Fantomas vs Ormolu

Fantomas formats F# source code according to configuration, using default rules based on Microsoft’s F# style guide. Settings are also available for G-Research conventions. It runs as a .NET tool, and local installation is recommended when a repository needs to keep a fixed version. The command line accepts folders or files with `.fs`, `.fsi`, `.fsx`, `.ml` or `.mli` extensions; source files are expected to parse with the F# compiler before formatting. A limited selection of options can be placed in `.editorconfig` for automatic use by the command-line tool. For continuous integration checks, `dotnet fantomas check` reports formatting drift and exits with a failure code when files need formatting. Setup guides are available for JetBrains Rider, Visual Studio Code and Visual Studio, and the official site links to an online tool for trying the formatter and its settings. Fantomas and its library are available under the Apache 2.0 license. The project is described as an fsprojects incubation project. It is free and open source, with web access listed alongside Linux, macOS and Windows.

Ormolu is a formatter for Haskell source code. It uses GHC’s parser and applies one consistent style, with the aim of keeping diffs small. That style cannot be configured, and the project aims to leave code unchanged when it is formatted again after already meeting the style. Release binaries are available for Linux, macOS, and Windows; installation through cabal or stack is also supported. Ormolu Live provides a browser version. Listed editor integrations cover Emacs, VS Code, and Vim through neoformat or vim-ormolu, and Haskell Language Server has built-in support for Ormolu. For continuous integration, the project recommends the run-ormolu GitHub Action. It reads default language extensions and dependencies from a matching Cabal file;.ormolu files can specify fixity overrides and module re-export instructions. CPP support remains experimental and works only in simple cases where conditionals surround top-level declarations. Ormolu is open source and free, with a listed plan price of free.