Re: [Template-haskell] example of derive using Template Haskell?

I understand that '[d|...|]' creates a Q [Dec], but in practice GHC 6.2.2 interprets it as a syntax error. Do I need to do something to enable it? I've read the user_guide. The printf example is obsolete. What I would really like is an example somewhere of deriving a class using Template Haskell. If I can't figure this out, I'll try to learn Drift. -Alex- On Tue, 11 Jan 2005, Lemmih wrote:

Hey Alex.

You write sugared Haskell inside [| |]. It's just an easier way of constructing the various data structures.

'[| |]' creates a structure of type 'ExpQ' Prelude Language.Haskell.TH> runQ [| 10 |] >>= print LitE (IntegerL 10)

'[t| |]' creates a structure of type 'TypeQ' Prelude Language.Haskell.TH> runQ [t| Maybe Int |] >>= print AppT (ConT Data.Maybe.Maybe) (ConT GHC.Base.Int)

'[d| |]' creates a structure of type 'Q [Dec]' Prelude Language.Haskell.TH> runQ [d| foo = "bar" |] >>= print [ValD (VarP foo) (NormalB (LitE (StringL "bar"))) []]

This information is more or less available at http://www.haskell.org/ghc/docs/latest/html/users_guide/template-haskell.htm...

On Mon, 10 Jan 2005 21:45:20 -0500 (Eastern Standard Time), S. Alexander Jacobson wrote: [...]

...

fooFunc = [d|funD "foo" [clause [] (normalB $ litE $ StringL "bar") [] ] |] goo = [|2|]

---

{-# OPTIONS -fglasgow-exts #-} import Tth foo = $(goo) $(fooFunc)

If I eliminate the d in "[d|" I get an error about Dec conflicting with Exp. [...] When you do a toplevel splice then the variable you're splicing must have type :: Q [Dec].

-- Friendly, Lemmih

______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com