Hakyll + Sass

Sass.hs

module Sass (sass) where

import Control.Monad.IO.Class (liftIO)
import Text.Hakyll.File (makeDirectories, toDestination)
import Text.Hakyll.HakyllAction (HakyllAction(..), runHakyllActionIfNeeded)
import Text.Hakyll.HakyllMonad (Hakyll)

import System.FilePath (replaceExtension)
import System.Process (readProcess)

-- | Process a Sass stylesheet into a CSS file. Use like this:
--
-- > main = hakyll "http://example.com/" $ do
-- >     sass 'css/base.scss'
sass :: FilePath-> Hakyll ()
sass fp = runHakyllActionIfNeeded sass'
  where
    url = replaceExtension fp "css"
    sass' = HakyllAction
        { actionDependencies = [fp]
        , actionUrl = Left $ return url
        , actionFunction = \() -> do
            destination <- toDestination url
            makeDirectories destination
            liftIO $ readProcess "sass" [fp, destination] ""
            return ()
        }