Lesson 2: Functions as contracts

Write functions and let types take care of what goes in and what comes out.

Goal

In one sentence: declare functions with readable signatures and explicit types.

Code

func greet(name: str): str {
    return "Hello, " + name
}

func double(value: int): int {
    return value * 2
}

Types come after the parameters and after the : of the return. Explicit signatures make a function boundary and its contract visible to both the reader and the compiler.

Try it

Call double with a number, then try passing a str. The compiler stops the error right away, before anything even runs.

Next, we ask who may modify each value and for how long.