[GHC] #7838: ghc(i) crashes on instance declaration

[GHC]

#7838: ghc(i) crashes on instance declaration
--------------------------------------+-------------------------------------
    Reporter:  alios                  |        Owner:                  
        Type:  bug                    |       Status:  closed          
    Priority:  normal                 |    Component:  Compiler        
     Version:  7.6.2                  |   Resolution:  fixed           
    Keywords:  MultiParamTypeClasses  |           Os:  Unknown/Multiple
Architecture:  Unknown/Multiple       |      Failure:  None/Unknown    
   Blockedby:                         |     Blocking:                  
     Related:                         |  
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Changes (by monoidal):

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


Comment:

 Thanks for the report. The bug is already fixed in HEAD. Now you get:

 {{{
 A.hs:28:13:
     Expected a constraint, but ‛C (TPI t) m (TPI t)’ has kind ‛*’
     In the class declaration for ‛TS’
 }}}

 Here's a reduced version:

 {{{
 {-# LANGUAGE ConstraintKinds, UndecidableInstances, FlexibleInstances #-}

 module Crash where

 data C m

 class (C m) => TS m

 instance TS m where
 }}}

 Once you change "data C m" to "class C m", there's no panic. Sometimes 7.6
 does not enforce the difference between kinds Constraint and * during
 type-checking.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7838#comment:1>
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