My original programming language, Expresso -- About functions

Hi, this is HAZAMA. And this is an-another blog entry for Expresso this month. We'll be talking a bit about the grammar this time around.

One of the commonest language constructs is the functions and Expresso, of course, has ones. Specifically, Expresso has module-level functions and methods in class definitions. They are implemented as static methods in module classes, and ordinary methods in class definitions, respectively.

module main;


def test()
{
    let a = 10;
    return a + 10;
}

def test2(n (- int)
{
    return n + 10;
}

def test3(n (- int) -> int
{
    return n + 20;
}

def test4(n (- int) -> int
{
    if n >= 100 {
        return n;
    }else{
        return test4(n + 10);
    }
}

def main()
{
    let a = test();
    let b = test2(20);
    let c = test3(20);
    let d = test4(80);

    println(a, b, c, d);
}

This code snippet originated from the test codes again. Return types of Expresso functions will be inferred from the body, but I'm worried about whether to change it or not(In the code above, all the functions will be inferred to return an int). In Kotlin, they are inferred only if the return type is Unit(Void), so I've not decided to make Expresso do that.
Parameters of functions are inferred only when they have the optional values(In the code above there isn't). In the code above, each of the functions:

1. takes no parameters, and the return type is implicit.
2. takes a parameter, and the return type is implicit.
3. takes a parameter, and the return type is explicit.
4. takes a parameter, and the return type is explicit and it contains a recursive call.

I guess there are no special differences to those in other programming languages.
Note that these are unnecessary comments. Although the parser can parse variadic parameters, the program isn't emitting any code for that so you can't use variadic parameters yet. I added those for the print* functions, but I don't come up with many use cases so I've not decided whether to implement them. Maybe I should implement them because doing so isn't that hard. Likewise, I've not decided to implement so-called string interpolation. This will replace the printFormat function if it exists. This is a difficult problem.(Apr. 8 2018 added: The string interpolation has been implemented and the printFormat function has been removed)