On Thu, Jan 10, 2019 at 04:23:49PM +0100, Damien Mattei wrote:
Le 10/01/2019 15:27, Tom Ellis a écrit :
On Thu, Jan 10, 2019 at 12:34:04PM +0100, Damien Mattei wrote:
i have this definition:
{-# LANGUAGE FlexibleInstances #-}
class ConcatenateMaybeString a where cms :: Maybe String -> a -> Maybe String
instance ConcatenateMaybeString (Maybe String) where cms mf ms = mf >>= (\f -> ms >>= (\s -> return (f ++ s)))
instance ConcatenateMaybeString String where cms mf s = mf >>= (\f -> return (f ++ s))
Trying to simulate overloading like this is ultimately going to lead to more frustration than benefit. I strongly suggest you just define two different functions.
those functions could be seen as a "style exercise" , for me,coming from untyped languages such as Scheme or LisP it's Haskell which is a frustration :-)
I think you're going to get significantly more frustrated with Haskell if you try to learn it like this by yourself rather than by working through some widely approved teaching resource. Of course, how you spend your time is up to you, but if you're frustrated with Haskell then trying to make it up as you go along is only going to worsen the feeling!