[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 isaacdupree):

 Who implements GHC's version of the syntax currently? GHC and haskell-src-
 exts, I guess.  Both well-maintained.

 If we choose (B), I guess the current GADT-records syntax can/should be
 kept with a 'deprecated' warning for a few releases?

 (A) reminds me a little too much of how C tried to make declarations and
 uses look the same (e.g. function-pointers) and ended up with something
 nearly incomprehensible!

 With (A) and (B), I have a silly question.
 {{{
 data Silly a where
   Silly :: a -> forall b. b -> Silly a
 (which would parse like
   Silly :: a -> (forall b. b -> Silly a)
 )
 }}}
 Is that allowed or useful? (interacts with impredicativity, IIRC)...
 Because neither records syntax allows you even to attempt that.

 -Isaac

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3306#comment:1>
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