first-steps6 min

Writing Your Own Functions

As your programs grow, you'll find yourself writing the same code in different places. Functions are the solution — write something once, use it anywhere.

In Clean Language, functions live in a functions: block:

functions:
    string greet(string name)
        return "Hello, {name}! Welcome to Clean Language."

start:
    print(greet("Alice"))
    print(greet("Bob"))
    print(greet("everyone"))

Hello, Alice! Welcome to Clean Language.
Hello, Bob! Welcome to Clean Language.
Hello, everyone! Welcome to Clean Language.

The function is named greet, takes one string input called name, and returns a string. Write the return type first, then the function name, then parameters in parentheses.

Functions can do calculations too:

functions:
    integer double(integer n)
        return n * 2

    integer addTen(integer n)
        return n + 10

start:
    print(double(5).toString())
    print(addTen(7).toString())
    print(double(addTen(3)).toString())

10
17
26

You can pass a function's result directly into another function. addTen(3) gives 13, then double(13) gives 26. Functions compose naturally.

Quick recap

Declare functions in a functions: block, outside of start:
Write the return type first: integer, string, boolean, void
Parameters go inside parentheses: (string name, integer age)
Use return to send a value back
Call a function by name: greet("Alice")