Queue.XtExplicit transaction log passing on queues.
swap q1 q2 exchanges the contents of the queues q1 and q2.
to_seq s returns a domain safe sequence for iterating through the elements of the queue front to back.
The sequence is based on a constant time, O(1), snapshot of the queue and modifications of the queue have no effect on the sequence.
add q x adds the element x at the end of the queue q.
peek_opt q returns the first element in queue q, without removing it from the queue, or returns None if the queue is empty.