generic-maybe utilizes GHC.Generics to generalize the functions of Data.Maybe to arbitrary sum types with two constructors, with one "empty."

Here is a quick example:

ë> :set -XDeriveGeneric

ë> import GHC.Generics

ë> data Result a = Success a | Fail deriving (Show, Generic)

ë> fromMaybe 'a' Fail

'a'

ë> fromMaybe 'a' $ Success 'b'

'b'

Additionally, it lets you convert between two representations:

ë> convert (Just 'a') :: Result Char

Success 'a'

Documentation on Hackage:

-Jonathan Fischoff