Template Haskell Example

CustomShow.hs

{-# LANGUAGE TemplateHaskell, FlexibleInstances #-}

module CustomShow where

import Language.Haskell.TH
import Data.List (intercalate)

emptyShow :: Name -> Q [Dec]
emptyShow name = [d|instance Show $(conT name) where show _ = ""|]

listFields :: Name -> Q [Dec]
listFields name = do
    TyConI (DataD _ _ _ [RecC _ fields] _) <- reify name

    let names = map (\(name,_,_) -> name) fields

        showField :: Name -> Q Exp
        showField name = [|\x -> s ++ " = " ++ show ($(global name) x)|] where
            s = nameBase name

        showFields :: Q Exp
        showFields = listE $ map showField names

    [d|instance Show $(conT name) where
        show x = intercalate ", " (map ($ x) $showFields)|]

test_show.hs

{-# LANGUAGE TemplateHaskell #-}

import CustomShow

data MyData = MyData
    { foo :: String
    , bar :: Int
    }

listFields ''MyData

main = print $ MyData { foo = "bar", bar = 5 }

This code is causing GHC to crash on me.

http://hpaste.org/88499
http://hpaste.org/88498
http://hpaste.org/88500

The Glorious Glasgow Haskell Compilation System, version 7.4.2
cabal-install version 1.16.0.2
using version 1.16.0.3 of the Cabal library