:: a -> Maybe b -> Either a b -package:stamina

Given a Maybe, convert it to an Either, providing a suitable value for the Left should the value be Nothing.

\a b -> maybeToEither a (Just b) == Right b
\a -> maybeToEither a Nothing == Left a

Tag the Nothing value of a Maybe

Maybe produce a Right, otherwise produce a Left.

>>> maybeToRight "default" (Just 12)
Right 12

>>> maybeToRight "default" Nothing
Left "default"

Transform a Maybe value into an Either value. Just is mapped to Right and Nothing is mapped to Left. Default Left required.

A fromJust that fails in the Either monad

Convert Maybe to Either e, given an error e for the Nothing case.

Convert a Maybe to an Either. If the Maybe is Just, then return the value in Right.

>>> maybeToEither 3 $ Just "hello"
Right "hello"

If the Maybe is Nothing, then use the given e as Left.

>>> maybeToEither 3 Nothing
Left 3

Maps Maybe to Either wrapping default value into Left.

>>> maybeToRight True (Just "aba")
Right "aba"

>>> maybeToRight True Nothing
Left True

Turn Just into Right and Nothing into Left with the supplied value.

Create a Parse result from a Textual error message and a Maybe value

A fliped version of maybeToEither.

>>> maybeToEitherOr (Just "hello") 3
Right "hello"

>>> maybeToEitherOr Nothing 3
Left 3