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Basic Functions and Procedures

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In this section, we will explore the fundamental concepts of functions and procedures in MUMPS. Understanding these concepts is crucial for writing modular and maintainable code. We will cover the following topics:

  1. What are Functions and Procedures?
  2. Defining a Procedure
  3. Calling a Procedure
  4. Defining a Function
  5. Calling a Function
  6. Practical Examples
  7. Exercises

  1. What are Functions and Procedures?

In MUMPS, functions and procedures are blocks of code designed to perform specific tasks. They help in organizing code, making it reusable, and improving readability.

  • Procedure: A block of code that performs a task but does not return a value.
  • Function: A block of code that performs a task and returns a value.

  1. Defining a Procedure

A procedure in MUMPS is defined using a label followed by a series of commands. Here is the basic syntax:

Label
    ; Commands
    QUIT

Example:

GREET
    WRITE "Hello, welcome to MUMPS!", !
    QUIT

In this example, GREET is a procedure that prints a welcome message.

  1. Calling a Procedure

To call a procedure, you use the DO command followed by the procedure's label.

Example:

DO GREET

This will execute the GREET procedure and print the welcome message.

  1. Defining a Function

A function in MUMPS is similar to a procedure but it returns a value. The syntax is as follows:

Label()
    ; Commands
    QUIT value

Example:

ADD(x, y)
    NEW result
    SET result = x + y
    QUIT result

In this example, ADD is a function that takes two arguments, x and y, adds them, and returns the result.

  1. Calling a Function

To call a function, you use the WRITE command or assign the function's return value to a variable.

Example:

SET sum = $$ADD(5, 3)
WRITE "The sum is: ", sum, !

This will call the ADD function with arguments 5 and 3, and print the result.

  1. Practical Examples

Example 1: Procedure to Print a Message

PRINTMSG
    WRITE "This is a message from a procedure.", !
    QUIT

DO PRINTMSG

Example 2: Function to Multiply Two Numbers

MULTIPLY(a, b)
    NEW product
    SET product = a * b
    QUIT product

SET result = $$MULTIPLY(4, 7)
WRITE "The product is: ", result, !

  1. Exercises

Exercise 1: Create a Procedure

Create a procedure named FAREWELL that prints "Goodbye, see you next time!".

Solution:

FAREWELL
    WRITE "Goodbye, see you next time!", !
    QUIT

DO FAREWELL

Exercise 2: Create a Function

Create a function named SUBTRACT that takes two arguments and returns their difference.

Solution:

SUBTRACT(x, y)
    NEW difference
    SET difference = x - y
    QUIT difference

SET diff = $$SUBTRACT(10, 4)
WRITE "The difference is: ", diff, !

Common Mistakes and Tips

  • Forgetting to use QUIT: Always ensure that your procedures and functions end with a QUIT statement to avoid unexpected behavior.
  • Not using NEW for local variables: Use the NEW command to declare local variables within functions and procedures to prevent variable conflicts.

Conclusion

In this section, we covered the basics of defining and using functions and procedures in MUMPS. These constructs are essential for writing organized and reusable code. Make sure to practice the exercises to reinforce your understanding. In the next module, we will delve into working with data, starting with an introduction to global variables.

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