#2157: Equality Constraints with Type Families
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Reporter: hpacheco | Owner: chak
Type: feature request | Status: new
Priority: normal | Milestone:
Component: Compiler (Type checker) | Version: 6.9
Severity: normal | Resolution:
Keywords: | Testcase:
Architecture: Multiple | Os: Multiple
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Comment (by hpacheco):
Well, it seems to work if the add a "magic" dummy argument to fmapF.
{{{
class FunctorF x where
fmapF :: d -> (a -> b) -> F x a -> F x b
hylo :: (FunctorF d) => d -> (F d c -> c) -> (a -> F d a) -> a -> c
hylo d g h = g . fmapF d (hylo d g h) . h
}}}
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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2157#comment:5>
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