[GHC] #11658: Type synonym with context in pattern synonym

[GHC]

#11658: Type synonym with context in pattern synonym
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        Reporter:  Iceland_jack      |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 While I understand why the syntax might suggest that this is a good idea.
 I don't support this proposal. The thing after `pattern Blah ::` is
 '''not''' a type. It's a pattern synonym type, which is something else. Of
 course, type synonyms should be allowed in pattern synonym types, but we
 shouldn't confuse the normal `=>` that might appear in a type synonym with
 the `=>` that appears in a pattern synonym type.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11658#comment:1>
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