PUSH Function
Adds current (XLAST, YLAST) and (XLSTT, YLSTT) values
to the LIFO stack.
Comparisons
The LIFO (last-in-first-out)
stack is a storage area where you can keep internal coordinate values
for later use by utility functions without recalculating those values.
LIFO stacks manage the stored data so that the last data stored in
the stack is the first data removed from the stack.
Use the stack to save
the current values of (XLAST, YLAST) and (XLSTT, YLSTT) and use them
with functions later in the DATA step. You store and retrieve these
values from the stack with the PUSH and POP functions. The PUSH function
copies the current values of XLAST, YLAST, XLSTT, and YLSTT onto the
stack. The POP function copies values from the stack into XLAST, YLAST.
XLSTT, and YLSTT.