[GHC] #1470: Overlapping (etc) instances

[GHC]

#1470: Overlapping (etc) instances
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 Reporter:  igloo                    |          Owner:  simonpj    
     Type:  bug                      |         Status:  closed     
 Priority:  normal                   |      Milestone:  6.10 branch
Component:  Compiler (Type checker)  |        Version:  6.6.1      
 Severity:  normal                   |     Resolution:  fixed      
 Keywords:                           |     Difficulty:  Unknown    
 Testcase:                           |   Architecture:  Unknown    
       Os:  Unknown                  |  
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Changes (by simonpj):

  * status:  new => closed
  * resolution:  => fixed

Comment:

 Fixed by
 {{{
 Thu Sep 18 17:17:19 GMT Daylight Time 2008  simonpj at microsoft.com
   * Fix Trac #1470: improve handling of recursive instances (needed for
 SYB3)

   This bug has been hanging around for a long time, as you'll see by its
   number. The fix implements a feature that is really needed by SYB3, to
   allow an instance to (rather indirectly) refer to itself.  The
 trickiness
   comes when solving the superclass constraints.

   The whoel issue is explained in Note [Recursive instances and
 superclases]
   in TcSimplify.

   In cracking this one I found I could remove the WantSCs argument to the
   ReduceMe flag, which is a worthwhile simplification.  Good!
 }}}
 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1470#comment:3>
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