[GHC] #4347: Bug in unification of polymorphic and not-yet-polymorphic type

[GHC]

#4347: Bug in unification of polymorphic and not-yet-polymorphic type
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              Reporter:  dolio       |            Owner:
                  Type:  bug         |           Status:  closed
              Priority:  normal      |        Milestone:  7.10.1
             Component:  Compiler    |          Version:  7.1
  (Type checker)                     |         Keywords:
            Resolution:  wontfix     |     Architecture:  x86_64 (amd64)
      Operating System:  Linux       |       Difficulty:  Unknown
       Type of failure:  GHC         |       Blocked By:
  rejects valid program              |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Changes (by simonpj):

 * status:  new => closed
 * resolution:   => wontfix


Comment:

 Dolio is right here.  I've backed off from making ANY claims about what
 GHC does or does not do for impredicative polymorphism.  Really the
 language extension flag should be deprecated because it is not supported
 either by proper theory about what inference should do, or by an
 implementation of that theory.  Whatever happens right now happens by
 luck.

 I'm sure there is a route to a better story for impredicativity; but it is
 complex territory and there has been much else to do.

 So yes I'll close this ticket

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4347#comment:16>
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