Let stylish-haskell loose on a directory and all its subdirectories.

StyleAll.hs

{-# LANGUAGE UnicodeSyntax #-}
module StyleAll where


import           Control.Monad
import           Control.Monad.Unicode
import           Data.Bool
import           Prelude.Unicode
import           System.Directory
import           System.Environment
import           System.FilePath
import           System.Process


styleCmd = callCommand ∘ ("stylish-haskell -i " ⧺)


handleOne file =
  doesFileExist file ≫=
    bool
      (getDirectoryContents file ≫= mapM_ (handleOne ∘ (file </>)) ∘ filter (not ∘ (∈ [".", ".."])) )
      (when (takeExtension file ∈ [".hs", ".lhs"]) $ styleCmd file)


main =
  getArgs ≫= mapM_ handleOne