[GHC] #7804: Ambiguity check too eager in presence of RankNTypes and TypeFamilies

[GHC]

#7804: Ambiguity check too eager in presence of RankNTypes and TypeFamilies
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Reporter:  goldfire                   |          Owner:                  
    Type:  bug                        |         Status:  new             
Priority:  normal                     |      Component:  Compiler        
 Version:  7.7                        |       Keywords:  AmbiguityCheck  
      Os:  Unknown/Multiple           |   Architecture:  Unknown/Multiple
 Failure:  GHC rejects valid program  |      Blockedby:                  
Blocking:                             |        Related:                  
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Comment(by simonpj@…):

 commit f3bfbd585afe178edb3d6afafceb116041eaafb6
 {{{
 Author: Simon Peyton Jones <simonpj at microsoft.com>
 Date:   Wed Apr 3 18:20:07 2013 +0100

     Fix Trac #7804, about floating equalites

     We float unsolved equalities from underneath a 'forall', to
     help solve them, in TcSimplify.floatEqualities.

     It's regrettably delicate though,as this bug shows. I'm not
     happy with the new code; but there are copious notes; see
     Note [Float equalities from under a skolem binding].

  compiler/typecheck/TcSimplify.lhs |   69
 +++++++++++++++++++++++++++++-------
  1 files changed, 55 insertions(+), 14 deletions(-)
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7804#comment:1>
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