mkName problem

Tomasz Zielonka <[email protected]> Fri, 7 Oct 2005 15:12:24 +0200

Newsgroups	gmane.comp.lang.haskell.template
Message-ID	<[email protected]>

Hello!

The attached code shows a behaviour which I don't understand. This could
be a bug in TH or a misunderstanding on my side. The problem is that
dynamically
bound Names made with mkName sometimes "don't see" the variable. See
the code for details. It could be a bit shorter, but I wanted to show why I
cat't
use the 'var syntax. Try to --make T, then uncomment the marked line in T.hs
.

Best regards
Tomasz

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T.hs (text/x-haskell, 234 B)

{-# OPTIONS -fglasgow-exts #-}

import Mod

variable = "foo"
variable2 = "bar"

main = do
    putStrLn $(expandVars "variable, variable2")
    -- It compiles when I uncomment the following line
    -- let _ = variable
    return ()

Mod.hs (text/x-haskell, 329 B)

{-# OPTIONS -fglasgow-exts #-}

module Mod where

import Language.Haskell.TH
import List
import Char

expandVars :: String -> Q Exp
expandVars s =
    [| concat $(return (ListE (map f (groupBy (\x y -> g x == g y) s)))) |]
  where
    f x | all g x   = VarE (mkName x)
        | otherwise = LitE (StringL x)
    g = isAlphaNum