recursion depth exceeded when relations are inter dependent

[vitrun]

B and C are both on line AD, length of AC is 3, length of AB is 2.

The followings are expected to be infered:

• B is on AC
• length of BC is 1

My code fails because of RecursionError as lineLen and pointOn are dependent on each other:

Len = Relation()
On = Relation()


def lineLen(a, b, l):
    """
    Length of Line ab is l
    """
    c, l1, l2 = vars(3)
    return lany(
        Len(a, b, l),
        lall(  # when c in on ab, we have ab=ac+cb
            pointOn(c, a, b),
            Len(a, c, l1),
            Len(b, c, l2),
            applyo(add, (l1, l2), l)),
        lall(  # when a is on bc, we have ab=bc-ac
            pointOn(a, b, c),
            Len(b, c, l1),
            Len(a, c, l2),
            applyo(sub, (l1, l2), l)
        ),
        lall(  # when b is on ac, we have ab=ac-bc
            pointOn(b, a, c),
            Len(a, c, l1),
            Len(b, c, l2),
            applyo(sub, (l1, l2), l)
        )
    )


def pointOn(p, a, b):
    """
    Point p is on Line ab
    """
    d, l1, l2, r = vars(4)
    return lany(
        On(p, a, b),
        On(p, b, a),
	#  when p and b are both on line ad, and ab > ap, we know p is on ab
        lall(On(p, a, d), On(b, a, d), lineLen(a, p, l1),
             lineLen(a, b, l2), applyo(gt, (l2, l1), r), eq(r, True))
    )


facts(On,
      ('B', 'A', 'D'),
      ('C', 'A', 'D'),
      )

facts(Len,
      ('A', 'B', 3),
      ('A', 'C', 4),
      )

a, b, c = vars(3)
res = run(0, (a, b, c), pointOn(a, b, c))
for p in res:
    print(f'{p[0]} is on {p[1]}{p[2]}')

The case is simple, but seems not that easy to implement, any advice? BTW, using kanren, I find it easy to meet recursion error evenZzz is used.

[rlouf]

Could it be related to #59?