Re: [GHC] #4355: Coud not deduce (Typeable a) from context (Typeable a, …)

[GHC]

#4355: Coud not deduce (Typeable a) from context (Typeable a, …)
---------------------------------------------+------------------------------
  Reporter:  maltem                          |          Owner:  simonpj         
      Type:  bug                             |         Status:  closed          
  Priority:  high                            |      Milestone:  7.0.1           
 Component:  Compiler (Type checker)         |        Version:  7.1             
Resolution:  fixed                           |       Keywords:                  
  Testcase:  typecheck/should_compile/T4355  |      Blockedby:                  
Difficulty:                                  |             Os:  Unknown/Multiple
  Blocking:                                  |   Architecture:  Unknown/Multiple
   Failure:  None/Unknown                    |  
---------------------------------------------+------------------------------
Changes (by simonpj):

  * status:  new => closed
  * testcase:  => typecheck/should_compile/T4355
  * resolution:  => fixed


Comment:

 Excellent.  Fixed by this lovely patch:
 {{{
 Fri Oct  8 06:37:51 PDT 2010  simonpj at microsoft.com
   * Beautiful new approach to the skolem-escape check and untouchable

   Instead of keeping a *set* of untouchable variables in each
   implication contraints, we keep a *range* of uniques for the
   *touchable* variables of an implication.  This are precisely
   the ones we would call the "existentials" if we were French.

   It turns out that the code is more efficient, and vastly easier
   to get right, than the set-based approach.

   Fixes Trac #4355 among others

     M ./compiler/ghci/RtClosureInspect.hs -2 +2
     M ./compiler/typecheck/TcBinds.lhs -2 +2
     M ./compiler/typecheck/TcMType.lhs -8 +8
     M ./compiler/typecheck/TcPat.lhs -4 +5
     M ./compiler/typecheck/TcRnDriver.lhs -5 +5
     M ./compiler/typecheck/TcRnMonad.lhs -13 +27
     M ./compiler/typecheck/TcRnTypes.lhs -4 +29
     M ./compiler/typecheck/TcRules.lhs -2 +2
     M ./compiler/typecheck/TcSMonad.lhs -19 +23
     M ./compiler/typecheck/TcSimplify.lhs -15 +14
     M ./compiler/typecheck/TcSplice.lhs -2 +2
     M ./compiler/typecheck/TcUnify.lhs -13 +11
 }}}
 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4355#comment:3>
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