[Tyr42]

So, Either String a <=> Maybe a, but with a nice reason something went wrong.

[mercurial]

Not quite. They are not restricted to error handling. You can have methods returning a Maybe something without it being an error (just like there are plenty of valid reasons for returning null instead of throwing an exception). You can also use Maybe in a data structure:

  data Employee = Employee { name : Text, spouse : Maybe Text }

You may also want to use Either to store two possible outcomes of an operation, though I would recommend using your own sum type for clarity:

  data MyOwnEither a b = MyLeft a | MyRight b