[GHC] #7786: strange errors when deducing constraints

[GHC]

#7786: strange errors when deducing constraints
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    Reporter:  heisenbug         |       Owner:  simonpj         
        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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Comment(by simonpj@…):

 commit 6ebab3df7e68f8325ef60111c0c7755dd6ffcc91
 {{{
 Author: Simon Peyton Jones <simonpj at microsoft.com>
 Date:   Mon Apr 22 12:50:24 2013 +0100

     Never unify a SigTyVar with a non-tyvar type (fixes Trac #7786)

     This unwanted unification was happening in the zonking phase
     which un-flattens type-function applications (TcMType.zonkFlats,
     try_zonk_fun_eq).  The main unifier is careful to make the check,
     but I'd forgotten it here.  That in turn led to a very confusing
     error message.

  compiler/typecheck/TcMType.lhs |    4 ++--
  1 files changed, 2 insertions(+), 2 deletions(-)
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7786#comment:3>
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