Tarai (TAO/ELIS)

tarai.tao

(de tarai (x y z)
    (cond ((> x y)
           (& (:aux _ans)
              (&tarai ,(tarai (1- x) y z)
                      ,(tarai (1- y) z x)
                      ,(tarai (1- z) x y)
                      _ans)
              _ans))
          (t y) ))

(defrel &tarai
    ((    _x _y _z _ans)
     (:aux _a0 _a1 _a2)
     (> _x _y) !
     (&tarai ,[_x - 1] _y _z _a0)
     (&tarai ,[_y - 1] _z _x _a1)
     (&tarai ,[_z - 1] _x _y _a2)
     (== _ans ,[_a0 :tarai _a1 _a2]))
    ((    _x _y _z _y)
     (not (> _x _y)) !))

(defmethod (integer :tarai) (y z)
    (cond ([self > y]
           (tarai [[self - 1] :tarai y z]
                  [[y - 1] :tarai z self]
                  [[z - 1] :tarai self y] ))
          (t y) ))

(tarai 12 6 0)
→ 12