Re: Proposal: Deprecate ExistentialQuantification

Hi, True, but then you have to declare the kind manually. -Iavor On Thu, Jul 23, 2009 at 7:36 PM, Sittampalam, Ganesh wrote:

One can use the following style of GADT definition, which avoids the type variables in the declaration:

{-# LANGUAGE GADTs, KindSignatures #-} module GADT where

data Foo :: * -> * where  Foo :: Int -> Foo Int

Iavor Diatchki wrote:

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Hello,

Sorry for responding so late---I just saw the thread.  I don't think that we should deprecate the usual way to define existentials.  While the GADT syntax is nice in some cases, there are also examples when it is quite verbose. For example, there is a lot of repetition in datatypes that have many constructors, especially if the datatype has parameters and a slightly longer name.  Furthermore, I find the type variables in the declaration of the type quite confusing because they have no relation to the type variables in the constructors.  Finally, there is quite a lot of literature about the semantics of existential types, while the semantics of GADTs seems quite complex, so it seems a bit risky to mix up the two.

-Iavor

On Thu, Jul 23, 2009 at 2:47 PM, Niklas Broberg wrote:

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Discussion period: 2 weeks

Returning to this discussion, I'm surprised that so few people have actually commented yea or nay. Seems to me though that... * Some people are clearly in favor of a move in this direction, as seen both by their replies here and discussion over other channels. * Others are wary of deprecating anything of this magnitude for practical reasons. * No one has commented in true support of the classic existential syntax, only wanting to keep it for "legacy" reasons.

I'm in no particular hurry to see this deprecation implemented, and I certainly understand the practical concerns, but I would still very much like us to make a statement that this is the direction we intend to go in the longer run. I'm not sure what the best procedure for doing so would be, but some sort of soft deprecation seems reasonable to me.

Further thoughts?

Cheers,

/Niklas _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime

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