Re: Changes to Typeable

Sorry, I got a bit lost in this discussion. Let me try to provide a summary. Current status: I have a local branch with the new poly-kinded Typeable working fine. It works as described in [1]. It actually allows deriving Typeable for things involving the Constraint kind, but this can be easily disabled. Either way, I think most of this is necessary for whatever might follow next. But I'm not sure of how to push the changes, because I had to make some changes to these repos: array, containers, dph, template-haskell, and vector. Worse, I also had to change time, which gets built from a tarball. It might not be worth contacting the authors of these packages for changes if we're still going to get rid of "deriving Typeable" altogether, so I've been holding this back. It's been proposed to remove the possibility to derive Typeable or write instances for it. I'm supposing the way that this would be implemented would be: 7.8: Any uses of "deriving Typeable" would give rise to a warning saying that it is no longer necessary. Any instances of Typeable would give rise to a warning saying that this code is being ignored, and replaced by an internal Typeable instance. Packages might break, or change runtime behaviour due to this change. 7.10: Explicit uses of "deriving Typeable" or instances are an error. Regarding split :: (a ~ f i) => Dict (Typeable f, Typeable i), I'm not sure I can judge how much work that would be. But let's first try to draft a plan for removing Typeable definitions from the user, and then consider more extensions. Cheers, Pedro [1] http://hackage.haskell.org/trac/ghc/wiki/GhcKinds/PolyTypeable On Tue, Oct 16, 2012 at 8:32 AM, Emil Axelsson wrote:

2012-10-15 23:50, Gábor Lehel skrev:

On Mon, Oct 15, 2012 at 7:58 AM, Emil Axelsson wrote:

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I have a use case:

http://hackage.haskell.org/**packages/archive/syntactic/1.** 3/doc/html/Data-DynamicAlt.**htmlhttp://hackage.haskell.org/packages/archive/syntactic/1.3/doc/html/Data-Dyna...

This is a reimplementation of Data.Dynamic to support casting type `a` to `Dynamic` given a constraint `Typeable (a -> b)`:

toDyn :: Typeable (a -> b) => P (a -> b) -> a -> Dynamic

With your suggestion, it seems I should be able to use the ordinary Data.Dynamic instead.

/ Emil

Great! Do you like my plan? Or perhaps know of a better one?

(Relatedly, *does* this have to go through a separate libraries process? Or are we considering Typeable as getting completely replaced, and everything pertaining to it gets discussed here?)

Your plan certainly seems general enough! But I'm afraid I can't really speak about the implications on libraries etc.

/ Emil