[GHC] #15244: Ambiguity checks in QuantifiedConstraints

[GHC]

#15244: Ambiguity checks in QuantifiedConstraints
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        Reporter:  bitwiseshiftleft  |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.5
      Resolution:                    |             Keywords:
                                     |  QuantifiedConstraints
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 Simon Peyton Jones <simonpj@…>):

 In [changeset:"a169149ce80de3676adb3ece43d5164b6a875b9c/ghc"
 a169149c/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="a169149ce80de3676adb3ece43d5164b6a875b9c"
 Remove duplicate quantified constraints

 This is an easy fix for Trac #15244: just avoid adding
 the same quantified Given constraint to the inert set twice.

 See TcSMonad Note [Do not add duplicate quantified instances].
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15244#comment:4>
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