Optional arguments

Parameters can be defined as optionals, but these cannot be excluded from the function call if they are not defined. You must pass in none as an argument if you are using an optional argument.

fn optAddNum(int a, int? b) -> int {
  if (b == none) {
    return a
  }

  return a + b
}

int c = optAddNum(5, none)

Not passing the second value will create a partially applied function instead:

fn optAddTo5 = optAddNum(5)
int c = optAddTo5(none)