[GHC] #10928: Refine pattern synonym signatures

[GHC]

#10928: Refine pattern synonym signatures
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        Reporter:  mpickering        |                Owner:
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Other             |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by simonpj):

 * priority:  normal => highest


Comment:

 I think we should get on and reverse the order for 8.0.  And make sure
 that in
 {{{
 pattern P :: req => prov => t1 -> ... -> tn -> T s1 .. sm
 }}}
 then
  * The "universal" tyvars are fv(s1..sm)
  * The "existential" tyvars are fv(t1..tn) minus the universals
 and the fvs of req must be all universal!

 Since this is breaking change, we'd better get it done asap.

 Agreed?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10928#comment:21>
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