値の合成・検証・materialization に直接必要なものを core に残し、重い依存や高度な推論は optional feature または外部 tooling に分ける。
+
+## Core feature boundary
+
+Core に入れる機能は、基本的に deterministic な value transformation に限る。
+
+- arithmetic / logical / comparison operators
+- array concat
+- object / constraint composition
+- asymmetric range refinement, `Unknown`, map constraints, and object rest constraints
+- default materialization
+- pure function evaluation
+- host supplied import evaluation
+
+Core に入れないものは以下である。
+
+- filesystem / network / environment access
+- time / random
+- mutation
+- reflection or existence probing
+- arbitrary host function calls
+- symbolic constraint solving beyond simple normalization
+
+未解決 identifier や missing field は明示的な `Unknown` range とは異なり、diagnostic になる。
+この方針により、存在チェックや optional chaining のような dynamic object inspection は core language の対象外とする。
+
+## Constraint reasoning
+
+Constraint normalization は軽量な範囲に留める。
+primitive type conflict や明らかな numeric bound conflict は合成時に検出してよい。
+一方で、symbolic arithmetic、boolean algebra、regex intersection、array length dependent typing のような重い推論は行わない。
+
+評価済みの concrete value に対する検証は runtime / materialization で行う。
+静的に完全な型検査フェーズを増やすのではなく、parse、evaluate、compose、materialize の各段階で自然に分かる error を diagnostic として返す。

 ## Core defaults

-`decodal-core` defaults to `std` only.
+`decodal` defaults to `std` only.

 ```toml
 [features]
@@ -13,7 +47,7 @@ std = []
 regex = ["std", "dep:regex"]
 ```

-Building `decodal-core` with `--no-default-features` keeps the core in `no_std + alloc` mode and avoids optional dependencies.
+Building `decodal` with `--no-default-features` keeps the core in `no_std + alloc` mode and avoids optional dependencies.

 ## Regex

@@ -21,7 +55,7 @@ Regex constraints are implemented behind the `regex` feature.
 When the feature is disabled, regex constraints parse and compose, but validating a concrete value against them returns an unsupported feature diagnostic.

 ```sh
-cargo run -q -p decodal --features regex -- examples/regex/main.dcdl
+cargo run -q -p decodal-cli --features regex -- examples/regex/main.dcdl
 ```

 Regex constraints are accumulated during `&` composition.
@@ -30,5 +64,5 @@ Concrete strings must match every regex constraint attached to the abstract valu

 ## CLI features

-`decodal-cli` exposes a matching `regex` feature that enables `decodal-core/regex`.
+`decodal-cli` exposes a matching `regex` feature that enables `decodal/regex`.
 The feature is not enabled by default so the default CLI binary remains small.
@@ -6,7 +6,7 @@
 ## 方針

 初期処理系は AST interpreter として実装する。
-bytecode VM や JIT ではなく、AST を demand-driven に評価することで、遅延評価、循環参照、`default`、`&`、`//` の意味論を小さく実装する。
+bytecode VM や JIT ではなく、AST を demand-driven に評価することで、遅延評価、循環参照、`default`、`&`、`//`、`as` の意味論を小さく実装する。

 ## 構成

@@ -14,6 +14,10 @@ RuntimeValue =
 `Concrete` は明示的な値である。
 `Abstract` は、まだ具体値に確定していない制約付きの値である。

+Decodal は `Unknown` を、すべてのDecodal値を包含する最上位の abstract range として持つ。
+これは存在する具体値の型情報を消す `Any` ではない。具体値を `Unknown` に対して検証した場合は具体値を保持し、`Unknown` のままmaterializeしようとした場合は diagnostic になる。
+識別子や field が解決できない状態とは区別し、それらは従来どおりその場で diagnostic になる。
+
 ## ConcreteValue

 ```text
@@ -32,7 +36,16 @@ object は concrete structure として扱う。

 ```text
 ObjectValue:
-  fields: Map<Symbol, ThunkId>
+  fields: Map<Symbol, ObjectField>
+  rest: Option<ObjectRest>
+
+ObjectField:
+  value: ThunkId
+  span: Span
+
+ObjectRest:
+  value: ThunkId
+  span: Span
 ```

 例えば以下の schema object は、object 自体は concrete だが、field の値は abstract value になる。
@@ -57,9 +70,14 @@ Concrete(Object {

 ```text
 AbstractValue {
-  constraints: Vec<Constraint>
+  constraints: Vec<ConstraintEntry>
  default: Option<ThunkId>
 }
+
+ConstraintEntry {
+  constraint: Constraint
+  span: Span
+}
 ```

 `default` は `AbstractValue` にだけ存在する。
@@ -88,19 +106,45 @@ port = 8000;
 Concrete(Int(8000))
 ```

+## Runtime scope
+
+Decodal runtime は application runtime ではなく、pure value evaluator である。
+同じ source、同じ import results、同じ host globals が与えられた場合、評価結果は決定的である。
+
+runtime が扱う責務は以下に限る。
+
+- expression を評価する。
+- thunk を必要に応じて force する。
+- concrete / abstract value を合成する。
+- materialize 時に constraint を検証する。
+
+runtime は filesystem、network、environment variable、time、random、mutation を扱わない。
+core における import は host supplied source または structured value を受け取る境界であり、filesystem access ではない。
+
 ## Constraint

 constraint は concrete value とは別の型として扱う。

 ```text
 Constraint =
+  Unknown
  Type(PrimitiveType)
+  ArrayItems(ThunkId)
+  MapValues(ThunkId)
  Compare(Op, Literal)
  Regex(Pattern)
  BuiltinPredicate(Symbol)
  ObjectConstraint(...)
 ```

+`ArrayItems` は配列そのものの型と、すべての要素へ合成する schema thunk を表す。
+配列用の primitive type は持たず、抽象配列には必ず要素制約が必要である。
+
+`MapValues` は object の key 集合を制限せず、すべての field value へ適用する schema thunk を表す。
+連想配列は materialize 後も `Data::Object` になり、別の data variant は持たない。
+
+`ObjectValue.rest` は名前付きfieldを持つobjectの残余field rangeを表す。rest自体はfieldを生成せず、materializeは実在するfieldだけを出力する。
+
 初期実装では、object の形は主に `Concrete(Object)` の field に `Abstract` を置くことで表現する。
 object 全体にかかる constraint は必要になった時点で追加する。

@@ -84,5 +84,5 @@ module root や field は thunk として保持され、参照されたときだ
 関数引数は thunk として関数の environment に束縛する。
 関数本体で引数が参照されたときだけ force する。

-任意の関数呼び出し結果をグローバルに memoize する必要はない。
+関数呼び出し結果そのものはグローバルには memoize しない。
 field に束縛された関数呼び出し結果は、その field thunk の評価結果として memoize される。
@@ -9,15 +9,158 @@ Run the normal Rust checks from the repository root.
 ```sh
 cargo fmt --check
 cargo test
-cargo check -p decodal-core --no-default-features
+cargo check -p decodal --no-default-features
 nix flake check
 ```

+Run the default stdio language server with:
+
+```sh
+cargo run -q -p decodal-lsp
+```
+
+The protocol integration tests use an in-memory LSP connection and can be run independently:
+
+```sh
+cargo test -p decodal-lsp
+```
+
 Regex support is optional and should be tested explicitly when touched.

 ```sh
-cargo test -p decodal-core --features regex
-cargo run -q -p decodal --features regex -- examples/regex/main.dcdl
+cargo test -p decodal --features regex
+cargo run -q -p decodal-cli --features regex -- examples/regex/main.dcdl
+```
+
+## crates.io release
+
+The crates.io release contains `decodal`, `decodal-derive`, `decodal-language-service`, `decodal-language-tools`, and `decodal-lsp`.
+`decodal-cli` and the Rust source crate `decodal-wasm` remain repository-only packages.
+The generated WebAssembly package under `packages/decodal-wasm/` is published to npm and JSR.
+The CodeMirror package bundles the generated formatter WebAssembly from `decodal-language-tools`.
+The project is dual licensed as `MIT OR Apache-2.0`.
+
+The authoritative validation commands, dependency order, and publish commands are maintained in `RELEASING.md` at the repository root.
+
+## Web site and playground
+
+The Astro documentation site and browser playground are kept in:
+
+```text
+site/decodal-site/
+```
+
+The site imports Markdown files from `doc/manual/souce/` and renders them as mdBook-style pages.
+The playground loads `decodal-wasm` for evaluation and `decodal-codemirror` for editor features and source formatting.
+
+Important files:
+
+```text
+site/decodal-site/src/pages/docs/[...slug].astro
+site/decodal-site/src/pages/playground.astro
+site/decodal-site/src/scripts/playground.js
+site/decodal-site/src/scripts/playground-examples.js
+site/decodal-site/src/layouts/ManualLayout.astro
+site/decodal-site/src/lib/docs.js
+site/decodal-site/src/lib/highlight.js
+packages/decodal-codemirror/src/decodal.js
+packages/decodal-codemirror/src/decodal-parser.js
+packages/decodal-wasm/decodal_wasm.js
+packages/decodal-wasm/decodal_wasm_bg.wasm
+packages/decodal-codemirror/wasm/decodal_language_tools.js
+packages/decodal-codemirror/wasm/decodal_language_tools_bg.wasm
+crates/decodal-wasm/src/lib.rs
+crates/decodal-language-tools/src/lib.rs
+```
+
+Build the WebAssembly packages before building the site:
+
+```sh
+cd site/decodal-site
+npm install
+npm run build:wasm
+npm run build
+```
+
+`npm run build:wasm` builds both generated WebAssembly packages.
+`npm run build:wasm:runtime` writes generated runtime files into `packages/decodal-wasm/`.
+`npm run build:wasm:formatter` writes generated formatter files into `packages/decodal-codemirror/wasm/`.
+`npm run build` builds only the static site from the current package files.
+Use `npm run build:all` to regenerate both WebAssembly packages and then build the static site in one command.
+
+These generated files are committed so the site can be built without requiring every consumer to regenerate the wasm packages first.
+
+Publish the generated WebAssembly package from its package directory:
+
+```sh
+cd packages/decodal-wasm
+npm publish
+npx jsr publish
+```
+
+Run dry-runs first when preparing a release:
+
+```sh
+npm pack --dry-run
+npx jsr publish --dry-run
+```
+
+The npm package name is `decodal-wasm`.
+The JSR package name is `@hare/decodal-wasm`.
+The npm package advertises `MIT OR Apache-2.0`; JSR metadata uses `MIT` because its publisher requires a single recognized license identifier. Both license files are included in the package.
+
+The playground editor uses the `decodal-codemirror` package with the generated Lezer parser in `packages/decodal-codemirror/src/decodal-parser.js`.
+The canonical grammar is documented in `doc/manual/souce/language/grammar.md`; regenerate the Lezer parser when that grammar or `editors/lezer-decodal/decodal.grammar` changes.
+
+Publish the CodeMirror package from its package directory:
+
+```sh
+cd packages/decodal-codemirror
+npm install
+npm publish
+npx jsr publish
+```
+
+Run dry-runs first when preparing a release:
+
+```sh
+npm install
+npm pack --dry-run
+npx jsr publish --dry-run
+```
+
+The npm package name is `decodal-codemirror`.
+The JSR package name is `@hare/decodal-codemirror`.
+As with `decodal-wasm`, JSR metadata uses `MIT` while both the MIT and Apache-2.0 license files remain included.
+
+The documentation build still uses the lightweight JavaScript fallback highlighter so Astro can render Markdown without initializing WASM at build time.
+
+To run the site locally:
+
+```sh
+cd site/decodal-site
+npm run dev
+```
+
+Deploy the static site to Cloudflare Pages with Wrangler direct upload:
+
+```sh
+cd site/decodal-site
+npm run deploy
+```
+
+The deploy script runs `npm run build` and then uploads `dist/` to the Pages project named `decodal-site` on branch `master`.
+Cloudflare Pages treats this as production when the project production branch is `master`.
+Use `CLOUDFLARE_PROJECT_NAME` when deploying to a differently named Pages project.
+
+```sh
+CLOUDFLARE_PROJECT_NAME=my-pages-project npm run deploy
+```
+
+If the committed WASM package must be regenerated before deploy, use:
+
+```sh
+npm run deploy:all
 ```

 ## Tree-sitter grammar
@@ -64,16 +207,22 @@ The generated parser files under `editors/tree-sitter-decodal/src/` are committe

 When the Decodal syntax changes:

-1. Update `grammar.js`.
-2. Run `npx tree-sitter generate`.
-3. Add or update corpus tests in `corpus/`.
-4. Update highlight queries in `queries/highlights.scm` if token names changed.
-5. Run `npx tree-sitter test`.
-6. Run Rust checks from the repository root if the language parser or examples also changed.
+1. Update the canonical EBNF in `doc/manual/souce/language/grammar.md`.
+2. Update the Rust parser/lexer as needed.
+3. Update `editors/tree-sitter-decodal/grammar.js` and run `npx tree-sitter generate` / `npx tree-sitter test`.
+4. Update `editors/lezer-decodal/decodal.grammar` and regenerate the CodeMirror parser:
+
+```sh
+cd site/decodal-site
+npx lezer-generator ../../editors/lezer-decodal/decodal.grammar -o ../../packages/decodal-codemirror/src/decodal-parser.js
+```
+
+5. Add or update corpus/tests/examples.
+6. Run Rust and site checks from the repository root.

 ## Development shell

-The Nix development shell includes Rust tooling, Node.js, and Tree-sitter CLI tooling.
+The Nix development shell includes Rust tooling, Node.js, Tree-sitter CLI tooling, and wasm-pack tooling.

 ```sh
 nix develop
@@ -87,5 +236,7 @@ The shell provides:
 - `clippy`
 - `node`
 - `npm`
+- `wasm-pack`
+- `lld`
 - `tree-sitter`
 - `nixfmt`
@@ -6,7 +6,8 @@ Decodal は Deferred Constraint Data Language、略称 DCDL のプロジェク
 ## 目次

 1. [Introduction](./introduction.md)
-2. [Language Specification](./language/index.md)
+2. [Components](./components.md)
+3. [Language Specification](./language/index.md)
   1. [Lexical Structure and Syntax](./language/syntax.md)
   2. [Value](./language/value/index.md)
      1. [String](./language/value/string.md)
@@ -25,8 +26,9 @@ Decodal は Deferred Constraint Data Language、略称 DCDL のプロジェク
      9. [Match](./language/expression/match.md)
      10. [Import](./language/expression/import.md)
      11. [Composition](./language/expression/composition.md)
-      12. [Default](./language/expression/default.md)
-      13. [String Interpolation](./language/expression/string-interpolation.md)
+      12. [Range Refinement](./language/expression/ascription.md)
+      13. [Default](./language/expression/default.md)
+      14. [String Interpolation](./language/expression/string-interpolation.md)
   4. [Constraints and Defaults](./language/constraints-and-defaults.md)
   5. [Composition Operators](./language/operators.md)
   6. [Functions](./language/functions.md)
@@ -35,7 +37,7 @@ Decodal は Deferred Constraint Data Language、略称 DCDL のプロジェク
   9. [Materialization and Errors](./language/materialization-and-errors.md)
   10. [Naming Conventions](./language/naming.md)
   11. [Examples](./language/examples.md)
-3. [Implementation Design](./design/index.md)
+4. [Implementation Design](./design/index.md)
   1. [Execution Pipeline](./design/execution-pipeline.md)
   2. [Runtime Model](./design/runtime-model.md)
   3. [Thunk and Lazy Evaluation](./design/thunk-and-lazy-evaluation.md)
@@ -43,5 +45,5 @@ Decodal は Deferred Constraint Data Language、略称 DCDL のプロジェク
   5. [Diagnostics and Fallback](./design/diagnostics-and-fallback.md)
   6. [Embedding API](./design/embedding-api.md)
   7. [Features](./design/features.md)
-4. [Development](./development.md)
-5. [Open Issues](./open-issues.md)
+5. [Development](./development.md)
+6. [Open Issues](./open-issues.md)
@@ -82,12 +82,27 @@ Int & >= 10 & <= 10 # OK
 最小の組み込み制約は以下である。

 ```dcdl
+Unknown
 String
 Int
 Float
 Bool
 ```

+`Unknown` はすべてのDecodal値を含む最上位rangeである。検査を無効化する `Any` ではなく、具体的な値またはより狭いrangeがまだ決まっていないことを表す。
+
+```dcdl
+Int & Unknown       # Int
+42 as Unknown       # 42
+Unknown as Int      # エラー
+```
+
+`Unknown` 自体は具体値を持たないためmaterializeできない。defaultを与えるか、具体値で絞り込む必要がある。
+
+```dcdl
+Unknown default {}  # {}
+```
+
 追加の述語制約はライブラリまたは組み込みとして提供できる。

 ```dcdl
@@ -124,6 +139,43 @@ String & /^a$/ & /^b$/
 Host = IPv4Address;
 ```

+## 配列制約
+
+配列制約には要素制約が必須であり、`[...T]` と書く。
+
+```dcdl
+Names = [...String];
+PositiveInts = [...(Int & > 0)];
+```
+
+複数の配列制約を `&` で合成した場合、各 concrete 要素をすべての要素 range で絞り込む。
+要素が object range の場合、右辺にしかない field は default の有無にかかわらず abstract のまま各要素へ残る。
+左辺にしかない field は右辺の field domain 外なのでエラーになる。
+要素制約のない `Array` primitive type は存在しない。
+
+## 連想配列制約
+
+連想配列制約は `{...T}` と書き、object の任意の field value を `T` に対して絞り込む。
+
+```dcdl
+Services = {...{
+    port = Int;
+    enabled = Bool default true;
+}};
+```
+
+key は schema で列挙せず、空 object も許容する。
+固定 object field と任意 key の value constraint は、末尾の `...T` で混在できる。
+
+```dcdl
+{
+    enabled = Bool default true;
+    ...Unknown
+}
+```
+
+このrest constraintは明示されていないfieldだけに適用され、field自体は生成しない。
+
 ## default

 `default` は制約ではない。
@@ -188,11 +240,12 @@ RuntimeValue =

 ## default の合成

-同じフィールドに複数の `default` が合成された場合の詳細規則は未確定である。
-現時点の単純な方針は以下である。
+`default` の合成規則は以下である。

- `&` による default 同士の衝突はエラーにする。
- 同一 default 値は許可してよい。
- `//` による patch では右辺 default が左辺 default を置き換える。
+- `&` で片方だけが default を持つ場合、その default を保持する。
+- `&` で両方が異なる default を持つ場合、conflict になる。
+- `Abstract & Concrete` が成功した場合、結果は concrete value になり default は消える。
+- `//` では右辺が左辺を置き換える。object/object の場合は field ごとに再帰 patch されるため、右辺 field の default が左辺 field の default を置き換える。

-この方針により、`&` は制約を保った合成、`//` は上書き操作として説明できる。
+`default` thunk は materialize 時に必要になった時点で評価する。
+評価された default value は、同じ abstract value に残っている制約を満たす必要がある。
@@ -74,5 +74,5 @@ Error        評価失敗
 関数引数は thunk として渡せる。
 関数本体内で引数が参照されたときに評価する。

-任意の関数呼び出し結果をグローバルに memoize することは必須ではない。
+関数呼び出し結果そのものはグローバルには memoize しない。
 ただし、フィールドに束縛された呼び出し結果は、そのフィールド thunk の評価結果として memoize される。
@@ -5,21 +5,19 @@
 ## 基本的な設定スキーマ

 ```dcdl
-rec {
-    Host = IPv4Address;
+Host = IPv4Address;

-    Port = Int & >= 1 & <= 65535;
-    NarrowedPort = Port & > 443;
+Port = Int & >= 1 & <= 65535;
+NarrowedPort = Port & > 443;

-    MyConfig = {
-        host = Host;
-        port = NarrowedPort default 8080;
-        feature_hoge = {
-            enable = Bool default true;
-            fuga = Int default 10;
-        };
+MyConfig = {
+    host = Host;
+    port = NarrowedPort default 8080;
+    feature_hoge = {
+        enable = Bool default true;
+        fuga = Int default 10;
    };
-}
+};

 NewConfig = MyConfig & {
    host = "127.0.0.1";
@@ -33,28 +31,54 @@ disabled_config = NewConfig & {
 enabled_config = NewConfig;
 ```

-## 関数と文字列生成
+## 配列スキーマ
+
+```dcdl
+Services = [...{
+    name = String;
+    port = Int default 8080;
+}];
+
+[
+    { name = "api"; },
+    { name = "worker"; port = 9000; },
+] as Services
+```
+
+抽象配列には要素制約が必須である。
+この例では、1 番目の要素の `port` は `8080` に materialize される。
+
+## 連想配列と範囲絞り込み
+
+```dcdl
+Service = {
+    port = Int;
+    enabled = Bool default true;
+};
+
+services = {
+    api = { port = 8080; };
+    worker = { port = 8081; enabled = false; };
+} as {...Service};
+```
+
+`api` と `worker` は任意の key であり、それぞれの value は `Service` より狭い範囲へ絞り込まれる。
+`as` の結果では `api.enabled` は abstract のまま残り、最終的に結果全体を materialize した時点で default の `true` が使われる。
+
+## 関数と制約

 ```dcdl
 let
-    maybe_hw = String & /Hello! .*/;
-    part = {
-        greet = String;
-        target = String;
-    };
-    mk_hw = (part: part) =>
-        maybe_hw & "${part.greet}! ${part.target}";
+    Port = Int & >= 1 & <= 65535;
+    add_offset = (base: Port, offset: Int) => base + offset;
 in
-    mk_hw({
-        greet = "Hello";
-        target = "World";
-    })
+    add_offset(8000, 80)
 ```

 評価結果:

 ```text
-"Hello! World"
+8080
 ```

 ## match
@@ -0,0 +1,43 @@
+# Arithmetic Expression
+
+Decodal supports arithmetic over concrete numeric values.
+
+```dcdl
+{
+    workers = 2 + 2;
+    timeout = 30.0 / 2;
+    port = 8000 + 80;
+    negative = -1;
+}
+```
+
+## Operators
+
+- `+` addition
+- `-` subtraction
+- `*` multiplication
+- `/` division
+- unary `-` negation
+
+`*` and `/` bind tighter than `+` and `-`.
+Parentheses can be used to make grouping explicit.
+
+```dcdl
+2 + 3 * 4     # 14
+(2 + 3) * 4   # 20
+```
+
+## Numeric behavior
+
+Arithmetic requires concrete `Int` or `Float` operands.
+`Int + Int`, `Int - Int`, and `Int * Int` produce `Int` when no overflow occurs.
+Mixed `Int` / `Float` arithmetic produces `Float`.
+Division always produces `Float`.
+
+Division by zero and integer overflow are evaluation errors.
+
+Arithmetic expressions can be used anywhere a concrete numeric expression is expected, including defaults and numeric constraints.
+
+```dcdl
+port = Int & > 4000 + 42 default 8080;
+```
@@ -7,9 +7,65 @@ array expression は、順序付きの値の列を表す。
 ["a", "b", "c"]
 ```

-## 未確定事項
+配列リテラルは concrete value であり、要素型を揃える必要はない。

- 配列要素の制約表現。
- 異種配列を許可するか。
- `//` による patch を右辺置換だけにするか。
- append / prepend / remove などの操作を提供するか。
+```dcdl
+["api", 8080, true]
+```
+
+## Array constraint
+
+配列制約は `[` の直後に ellipsis を置き、その後へ要素制約を記述する。
+
+```dcdl
+Names = [...String];
+Ports = [...(Int & >= 1 & <= 65535)];
+```
+
+`[...T]` は、すべての要素が `T` を満たす長さ 0 以上の配列を表す。
+空配列は任意の配列制約を満たす。
+
+```dcdl
+[...String] & []
+[...String] & ["api", "worker"]
+```
+
+要素制約は object range にもできる。
+右辺だけにある default 付き field は、配列へ制約を合成した時点では abstract のまま各要素に残る。
+その配列を後から materialize した場合にだけ default が使われる。
+
+```dcdl
+Services = [...{
+    name = String;
+    enabled = Bool default true;
+}];
+
+Services & [{ name = "api"; }]
+```
+
+配列制約を concrete array に適用すると、各要素は要素 range に対して `as` と同じ規則で絞り込まれる。
+object の要素 range では左辺にしかない field がエラーになり、右辺にしかない field は abstract のまま残る。
+
+要素制約のない抽象配列型は提供しない。
+旧来の `Array` primitive type は使用できず、`[...T]` の `T` は必須である。
+`[String]` は配列制約ではなく、未解決の `String` 制約を 1 要素に持つ concrete array になる。
+長さ制約、位置別の tuple 制約、unique 制約は現在サポートしない。
+
+## Array concat
+
+`++` は concrete array 同士を連結する。
+
+```dcdl
+base = ["read", "write"];
+extra = ["admin"];
+roles = base ++ extra;
+```
+
+`roles` は以下と同じ値になる。
+
+```dcdl
+["read", "write", "admin"]
+```
+
+`++` は配列要素を変換しない。
+左辺の要素の後に右辺の要素が並ぶ。
@@ -0,0 +1,75 @@
+# Range Refinement
+
+`narrower as wider` は、左辺が右辺より具体的で狭い範囲であることを確認し、両者を非対称に合成する演算である。
+
+```dcdl
+Int & > 10 as Int & > 0
+```
+
+この例は成功し、結果は左辺の狭い範囲 `Int & > 10` のままになる。逆向きの `Int as Int & > 0` は、左辺が右辺を満たすとは限らないため失敗する。
+
+## Object
+
+object では、右辺を field domain として左辺の field を確認する。
+
+- 左辺にしかない field は、右辺の domain 外なのでエラーになる。
+- 両側にある field は、左辺が右辺より狭いかを再帰的に確認し、左辺の狭い結果を使う。
+- 右辺にしかない field は、default の有無に関係なく未評価のまま結果へ残す。
+- 結果の field order は右辺の順序に従う。
+
+```dcdl
+partial = {
+    port = 8080;
+} as {
+    host = String;
+    port = Int;
+    enabled = Bool default true;
+};
+```
+
+`partial.port` は `8080` に具体化される。`partial.host` と `partial.enabled` は右辺由来の abstract field のままであり、`as` は `enabled` の default を選択も force もしない。
+
+その後 `partial` 全体を materialize すれば、通常の materialize 規則が適用される。この例では unresolved な `host` がエラーになり、`host` も具体化されていれば `enabled` の default がその時点で利用される。
+
+## Default
+
+default は範囲包含の根拠ではない。両側に同じ field がある場合、結果には左辺を使うため、右辺の default を左辺へ注入しない。
+
+```dcdl
+Int & > 0 as (Int default 1)
+```
+
+結果は default のない `Int & > 0` である。一方、右辺だけに残る object field は field 全体を保持するため、その abstract value が元から持つ default も保持される。
+
+## Map and array ranges
+
+`{...T}` は任意の object key を許可し、各 value が `T` より狭いことを確認する。
+
+```dcdl
+ports = {
+    http = 80;
+    https = 443;
+} as {...(Int & >= 1 & <= 65535)};
+```
+
+`[...T]` を右辺に使う場合も、すべての array element を `T` に対して絞り込む。
+
+## Concrete right-hand ranges
+
+primitive constraint や合成 constraint は通常どおり値を検証する。
+右辺が concrete scalar または array literal の場合は、左辺も同じ値または同じ長さ・要素構造である必要がある。
+function は右辺の範囲として使用できない。
+
+左辺は concrete value に限らない。処理系が包含を確認できる constraint 同士であれば abstract value も使用できる。primitive type、numeric bound、同一 regex / predicate、array/map の要素範囲は包含確認の対象になる。
+
+関数 parameter の `name: range` も、引数が force された時点で `as` と同じ絞り込み規則を使う。
+
+## Precedence
+
+`as` は `default` より低い、最も低い優先順位を持ち、左結合である。
+
+```dcdl
+narrow & overrides as Wider
+```
+
+これは `(narrow & overrides) as Wider` と解釈される。
@@ -11,6 +11,9 @@ Port = Int & >= 1 & <= 65535;
 Config = MyConfig & { port = 8000; };
 ```

+object 同士では片側だけにある field も保持するため、`&` は方向を持たない。
+左辺が右辺より狭いことを確認し、右辺を field domain として合成したい場合は [`as`](./ascription.md) を使う。
+
 ## `//`

 `//` は右辺優先の構造的 patch を行う。
@@ -3,15 +3,15 @@
 function call expression は、関数値を引数に適用する式である。

 ```dcdl
-mk_hw({
-    greet = "Hello";
-    target = "World";
-})
+increment(41)
 ```

 ## 評価

 引数は thunk として渡せる。
 関数本体内で引数が参照されたときに評価する。
+parameter に range が指定されている場合、引数は `narrower as wider` と同じ規則で絞り込まれる。
+parameter 側だけにある field は abstract のまま残り、default はこの時点では選択されない。

-任意の関数呼び出し結果をグローバルに memoize することは必須ではない。
+関数呼び出し結果そのものはグローバルには memoize しない。
+フィールドに束縛された呼び出し結果は、そのフィールド thunk の評価結果として memoize される。
@@ -3,11 +3,7 @@
 function expression は、引数を受け取り式を返す値である。

 ```dcdl
-(part: {
-    greet = String;
-    target = String;
-}) =>
-    "${part.greet}! ${part.target}"
+(value: Int) => value + 1
 ```

 関数仕様の詳細は [関数](../functions.md) に置く。
@@ -10,13 +10,16 @@ Expr
 ├─ identifier
 ├─ path reference
 ├─ object
+├─ map constraint
 ├─ array
+├─ array constraint
 ├─ function
 ├─ function call
 ├─ let
 ├─ match
 ├─ import
 ├─ composition
+├─ range refinement (`as`)
 ├─ default
 └─ string interpolation
 ```
@@ -4,12 +4,10 @@ let expression は、ローカル束縛を作る。

 ```dcdl
 let
-    part = {
-        greet = "Hello";
-        target = "World";
-    };
+    base = 8000;
+    offset = 80;
 in
-    "${part.greet}! ${part.target}"
+    base + offset
 ```

 ## 評価
@@ -0,0 +1,41 @@
+# Logical and Comparison Expressions
+
+Decodal supports boolean logic over concrete `Bool` values and comparison over concrete scalar values.
+
+```dcdl
+{
+    is_prod = env == "prod";
+    high_port = port > 9000;
+    enabled = is_prod && high_port;
+    disabled = !enabled;
+}
+```
+
+## Logical operators
+
+- `!expr` negates a concrete `Bool`.
+- `lhs && rhs` returns boolean AND.
+- `lhs || rhs` returns boolean OR.
+
+`&&` and `||` short-circuit: the right-hand side is evaluated only when needed.
+Logical operands must evaluate to concrete `Bool` values.
+
+## Comparison operators
+
+- `==`
+- `!=`
+- `<`
+- `<=`
+- `>`
+- `>=`
+
+`==` and `!=` compare concrete scalar values: `String`, `Bool`, `Int`, and `Float`.
+`Int` and `Float` can be compared to each other numerically.
+
+Ordering operators `<`, `<=`, `>`, and `>=` compare concrete numeric values only.
+They are separate from prefix comparison constraints such as `> 443`.
+
+```dcdl
+port = Int & > 443 default 9443;
+is_high = port > 9000;
+```
@@ -37,3 +37,52 @@ MyConfig = {
    };
 }
 ```
+
+## Map constraint
+
+連想配列の制約は、object の任意の field value に同じ schema を適用する。
+
+```dcdl
+Services = {...{
+    port = Int;
+    enabled = Bool default true;
+}};
+```
+
+`{...T}` は key の集合を固定せず、すべての value が `T` を満たす object を表す。
+空 object も許容される。runtime と materialize 後の表現は通常の object と共通であり、別の map value variant は持たない。
+
+```dcdl
+services = {
+    api = { port = 8080; };
+    worker = { port = 8081; enabled = false; };
+} as Services;
+```
+
+各 entry は `as` によって右辺の field domain 内へ絞り込まれるため、左辺に `port` や `enabled` 以外の field があればエラーになる。
+右辺にしかない field は default の有無にかかわらず abstract のまま残る。
+host から渡した object は識別子構文に収まらない文字列 key も保持できるが、DCDL source の object field name は通常の識別子に限られる。
+
+## Object rest constraint
+
+固定 field と任意 key の value range は、一つの object に混在できる。
+
+```dcdl
+OpenConfig = {
+    enabled = Bool default true;
+    ...Unknown
+};
+```
+
+`...T` は明示されていない残余 field にだけ適用する。明示 field にはそれぞれの field range を適用し、rest range を重ねて適用しない。
+rest constraint は field を生成せず、materialize 時には実際に存在する追加 field だけを出力する。
+
+```dcdl
+{
+    enabled = false;
+    plugin = { name = "cache"; };
+} as OpenConfig
+```
+
+`...T` は object の末尾に一つだけ書ける。省略した object は閉じており、`as` の左辺に未宣言 field があればエラーになる。
+名前付き field を持たない `{...T}` は従来どおり抽象的な map constraint であり、単独でmaterializeするにはdefaultまたは具体値が必要になる。
@@ -12,4 +12,5 @@ config.feature_hoge.enable
 左側の式を object として評価し、指定された field を参照する。
 参照先 field は必要になるまで評価されない。

-存在しない field への参照をエラーにするか、open schema として扱うかは未確定である。
+存在しない field への参照は diagnostic になる。
+明示的な `Unknown` range は存在しないfieldを表さないため、fieldの有無を曖昧にはしない。
@@ -1,12 +1,8 @@
-# String Interpolation Expression
+# String Interpolation

-string interpolation は、文字列内に式を埋め込む候補機能である。
+文字列補間は初期実装には含めない。

-```dcdl
-"${part.greet}! ${part.target}"
-```
+Decodal の string literal は、現時点では literal text として扱う。
+式を埋め込む構文は定義しない。

-## 評価
-
-補間式の評価タイミングは通常の遅延評価に従う。
-文字列補間を初期実装に含めるかは未確定である。
+必要になった場合は、文字列連結や明示的な formatting function として別途設計する。
@@ -5,54 +5,48 @@
 ## 構文

 ```dcdl
-(part: {
-    greet = String;
-    target = String;
-}) =>
-    "${part.greet}! ${part.target}"
+(value: Int) => value + 1
 ```

 関数呼び出しは通常の呼び出し構文で行う。

 ```dcdl
-mk_hw({
-    greet = "Hello";
-    target = "World";
-})
+let
+    increment = (value: Int) => value + 1;
+in
+    increment(41)
 ```

-複数引数の構文は候補として以下を想定する。
+複数引数も指定できる。

 ```dcdl
-(
-    input_a: {
-        hoge = Int & >= 0;
-    },
-    input_b: {
-        fuga = 20;
-    }
-) =>
+(input_a: { hoge = Int & >= 0; }, input_b: { fuga = Int; }) =>
 {
-    # ...
+    hoge = input_a.hoge;
+    fuga = input_b.fuga;
 }
 ```

 ## 関数の意味

-関数は値として扱える。
-ただし、最終データとして関数値を出力できるかどうかは別途定める。
-設定ファイルを materialize する段階では、未適用の関数値は出力不能な値として扱うのが自然である。
+関数は runtime value として扱えるが、最終データとして materialize することはできない。
+未適用の関数値が materialize 対象に残っている場合は diagnostic になる。
+
+関数値は opaque であり、関数値同士の等価性は提供しない。
+`&` で関数値同士を合成すると conflict になる。

 ## 評価方針

-関数は以下の方針を基本とする。
+関数は以下の方針で評価する。

 - 関数は純粋である。
 - 関数はレキシカルスコープを持つ。
 - 関数は定義時の環境を参照として保持する。
- 引数は必要になるまで評価しない。
- フィールドに束縛された関数呼び出し結果は、そのフィールド評価結果として memoize される。
- 任意の関数呼び出しそのものをグローバルに memoize することは必須ではない。
+- 引数は thunk として渡され、必要になるまで評価されない。
+- parameter range がある引数は、force 時に `as` と同じ範囲包含・絞り込み規則で合成される。
+- 関数呼び出し結果そのものはグローバルには memoize しない。
+- フィールドに束縛された関数呼び出し結果は、そのフィールド thunk の評価結果として memoize される。
+- 再帰的な依存は thunk cycle として diagnostic になる。

 関数値の内部モデル例:

@@ -63,29 +57,3 @@ Function {
  env: EnvRef
 }
 ```
-
-## 関数と重さ
-
-関数の文法・パーサー自体は大きくない。
-実装上の重さは、主に評価モデルと意味論から発生する。
-
-注意点:
-
- クロージャが環境を掴む。
- 引数を lazy にするか strict にするかを決める必要がある。
- 関数呼び出し結果をどこまで memoize するかを決める必要がある。
- 再帰関数を許可するかを決める必要がある。
- 関数値同士の `&` をどう扱うかを決める必要がある。
- 関数値を object に入れたとき、materialize 可能かを決める必要がある。
- import 循環と関数適用が絡んだときの cycle detection が必要になる。
-
-軽量に保つため、初期仕様では以下の制限を検討できる。
-
- 関数は pure。
- lexical closure は許可。
- 引数は thunk として渡す。
- 関数本体は必要になるまで評価しない。
- 関数値は opaque。
- 関数同士の `&` は、同一関数参照以外は conflict。
- 関数値は最終データとして出力できない。
- 再帰は cycle error として扱う、または v1 では禁止する。
@@ -0,0 +1,119 @@
+# Grammar
+
+This page is the canonical grammar reference for Decodal syntax.
+Parser implementations such as the Rust parser, Tree-sitter grammar, and Lezer grammar should follow this grammar and may add implementation-specific precedence annotations where needed.
+
+## Lexical grammar
+
+```ebnf
+source_character = ? any Unicode scalar value ? ;
+newline          = "\n" | "\r\n" | "\r" ;
+space            = " " | "\t" | newline ;
+comment          = "#" , { ? any character except newline ? } ;
+
+digit            = "0" … "9" ;
+letter           = "A" … "Z" | "a" … "z" ;
+identifier       = letter , { letter | digit | "_" } ;
+
+integer          = digit , { digit } ;
+float            = digit , { digit } , "." , digit , { digit } ;
+
+string           = '"' , { string_character | escape } , '"' ;
+string_character = ? any character except '"', "\\", or newline ? ;
+escape           = "\\" , source_character ;
+
+regex            = "/" , regex_character , { regex_character } , "/" ;
+regex_character  = escape | ? any character except "/", "\\", or newline ? ;
+```
+
+Whitespace and comments separate tokens and are otherwise ignored by the parser.
+
+## Syntactic grammar
+
+```ebnf
+module          = { statement } ;
+statement       = field_definition , [ ";" ]
+                | expression , [ ";" ] ;
+
+expression      = as_expression ;
+
+as_expression      = default_expression , { "as" , default_expression } ;
+default_expression = patch_expression , [ "default" , default_expression ] ;
+patch_expression   = compose_expression , { "//" , compose_expression } ;
+compose_expression = logical_or_expression , { "&" , logical_or_expression } ;
+
+logical_or_expression  = logical_and_expression , { "||" , logical_and_expression } ;
+logical_and_expression = comparison_expression , { "&&" , comparison_expression } ;
+comparison_expression  = concat_expression , [ comparison_operator , concat_expression ] ;
+concat_expression      = additive_expression , { "++" , additive_expression } ;
+additive_expression    = multiplicative_expression , { ( "+" | "-" ) , multiplicative_expression } ;
+multiplicative_expression = unary_expression , { ( "*" | "/" ) , unary_expression } ;
+
+unary_expression   = [ "!" | "-" ] , postfix_expression ;
+postfix_expression = primary_expression , { call_suffix | path_suffix } ;
+call_suffix        = "(" , [ argument_list ] , ")" ;
+path_suffix        = "." , identifier ;
+
+primary_expression = literal
+                   | identifier
+                   | comparison_constraint
+                   | map_constraint
+                   | object
+                   | array_constraint
+                   | array
+                   | let_expression
+                   | function_expression
+                   | match_expression
+                   | import_expression
+                   | "(" , expression , ")" ;
+
+literal            = string | integer | float | "true" | "false" | regex ;
+comparison_operator = "==" | "!=" | "<" | "<=" | ">" | ">=" ;
+comparison_constraint = ( "<" | "<=" | ">" | ">=" ) , expression ;
+
+object             = "{" , [ field_definition , { ";" , field_definition }
+                       , [ ";" , object_rest ] , [ ";" ] ] , "}" ;
+object_rest        = "..." , expression ;
+map_constraint     = "{" , "..." , expression , "}" ;
+field_definition   = field_path , "=" , expression ;
+field_path         = identifier , { "." , identifier } ;
+
+array              = "[" , [ expression , { "," , expression } , [ "," ] ] , "]" ;
+array_constraint   = "[" , "..." , expression , [ "," ] , "]" ;
+
+let_expression     = "let" , { field_definition , ";" } , "in" , expression ;
+function_expression = "(" , [ parameter_list ] , ")" , "=>" , expression ;
+parameter_list     = parameter , { "," , parameter } , [ "," ] ;
+parameter          = identifier , [ ":" , expression ] ;
+
+match_expression   = "match" , expression , "{" , [ match_arm , { ";" , match_arm } , [ ";" ] ] , "}" ;
+match_arm          = pattern , ":" , expression ;
+pattern            = "_" | expression ;
+
+import_expression  = "import" , string ;
+argument_list      = expression , { "," , expression } , [ "," ] ;
+```
+
+## Precedence
+
+Precedence is highest first.
+
+1. function call and field path reference
+2. unary `!` and `-`
+3. `*` and `/`
+4. `+` and `-`
+5. `++`
+6. `==`, `!=`, `<`, `<=`, `>`, `>=`
+7. `&&`
+8. `||`
+9. `&`
+10. `//`
+11. `default`
+12. `as`
+
+Binary operators are left-associative except `default`, which is right-associative.
+
+## Tooling mapping
+
+Syntax tooling should derive token categories from this grammar rather than making a tool-specific grammar canonical.
+Tree-sitter and Lezer grammars are implementation artifacts that follow this page.
@@ -95,4 +95,5 @@ match value {
 通常の式はエラー内容に基づいて分岐できない。

 汎用 `try / catch` は core には含めない。
-fallback は `default`、`match`、および将来的な optional import / optional field access のような限定された仕組みで表現する。
+fallback は `default` と `match` で表現する。
+optional import や optional field access は core には含めない。
@@ -29,17 +29,80 @@ result = schema;
 ```

 この場合、`result` の右辺の `schema` は同じ module の top-level field `schema` を参照する。
-通常の object literal 内の field を暗黙に recursive scope にするかは別仕様とする。
+通常の object literal 内の field は、その object 内の sibling field を暗黙には識別子として参照できない。
+object 内の値を参照する場合は、外側で束縛された値や明示的な path reference を使う。

-## SourceLoader
+## ImportLoader

-`import` specifier の解決は処理系 core ではなく host 側の `SourceLoader` が行う。
+`import` specifier の解決は処理系 core ではなく host 側の `ImportLoader` が行う。
 CLI では、specifier を現在の module path からの相対 path として解決する。
 組み込み利用では、resource table や static source map など、filesystem 以外の loader を使える。

 module cache の key は loader が返す安定 key を使う。
 CLI では canonical path を key とする。

+### 構造化 import
+
+`ImportLoader::load` は DCDL source または host が構築した `Value` を import 結果として返す。
+Markdown、JSON、TOML などの解釈規則は core に固定せず、loader がファイル種別を判定して構造化する。
+
+```rust
+use decodal::{Value, ImportLoader, LoadedImport};
+
+struct ContentLoader;
+
+impl ImportLoader for ContentLoader {
+    fn load(
+        &mut self,
+        current_key: Option<&str>,
+        specifier: &str,
+    ) -> decodal::Result<LoadedImport> {
+        if specifier.ends_with(".md") {
+            let markdown = read_content(current_key, specifier)?;
+            let parsed = parse_frontmatter(&markdown)?;
+            return Ok(LoadedImport::value(
+                parsed.key,
+                Value::object([
+                    ("frontmatter", parsed.frontmatter),
+                    ("body", Value::string(parsed.body)),
+                ]),
+            ));
+        }
+
+        let source = read_dcdl(current_key, specifier)?;
+        Ok(LoadedImport::source(
+            source.key,
+            specifier,
+            source.text,
+        ))
+    }
+}
+```
+
+`read_content` と `parse_frontmatter` は host 独自の処理であり、Decodal core は Markdown や YAML parser に依存しない。
+上の loader を使うと、DCDL 側から次のように扱える。
+
+```dcdl
+Post = {
+    frontmatter = {
+        title = String;
+        draft = Bool default false;
+    };
+    body = String;
+};
+
+post = Post & import "./hello.md";
+title = post.frontmatter.title;
+body = post.body;
+```
+
+`LoadedImport::Value` は通常の concrete runtime value に internalize される。
+そのため、path reference、object composition、constraint validation、materialize は source 由来の値と同じ規則を使う。
+安定した `key` が同じ構造化 import は、engine 内で同じ値としてキャッシュされる。
+
+`load` が唯一の import hook である。
+loader は拡張子、media type、または host 独自の規則で振り分け、対応する `LoadedImport` variant を直接返す。
+
 ## 循環 import

 モジュール間に循環参照があっても、必要なフィールドの依存関係が循環していなければ評価できる。
@@ -92,4 +155,5 @@ Module func
 - ファイルが読めない。
 - import 先の構文解析に失敗する。
 - import 先の評価で必要な値がエラーになる。
+- host による非 DCDL content の読み込みまたは構造化に失敗する。
 - 実装が禁止する import 循環に該当する。
@@ -1,6 +1,81 @@
-# 合成演算子
+# 演算子

-この章では、`&` と `//` の意味を定義する。
+この章では、Decodal の演算子の意味を定義する。
+
+## 演算子一覧
+
+| 演算子 | 形 | 種類 | 対象 | 結果 / 意味 |
+|---|---|---|---|---|
+| `.` | `object.field` | field reference | object / abstract object | field value |
+| call | `fn(arg)` | function call | function | function result |
+| `!` | `!expr` | unary logical | concrete `Bool` | concrete `Bool` |
+| `-` | `-expr` | unary arithmetic | concrete `Int` / `Float` | negated number |
+| `*` | `lhs * rhs` | arithmetic | concrete `Int` / `Float` | numeric product |
+| `/` | `lhs / rhs` | arithmetic | concrete `Int` / `Float` | `Float` quotient |
+| `+` | `lhs + rhs` | arithmetic | concrete `Int` / `Float` | numeric sum |
+| `-` | `lhs - rhs` | arithmetic | concrete `Int` / `Float` | numeric difference |
+| `++` | `lhs ++ rhs` | array concat | concrete arrays | concatenated array |
+| `==` | `lhs == rhs` | equality | concrete scalar | concrete `Bool` |
+| `!=` | `lhs != rhs` | equality | concrete scalar | concrete `Bool` |
+| `<` | `lhs < rhs` | ordering | concrete `Int` / `Float` | concrete `Bool` |
+| `<=` | `lhs <= rhs` | ordering | concrete `Int` / `Float` | concrete `Bool` |
+| `>` | `lhs > rhs` | ordering | concrete `Int` / `Float` | concrete `Bool` |
+| `>=` | `lhs >= rhs` | ordering | concrete `Int` / `Float` | concrete `Bool` |
+| `>` | `> value` | comparison constraint | numeric constraint value | abstract constraint |
+| `>=` | `>= value` | comparison constraint | numeric constraint value | abstract constraint |
+| `<` | `< value` | comparison constraint | numeric constraint value | abstract constraint |
+| `<=` | `<= value` | comparison constraint | numeric constraint value | abstract constraint |
+| `&&` | `lhs && rhs` | logical | concrete `Bool` | short-circuit AND |
+| `||` | `lhs || rhs` | logical | concrete `Bool` | short-circuit OR |
+| `&` | `lhs & rhs` | composition | value / constraint / object | constraint-preserving composition |
+| `//` | `lhs // rhs` | patch | object / value | right-biased structural patch |
+| `default` | `base default fallback` | default | abstract value | materialization fallback |
+| `as` | `narrower as wider` | range refinement | value / constraint / structure | narrower result plus untouched right-only ranges |
+
+`concrete scalar` は `String`、`Bool`、`Int`、`Float` を指す。
+
+## 優先順位
+
+優先順位は高い順に以下である。
+
+1. 関数呼び出しとフィールド参照
+2. unary `!` `-`
+3. `*` `/`
+4. `+` `-`
+5. `++`
+6. `==` `!=` `<` `<=` `>` `>=`
+7. `&&`
+8. `||`
+9. `&`
+10. `//`
+11. `default`
+12. `as`
+
+同じ優先順位の二項演算子は左結合である。
+`default` は右結合である。
+
+## Arithmetic operators
+
+`+` `-` `*` `/` は具体的な `Int` / `Float` に対する四則演算である。
+詳しくは [Arithmetic Expression](./expression/arithmetic.md) を参照する。
+
+## Array concat operator
+
+`++` は concrete array 同士を連結する演算子である。
+要素は変換されず、左辺の要素の後に右辺の要素が並ぶ。
+
+```dcdl
+["read", "write"] ++ ["admin"]
+```
+
+## Logical and comparison operators
+
+`!` `&&` `||` は concrete `Bool` に対する論理演算である。
+`&&` と `||` は短絡評価される。
+
+`==` `!=` は concrete scalar value を比較する。
+`<` `<=` `>` `>=` は concrete numeric value を比較する。
+詳しくは [Logical and Comparison Expressions](./expression/logical-and-comparison.md) を参照する。

 ## `&`: 制約合成

@@ -18,6 +93,7 @@ A & B
 - 両方が異なる具体値なら conflict になる。
 - 両方が object なら、フィールドごとに合成する。
 - 同じフィールドが両方にある場合、そのフィールド値を `&` で合成する。
+- 片方にしかないフィールドは、そのまま結果に保持する。
 - 矛盾が発生した場合はエラーになる。

 例:
@@ -110,26 +186,49 @@ Patched = Base // {

 ## object 全体の置換

-`//` が deep patch である場合、object 全体を置き換えたいときの escape hatch が必要になる。
+`//` では object/object は常に deep patch される。
+object field 全体を特別に置き換えるための `replace(...)` 構文や組み込み関数は core には含めない。

-候補として、`replace(...)` を組み込み関数として提供する。
+object 全体を別構造にしたい場合は、patch 対象より外側で値を作り直す。
+
+## `as`: range refinement
+
+`as` は左辺が右辺より具体的で狭い範囲であることを確認する、非対称な絞り込み演算子である。

 ```dcdl
-Replaced = Base // {
-    feature_hoge = replace({
-        enable = false;
-    });
+Refined = {
+    port = 8000;
+} as {
+    port = Int & >= 1 & <= 65535;
+    host = String;
+    enabled = Bool default true;
 };
 ```

-この場合、`feature_hoge` は再帰 patch されず、右辺の object に丸ごと置き換わる。
+`port` は左辺の `8000` に具体化される。
+右辺にしかない `host` と `enabled` は abstract のまま結果へ残る。default の有無は、右辺だけの field を保持するかどうかに影響しない。
+`as` 自体は default を選択せず、後から結果を materialize した場合だけ通常の default 規則が働く。

-## `&` と `//` の使い分け
+左辺にしかない object field は右辺の field domain 外なのでエラーになる。
+両側にある nested object、array constraint、map constraint は同じ規則で再帰的に絞り込む。

-`&` は制約を満たす具体化に使う。
+abstract range 同士も包含を確認できる。

 ```dcdl
-ValidConfig = MyConfig & {
+Int & > 10 as Int & > 0 # 成功し、Int & > 10 を返す
+Int as Int & > 0        # 失敗
+```
+
+`&` は対称な合成であり、片方だけにある object field を保持する。
+したがって、左右に方向を持つ絞り込みを `&` で代用しない。
+詳細は [Range Refinement](./expression/ascription.md) を参照する。
+
+## `&`、`//`、`as` の使い分け
+
+`&` は制約や部分構造を失わず、対称に合成する。
+
+```dcdl
+Combined = MyConfig & {
    port = 8000;
 };
 ```
@@ -144,3 +243,9 @@ ModifiedSchema = MyConfig // {

 `//` は右辺優先の patch であり、左辺の制約を常に保持するとは限らない。
 制約を保持したい場合は `&` を使う。
+
+左辺が右辺より狭いことを検証しながら合成する場合は `as` を使う。
+
+```dcdl
+RefinedConfig = NarrowConfig as WideConfig;
+```
@@ -1,7 +1,7 @@
 # 構文と字句

 この章では、表層構文の方針をまとめる。
-厳密な EBNF は未確定であり、今後このファイルに詳細化する。
+厳密な構文は [Grammar](./grammar.md) の EBNF を参照する。

 ## 言語名と拡張子

@@ -93,9 +93,9 @@ config.feature_hoge.enable
 }
 ```

-## 予約語候補
+## 予約語

-以下は予約語または予約構文として扱う候補である。
+以下は予約語として扱う。

 ```text
 let
@@ -103,24 +103,27 @@ in
 match
 import
 default
+as
 true
 false
-rec
 ```

-`rec` の扱いは未確定である。
-
 ## 演算子

 主要な演算子は以下である。

 ```text
-&       制約合成
-//      patch 合成
-default fallback 指定
-=>      関数
-.       フィールド参照 / ドットパス定義
+ - * /       四則演算
++            配列結合
+! && ||       論理演算
+== != < <= > >= 比較式
+&             制約合成
+//            patch 合成
+default       fallback 指定
+as            左辺から右辺への範囲包含確認と絞り込み
+=>            関数
+.             フィールド参照 / ドットパス定義
+...           配列または連想配列の値制約
 ```

-演算子の優先順位は未確定である。
-詳細は [合成演算子](./operators.md) で定義する。
+演算子の優先順位は [合成演算子](./operators.md) で定義する。
@@ -9,7 +9,10 @@ ratio = Float;
 threshold = Float default 0.5;
 ```

-## 未確定事項
+## Int との関係

-`Int` と `Float` の暗黙変換を許可するかは未確定である。
-軽量実装では、両者を明確に分ける方が単純である。
+`Int` と `Float` は primitive type constraint としては別の型である。
+`Float` constraint は concrete `Float` を要求し、`Int` constraint は concrete `Int` を要求する。
+
+数値演算や比較式では `Int` と `Float` を同じ numeric value として扱える。
+混在した四則演算の結果は `Float` になる。
@@ -9,9 +9,12 @@ name = String;
 retry = Int default 3;
 ratio = Float;
 enable = Bool default true;
+tags = [...String];
 ```

 現在の primitive type は `String`、`Int`、`Float`、`Bool` である。
+`Unknown` はprimitive typeではなく、すべてのDecodal値を含む最上位の抽象rangeである。具体値またはdefaultがない `Unknown` はmaterializeできない。
+配列は primitive type ではなく、必須の要素制約を持つ `[...T]` で表現する。
 各型の個別仕様へのリンクは [Manual Index](../../index.md) に集約する。

 primitive type と制約合成の詳細は [制約と default](../constraints-and-defaults.md) も参照する。
@@ -17,4 +17,5 @@ greeting = String default "hello";
 message = String & /Hello! .*/;
 ```

-正規表現制約を必須機能にするかは未確定である。
+正規表現制約の検証は Rust crate の `regex` feature で有効化される。
+feature が無効な場合、正規表現制約は具体 string に対して検証できず diagnostic になる。
@@ -1,60 +1,23 @@
 # 未確定事項

 今後決める必要がある事項を管理する。
-詳細化するときは、各項目を該当する仕様ファイルへ移動または反映する。
+実装または仕様方針が固まった項目は、該当する仕様ファイルへ反映してここから外す。

-## 構文
+## Materialize target and host projection

- 正式な字句・構文仕様。
- 演算子の優先順位。
- `rec` の扱い。
- コメント構文を `#` のみにするか。
+Decodal の評価結果は、制約・default・関数値を含む中間値になり得る。
+そのため、Decodal 単独で常に「最終成果物」を一意に決めるのではなく、host 側が期待する型や出力形式を与えて materialize / decode する経路を明確にする必要がある。

-## 型・制約
+決めること:

- 配列要素の制約表現。
- object の open/closed schema の扱い。
- 正規表現を必須機能にするか optional feature にするか。
- 代表的な組み込み述語の範囲。
+- Rust API で評価結果の field/path を選択して decode / materialize できるようにするか。
+- `decodal-derive` の struct schema と評価結果を合成して decode する経路を、主要な materialize path として位置づけるか。
+- CLI / WASM では target path を指定して JSON-compatible value へ materialize する形にするか。
+- 制約や関数値が残った値を出力したい場合、materialize ではなく inspect/debug API として分けるか。

-## default
+現時点の案:

- `default` 同士の conflict 解決規則。
- `&` による default 合成の厳密な規則。
- `//` による default 置換の厳密な規則。
- default thunk の評価失敗をどの段階で報告するか。
-
-## 演算子
-
- `//` による制約・default の置換詳細。
- `replace(...)` を採用するか、別構文を設けるか。
- 配列に対する patch 操作を右辺置換だけにするか。
- 配列 append / prepend / remove などを提供するか。
-
-## 関数
-
- 関数値の最終出力可否。
- 再帰関数を許可するか。
- 関数同士の `&` の扱い。
- 関数値の等価性。
- 関数呼び出し結果の memoize 範囲。
-
-## 評価
-
- thunk のエラー memoize 方針。
- import cache の単位。
- 循環 import の診断メッセージ。
- materialize 対象の範囲指定方法。
-
-## match
-
- match の網羅性チェックを行うか。
- 到達不能分岐を警告するか。
- パターン構文の範囲。
-
-## エラー処理
-
- optional import を導入するか。
- optional field access を導入するか。
- optional fallback が捕捉できる失敗の範囲。
- エラー報告に制約由来の説明をどこまで含めるか。
+- Rust では `evaluate -> select field/path -> expected schema と合成 -> decode` を主経路にする。
+- CLI / WASM では、明示された target path または module 全体を JSON-compatible value として materialize する。
+- materialize できない unresolved abstract value、default のない制約値、関数値は diagnostic にする。
+- Decodal 言語内には materialize 構文を追加せず、host API / CLI / WASM の責務として扱う。
@@ -0,0 +1,18 @@
+# lezer-decodal
+
+Lezer implementation of the Decodal grammar for CodeMirror 6.
+
+The canonical grammar is documented in:
+
+```text
+../../doc/manual/souce/language/grammar.md
+```
+
+Regenerate the CodeMirror parser from the site directory:
+
+```sh
+cd ../../site/decodal-site
+npx lezer-generator ../../editors/lezer-decodal/decodal.grammar -o ../../packages/decodal-codemirror/src/decodal-parser.js
+```
+
+The generated parser is committed with the `decodal-codemirror` package because both the playground and external Web editors consume it.
@@ -0,0 +1,190 @@
+@top Source { Statement* }
+
+Statement {
+  FieldDefinition Semicolon? |
+  Expression Semicolon?
+}
+
+Expression { AsExpression }
+
+AsExpression {
+  DefaultExpression |
+  AsExpression !as As DefaultExpression
+}
+
+DefaultExpression {
+  PatchExpression |
+  PatchExpression !default Default DefaultExpression
+}
+
+PatchExpression {
+  ComposeExpression |
+  PatchExpression !patch SlashSlash ComposeExpression
+}
+
+ComposeExpression {
+  LogicalOrExpression |
+  ComposeExpression !compose Amp LogicalOrExpression
+}
+
+LogicalOrExpression {
+  LogicalAndExpression |
+  LogicalOrExpression !or PipePipe LogicalAndExpression
+}
+
+LogicalAndExpression {
+  ComparisonExpression |
+  LogicalAndExpression !and AmpAmp ComparisonExpression
+}
+
+ComparisonExpression {
+  ConcatExpression |
+  ConcatExpression !compare CompareOperator ConcatExpression
+}
+
+ConcatExpression {
+  AdditiveExpression |
+  ConcatExpression !concat PlusPlus AdditiveExpression
+}
+
+AdditiveExpression {
+  MultiplicativeExpression |
+  AdditiveExpression !add (Plus | Minus) MultiplicativeExpression
+}
+
+MultiplicativeExpression {
+  UnaryExpression |
+  MultiplicativeExpression !multiply (Star | Slash) UnaryExpression
+}
+
+UnaryExpression {
+  PostfixExpression |
+  (Bang | Minus) !unary UnaryExpression
+}
+
+PostfixExpression {
+  PrimaryExpression |
+  PostfixExpression !call CallSuffix |
+  PostfixExpression !path Dot Identifier
+}
+
+CallSuffix { LParen ArgumentList? RParen }
+ArgumentList { Expression (Comma Expression)* Comma? }
+
+PrimaryExpression {
+  Literal |
+  Identifier |
+  ComparisonConstraint |
+  MapConstraint |
+  Object |
+  ArrayConstraint |
+  Array |
+  LetExpression |
+  FunctionExpression |
+  MatchExpression |
+  ImportExpression |
+  LParen Expression RParen
+}
+
+Literal { String | Integer | Float | True | False | Regex }
+CompareOperator { EqualEqual | BangEqual | Lt | Lte | Gt | Gte }
+ComparisonConstraint { (Lt | Lte | Gt | Gte) Expression }
+
+Object {
+  LBrace
+  (FieldDefinition (Semicolon FieldDefinition)* (Semicolon ObjectRest)? Semicolon?)?
+  RBrace
+}
+ObjectRest { Ellipsis Expression }
+MapConstraint { LBrace Ellipsis Expression RBrace }
+FieldDefinition { FieldPath Equal Expression }
+FieldPath { Identifier !fieldPath (Dot Identifier)* }
+
+Array { LBracket (Expression (Comma Expression)* Comma?)? RBracket }
+ArrayConstraint { LBracket Ellipsis Expression Comma? RBracket }
+
+LetExpression { Let FieldDefinitionList In Expression }
+FieldDefinitionList { (FieldDefinition Semicolon)* }
+
+FunctionExpression { LParen ParameterList? RParen Arrow Expression }
+ParameterList { Parameter (Comma Parameter)* Comma? }
+Parameter { Identifier Colon Expression }
+
+MatchExpression { Match Expression LBrace (MatchArm (Semicolon MatchArm)* Semicolon?)? RBrace }
+MatchArm { Pattern Colon Expression }
+Pattern { Underscore | Expression }
+
+ImportExpression { Import String }
+
+As { @specialize<Identifier, "as"> }
+
+@precedence {
+  fieldPath @left,
+  as @left,
+  default @right,
+  patch @left,
+  compose @left,
+  or @left,
+  and @left,
+  compare @left,
+  concat @left,
+  add @left,
+  multiply @left,
+  unary,
+  call @left,
+  path @left
+}
+
+@tokens {
+  Let { "let" }
+  In { "in" }
+  Match { "match" }
+  Import { "import" }
+  Default { "default" }
+  True { "true" }
+  False { "false" }
+
+  Identifier { $[A-Za-z_] $[A-Za-z0-9_]* }
+  Integer { $[0-9]+ }
+  Float { $[0-9]+ "." $[0-9]+ }
+  String { '"' (!["\\\n] | "\\" _)* '"' }
+  Regex { "/" (![/\\\n] | "\\" _)+ "/" }
+  Comment { "#" ![\n]* }
+
+  LBrace { "{" }
+  RBrace { "}" }
+  LBracket { "[" }
+  RBracket { "]" }
+  LParen { "(" }
+  RParen { ")" }
+  Semicolon { ";" }
+  Comma { "," }
+  Dot { "." }
+  Ellipsis { "..." }
+  Colon { ":" }
+  Equal { "=" }
+  EqualEqual { "==" }
+  Bang { "!" }
+  BangEqual { "!=" }
+  Arrow { "=>" }
+  Amp { "&" }
+  AmpAmp { "&&" }
+  PipePipe { "||" }
+  Plus { "+" }
+  PlusPlus { "++" }
+  Minus { "-" }
+  Star { "*" }
+  Slash { "/" }
+  SlashSlash { "//" }
+  Gt { ">" }
+  Gte { ">=" }
+  Lt { "<" }
+  Lte { "<=" }
+  Underscore { "_" }
+
+  whitespace { @whitespace+ }
+
+  @precedence { Let, In, Match, Import, Default, True, False, Float, Integer, Underscore, Identifier }
+}
+
+@skip { whitespace | Comment }
@@ -6,7 +6,7 @@ license = "MIT"
 readme = "README.md"
 keywords = ["incremental", "parsing", "tree-sitter", "decodal"]
 categories = ["parsing", "text-editors"]
-repository = "https://github.com/tree-sitter/tree-sitter-decodal"
+repository = "https://gitea.hareworks.net/Hare/Decodal"
 edition = "2021"
 autoexamples = false

@@ -17,7 +17,7 @@ include = ["bindings/rust/*", "grammar.js", "queries/*", "src/*"]
 path = "bindings/rust/lib.rs"

 [dependencies]
-tree-sitter = ">=0.22.6"
+tree-sitter = "0.22.6"

 [build-dependencies]
 cc = "1.0.87"
@@ -0,0 +1,12 @@
+# tree-sitter-decodal
+
+Tree-sitter implementation of the Decodal grammar.
+
+The canonical grammar is documented in:
+
+```text
+../../doc/manual/souce/language/grammar.md
+```
+
+This grammar is an editor/tooling implementation of that EBNF reference.
+Generated parser files under `src/` are committed.
@@ -74,3 +74,165 @@ base // {
            body: (literal (string)))
          (match_arm
            body: (literal (string))))))))
+
+==================
+Arithmetic
+==================
+{
+  value = 1 + 2 * 3;
+  grouped = (1 + 2) / -3;
+}
+---
+
+(source_file
+  (object
+    (field_definition
+      path: (field_path (identifier))
+      value: (binary_expression
+        left: (literal (integer))
+        right: (binary_expression
+          left: (literal (integer))
+          right: (literal (integer)))))
+    (field_definition
+      path: (field_path (identifier))
+      value: (binary_expression
+        left: (parenthesized_expression
+          (binary_expression
+            left: (literal (integer))
+            right: (literal (integer))))
+        right: (unary_expression
+          operand: (literal (integer)))))))
+
+==================
+Logical and comparison
+==================
+{
+  enabled = env == "prod" && replicas > 1;
+  disabled = !enabled || false;
+}
+---
+
+(source_file
+  (object
+    (field_definition
+      path: (field_path (identifier))
+      value: (binary_expression
+        left: (binary_expression
+          left: (identifier)
+          right: (literal (string)))
+        right: (binary_expression
+          left: (identifier)
+          right: (literal (integer)))))
+    (field_definition
+      path: (field_path (identifier))
+      value: (binary_expression
+        left: (unary_expression
+          operand: (identifier))
+        right: (literal (boolean))))))
+
+==================
+Array concat
+==================
+{
+  roles = ["read"] ++ ["write", "admin"];
+  ports = [8000 + 80] ++ [9443];
+}
+---
+
+(source_file
+  (object
+    (field_definition
+      path: (field_path (identifier))
+      value: (binary_expression
+        left: (array
+          (literal (string)))
+        right: (array
+          (literal (string))
+          (literal (string)))))
+    (field_definition
+      path: (field_path (identifier))
+      value: (binary_expression
+        left: (array
+          (binary_expression
+            left: (literal (integer))
+            right: (literal (integer))))
+        right: (array
+          (literal (integer)))))))
+
+==================
+Array constraints
+==================
+{
+  tags = [...String];
+  ports = [...(Int & >= 1),];
+}
+---
+
+(source_file
+  (object
+    (field_definition
+      path: (field_path (identifier))
+      value: (array_constraint
+        element: (identifier)))
+    (field_definition
+      path: (field_path (identifier))
+      value: (array_constraint
+        element: (parenthesized_expression
+          (binary_expression
+            left: (identifier)
+            right: (comparison_constraint
+              value: (integer))))))))
+
+==================
+Map constraint and ascription
+==================
+{
+  services = {
+    api = { port = 8080; };
+  } as {...{ port = Int; }};
+}
+---
+
+(source_file
+  (object
+    (field_definition
+      path: (field_path (identifier))
+      value: (as_expression
+        narrower: (object
+          (field_definition
+            path: (field_path (identifier))
+            value: (object
+              (field_definition
+                path: (field_path (identifier))
+                value: (literal (integer))))))
+        wider: (map_constraint
+          value: (object
+            (field_definition
+              path: (field_path (identifier))
+              value: (identifier))))))))
+
+==================
+Unknown object rest constraint
+==================
+{
+  value = {
+    hoge = Int;
+    fuga = String;
+    ...Unknown
+  };
+}
+---
+
+(source_file
+  (object
+    (field_definition
+      path: (field_path (identifier))
+      value: (object
+        (field_definition
+          path: (field_path (identifier))
+          value: (identifier))
+        (field_definition
+          path: (field_path (identifier))
+          value: (identifier))
+        (object_rest
+          value: (identifier))))))
@@ -1,9 +1,20 @@
+// Tree-sitter implementation of the canonical EBNF grammar in
+// doc/manual/souce/language/grammar.md.
+
 const PREC = {
+  AS: 0,
  DEFAULT: 1,
  PATCH: 2,
-  AND: 3,
-  CALL: 7,
-  PATH: 8,
+  COMPOSE: 3,
+  OR: 4,
+  LOGICAL_AND: 5,
+  COMPARE: 6,
+  CONCAT: 7,
+  ADD: 8,
+  MUL: 9,
+  UNARY: 10,
+  CALL: 11,
+  PATH: 12,
 };

 function commaSep(rule) {
@@ -43,7 +54,9 @@ module.exports = grammar({
      $.identifier,
      $.regex_literal,
      $.comparison_constraint,
+      $.map_constraint,
      $.object,
+      $.array_constraint,
      $.array,
      $.let_expression,
      $.function_expression,
@@ -52,8 +65,10 @@ module.exports = grammar({
      $.parenthesized_expression,
      $.call_expression,
      $.path_expression,
+      $.unary_expression,
      $.binary_expression,
      $.default_expression,
+      $.as_expression,
    ),

    literal: $ => choice(
@@ -84,7 +99,24 @@ module.exports = grammar({

    object: $ => seq(
      '{',
-      semiSep($.field_definition),
+      optional(seq(
+        $.field_definition,
+        repeat(seq(';', $.field_definition)),
+        optional(seq(';', $.object_rest)),
+        optional(';'),
+      )),
+      '}',
+    ),
+
+    object_rest: $ => seq(
+      '...',
+      field('value', $._expression),
+    ),
+
+    map_constraint: $ => seq(
+      '{',
+      '...',
+      field('value', $._expression),
      '}',
    ),

@@ -105,12 +137,20 @@ module.exports = grammar({
      ']',
    ),

-    let_expression: $ => seq(
+    array_constraint: $ => seq(
+      '[',
+      '...',
+      field('element', $._expression),
+      optional(','),
+      ']',
+    ),
+
+    let_expression: $ => prec.right(seq(
      'let',
      repeat(seq($.field_definition, ';')),
      'in',
      field('body', $._expression),
-    ),
+    )),

    function_expression: $ => prec.right(seq(
      '(',
@@ -159,13 +199,48 @@ module.exports = grammar({
      field('field', $.identifier),
    )),

-    comparison_constraint: $ => prec(6, seq(
+    comparison_constraint: $ => prec.right(PREC.UNARY + 1, seq(
      field('operator', choice('>', '>=', '<', '<=')),
-      field('value', choice($.integer, $.float)),
+      field('value', $._expression),
+    )),
+
+    unary_expression: $ => prec(PREC.UNARY, seq(
+      field('operator', choice('-', '!')),
+      field('operand', $._expression),
    )),

    binary_expression: $ => choice(
-      prec.left(PREC.AND, seq(
+      prec.left(PREC.OR, seq(
+        field('left', $._expression),
+        field('operator', token(prec(2, '||'))),
+        field('right', $._expression),
+      )),
+      prec.left(PREC.LOGICAL_AND, seq(
+        field('left', $._expression),
+        field('operator', token(prec(2, '&&'))),
+        field('right', $._expression),
+      )),
+      prec.left(PREC.COMPARE, seq(
+        field('left', $._expression),
+        field('operator', choice('==', '!=', '>', '>=', '<', '<=')),
+        field('right', $._expression),
+      )),
+      prec.left(PREC.CONCAT, seq(
+        field('left', $._expression),
+        field('operator', token(prec(2, '++'))),
+        field('right', $._expression),
+      )),
+      prec.left(PREC.ADD, seq(
+        field('left', $._expression),
+        field('operator', choice('+', '-')),
+        field('right', $._expression),
+      )),
+      prec.left(PREC.MUL, seq(
+        field('left', $._expression),
+        field('operator', choice('*', '/')),
+        field('right', $._expression),
+      )),
+      prec.left(PREC.COMPOSE, seq(
        field('left', $._expression),
        field('operator', '&'),
        field('right', $._expression),
@@ -182,5 +257,11 @@ module.exports = grammar({
      'default',
      field('fallback', $._expression),
    )),
+
+    as_expression: $ => prec.left(PREC.AS, seq(
+      field('narrower', $._expression),
+      'as',
+      field('wider', $._expression),
+    )),
  },
 });
@@ -12,11 +12,23 @@
  "match"
  "import"
  "default"
+  "as"
 ] @keyword

 [
  "&"
  "//"
+  "+"
+  "-"
+  "*"
+  "/"
+  "++"
+  "..."
+  "&&"
+  "||"
+  "!"
+  "=="
+  "!="
  "=>"
  "="
  ">"
@@ -42,7 +54,7 @@
 ] @punctuation.delimiter

 ((identifier) @type.builtin
- (#match? @type.builtin "^(String|Int|Float|Bool)$"))
+ (#match? @type.builtin "^(String|Int|Float|Bool|Unknown)$"))

 (field_definition
  path: (field_path (identifier) @property))
@@ -91,10 +91,18 @@
          "type": "SYMBOL",
          "name": "comparison_constraint"
        },
+        {
+          "type": "SYMBOL",
+          "name": "map_constraint"
+        },
        {
          "type": "SYMBOL",
          "name": "object"
        },
+        {
+          "type": "SYMBOL",
+          "name": "array_constraint"
+        },
        {
          "type": "SYMBOL",
          "name": "array"
@@ -127,6 +135,10 @@
          "type": "SYMBOL",
          "name": "path_expression"
        },
+        {
+          "type": "SYMBOL",
+          "name": "unary_expression"
+        },
        {
          "type": "SYMBOL",
          "name": "binary_expression"
@@ -134,6 +146,10 @@
        {
          "type": "SYMBOL",
          "name": "default_expression"
+        },
+        {
+          "type": "SYMBOL",
+          "name": "as_expression"
        }
      ]
    },
@@ -286,6 +302,27 @@
                    ]
                  }
                },
+                {
+                  "type": "CHOICE",
+                  "members": [
+                    {
+                      "type": "SEQ",
+                      "members": [
+                        {
+                          "type": "STRING",
+                          "value": ";"
+                        },
+                        {
+                          "type": "SYMBOL",
+                          "name": "object_rest"
+                        }
+                      ]
+                    },
+                    {
+                      "type": "BLANK"
+                    }
+                  ]
+                },
                {
                  "type": "CHOICE",
                  "members": [
@@ -311,6 +348,48 @@
        }
      ]
    },
+    "object_rest": {
+      "type": "SEQ",
+      "members": [
+        {
+          "type": "STRING",
+          "value": "..."
+        },
+        {
+          "type": "FIELD",
+          "name": "value",
+          "content": {
+            "type": "SYMBOL",
+            "name": "_expression"
+          }
+        }
+      ]
+    },
+    "map_constraint": {
+      "type": "SEQ",
+      "members": [
+        {
+          "type": "STRING",
+          "value": "{"
+        },
+        {
+          "type": "STRING",
+          "value": "..."
+        },
+        {
+          "type": "FIELD",
+          "name": "value",
+          "content": {
+            "type": "SYMBOL",
+            "name": "_expression"
+          }
+        },
+        {
+          "type": "STRING",
+          "value": "}"
+        }
+      ]
+    },
    "field_definition": {
      "type": "SEQ",
      "members": [
@@ -423,43 +502,84 @@
        }
      ]
    },
-    "let_expression": {
+    "array_constraint": {
      "type": "SEQ",
      "members": [
        {
          "type": "STRING",
-          "value": "let"
-        },
-        {
-          "type": "REPEAT",
-          "content": {
-            "type": "SEQ",
-            "members": [
-              {
-                "type": "SYMBOL",
-                "name": "field_definition"
-              },
-              {
-                "type": "STRING",
-                "value": ";"
-              }
-            ]
-          }
+          "value": "["
        },
        {
          "type": "STRING",
-          "value": "in"
+          "value": "..."
        },
        {
          "type": "FIELD",
-          "name": "body",
+          "name": "element",
          "content": {
            "type": "SYMBOL",
            "name": "_expression"
          }
+        },
+        {
+          "type": "CHOICE",
+          "members": [
+            {
+              "type": "STRING",
+              "value": ","
+            },
+            {
+              "type": "BLANK"
+            }
+          ]
+        },
+        {
+          "type": "STRING",
+          "value": "]"
        }
      ]
    },
+    "let_expression": {
+      "type": "PREC_RIGHT",
+      "value": 0,
+      "content": {
+        "type": "SEQ",
+        "members": [
+          {
+            "type": "STRING",
+            "value": "let"
+          },
+          {
+            "type": "REPEAT",
+            "content": {
+              "type": "SEQ",
+              "members": [
+                {
+                  "type": "SYMBOL",
+                  "name": "field_definition"
+                },
+                {
+                  "type": "STRING",
+                  "value": ";"
+                }
+              ]
+            }
+          },
+          {
+            "type": "STRING",
+            "value": "in"
+          },
+          {
+            "type": "FIELD",
+            "name": "body",
+            "content": {
+              "type": "SYMBOL",
+              "name": "_expression"
+            }
+          }
+        ]
+      }
+    },
    "function_expression": {
      "type": "PREC_RIGHT",
      "value": 0,
@@ -712,7 +832,7 @@
    },
    "call_expression": {
      "type": "PREC_LEFT",
-      "value": 7,
+      "value": 11,
      "content": {
        "type": "SEQ",
        "members": [
@@ -782,7 +902,7 @@
    },
    "path_expression": {
      "type": "PREC_LEFT",
-      "value": 8,
+      "value": 12,
      "content": {
        "type": "SEQ",
        "members": [
@@ -810,8 +930,8 @@
      }
    },
    "comparison_constraint": {
-      "type": "PREC",
-      "value": 6,
+      "type": "PREC_RIGHT",
+      "value": 11,
      "content": {
        "type": "SEQ",
        "members": [
@@ -843,19 +963,44 @@
          {
            "type": "FIELD",
            "name": "value",
+            "content": {
+              "type": "SYMBOL",
+              "name": "_expression"
+            }
+          }
+        ]
+      }
+    },
+    "unary_expression": {
+      "type": "PREC",
+      "value": 10,
+      "content": {
+        "type": "SEQ",
+        "members": [
+          {
+            "type": "FIELD",
+            "name": "operator",
            "content": {
              "type": "CHOICE",
              "members": [
                {
-                  "type": "SYMBOL",
-                  "name": "integer"
+                  "type": "STRING",
+                  "value": "-"
                },
                {
-                  "type": "SYMBOL",
-                  "name": "float"
+                  "type": "STRING",
+                  "value": "!"
                }
              ]
            }
+          },
+          {
+            "type": "FIELD",
+            "name": "operand",
+            "content": {
+              "type": "SYMBOL",
+              "name": "_expression"
+            }
          }
        ]
      }
@@ -863,6 +1008,268 @@
    "binary_expression": {
      "type": "CHOICE",
      "members": [
+        {
+          "type": "PREC_LEFT",
+          "value": 4,
+          "content": {
+            "type": "SEQ",
+            "members": [
+              {
+                "type": "FIELD",
+                "name": "left",
+                "content": {
+                  "type": "SYMBOL",
+                  "name": "_expression"
+                }
+              },
+              {
+                "type": "FIELD",
+                "name": "operator",
+                "content": {
+                  "type": "TOKEN",
+                  "content": {
+                    "type": "PREC",
+                    "value": 2,
+                    "content": {
+                      "type": "STRING",
+                      "value": "||"
+                    }
+                  }
+                }
+              },
+              {
+                "type": "FIELD",
+                "name": "right",
+                "content": {
+                  "type": "SYMBOL",
+                  "name": "_expression"
+                }
+              }
+            ]
+          }
+        },
+        {
+          "type": "PREC_LEFT",
+          "value": 5,
+          "content": {
+            "type": "SEQ",
+            "members": [
+              {
+                "type": "FIELD",
+                "name": "left",
+                "content": {
+                  "type": "SYMBOL",
+                  "name": "_expression"
+                }
+              },
+              {
+                "type": "FIELD",
+                "name": "operator",
+                "content": {
+                  "type": "TOKEN",
+                  "content": {
+                    "type": "PREC",
+                    "value": 2,
+                    "content": {
+                      "type": "STRING",
+                      "value": "&&"
+                    }
+                  }
+                }
+              },
+              {
+                "type": "FIELD",
+                "name": "right",
+                "content": {
+                  "type": "SYMBOL",
+                  "name": "_expression"
+                }
+              }
+            ]
+          }
+        },
+        {
+          "type": "PREC_LEFT",
+          "value": 6,
+          "content": {
+            "type": "SEQ",
+            "members": [
+              {
+                "type": "FIELD",
+                "name": "left",
+                "content": {
+                  "type": "SYMBOL",
+                  "name": "_expression"
+                }
+              },
+              {
+                "type": "FIELD",
+                "name": "operator",
+                "content": {
+                  "type": "CHOICE",
+                  "members": [
+                    {
+                      "type": "STRING",
+                      "value": "=="
+                    },
+                    {
+                      "type": "STRING",
+                      "value": "!="
+                    },
+                    {
+                      "type": "STRING",
+                      "value": ">"
+                    },
+                    {
+                      "type": "STRING",
+                      "value": ">="
+                    },
+                    {
+                      "type": "STRING",
+                      "value": "<"
+                    },
+                    {
+                      "type": "STRING",
+                      "value": "<="
+                    }
+                  ]
+                }
+              },
+              {
+                "type": "FIELD",
+                "name": "right",
+                "content": {
+                  "type": "SYMBOL",
+                  "name": "_expression"
+                }
+              }
+            ]
+          }
+        },
+        {
+          "type": "PREC_LEFT",
+          "value": 7,
+          "content": {
+            "type": "SEQ",
+            "members": [
+              {
+                "type": "FIELD",
+                "name": "left",
+                "content": {
+                  "type": "SYMBOL",
+                  "name": "_expression"
+                }
+              },
+              {
+                "type": "FIELD",
+                "name": "operator",
+                "content": {
+                  "type": "TOKEN",
+                  "content": {
+                    "type": "PREC",
+                    "value": 2,
+                    "content": {
+                      "type": "STRING",
+                      "value": "++"
+                    }
+                  }
+                }
+              },
+              {
+                "type": "FIELD",
+                "name": "right",
+                "content": {
+                  "type": "SYMBOL",
+                  "name": "_expression"
+                }
+              }
+            ]
+          }
+        },
+        {
+          "type": "PREC_LEFT",
+          "value": 8,
+          "content": {
+            "type": "SEQ",
+            "members": [
+              {
+                "type": "FIELD",
+                "name": "left",
+                "content": {
+                  "type": "SYMBOL",
+                  "name": "_expression"
+                }
+              },
+              {
+                "type": "FIELD",
+                "name": "operator",
+                "content": {
+                  "type": "CHOICE",
+                  "members": [
+                    {
+                      "type": "STRING",
+                      "value": "+"
+                    },
+                    {
+                      "type": "STRING",
+                      "value": "-"
+                    }
+                  ]
+                }
+              },
+              {
+                "type": "FIELD",
+                "name": "right",
+                "content": {
+                  "type": "SYMBOL",
+                  "name": "_expression"
+                }
+              }
+            ]
+          }
+        },
+        {
+          "type": "PREC_LEFT",
+          "value": 9,
+          "content": {
+            "type": "SEQ",
+            "members": [
+              {
+                "type": "FIELD",
+                "name": "left",
+                "content": {
+                  "type": "SYMBOL",
+                  "name": "_expression"
+                }
+              },
+              {
+                "type": "FIELD",
+                "name": "operator",
+                "content": {
+                  "type": "CHOICE",
+                  "members": [
+                    {
+                      "type": "STRING",
+                      "value": "*"
+                    },
+                    {
+                      "type": "STRING",
+                      "value": "/"
+                    }
+                  ]
+                }
+              },
+              {
+                "type": "FIELD",
+                "name": "right",
+                "content": {
+                  "type": "SYMBOL",
+                  "name": "_expression"
+                }
+              }
+            ]
+          }
+        },
        {
          "type": "PREC_LEFT",
          "value": 3,
@@ -966,6 +1373,35 @@
          }
        ]
      }
+    },
+    "as_expression": {
+      "type": "PREC_LEFT",
+      "value": 0,
+      "content": {
+        "type": "SEQ",
+        "members": [
+          {
+            "type": "FIELD",
+            "name": "narrower",
+            "content": {
+              "type": "SYMBOL",
+              "name": "_expression"
+            }
+          },
+          {
+            "type": "STRING",
+            "value": "as"
+          },
+          {
+            "type": "FIELD",
+            "name": "wider",
+            "content": {
+              "type": "SYMBOL",
+              "name": "_expression"
+            }
+          }
+        ]
+      }
    }
  },
  "extras": [
@@ -16,7 +16,7 @@ This example exercises multiple current Decodal features together:
 Run it with:

 ```sh
-cargo run -q -p decodal -- examples/advanced/main.dcdl
+cargo run -q -p decodal-cli -- examples/advanced/main.dcdl
 ```

 The entrypoint is `main.dcdl`.
@@ -0,0 +1,7 @@
+{
+  workers = 2 + 2;
+  memory_gib = 1.5 * 4;
+  port = 9000 + 443;
+  timeout_seconds = 30 / 2;
+  negative_offset = -3;
+}
@@ -0,0 +1,6 @@
+{
+  base_roles = ["read", "write"];
+  extra_roles = ["admin"];
+  roles = ["read", "write"] ++ ["admin"];
+  ports = [8000 + 80] ++ [9000 + 443];
+}
@@ -0,0 +1,11 @@
+let
+    Service = {
+        name = String;
+        enabled = Bool default true;
+    };
+    Services = [...Service];
+in
+    Services & [
+        { name = "api"; },
+        { name = "worker"; enabled = false; },
+    ]
@@ -0,0 +1,11 @@
+let
+  env = "prod";
+  replicas = 3;
+in
+{
+  is_prod = env == "prod";
+  scaled = replicas > 1;
+  enabled = env == "prod" && replicas > 1;
+  disabled = !(env == "prod" && replicas > 1);
+  safe = env != "dev" || replicas >= 1;
+}
@@ -0,0 +1,15 @@
+let
+    Service = {
+        port = Int & >= 1 & <= 65535;
+        enabled = Bool default true;
+    };
+in
+    {
+        api = {
+            port = 8080;
+        };
+        worker = {
+            port = 8081;
+            enabled = false;
+        };
+    } as {...Service}
@@ -0,0 +1,11 @@
+OpenConfig = {
+    enabled = Bool default true;
+    ...Unknown
+};
+
+config = {
+    enabled = false;
+    plugin = {
+        name = "cache";
+    };
+} as OpenConfig;
@@ -3,7 +3,7 @@
 Regex constraints are optional. Run this example with the `regex` feature enabled:

 ```sh
-cargo run -q -p decodal --features regex -- examples/regex/main.dcdl
+cargo run -q -p decodal-cli --features regex -- examples/regex/main.dcdl
 ```

 Without the feature, regex validation returns an unsupported feature diagnostic.
@@ -29,6 +29,7 @@

        apps.default = mkApp "decodal" "Run Decodal";
        apps.decodal = mkApp "decodal" "Run Decodal";
+        apps.decodal-lsp = mkApp "decodal-lsp" "Run the Decodal language server";

        checks.default = decodal;

@@ -24,7 +24,7 @@ let
 in
 rustPlatform.buildRustPackage {
  pname = "decodal";
-  version = "0.1.0";
+  version = "0.1.2";

  src = lib.cleanSourceWith {
    src = srcRoot;
@@ -37,7 +37,9 @@ rustPlatform.buildRustPackage {

  cargoBuildFlags = [
    "-p"
-    "decodal"
+    "decodal-cli"
+    "-p"
+    "decodal-lsp"
  ];

  doInstallCheck = true;
@@ -45,6 +47,7 @@ rustPlatform.buildRustPackage {
    runHook preInstallCheck

    test -x "$out/bin/decodal"
+    test -x "$out/bin/decodal-lsp"
    "$out/bin/decodal" >/dev/null

    runHook postInstallCheck
@@ -0,0 +1,173 @@
+                              Apache License
+                        Version 2.0, January 2004
+                     http://www.apache.org/licenses/
+
+TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+1. Definitions.
+
+   "License" shall mean the terms and conditions for use, reproduction,
+   and distribution as defined by Sections 1 through 9 of this document.
+
+   "Licensor" shall mean the copyright owner or entity authorized by
+   the copyright owner that is granting the License.
+
+   "Legal Entity" shall mean the union of the acting entity and all
+   other entities that control, are controlled by, or are under common
+   control with that entity. For the purposes of this definition,
+   "control" means (i) the power, direct or indirect, to cause the
+   direction or management of such entity, whether by contract or
+   otherwise, or (ii) ownership of fifty percent (50%) or more of the
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+
+END OF TERMS AND CONDITIONS
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Decodal contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
@@ -0,0 +1,74 @@
+# decodal-codemirror
+
+CodeMirror 6 language support for Decodal.
+
+This package provides the Lezer parser metadata, highlighting tags, indentation rules, block folding, and formatter command used by the Decodal Web playground.
+It does not include the Decodal runtime evaluator.
+Use `decodal-wasm` when you want to evaluate Decodal in a browser.
+
+## Install
+
+```sh
+npm install decodal-codemirror
+```
+
+JSR:
+
+```sh
+deno add jsr:@hare/decodal-codemirror
+```
+
+## Usage
+
+```js
+import { basicSetup } from 'codemirror';
+import { EditorView } from '@codemirror/view';
+import { decodal } from 'decodal-codemirror';
+
+new EditorView({
+  doc: 'Server = { port = Int default 8080; };',
+  extensions: [
+    basicSetup,
+    decodal(),
+  ],
+  parent: document.querySelector('#editor'),
+});
+```
+
+## Exports
+
+```js
+import {
+  decodal,
+  decodalLanguage,
+  decodalHighlightStyle,
+} from 'decodal-codemirror';
+```
+
+`decodal()` accepts a small options object:
+
+```js
+decodal({ highlight: false })
+```
+
+Use this when you want the language support without the bundled highlight style.
+
+## Formatting
+
+The formatter is exposed as a separate subpath so plain syntax highlighting does not force callers to initialize WebAssembly.
+
+```js
+import {
+  formatDecodal,
+  formatDecodalCommand,
+  initDecodalFormatter,
+} from 'decodal-codemirror/format';
+import formatterWasm from 'decodal-codemirror/wasm/decodal_language_tools_bg.wasm?url';
+
+await initDecodalFormatter(formatterWasm);
+
+const result = formatDecodal('Server={port=Int default 8080;};');
+if (result.ok) console.log(result.source);
+
+formatDecodalCommand(view);
+```
--- a/Show More
+++ b/Show More
Author	SHA1	Message	Date
Hare	e0a9a8efb7	Bump packages for open value release	2026-08-14 08:03:25 +09:00
Hare	848c7f169f	Add unknown ranges and open object values	2026-08-14 08:00:22 +09:00
Hare	8c50dd202d	Bump packages for range refinement release	2026-08-14 06:29:48 +09:00
Hare	cc6ab40807	Add associative map constraints and range refinement	2026-08-14 06:26:15 +09:00
Hare	8198b615a8	Clarify site build and deploy scripts	2026-08-13 19:53:38 +09:00
Hare	62aa81b91c	Fix JSR license metadata	2026-08-13 19:45:04 +09:00
Hare	9c46635ee0	Bump Rust crates for breaking release	2026-08-13 19:40:08 +09:00
Hare	515adc2533	Unify formatting on canonical syntax	2026-08-13 19:31:21 +09:00
Hare	d9cf24d0eb	Prepare Decodal packages for release	2026-08-13 19:01:14 +09:00
Hare	d28edcf041	Share host-aware completion across runtimes	2026-08-13 18:55:03 +09:00
Hare	e862e53f3e	Add project-aware playground completion	2026-08-13 18:07:24 +09:00
Hare	610358110f	Add host-configurable LSP server	2026-08-12 05:42:45 +09:00
Hare	bdaccd9803	Add host-configurable language service	2026-08-11 22:05:17 +09:00
Hare	08603dc4b5	Report structured import origins in diagnostics	2026-08-11 19:20:11 +09:00
Hare	165daada23	Add host-structured imports	2026-08-11 18:33:49 +09:00
Hare	46b2b3b1b6	Add required array element constraints	2026-08-11 17:24:04 +09:00
Hare	5a05da6fe4	Use non-underscore Astro asset directory	2026-07-10 04:36:22 +09:00
Hare	aa0f464320	Bump CodeMirror package to 0.1.5	2026-07-10 04:30:38 +09:00
Hare	fc1f3e0b25	Improve JSR package metadata	2026-07-10 04:19:00 +09:00
Hare	8eac5c5cb4	Bundle language tools with CodeMirror package	2026-07-09 21:25:04 +09:00
Hare	59cb8f31e4	Simplify package link labels	2026-07-09 20:50:09 +09:00
Hare	4eee2cd2c9	Make package links flex layout	2026-07-09 20:45:16 +09:00
Hare	44b6041e60	Compact package links on landing page	2026-07-09 20:36:57 +09:00
Hare	a95afe0463	Align playground control heights	2026-07-09 19:36:15 +09:00
Hare	43ab6244ef	Reduce button vertical padding	2026-07-09 19:34:33 +09:00
Hare	1d4503b015	Simplify playground action separator	2026-07-09 19:33:48 +09:00
Hare	250e29e00c	Remove playground helper copy	2026-07-09 19:29:22 +09:00
Hare	1080081cec	Reset state before loading playground examples	2026-07-09 19:27:19 +09:00
Hare	43f692e75c	Add playground entry selector	2026-07-09 19:21:12 +09:00
Hare	5b26d071ca	Run playground examples from entrypoint	2026-07-09 19:12:18 +09:00
Hare	a653f0b7c6	Nest repeated playground fields	2026-07-09 19:06:28 +09:00
Hare	384d17b539	Replace playground examples	2026-07-09 19:02:11 +09:00
Hare	09a84264ab	Format playground examples	2026-07-09 18:54:29 +09:00
Hare	0a8c261545	Load playground wasm assets through Vite	2026-07-09 18:50:26 +09:00
Hare	a8a46998a8	Make build:wasm build all wasm packages	2026-07-09 18:46:24 +09:00
Hare	e4a9f80617	Dedupe CodeMirror dependencies	2026-07-09 18:43:09 +09:00
Hare	0e2a7b35d2	Add language tools package	2026-07-09 18:34:41 +09:00
Hare	ac99c4cb4e	Revert "Add Decodal formatter" This reverts commit `22f6bc1ab9`.	2026-07-09 17:46:24 +09:00
Hare	22f6bc1ab9	Add Decodal formatter	2026-07-09 17:39:32 +09:00
Hare	16006d000a	Move wasm package under packages	2026-07-09 04:13:08 +09:00
Hare	e4b9247c45	Extract CodeMirror language package	2026-07-09 03:49:44 +09:00
Hare	375bc80a57	Add package links to landing page	2026-07-09 03:31:20 +09:00
Hare	335ecde816	Fix JSR wasm package license	2026-07-09 03:29:27 +09:00
Hare	4142fcd46a	Prepare 0.1.2 release	2026-07-09 03:12:09 +09:00
Hare	2d06dc3277	Add source link to header	2026-07-09 03:00:30 +09:00
Hare	37237dc1f7	Add source link to footer	2026-07-09 02:59:32 +09:00
Hare	2966d5b979	Add site footer	2026-07-09 02:58:53 +09:00
Hare	ea858ad28e	Remove landing page eyebrow	2026-07-09 02:57:55 +09:00
Hare	871d342e15	Add site landing page	2026-07-09 02:55:50 +09:00
Hare	6d80c66144	Trim open issues to materialization	2026-07-09 02:46:28 +09:00
Hare	8e1cb01f52	Document Decodal components	2026-07-09 01:47:28 +09:00
Hare	26d8495631	Remove public tokenizer API	2026-07-09 01:09:40 +09:00
Hare	c4332ffb9d	Restore CodeMirror syntax highlighting	2026-07-09 00:38:31 +09:00
Hare	33ea8b94f9	Fix CodeMirror folding ranges	2026-07-09 00:04:34 +09:00
Hare	720c71157e	Fold Decodal delimited blocks from opener	2026-07-08 23:55:04 +09:00
Hare	ee031bd2e8	Add canonical grammar and CodeMirror playground	2026-07-08 23:41:26 +09:00
Hare	a07f4c48aa	Expose tokenizer for web highlighting	2026-07-08 19:50:04 +09:00
Hare	fe127428f9	Update generated WASM package README	2026-06-26 01:26:23 +09:00
Hare	0b76a600b1	Make Pages deploy script portable	2026-06-26 01:25:22 +09:00
Hare	ada3578a1d	Expose derive macro behind feature	2026-06-26 00:59:39 +09:00
Hare	b8404df047	Add typed Decodal derive support	2026-06-26 00:39:33 +09:00
Hare	87fef44c68	Make decodal the published library crate	2026-06-25 22:51:16 +09:00
Hare	6e2363632b	Prepare crates.io release metadata	2026-06-25 22:25:01 +09:00
Hare	c26f9ca50a	Add playground example loader	2026-06-25 03:39:40 +09:00
Hare	f928028007	Deploy Pages production branch by default	2026-06-25 03:12:37 +09:00
Hare	d8af980f7d	Add Cloudflare Pages deploy script	2026-06-25 02:49:15 +09:00
Hare	a2a6dee025	Show source names in diagnostics	2026-06-22 18:05:26 +09:00
Hare	cc5ab63922	Improve composition diagnostics	2026-06-22 17:37:51 +09:00
Hare	8b3df21cfa	Document lightweight runtime boundaries	2026-06-19 22:48:33 +09:00
Hare	01ad6dca52	Add array concat operator	2026-06-19 01:01:04 +09:00
Hare	6da0ec4c77	Fix inline code escaping	2026-06-18 23:55:11 +09:00
Hare	683151f6bd	Remove unimplemented operator note	2026-06-18 23:54:10 +09:00
Hare	9e728fb634	Document operator reference	2026-06-18 23:42:53 +09:00
Hare	2fe54bda62	Add logical and comparison expressions	2026-06-17 23:38:44 +09:00
Hare	3f7dd7c692	Add arithmetic expressions	2026-06-17 23:00:14 +09:00
Hare	dc28cddbff	Add dark theme support	2026-06-17 14:39:44 +09:00
Hare	aa6e5c51c1	Number manual sidebar navigation	2026-06-17 13:37:53 +09:00
Hare	4ab47e5719	Add multi-file playground imports	2026-06-17 10:17:00 +09:00
Hare	19c9de1601	Add site syntax highlighting	2026-06-17 07:39:00 +09:00
Hare	0e873fbd51	Migrate documentation site to Astro	2026-06-17 00:22:32 +09:00
Hare	4020b7c2d5	Add Svelte docs site and WASM playground	2026-06-17 00:07:11 +09:00