;; lib/minikanren/tests/cyclic-graph.sx — demonstrates the naive-patho
;; behaviour on a cyclic graph. Without Phase-7 tabling/SLG, the search
;; produces ever-longer paths revisiting the cycle. `run n` truncates;
;; `run*` would diverge.

(define cyclic-edges (list (list :a :b) (list :b :a) (list :b :c)))

(define cyclic-edgeo (fn (x y) (membero (list x y) cyclic-edges)))

(define
  cyclic-patho
  (fn
    (x y path)
    (conde
      ((cyclic-edgeo x y) (== path (list x y)))
      ((fresh (z mid) (cyclic-edgeo x z) (cyclic-patho z y mid) (conso x mid path))))))

;; --- direct edge ---

(mk-test
  "cyclic-direct"
  (run 1 q (cyclic-patho :a :b q))
  (list (list :a :b)))

;; --- runs first 5 paths from a to b: bare edge, then increasing
;;     numbers of cycle traversals (a->b->a->b, etc.) ---

(mk-test
  "cyclic-enumerates-prefix-via-run-n"
  (let
    ((paths (run 5 q (cyclic-patho :a :b q))))
    (and
      (= (len paths) 5)
      (and
        (every? (fn (p) (= (first p) :a)) paths)
        (every? (fn (p) (= (last p) :b)) paths))))
  true)

(mk-test
  "cyclic-finds-c-via-cycle-or-direct"
  (let
    ((paths (run 3 q (cyclic-patho :a :c q))))
    (and
      (>= (len paths) 1)
      (some (fn (p) (= p (list :a :b :c))) paths)))
  true)

(mk-tests-run!)