Utils.hs

-- | These functions should be built-in haskell... But their not :(
--
-- The function type is the documentation for most of these functions

module Festung.Utils 
  ( eitherUnitToMaybe
  , hoistMEither
  , mapLeft
  , whenJust
  , getVersion
  ) where


import Paths_festung              (version)
import Data.Version               (showVersion)
import Data.Either                (either)
import Control.Monad.Trans.Class  (lift)
import Control.Monad.Trans.Either (hoistEither, EitherT)
import Control.Monad              (join)


getVersion :: String
getVersion = showVersion version


eitherUnitToMaybe :: Either () a -> Maybe a
eitherUnitToMaybe = either (const Nothing) Just


-- | Lift an @'Either' contain in a monad into an @'EitherT'
hoistMEither :: Monad m => m (Either e a) -> EitherT e m a
hoistMEither meither = join $ lift $ fmap hoistEither meither


mapLeft :: (a -> c) -> Either a b -> Either c b
mapLeft f = either (Left . f) Right


whenJust :: Monad m => Maybe a -> (a -> m ()) -> m ()
whenJust (Just x) f = f x
whenJust Nothing  _ = return ()