Hew

A statically-typed, actor-oriented programming language for concurrent and distributed systems.

Website | Documentation | Playground | Tutorial

Install

curl -fsSL https://hew.sh/install.sh | bash

Pre-built binaries for Linux (x86_64) and macOS (x86_64, ARM) are available on the Releases page. Also available via Homebrew, Docker, and system packages.

Quick Start

# Hello world
echo 'fn main() { println("Hello from Hew!"); }' > hello.hew
hew run hello.hew

# Start a new project
adze init my_project
cd my_project
hew run src/main.hew

# Interactive REPL
hew eval

See the Getting Started Guide for more.

Architecture

The compiler has three layers: Rust frontend → MLIR middle layer → LLVM backend.

source.hew → [hew: Rust frontend]
               ├─ Lexer (hew-lexer)
               ├─ Parser (hew-parser)
               ├─ Type Checker (hew-types)
               ├─ MessagePack Serialize (hew-serialize)
               └─ [hew-codegen: C++ MLIR middle layer]
                    ├─ MessagePack AST → Hew dialect MLIR
                    ├─ Hew dialect lowering → func/arith/scf/llvm
                    └─ LLVM backend → .o (x86_64, wasm32, etc.)
               └─ [hew: linker invocation]
                    └─ cc .o + libhew_runtime.a → executable

Repository Structure

Compiler

• hew-cli/ — Compiler driver (hew binary)
• hew-lexer/ — Tokenizer
• hew-parser/ — Recursive-descent + Pratt precedence parser
• hew-types/ — Bidirectional type checker with Hindley-Milner inference
• hew-serialize/ — MessagePack AST serialization
• hew-codegen/ — MLIR middle layer + LLVM backend (Hew dialect ops, lowering, code generation)
• hew-astgen/ — Generates C++ msgpack deserialization from AST definitions
• hew-runtime/ — Pure Rust actor runtime (libhew_runtime.a); also compiles for WASM targets
• hew-cabi/ — C ABI bridge for stdlib FFI bindings

Package Manager & Tooling

• adze-cli/ — Package manager (adze binary) — init, install, publish, search
• hew-lsp/ — Language server (tower-lsp)
• hew-observe/ — Runtime observability TUI (hew-observe)
• hew-wasm/ — Frontend compiled to WASM for in-browser diagnostics

Standard Library & Build Support

• std/ — Standard library modules (.hew source files + Rust FFI crates)
• hew-export-macro/ — Proc macro for stdlib export declarations
• hew-export-types/ — Shared types for the export system
• hew-stdlib-gen/ — Generates stdlib module descriptors for the type checker

Distribution

• editors/ — Editor support (Emacs, Nano, Sublime)
• completions/ — Shell completions (bash, zsh, fish)
• installers/ — Package installers (Homebrew, Debian, RPM, Arch, Alpine, Nix, Docker)
• examples/ — Example programs and benchmarks
• scripts/ — Development scripts
• docs/ — Language specification and API references

Documentation

Full documentation at hew.sh/docs

Website source: github.com/hew-lang/hew.sh

Building from Source

Prerequisites

Dependency	Version	Purpose
Rust	stable (latest)	Frontend compiler, runtime, package manager
LLVM	21.1	MLIR code generation and LLVM backend
MLIR	(bundled with LLVM 21)	Hew dialect and lowering passes
CMake	>= 3.20	Builds hew-codegen (C++ MLIR backend)
Ninja	any	CMake build generator
clang/clang++	any (LLVM 21 preferred)	C/C++ compilation of hew-codegen

Install on Ubuntu/Debian:

# Rust
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

# LLVM 21 + MLIR
sudo mkdir -p /etc/apt/keyrings
wget -qO- https://apt.llvm.org/llvm-snapshot.gpg.key \
  | sudo tee /etc/apt/keyrings/llvm.asc >/dev/null
echo "deb [signed-by=/etc/apt/keyrings/llvm.asc] http://apt.llvm.org/noble/ llvm-toolchain-noble-21 main" \
  | sudo tee /etc/apt/sources.list.d/llvm.list >/dev/null
sudo apt-get update
sudo apt-get install -y cmake ninja-build \
  llvm-21-dev libmlir-21-dev mlir-21-tools clang-21

Install on macOS:

# Rust
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

# LLVM 21 + MLIR
brew install llvm@21 ninja cmake

Build

make          # Build everything (debug)
make release  # Build everything (optimized)
make test     # Run Rust + native codegen tests
make lint     # cargo clippy

See make help or the Makefile header for all targets.

Optional Dependencies

These are only needed for specific workflows:

Dependency	Install	Purpose
wasmtime	curl https://wasmtime.dev/install.sh -sSf | bash	Run WASM tests (make test-wasm)
wasm32-wasip1 target	rustup target add wasm32-wasip1	Build WASM runtime (make wasm-runtime)
Python 3	system package manager	Visualization and fuzzing scripts (scripts/)
Java 21 + ANTLR4	system package manager	Grammar validation (make grammar)
cargo-fuzz	cargo install cargo-fuzz	Parser fuzzing (hew-parser/fuzz/)

License

Hew is distributed under the terms of both the MIT license and the Apache License (Version 2.0).

See LICENSE-MIT and LICENSE-APACHE for details.