haskell-format

name	haskell-format
description	Format Haskell source files — `*.hs`, `*.lhs`, `*.hsig` — with the project's configured formatter (fourmolu, ormolu, or stylish-haskell). Use when: (1) formatting Haskell source before compiling, (2) tidying code after edits, (3) applying a project's fourmolu/stylish style. Picks the formatter from project config, falling back to the first available. Trigger: "/haskell-format", "format Haskell", "fourmolu", "ormolu", "stylish-haskell".
allowed-tools	["Bash","Read","Glob","Grep"]

Format Haskell source (.hs / .lhs / .hsig)

Formats Haskell source files with the project's formatter. (.cabal / cabal.project files are handled by /haskell-cabal-gild, not here.) Always format before compiling.

Choosing the formatter

Walk up from the file's directory and pick by config, else the first tool available:

1. fourmolu.yaml / .fourmolu.yaml present → fourmolu
2. .stylish-haskell.yaml present → stylish-haskell
3. otherwise the first of fourmolu → ormolu → stylish-haskell found on PATH.

Format in place

All three accept -i as the in-place shortcut:

fourmolu -i <file>        # or: ormolu -i <file> / stylish-haskell -i <file>

Automatic on save

This plugin installs a PostToolUse hook (scripts/haskell-format-on-save.sh) that formats any .hs/.lhs/.hsig file in place right after it is written. After the hook reformats a file, re-read it before editing again. Manual invocation is mainly for bulk formatting.

Companion

.cabal / cabal.project files are formatted by /haskell-cabal-gild.