IBM SC34-5764-01, Manual, Page: 52 / 481

When you run the example, the SAY instruction produces:
9 *-* IF a + 1 > 5 * y
>V> "9"
>L> "1"
>O> "10"
>L> "5"
>V> "2"
>O> "10"
>O> "0"
The
9
is the line number. The
*-*
indicates that what follows is the data from the program,
IF a + 1 < 5 * y
. The remaining lines break down all the expressions.
Tracing Results
To trace only the final result of an expression, use the TRACE R (TRACE Results) form of the TRACE
instruction. The language processor analyzes all expressions that follow the instruction as follows:
>>> Final result of an expression
If you changed the TRACE instruction operand in the previous example from an I to an R, you would see
the following results.
9 *-* IF a + 1 > 5 * y
>>> "0"
In addition to tracing operations and results, the TRACE instruction offers other types of tracing, see
section “TRACE” on page 166.
Exercises - Using the TRACE Instruction
Write a program with a complex expression, such as:
IF (a > z) | (c < 2 * d) THEN ....
Define a , z , c , and d in the program and use the TRACE I instruction.
ANSWER
1 /************************* REXX ***************************/
2 /*
This program uses the TRACE instruction to show how */
3 /* an expression is evaluated, operation by operation. */
4 /**********************************************************/
5
a = 9
6 y = 2
7 TRACE I
8
9
IF a + 1 > 5 * y THEN
10 SAY 'a is big enough.'
11 ELSE NOP /* No operation on the ELSE path */
Figure 15. TRACE Shows How REXX Evaluates an Expression
Using Variables and Expressions
30
CICS TS for VSE/ESA: REXX Guide