ZinzaPrelude.hs

-- | A small prelude used in @zinza@ generated
-- template modules.
module Distribution.ZinzaPrelude
  ( Writer
  , execWriter
  , tell

    -- * Re-exports
  , forM_
  , Generic
  , PackageName
  , Version
  , prettyShow
  ) where

import Distribution.Compat.Prelude
import Prelude ()

import Control.Monad (forM_)
import Distribution.Pretty (prettyShow)
import Distribution.Types.PackageName (PackageName)
import Distribution.Types.Version (Version)

newtype Writer a = W {unW :: ShowS -> (ShowS, a)}

instance Functor Writer where
  fmap = liftM

instance Applicative Writer where
  pure x = W $ \ss -> (ss, x)
  (<*>) = ap

instance Monad Writer where
  return = pure
  m >>= k = W $ \s1 ->
    let (s2, x) = unW m s1
     in unW (k x) s2
  {-# INLINE (>>=) #-}

execWriter :: Writer a -> String
execWriter w = fst (unW w id) ""

tell :: String -> Writer ()
tell s = W $ \s' -> (s' . showString s, ())