Function

Definition

A function is a self-contained, named block of code designed to perform a single, well-defined task. Instead of writing the same logic repeatedly throughout a program, you define it once as a function and then call (invoke) it whenever you need it.

Functions are one of the most important tools for writing clean, maintainable code.

Defining and Calling a Function

DEFINE greet(personName):
    PRINT "Hello, " + personName + "!"

greet("Alice")   # Output: Hello, Alice!
greet("Bob")     # Output: Hello, Bob!

The DEFINE keyword introduces the function. Everything indented beneath it is the function body — the code that runs each time the function is called. The name in brackets (personName) is a parameter.

Parameters and Return Values

Parameters are variables listed in the function definition that receive input values when the function is called. The actual values passed in are called arguments.

Return values are values that the function sends back to the code that called it.

DEFINE add(a, b):
    result = a + b
    RETURN result

total = add(3, 5)    # total is 8
total = add(10, 20)  # total is 30

A function does not have to return a value — some functions only perform an action (like printing a message) without producing a result.

Why Functions Reduce Repetition

Consider a program that needs to calculate the area of a rectangle in five different places. Without functions:

area1 = 4 * 7
area2 = 10 * 3
area3 = 6 * 6
# ... and so on, with the same formula repeated

With a function:

DEFINE rectangleArea(width, height):
    RETURN width * height

area1 = rectangleArea(4, 7)
area2 = rectangleArea(10, 3)
area3 = rectangleArea(6, 6)

Now the formula exists in exactly one place. If you need to change the logic, you change it once and the fix applies everywhere.

This principle — writing each piece of logic only once — is called DRY (Don't Repeat Yourself).