start
   def s(a, b, s, e) {
      start
         if (s < e) {
            start
               a := a + b;
               s := s + 1;
               forward a;
               turn 90;
               call s(a,  b, s, e);
            end
         }
      end
   }
   forward 0-25;
   down;
   call s(50, 5, 0, 120);
end