[GHC] #2157: Equality Constraints with Type Families

[GHC]

#2157: Equality Constraints with Type Families
----------------------------------------+-----------------------------------
    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):

 Curiously if I have


 {{{
 fff a = fmapF a id
 }}}


 it compiles correctly.
 But if I infer the type signature of fff I get


 {{{
 fff :: forall d x. (FunctorF d) => d -> F d x -> F d x
 }}}


 On the other side, a similar problem as before arises when


 {{{
 fff :: forall d x. (FunctorF d) => d -> F d x -> F d x
 fff a = fmapF a id
 }}}


 fails to compile.
 This must be a bug. Sorry for all this posts.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2157#comment:6>
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