tasks a-s

Task/Queue-Definition/PL-I/queue-definition.pli

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+/* To push a node onto the end of the queue. */
+push: procedure (tail);
+   declare tail handle (node), t handle (node);
+   t = new(:node:);
+   get (t => value);
+   if tail ^= bind(:null, node:) then
+      tail => link = t;
+      /* If the queue was non-empty, points the tail of the queue */
+      /* to the new node. */
+   tail = t; /* Point "tail" at the end of the queue. */
+   tail => link = bind(:node, null:);
+end push;
+
+/* To pop a node from the head of the queue. */
+pop: procedure (head, val);
+   declare head handle (node), val fixed binary;
+   if head = bind(:node, null:) then signal error;
+   val = head => value;
+   head = head => pointer; /* pops the top node. */
+   if head = bind(:node, null:) then tail = head;
+      /* (If the queue is now empty, make tail null also.) */
+end pop;
+
+/* Queue status: the EMPTY function, returns true for empty queue. */
+empty: procedure (h) returns (bit(1));
+   declare h handle (Node);
+   return (h = bind(:Node, null:) );
+end empty;