genvalidity-sydtest-1.0.0.0: src/Test/Syd/Validity/Types.hs

{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE ScopedTypeVariables #-}

module Test.Syd.Validity.Types
  ( CanFail (..),
  )
where

-- | A class of types that are the result of functions that can fail
class CanFail f where
  hasFailed :: f a -> Bool
  resultIfSucceeded :: f a -> Maybe a

instance CanFail Maybe where
  hasFailed Nothing = True
  hasFailed _ = False
  resultIfSucceeded Nothing = Nothing
  resultIfSucceeded (Just r) = Just r

instance CanFail (Either e) where
  hasFailed (Left _) = True
  hasFailed _ = False
  resultIfSucceeded (Left _) = Nothing
  resultIfSucceeded (Right r) = Just r