hw-polysemy-0.2.4.0: core/HaskellWorks/Error.hs

module HaskellWorks.Error
  ( onLeft
  , onNothing
  , onLeftM
  , onNothingM
  ) where

import           HaskellWorks.Polysemy.Prelude

onLeft :: forall e m a. Monad m => (e -> m a) -> Either e a -> m a
onLeft f = either f pure

onNothing :: forall a m. Monad m => m a -> Maybe a -> m a
onNothing h = maybe h return

onLeftM :: forall e m a. Monad m => (e -> m a) -> m (Either e a) -> m a
onLeftM f action = onLeft f =<< action

onNothingM :: forall a m. Monad m => m a -> m (Maybe a) -> m a
onNothingM h f = onNothing h =<< f