Add host-structured imports

crates/decodal-core/src/module.rs

@@ -1,7 +1,7 @@
 use alloc::string::String;
 
 use crate::{
-    Ast, ExprId, SourceForm, SourceId,
+    Ast, ExprId, HostValue, SourceForm, SourceId,
     runtime::{EnvId, ThunkId},
 };
 
@@ -24,15 +24,48 @@ pub struct LoadedSource {
     pub source: String,
 }
 
-pub trait SourceLoader {
-    fn load(&mut self, current_key: Option<&str>, specifier: &str) -> crate::Result<LoadedSource>;
+#[derive(Debug, Clone)]
+pub struct LoadedValue {
+    pub key: String,
+    pub value: HostValue,
+}
+
+#[derive(Debug, Clone)]
+pub enum LoadedImport {
+    Source(LoadedSource),
+    Value(LoadedValue),
+}
+
+impl LoadedImport {
+    pub fn source(
+        key: impl Into<String>,
+        name: impl Into<String>,
+        source: impl Into<String>,
+    ) -> Self {
+        Self::Source(LoadedSource {
+            key: key.into(),
+            name: name.into(),
+            source: source.into(),
+        })
+    }
+
+    pub fn value(key: impl Into<String>, value: HostValue) -> Self {
+        Self::Value(LoadedValue {
+            key: key.into(),
+            value,
+        })
+    }
+}
+
+pub trait ImportLoader {
+    fn load(&mut self, current_key: Option<&str>, specifier: &str) -> crate::Result<LoadedImport>;
 }
 
 #[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(),