[Haskell-cafe] Why can't we make an instance declaration on a
daniel.is.fischer at web.de
Sun Jan 3 00:18:34 EST 2010
Am Sonntag 03 Januar 2010 05:37:31 schrieb Jason Dusek:
> Well, you can, with:
> though I'm not sure it addresses your specific need.
Doesn't help him here, he would need
instance Monad (State s) where ...
but that would be a partially applied type synonym. He would also need type level lambdas,
type State s = /\ a -> (s -> (a,s))
But type level lambdas and partially applied type synonyms make type inference undecidable
if I remember correctly (if it wasn't that, they'd have other dire consequences).
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