Hi.
I've started using template haskell (replacing some preprocessor stuff)
However I had real trouble when trying to convert
instance (Show d) => Show (C d)
where show _ = "C " ++ (show (undefined :: d))
into th.
Why? It didn't compile (http://hpaste.org/289)
Heffalump on #haskell suggested that the d is already in scope so I
don't need the first list item of ForallT ..
And that does work fine.
So is this a bug in the [d| .. parser / to abstract syntax tree
transformer ?
Session showing this behviour:
[EMAIL PROTECTED] ~ $ cat ABC.hs
{-# OPTIONS_GHC -fglasgow-exts #-}
module ABC where
data C d
[EMAIL PROTECTED] ~ $ ghci -fth
___ ___ _
/ _ \ /\ /\/ __(_)
/ /_\// /_/ / / | | GHC Interactive, version 6.6, for Haskell 98.
/ /_\\/ __ / /___| | http://www.haskell.org/ghc/
\____/\/ /_/\____/|_| Type :? for help.
Loading package base ... linking ... done.
Prelude> :l ABC
[1 of 1] Compiling ABC ( ABC.hs, interpreted )
Ok, modules loaded: ABC.
*ABC> :m +Language.Haskell.TH
*ABC Language.Haskell.TH> runQ [d| instance (Show d) => Show (C d) where show
_ = "C " ++ (show (undefined :: d)) |] >>= print
Loading package template-haskell ... linking ... done.
[InstanceD [AppT (ConT GHC.Show.Show) (VarT d_0)] (AppT (ConT GHC.Show.Show)
(AppT (ConT ABC.C) (VarT d_0))) [FunD show [Clause [WildP] (NormalB (InfixE
(Just (LitE (StringL "C "))) (VarE GHC.Base.++) (Just (AppE (VarE show) (SigE
(VarE GHC.Err.undefined) (ForallT [d_1] [] (VarT d_1))))))) []]]]
*ABC Language.Haskell.TH>
Now
(ForallT [d_1] [] (VarT d_1)
should be
(ForallT [] [] (VarT d_1)
shouldn't it?
Marc Weber
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