StrictData and the parser

[Simon Peyton Jones]

There is some similar stuff in GHC already, to do with "!".  It is both an infix operator and (in some contexts) a unary prefix to a function argument 
	f !x y = ...rhs...
See RdrHsSyn.splitBang.

Just possibly the same kind of stuff will help with "~"?

S

|  -----Original Message-----
|  From: ghc-devs [mailto:ghc-devs-bounces at haskell.org] On Behalf Of
|  Edward Z. Yang
|  Sent: 05 June 2015 01:08
|  To: Johan Tibell
|  Cc: "ghc-devs at haskell.org"
|  Subject: Re: StrictData and the parser
|  
|  Excerpts from Johan Tibell's message of 2015-06-04 16:52:30 -0700:
|  > I guess we should parse it as T a (~b), just as we have unary minus
|  > bind "tighter" with the following token.
|  
|  Not in all contexts.
|  
|  It is true that if you have 'data SLPair a b = SLP a ~ b' you want to
|  parse 'SLP a (~b)'
|  
|  But if you have 'Maybe a ~ b' you want to parse '(Maybe a) ~ b'.
|  
|  But in GADTs, if you have
|  
|      data SLPair a b where
|          SLP :: a -> ~ b -> SLPair a b
|  
|  you want a -> (~ b) -> SLPair a b
|  
|  If the twiddle is not immediately after an arrow you don't want that,
|  e.g.
|  
|      data T a b where
|          T :: a -> a ~ b -> SLPair a b
|  
|  you want T :: a -> (a ~ b) -> SLPair a b
|  
|  Edward
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