Add this item to the queue.

Return the count of items currently in the queue.

TODO: write docs

TODO: write docs

Apply this process, assumed to be a function of one argument, to the next item in the queue, if the queue is not currently locked; return the value returned by process.

Create a new queue

Look at the next item which could be removed from the queue.

True if x is a queue, else false.

Return the first item from the queue, rebind the queue to the remaining items. If the queue is empty return nil.

TODO: write docs