[GHC] #11715: There's something fishy going on with Constraint

[GHC]

#11715: There's something fishy going on with Constraint
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  8.0.1-rc1
  checker)                           |
      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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Comment (by bgamari):

 I just remembered another little nugget that I noticed during #11334:
 There is a bizarre order dependence to this bug. For instance,
 {{{#!hs
 main = do
     print $ typeof (proxy :: proxy (Eq int))
     print $ typeof (proxy :: proxy Eq)
 }}}
 will emit,
 {{{
 Proxy Constraint (Eq Int)
 Proxy (Constraint -> Constraint) Eq
 }}}

 Whereas if you flip the order of the `print`s (presumably such that the
 solver encounters `*` first rather than `Constraint`) you see what I
 reported in the ticket description,
 {{{
 Proxy (* -> *) Eq
 Proxy * (Eq Int)
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11715#comment:1>
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