Fourmolu vs Prettier

Fourmolu is a configurable formatter for Haskell source code and a fork of Ormolu. It uses GHC’s parser and aims to keep diffs small, produce idempotent output, and handle large projects. Set formatting options in `fourmolu.yaml` or pass them on the command line. Controls include indentation, line length, import grouping, record layout, Haddock comments, Unicode output, and operator fixities. Fourmolu can find the relevant Cabal file to read default extensions and dependencies that help determine fixities. Magic comments can disable formatting for selected code, and command-line options can target a line region. There is an interactive browser demo with configurable formatting and program options. Installation instructions cover GHCup, Cabal, Stack, and dotslash; editor integration is documented through Haskell Language Server. The project recommends a GitHub Action to keep projects formatted. Its listed current release is v0.21.0.0. CPP handling is experimental and limited to simple cases where conditionals surround top-level declarations. Output always uses LF line endings, which can cause check mode to fail on CRLF files.

Prettier is an open-source code formatter that parses source files and prints them in a consistent style while accounting for line length. Its built-in languages include JavaScript, JSX, Angular, Vue, Flow, TypeScript, CSS, Less, SCSS, HTML, JSON, GraphQL, Markdown, YAML, LWC, and MJML. The command-line interface can write formatted files with --write or check formatting with --check in continuous integration. Listed editor integrations include VS Code, Emacs, Vim, Helix, Sublime Text, JetBrains IDEs, Visual Studio, and Espresso; formatting can run from a shortcut or on save. Prettier has configuration options but keeps them limited. Plugins can add languages and formatting rules, and languages outside the built-in set require a plugin. For ESLint integration, the installation guidance recommends eslint-config-prettier to disable rules that are unnecessary or may conflict. Prettier supports browser and JavaScript API use, along with Linux, macOS, and Windows. The listed plan is free. Commercial support and maintenance are available through the Tidelift Subscription.