[Haskell-cafe] A type class puzzle

Jim Apple jbapple+haskell-cafe at gmail.com
Sat Nov 4 16:54:46 EST 2006

On 11/2/06, Yitzchak Gale <gale at sefer.org> wrote:
> GHC says:
>     Functional dependencies conflict between instance declarations:
>       instance Replace Zero a a (a -> a -> a)
>       instance (...) => Replace (Succ n) a [l] f'
> Not true. The type constraints on the second instance
> prevent any overlap.

GHC doesn't take constraints into account when checking fundeps.
You're looking for Sulzmann's Chameleon, which does all sorts of
constraint magic.


Also, I'd be surprized if Oleg didn't have a work-around in GHC.


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