No special magic. Just make sure you get the th-new branches of ghc, libraries/template-haskell, and testsuite. If you hit any snags let me know---happy to help you get running. Geoff On 05/17/2013 07:12 PM, Jacques Carette wrote:
Fantastic! I will definitely be trying it out early next week.
Are there any special instructions regarding how to compile this branch? I will work on adding test cases, which would be translations of larger metaocaml programs.
Jacques
On 13-05-16 11:21 AM, Geoffrey Mainland wrote:
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