Hello Yorick,
Thanks for taking this one on!
First off, this kind of question/post is appropriate for putting right into the
ticket itself. Posting a comment to the ticket makes it more likely that you'll
get a response and saves your thoughts for posterity.
Now, on to your question:
That seems somewhat reasonable, but I think your work could go a little
further. It looks like you've introduced TupleP as a new constructor for Pred.
This, I believe, would work. But, I think it would be better to have a way of
using *any* type as a predicate in TH, as allowed by ConstraintKinds. Perhaps
one way to achieve this is to make Pred a synonym of Type, or there could be a
TypeP constructor for Pred.
In any case, I would recommend writing a wiki page up with a proposed new TH
syntax for predicates and then posting a link to the proposal on the #7021
ticket. Then, it will be easier to debate the merits of any particular approach.
Once again, thanks!
Richard
On Jan 3, 2014, at 6:13 PM, Yorick Laupa wrote:
> Hi,
>
> I try to make my way through #7021 [1]. Unfortunately, there is nothing in
> the ticket about what should be expected from the code given as example.
>
> I came with an implementation and I would like feedback from you guys. So,
> considering this snippet:
>
> --
> {-# LANGUAGE ConstraintKinds #-}
>
> type IOable a = (Show a, Read a)
>
> foo :: IOable a => a
> foo = undefined
> --
>
> This is what I got now when pretty-printing TH.Info after reify "foo" call:
>
> VarI Tuple.foo (ForallT [PlainTV a_1627398594] [TupleP 2 [AppT (ConT
> GHC.Show.Show) (VarT a_1627398594),AppT (ConT GHC.Read.Read) (VarT
> a_1627398594)]] (VarT a_1627398594)) Nothing (Fixity 9 InfixL)
>
> Does that sound right to you ?
>
> Thanks for your time
>
> -- Yorick
>
> [1] https://ghc.haskell.org/trac/ghc/ticket/7021
> _______________________________________________
> ghc-devs mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/ghc-devs
_______________________________________________
ghc-devs mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/ghc-devs
