[Haskell-cafe] Aren't type system extensions fun?
dons at galois.com
Mon May 26 17:22:15 EDT 2008
> Today I was reading a potentially interesting paper, and I stumbled
> across something referred to as a "rank-2 type". Specifically,
> class Typable x => Term x where
> gmapT :: (forall y. Term y => y -> y) -> x -> x
> At this point, I am at a complete loss as to how this is any different from
> gmapT :: Term y => (y -> y) -> x -> x
> Can anybody enlighten me?
If in doubt, consult the fine user's guide:
Section 8.7.4. Arbitrary-rank polymorphism
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