[GHC] #14975: Refactor (Maybe Coercion)

[GHC]

#14975: Refactor (Maybe Coercion)
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        Reporter:  tdammers          |                Owner:  (none)
            Type:  task              |               Status:  patch
        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):  Phab:D4699
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"9aac442f70b0b58decd56fb52dd4ec2289b03759/ghc" 9aac442/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="9aac442f70b0b58decd56fb52dd4ec2289b03759"
 Define MCoercion type

 An attempt on #14975:
 During compilation, reflexive casts is discarded for computation.
 Currently in some places we use Maybe coercion as inputs. So if a cast
 is reflexive it is denoted as Nothing, otherwise Just coercion.

 This patch defines the type

 data MCoercion = MRefl | MCo Coercion

 which is isomorphic to Maybe Coercion but useful in a number of places,
 and super-helpful documentation.

 Test Plan: validate

 Reviewers: bgamari, goldfire, simonpj

 Reviewed By: goldfire

 Subscribers: mpickering, rwbarton, thomie, carter

 GHC Trac Issues: #14975

 Differential Revision: https://phabricator.haskell.org/D4699
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14975#comment:10>
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