[GHC] #4020: Please consider adding support for local type synonyms

[GHC]

#4020: Please consider adding support for local type synonyms
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        Reporter:  nr                |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  low               |            Milestone:
       Component:  Compiler (Type    |              Version:  6.12.2
  checker)                           |
      Resolution:                    |             Keywords:  type synonym
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by AntC):

 Replying to [comment:18 ezyang]:
 > Yeah, local type synonyms are probably the least controversial

 Thanks Edward, but I see no controversy. Only the usual questions about
 what are the use cases/benefits? what does it provide that can't be
 written now/only written clumsily? how does it work? what complications
 does the user need to understand? what complications does the compiler
 need to understand?

 > of "make global things possible locally" proposals. There are pretty
 clear semantics for how it works in all cases.

 Then it should be easy for someone to write up a proposal on github. I've
 seen plenty of "make global things possible locally" proposals. None of
 them have given a coherent explanation for how the local thing is to
 behave when something containing it or mentioning it or bound to it gets
 exported globally. (For example with class instances; that's why Wadler
 made them global despite his initial proposal making them let-bound.)

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4020#comment:20>
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