Data commit

Task/Queue-Usage/00-META.yaml

@@ -0,0 +1,3 @@
+---
+from: http://rosettacode.org/wiki/Queue/Usage
+note: Data Structures

Task/Queue-Usage/00-TASK.txt

@@ -0,0 +1,18 @@
+{{Data structure}}
+[[File:Fifo.gif|frame|right|Illustration of FIFO behavior]]
+
+;Task:
+Create a queue data structure and demonstrate its operations. 
+
+(For implementations of queues, see the [[FIFO]] task.)
+
+
+Operations:
+::*   push                (aka ''enqueue'') - add element
+::*   pop            (aka ''dequeue'') - pop first element
+::*   empty                    - return truth value when empty
+
+<br>
+{{Template:See also lists}}
+<br><br>
+

Task/Queue-Usage/11l/queue-usage.11l

@@ -0,0 +1,9 @@
+Deque[String] my_queue
+
+my_queue.append(‘foo’)
+my_queue.append(‘bar’)
+my_queue.append(‘baz’)
+
+print(my_queue.pop_left())
+print(my_queue.pop_left())
+print(my_queue.pop_left())

Task/Queue-Usage/6502-Assembly/queue-usage-1.6502

@@ -0,0 +1,34 @@
+queuePointerStart equ #$FD
+queuePointerMinus1 equ #$FC     ;make this equal whatever "queuePointerStart" is, minus 1.
+pushQueue:
+STA 0,x
+DEX
+RTS
+
+popQueue:
+STX temp
+LDX #queuePointerStart
+LDA 0,x ;get the item that's first in line
+PHA
+    LDX #queuePointerMinus1
+loop_popQueue:
+    LDA 0,X
+    STA 1,X
+    DEX
+    CPX temp
+    BNE loop_popQueue
+    LDX temp
+    INX
+PLA ;return the item that just left the queue
+RTS
+
+isQueueEmpty:
+LDA #1
+CPX #queuePointerStart
+BEQ yes  ;return 1
+
+SEC
+SBC #1   ;return 0
+
+yes:
+RTS

Task/Queue-Usage/6502-Assembly/queue-usage-2.6502

@@ -0,0 +1,16 @@
+define temp $00
+define queueEmpty $FD
+define queueAlmostEmpty $FC
+
+LDX #queueEmpty  ;set up software queue
+
+LDA #$40
+jsr pushQueue
+
+LDA #$80
+jsr pushQueue
+
+LDA #$C0
+jsr pushQueue
+
+brk

Task/Queue-Usage/6502-Assembly/queue-usage-3.6502

@@ -0,0 +1,18 @@
+define temp $00
+define queueEmpty $FD
+define queueAlmostEmpty $FC
+
+LDX #queueEmpty  ;set up software queue
+
+LDA #$40
+jsr pushQueue
+
+LDA #$80
+jsr pushQueue
+
+LDA #$C0
+jsr pushQueue
+
+jsr popQueue
+
+brk

Task/Queue-Usage/6502-Assembly/queue-usage-4.6502

@@ -0,0 +1,22 @@
+define temp $00
+define queueEmpty $FD
+define queueAlmostEmpty $FC
+
+
+LDX #queueEmpty  ;set up software queue
+
+LDA #$40
+jsr pushQueue
+
+LDA #$80
+jsr pushQueue
+
+LDA #$C0
+jsr pushQueue
+
+jsr popQueue
+
+lda #$ff
+jsr pushQueue
+
+brk

Task/Queue-Usage/8th/queue-usage.8th

@@ -0,0 +1,7 @@
+10 q:new  \ create a new queue 10 deep
+123 q:push
+341 q:push  \ push 123, 341 onto the queue
+q:pop . cr  \ displays 123
+q:len . cr  \ displays 1
+q:pop . cr  \ displays 341
+q:len . cr  \ displays 0

Task/Queue-Usage/ALGOL-68/queue-usage-1.alg

@@ -0,0 +1,15 @@
+# -*- coding: utf-8 -*- #
+MODE DIETITEM = STRUCT(
+  STRING food, annual quantity, units, REAL cost
+);
+
+# Stigler's 1939 Diet ... #
+FORMAT diet item fmt = $g": "g" "g" = $"zd.dd$;
+[]DIETITEM stigler diet = (
+  ("Cabbage",           "111","lb.",  4.11),
+  ("Dried Navy Beans",  "285","lb.", 16.80),
+  ("Evaporated Milk",    "57","cans", 3.84),
+  ("Spinach",            "23","lb.",  1.85),
+  ("Wheat Flour",       "370","lb.", 13.33),
+  ("Total Annual Cost",    "","",    39.93)
+)

Task/Queue-Usage/ALGOL-68/queue-usage-2.alg

@@ -0,0 +1,20 @@
+#!/usr/bin/a68g --script #
+# -*- coding: utf-8 -*- #
+
+MODE OBJVALUE = DIETITEM;
+PR read "prelude/link.a68" PR;# c.f. [[rc:Queue/Definition]] #
+PR read "prelude/queue_base.a68" PR; # c.f. [[rc:Queue/Definition]] #
+
+PR read "test/data_stigler_diet.a68" PR;
+OBJQUEUE example queue; obj queue init(example queue);
+
+FOR i TO UPB stigler diet DO
+# obj queue put(example queue, stigler diet[i]) or ... #
+  stigler diet[i] +=: example queue
+OD;
+
+printf($"Get remaining values from queue:"l$);
+WHILE NOT obj queue is empty(example queue) DO
+# OR example queue ISNT obj queue empty #
+  printf((diet item fmt, obj queue get(example queue), $l$))
+OD

Task/Queue-Usage/AWK/queue-usage.awk

@@ -0,0 +1,55 @@
+function deque(arr) {
+    arr["start"] = 0
+    arr["end"] = 0
+}
+
+function dequelen(arr) {
+    return arr["end"] - arr["start"]
+}
+
+function empty(arr) {
+    return dequelen(arr) == 0
+}
+
+function push(arr, elem) {
+    arr[++arr["end"]] = elem
+}
+
+function pop(arr) {
+    if (empty(arr)) {
+        return
+    }
+    return arr[arr["end"]--]
+}
+
+function unshift(arr, elem) {
+    arr[arr["start"]--] = elem
+}
+
+function shift(arr) {
+    if (empty(arr)) {
+        return
+    }
+    return arr[++arr["start"]]
+}
+
+function printdeque(arr,    i, sep) {
+    printf("[")
+    for (i = arr["start"] + 1; i <= arr["end"]; i++) {
+        printf("%s%s", sep, arr[i])
+        sep = ", "
+    }
+    printf("]\n")
+}
+
+BEGIN {
+    deque(q)
+    for (i = 1; i <= 10; i++) {
+        push(q, i)
+    }
+    printdeque(q)
+    for (i = 1; i <= 10; i++) {
+        print shift(q)
+    }
+    printdeque(q)
+}

Task/Queue-Usage/Action-/queue-usage.action

@@ -0,0 +1,86 @@
+CARD EndProg ;required for ALLOCATE.ACT
+
+INCLUDE "D2:ALLOCATE.ACT" ;from the Action! Tool Kit. You must type 'SET EndProg=*' from the monitor after compiling, but before running this program!
+
+DEFINE PTR="CARD"
+DEFINE NODE_SIZE="4"
+TYPE QueueNode=[PTR data,nxt]
+
+QueueNode POINTER queueFront,queueRear
+
+BYTE FUNC IsEmpty()
+  IF queueFront=0 THEN
+    RETURN (1)
+  FI
+RETURN (0)
+
+PROC Push(CHAR ARRAY v)
+  QueueNode POINTER node
+
+  node=Alloc(NODE_SIZE)
+  node.data=v
+  node.nxt=0
+  IF IsEmpty() THEN
+    queueFront=node
+  ELSE
+    queueRear.nxt=node
+  FI
+  queueRear=node
+RETURN
+
+PTR FUNC Pop()
+  QueueNode POINTER node
+  CHAR ARRAY v
+
+  IF IsEmpty() THEN
+    PrintE("Error: queue is empty!")
+    Break()
+  FI
+
+  node=queueFront
+  v=node.data
+  queueFront=node.nxt
+  Free(node,NODE_SIZE)
+RETURN (v)
+
+PROC TestIsEmpty()
+  IF IsEmpty() THEN
+    PrintE("Queue is empty")
+  ELSE
+    PrintE("Queue is not empty")
+  FI
+RETURN
+
+PROC TestPush(CHAR ARRAY v)
+  PrintF("Push: %S%E",v)
+  Push(v)
+RETURN
+
+PROC TestPop()
+  CHAR ARRAY v
+
+  Print("Pop: ")
+  v=Pop()
+  PrintE(v)
+RETURN
+
+PROC Main()
+  AllocInit(0)
+  queueFront=0
+  queueRear=0
+
+  Put(125) PutE() ;clear screen
+
+  TestIsEmpty()
+  TestPush("foo")
+  TestIsEmpty()
+  TestPush("bar")
+  TestPop()
+  TestIsEmpty()
+  TestPush("baz")
+  TestPop()
+  TestIsEmpty()
+  TestPop()
+  TestIsEmpty()
+  TestPop()
+RETURN

Task/Queue-Usage/Ada/queue-usage.ada

@@ -0,0 +1,21 @@
+with FIFO;
+with Ada.Text_Io; use Ada.Text_Io;
+
+procedure Queue_Test is
+   package Int_FIFO is new FIFO (Integer);
+   use Int_FIFO;
+   Queue : FIFO_Type;
+   Value : Integer;
+begin
+   Push (Queue, 1);
+   Push (Queue, 2);
+   Push (Queue, 3);
+   Pop (Queue, Value);
+   Pop (Queue, Value);
+   Push (Queue, 4);
+   Pop (Queue, Value);
+   Pop (Queue, Value);
+   Push (Queue, 5);
+   Pop (Queue, Value);
+   Put_Line ("Is_Empty " & Boolean'Image (Is_Empty (Queue)));
+end Queue_Test;

Task/Queue-Usage/AppleScript/queue-usage.applescript

@@ -0,0 +1,29 @@
+on push(StackRef, value)
+    set StackRef's contents to {value} & StackRef's contents
+    return StackRef
+end push
+
+on pop(StackRef)
+    set R to missing value
+    if StackRef's contents ≠ {} then
+        set R to StackRef's contents's item 1
+        set StackRef's contents to {} & rest of StackRef's contents
+    end if
+    return R
+end pop
+
+on isStackEmpty(StackRef)
+    if StackRef's contents = {} then return true
+    return false
+end isStackEmpty
+
+
+set theStack to {}
+repeat with i from 1 to 5
+    push(a reference to theStack, i)
+    log result
+end repeat
+repeat until isStackEmpty(theStack) = true
+    pop(a reference to theStack)
+    log result
+end repeat

Task/Queue-Usage/Arturo/queue-usage.arturo

@@ -0,0 +1,35 @@
+define :queue [][
+    init: [
+        this\items: []
+    ]
+]
+
+empty?: function [this :queue][
+    zero? this\items
+]
+
+push: function [this :queue, item][
+    this\items: this\items ++ item
+]
+
+pop: function [this :queue][
+    ensure -> not? empty? this
+
+    result: this\items\0
+    this\items: remove.index this\items 0
+    return result
+]
+
+Q: to :queue []
+
+push Q 1
+push Q 2
+push Q 3
+
+print ["queue is empty?" empty? Q]
+
+print ["popping:" pop Q]
+print ["popping:" pop Q]
+print ["popping:" pop Q]
+
+print ["queue is empty?" empty? Q]

Task/Queue-Usage/Astro/queue-usage.astro

@@ -0,0 +1,9 @@
+let my_queue = Queue()
+
+my_queue.push!('foo')
+my_queue.push!('bar')
+my_queue.push!('baz')
+
+print my_queue.pop!() # 'foo'
+print my_queue.pop!() # 'bar'
+print my_queue.pop!() # 'baz'

Task/Queue-Usage/AutoHotkey/queue-usage.ahk

@@ -0,0 +1,31 @@
+push("qu", 2), push("qu", 44), push("qu", "xyz") ; TEST
+
+MsgBox % "Len = " len("qu") ; Number of entries
+While !empty("qu")          ; Repeat until queue is not empty
+    MsgBox % pop("qu")      ; Print popped values (2, 44, xyz)
+MsgBox Error = %ErrorLevel% ; ErrorLevel =  0: OK
+MsgBox % pop("qu")          ; Empty
+MsgBox Error = %ErrorLevel% ; ErrorLevel = -1: popped too much
+MsgBox % "Len = " len("qu") ; Number of entries
+
+push(queue,_) {             ; push _ onto queue named "queue" (!=_), _ string not containing |
+    Global
+    %queue% .= %queue% = "" ? _ : "|" _
+}
+
+pop(queue) {                ; pop value from queue named "queue" (!=_,_1,_2)
+    Global
+    RegExMatch(%queue%, "([^\|]*)\|?(.*)", _)
+    Return _1, ErrorLevel := -(%queue%=""), %queue% := _2
+}
+
+empty(queue) {              ; check if queue named "queue" is empty
+    Global
+    Return %queue% = ""
+}
+
+len(queue) {                ; number of entries in "queue"
+    Global
+    StringReplace %queue%, %queue%, |, |, UseErrorLevel
+    Return %queue% = "" ? 0 : ErrorLevel+1
+}

Task/Queue-Usage/BBC-BASIC/queue-usage.basic

@@ -0,0 +1,31 @@
+      FIFOSIZE = 1000
+
+      FOR n = 3 TO 5
+        PRINT "Push ";n : PROCenqueue(n)
+      NEXT
+      PRINT "Pop " ; FNdequeue
+      PRINT "Push 6" : PROCenqueue(6)
+      REPEAT
+        PRINT "Pop " ; FNdequeue
+      UNTIL FNisempty
+      PRINT "Pop " ; FNdequeue
+      END
+
+      DEF PROCenqueue(n) : LOCAL f%
+      DEF FNdequeue : LOCAL f% : f% = 1
+      DEF FNisempty : LOCAL f% : f% = 2
+      PRIVATE fifo(), rptr%, wptr%
+      DIM fifo(FIFOSIZE-1)
+      CASE f% OF
+        WHEN 0:
+          wptr% = (wptr% + 1) MOD FIFOSIZE
+          IF rptr% = wptr% ERROR 100, "Error: queue overflowed"
+          fifo(wptr%) = n
+        WHEN 1:
+          IF rptr% = wptr% ERROR 101, "Error: queue empty"
+          rptr% = (rptr% + 1) MOD FIFOSIZE
+          = fifo(rptr%)
+        WHEN 2:
+          = (rptr% = wptr%)
+      ENDCASE
+      ENDPROC

Task/Queue-Usage/Bracmat/queue-usage.bracmat

@@ -0,0 +1,38 @@
+  ( queue
+  =   (list=)
+      (enqueue=.(.!arg) !(its.list):?(its.list))
+      ( dequeue
+      =   x
+        .   !(its.list):?(its.list) (.?x)
+          & !x
+      )
+      (empty=.!(its.list):)
+  )
+& new$queue:?Q
+& (   (Q..enqueue)$1
+    & (Q..enqueue)$2
+    & (Q..enqueue)$3
+    & out$((Q..dequeue)$)
+    & (Q..enqueue)$4
+    & out$((Q..dequeue)$)
+    & out$((Q..dequeue)$)
+    &   out
+      $ ( The
+          queue
+          is
+          ((Q..empty)$&|not)
+          empty
+        )
+    & out$((Q..dequeue)$)
+    &   out
+      $ ( The
+          queue
+          is
+          ((Q..empty)$&|not)
+          empty
+        )
+    & out$((Q..dequeue)$)
+    & out$Success!
+  | out$"Attempt to dequeue failed"
+  )
+;

Task/Queue-Usage/C++/queue-usage-1.cpp

@@ -0,0 +1,46 @@
+#include <queue>
+#include <cassert> // for run time assertions
+
+int main()
+{
+  std::queue<int> q;
+  assert( q.empty() );        // initially the queue is empty
+
+  q.push(1);                  // add an element
+  assert( !q.empty() );       // now the queue isn't empty any more
+  assert( q.front() == 1 );   // the first element is, of course, 1
+
+  q.push(2);                  // add another element
+  assert( !q.empty() );       // it's of course not empty again
+  assert( q.front() == 1 );   // the first element didn't change
+
+  q.push(3);                  // add yet an other element
+  assert( !q.empty() );       // the queue is still not empty
+  assert( q.front() == 1 );   // and the first element is still 1
+
+  q.pop();                    // remove the first element
+  assert( !q.empty() );       // the queue is not yet empty
+  assert( q.front() == 2);    // the first element is now 2 (the 1 is gone)
+
+  q.pop();
+  assert( !q.empty() );
+  assert( q.front() == 3);
+
+  q.push(4);
+  assert( !q.empty() );
+  assert( q.front() == 3);
+
+  q.pop();
+  assert( !q.empty() );
+  assert( q.front() == 4);
+
+  q.pop();
+  assert( q.empty() );
+
+  q.push(5);
+  assert( !q.empty() );
+  assert( q.front() == 5);
+
+  q.pop();
+  assert( q.empty() );
+}

Task/Queue-Usage/C++/queue-usage-2.cpp

@@ -0,0 +1 @@
+  std::queue<int, std::list<int> >

Task/Queue-Usage/C-sharp/queue-usage.cs

@@ -0,0 +1,37 @@
+using System;
+using System.Collections.Generic;
+
+namespace RosettaCode
+{
+    class Program
+    {
+        static void Main()
+        {
+            // Create a queue and "push" items into it
+            Queue<int> queue  = new Queue<int>();
+            queue.Enqueue(1);
+            queue.Enqueue(3);
+            queue.Enqueue(5);
+
+            // "Pop" items from the queue in FIFO order
+            Console.WriteLine(queue.Dequeue()); // 1
+            Console.WriteLine(queue.Dequeue()); // 3
+            Console.WriteLine(queue.Dequeue()); // 5
+
+            // To tell if the queue is empty, we check the count
+            bool empty = queue.Count == 0;
+            Console.WriteLine(empty); // "True"
+
+            // If we try to pop from an empty queue, an exception
+            // is thrown.
+            try
+            {
+                queue.Dequeue();
+            }
+            catch (InvalidOperationException exception)
+            {
+                Console.WriteLine(exception.Message); // "Queue empty."
+            }
+        }
+    }
+}

Task/Queue-Usage/C/queue-usage.c

@@ -0,0 +1,31 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+#include <sys/queue.h>
+
+/* #include "fifolist.h" */
+
+int main()
+{
+  int i;
+  FIFOList head;
+
+  TAILQ_INIT(&head);
+
+  /* insert 20 integer values */
+  for(i=0; i < 20; i++) {
+    m_enqueue(i, &head);
+  }
+
+  /* dequeue and print */
+  while( m_dequeue(&i, &head) )
+    printf("%d\n", i);
+
+  fprintf(stderr, "FIFO list %s\n",
+      ( m_dequeue(&i, &head) ) ?
+      "had still an element" :
+      "is void!");
+
+  exit(0);
+}

Task/Queue-Usage/Clojure/queue-usage-1.clj

@@ -0,0 +1,11 @@
+(def q (make-queue))
+
+(enqueue q 1)
+(enqueue q 2)
+(enqueue q 3)
+
+(dequeue q) ; 1
+(dequeue q) ; 2
+(dequeue q) ; 3
+
+(queue-empty? q) ; true

Task/Queue-Usage/Clojure/queue-usage-2.clj

@@ -0,0 +1,11 @@
+(def q (java.util.LinkedList.))
+
+(.add q 1)
+(.add q 2)
+(.add q 3)
+
+(.remove q) ; 1
+(.remove q) ; 2
+(.remove q) ; 3
+
+(.isEmpty q) ; true

Task/Queue-Usage/CoffeeScript/queue-usage-1.coffee

@@ -0,0 +1,32 @@
+# We build a Queue on top of an ordinary JS array, which supports push
+# and shift.  For simple queues, it might make sense to just use arrays
+# directly, but this code shows how to encapsulate the array behind a restricted
+# API.  For very large queues, you might want a more specialized data
+# structure to implement the queue, in case arr.shift works in O(N) time, which
+# is common for array implementations.  On my laptop I start noticing delay
+# after about 100,000 elements, using node.js.
+Queue = ->
+  arr = []
+  enqueue: (elem) ->
+    arr.push elem
+  dequeue: (elem) ->
+    throw Error("queue is empty") if arr.length == 0
+    arr.shift elem
+  is_empty: (elem) ->
+    arr.length == 0
+
+# test
+do ->
+  q = Queue()
+  for i in [1..100000]
+    q.enqueue i
+
+  console.log q.dequeue() # 1
+  while !q.is_empty()
+    v = q.dequeue()
+  console.log v # 1000
+
+  try
+    q.dequeue() # throws Error
+  catch e
+    console.log "#{e}"

Task/Queue-Usage/CoffeeScript/queue-usage-2.coffee

@@ -0,0 +1,4 @@
+> coffee queue.coffee
+1
+100000
+Error: queue is empty

Task/Queue-Usage/Common-Lisp/queue-usage.lisp

@@ -0,0 +1,7 @@
+(let ((queue (make-queue)))
+  (enqueue 38 queue)
+  (assert (not (queue-empty-p queue)))
+  (enqueue 23 queue)
+  (assert (eql 38 (dequeue queue)))
+  (assert (eql 23 (dequeue queue)))
+  (assert (queue-empty-p queue)))

Task/Queue-Usage/Component-Pascal/queue-usage.pas

@@ -0,0 +1,23 @@
+MODULE UseQueue;
+IMPORT
+  Queue,
+  Boxes,
+  StdLog;
+
+PROCEDURE Do*;
+VAR
+  q: Queue.Instance;
+  b: Boxes.Box;
+BEGIN
+  q := Queue.New(10);
+  q.Push(Boxes.NewInteger(1));
+  q.Push(Boxes.NewInteger(2));
+  q.Push(Boxes.NewInteger(3));
+  b := q.Pop();
+  b := q.Pop();
+  q.Push(Boxes.NewInteger(4));
+  b := q.Pop();
+  b := q.Pop();
+  StdLog.String("Is empty:> ");StdLog.Bool(q.IsEmpty());StdLog.Ln
+END Do;
+END UseQueue.

Task/Queue-Usage/Cowgol/queue-usage.cowgol

@@ -0,0 +1,28 @@
+include "cowgol.coh";
+
+typedef QueueData is uint8; # the queue will contain bytes
+include "queue.coh"; # from the Queue/Definition task
+
+var queue := MakeQueue();
+
+# enqueue bytes 0 to 20
+print("Enqueueing: ");
+var n: uint8 := 0;
+while n < 20 loop
+    print_i8(n);
+    print_char(' ');
+    Enqueue(queue, n);
+    n := n + 1;
+end loop;
+print_nl();
+
+# dequeue and print everything in the queue
+print("Dequeueing: ");
+while QueueEmpty(queue) == 0 loop
+    print_i8(Dequeue(queue));
+    print_char(' ');
+end loop;
+print_nl();
+
+# free the queue
+FreeQueue(queue);

Task/Queue-Usage/D/queue-usage-1.d

@@ -0,0 +1,44 @@
+class LinkedQueue(T) {
+    private static struct Node {
+        T data;
+        Node* next;
+    }
+
+    private Node* head, tail;
+
+    bool empty() { return head is null; }
+
+    void push(T item) {
+        if (empty())
+            head = tail = new Node(item);
+        else {
+            tail.next = new Node(item);
+            tail = tail.next;
+        }
+    }
+
+    T pop() {
+        if (empty())
+            throw new Exception("Empty LinkedQueue.");
+        auto item = head.data;
+        head = head.next;
+        if (head is tail) // Is last one?
+            // Release tail reference so that GC can collect.
+            tail = null;
+        return item;
+    }
+
+    alias push enqueue;
+    alias pop dequeue;
+}
+
+void main() {
+    auto q = new LinkedQueue!int();
+    q.push(10);
+    q.push(20);
+    q.push(30);
+    assert(q.pop() == 10);
+    assert(q.pop() == 20);
+    assert(q.pop() == 30);
+    assert(q.empty());
+}

Task/Queue-Usage/D/queue-usage-2.d

@@ -0,0 +1,75 @@
+module queue_usage2;
+
+import std.traits: hasIndirections;
+
+struct GrowableCircularQueue(T) {
+    public size_t length;
+    private size_t first, last;
+    private T[] A = [T.init];
+
+    this(T[] items...) pure nothrow @safe {
+        foreach (x; items)
+            push(x);
+    }
+
+    @property bool empty() const pure nothrow @safe @nogc {
+        return length == 0;
+    }
+
+    @property T front() pure nothrow @safe @nogc {
+        assert(length != 0);
+        return A[first];
+    }
+
+    T opIndex(in size_t i) pure nothrow @safe @nogc {
+        assert(i < length);
+        return A[(first + i) & (A.length - 1)];
+    }
+
+    void push(T item) pure nothrow @safe {
+        if (length >= A.length) { // Double the queue.
+            immutable oldALen = A.length;
+            A.length *= 2;
+            if (last < first) {
+                A[oldALen .. oldALen + last + 1] = A[0 .. last + 1];
+                static if (hasIndirections!T)
+                    A[0 .. last + 1] = T.init; // Help for the GC.
+                last += oldALen;
+            }
+        }
+        last = (last + 1) & (A.length - 1);
+        A[last] = item;
+        length++;
+    }
+
+    @property T pop() pure nothrow @safe @nogc {
+        assert(length != 0);
+        auto saved = A[first];
+        static if (hasIndirections!T)
+            A[first] = T.init; // Help for the GC.
+        first = (first + 1) & (A.length - 1);
+        length--;
+        return saved;
+    }
+}
+
+version (queue_usage2_main) {
+    void main() {
+        GrowableCircularQueue!int q;
+        q.push(10);
+        q.push(20);
+        q.push(30);
+        assert(q.pop == 10);
+        assert(q.pop == 20);
+        assert(q.pop == 30);
+        assert(q.empty);
+
+        uint count = 0;
+        foreach (immutable i; 1 .. 1_000) {
+            foreach (immutable j; 0 .. i)
+                q.push(count++);
+            foreach (immutable j; 0 .. i)
+                q.pop;
+        }
+    }
+}

Task/Queue-Usage/Delphi/queue-usage.delphi

@@ -0,0 +1,25 @@
+program QueueUsage;
+
+{$APPTYPE CONSOLE}
+
+uses Generics.Collections;
+
+var
+  lStringQueue: TQueue<string>;
+begin
+  lStringQueue := TQueue<string>.Create;
+  try
+    lStringQueue.Enqueue('First');
+    lStringQueue.Enqueue('Second');
+    lStringQueue.Enqueue('Third');
+
+    Writeln(lStringQueue.Dequeue);
+    Writeln(lStringQueue.Dequeue);
+    Writeln(lStringQueue.Dequeue);
+
+    if lStringQueue.Count = 0 then
+      Writeln('Queue is empty.');
+  finally
+    lStringQueue.Free;
+  end
+end.

Task/Queue-Usage/Diego/queue-usage.diego

@@ -0,0 +1,31 @@
+set_ns(rosettacode)_me();
+
+    add_queue({int},q)_values(1..4);    // 1,2,3,4 (1 is first/bottom, 4 is last/top)
+    with_queue(q)_pop();                // 2,3,4
+    with_queue(q)_dequeue();            // 3,4
+    with_queue(q)_enqueue(5);           // 3,4,5
+
+    with_queue(q)_push()_v(6,7);        // 3,4,5,6,7
+
+    add_var({int},b)_value(8);
+    with_queue(q)_push[b];              // 3,4,5,6,7,8
+
+    with_queue(q)_pluck()_at(2);        // callee will return `with_queue(q)_err(pluck invalid with queue);`
+
+    me_msg()_queue(q)_top();            // "8"
+    me_msg()_queue(q)_last();           // "8"
+    me_msg()_queue(q)_peek();           // "8"
+
+    me_msg()_queue(q)_bottom();         // "3"
+    me_msg()_queue(q)_first();          // "3"
+    me_msg()_queue(q)_peer();           // "3"
+
+    me_msg()_queue(q)_isempty();            // "false"
+    with_queue(q)_empty();
+    with_queue(q)_msg()_isempty()_me();     // "true" (alternative syntax)
+
+    with_queue()_pop();                 // callee will return `with_queue(q)_err(pop invalid with empty queue);`
+
+    me_msg()_queue(q)_history()_all();      // returns the entire history of queue 'q' since its creation
+
+reset_namespace[];

Task/Queue-Usage/E/queue-usage.e

@@ -0,0 +1,9 @@
+def [reader, writer] := makeQueue()
+require(escape empty { reader.dequeue(empty); false } catch _ { true })
+writer.enqueue(1)
+writer.enqueue(2)
+require(reader.dequeue(throw) == 1)
+writer.enqueue(3)
+require(reader.dequeue(throw) == 2)
+require(reader.dequeue(throw) == 3)
+require(escape empty { reader.dequeue(empty); false } catch _ { true })

Task/Queue-Usage/Elena/queue-usage.elena

@@ -0,0 +1,24 @@
+import system'collections;
+import extensions;
+
+public program()
+{
+    // Create a queue and "push" items into it
+    var queue := new Queue();
+
+    queue.push:1;
+    queue.push:3;
+    queue.push:5;
+
+    // "Pop" items from the queue in FIFO order
+    console.printLine(queue.pop()); // 1
+    console.printLine(queue.pop()); // 3
+    console.printLine(queue.pop()); // 5
+
+    // To tell if the queue is empty, we check the count
+    console.printLine("queue is ",(queue.Length == 0).iif("empty","nonempty"));
+
+    // If we try to pop from an empty queue, an exception
+    // is thrown.
+    queue.pop() | on:(e){ console.writeLine:"Queue empty." }
+}

Task/Queue-Usage/Elixir/queue-usage-1.elixir

@@ -0,0 +1,10 @@
+defmodule Queue do
+  def empty?([]), do: true
+  def empty?(_), do: false
+
+  def pop([h|t]), do: {h,t}
+
+  def push(q,t), do: q ++ [t]
+
+  def front([h|_]), do: h
+end

Task/Queue-Usage/Elixir/queue-usage-2.elixir

@@ -0,0 +1,14 @@
+iex(2)> q = [1,2,3,4,5]
+[1, 2, 3, 4, 5]
+iex(3)> Queue.push(q,10)
+[1, 2, 3, 4, 5, 10]
+iex(4)> front=Queue.front(q)
+1
+iex(5)> Queue.empty?(q)
+false
+iex(6)> Queue.pop(q)
+{1, [2, 3, 4, 5]}
+iex(7)> l=[]
+[]
+iex(8)> Queue.empty?(l)
+true

Task/Queue-Usage/Erlang/queue-usage.erl

@@ -0,0 +1,17 @@
+1> Q = fifo:new().
+{fifo,[],[]}
+2> fifo:empty(Q).
+true
+3> Q2 = fifo:push(Q,1).
+{fifo,[1],[]}
+4> Q3 = fifo:push(Q2,2).
+{fifo,[2,1],[]}
+5> fifo:empty(Q3).
+false
+6> fifo:pop(Q3).
+{1,{fifo,[],[2]}}
+7> {Popped, Q} = fifo:pop(Q2).
+{1,{fifo,[],[]}}
+8> fifo:pop(fifo:new()).
+** exception error: 'empty fifo'
+     in function  fifo:pop/1

Task/Queue-Usage/Factor/queue-usage-1.factor

@@ -0,0 +1,13 @@
+USING: combinators deques dlists kernel prettyprint ;
+IN: rosetta-code.queue-usage
+
+DL{ } clone {                ! make new queue
+    [ [ 1 ] dip push-front ] ! push 1
+    [ [ 2 ] dip push-front ] ! push 2
+    [ [ 3 ] dip push-front ] ! push 3
+    [ .                    ] ! DL{ 3 2 1 }
+    [ pop-back drop        ] ! pop 1 (and discard)
+    [ pop-back drop        ] ! pop 2 (and discard)
+    [ pop-back drop        ] ! pop 3 (and discard)
+    [ deque-empty? .       ] ! t
+} cleave

Task/Queue-Usage/Factor/queue-usage-2.factor

@@ -0,0 +1,6 @@
+DL{ } clone {
+    [ [ { 1 2 3 } ] dip push-all-front ] ! push all from sequence
+    [ .                                ] ! DL{ 3 2 1 }
+    [ [ drop ] slurp-deque             ] ! pop and discard all
+    [ deque-empty? .                   ] ! t
+} cleave

Task/Queue-Usage/Fantom/queue-usage.fantom

@@ -0,0 +1,14 @@
+class Main
+{
+  public static Void main ()
+  {
+    q := Queue()
+    q.push (1)
+    q.push ("a")
+    echo ("Is empty? " + q.isEmpty)
+    echo ("Element: " + q.pop)
+    echo ("Element: " + q.pop)
+    echo ("Is empty? " + q.isEmpty)
+    try { q.pop } catch (Err e) { echo (e.msg) }
+  }
+}

Task/Queue-Usage/Forth/queue-usage-1.fth

@@ -0,0 +1,45 @@
+: cqueue: ( n -- <text>)
+    create                                                 \ compile time: build the data structure in memory
+        dup
+        dup 1- and abort" queue size must be power of 2"
+        0 ,                                                \ write pointer "HEAD"
+        0 ,                                                \ read  pointer "TAIL"
+        0 ,                                                \ byte counter
+        dup 1- ,                                           \ mask value used for wrap around
+        allot ;                                            \ run time: returns the address of this data structure
+
+\ calculate offsets into the queue data structure
+: ->head ( q -- adr )      ;                               \ syntactic sugar
+: ->tail ( q -- adr ) cell+   ;
+: ->cnt  ( q -- adr ) 2 cells +   ;
+: ->msk  ( q -- adr ) 3 cells +   ;
+: ->data ( q -- adr ) 4 cells +   ;
+
+: head++ ( q -- )                                         \ circular increment head pointer of a queue
+         dup >r ->head @ 1+  r@ ->msk @ and r> ->head ! ;
+
+: tail++ ( q -- )                                         \ circular increment tail pointer of a queue
+        dup >r  ->tail @ 1+  r@ ->msk @ and r> ->tail ! ;
+
+: qempty ( q -- flag)
+        dup ->head off   dup ->tail off  dup ->cnt  off    \ reset all fields to "off" (zero)
+        ->cnt @ 0=  ;                                      \ per the spec qempty returns a flag
+
+: cnt=msk?   ( q -- flag)  dup >r  ->cnt @ r> ->msk @ = ;
+: ?empty     ( q -- )     ->cnt @ 0=  abort" queue is empty" ;
+: ?full      ( q -- )     cnt=msk? abort" queue is full" ;
+: 1+!   ( adr -- )  1 swap +! ;                            \ increment contents of adr
+: 1-!   ( adr -- ) -1 swap +! ;          \ decrement contents of adr
+
+: qc@    ( queue -- char )                                 \ fetch next char in queue
+       dup >r ?empty                                       \ abort if empty
+       r@ ->cnt 1-!                                        \ decr. the counter
+       r@ tail++
+       r@ ->data  r> ->tail @ + c@ ;                       \ calc. address and fetch the byte
+
+
+: qc!    ( char queue -- )
+       dup >r ?full                                        \ abort if q full
+       r@ ->cnt 1+!                                        \ incr. the counter
+       r@ head++
+       r@ ->data  r> ->head @ + c! ;                       \ data+head = adr, and store the char

Task/Queue-Usage/Forth/queue-usage-2.fth

@@ -0,0 +1,16 @@
+make-queue constant q1
+make-queue constant q2
+q1 empty? .
+5 q1 enqueue
+q1 empty? .
+7 q1 enqueue
+9 q1 enqueue
+q2 empty? .
+3 q2 enqueue
+q2 empty? .
+q1 dequeue .
+q1 dequeue .
+q1 dequeue .
+q1 empty? .
+q2 dequeue .
+q2 empty? .

Task/Queue-Usage/Fortran/queue-usage.f

@@ -0,0 +1,33 @@
+module fifo_nodes
+  type fifo_node
+     integer :: datum
+     ! the next part is not variable and must be present
+     type(fifo_node), pointer :: next
+     logical :: valid
+  end type fifo_node
+end module fifo_nodes
+
+program FIFOTest
+  use fifo
+  implicit none
+
+  type(fifo_head) :: thehead
+  type(fifo_node), dimension(5) :: ex, xe
+  integer :: i
+
+  call new_fifo(thehead)
+
+  do i = 1, 5
+     ex(i)%datum = i
+     call fifo_enqueue(thehead, ex(i))
+  end do
+
+  i = 1
+  do
+     call fifo_dequeue(thehead, xe(i))
+     print *, xe(i)%datum
+     i = i + 1
+     if ( fifo_isempty(thehead) ) exit
+  end do
+
+end program FIFOTest

Task/Queue-Usage/FreeBASIC/queue-usage.basic

@@ -0,0 +1,28 @@
+' FB 1.05.0 Win64
+
+#Include "queue_rosetta.bi"  '' include macro-based generic Queue type used in earlier task
+
+Declare_Queue(String) '' expand Queue type for Strings
+
+Dim stringQueue As Queue(String)
+With stringQueue  '' push some strings into the Queue
+  .push("first")
+  .push("second")
+  .push("third")
+  .push("fourth")
+  .push("fifth")
+End With
+Print "Number of Strings in the Queue :" ; stringQueue.count
+Print "Capacity of string Queue       :" ; stringQueue.capacity
+Print
+' now pop them
+While Not stringQueue.empty
+  Print stringQueue.pop(); " popped"
+Wend
+Print
+Print "Number of Strings in the Queue :" ; stringQueue.count
+Print "Capacity of string Queue       :" ; stringQueue.capacity   '' capacity should be unchanged
+Print "Is Queue empty now             : "; stringQueue.empty
+Print
+Print "Press any key to quit"
+Sleep

Task/Queue-Usage/Go/queue-usage-1.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+    "fmt"
+    "queue"
+)
+
+func main() {
+    q := new(queue.Queue)
+    fmt.Println("empty?", q.Empty())
+
+    x := "black"
+    fmt.Println("push", x)
+    q.Push(x)
+
+    fmt.Println("empty?", q.Empty())
+    r, ok := q.Pop()
+    if ok {
+        fmt.Println(r, "popped")
+    } else {
+        fmt.Println("pop failed")
+    }
+
+    var n int
+    for _, x := range []string{"blue", "red", "green"} {
+        fmt.Println("pushing", x)
+        q.Push(x)
+        n++
+    }
+
+    for i := 0; i < n; i++ {
+        r, ok := q.Pop()
+        if ok {
+            fmt.Println(r, "popped")
+        } else {
+            fmt.Println("pop failed")
+        }
+    }
+}

Task/Queue-Usage/Go/queue-usage-2.go

@@ -0,0 +1,36 @@
+package main
+
+import "fmt"
+
+func main() {
+    q := make(chan string, 3)
+    fmt.Println("empty?", len(q) == 0)
+
+    x := "black"
+    fmt.Println("push", x)
+    q <- x
+
+    fmt.Println("empty?", len(q) == 0)
+    select {
+    case r := <-q:
+        fmt.Println(r, "popped")
+    default:
+        fmt.Println("pop failed")
+    }
+
+    var n int
+    for _, x := range []string{"blue", "red", "green"} {
+        fmt.Println("pushing", x)
+        q <- x
+        n++
+    }
+
+    for i := 0; i < n; i++ {
+        select {
+        case r := <-q:
+            fmt.Println(r, "popped")
+        default:
+            fmt.Println("pop failed")
+        }
+    }
+}

Task/Queue-Usage/Go/queue-usage-3.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+    "fmt"
+    "container/list"
+)
+
+func main() {
+    q := list.New()
+    fmt.Println("empty?", q.Len() == 0)
+
+    x := "black"
+    fmt.Println("push", x)
+    q.PushBack(x)
+
+    fmt.Println("empty?", q.Len() == 0)
+    if e := q.Front(); e != nil {
+        r := q.Remove(e)
+        fmt.Println(r, "popped")
+    } else {
+        fmt.Println("pop failed")
+    }
+
+    var n int
+    for _, x := range []string{"blue", "red", "green"} {
+        fmt.Println("pushing", x)
+        q.PushBack(x)
+        n++
+    }
+
+    for i := 0; i < n; i++ {
+        if e := q.Front(); e != nil {
+            r := q.Remove(e)
+            fmt.Println(r, "popped")
+        } else {
+            fmt.Println("pop failed")
+        }
+    }
+}

Task/Queue-Usage/Groovy/queue-usage-1.groovy

@@ -0,0 +1 @@
+def q = new LinkedList()

Task/Queue-Usage/Groovy/queue-usage-2.groovy

@@ -0,0 +1,46 @@
+assert q.empty
+println q
+// "push" adds to end of "queue" list
+q.push('Stuart')
+println q
+assert !q.empty
+// "add" adds to end of "queue" list
+q.add('Pete')
+println q
+assert !q.empty
+// left shift operator ("<<") adds to end of "queue" list
+q << 'John'
+println q
+assert !q.empty
+// add assignment ("+=") adds the list elements
+// to the end of the "queue" list in list order
+q += ['Paul', 'George']
+println q
+assert !q.empty
+// "poll" removes and returns the first element in the
+// "queue" list ("pop" exists for Groovy lists, but it
+// removes and returns the LAST element for "Stack"
+// semantics). "poll" only exists in objects that
+// implement java.util.Queue, like java.util.LinkedList
+assert q.poll() == 'Stuart'
+println q
+assert !q.empty
+assert q.poll() == 'Pete'
+println q
+assert !q.empty
+q << 'Ringo'
+println q
+assert !q.empty
+assert q.poll() == 'John'
+println q
+assert !q.empty
+assert q.poll() == 'Paul'
+println q
+assert !q.empty
+assert q.poll() == 'George'
+println q
+assert !q.empty
+assert q.poll() == 'Ringo'
+println q
+assert q.empty
+assert q.poll() == null

Task/Queue-Usage/Haskell/queue-usage.hs

@@ -0,0 +1,25 @@
+Prelude> :l fifo.hs
+[1 of 1] Compiling Main             ( fifo.hs, interpreted )
+Ok, modules loaded: Main.
+*Main> let q = emptyFifo
+*Main> isEmpty q
+True
+*Main> let q' = push q 1
+*Main> isEmpty q'
+False
+*Main> let q'' = foldl push q' [2..4]
+*Main> let (v,q''') = pop q''
+*Main> v
+Just 1
+*Main> let (v',q'''') = pop q'''
+*Main> v'
+Just 2
+*Main> let (v'',q''''') = pop q''''
+*Main> v''
+Just 3
+*Main> let (v''',q'''''') = pop q'''''
+*Main> v'''
+Just 4
+*Main> let (v'''',q''''''') = pop q''''''
+*Main> v''''
+Nothing

Task/Queue-Usage/Icon/queue-usage.icon

@@ -0,0 +1,18 @@
+procedure main(arglist)
+queue := []
+write("Usage:\nqueue x x x - x - - - - -\n\t- pops elements\n\teverything else pushes")
+write("Queue is:")
+every x := !arglist do {
+   case x of {
+      "-"     : pop(queue)  | write("pop(empty) failed.")    # pop if the next arglist[i] is a -
+      default : put(queue,x)                                 # push arglist[i]
+      }
+   if empty(queue) then writes("empty")
+   else every writes(!queue," ")
+   write()
+   }
+end
+
+procedure empty(X)        #: fail if X is not empty
+if *X = 0 then return
+end

Task/Queue-Usage/J/queue-usage-1.j

@@ -0,0 +1,19 @@
+   queue=: conew 'fifo'
+   isEmpty__queue ''
+1
+   push__queue 9
+9
+   push__queue 8
+8
+   push__queue 7
+7
+   isEmpty__queue ''
+0
+   pop__queue ''
+9
+   pop__queue ''
+8
+   pop__queue ''
+7
+   isEmpty__queue ''
+1

Task/Queue-Usage/J/queue-usage-2.j

@@ -0,0 +1,17 @@
+   is_empty make_empty _
+1
+   first_named_state =: push 9 onto make_empty _
+   newer_state =: push 8 onto first_named_state
+   this_state =: push 7 onto newer_state
+   is_empty this_state
+0
+   tell_queue this_state
+9 8 7
+   tell_atom pop this_state
+9
+   tell_atom pop pop this_state
+8
+   tell_atom pop pop pop this_state
+7
+   is_empty pop pop pop this_state
+1

Task/Queue-Usage/Java/queue-usage-1.java

@@ -0,0 +1,13 @@
+import java.util.LinkedList;
+import java.util.Queue;
+...
+Queue<Integer> queue = new LinkedList<Integer>();
+System.out.println(queue.isEmpty());      // empty test - true
+// queue.remove();       // would throw NoSuchElementException
+queue.add(1);
+queue.add(2);
+queue.add(3);
+System.out.println(queue);                // [1, 2, 3]
+System.out.println(queue.remove());       // 1
+System.out.println(queue);                // [2, 3]
+System.out.println(queue.isEmpty());      // false

Task/Queue-Usage/Java/queue-usage-2.java

@@ -0,0 +1,11 @@
+import java.util.LinkedList;
+...
+LinkedList queue = new LinkedList();
+System.out.println(queue.isEmpty());      // empty test - true
+queue.add(new Integer(1));
+queue.add(new Integer(2));
+queue.add(new Integer(3));
+System.out.println(queue);                // [1, 2, 3]
+System.out.println(queue.removeFirst());  // 1
+System.out.println(queue);                // [2, 3]
+System.out.println(queue.isEmpty());      // false

Task/Queue-Usage/JavaScript/queue-usage.js

@@ -0,0 +1,10 @@
+var f = new Array();
+print(f.length);
+f.push(1,2);         // can take multiple arguments
+f.push(3);
+f.shift();
+f.shift();
+print(f.length);
+print(f.shift())
+print(f.length == 0);
+print(f.shift());

Task/Queue-Usage/Julia/queue-usage.julia

@@ -0,0 +1,7 @@
+using DataStructures
+
+queue = Queue(String)
+@show enqueue!(queue, "foo")
+@show enqueue!(queue, "bar")
+@show dequeue!(queue) # -> foo
+@show dequeue!(queue) # -> bar

Task/Queue-Usage/Kotlin/queue-usage.kotlin

@@ -0,0 +1,22 @@
+// version 1.1.2
+
+import java.util.*
+
+fun main(args: Array<String>) {
+    val q: Queue<Int> = ArrayDeque<Int>()
+    (1..5).forEach { q.add(it) }
+    println(q)
+    println("Size of queue = ${q.size}")
+    print("Removing: ")
+    (1..3).forEach { print("${q.remove()} ") }
+    println("\nRemaining in queue: $q")
+    println("Head element is now ${q.element()}")
+    q.clear()
+    println("After clearing, queue is ${if(q.isEmpty()) "empty" else "not empty"}")
+    try {
+        q.remove()
+    }
+    catch (e: NoSuchElementException) {
+        println("Can't remove elements from an empty queue")
+    }
+}

Task/Queue-Usage/Lambdatalk/queue-usage.lambdatalk

@@ -0,0 +1,30 @@
+{def queue.add
+ {lambda {:v :q}
+  {let { {_ {A.addlast! :v :q}}}
+       } ok}}
+-> queue.add
+
+{def queue.get
+ {lambda {:q}
+  {let { {:v {A.first :q}}
+         {_ {A.subfirst! :q}}
+       } :v}}}
+-> queue.get
+
+{def queue.empty?
+ {lambda {:q}
+  {A.empty? :q}}}
+-> queue.empty?
+
+{def Q {A.new}}    -> Q      []
+{queue.add 1 {Q}}  ->  ok    [1]
+{queue.add 2 {Q}}  ->  ok    [1,2]
+{queue.add 3 {Q}}  ->  ok    [1,2,3]
+{queue.get {Q}}    -> 1      [2,3]
+{queue.add 4 {Q}}  ->  ok    [2,3,4]
+{queue.empty? {Q}} -> false
+{queue.get {Q}}    -> 2      [3,4]
+{queue.get {Q}}    -> 3      [4]
+{queue.get {Q}}    -> 4      []
+{queue.get {Q}}    -> undefined
+{queue.empty? {Q}} -> true

Task/Queue-Usage/Lasso/queue-usage.lasso

@@ -0,0 +1,20 @@
+local(queue) = queue
+#queue->size
+// => 0
+
+#queue->insert('a')
+#queue->insert('b')
+#queue->insert('c')
+#queue->size
+// => 3
+
+loop(#queue->size) => {
+  stdoutnl(#queue->get)
+}
+// =>
+// a
+// b
+// c
+
+#queue->size == 0
+// => true

Task/Queue-Usage/Logo/queue-usage.logo

@@ -0,0 +1,9 @@
+make "fifo []
+print empty? :fifo    ; true
+queue "fifo 1
+queue "fifo 2
+queue "fifo 3
+show :fifo            ; [1 2 3]
+print dequeue "fifo   ; 1
+show :fifo            ; [2 3]
+print empty? :fifo    ; false

Task/Queue-Usage/Lua/queue-usage-1.lua

@@ -0,0 +1,7 @@
+q = Queue.new()
+Queue.push( q, 5 )
+Queue.push( q, "abc" )
+
+while not Queue.empty( q ) do
+    print( Queue.pop( q ) )
+end

Task/Queue-Usage/Lua/queue-usage-2.lua

@@ -0,0 +1,16 @@
+> -- create queue:
+> q = {}
+> -- push:
+> q[#q+1] = "first"
+> q[#q+1] = "second"
+> q[#q+1] = "third"
+> -- pop:
+> =table.remove(q, 1)
+first
+> =table.remove(q, 1)
+second
+> =table.remove(q, 1)
+third
+> -- empty?
+> =#q == 0
+true

Task/Queue-Usage/M2000-Interpreter/queue-usage.m2000

@@ -0,0 +1,38 @@
+Module CheckStackAsLIFO {
+	a=stack
+	Stack a {
+		Push 1, 2, 3
+		Print number=3
+		Print number=2
+		Print number=1
+		Print Empty=True
+		Push "A", "B", "C"
+		Print letter$="C"
+		Print letter$="B"
+		Print letter$="A"
+		Print Empty=True
+		Push 1,"OK"
+	}
+	Print Len(a)=2, StackItem(a, 2)=1, StackItem$(a, 1)="OK"
+	Print StackType$(a, 1)="String", StackType$(a,2)="Number"
+}
+CheckStackAsLIFO
+Module CheckStackAsFIFO {
+	a=stack
+	Stack a {
+		Data 1, 2, 3
+		Print number=1		
+		Print number=2		
+		Print number=3
+		Print Empty=True
+		Data "A", "B", "C"
+		Print letter$="A"
+		Print letter$="B"
+		Print letter$="C"
+		Print Empty=True
+		Push 1,"OK"
+	}
+	Print Len(a)=2, StackItem(a, 2)=1, StackItem$(a, 1)="OK"
+	Print StackType$(a, 1)="String", StackType$(a,2)="Number"
+}
+CheckStackAsFIFO

Task/Queue-Usage/Maple/queue-usage.maple

@@ -0,0 +1,14 @@
+q := queue[new]();
+queue[enqueue](q,1);
+queue[enqueue](q,2);
+queue[enqueue](q,3);
+queue[empty](q);
+>>>false
+queue[dequeue](q);
+>>>1
+queue[dequeue](q);
+>>>2
+queue[dequeue](q);
+>>>3
+queue[empty](q);
+>>>true

Task/Queue-Usage/Mathematica/queue-usage.math

@@ -0,0 +1,16 @@
+Empty[a_] := If[Length[a] == 0, True, False]
+SetAttributes[Push, HoldAll]; Push[a_, elem_] := AppendTo[a, elem]
+SetAttributes[Pop, HoldAllComplete]; Pop[a_] := If[EmptyQ[a], False, b = First[a]; Set[a, Most[a]]; b]
+
+Queue = {}
+-> {}
+Empty[Queue]
+-> True
+Push[Queue, "1"]
+-> {"1"}
+EmptyQ[Queue]
+->False
+Pop[Queue]
+->1
+Pop[Queue]
+->False

Task/Queue-Usage/Nemerle/queue-usage.nemerle

@@ -0,0 +1,4 @@
+mutable q = Queue(); // or use immutable version as per Haskell example
+def empty = q.IsEmpty(); // true at this point
+q.Push(empty); // or Enqueue(), or Add()
+def a = q.Pop(); // or Dequeue() or Take()

Task/Queue-Usage/NetRexx/queue-usage.netrexx

@@ -0,0 +1,65 @@
+/* NetRexx */
+options replace format comments java crossref savelog symbols nobinary
+
+-- Queue Usage Demonstration Program -------------------------------------------
+method main(args = String[]) public constant
+  kew = RCQueueImpl()
+  do
+    say kew.pop()
+  catch ex = IndexOutOfBoundsException
+    say ex.getMessage
+    say
+  end
+
+  melancholyDane = ''
+  melancholyDane[0] = 4
+  melancholyDane[1] = 'To be'
+  melancholyDane[2] = 'or'
+  melancholyDane[3] = 'not to be?'
+  melancholyDane[4] = 'That is the question.'
+
+  loop p_ = melancholyDane[0] to 1 by -1
+    kew.push(melancholyDane[p_])
+    end p_
+
+  loop while \kew.empty
+    popped = kew.pop
+    say popped '\-'
+    end
+  say; say
+
+  -- demonstrate stowing something other than a text string in the queue
+  kew.push(melancholyDane)
+  md = kew.pop
+  loop l_ = 1 to md[0]
+    say md[l_] '\-'
+    end l_
+  say
+
+  return
+
+-- Queue implementation --------------------------------------------------------
+class RCQueueImpl
+  properties private
+    qqq = Deque
+
+method RCQueueImpl() public
+  qqq = ArrayDeque()
+  return
+
+method push(stuff) public
+  qqq.push(stuff)
+  return
+
+method pop() public returns Rexx signals IndexOutOfBoundsException
+  if qqq.isEmpty then signal IndexOutOfBoundsException('The queue is empty')
+  return Rexx qqq.pop()
+
+method empty() public binary returns boolean
+  return qqq.isEmpty
+
+method isTrue public constant binary returns boolean
+  return 1 == 1
+
+method isFalse public constant binary returns boolean
+  return \isTrue

Task/Queue-Usage/Nim/queue-usage.nim

@@ -0,0 +1,12 @@
+import deques
+
+var queue = initDeque[int]()
+
+queue.addLast(26)
+queue.addLast(99)
+queue.addLast(2)
+echo "Queue size: ", queue.len()
+echo "Popping: ", queue.popFirst()
+echo "Popping: ", queue.popFirst()
+echo "Popping: ", queue.popFirst()
+echo "Popping: ", queue.popFirst()

Task/Queue-Usage/OCaml/queue-usage.ocaml

@@ -0,0 +1,37 @@
+# let q = Queue.create ();;
+val q : '_a Queue.t = <abstr>
+# Queue.is_empty q;;
+- : bool = true
+# Queue.add 1 q;;
+- : unit = ()
+# Queue.is_empty q;;
+- : bool = false
+# Queue.add 2 q;;
+- : unit = ()
+# Queue.add 3 q;;
+- : unit = ()
+# Queue.peek q;;
+- : int = 1
+# Queue.length q;;
+- : int = 3
+# Queue.iter (Printf.printf "%d, ") q; print_newline ();;
+1, 2, 3,
+- : unit = ()
+# Queue.take q;;
+- : int = 1
+# Queue.take q;;
+- : int = 2
+# Queue.peek q;;
+- : int = 3
+# Queue.length q;;
+- : int = 1
+# Queue.add 4 q;;
+- : unit = ()
+# Queue.take q;;
+- : int = 3
+# Queue.peek q;;
+- : int = 4
+# Queue.take q;;
+- : int = 4
+# Queue.is_empty q;;
+- : bool = true

Task/Queue-Usage/Objeck/queue-usage.objeck

@@ -0,0 +1,14 @@
+class Test {
+  function : Main(args : String[]) ~ Nil {
+    q := Struct.IntQueue->New();
+    q->Add(1);
+    q->Add(2);
+    q->Add(3);
+
+    q->Remove()->PrintLine();
+    q->Remove()->PrintLine();
+    q->Remove()->PrintLine();
+
+    q->IsEmpty()->PrintLine();
+  }
+}

Task/Queue-Usage/Oforth/queue-usage.fth

@@ -0,0 +1,5 @@
+: testQueue
+| q i |
+   Queue new ->q
+   20 loop: i [ i q push ]
+   while ( q empty not ) [ q pop . ] ;

Task/Queue-Usage/OoRexx/queue-usage.rexx

@@ -0,0 +1,5 @@
+q = .queue~new      -- create an instance
+q~queue(3)          -- adds to the end, but this is at the front
+q~push(1)           -- push on the front
+q~queue(2)          -- add to the end
+say q~pull q~pull q~pull q~isempty  -- should display all and be empty

Task/Queue-Usage/Oz/queue-usage.oz

@@ -0,0 +1,12 @@
+declare
+  [Queue] = {Link ['x-oz://system/adt/Queue.ozf']}
+  MyQueue = {Queue.new}
+in
+  {MyQueue.isEmpty} = true
+  {MyQueue.put foo}
+  {MyQueue.put bar}
+  {MyQueue.put baz}
+  {MyQueue.isEmpty} = false
+  {Show {MyQueue.get}}  %% foo
+  {Show {MyQueue.get}}  %% bar
+  {Show {MyQueue.get}}  %% baz

Task/Queue-Usage/PHP/queue-usage.php

@@ -0,0 +1,10 @@
+<?php
+$queue = new SplQueue;
+echo $queue->isEmpty() ? 'true' : 'false', "\n";  // empty test - returns true
+// $queue->dequeue();                             // would raise RuntimeException
+$queue->enqueue(1);
+$queue->enqueue(2);
+$queue->enqueue(3);
+echo $queue->dequeue(), "\n";                     // returns 1
+echo $queue->isEmpty() ? 'true' : 'false', "\n";  // returns false
+?>

Task/Queue-Usage/PL-I/queue-usage-1.pli

@@ -0,0 +1,40 @@
+test: proc options (main);
+
+
+   /* To implement a queue. */
+   define structure
+      1 node,
+         2 value fixed,
+         2 link handle(node);
+   declare (head, tail, t) handle (node);
+   declare null builtin;
+   declare i fixed binary;
+
+   head, tail = bind(:node, null:);
+
+   do i = 1 to 10; /* Add ten items to the tail of the queue. */
+      if head = bind(:node, null:) then
+         do;
+            head,tail = new(:node:);
+            get list (head => value);
+            put skip list (head => value);
+            head => link = bind(:node, null:); /* A NULL link */
+         end;
+      else
+         do;
+            t = new(:node:);
+            tail => link = t; /* Point the tail to the new node. */
+            tail = t;
+            tail => link = bind(:node, null:); /* Set the tail link to NULL */
+            get list (tail => value) copy;
+            put skip list (tail => value);
+         end;
+   end;
+
+   /* Pop all the items in the queue. */
+   put skip list ('The queue has:');
+   do while (head ^= bind(:node, null:));
+      put skip list (head => value);
+      head = head => link;
+   end;
+end test;

Task/Queue-Usage/PL-I/queue-usage-2.pli

@@ -0,0 +1,21 @@
+       1
+       3
+       5
+       7
+       9
+      11
+      13
+      15
+      17
+      19
+The queue has:
+       1
+       3
+       5
+       7
+       9
+      11
+      13
+      15
+      17
+      19

Task/Queue-Usage/Perl/queue-usage-1.pl

@@ -0,0 +1,11 @@
+@queue = (); # we will simulate a queue in a array
+
+push @queue, (1..5); # enqueue numbers from 1 to 5
+
+print shift @queue,"\n"; # dequeue
+
+print "array is empty\n" unless @queue; # is empty ?
+
+print $n while($n = shift @queue); # dequeue all
+print "\n";
+print "array is empty\n" unless @queue; # is empty ?

Task/Queue-Usage/Perl/queue-usage-2.pl

@@ -0,0 +1,3 @@
+1
+2345
+array is empty

Task/Queue-Usage/Phix/queue-usage-1.phix

@@ -0,0 +1,10 @@
+(phixonline)-->
+ <span style="color: #008080;">with</span> <span style="color: #008080;">javascript_semantics</span>
+ <span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"empty:%t\n"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">empty</span><span style="color: #0000FF;">())</span>          <span style="color: #000080;font-style:italic;">-- true</span>
+ <span style="color: #000000;">push_item</span><span style="color: #0000FF;">(</span><span style="color: #000000;">5</span><span style="color: #0000FF;">)</span>
+ <span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"empty:%t\n"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">empty</span><span style="color: #0000FF;">())</span>          <span style="color: #000080;font-style:italic;">-- false</span>
+ <span style="color: #000000;">push_item</span><span style="color: #0000FF;">(</span><span style="color: #000000;">6</span><span style="color: #0000FF;">)</span>
+ <span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"pop_item:%v\n"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">pop_item</span><span style="color: #0000FF;">())</span>    <span style="color: #000080;font-style:italic;">-- 5</span>
+ <span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"pop_item:%v\n"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">pop_item</span><span style="color: #0000FF;">())</span>    <span style="color: #000080;font-style:italic;">-- 6</span>
+ <span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"empty:%t\n"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">empty</span><span style="color: #0000FF;">())</span>          <span style="color: #000080;font-style:italic;">-- true</span>
+<!--

Task/Queue-Usage/Phix/queue-usage-2.phix

@@ -0,0 +1,11 @@
+(phixonline)-->
+ <span style="color: #008080;">with</span> <span style="color: #008080;">javascript_semantics</span>
+ <span style="color: #008080;">constant</span> <span style="color: #000000;">queue</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">new_queue</span><span style="color: #0000FF;">()</span>
+ <span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"empty:%t\n"</span><span style="color: #0000FF;">,</span><span style="color: #7060A8;">queue_empty</span><span style="color: #0000FF;">(</span><span style="color: #000000;">queue</span><span style="color: #0000FF;">))</span>
+ <span style="color: #7060A8;">push</span><span style="color: #0000FF;">(</span><span style="color: #000000;">queue</span><span style="color: #0000FF;">,</span><span style="color: #000000;">5</span><span style="color: #0000FF;">)</span>
+ <span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"empty:%t\n"</span><span style="color: #0000FF;">,</span><span style="color: #7060A8;">queue_empty</span><span style="color: #0000FF;">(</span><span style="color: #000000;">queue</span><span style="color: #0000FF;">))</span>
+ <span style="color: #7060A8;">push</span><span style="color: #0000FF;">(</span><span style="color: #000000;">queue</span><span style="color: #0000FF;">,</span><span style="color: #000000;">6</span><span style="color: #0000FF;">)</span>
+ <span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"pop:%v\n"</span><span style="color: #0000FF;">,</span><span style="color: #7060A8;">pop</span><span style="color: #0000FF;">(</span><span style="color: #000000;">queue</span><span style="color: #0000FF;">))</span>
+ <span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"pop:%v\n"</span><span style="color: #0000FF;">,</span><span style="color: #7060A8;">pop</span><span style="color: #0000FF;">(</span><span style="color: #000000;">queue</span><span style="color: #0000FF;">))</span>
+ <span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"empty:%t\n"</span><span style="color: #0000FF;">,</span><span style="color: #7060A8;">queue_empty</span><span style="color: #0000FF;">(</span><span style="color: #000000;">queue</span><span style="color: #0000FF;">))</span>
+<!--

Task/Queue-Usage/PicoLisp/queue-usage.l

@@ -0,0 +1,5 @@
+(println (fifo 'Queue))    # Retrieve the number '1'
+(println (fifo 'Queue))    # Retrieve an internal symbol 'abc'
+(println (fifo 'Queue))    # Retrieve a transient symbol "abc"
+(println (fifo 'Queue))    # and a list (abc)
+(println (fifo 'Queue))    # Queue is empty -> NIL

Task/Queue-Usage/PostScript/queue-usage.ps

@@ -0,0 +1,6 @@
+ [1 2 3 4 5] 6 exch tadd
+ = [1 2 3 4 5 6]
+ uncons
+ = 1 [2 3 4 5 6]
+ [] empty?
+ =true

Task/Queue-Usage/PowerShell/queue-usage-1.psh

@@ -0,0 +1,26 @@
+[System.Collections.ArrayList]$queue = @()
+# isEmpty?
+if ($queue.Count -eq 0) {
+    "isEmpty? result : the queue is empty"
+} else {
+    "isEmpty? result : the queue is not empty"
+}
+"the queue contains : $queue"
+$queue += 1                    # push
+"push result : $queue"
+$queue += 2                    # push
+$queue += 3                    # push
+"push result : $queue"
+
+$queue.RemoveAt(0)             # pop
+"pop result : $queue"
+
+$queue.RemoveAt(0)             # pop
+"pop result : $queue"
+
+if ($queue.Count -eq 0) {
+    "isEmpty? result : the queue is empty"
+} else {
+    "isEmpty? result : the queue is not empty"
+}
+"the queue contains : $queue"

Task/Queue-Usage/PowerShell/queue-usage-2.psh

@@ -0,0 +1,3 @@
+$queue = New-Object -TypeName System.Collections.Queue
+#or
+$queue = [System.Collections.Queue] @()

Task/Queue-Usage/PowerShell/queue-usage-3.psh

@@ -0,0 +1 @@
+Get-Member -InputObject $queue

Task/Queue-Usage/PowerShell/queue-usage-4.psh

@@ -0,0 +1 @@
+1,2,3 | ForEach-Object {$queue.Enqueue($_)}

Task/Queue-Usage/PowerShell/queue-usage-5.psh

@@ -0,0 +1 @@
+$queue.Peek()

Task/Queue-Usage/PowerShell/queue-usage-6.psh

@@ -0,0 +1 @@
+$queue.Dequeue()

Task/Queue-Usage/PowerShell/queue-usage-7.psh

@@ -0,0 +1 @@
+$queue.Clear()

Task/Queue-Usage/PowerShell/queue-usage-8.psh

@@ -0,0 +1 @@
+if (-not $queue.Count) {"Queue is empty"}

Task/Queue-Usage/Prolog/queue-usage.pro

@@ -0,0 +1,48 @@
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% definitions of queue
+empty(U-V) :-
+    unify_with_occurs_check(U, V).
+
+push(Queue, Value, NewQueue) :-
+    append_dl(Queue, [Value|X]-X, NewQueue).
+
+
+pop([X|V]-U, X, V-U) :-
+    \+empty([X|V]-U).
+
+
+
+append_dl(X-Y, Y-Z, X-Z).
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% use of queue
+queue :-
+    % create an empty queue
+    empty(Q),
+    format('Create queue ~w~n~n', [Q]),
+
+    % add numbers 1 and 2
+    write('Add numbers 1 and 2 : '),
+    push(Q, 1, Q1),
+    push(Q1, 2, Q2),
+
+    % display queue
+    format('~w~n~n', [Q2]),
+
+    % pop element
+    pop(Q2, V, Q3),
+
+    % display results
+    format('Pop : Value ~w Queue : ~w~n~n', [V, Q3]),
+
+    % test the queue
+    write('Test of the queue : '),
+    (   empty(Q3) -> writeln('Queue empy'); writeln('Queue not empty')), nl,
+
+    % pop the elements
+    write('Pop the queue : '),
+    pop(Q3, V1, Q4),
+    format('Value ~w Queue : ~w~n~n', [V1, Q4]),
+
+    write('Pop the queue : '),
+    pop(Q4, _V, _Q5).

Task/Queue-Usage/PureBasic/queue-usage.basic

@@ -0,0 +1,36 @@
+NewList MyStack()
+
+Procedure Push(n)
+  Shared MyStack()
+  LastElement(MyStack())
+  AddElement(MyStack())
+  MyStack()=n
+EndProcedure
+
+Procedure Pop()
+  Shared MyStack()
+  Protected n
+  If FirstElement(MyStack())  ; e.g. Stack not empty
+    n=MyStack()
+    DeleteElement(MyStack(),1)
+  EndIf
+  ProcedureReturn n
+EndProcedure
+
+Procedure Empty()
+  Shared MyStack()
+  If  ListSize(MyStack())=0
+    ProcedureReturn #True
+  EndIf
+  ProcedureReturn #False
+EndProcedure
+
+;----   Example of implementation ----
+Push(3)
+Push(1)
+Push(4)
+Push(1)
+Push(5)
+While Not Empty()
+  Debug Pop()
+Wend

Task/Queue-Usage/Python/queue-usage.py

@@ -0,0 +1,8 @@
+import Queue
+my_queue = Queue.Queue()
+my_queue.put("foo")
+my_queue.put("bar")
+my_queue.put("baz")
+print my_queue.get()  # foo
+print my_queue.get()  # bar
+print my_queue.get()  # baz

Task/Queue-Usage/Quackery/queue-usage.quackery

@@ -0,0 +1,7 @@
+[ [] ]          is queue  (     --> q   )
+
+[ nested join ] is push   ( q x --> q   )
+
+[ behead ]      is pop    (   q --> q x )
+
+[ [] = ]        is empty? (   q --> b   )

Task/Queue-Usage/REBOL/queue-usage.rebol

@@ -0,0 +1,15 @@
+; Create and populate a FIFO:
+
+q: make fifo []
+q/push 'a
+q/push 2
+q/push USD$12.34              ; Did I mention that REBOL has 'money!' datatype?
+q/push [Athos Porthos Aramis] ; List elements pushed on one by one.
+q/push [[Huey Dewey Lewey]]   ; This list is preserved as a list.
+
+; Dump it out, with narrative:
+
+print rejoin ["Queue is "  either q/empty [""]["not "]  "empty."]
+while [not q/empty][print ["  " q/pop]]
+print rejoin ["Queue is "  either q/empty [""]["not "]  "empty."]
+print ["Trying to pop an empty queue yields:" q/pop]

Task/Queue-Usage/REXX/queue-usage.rexx

@@ -0,0 +1,22 @@
+/*REXX program demonstrates four  queueing  operations:   push,  pop,  empty,  query.   */
+say '══════════════════════════════════ Pushing five values to the stack.'
+        do j=1  for 4                            /*a  DO  loop to  PUSH  four values.   */
+        call push  j * 10                        /*PUSH   (aka:   enqueue to the stack).*/
+        say 'pushed value:'    j * 10            /*echo the pushed value.               */
+        if j\==3  then iterate                   /*Not equal 3?   Then use a new number.*/
+        call push                                /*PUSH   (aka:   enqueue to the stack).*/
+        say 'pushed a "null" value.'             /*echo what was  pushed  to the stack. */
+        end   /*j*/
+say '══════════════════════════════════ Quering the stack  (number of entries).'
+        say  queued()  ' entries in the stack.'
+say '══════════════════════════════════ Popping all values from the stack.'
+        do k=1  while  \empty()                  /*EMPTY (returns  TRUE  [1]  if empty).*/
+        call pop                                 /*POP   (aka:  dequeue from the stack).*/
+        say k': popped value='  result           /*echo the popped value.               */
+        end   /*k*/
+say '══════════════════════════════════ The stack is now empty.'
+exit                                             /*stick a fork in it,  we're all done. */
+/*──────────────────────────────────────────────────────────────────────────────────────*/
+push:   queue arg(1);              return        /*(The  REXX  QUEUE   is FIFO.)        */
+pop:    procedure;  parse pull x;  return x      /*REXX   PULL   removes a stack item.  */
+empty:  return queued()==0                       /*returns the status of the stack.     */

Task/Queue-Usage/Racket/queue-usage.rkt

@@ -0,0 +1,17 @@
+#lang racket
+
+(require data/queue)
+
+(define queue (make-queue))
+
+(enqueue! queue 'black)
+(queue-empty? queue) ; #f
+
+(enqueue! queue 'red)
+(enqueue! queue 'green)
+
+(dequeue! queue) ; 'black
+(dequeue! queue) ; 'red
+(dequeue! queue) ; 'green
+
+(queue-empty? queue) ; #t