Weir

Warning: Heads-up, this is a fun personal project to drive Claude Code very hard and make a domain-specific programming language. It's a fun personal project, but should probably not be used by anyone.

Weir is a statically typed, Lisp-family programming language targeting native code via Cranelift. It's designed for fast iteration in small-scale game development, combining S-expression syntax with a modern type system and function-level live reloading.

Key Features

• S-expression syntax with type annotations, collection literals ([], {}), and threading macros (->, ->>)
• Declarative static types — explicit function signatures, locally inferred locals, algebraic data types, exhaustive pattern matching
• Typeclasses with higher-kinded types, multi-parameter support, and coherence rules
• Hygienic macros — purely syntactic, can generate type definitions and typeclass instances
• Native compilation — Cranelift JIT for dev mode, AOT compilation for release binaries
• Live reloading — function-level hot-swap in dev mode with cascade recompilation
• Tracing GC with opt-in arena allocation for hot paths
• Package system — weir.pkg manifests, path-based dependencies, native C source compilation
• C FFI — extern "C" declarations with unsafe blocks

Current Status

Working today:

• Compiler pipeline: lexer, parser, macro expander, type checker, Cranelift codegen
• Three execution modes: JIT (weir run), AOT (weir build), tree-walking interpreter (weir interp)
• Dev mode: weir dev with file watching and function-level live reload
• Package system: multi-package projects with dependency resolution and native code support
• OpenGL Tetris demo: full game built with Weir + GLFW/OpenGL via C FFI (just tetris)
• LSP server: diagnostics, hover, completion, go-to-definition, document symbols
• Zed extension: syntax highlighting and LSP integration
• 647 tests across the workspace

Getting Started

Requires Nix with flakes enabled:

git clone <repo-url> && cd weirlang
nix develop                        # activate dev environment
just test                          # run all tests

Run a single file:

weir run examples/hello.weir       # JIT compile and run
weir build examples/hello.weir     # AOT compile to binary
weir dev examples/hello.weir       # dev mode with live reload

Run a package project:

cd demos/tetris && weir run        # discovers weir.pkg, resolves deps, runs via JIT

Project Structure

crates/
  weir-lexer/       Tokenizer
  weir-parser/      S-expression parser → AST
  weir-macros/      Macro expander
  weir-typeck/      Type checker (local inference, typeclasses, ADTs)
  weir-codegen/     Cranelift JIT/AOT backend + dev mode live reload
  weir-interp/      Tree-walking interpreter
  weir-runtime/     GC, arenas, runtime support
  weir-pkg/         Package system (manifest parsing, dependency resolution)
  weir-cli/         CLI frontend (clap)
  weir-lsp/         Language Server Protocol implementation
  weir-ast/         AST types, pretty printer, TCO analysis
design/             Language design documents
std/                Standard library (prelude)
demos/              Demo projects (tetris)
docs/               Documentation website (Astro + Starlight)

Documentation

See docs/ for the full documentation site, or run just docs-dev to browse locally.