void setup() {
  size(300, 400);
  ladder(50, 50, 20, 200, 10);
  ladder(100, 50, 40, 300, 30);
  ladder(175, 200, 80, 80, 3);
}

/* Render a ladder with the following characteristics.
It should have top-left corner at (x,y), width w
and total height h, and then n evenly spaced rungs
*/
void ladder(int x, int y, int w, int h, int n) {
  line(x, y, x, y+h);
  line(x+w, y, x+w, y+h);
  float gap = 1.0 * h / (1+n);   // with n rungs, we consider n+1 gaps
  for (int r=1; r <= n; r++) {
    line(x, y+r*gap, x+w, y+r*gap);
  }
}