dexpr/CLAUDE.md

CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Project Overview

dexpr is an embeddable expression evaluator and bytecode VM written in Rust. It parses expressions and simple scripts (.dexpr files), compiles to bytecode, and executes on a register-based virtual machine. Designed to be embedded in other projects as a rule engine, formula evaluator, or expression calculator.

Common Commands

# Run tests
cargo test

# Run benchmarks
cargo bench --bench my_benchmark

# Run the main program (executes basic_long.dexpr by default)
cargo run --release

# Profile with samply
cargo build --profile profiling
samply record ./target/profiling/dexpr

Architecture

The pipeline flows: Parser → AST → Compiler → Bytecode → VM

Core Modules

• parser/: PEG-based parser (grammar.rs) that produces AST nodes
• ast/: Expression (expr.rs), statement (stmt.rs), and value (value.rs) types
• compiler.rs: Transforms AST into bytecode; single-pass, globals-only, register allocation
• bytecode.rs: BytecodeWriter for compilation, BytecodeReader for VM consumption
• opcodes.rs: Defines OpCodeByte enum and Register type
• vm/vm.rs: Register-based VM with global variable support; executes bytecode

Key Types

• Value (ast/value.rs): Runtime values (Number using rust_decimal, String, Boolean, Object using indexmap, etc.)
• Compiler: Stateful compiler with register allocation
• VM<'a>: Bytecode interpreter with global variable support via set_global/get_global

Typical Usage Pattern

use dexpr::{ast::value::Value, compiler::Compiler, parser, vm::VM};

let ast = parser::program(source_code)?;
let mut compiler = Compiler::new();
let bytecode = compiler.compile(ast)?;
let mut vm = VM::new(&bytecode);
vm.set_global("input", Value::Number(dec!(42)));
vm.register_function("getRate", |args| Ok(Value::Number(dec!(34.5))));
let result = vm.execute()?; // Returns last expression's value
// Or use globals: let output = vm.get_global("output");

Language Features

The dexpr language supports:

• If/else conditionals with if ... then ... else ... end
• String methods (e.g., .upper(), .lower(), .trim(), .trimStart(), .trimEnd(), .split(), .replace(), .contains(), .startsWith(), .endsWith(), .length, .charAt(), .substring())
• Arithmetic (+, -, *, /, %, **), comparison, and logical operators
• in operator for membership testing ("finans" in categories, 5 in numbers, "hello" in "hello world", "key" in obj)
• Compound assignments (+=, -=, *=, /=, %=)
• Built-in log() function for output and rand(min, max) for random integers
• External (host) function registration via vm.register_function()
• External (host) method registration via vm.register_method()
• Expression return value: execute() returns the last expression's value
• Line comments (//) and block comments (/* */)
• Lists: NumberList and StringList types with methods (sum, avg, min, max, first, last, get, join, contains, indexOf, slice, reverse, sort, isEmpty, etc.)
• Objects: Object type (provided externally via set_global) with property access (obj.field), nested access (obj.a.b), property assignment (obj.field = value), and methods (keys(), values(), length(), contains(key), get(key))

Detailed Module Documentation

IMPORTANT: Before making any changes to the codebase, read the relevant documentation files in the docs/ folder to understand how that module works in detail. After making changes to any module, update the corresponding documentation file to keep it in sync.

• docs/architecture.md — Overall architecture, pipeline, design decisions, dependencies
• docs/ast.md — AST module: Expr, Stmt, Value types, Span, serialization format
• docs/parser.md — Parser: PEG grammar rules, operator precedence, reserved keywords
• docs/opcodes.md — Opcodes: full instruction set with hex values and categories
• docs/bytecode.md — Bytecode: BytecodeWriter/Reader API, data format, disassembler
• docs/compiler.md — Compiler: single-pass compilation, register allocation, label/jump system
• docs/vm.md — VM: execution loop, opcode handlers, error types, DebugInfo
• docs/language_info.md — Language Info: editor metadata generation, JSON format, host integration
• docs/editor.md — Editor: CodeMirror 6 language support, Lezer grammar, type-aware autocomplete

Rule: Any code change that modifies the behavior, API, or structure of a module MUST be accompanied by an update to the corresponding docs/ file. Documentation and code must always stay in sync.