Functions

Functions are defined with the fn keyword. The keyword void indicates that the function does not return a value.

fn doSomething() void {
    // code...
}

Functions may accept parameters and return values.

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

First Class Functions

Functions are first class objects in Aspen, a variable with a function type can be declared like so:

let func fn(i64, i64)string;

Here func is a variable of type fn(i64, i64)string, i.e. a function that takes 2 integer parameters and returns a string. Variables with a function type must be initialized, so the code example above is actually illegal. Here is a complete example.

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

fn sub(a i64, b i64) i64 {
    return a - b;
}

fn mul(a i64, b i64) i64 {
    return a * b;
}

fn div(a i64, b i64) i64 {
    return a / b;
}

fn calc(op fn(i64, i64)i64, a i64, b i64) void {
    print op(a, b);
}

calc(add, 5, 7);
calc(sub, 4, 1);
calc(mul, 3, 6);
calc(div, 8, 2);

Closures

Functions defined in a local scope will capture the variables visible from that scope.

fn makeCounter() fn()void {
    let i i64 = 0;
    fn count() void {
        i = i + 1;
        print "called " + itoa(i) + " times.";
    }
    return count;
}

let counter fn()void = makeCounter();
counter();
counter();
counter();