[GHC] #7903: Failure to find class instance specified with extra parentheses

[GHC]

#7903: Failure to find class instance specified with extra parentheses
-----------------------------+----------------------------------------------
Reporter:  conal             |          Owner:                  
    Type:  bug               |         Status:  new             
Priority:  normal            |      Component:  Compiler        
 Version:  7.6.3             |       Keywords:                  
      Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
 Failure:  None/Unknown      |      Blockedby:                  
Blocking:                    |        Related:                  
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 The following two-line program fails to compile under GHC 7.6.3 and
 compiles fine with GHC 7.4.1:

 {{{
 instance Eq (((->) a) b)
 instance (Ord b) => Ord (((->) a) b)
 }}}

 Error message:

 {{{
     Could not deduce (Eq (a -> b))
       arising from the superclasses of an instance declaration
     from the context (Ord b)
 }}}
 Compilation goes through if I tweak the {{{Eq}}} instance to use "{{{((->)
 a b)}}}" or "{{{(a -> b)}}}" in place of "{{{(((->) a) b)}}}".

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7903>
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