[GHC] #5267: Missing type checks for arrow command combinators

[GHC]

#5267: Missing type checks for arrow command combinators
-------------------------------------+-------------------------------------
              Reporter:  peteg       |            Owner:  ross
                  Type:  bug         |           Status:  new
              Priority:  low         |        Milestone:  7.10.1
             Component:  Compiler    |          Version:  7.0.3
  (Type checker)                     |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:  GHC         |  Related Tickets:
  accepts invalid program            |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------
Changes (by simonpj):

 * difficulty:   => Unknown


Comment:

 There *is* something to do in the type checker, namely to plumb the type
 constraints correctly.  See the changes to `newArrowScope` and
 `escapeArrowScope` in the above patch. This fixes the assertion failure.

 I'm still not confident about all this, and I'd love someone who
 understands arrows to review the type inference code for arrows.  So I'll
 leave the ticket open. But it's better, I think.

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5267#comment:23>
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