[GHC] #10242: Multiple constraint wildcards allowed with PartialTypeSignatures

[GHC]

#10242: Multiple constraint wildcards allowed with PartialTypeSignatures
-------------------------------------+-------------------------------------
              Reporter:  mpickering  |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.10.1
              Keywords:              |  Operating System:  Unknown/Multiple
  PartialTypeSignatures              |   Type of failure:  GHC accepts
          Architecture:              |  invalid program
  Unknown/Multiple                   |        Blocked By:
             Test Case:              |   Related Tickets:
              Blocking:              |
Differential Revisions:              |
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 The [https://ghc.haskell.org/trac/ghc/wiki/PartialTypeSignatures wiki]
 states that

 > As a single extra-constraints wildcard is enough to infer any number of
 constraints, only one is allowed in a type signature and it should come
 last in the list of constraints.

 However the following program compiles with GHC 7.10.1

 {{{#!hs
 {-# LANGUAGE PartialTypeSignatures #-}

 f :: (Eq a, _, _) => a -> a -> Bool
 f x y = x == y
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10242>
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