Re: [Camllist] Generalized Algebraic Datatypes
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Date:  20101029 (15:54) 
From:  Jacques Le Normand <rathereasy@g...> 
Subject:  Re: [Camllist] Generalized Algebraic Datatypes 
Assuming I understand this syntax, the following currently valid type definition would have two interpretations: type 'a t = IntLit of 'a constraint 'a = int One interpretation as a standard constrained ADT and one interpretation as a GADT. We could use another token, other than constraint, for example: type 'a t = IntLit of 'a : 'a = int to which I have no objections. As you pointed out, though, the current syntax is more concise. cheers, Jacques On Fri, Oct 29, 2010 at 10:32 AM, Dario Teixeira <darioteixeira@yahoo.com>wrote: > Hi, > > > I am pleased to announce an experimental branch of the O'Caml compiler: > > O'Caml extended with Generalized Algebraic Datatypes. You can find more > > information on this webpage: > > I have a couple of questions regarding the syntax you've chosen for GADT > declaration. For reference, let's consider the first example you've > provided: > > type _ t = >  IntLit : int > int t >  BoolLit : bool > bool t >  Pair : 'a t * 'b t > ('a * 'b) t >  App : ('a > 'b) t * 'a t > 'b t >  Abs : ('a > 'b) > ('a > 'b) t > > > There's something "Haskellish" about this syntax, in the sense that type > constructors are portrayed as being like functions. While this does make > sense in Haskell, in Ocaml it feels a bit out of place, because you cannot, > for example, partially apply a type constructor. > > Also, note that in all the variant declarations the final token is 't'. > Are there any circumstances at all where a GADT constructor will not end > by referencing the type being defined? If there are not, then this syntax > imposes some syntactic salt into the GADT declaration. > > I know this is not the sole syntax that was considered for GADTs in Ocaml. > Xavier Leroy's presentation in CUG 2008 shows a different one, which even > though slightly more verbose, does have the advantage of being more > "Camlish". > Is there any shortcoming to the 2008 syntax that resulted in it being > dropped > in favour of this new one? > > Best regards, > Dario Teixeira > > > > >