Error handling and debugging are crucial skills for any programmer. In MUMPS, understanding how to manage errors and debug your code effectively can save you a lot of time and frustration. This section will cover the following topics:

1. Understanding Errors in MUMPS
2. Error Handling Techniques
3. Debugging Tools and Techniques
4. Practical Examples and Exercises

Errors in MUMPS can occur due to various reasons such as syntax mistakes, logical errors, or runtime issues. Common types of errors include:

• Syntax Errors: These occur when the code does not conform to the syntax rules of MUMPS.
• Runtime Errors: These occur during the execution of the program, such as division by zero or accessing an undefined variable.
• Logical Errors: These are errors in the logic of the program that produce incorrect results.

Here are some common error messages you might encounter in MUMPS:

MUMPS provides mechanisms to handle errors gracefully and ensure that your program can recover from unexpected situations.

The $ZTRAP special variable is used to specify an error handling routine. When an error occurs, control is transferred to the routine specified by $ZTRAP.

In this example, if an error occurs, the program will jump to the ERROR label and execute the error handling code.

The $ZERROR special variable contains the error message of the last error that occurred. It can be used within the error handling routine to get details about the error.

Debugging is the process of identifying and fixing errors in your code. MUMPS provides several tools and techniques to help with debugging.

You can set breakpoints in your code to pause execution at specific points. This allows you to inspect the state of the program and variables.

The $ZSTEP special variable is used to control single-stepping through the code. Setting $ZSTEP to 1 enables single-stepping.

The $ZSHOW special variable can be used to display the current state of the program, including variables and the call stack.

Task: Write a MUMPS program that attempts to use an undefined variable and handles the error gracefully.

Solution:

Task: Write a MUMPS program that sets several variables and uses $ZSHOW to display their values when an error occurs.

Solution:

In this section, we covered the basics of error handling and debugging in MUMPS. You learned about common error messages, how to use $ZTRAP and $ZERROR for error handling, and various debugging tools and techniques such as breakpoints, $ZSTEP, and $ZSHOW. By mastering these skills, you can write more robust and reliable MUMPS programs. In the next module, we will delve into advanced control structures to further enhance your programming capabilities.