Install hlint with Homebrew, apk, apt, dnf, MacPorts, Nix, pacman, zypper

Project links

• Homepage
• Upstream docs
• Package manager page

Commands and aliases

• hlint

Project history

The hlint.cabal file gives Neil Mitchell as author and maintainer and carries a copyright line beginning in 2006. Neil Mitchell's publication page ties HLint to a longer research and tooling thread around transformation and analysis of Haskell source code, including a 2007 thesis seminar and a 2008 PhD thesis on functional-program transformation and analysis.

HLint's README describes its core purpose as suggesting possible improvements such as alternative functions, code simplification, and spotting redundancies. It deliberately operates on modules in isolation rather than typechecking whole projects, a tradeoff that lets it parallelize, run incrementally, and analyze code that may not compile yet.

In 2017, HLint 2.0 moved configuration toward YAML. Neil Mitchell's release post says earlier configuration used specially crafted Haskell files, while HLint 2.0 added .hlint.yaml search from the working directory upward and encouraged YAML because the Haskell-based format had become overloaded.

By 2020, HLint had undergone a major parser migration. Mitchell's MuniHac talk abstract describes HLint as over 14 years old, notes changes in license, project name, source control, and configuration, and explains the move from haskell-src-exts toward the GHC API via ghc-lib as GHC compatibility became more important.

Adoption history

HLint became a standard Haskell development utility because it can be run cheaply during local development, code review, and CI. The README documents installation through the ordinary Haskell toolchain, direct binary use in CI, and workflows that generate an initial report before committing a project-specific .hlint.yaml baseline.

The README also documents broad integration: editor plugins, Haskell Language Server, ghc-mod, Intero, GHC source plugins, Code Climate, Danger, Restyled, HLint test helpers, GitHub Actions, and code-scanning workflows. That integration footprint made HLint visible both to individual Haskell developers and to larger codebases enforcing house style.

How it is used

A normal run is hlint source, where source is a file or directory. HLint recursively scans .hs and .lhs files, reports file/line locations, severity, the code it found, and a possible replacement. For larger projects, hlint . --report creates an HTML report, and hlint . --default can create a .hlint.yaml file that records outstanding hints.

HLint suggestions are intentionally advisory. The README warns that most hints are good ideas in many circumstances but should not be applied blindly, especially when contributing to another project or when language extensions and laziness semantics matter.

Why package nerds care

HLint is one of the canonical Haskell developer-tool packages: small enough to run locally, opinionated enough to teach idioms, and integrated enough to show up in editors, CI, code review bots, and language-server diagnostics.

For package maintainers, HLint matters because it externalizes style and simplification rules into a configurable tool. Projects can ship .hlint.yaml to encode local decisions, silence accepted warnings, and add custom hints without requiring every contributor to internalize the entire style guide.

Its long parser and configuration evolution also mirrors the Haskell ecosystem's own tooling history: from custom parsers and Haskell-flavored config toward YAML project files, ghc-lib, and tighter integration with the compiler and language-server stack.

Timeline

• 2006: HLint authorship/copyright line begins in hlint.cabal.
• 2007: Neil Mitchell presented work on transformation and analysis of Haskell source code.
• 2008: Neil Mitchell's PhD thesis on transformation and analysis of functional programs was published.
• 2013: The ndmitchell/hlint GitHub repository was created.
• 2017-04-06: HLint 2.0 introduced YAML configuration and .hlint.yaml search.
• 2020-09-11: The MuniHac talk described HLint's migration to the GHC API parser via ghc-lib.

Related projects

• GHC and ghc-lib: parser/compiler infrastructure used by HLint's later parser architecture.
• haskell-src-exts: the parser library HLint used before the GHC API migration.
• Haskell Language Server, ghc-mod, Intero: Haskell tooling integrations named by the README.
• apply-refact: the refactoring helper used when HLint applies suggestions with --refactor.

Sources

• https://api.github.com/repos/ndmitchell/hlint
• https://ndmitchell.com/
• https://neilmitchell.blogspot.com/2017/04/hlint-20-with-yaml-configuration.html
• https://raw.githubusercontent.com/ndmitchell/hlint/master/README.md
• https://raw.githubusercontent.com/ndmitchell/hlint/master/hlint.cabal
• input: source_facts.package-manager