{-# OPTIONS -fglasgow-exts #-}
 
module GShow (tests) where

{-
 
The generic show example from the 2nd boilerplate paper.
(There were some typos in the ICFP 2004 paper.)
Also check out Data.Generics.Text.
 
-}

import Test.HUnit

import Data.Generics hiding (gshow)
import Prelude hiding (showString)

 
gshow :: Data a => a -> String
gshow = gshow_help `extQ` showString

gshow_help :: Data a => a -> String
gshow_help t 
     =  "("
     ++ showConstr (toConstr t)
     ++ concat (intersperse " " (gmapQ gshow t))
     ++ ")"

showString :: String -> String
showString s = "\"" ++ concat (map escape s) ++ "\"" 
               where
                 escape '\n' = "\\n"
                 escape other_char = [other_char]

gshowList :: Data b => [b] -> String
gshowList xs
    = "[" ++ concat (intersperse "," (map gshow xs)) ++ "]"

gshow' :: Data a => a -> String
gshow' = gshow_help `ext1Q` gshowList 
                    `extQ`  showString

intersperse :: a -> [a] -> [a]
intersperse _ []     = []
intersperse x [e]    = [e]
intersperse x (e:es) = (e:(x:intersperse x es))

tests = ( gshow' "foo"
        , gshow' [True,False]
        ) ~=? output

output = ("\"foo\"","[(True),(False)]")