[Haskell-cafe] Re: Type parameters in type families
Ryan Ingram
ryani.spam at gmail.com
Tue Mar 18 15:03:40 EDT 2008
On 3/17/08, Hugo Pacheco <hpacheco at gmail.com> wrote:
> On the other side, it fails to compile when this signature is explicit:
> fff :: forall d x. (FunctorF d) => d -> F d x -> F d x
> fff a = fmapF a id
Interestingly, this works when you also give a type signature to "id":
fff :: forall d x. (FunctorF d) => d -> F d x -> F d x
fff a = fmapF a (id :: x -> x)
compiles for me (ghc6.8.2). There's probably a bug in the type
checker; inference is working with no type signatures, but checking
fails.
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