1 Imperative Queues

Version: 5.3

This module provides a simple mutable queue representation, first-in/first-out only. Operations on queues mutate it in a thread-unsafe way.

procedure
(make-queue) → queue/c

Produces an empty queue.

procedure
(enqueue! q v) → void?
q : queue/c
v : any/c

Adds an element to the back of a queue.

procedure
(dequeue! q) → any/c
q : nonempty-queue/c

Removes an element from the front of a nonempty queue, and returns that element.

Examples:
(define q (make-queue))

> (enqueue! q 1)
> (dequeue! q)
1
> (enqueue! q 2)
> (enqueue! q 3)
> (dequeue! q)
2
> (dequeue! q)
3

procedure
(queue->list queue) → (listof any/c)
queue : queue/c

Returns an immutable list containing the elements of the queue in the order the elements were added.

Examples:
(define queue (make-queue))

> (enqueue! queue 8)
> (enqueue! queue 9)
> (enqueue! queue 0)
> (queue->list queue)
'(8 9 0)

procedure
(queue-length queue) → integer?
queue : queue/c

Returns the number of elements in the queue.

Examples:
(define queue (make-queue))

> (queue-length queue)
0
> (enqueue! queue 5)
> (enqueue! queue 12)
> (queue-length queue)
2
> (dequeue! queue)
5
> (queue-length queue)
1

procedure
(queue-empty? q) → boolean?
q : queue/c

Recognizes whether a queue is empty or not.

procedure
(queue? v) → boolean?
v : any/c

This predicate recognizes queues.

Examples:
> (queue? (make-queue))
#t
> (queue? 'not-a-queue)
#f

procedure
(in-queue queue) → sequence?
queue : queue?

Returns a sequence whose elements are the elements of queue.

value
queue/c : flat-contract?
value
nonempty-queue/c : flat-contract?

These contracts recognize queues; the latter requires the queue to contain at least one value.

1	Imperative Queues
2	Growable Vectors
3	Orders and Ordered Dictionaries
4	Splay Trees
5	Skip Lists
6	Interval Maps
7	Binary Heaps