Functions

Declaration

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fn <name>(<params>) -> <return_type> {
    <body>
}

Parameters are comma-separated and require type annotations. The return type after -> is optional and defaults to ().

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fn add(a: i64, b: i64) -> i64 {
    return a + b;
}

Explicit return type is written after ->:

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fn square(x: u64) -> u64 {
    return x * x;
}

Omitting -> is equivalent to -> ():

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fn greet() {
    print(72); // 'H'
}

The last expression in a function body without a trailing ; is the return value:

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fn mul(a: u64, b: u64) -> u64 {
    a * b
}

Every program must define a main function. It should return 0.

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

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let result = add(3, 4);

Arguments can be arbitrary expressions:

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let x = add(2 * 3, 10 - 4); // add(6, 6) = 12

Calls can be nested:

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print(double(inc(5))); // 12

print is a built-in that prints a single value to stdout. It accepts any primitive type:

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print(42);
print(3.14);
print(true);  // 1
print('A');   // 65