[GHC] #7701: compiler exception when -> is used instead of => in instance definition

[GHC]

#7701: compiler exception when -> is used instead of => in instance definition
-------------------------------+--------------------------------------------
Reporter:  erantapaa           |          Owner:          
    Type:  bug                 |         Status:  new     
Priority:  normal              |      Component:  Compiler
 Version:  7.4.2               |       Keywords:          
      Os:  MacOS X             |   Architecture:  x86     
 Failure:  Compile-time crash  |      Blockedby:          
Blocking:                      |        Related:          
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 When running ghci on the attached file, the following exception is raised:

 {{{
 *** Exception: compiler/rename/RnSource.lhs:430:14-81: Irrefutable pattern
 failed for pattern Data.Maybe.Just (inst_tyvars,
                                                         _,
                                                         SrcLoc.L _ cls,
                                                         _)
 }}}

 It seems to stem from accidentally using -> instead of => in the following
 instance definition:

 {{{
 instance (ListConcat xs ys zs) -> ListConcat (x ::: xs) ys (x ::: zs)
   where listConcat = undefined
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7701>
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