[GHC] #4841: TypeSynonymInstances allow some flexible instances

[GHC]

#4841: TypeSynonymInstances allow some flexible instances
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  Reporter:  benmachine                   |          Owner:                  
      Type:  bug                          |         Status:  closed          
  Priority:  normal                       |      Milestone:                  
 Component:  Compiler                     |        Version:  7.0.1           
Resolution:  fixed                        |       Keywords:                  
  Testcase:                               |      Blockedby:                  
Difficulty:                               |             Os:  Unknown/Multiple
  Blocking:                               |   Architecture:  Unknown/Multiple
   Failure:  GHC accepts invalid program  |  
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Changes (by simonpj):

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


Comment:

 Fixed by
 {{{
 Tue Dec 14 09:47:55 PST 2010  simonpj at microsoft.com
   * Fix Trac #4841: behave right with TypeSynonymInstances and
 NoFlexibleInstances

   When we have TypeSynonymInstances without FlexibleInstances we should
 still
   insist on a H98-style instance head, after looking through the synonym.

   This patch also make FlexibleInstances imply TypeSynonymInstances.
 Anything
   else is a bit awkward, and not very useful.


     M ./compiler/main/DynFlags.hs +1
     M ./compiler/typecheck/TcType.lhs +3
     M ./docs/users_guide/flags.xml -2 +3
 }}}
 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4841#comment:2>
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