> module Process
>        (process)
>        where

> data State = O | I

> acc ::  Eq a => State -> a  -> a -> [a] -> Bool
> acc O c1 c2 l  | length l > 0 && head l == c1 = acc I c1 c2 (tail l)
>                | length l > 0 && head l /= c1 = acc O c1 c2 (tail l)
>                | l == [] = True
>                | otherwise = True
> acc I c1 c2 l  | length l > 0 && head l == c2 = acc O c1 c2 (tail l)
>                | length l > 0 && head l /= c2 = acc I c1 c2 (tail l)
>                | l == [] = False
>                | otherwise = False

> dec :: Eq a => a -> a -> [a] -> Bool
> dec c1 c2 = acc O c1 c2

> inout :: Eq a => a -> a -> [a] -> [Bool]
> inout c1 c2 l = map (dec c1 c2) [take k l | k <- [1..length l]]

> pairs :: Eq t => t -> t -> [t] -> [(t, Bool)]
> pairs c1 c2 t = zipWith (\ x y  -> (x,y)) t (inout c1 c2 t)

> pairstotags :: Eq t => t -> t -> [t] -> [t] -> (t, Bool) -> [t]
> pairstotags c1 c2 p q (a, b) | (a == c1 && b == False) = p
>                              | (a == c2 && b == True ) = q
>                              | otherwise = [a]

> process :: Eq t => t -> t -> [t] -> [t] -> [t] -> [t]
> process c1 c2 p q x = concatMap (pairstotags c1 c2 p q) (pairs c1 c2 x)