[GHC] #5267: Arrow command combinators

[GHC]

#5267: Arrow command combinators
----------------------------------------+-----------------------------------
  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 ross):

 This seems to result from the deletion of
 {{{
                -- Check that the polymorphic variable hasn't been unified
 with anything
                -- and is not free in res_ty or the cmd_stk  (i.e.  t,
 t1..tn)
        ; checkSigTyVarsWrt (tyVarsOfTypes (res_ty:cmd_stk)) [w_tv]
 }}}
 from the {{{ArrForm}}} case of tc_cmd in this patch:
 {{{
 commit d2ce0f52d42edf32bb9f13796e6ba6edba8bd516
 Author: simonpj at microsoft.com <unknown>
 Date:   Mon Sep 13 09:50:48 2010 +0000

     Super-monster patch implementing the new typechecker -- at last
 }}}
 Apparently the replacement code doesn't perform the same check.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5267#comment:8>
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