:: Either a b -> b package:either

Extracts the element out of a Right and throws an error if its argument take the form Left _. Using Control.Lens:

fromRight' x ≡ x^?!_Right

>>> fromRight' (Right 12)
12

Maybe get the Right side of an Either.

rightToMaybe ≡ either (const Nothing) Just

Using Control.Lens:

rightToMaybe ≡ preview _Right
rightToMaybe x ≡ x^?_Right

>>> rightToMaybe (Left 12)
Nothing

>>> rightToMaybe (Right 12)
Just 12