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When you run the example, the SAY instruction produces:
9*-*IFa+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,
IFa+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*-*IFa+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 IFa+1>5*yTHEN
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