Data commit

Task/Stack/PL-I/stack.pli

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+/* Any controlled variable may behave as a stack. */
+
+declare s float controlled;
+
+/* to push a value on the stack. */
+allocate s;
+s = 10;
+
+/* To pop a value from the stack. */
+put (s);
+free s;
+
+/* to peek at the top of stack> */
+put (s);
+
+/* To see whether the stack is empty */
+if allocation(s) = 0 then ...
+
+/* Note: popping a value from the stack, or peeking,          */
+/* would usually require a check that the stack is not empty. */
+
+/* Note: The above is a simple stack for S. */
+/* S can be any kind of data structure, an array, etc. */
+
+/* Example to push ten values onto the stack, and then to */
+/* remove them.                                           */
+
+/* Push ten values, obtained from the input, onto the stack: */
+declare S float controlled;
+do i = 1 to 10;
+   allocate s;
+   get list (s);
+end;
+/* To pop those values from the stack: */
+do while (allocation(s) > 0);
+   put skip list (s);
+   free s;
+end;
+/* The values are printed in the reverse order, of course. */