[GHC] #902: Deriving for H98 types using GADT syntax fails

[GHC]

#902: Deriving for H98 types using GADT syntax fails
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  Reporter:  bringert at cs.chalmers.se  |          Owner:         
      Type:  bug                      |         Status:  new    
  Priority:  normal                   |      Milestone:         
 Component:  Compiler                 |        Version:  6.5    
  Severity:  normal                   |     Resolution:         
  Keywords:                           |             Os:  Unknown
Difficulty:  Unknown                  |   Architecture:  Unknown
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Comment (by bringert at cs.chalmers.se):

 In compiler/typecheck/TcDeriv.lhs, mkDataTypeEqn, ordinary_constraints,
 constraints are added for all argument types of all data constructors.
 However, with GADTs, type variables which are data constructor arguments
 are distinct from the type constructor arguments. simonpj suggested fixing
 this by using dataConInstOrigArgTys to instantiate the type variables.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/902>
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