[Haskell-cafe] Re: The Proliferation of List-Like Types

Neil Mitchell ndmitchell at gmail.com
Wed Feb 20 11:31:48 EST 2008


>  >       full -> Maybe (item, full)
>  Hrm, what exactly is the return data here?  Is is the head and the
>  tail if the list has >= 1 item, or Nothing otherwise?  Or...?

Yes, its the projection onto another type:

[] = Nothing
(x:xs) = Just (x, xs)

>  What is the problem with MPTC in base?

MPTC is not a part of any Haskell standard. The rules surrounding MPTC
are not clear. People want to remove MPTC's/functional dependencies,
or modify them with associated types. Compilers such as nhc and yhc
can't implement them. Once they are in Haskell', with an associated
set of restrictions/overlap rules etc, then they can be freely used
with the base library.



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