[GHC] #5676: Typeclass instance function type declarations

[GHC]

#5676: Typeclass instance function type declarations
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  Reporter:  drb226                          |          Owner:  simonpj                                     
      Type:  feature request                 |         Status:  closed                                      
  Priority:  normal                          |      Milestone:  7.6.1                                       
 Component:  Compiler (Type checker)         |        Version:                                              
Resolution:  fixed                           |       Keywords:  typeclass instance function type declaration
        Os:  Unknown/Multiple                |   Architecture:  Unknown/Multiple                            
   Failure:  GHC rejects valid program       |     Difficulty:  Unknown                                     
  Testcase:  typecheck/should_compile/T5676  |      Blockedby:                                              
  Blocking:                                  |        Related:                                              
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Comment(by mgsloan1):

 Glad to see that there's a fix for this!

 I ran into this recently.  For now I will place the implementation
 elsewhere, but I wanted to mention an additional reason for this to be
 possible - ScopedTypeVariables.  You can't get type variables in scope, to
 reference in where declarations unless you allow type signatures in
 instances.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5676#comment:9>
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