Drawing Dragon Curve with Logica

[EvgSkv]

Here is a twitter thread on drawing a Dragon Curve with Logica.

Curve:

Set:

Logical code:

@Engine("sqlite");

F1(x, y, new_x, new_y) :-
  new_x == 0.5 * x - 0.5 * y,
  new_y == 0.5 * x + 0.5 * y;

F2(x, y, new_x, new_y) :-
  new_x == -0.5 * x - 0.5 * y + 1,
  new_y == 0.5 * x - 0.5 * y;

@Ground(Dragon);
@Recursive(Dragon, 20);
@OrderBy(Dragon, "logica_value");
Dragon(0, 0, 0) = 0 distinct;
Dragon(new_x, new_y, level + 1) = v distinct :-
  Dragon(x, y, level) == n, (
      (F1(x, y, new_x, new_y), v == n) |
      (F2(x, y, new_x, new_y), v == 2 ^ level - n) );

@OrderBy(DragonCurve, "logica_value");
DragonCurve(x, y, level) = v :-
  Dragon(x1, y1, level) == v1,
  Dragon(x2, y2, level) == v1 + 1,
  (
      (
          x == x1 + (x2 - x1) * 0.3,
          y == y1 + (y2 - y1) * 0.3,
          v == v1 + 0.2
      ) | (
          x == x2 + (x1 - x2) * 0.3,
          y == y2 + (y1 - y2) * 0.3,
          v == v1 + 0.8
      )
  );