stdin

stdin.txt

{-# LANGUAGE FunctionalDependencies,UndecidableInstances,FlexibleInstances #-}
class ReadObj a p | a -> p where
  readObj :: p -> [[String]] -> (a, [[String]])

consNE :: [a] -> [[a]] -> [[a]]
consNE [] t = t
consNE h t = h:t

-- grab an integer off of the stream
instance ReadObj Integer () where
  readObj _ ((h:t):t') = (read h, consNE t t')

-- read a pair of objects, make sure they are on the same line.
instance (ReadObj a pa, ReadObj b pb) => ReadObj (a,b) (pa, pb) where
  readObj (pa,pb) (h:rest) = let (a,[t]) = readObj pa [h]
                                 (b,[t']) = readObj pb [t] in
                             ((a,b),consNE t' rest)

-- should assume that the entire list is going to be on one line
instance (ReadObj a pa) => ReadObj [a] (Integer, [pa]) where
  readObj (0, _) l =  ([], l)
  readObj  (n, (ph:pt)) l =
    let (retH, listTail) = (readObj) (ph) l
        (retT, realTail) = readObj (n-1, pt) listTail in
    (retH:retT, realTail)