[GHC] #13524: GHC does not preserve order of forall'd vars with TypeApplications

[GHC]

#13524: GHC does not preserve order of forall'd vars with TypeApplications
-------------------------------------+-------------------------------------
        Reporter:  crockeea          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
                                     |  TypeApplications
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:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 >  Perhaps even better, we could label variables in partial type
 signatures as "inferred", meaning that GHC will prevent them from being
 available for type application.

 Yes!  After all, if you write
 {{{
 f :: forall a. _ -> a -> a
 f = ...
 }}}
 you might end up with more type variables; e.g. f's signature might really
 be
 {{{
 f :: forall a b c. (b,c) -> a -> a
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13524#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler