Add arithmetic expressions

crates/decodal-core/src/ast.rs

@@ -71,6 +71,10 @@ pub enum Expr {
         scrutinee: ExprId,
         arms: Vec<MatchArm>,
     },
+    Unary {
+        op: UnaryOp,
+        expr: ExprId,
+    },
     Binary {
         op: BinaryOp,
         lhs: ExprId,
@@ -117,8 +121,17 @@ pub enum Literal {
     Bool(bool),
 }
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum UnaryOp {
+    Neg,
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum BinaryOp {
+    Add,
+    Sub,
+    Mul,
+    Div,
     And,
     Patch,
 }

crates/decodal-core/src/eval.rs

@@ -2,7 +2,7 @@ use alloc::{format, string::String, vec, vec::Vec};
 
 use crate::{
     ExprId, SourceForm, SourceId, Span,
-    ast::{Ast, BinaryOp, CompareOp, Expr, Field, Literal},
+    ast::{Ast, BinaryOp, CompareOp, Expr, Field, Literal, UnaryOp},
     constraints::normalize_constraints,
     diagnostic::{Diagnostic, DiagnosticKind, Result},
     embedding::HostValue,
@@ -337,6 +337,18 @@ impl<L: SourceLoader> Engine<L> {
                     "no match arm matched",
                 ))
             }
+            Expr::Unary { op, expr } => {
+                let value = self.eval_expr(
+                    ExprRef {
+                        module: reference.module,
+                        expr,
+                    },
+                    env,
+                )?;
+                match op {
+                    UnaryOp::Neg => negate_number(value, span),
+                }
+            }
             Expr::Binary { op, lhs, rhs } => {
                 let lhs = self.eval_expr(
                     ExprRef {
@@ -353,6 +365,10 @@ impl<L: SourceLoader> Engine<L> {
                     env,
                 )?;
                 match op {
+                    BinaryOp::Add => arithmetic(lhs, rhs, ArithmeticOp::Add, span),
+                    BinaryOp::Sub => arithmetic(lhs, rhs, ArithmeticOp::Sub, span),
+                    BinaryOp::Mul => arithmetic(lhs, rhs, ArithmeticOp::Mul, span),
+                    BinaryOp::Div => arithmetic(lhs, rhs, ArithmeticOp::Div, span),
                     BinaryOp::And => self.compose_and(lhs, rhs, span),
                     BinaryOp::Patch => self.patch(lhs, rhs),
                 }
@@ -999,6 +1015,116 @@ fn satisfies_regex(_value: &RuntimeValue, _pattern: &str, span: Span) -> Result<
     ))
 }
 
+#[derive(Debug, Clone, Copy)]
+enum ArithmeticOp {
+    Add,
+    Sub,
+    Mul,
+    Div,
+}
+
+#[derive(Debug, Clone, Copy)]
+enum Number {
+    Int(i64),
+    Float(f64),
+}
+
+fn negate_number(value: RuntimeValue, span: Span) -> Result<RuntimeValue> {
+    match value {
+        RuntimeValue::Concrete(ConcreteValue::Int(value)) => value
+            .checked_neg()
+            .map(|value| RuntimeValue::Concrete(ConcreteValue::Int(value)))
+            .ok_or_else(|| arithmetic_error(span, "integer negation overflow")),
+        RuntimeValue::Concrete(ConcreteValue::Float(value)) => {
+            Ok(RuntimeValue::Concrete(ConcreteValue::Float(-value)))
+        }
+        _ => Err(Diagnostic::new(
+            DiagnosticKind::TypeMismatch,
+            span,
+            "unary '-' expects a numeric value",
+        )),
+    }
+}
+
+fn arithmetic(
+    lhs: RuntimeValue,
+    rhs: RuntimeValue,
+    op: ArithmeticOp,
+    span: Span,
+) -> Result<RuntimeValue> {
+    let lhs = number_from_runtime(lhs).ok_or_else(|| arithmetic_type_error(span))?;
+    let rhs = number_from_runtime(rhs).ok_or_else(|| arithmetic_type_error(span))?;
+    match (lhs, rhs) {
+        (Number::Int(lhs), Number::Int(rhs)) => arithmetic_int(lhs, rhs, op, span),
+        (lhs, rhs) => arithmetic_float(number_to_f64(lhs), number_to_f64(rhs), op, span),
+    }
+}
+
+fn arithmetic_int(lhs: i64, rhs: i64, op: ArithmeticOp, span: Span) -> Result<RuntimeValue> {
+    match op {
+        ArithmeticOp::Add => lhs
+            .checked_add(rhs)
+            .map(|value| RuntimeValue::Concrete(ConcreteValue::Int(value)))
+            .ok_or_else(|| arithmetic_error(span, "integer addition overflow")),
+        ArithmeticOp::Sub => lhs
+            .checked_sub(rhs)
+            .map(|value| RuntimeValue::Concrete(ConcreteValue::Int(value)))
+            .ok_or_else(|| arithmetic_error(span, "integer subtraction overflow")),
+        ArithmeticOp::Mul => lhs
+            .checked_mul(rhs)
+            .map(|value| RuntimeValue::Concrete(ConcreteValue::Int(value)))
+            .ok_or_else(|| arithmetic_error(span, "integer multiplication overflow")),
+        ArithmeticOp::Div => {
+            if rhs == 0 {
+                return Err(arithmetic_error(span, "division by zero"));
+            }
+            Ok(RuntimeValue::Concrete(ConcreteValue::Float(
+                lhs as f64 / rhs as f64,
+            )))
+        }
+    }
+}
+
+fn arithmetic_float(lhs: f64, rhs: f64, op: ArithmeticOp, span: Span) -> Result<RuntimeValue> {
+    if matches!(op, ArithmeticOp::Div) && rhs == 0.0 {
+        return Err(arithmetic_error(span, "division by zero"));
+    }
+    let value = match op {
+        ArithmeticOp::Add => lhs + rhs,
+        ArithmeticOp::Sub => lhs - rhs,
+        ArithmeticOp::Mul => lhs * rhs,
+        ArithmeticOp::Div => lhs / rhs,
+    };
+    Ok(RuntimeValue::Concrete(ConcreteValue::Float(value)))
+}
+
+fn number_from_runtime(value: RuntimeValue) -> Option<Number> {
+    match value {
+        RuntimeValue::Concrete(ConcreteValue::Int(value)) => Some(Number::Int(value)),
+        RuntimeValue::Concrete(ConcreteValue::Float(value)) => Some(Number::Float(value)),
+        _ => None,
+    }
+}
+
+fn number_to_f64(value: Number) -> f64 {
+    match value {
+        Number::Int(value) => value as f64,
+        Number::Float(value) => value,
+    }
+}
+
+fn arithmetic_type_error(span: Span) -> Diagnostic {
+    Diagnostic::new(
+        DiagnosticKind::TypeMismatch,
+        span,
+        "arithmetic operators expect numeric values",
+    )
+}
+
+fn arithmetic_error(span: Span, message: &'static str) -> Diagnostic {
+    Diagnostic::new(DiagnosticKind::Conflict, span, message)
+}
+
 fn compare_value(value: &RuntimeValue, op: CompareOp, expected: &LiteralValue) -> bool {
     match (value, expected) {
         (RuntimeValue::Concrete(ConcreteValue::Int(actual)), LiteralValue::Int(expected)) => {
@@ -1072,6 +1198,41 @@ mod tests {
         assert!(matches!(data, Data::Object(_)));
     }
 
+    #[test]
+    fn evaluates_arithmetic_expressions() {
+        let data = eval_data(
+            r#"
+            {
+                sum = 1 + 2 * 3;
+                diff = 10 - 4;
+                product = (2 + 3) * 4;
+                quotient = 5 / 2;
+                negative = -3 + 1;
+            }
+            "#,
+        );
+        let Data::Object(fields) = data else { panic!() };
+        assert_eq!(fields[0].value, Data::Int(7));
+        assert_eq!(fields[1].value, Data::Int(6));
+        assert_eq!(fields[2].value, Data::Int(20));
+        assert_eq!(fields[3].value, Data::Float(2.5));
+        assert_eq!(fields[4].value, Data::Int(-2));
+    }
+
+    #[test]
+    fn arithmetic_can_feed_constraints() {
+        let data = eval_data("port = Int & > 4000 + 42 default 8080;");
+        let Data::Object(fields) = data else { panic!() };
+        assert_eq!(fields[0].value, Data::Int(8080));
+    }
+
+    #[test]
+    fn rejects_division_by_zero() {
+        let parsed = parse_source("1 / 0").unwrap();
+        let mut engine = Engine::from_parse(parsed.ast, parsed.root);
+        assert!(engine.eval_root().is_err());
+    }
+
     #[test]
     fn composes_schema_and_value() {
         let data = eval_data(

crates/decodal-core/src/lexer.rs

@@ -36,6 +36,10 @@ pub enum TokenKind {
     Equal,
     Arrow,
     Amp,
+    Plus,
+    Minus,
+    Star,
+    Slash,
     SlashSlash,
     Gt,
     Gte,
@@ -67,9 +71,13 @@ impl<'a> Lexer<'a> {
 
     pub fn tokenize(mut self) -> Result<Vec<Token>> {
         let mut tokens = Vec::new();
+        let mut previous = None;
         loop {
-            let token = self.next_token()?;
+            let token = self.next_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);
@@ -77,7 +85,7 @@ impl<'a> Lexer<'a> {
         }
     }
 
-    fn next_token(&mut self) -> Result<Token> {
+    fn next_token(&mut self, previous: Option<&TokenKind>) -> Result<Token> {
         self.skip_ws_and_comments();
         let start = self.pos;
         let Some(ch) = self.peek() else {
@@ -136,6 +144,18 @@ impl<'a> Lexer<'a> {
                 self.pos += 1;
                 TokenKind::Amp
             }
+            b'+' => {
+                self.pos += 1;
+                TokenKind::Plus
+            }
+            b'-' => {
+                self.pos += 1;
+                TokenKind::Minus
+            }
+            b'*' => {
+                self.pos += 1;
+                TokenKind::Star
+            }
             b'=' => {
                 self.pos += 1;
                 if self.consume(b'>') {
@@ -164,6 +184,8 @@ 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)?
                 }
@@ -341,6 +363,23 @@ 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::*;

crates/decodal-core/src/parser.rs

@@ -2,7 +2,7 @@ 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, Param, UnaryOp},
     diagnostic::{Diagnostic, Result},
     lexer::{Lexer, Token, TokenKind},
 };
@@ -115,6 +115,38 @@ 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::And => self.ast.push(
                     Expr::Binary {
                         op: BinaryOp::And,
@@ -173,6 +205,17 @@ 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(11)?;
+                let span = token.span.join(self.ast.span(expr));
+                Ok(self.ast.push(
+                    Expr::Unary {
+                        op: UnaryOp::Neg,
+                        expr,
+                    },
+                    span,
+                ))
+            }
             TokenKind::Gt | TokenKind::Gte | TokenKind::Lt | TokenKind::Lte => {
                 let op = match token.kind {
                     TokenKind::Gt => CompareOp::Gt,
@@ -181,7 +224,7 @@ impl Parser {
                     TokenKind::Lte => CompareOp::Lte,
                     _ => unreachable!(),
                 };
-                let value = self.parse_expr(8)?;
+                let value = self.parse_expr(6)?;
                 let span = token.span.join(self.ast.span(value));
                 Ok(self.ast.push(Expr::CompareConstraint { op, value }, span))
             }
@@ -406,6 +449,10 @@ impl Parser {
             TokenKind::Default => Some((InfixKind::Default, 1, 2)),
             TokenKind::SlashSlash => Some((InfixKind::Patch, 3, 4)),
             TokenKind::Amp => Some((InfixKind::And, 5, 6)),
+            TokenKind::Plus => Some((InfixKind::Add, 7, 8)),
+            TokenKind::Minus => Some((InfixKind::Sub, 7, 8)),
+            TokenKind::Star => Some((InfixKind::Mul, 9, 10)),
+            TokenKind::Slash => Some((InfixKind::Div, 9, 10)),
             _ => None,
         }
     }
@@ -498,6 +545,10 @@ impl Parser {
 
 #[derive(Debug, Clone, Copy)]
 enum InfixKind {
+    Add,
+    Sub,
+    Mul,
+    Div,
     And,
     Patch,
     Default,

doc/manual/souce/language/expression/arithmetic.md

@@ -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;
+```

doc/manual/souce/language/operators.md

@@ -1,6 +1,26 @@
-# 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。
+
+## 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. `default`
+
+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。
 
 ## `&`: 制約合成
 

doc/manual/souce/language/syntax.md

@@ -115,6 +115,7 @@ rec
 主要な演算子は以下である。
 
 ```text
++ - * / 四則演算
 &       制約合成
 //      patch 合成
 default fallback 指定
@@ -122,5 +123,4 @@ default fallback 指定
 .       フィールド参照 / ドットパス定義
 ```
 
-演算子の優先順位は未確定である。
+演算子の優先順位は [合成演算子](./operators.md) で定義する。
-詳細は [合成演算子](./operators.md) で定義する。

editors/tree-sitter-decodal/corpus/basic.txt

@@ -74,3 +74,31 @@ 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)))))))

editors/tree-sitter-decodal/grammar.js

@@ -2,6 +2,9 @@ const PREC = {
   DEFAULT: 1,
   PATCH: 2,
   AND: 3,
+  ADD: 4,
+  MUL: 5,
+  UNARY: 6,
   CALL: 7,
   PATH: 8,
 };
@@ -52,6 +55,7 @@ module.exports = grammar({
       $.parenthesized_expression,
       $.call_expression,
       $.path_expression,
+      $.unary_expression,
       $.binary_expression,
       $.default_expression,
     ),
@@ -161,10 +165,25 @@ module.exports = grammar({
 
     comparison_constraint: $ => prec(6, seq(
       field('operator', choice('>', '>=', '<', '<=')),
-      field('value', choice($.integer, $.float)),
+      field('value', $._expression),
+    )),
+
+    unary_expression: $ => prec(PREC.UNARY, seq(
+      field('operator', '-'),
+      field('operand', $._expression),
     )),
 
     binary_expression: $ => choice(
+      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.AND, seq(
         field('left', $._expression),
         field('operator', '&'),

editors/tree-sitter-decodal/queries/highlights.scm

@@ -17,6 +17,10 @@
 [
   "&"
   "//"
+  "+"
+  "-"
+  "*"
+  "/"
   "=>"
   "="
   ">"

editors/tree-sitter-decodal/src/grammar.json

@@ -127,6 +127,10 @@
           "type": "SYMBOL",
           "name": "path_expression"
         },
+        {
+          "type": "SYMBOL",
+          "name": "unary_expression"
+        },
         {
           "type": "SYMBOL",
           "name": "binary_expression"
@@ -844,18 +848,34 @@
             "type": "FIELD",
             "name": "value",
             "content": {
-              "type": "CHOICE",
-              "members": [
-                {
               "type": "SYMBOL",
-                  "name": "integer"
+              "name": "_expression"
-                },
+            }
-                {
-                  "type": "SYMBOL",
-                  "name": "float"
           }
         ]
       }
+    },
+    "unary_expression": {
+      "type": "PREC",
+      "value": 6,
+      "content": {
+        "type": "SEQ",
+        "members": [
+          {
+            "type": "FIELD",
+            "name": "operator",
+            "content": {
+              "type": "STRING",
+              "value": "-"
+            }
+          },
+          {
+            "type": "FIELD",
+            "name": "operand",
+            "content": {
+              "type": "SYMBOL",
+              "name": "_expression"
+            }
           }
         ]
       }
@@ -863,6 +883,90 @@
     "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": "CHOICE",
+                  "members": [
+                    {
+                      "type": "STRING",
+                      "value": "+"
+                    },
+                    {
+                      "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": "CHOICE",
+                  "members": [
+                    {
+                      "type": "STRING",
+                      "value": "*"
+                    },
+                    {
+                      "type": "STRING",
+                      "value": "/"
+                    }
+                  ]
+                }
+              },
+              {
+                "type": "FIELD",
+                "name": "right",
+                "content": {
+                  "type": "SYMBOL",
+                  "name": "_expression"
+                }
+              }
+            ]
+          }
+        },
         {
           "type": "PREC_LEFT",
           "value": 3,

editors/tree-sitter-decodal/src/node-types.json

@@ -66,6 +66,10 @@
         {
           "type": "regex_literal",
           "named": true
+        },
+        {
+          "type": "unary_expression",
+          "named": true
         }
       ]
     }
@@ -137,6 +141,10 @@
           {
             "type": "regex_literal",
             "named": true
+          },
+          {
+            "type": "unary_expression",
+            "named": true
           }
         ]
       },
@@ -148,6 +156,22 @@
             "type": "&",
             "named": false
           },
+          {
+            "type": "*",
+            "named": false
+          },
+          {
+            "type": "+",
+            "named": false
+          },
+          {
+            "type": "-",
+            "named": false
+          },
+          {
+            "type": "/",
+            "named": false
+          },
           {
             "type": "//",
             "named": false
@@ -217,6 +241,10 @@
           {
             "type": "regex_literal",
             "named": true
+          },
+          {
+            "type": "unary_expression",
+            "named": true
           }
         ]
       }
@@ -294,6 +322,10 @@
           {
             "type": "regex_literal",
             "named": true
+          },
+          {
+            "type": "unary_expression",
+            "named": true
           }
         ]
       }
@@ -361,6 +393,10 @@
         {
           "type": "regex_literal",
           "named": true
+        },
+        {
+          "type": "unary_expression",
+          "named": true
         }
       ]
     }
@@ -396,11 +432,67 @@
         "required": true,
         "types": [
           {
-            "type": "float",
+            "type": "array",
             "named": true
           },
           {
-            "type": "integer",
+            "type": "binary_expression",
+            "named": true
+          },
+          {
+            "type": "call_expression",
+            "named": true
+          },
+          {
+            "type": "comparison_constraint",
+            "named": true
+          },
+          {
+            "type": "default_expression",
+            "named": true
+          },
+          {
+            "type": "function_expression",
+            "named": true
+          },
+          {
+            "type": "identifier",
+            "named": true
+          },
+          {
+            "type": "import_expression",
+            "named": true
+          },
+          {
+            "type": "let_expression",
+            "named": true
+          },
+          {
+            "type": "literal",
+            "named": true
+          },
+          {
+            "type": "match_expression",
+            "named": true
+          },
+          {
+            "type": "object",
+            "named": true
+          },
+          {
+            "type": "parenthesized_expression",
+            "named": true
+          },
+          {
+            "type": "path_expression",
+            "named": true
+          },
+          {
+            "type": "regex_literal",
+            "named": true
+          },
+          {
+            "type": "unary_expression",
             "named": true
           }
         ]
@@ -474,6 +566,10 @@
           {
             "type": "regex_literal",
             "named": true
+          },
+          {
+            "type": "unary_expression",
+            "named": true
           }
         ]
       },
@@ -540,6 +636,10 @@
           {
             "type": "regex_literal",
             "named": true
+          },
+          {
+            "type": "unary_expression",
+            "named": true
           }
         ]
       }
@@ -622,6 +722,10 @@
           {
             "type": "regex_literal",
             "named": true
+          },
+          {
+            "type": "unary_expression",
+            "named": true
           }
         ]
       }
@@ -709,6 +813,10 @@
           {
             "type": "regex_literal",
             "named": true
+          },
+          {
+            "type": "unary_expression",
+            "named": true
           }
         ]
       }
@@ -807,6 +915,10 @@
           {
             "type": "regex_literal",
             "named": true
+          },
+          {
+            "type": "unary_expression",
+            "named": true
           }
         ]
       }
@@ -916,6 +1028,10 @@
           {
             "type": "regex_literal",
             "named": true
+          },
+          {
+            "type": "unary_expression",
+            "named": true
           }
         ]
       },
@@ -986,6 +1102,10 @@
           {
             "type": "regex_literal",
             "named": true
+          },
+          {
+            "type": "unary_expression",
+            "named": true
           }
         ]
       }
@@ -1058,6 +1178,10 @@
           {
             "type": "regex_literal",
             "named": true
+          },
+          {
+            "type": "unary_expression",
+            "named": true
           }
         ]
       }
@@ -1155,6 +1279,10 @@
           {
             "type": "regex_literal",
             "named": true
+          },
+          {
+            "type": "unary_expression",
+            "named": true
           }
         ]
       },
@@ -1237,6 +1365,10 @@
         {
           "type": "regex_literal",
           "named": true
+        },
+        {
+          "type": "unary_expression",
+          "named": true
         }
       ]
     }
@@ -1318,6 +1450,10 @@
           {
             "type": "regex_literal",
             "named": true
+          },
+          {
+            "type": "unary_expression",
+            "named": true
           }
         ]
       }
@@ -1394,10 +1530,100 @@
         {
           "type": "regex_literal",
           "named": true
+        },
+        {
+          "type": "unary_expression",
+          "named": true
         }
       ]
     }
   },
+  {
+    "type": "unary_expression",
+    "named": true,
+    "fields": {
+      "operand": {
+        "multiple": false,
+        "required": true,
+        "types": [
+          {
+            "type": "array",
+            "named": true
+          },
+          {
+            "type": "binary_expression",
+            "named": true
+          },
+          {
+            "type": "call_expression",
+            "named": true
+          },
+          {
+            "type": "comparison_constraint",
+            "named": true
+          },
+          {
+            "type": "default_expression",
+            "named": true
+          },
+          {
+            "type": "function_expression",
+            "named": true
+          },
+          {
+            "type": "identifier",
+            "named": true
+          },
+          {
+            "type": "import_expression",
+            "named": true
+          },
+          {
+            "type": "let_expression",
+            "named": true
+          },
+          {
+            "type": "literal",
+            "named": true
+          },
+          {
+            "type": "match_expression",
+            "named": true
+          },
+          {
+            "type": "object",
+            "named": true
+          },
+          {
+            "type": "parenthesized_expression",
+            "named": true
+          },
+          {
+            "type": "path_expression",
+            "named": true
+          },
+          {
+            "type": "regex_literal",
+            "named": true
+          },
+          {
+            "type": "unary_expression",
+            "named": true
+          }
+        ]
+      },
+      "operator": {
+        "multiple": false,
+        "required": true,
+        "types": [
+          {
+            "type": "-",
+            "named": false
+          }
+        ]
+      }
+    }
+  },
   {
     "type": "&",
     "named": false
@@ -1410,14 +1636,30 @@
     "type": ")",
     "named": false
   },
+  {
+    "type": "*",
+    "named": false
+  },
+  {
+    "type": "+",
+    "named": false
+  },
   {
     "type": ",",
     "named": false
   },
+  {
+    "type": "-",
+    "named": false
+  },
   {
     "type": ".",
     "named": false
   },
+  {
+    "type": "/",
+    "named": false
+  },
   {
     "type": "//",
     "named": false

examples/arithmetic.dcdl

@@ -0,0 +1,7 @@
+{
+  workers = 2 + 2;
+  memory_gib = 1.5 * 4;
+  port = 9000 + 443;
+  timeout_seconds = 30 / 2;
+  negative_offset = -3;
+}

site/decodal-site/src/lib/docs.js

@@ -50,6 +50,7 @@ export const nav = [
           { title: 'Import', slug: 'language/expression/import' },
           { title: 'Composition', slug: 'language/expression/composition' },
           { title: 'Default', slug: 'language/expression/default' },
+          { title: 'Arithmetic', slug: 'language/expression/arithmetic' },
           { title: 'String Interpolation', slug: 'language/expression/string-interpolation' },
         ],
       },

site/decodal-site/src/lib/highlight.js

@@ -28,12 +28,13 @@ export function highlightCode(code, language = '') {
 export function highlightDecodal(source) {
   let html = '';
   let index = 0;
+  let canEndExpression = false;
 
   while (index < source.length) {
     const char = source[index];
     const next = source[index + 1];
 
-    if (char === '/' && next === '/') {
+    if (char === '#') {
       const end = readUntilLineEnd(source, index);
       html += token('comment', source.slice(index, end));
       index = end;
@@ -44,13 +45,15 @@ export function highlightDecodal(source) {
       const end = readString(source, index);
       html += token('string', source.slice(index, end));
       index = end;
+      canEndExpression = true;
       continue;
     }
 
-    if (char === '/' && next && next !== '/') {
+    if (char === '/' && next && next !== '/' && !canEndExpression) {
       const end = readRegex(source, index);
       html += token('regex', source.slice(index, end));
       index = end;
+      canEndExpression = true;
       continue;
     }
 
@@ -58,6 +61,7 @@ export function highlightDecodal(source) {
       const end = readNumber(source, index);
       html += token('number', source.slice(index, end));
       index = end;
+      canEndExpression = true;
       continue;
     }
 
@@ -68,6 +72,7 @@ export function highlightDecodal(source) {
       else if (DECODAL_TYPES.has(ident)) html += token('type', ident);
       else if (DECODAL_LITERALS.has(ident)) html += token('literal', ident);
       else html += escapeHtml(ident);
+      canEndExpression = true;
       index = end;
       continue;
     }
@@ -75,6 +80,7 @@ export function highlightDecodal(source) {
     if (isOperatorStart(char)) {
       const end = readOperator(source, index);
       html += token('operator', source.slice(index, end));
+      canEndExpression = /[})\]]/.test(char);
       index = end;
       continue;
     }
@@ -184,11 +190,12 @@ function readIdentifier(source, start) {
 }
 
 function isOperatorStart(char) {
-  return /[&=<>!|:;,.{}()[\]]/.test(char ?? '');
+  return '&=<>!|:;,.{}()[]+-*/'.includes(char ?? '');
 }
 
 function readOperator(source, start) {
   let index = start + 1;
+  if (source[start] === '/' && source[index] === '/') return index + 1;
   if ((source[start] === '<' || source[start] === '>' || source[start] === '=' || source[start] === '!') && source[index] === '=') {
     index += 1;
   }

site/decodal-site/src/scripts/playground.js

@@ -9,7 +9,7 @@ const starterFiles = {
 in
   schema.Service & {
     name = "api";
-    port = 9443;
+    port = 9000 + 443;
   }
 `,
   'schemas/service.dcdl': `Service = {