2016 Update

Task/Queue-Usage/00DESCRIPTION

@@ -1,10 +1,17 @@
 {{Data structure}}
 [[File:Fifo.gif|frame|right|Illustration of FIFO behavior]]
-Create a queue data structure and demonstrate its operations. (For implementations of queues, see the [[FIFO]] task.)
+
+;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
+::*   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/Elena/queue-usage.elena

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+#import system.
+#import system'collections.
+#import extensions.
+
+#symbol program =
+[
+    // Create a queue and "push" items into it
+    #var queue := Queue new.
+
+    queue push:1.
+    queue push:3.
+    queue push:5.
+
+    // "Pop" items from the queue in FIFO order
+    console writeLine:(queue pop). // 1
+    console writeLine:(queue pop). // 3
+    console writeLine:(queue pop). // 5
+
+    // To tell if the queue is empty, we check the count
+    console writeLine:"queue is ":((queue length == 0) iif:"empty":"nonempty").
+
+    // If we try to pop from an empty queue, an exception
+    // is thrown.
+    queue pop | if &Error: e [ console writeLine:"Queue empty.". ].
+].

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

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+: 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

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+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/PowerShell/queue-usage-2.psh

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

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

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+Get-Member -InputObject $queue

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

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

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

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+$queue.Peek()

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

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+$queue.Dequeue()

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

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+$queue.Clear()

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

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