[GHC] #11977: ghc doesn't agree with its own inferred pattern type

[GHC]

#11977: ghc doesn't agree with its own inferred pattern type
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        Reporter:  Iceland_jack      |                Owner:
            Type:  bug               |               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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Changes (by goldfire):

 * cc: mpickering, cactus (added)


Comment:

 Very interesting test case!

 You've discovered that, once again, we've misunderstood pattern types.

 If you assign a pattern the type `a -> b -> c` (where `a`, `b`, and `c`
 are arbitrary types, not necessarily variables; that is, they are
 metavariables), we've been saying that `a` and `b` are arguments to the
 pattern and `c` is the result type. But in your case, the type is `a ->
 Char -> a`, and `Char -> a` is the result type. Yet there is no way to
 indicate this in a type signature. I even tried `a -> (Char -> a)` to no
 avail.

 I have no suggestions (other than parentheses, which would be awkward) for
 how to fix this.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11977#comment:1>
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