[GHC] #5267: Arrow command combinators

[GHC]

#5267: Arrow command combinators
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  Reporter:  peteg                      |          Owner:  ross            
      Type:  bug                        |         Status:  new             
  Priority:  normal                     |      Milestone:  7.4.1           
 Component:  Compiler                   |        Version:  7.0.3           
Resolution:                             |       Keywords:                  
  Testcase:                             |      Blockedby:                  
Difficulty:                             |             Os:  Unknown/Multiple
  Blocking:                             |   Architecture:  Unknown/Multiple
   Failure:  GHC rejects valid program  |  
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Comment(by simonpj):

 I think if you could help me refactor the code
 {{{
                 -- Check that it has the right shape:
                 --      ((w,s1) .. sn)
                 -- where the si do not mention w
            ; checkTc (corner_ty `eqType` mkTyVarTy w_tv &&
                       not (w_tv `elemVarSet` tyVarsOfTypes arg_tys))
                      (badFormFun i tup_ty')
 }}}
 so that it used `unifyType`, and made proper use of the coerion that
 `unifyType` returns (see `matchExpectedListTy` and friends), we'd be in
 much better shape.  I'm pretty sure that the stuff you describe will be
 fine; but I don't understand enough detail to be sure.  Can you give a
 link to the paper with the typing rules?  Are they still the ones you
 think are correct?

 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5267#comment:12>
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