Format.zl

export Show;
import Numeric;

class Show T {
        String show(T);
}

instance Show int {
        String show(int x) {
                return /* whatever */;
        }
}

Main.zl

export Main;
import Numeric, Format;
import IO;

pure T sq[Numeric T](T x) {
        return x * x;
}

int main() {
        out.print(show(sq(42)));
        return 0;
}

Numeric.zl

export Numeric, int;

infixl `*` 5;

class Numeric T {               // type classes!
        T `*`(T, T);            // * operator
}

type int {
public:
        __int value;            // __int is primitive
}

instance Numeric int {
        int `*`(int a, int b) {
                return __imul(a.value, b.value);
        }
}