[GHC] #3306: Improve syntax for GADT + records

[GHC]

#3306: Improve syntax for GADT + records
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    Reporter:  simonpj           |        Owner:                  
        Type:  feature request   |       Status:  new             
    Priority:  normal            |    Milestone:                  
   Component:  Compiler          |      Version:  6.10.2          
    Severity:  normal            |   Resolution:                  
    Keywords:                    |   Difficulty:  Unknown         
    Testcase:                    |           Os:  Unknown/Multiple
Architecture:  Unknown/Multiple  |  
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Comment (by SamB):

 I really don't like the way (B) implies the existance of record types --
 unless you would like to add those too?

 I am one of those who wants to see the current data type declaration
 syntax die as soon as reasonably possible, i.e., in H'', and do not
 approve of it's being used as a precedent for anything. In that light, I
 don't think that (A) looks much like a repeat of C's mistake -- the part
 to the left of the {{{::}}} is obviously supposed to be a term. The one
 issue I have with (A) is the location of the context, and that doesn't
 seem like a good enough reason to use (B) instead, unless we want to make
 this possible too:
 {{{
 { x::ty, y::ty } -> ty
 }}}

 I'll grant that even (B) isn't nearly as bad as what a context on an old-
 style "data" declaration does, though.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3306#comment:3>
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