[GHC] #8034: Missing ambiguity test for class methods

3 Jul 2013


      #8034: Missing ambiguity test for class methods
---------------------------------+------------------------------------------
    Reporter:  simonpj           |       Owner:                  
        Type:  bug               |      Status:  new             
    Priority:  normal            |   Milestone:  7.8.1           
   Component:  Compiler          |     Version:  7.7             
    Keywords:                    |          Os:  Unknown/Multiple
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown    
  Difficulty:  Unknown           |    Testcase:                  
   Blockedby:                    |    Blocking:                  
     Related:                    |  
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 If you write
 {{{
 type family F a
 foo :: F a -> F a
 foo = ...
 }}}
 then `foo` is rejected as having an ambiguous type.  But if instead you
 write
 {{{
 class C a where
   type F a
   foo :: F a -> F a
 }}}
 no such test is made.  That's inconsistent, and leads to downstream errors
 (see #8030 for example).  Better to do an ambiguity test.

-- 
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/8034
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