Module Queue2 (Queue, mtq, ismt, addq, remq) where

---- Interface ----------------

mtq :: Queue a -- empty queue

ismt :: Queue a -> Bool -- is the queue empty?

addq :: a -> Queue a -> Queue a -- add element to front of queue

remq :: Queue a -> (a, Queue a) -- remove element from back of queue;

-- produces error "Can't remove an element

-- from an empty queue" on empty

--- Implementation -----------

{- In this implementation, a queue is represented as a pair of lists.

The "front" of the queue is at the head of the first list, and the

"back" of the queue is at the HEAD of the second list. When the

second list is empty and we want to remove an element, we REVERSE the

elements in the first list and move them to the back, leaving the

first list empty. We can now process the removal request in the usual way.

-}

data Queue a = Queue2 [a] [a] -- deriving Show

mtq = undefined

ismt = undefined

addq x q = undefined

remq q = undefined

.