// Global code will be evaluated once.
const turtle = new Turtle(200, 200);
turtle.penup();
turtle.goto(-100, -90);
turtle.pendown();

// The walk function will be called until it returns false.
function walk(i) {
    turtle.forward(10);
    turtle.right(i % 2 == 1 ? -90 : 90);
    return i < 50;
}