Re: #2846: Impredicativity bug: GHC crash by type signature

#2846: Impredicativity bug: GHC crash by type signature
----------------------------+-----------------------------------------------
  Reporter:  mm_freak       |          Owner:  simonpj         
      Type:  bug            |         Status:  closed          
  Priority:  low            |      Milestone:  7.0.1           
 Component:  Compiler       |        Version:  6.10.1          
Resolution:  fixed          |       Keywords:  crash, type     
  Testcase:  T2846, T2846b  |      Blockedby:                  
Difficulty:  Unknown        |             Os:  Unknown/Multiple
  Blocking:                 |   Architecture:  Unknown/Multiple
   Failure:  None/Unknown   |  
----------------------------+-----------------------------------------------
Changes (by simonpj):

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

Comment:

 Yes, that's fine.  The error message Michal gives is with
 `-XImpredicativeTypes`. Without we get
 {{{
 T2846.hs:4:5:
     Illegal polymorphic or qualified type: Num a => a
     Perhaps you intended to use -XImpredicativeTypes
     In an expression type signature: [Num a => a]
     In the expression: [1, 2, 3] :: [Num a => a]
     In an equation for `x': x = [1, 2, 3] :: [Num a => a]
 }}}

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2846#comment:9>