Control.Exceptional

Documentation

data Exceptional x

This is basically specialized 'Either String', or Maybe with error messages.

Constructors

Failure String

Success x

Instances

Monad Exceptional

This is fail-safe, so to speak. That is,

fail = Failure

Functor Exceptional

Applicative Exceptional

Alternative Exceptional

Eq x => Eq (Exceptional x)

Read x => Read (Exceptional x)

Show x => Show (Exceptional x)

runExceptional :: Monad m => Exceptional x -> m x

Convert Exceptional into another Monad. If you don't have proper exception handling in your monad, this can throw errors.

runExceptional (Failure s) = fail s
runExceptional (Success s) = pure s

fromMaybe :: String -> Maybe a -> Exceptional a

Convert a Maybe to an Exceptional

fromMaybe s Nothing = fail s
fromMaybe s (Just x) = pure x

toMaybe :: Exceptional a -> Maybe a

Convert an Exceptional into a Maybe. This function disregards the error message.

toMaybe (Success x) = Just x
toMaybe (Failure _) = Nothing

fromEither :: Either String a -> Exceptional a

Convert an Either String to an Exceptional

fromEither (Left s) = fail s
fromEither (Right x) = pure x

toEither :: Exceptional a -> Either String a

Convert an Exceptional to an Either String

toEither (Failure s) = Left s
toEither (Success x) = Right x