:: a -> Maybe b -> Either a b -package:from-sum

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

Convert a Maybe to an Either.

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.

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