Re: [GHC] #15334: (forall x. c x, forall x. d x) is not equivalent to forall x. (c x, d x)

2 Jul 2018

      #15334: (forall x. c x, forall x. d x) is not equivalent to forall x. (c x, d x)
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  8.5
  checker)                           |             Keywords:
      Resolution:                    |  QuantifiedConstraints
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 RyanGlScott):

 `c1` and `c2` are already superclasses of `(c1, c2)`. I suspect the issue
 is not in how constraint tuples are defined, because it I replace the
 constraint triple in my program with a hand-rolled one:

 {{{#!hs
 class    (a, b, c) => CTuple3 a b c
 instance (a, b, c) => CTuple3 a b c

 deriving instance (forall a. CTuple3 (Functor (WrappedF a))
                                      (Foldable (WrappedF a))
                                      (Traversable (WrappedF a))
                   ) => Traversable SomeF
 }}}

 Then I still get the same error as before.

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15334#comment:2
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