class  Show a  where
    showsPrec        :: Int -> a -> ShowS
    show       :: a -> String 
    showList         :: [a] -> ShowS

-- Mimimal complete definition:
-- show or showsPrec
    showsPrec _ x s   = show x ++ s

    show x        = showsPrec 0 x ""

    showList []       = showString "[]"
    showList (x:xs)   = showChar '[' . shows x . showl xs
                        where showl []     = showChar ']'
                              showl (x:xs) = showChar ',' . shows x .
                                             showl xs