[GHC] #14362: Allow: Coercing (a:~:b) to (b:~:a)

[GHC]

#14362: Allow: Coercing (a:~:b) to (b:~:a)
-------------------------------------+-------------------------------------
        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:  roles
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 > Is it not ultimately about implication of constraints?

 I don't thuink so. Take `:~:`.   Could I write this function?
 {{{
 convert :: (a :~: b) -> (b :~: a)
 }}}
 Sure! Thus
 {{{
 convert Refl = Refl
 }}}
 Plus, the two represntationns are the same.  So yes, they should be
 coercible.  No quantification stuff.  I think.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14362#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler