[GHC] #14975: Refactor (Maybe Coercion)

[GHC]

#14975: Refactor (Maybe Coercion)
-------------------------------------+-------------------------------------
           Reporter:  tdammers       |             Owner:  (none)
               Type:  task           |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  #11735
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 As discussed here: https://phabricator.haskell.org/D4395#inline-34607

 Define a type

 {{{#!hs
 data MCoercion = MRefl | MCo Coercion
 }}}

 This is isomorphic to {{{Maybe Coercion}}} but useful in a number of
 places, and super-helpful documentation. (eg {{{MRefl}}} is much more
 perspicuous than {{{Nothing}}}.

 Define this in {{{Coercion.hs}}} I think.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14975>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler