[GHC] #8968: Pattern synonyms and GADTs

[GHC]

#8968: Pattern synonyms and GADTs
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        Reporter:  kosmikus                   |            Owner:
            Type:  bug                        |           Status:  new
        Priority:  normal                     |        Milestone:
       Component:  Compiler (Type checker)    |          Version:
      Resolution:                             |  7.8.1-rc2
Operating System:  Unknown/Multiple           |         Keywords:
 Type of failure:  GHC rejects valid program  |     Architecture:
       Test Case:                             |  Unknown/Multiple
        Blocking:                             |       Difficulty:  Unknown
                                              |       Blocked By:
                                              |  Related Tickets:
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Comment (by kosmikus):

 > So it's not clear that a single signature for the two ways of looking at
 the RHS makes sense at all!  It look as though we need one for its use as
 a pattern and one for its use as an expression.  Sigh.

 Yes.

 > Mind you, the "type as an expression" is easily inferred, as you
 mention.  So perhaps the pattern signature (once we have them) can be
 taken as applying only to the pattern, not the expression?

 I guess it's not clear to me if the other information isn't available as
 well, if the synonym is used in a function that has a type signature. Is
 there really a theoretical need to supply a signature for the "pattern
 type"? See my example in the other comment, I actually wouldn't like to
 have to pick one.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8968#comment:10>
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