3.1 Subroutine tracing

Tracing the execution of a subroutine requires some effort. This is because we need to indicate the line to return to as a column that belongs to the subroutine. This column does not exist until the subroutine is called. The trace of algorithm 1 is in table 1.

Table 1: A trace of algorithm 1.

line #		comments
4		first line out of a subroutine
5	abc	subroutine ``abc'' stores the line # to return to
	return line #
	6
2		the only line in the subroutine to execute
3	return	we are ready to return, use the stored return line #
6		now we are back to the invoker's (caller's) code