[GHC] #7837: Rules involving equality constraints don't fire

[GHC]

#7837: Rules involving equality constraints don't fire
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Reporter:  akio                     |          Owner:                           
    Type:  bug                      |         Status:  new                      
Priority:  normal                   |      Component:  Compiler                 
 Version:  7.6.2                    |       Keywords:  equality constraint,rules
      Os:  Unknown/Multiple         |   Architecture:  Unknown/Multiple         
 Failure:  Runtime performance bug  |      Blockedby:                           
Blocking:                           |        Related:                           
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Comment(by simonpj@…):

 commit 29cc690e8a6c154973de27d7bb49aa2a47b51dc7
 {{{
 Author: Simon Peyton Jones <simonpj at microsoft.com>
 Date:   Tue Apr 16 10:33:13 2013 +0100

     Make the desugarer a tiny bit cleverer on coercions (fixes Trac #7837)

     The desugarer was generating a redundant box/unbox pair on the
     LHS of a RULE, which in turn made matching fail.

     See Note [Simple coercions] in DsBinds.

  compiler/deSugar/DsBinds.lhs |   33 +++++++++++++++++++++++++++++++--
  1 files changed, 31 insertions(+), 2 deletions(-)
 }}}

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7837#comment:2>
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