PureLint

A PureScript linter inspired by hlint, providing suggestions for cleaner, more idiomatic PureScript code.

Features

PureLint currently ships with 81 lint rules, covering common PureScript refactors and simplifications.

For a complete list, see lib/purslint/src/Purslint/Rules/.

Installation

npm (recommended)

npm install -g purslint

# CLI
purelint --help

Prerequisites

• PureScript compiler (purs)
• Spago package manager
• Go 1.19+
• psgo - PureScript to Go compiler

Building

# Install dependencies
spago install

# Build CLI
purs compile --codegen corefn 'lib/**/*.purs' 'bin/purslint-cli/**/*.purs' '.spago/**/*.purs'
psgo output/*/corefn.json
cp output/Main/Main.go main_cli.go
go build -o purelint main_cli.go

# Build LSP
purs compile --codegen corefn 'lib/**/*.purs' 'bin/purslint-lsp/**/*.purs' '.spago/**/*.purs'
psgo output/*/corefn.json
cp output/Main/Main.go main_lsp.go
go build -o purelint-lsp main_lsp.go

# Build and run tests
purs compile --codegen corefn 'lib/**/*.purs' 'test/**/*.purs' '.spago/**/*.purs'
psgo output/*/corefn.json
cp output/Test.Main/Test_Main.go test_main.go
go build -o test-runner test_main.go
./test-runner

Usage

CLI

# Lint a single file
./purelint src/Main.purs

# Lint multiple files
./purelint src/*.purs

# Lint with config file (optional)
./purelint --config purelint.json src/*.purs

LSP (Language Server Protocol)

The LSP binary (purelint-lsp) provides IDE integration. It communicates via stdio using the standard LSP protocol.

Zed Editor

A Zed extension is available in the zed-extension/ directory. To install:

1. Open Zed
2. Go to Extensions (Cmd+Shift+X)
3. Click "Install Dev Extension"
4. Select the zed-extension/ directory

The extension will automatically use the purelint-lsp binary.

Neovim (nvim-lspconfig)

After building purelint-lsp (see build steps below), you can configure Neovim like this:

require("lspconfig").purelint = {
  default_config = {
    cmd = { "/path/to/purelint-lsp" },
    filetypes = { "purescript" },
    root_dir = require("lspconfig.util").root_pattern(".git", "spago.yaml", "package.json"),
  },
}

require("lspconfig").purelint.setup({})

If you prefer to run the bundled JS directly:

cmd = { "node", "/path/to/dist/purelint-lsp.js" }

Configuration

Create a purelint.json file in your project root:

{
  "disabledRules": ["LetToWhere", "EtaReduce"]
}

Architecture

PureLint is written in PureScript and compiled to Go using psgo (purescript-native). This allows:

• Full access to the PureScript CST parser (purescript-language-cst-parser)
• Native binary performance
• Easy distribution without runtime dependencies

Project Structure

purelint/
├── lib/purslint/src/       # Core library
│   └── Purslint/
│       ├── Rules/          # Lint rules
│       ├── Runner.purs     # Rule runner
│       ├── Types.purs      # Core types
│       └── Imports.purs    # Import checking
├── bin/
│   ├── purslint-cli/       # CLI application
│   └── purslint-lsp/       # LSP server
├── test/                   # Test suite
└── zed-extension/          # Zed editor extension

Development

Publishing to npm

Publishing is handled by GitHub Actions. Add an NPM_TOKEN secret with an automation or granular token that has publish rights for purslint, then create a GitHub Release to trigger the workflow. You can also run it manually via the workflow dispatch.

Adding a New Rule

1. Create a new file in lib/purslint/src/Purslint/Rules/
2. Implement the rule using the CST traversal API
3. Export the rule from Purslint.Rules
4. Add tests in test/Test/Main.purs
5. Rebuild and test

Key Dependencies

• purescript-language-cst-parser - PureScript CST parser
• purescript-lsp - LSP protocol implementation (Go FFI)

License

MIT