IBM TSO/E REXX User Manual

Example of a Problem Caused by Passing Information in a Variable
/******************************* REXX ******************************/
/* NOTE: This exec contains an error. */
/* It uses a DO loop to call an internal subroutine and the */
/* subroutine also uses a DO loop with same control variable as */
/* the main exec. The DO loop in the main exec repeats only once. */
/*******************************************************************/
number1 = 5
number2 = 10
DOi=1TO5
CALL subroutine
SAY answer /* Displays 105 */
END
EXIT
subroutine:
DOi=1TO5
answer = number1 + number2
number1 = number2
number2 = answer
END
RETURN
To avoid this kind of problem in an internal subroutine, you can use:
v The PROCEDURE instruction as described in the next topic.
v Different variable names in a subroutine and pass arguments on the CALL
instruction as described in “Passing Information by Using Arguments” on page 74.
Protecting Variables with the PROCEDURE Instruction: When you use the
PROCEDURE instruction immediately after the subroutine label, all variables used
in the subroutine become local to the subroutine and are shielded from the main
part of the exec. You can also use the PROCEDURE EXPOSE instruction to protect
all but a few specified variables.
The following two examples show the differing results when a subroutine uses the
PROCEDURE instruction and when it doesn’t.
Example Using the PROCEDURE Instruction
/******************************* REXX ******************************/
/* This exec uses a PROCEDURE instruction to protect the variables */
/* within its subroutine. */
/*******************************************************************/
number1 = 10
CALL subroutine
SAY number1 number2 /* displays 10 NUMBER2 */
EXIT
subroutine: PROCEDURE
number1 = 7
number2 = 5
RETURN
Writing a Subroutine;
Chapter 6. Writing Subroutines and Functions 73

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