queue.hs

module Queue where

data Queue a = Queue [a] [a]
             deriving (Show, Eq)

emptyQueue :: Queue a
emptyQueue = Queue [] []

push :: a -> Queue a -> Queue a
push x (Queue d e) = Queue d (x:e)

pop :: Queue a -> (a, Queue a)
pop (Queue [] e) = pop $ Queue (reverse e) []
pop (Queue (x:d) e) = (x, Queue d e)