[GHC] #14203: GHC-inferred type signature doesn't actually typecheck

[GHC]

#14203: GHC-inferred type signature doesn't actually typecheck
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.2.1
  checker)                           |             Keywords:  TypeInType,
      Resolution:                    |  TypeFamilies
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 The original programs should be rejected, I think. Looking at your simpler
 example, the declaration for `Foo` should be rejected as ambiguous.
 There's no way to tell from `z` what `a`, `x`, or `p` should be. When I
 continue my bug sweep, I'll take a look at this.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14203#comment:2>
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