[GHC] #7368: kindFunResult panic in the

[GHC]

#7368: kindFunResult panic in the
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    Reporter:  ChrisN                   |       Owner:                             
        Type:  bug                      |      Status:  new                        
    Priority:  normal                   |   Milestone:                             
   Component:  Compiler (Type checker)  |     Version:  7.6.1                      
    Keywords:  Kinds, kindfunresult     |          Os:  Unknown/Multiple           
Architecture:  Unknown/Multiple         |     Failure:  Compile-time crash         
  Difficulty:  Unknown                  |    Testcase:  typecheck/should_fail/T7368
   Blockedby:                           |    Blocking:                             
     Related:                           |  
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Changes (by simonpj):

  * testcase:  => typecheck/should_fail/T7368
  * version:  7.7 => 7.6.1


Comment:

 Good bug.  Yes 7.6.1 fails, thus
 {{{
 T7368.hs:3:10:
     Couldn't match kind `* -> *' with `*'
     Expected type: a0 -> b0
       Actual type: a0 -> b0
     Kind incompatibility when matching types:
       b_w :: * -> *
       b0 :: *
     In the return type of a call of `l'
     In the first argument of `b', namely `(l ())'

 T7368.hs:3:13:ghc-stage1: panic! (the 'impossible' happened)
   (GHC version 7.6.1.20121011 for x86_64-unknown-linux):
         kindFunResult ghc-prim:GHC.Prim.*{(w) tc 34d}
 }}}
 However HEAD (will be 7.8) is (happily) ok:
 {{{
 T7368.hs:3:10:
     Couldn't match kind `* -> *' with `*'
     When matching types
       c0 :: (* -> *) -> *
       (->) a0 :: * -> *
     Expected type: a0 -> b0
       Actual type: c0 b1
     In the return type of a call of `l'
     Probable cause: `l' is applied to too many arguments
     In the first argument of `b', namely `(l ())'
     In the expression: b (l ())

 T7368.hs:3:13:
     Couldn't match type `()' with `b0 a1'
     Expected type: b1 a1
       Actual type: ()
     In the first argument of `l', namely `()'
     In the first argument of `b', namely `(l ())'
     In the expression: b (l ())
 }}}
 I don't know where exactly the problem lies in 7.6, and I'm very swamped,
 so I'm going to leave this open and unfixed.  If it turns out to bite some
 mission-critical package I can look into fixing it in 7.6, I'd prefer not
 to have to do that.

 I have added a regression test though.

 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7368#comment:3>
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