[Haskell-cafe] Short Cut / Rewrite Rules Problem in GHC

[Chris]

Hi All. I am a student and a noob to Haskell. I am having some  
trouble with an example from the paper "Playing by the rules:  
Rewriting as a practical optimisation technique in GHC" by Simon  
Peyton Jones, Andrew Tolmach and Tony Hoare, specifically, the Short- 
cut Deforestation example in section 3.1. I was trying to compile the  
following using GHC version 6.4 on Mac OS X 10.4. The definition for  
build and the rule are from the paper (the rule also appears in the  
GHC online doc in section 7.10.1).

  -----------------------------------------------------
  -- BOF

  -- File: Main.hs

  module Main where

  build :: (forall b. (a->b->b) -> b -> b) -> [a]
  build' g = g (:) []

  {-# RULES
  "foldr/build"
    forall k z (g::forall b. (a->b->b) -> b -> b) .
    foldr k z (build g) = g k z
  #-}

  main  :: IO ()
  main  =  do putStr ""

  -- EOF
  -----------------------------------------------------

When I enable the extensions for GHC I get the following error:

  chris$ ghc -fglasgow-exts --make Main.hs
  Chasing modules from: Main.hs
  Compiling Main             ( Main.hs, Main.o )

  Main.hs:15:1: lexical error


When I don't have them enabled it gives this error:

  chris$ ghc --make Main.hs
  Chasing modules from: Main.hs
  Compiling Main             ( Main.hs, Main.o )

  Main.hs:8:18: parse error on input `.'


I have also tried moving the RULES option to the top of of the file  
above "module Main", but I still get the same errors.

  Also, should the definition of build be:

  build   :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a]
  build g = g (:) []

If I try to load the Main.hs file in HUGS with the -98 option and the  
above version of build (with the forall a.), it works without a  
problem. However, it still gives the same errors in GHC.

Additionally, I tried this on a different version of GHC, 6.2.2 on a  
x86 box running Gentoo Linux, and it yielded the same results. I am  
completely lost and would greatly appreciate any help. Thanks so much.

- Chris.