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 ||]
$$(foo)
is too heavy a syntax, and will make it seem horrid an clunky. Two-character
brackets are bad enough. What about
[@ foo @]
&(foo)
Other suggestions welcome. Trivial yet important.
Simon
Microsoft Research Limited (company number 03369488) is registered in England
and Wales
Registered office 21 Station Road, Cambridge, CB1 2FB
| -----Original Message-----
| From: [email protected] [mailto:[email protected]]
| On Behalf Of Geoffrey Mainland
| Sent: 16 May 2013 16:22
| To: [email protected]
| Cc: [email protected]
| Subject: New branch implementing typed/untyped Template Haskell
|
| I have pushed a new branch, th-new, that partially implements the
| proposal outlined in Simon PJ's "New directions for Template Haskell"
| post at:
|
| http://hackage.haskell.org/trac/ghc/blog/Template%20Haskell%20Proposal
|
| The main missing features are top-level pattern splices and local
| declaration splices.
|
| Typed expression quotations and typed expression splices *are*
| implemented. Syntax is as in Simon's original proposal: [|| ||] for
| typed expression brackets and $$(...) 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
|
|
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