[GHC] #15474: Error message mentions Any

[GHC]

#15474: Error message mentions Any
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        Reporter:  monoidal          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  low               |            Milestone:  8.8.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Poor/confusing    |  Unknown/Multiple
  error message                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Yes, this is awkward.  What is happening is that we end up with this:
 {{{
 type Forall = forall (t :: Any). Proxy @Any t
 }}}
 I think that perhaps in this case we should kind-generalise the RHS of
 `Forall` to get
 {{{
 type Forall k = forall (t :: k) . Proxy @k t
 }}}
 I'm not sure why we don't do this.  We certainly do some kind-
 generalisation; e.g. if you write
 {{{
 type T x = x
 }}}
 we end up with
 {{{
 type T k (x :: k) = x
 }}}
 So why doesn't something like that happen for `Forall`?  Interesting.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15474#comment:2>
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