[GHC] #4099: Slighlty confusing error message with data families

[GHC]

#4099: Slighlty confusing error message with data families
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  Reporter:  rl                               |          Owner:                  
      Type:  bug                              |         Status:  closed          
  Priority:  normal                           |      Milestone:                  
 Component:  Compiler                         |        Version:  6.13            
Resolution:  fixed                            |       Keywords:                  
Difficulty:                                   |             Os:  Unknown/Multiple
  Testcase:  indexed-types/should_fail/T4099  |   Architecture:  Unknown/Multiple
   Failure:  None/Unknown                     |  
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Changes (by simonpj):

  * status:  new => closed
  * testcase:  => indexed-types/should_fail/T4099
  * resolution:  => fixed


Comment:

 Yes good point.  Fixed by
 {{{
 Mon May 31 15:04:13 BST 2010  simonpj at microsoft.com
   * Fix Trac #4099: better error message for type functions

   Now we only want about "T is a type function and might not be
   injective" when matchin (T x) against (T y), which is the case
   that is really confusing.

     M ./compiler/typecheck/TcTyFuns.lhs -14 +9
 }}}

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4099#comment:1>
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