Functions

A program is a sequence of instructions (or operations) that the computer executes to perform a specific task. Conceptually, a program is a function: it takes some input and produces some output. To write complex programs, we use functions as building blocks to decompose a program into smaller, manageable pieces. Similarly, libraries provide reusable functions that can be called from different programs. The Inference programming language is all about writing functions. As we saw in Hello World, the smallest Inference program is a function.

Anatomy of a Function

pub fn function_name(param1: Type1, param2: Type2) -> ReturnType {
    // function body
}

• pub makes the function exported from the compiled WebAssembly module. Without pub, a function is private to the file.
• -> ReturnType declares the return type. Functions without it return nothing.
• return is required to return a value — there are no implicit returns.

Parameters

Each parameter has a name and a type annotation:

pub fn add(a: i32, b: i32) -> i32 {
    return a + b;
}

Parameters are immutable by default. Declare with mut to allow modification inside the function body. All values are passed by copy — mutating a parameter does not affect the caller:

pub fn increment_and_return(mut x: i32) -> i32 {
    x = x + 1;
    return x;
}

Calling Functions

pub fn example() -> i32 {
    let result: i32 = add(10, 20);
    return result;
}

Function Body

A function body is a sequence of statements enclosed in curly braces {}.

Methods

Methods are functions defined inside an impl block. Instance methods take self as the first parameter:

struct Counter {
    value: i32;
}

impl Counter {
    fn new() -> Counter {
        return Counter { value: 0 };
    }

    fn get(self) -> i32 {
        return self.value;
    }

    fn increment(mut self) {
        self.value = self.value + 1;
    }
}

Call instance methods with dot syntax and associated functions with :::

pub fn example() -> i32 {
    let mut c: Counter = Counter::new();
    c.increment();
    return c.get();
}