IBM TSO/E REXX User Manual

Tracing Expressions with the TRACE Instruction
You can use the TRACE instruction to display how the language processor
evaluates each operation of an expression as it reads it, or to display the final result
of an expression. These two types of tracing are useful for debugging execs.
Tracing Operations
To trace operations within an expression, use the TRACE I (TRACE Intermediates)
form of the TRACE instruction. All expressions that follow the instruction are then
broken down by operation and analyzed as:
>V> - Variable value - The data traced is the contents
of a variable.
>L> - Literal value - The data traced is a literal
(string, uninitialized variable, or constant).
>O> - Operation result - The data traced is the result
of an operation on two terms.
The following example uses the TRACE I instruction.
EDIT ---- USERID.REXX.EXEC(SAMPLE) ---------------------- COLUMNS 009 080
COMMAND ===> SCROLL ===> HALF
******* ************************** TOP OF DATA ****************************
000001 /************************* REXX *****************************/
000002 /* This exec uses the TRACE instruction to show how an */
000003 /* expression is evaluated, operation by operation. */
000004 /********************************************************* */
000005 x = 9
000006 y = 2
000007 TRACE I
000008
000009 IF x+1>5*yTHEN
000010 SAY 'x is big enough.'
000011 ELSE NOP /* No operation on the ELSE path */
******* ********************** BOTTOM OF DATA *****************************
When you run the example, you see on your screen:
9*-*IFx+1>5*y
>V> "9"
>L> "1"
>O> "10"
>L> "5"
>V> "2"
>O> "10"
>O> "0"
First you see the line number (9 *-*) followed by the expression. Then the
expression is broken down by operation as follows:
>V> "9" (value of variable x)
>L> "1" (value of literal 1)
>O> "10" (result of operationx+1)
>L> "5" (value of literal 5)
>V> "2" (value of variable y)
>O> "10" (result of operation5*y)
>O> "0" (result of final operation 10 > 10 is false)
Tracing Expressions with the TRACE Instruction
Chapter 3. Using Variables and Expressions 37

IBM TSO/E REXX Specifications

General

Brand	IBM
Model	TSO/E REXX
Category	Computer Hardware
Language	English

Summary

Part 1. Learning the REXX Language

Chapter 1. Introduction

Explains the REXX programming language, its features, and suitability for various users.

Chapter 2. Writing and Running a REXX Exec

Details the process of writing, running, and understanding REXX execs, including syntax rules and common issues.

Chapter 3. Using Variables and Expressions

Covers REXX variables, expressions, operators, and tracing techniques for data manipulation and calculations.

Chapter 4. Controlling the Flow Within an Exec

Explains how to alter REXX exec execution using conditional, looping, and interrupt instructions.

Chapter 5. Using Functions

Describes REXX functions, including built-in, user-written, and packages, and how to use them.

Chapter 6. Writing Subroutines and Functions

Guides on writing, calling, and passing information to REXX subroutines and functions.

Chapter 7. Manipulating Data

Covers REXX data manipulation using compound variables, stems, and various parsing techniques.

Part 2. Using REXX

Chapter 8. Entering Commands from an Exec

Explains how REXX execs can interact with the operating system by issuing TSO/E and host commands.

Chapter 9. Diagnosing Problems Within an Exec

Details techniques for diagnosing and debugging REXX execs using tracing and special variables.

Chapter 10. Using TSO/E External Functions

Describes TSO/E external functions available for interacting with the system and performing specific tasks.

Chapter 11. Storing Information in the Data Stack

Explains how to use the REXX data stack for temporary storage, passing information, and managing buffers.

Chapter 12. Processing Data and Input/Output Processing

Covers dynamic REXX expression modification and processing data to/from data sets using EXECIO.

Chapter 13. Using REXX in TSO/E and Other MVS Address Spaces

Explains how to run REXX execs in TSO/E and non-TSO/E MVS address spaces and available services.

Part 3. Appendixes

Appendix A. Allocating Data Sets

Guides on creating and allocating data sets, including checklists for ISPF/PDF and ALLOCATE commands.

Appendix B. Specifying Alternate Libraries with the ALTLIB Command

Details using the ALTLIB command to specify and manage alternative libraries for implicit execution.

Appendix C. Comparisons Between CLIST and REXX

Compares REXX and CLIST languages, highlighting similarities and differences in features and capabilities.

Appendix D. Notices

Provides legal notices, warranty disclaimers, copyright, and trademark information.

Bibliography

TSO/E Publications

Lists IBM publications related to TSO/E, including administration, CLISTs, and general information.

Related Publications

Lists IBM publications related to z/OS MVS and ISPF, covering system programming and administration.

Index