[GHC] #14975: Refactor (Maybe Coercion)

[GHC]

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

Comment (by tdammers):

 I've been doing some work on this in between other stuff, but haven't
 gotten very far yet. I have a `MCoercion` type in place (which is
 trivial), and my first approach was to just naively replace all `Maybe
 Coercion`s with `MCoercion` and then follow the compiler errors. However,
 this doesn't work out all that well, because some of those `Maybe`s are
 actually morally justified as such (i.e., `Nothing` does not not mean
 "this is a Refl coercion", but it actually means "nothing found" /
 "failure"). I was going to go through the code and look at all occurrences
 individually, but haven't gotten around to this yet.

 If someone wants to take this off me, and do the work for free, I say go
 ahead, I'm not emotionally invested in this.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14975#comment:6>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler