A fast, opinionated, batteries-included toolchain for Haskell.
Haskell, finally fast.

Documentation • Features • Benchmarks • Contributing

---

hx is a modern toolchain CLI for Haskell, written in Rust. It wraps existing tools (GHC, Cabal, GHCup, HLS) in a fast, unified interface with excellent error messages and deterministic builds.

Features

• Fast feedback loop - Common workflows are snappy with parallel builds
• Deterministic builds - Lockfile + frozen plans for reproducibility
• Native builds - Direct GHC invocation without cabal for simple projects
• Excellent errors - Actionable messages with fix suggestions
• Watch mode - Auto-rebuild on file changes
• Test coverage - Integrated hpc support with HTML reports
• Plugin system - Extensible with Steel (Scheme) scripts
• Self-contained - Manages GHC versions directly, no ghcup required

Installation

From releases

# macOS/Linux
curl -fsSL https://raw.githubusercontent.com/raskell-io/hx/main/install.sh | sh

# Or download from releases
https://github.com/raskell-io/hx/releases

From source

cargo install --git https://github.com/raskell-io/hx hx-cli

Verify installation

hx --version
hx doctor

Quick Start

# Create a new project
hx init myapp
cd myapp

# Build and run
hx build
hx run

# Lock dependencies for reproducibility
hx lock
hx sync

# Watch for changes
hx watch

Commands

Project Management

hx init                      # Initialize in current directory
hx init myapp                # Create myapp/ and initialize
hx init --lib                # Create a library project
hx init --ci                 # Include GitHub Actions workflow

hx new webapp myapp          # Create web app (Servant)
hx new cli myapp             # Create CLI app (optparse-applicative)
hx new library mylib         # Create library with docs setup
hx new --template user/repo  # Create from git template

Building

hx build                     # Build the project
hx build --release           # Build with optimizations
hx build --native            # Use native GHC build (no cabal)
hx build -j4                 # Parallel build with 4 jobs
hx check                     # Fast type-check
hx clean                     # Clean build artifacts

Running & Testing

hx run                       # Build and run the executable
hx run -- arg1 arg2          # Pass arguments to the program
hx repl                      # Start an interactive GHCi session
hx test                      # Run tests
hx test --pattern "Unit"     # Filter tests by pattern
hx bench                     # Run benchmarks

Watch Mode

hx watch                     # Auto-rebuild on file changes
hx watch --test              # Auto-run tests on changes
hx watch --clear             # Clear terminal between runs

Dependencies

hx lock                      # Generate/update hx.lock
hx lock --update             # Update all dependencies
hx sync                      # Build with locked dependencies
hx fetch                     # Pre-fetch dependencies in parallel

hx add text                  # Add a dependency
hx add aeson ">=2.0"         # Add with version constraint
hx add --dev hspec           # Add dev dependency
hx rm text                   # Remove a dependency

hx why text                  # Show why a package is a dependency
hx info aeson                # Show package details from Hackage
hx info aeson --versions     # Include all available versions
hx outdated                  # Check for outdated dependencies
hx outdated --direct         # Only show direct dependencies
hx update                    # Update dependencies (minor/patch)
hx update --major            # Allow major version updates
hx update --dry-run          # Preview updates without applying
hx update aeson text         # Update specific packages

hx tree                      # Show dependency tree
hx tree --depth 2            # Limit tree depth
hx list                      # List all dependencies
hx list --direct             # List direct dependencies only

hx deps graph --format dot   # Generate Graphviz graph

hx search aeson              # Search Hackage for packages
hx audit                     # Check for vulnerabilities
hx audit --outdated          # Check for outdated packages

Code Quality

hx fmt                       # Format code with fourmolu
hx fmt --check               # Check formatting without changes
hx lint                      # Run hlint
hx lint --fix                # Apply automatic fixes

Test Coverage

hx coverage                  # Run tests with coverage
hx coverage --html           # Generate HTML report
hx coverage --html --open    # Generate and open in browser
hx coverage --threshold 80   # Fail if below 80% coverage
hx coverage --json           # Output JSON for CI

Profiling

hx profile                   # Run with time profiling
hx profile --heap            # Run with heap profiling
hx profile --time --heap     # Both time and heap

Documentation

hx docs                      # Generate documentation
hx docs --open               # Generate and open in browser
hx docs --deps               # Include dependency docs
hx docs --serve              # Serve locally on port 8080

Toolchain Management

hx toolchain status          # Show installed versions
hx toolchain list            # List all available versions
hx toolchain list --installed # List installed versions only

hx toolchain install 9.8.2   # Install GHC version
hx toolchain install --set   # Install and set as active
hx toolchain remove 9.6.4    # Remove a GHC version

hx toolchain use 9.8.2       # Switch GHC version
hx toolchain use project     # Use project's toolchain

IDE Integration

hx ide setup                 # Generate hie.yaml for HLS
hx ide status                # Check IDE configuration
hx lsp                       # Start language server

Publishing

hx publish                   # Publish to Hackage
hx publish --dry-run         # Validate without uploading
hx publish --docs            # Include documentation
hx changelog                 # Generate CHANGELOG from commits
hx changelog --preview       # Preview without writing

Distribution

hx dist                      # Build release archive
hx dist --target x86_64-unknown-linux-musl  # Cross-compile
hx dist formula              # Generate Homebrew formula
hx dist install-script       # Generate install script

Utilities

hx doctor                    # Diagnose setup issues
hx script file.hs            # Run single-file script
hx import --from stack       # Import from stack.yaml
hx nix flake                 # Generate flake.nix
hx nix shell                 # Generate shell.nix
hx completions install       # Auto-install completions for your shell
hx completions generate bash # Generate completions to stdout
hx upgrade                   # Upgrade hx to latest version

Cache Management

hx cache status              # Show cache statistics
hx cache prune --days 30     # Remove entries older than 30 days
hx cache clean               # Clear entire cache
hx index update              # Update Hackage package index
hx index status              # Show index status

Plugins

hx plugins list              # List available plugins
hx plugins status            # Show plugin system status
hx plugins run script.scm    # Run a Steel script

Configuration

hx uses hx.toml for project configuration:

[project]
name = "myapp"
kind = "bin"         # or "lib"
resolver = "cabal"

[toolchain]
ghc = "9.8.2"
cabal = "3.12.1.0"
hls = "2.9.0.0"

[build]
optimization = 2     # 0, 1, or 2
warnings = true
native = false       # Use native GHC builds

[format]
formatter = "fourmolu"

[lint]
hlint = true

[plugins]
enabled = true
hook_timeout_ms = 30000

[plugins.hooks]
pre_build = ["./scripts/check.scm"]
post_test = ["./scripts/notify.scm"]

Global Configuration

hx supports global configuration at ~/.config/hx/config.toml (Linux), ~/Library/Application Support/hx/config.toml (macOS), or %APPDATA%\hx\config\config.toml (Windows).

Global settings provide defaults that can be overridden by project-local hx.toml:

# ~/.config/hx/config.toml

[toolchain]
ghc = "9.8.2"
cabal = "3.12.1.0"

[build]
optimization = 1
warnings = true

[format]
formatter = "fourmolu"

[lint]
hlint = true

Managing Global Config

hx config show           # Show current global configuration
hx config path           # Show path to global config file
hx config edit           # Open config file in your $EDITOR
hx config init           # Create default config file
hx config set <key> <val> # Set a configuration value
hx config get <key>      # Get a configuration value

# Examples:
hx config set toolchain.ghc 9.8.2
hx config set build.optimization 2
hx config set format.formatter ormolu

Lockfile

The hx.lock file ensures reproducible builds:

version = 1
created_at = "2026-01-16T00:00:00Z"

[toolchain]
ghc = "9.8.2"
cabal = "3.12.1.0"

[plan]
compiler_id = "ghc-9.8.2"
platform = "x86_64-linux"
hash = "sha256:..."

[[packages]]
name = "text"
version = "2.1.1"

Environment Variables

Variable	Description
HX_VERBOSE	Enable verbose output
HX_QUIET	Suppress output
HX_NO_COLOR	Disable colored output
HX_CONFIG_FILE	Path to config file
HX_CACHE_DIR	Cache directory location
HX_AUTO_INSTALL	Auto-install missing toolchains
HX_NO_AUTO_INSTALL	Never auto-install toolchains

Exit Codes

Code	Meaning
0	Success
1	General error
2	Usage error
3	Configuration error
4	Toolchain error
5	Build/test failure
6	Plugin hook failure

Architecture

hx is a Rust workspace with these crates:

Crate	Purpose
hx-cli	Command-line interface
hx-core	Shared types and utilities
hx-config	Configuration parsing
hx-lock	Lockfile management
hx-toolchain	GHC/Cabal detection and installation
hx-cabal	Cabal wrapper and native builds
hx-cache	Build cache management
hx-doctor	Diagnostic checks
hx-solver	Native dependency resolver
hx-lsp	Language server protocol
hx-plugins	Steel plugin runtime
hx-ui	Terminal output utilities
hx-warnings	Warning system
hx-telemetry	Tracing and metrics

Development

# Build
cargo build

# Run tests
cargo test --workspace

# Run clippy
cargo clippy --workspace -- -D warnings

# Format
cargo fmt

# Run hx locally
cargo run -p hx-cli -- --help

Philosophy

hx follows the Astral approach:

1. Wrap first - Use existing tools (Cabal, GHC) rather than reimplementing
2. Tame second - Add better UX, error messages, and workflows
3. Replace last - Only replace components when truly necessary (native builds)

License

MIT