Re: [Haskell-cafe] Why Maybe exists if there is Either?

9 Jan 2014


      Brandon Allbery  writes:
...
On Thu, Jan 9, 2014 at 12:11 PM, Ben Foppa  wrote:
...
Aside from the point made about typeclass instances, I don't see an issue
with:
type Maybe = Either ()
nothing :: Maybe a
nothing = Left ()
just :: a -> Maybe a
just = Right
Not until you try to pattern match on it....
Although with pattern synonyms[1][2] this will become possible if I'm
not mistaken,

    pattern Nothing = Left ()
    pattern Just a = Right a

Cheers,

- Ben


[1] https://ghc.haskell.org/trac/ghc/ticket/5144
[2] https://ghc.haskell.org/trac/ghc/wiki/PatternSynonyms

Re: [Haskell-cafe] Why Maybe exists if there is Either?

Ben Gamari