The type of queues containing elements of type 'a.

Raised when peek_exn, pop_exn, N.keep_exn or N.shift_exn is applied to an empty queue.

Return true if the given queue is empty, false otherwise.

Return a new queue, initially empty.

Number of elements in the queue.

push q x adds the elements x at the end of the queue q.

pop q removes and returns the first element in queue q. If q is empty, it returns None.

pop_exn is the same as pop but it raises Empty when the given queue q is empty.

peek q returns the first element in the queue q, without removing it from the queue. If q is empty, it returns None.

Same as peek but it raises Empty if q is empty.

cons q x adds element x at the front of the given queue q. It returns None if it fails.

iter f q applies f in turn to all elements of q, from the least recently entered to the most recently entered. The queue itself is unchanged.

fold f a q is equivalent to List.fold_left f a l, where l is the list of q's elements. The queue remains unchanged.