cvs commit: fptools/ghc/compiler/typecheck TcUnify.lhs

[Simon Peyton Jones]

simonpj     2005/07/27 01:04:03 PDT

  Modified files:
    ghc/compiler/typecheck TcUnify.lhs 
  Log:
  	Try MERGE to STABLE
  
  GHC does not do type subsumption in patterns.  But it should be fine if
  the expected type and the pattern have the same type, even if they
  are polymorphic.  But that test (in TcUnify.tcSubPat) wasn't implemented
  right, which gave rise to perplexing messages like:
  
     Couldn't match `forall a. a -> b' against `forall a. a -> b'
  
  This fixes the bug.
  tc198 tests it, while tcfail145 tests the non-matching case.
  
  Revision  Changes    Path
  1.71      +24 -10    fptools/ghc/compiler/typecheck/TcUnify.lhs