Functions

Functions start with fn, take typed parameters, and return one value.

use "std/io.cnd";

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

fn describe(n: i32) -> []u8 {
    if n > 0 {
        return "positive";
    }
    return "not positive";
}

fn main() -> i32 {
    let v = add(2, 3);
    print(&v, .I32);
    putchar(10);

    println(describe(5));
    println(describe(-1));
    return 0;
}

$ ./fns
5
positive
not positive

Parameters

Parameters are read-only. Pass by value; pass a pointer to mutate the caller's

value (see Pointers).

fn scale(v: i32, k: i32) -> i32 {
    return v * k;
}

void

A function without a return type returns nothing.

use "std/io.cnd";

fn announce(tag: []u8) {
    let open: []u8 = "[";
    print(&open, .S);
    print(&tag, .S);

    let close: []u8 = "] ";
    print(&close, .S);
    println("running");
}

fn main() -> i32 {
    announce("boot");
    return 0;
}

$ ./void
[boot] running

Early return

return exits the function immediately.

use "std/io.cnd";

fn classify(v: i32) -> []u8 {
    if v < 0 {
        return "negative";
    }
    if v == 0 {
        return "zero";
    }
    return "positive";
}

fn main() -> i32 {
    println(classify(-5));
    println(classify(0));
    println(classify(5));
    return 0;
}

$ ./early
negative
zero
positive

unsafe fn

unsafe fn is deprecated and has no effect. The unsafe keyword before fn

is accepted for compatibility, but the function body and every call site behave

like any other function. The construct will be removed in a future version.

// docs: error-skip
unsafe fn peek(v: *u32) -> u32 {
    return *v;
}