SLAC-MCP: Instructions file for Codex

AGENTS.md

Project

Rust MCP server exposing SLAC (Simple Logic & Arithmetic Compiler) as tools via the Model Context Protocol.

• Single crate, edition 2024 (requires Rust 1.85+)
• rmcp 2.2.0 - official Rust MCP SDK (tokio-based)
• slac 1.1.0 - expression-to-AST compiler with built-in tree-walk interpreter

Purpose

Provide LLM agents a simple way to evaluate logical and arithmetic expressions at runtime via the SLAC expression language.

Tools

• evaluate(expression: string): string - Compiles and evaluates a SLAC expression, returns the result as a string.
• get_syntax(): string - Returns the full SLAC language reference (syntax, operators, functions, examples) via include_str!.

Non-Goals

• Exposing the compiled AST. SLAC supports this, but the MCP must not expose it.

Architecture

• src/main.rs - MCP server bootstrap (tracing, stdio transport)
• src/server.rs - SlacServer unit struct with tool handlers and ServerHandler impl
• src/get-syntax.md - SLAC language reference included by get_syntax

Key Constraint: !Send Environment

slac::StaticEnvironment is !Send + !Sync (contains Rc internally). It cannot be stored in the service struct behind Arc<Mutex<>>. Each evaluate call creates a fresh environment: StaticEnvironment::default() -> extend_environment() -> compile() -> execute().

Environment Variables

• OUTPUT_FORMAT=JSON - When set, evaluate returns pretty-printed JSON via serde_json instead of the default Rust Display representation.

Build & Run

cargo build
cargo run

For testing with MCP Inspector:

npx @modelcontextprotocol/inspector cargo run

No test, lint, or CI configuration exists yet.