[GHC] #12428: Allow pattern synonyms to optionally carry coerceability

[GHC]

#12428: Allow pattern synonyms to optionally carry coerceability
-------------------------------------+-------------------------------------
        Reporter:  dfeuer            |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
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 nomeata):

 I wonder if it makes sense to look at that feature request independently
 of pattern synonyms. Then it becomes:

 > Give library authors a way to allow newtype unwrapping for newtypes
 where the constructor is not imported.

 or, a bit more concrete

 > Give library authors a way to allow newtype unwrapping for newtypes
 where the constructor is not imported, by naming other symbols (functions,
 constructors, pattern synonyms) that, if in scope, give the user of their
 library the power to do newtype unwrapping.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12428#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler