On 5/16/13, Simon Peyton-Jones
Excellent. Jacques: do try it out!
I believe that there are new branches in these repos (Geoff yell if not) ghc testsuite base template-haskell
I can't help feeling that [|| foo ||] $$(foo) is too heavy a syntax, and will make it seem horrid an clunky. Two-character brackets are bad enough. What about [@ foo @] &(foo) Other suggestions welcome. Trivial yet important.
Why can't $(foo) be reused? I would guess that the surrounding brackets easily disambiguate the meaning... Or are classical TH brackets and typed-style ones nestable? I should probably go and read the original paper and shut up :-) Cheers, Gabor
Simon
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| -----Original Message----- | From: ghc-devs-bounces@haskell.org [mailto:ghc-devs-bounces@haskell.org] | On Behalf Of Geoffrey Mainland | Sent: 16 May 2013 16:22 | To: ghc-devs@haskell.org | Cc: carette@mcmaster.ca | Subject: New branch implementing typed/untyped Template Haskell | | I have pushed a new branch, th-new, that partially implements the | proposal outlined in Simon PJ's "New directions for Template Haskell" | post at: | | http://hackage.haskell.org/trac/ghc/blog/Template%20Haskell%20Proposal | | The main missing features are top-level pattern splices and local | declaration splices. | | Typed expression quotations and typed expression splices *are* | implemented. Syntax is as in Simon's original proposal: [|| ||] for | typed expression brackets and $$(...) for typed expression splices. One | can now write: | | power :: Int -> TExp (Int -> Int) | power n = [|| \x -> $$(go n [|| x ||]) ||] | where | go :: Int -> TExp Int -> TExp Int | go 0 x = [|| 1 ||] | go n x = [|| $$x * $$(go (n-1) x) ||] | | In fact, one can even write: | | power :: Num a => Int -> TExp (a -> a) | power n = [|| \x -> $$(go n [|| x ||]) ||] | where | go :: Num a => Int -> TExp a -> TExp a | go 0 x = [|| 1 ||] | go n x = [|| $$x * $$(go (n-1) x) ||] | | Writing the following | | f :: TExp Char -> TExp Integer | f x = [|| $$x * 3 ||] | | gives the error | | Main.hs:28:7: | Couldn't match type 'Char' with 'Integer' | Expected type: TExp Integer | Actual type: TExp Char | In the Template Haskell quotation [|| $$x * 3 ||] | In the expression: [|| $$x * 3 ||] | In an equation for 'f': f x = [|| $$x * 3 ||] | | The th-new branch of ghc has accompanying branches for template-haskell | and testsuite, both named th-new. These are mirrors of my local branch, | and I reserve the right to rebase them :). That said, please do try it | out! | | Geoff | | | _______________________________________________ | ghc-devs mailing list | ghc-devs@haskell.org | http://www.haskell.org/mailman/listinfo/ghc-devs _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://www.haskell.org/mailman/listinfo/ghc-devs