Queue/Definition: Difference between revisions

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 =={{header|Nim}}==
-<lang nim>import queues
+<lang nim>type
+  Node[T] = ref object
-# defining push & pop (obviously optional)
+    value: T
-proc push*[T](q: var TQueue[T]; item: T) =
-    add(q,item)
+    next: Node[T]
-proc pop*[T](q: var TQueue[T]): T =
-    result = dequeue(q)
+  Queue*[T] = object
-var fifo: TQueue[int] = initQueue[int]()
+    head, tail: Node[T]
+    length: Natural
+func initQueue*[T](): Queue[T] = Queue[T]()
+func len*(queue: Queue): Natural =
+  queue.length
+func isEmpty*(queue: Queue): bool {.inline.} =
+  queue.len == 0
+func push*[T](queue: var Queue[T]; value: T) =
+  let node = Node[T](value: value, next: nil)
+  if queue.isEmpty: queue.head = node
+  else: queue.tail.next = node
+  queue.tail = node
+  inc queue.length
+func pop*[T](queue: var Queue[T]): T =
+  if queue.isEmpty:
+    raise newException(ValueError, "popping from empty queue.")
+  result = queue.head.value
+  queue.head = queue.head.next
+  dec queue.length
+  if queue.isEmpty: queue.tail = nil
+var fifo = initQueue[int]()
 fifo.push(26)
 fifo.push(99)
 fifo.push(2)
-echo("Fifo size: ", fifo.len())
+echo "Fifo size: ", fifo.len()
-echo("Popping: ", fifo.pop())
+echo "Popping: ", fifo.pop()
-echo("Popping: ", fifo.pop())
+echo "Popping: ", fifo.pop()
-echo("Popping: ", fifo.pop())
+echo "Popping: ", fifo.pop()
+try:
-#echo("Popping: ", fifo.pop())     # popping an empty stack raises [EAssertionFailed]</lang>
+  echo "Popping: ", fifo.pop()
+except ValueError:
+  echo "Exception catched: ", getCurrentExceptionMsg()</lang>
 {{out}}
 <pre>Fifo size: 3
 Popping: 26
 Popping: 99
-Popping: 2</pre>
+Popping: 2
+Exception catched: popping from empty queue.</pre>
 =={{header|OCaml}}==