Querying

(query-prolog rb '(ancestor tom ?who))          ; all solutions
(query-prolog rb '(ancestor tom ?who) :limit 2) ; bounded search
(query-prolog-first rb '(ancestor ?x bob))      ; first solution or NIL
(prolog-succeeds-p rb '(ancestor tom eve))      ; boolean, stops at first proof

;; streaming: the function is called as each solution is proven
(map-prolog-solutions
 (lambda (solution) (format t "~&=> ~S~%" solution))
 rb '(ancestor tom ?who))

with-prolog-query binds variables from the first solution; prolog-match dispatches like cond over queries.

Entry points

• map-prolog-solutions — the primitive. Calls a function once per solution as it is proven (streaming CPS). Keywords: :max-depth, :environment, :project, :limit.
• query-prolog — collect solutions into a list. Same keywords.
• query-prolog-first — first solution or nil (searches with :limit 1).
• prolog-succeeds-p — boolean; stops at the first proof.
• solution-binding — look one variable up in a solution alist.

Conventions

• a solution is an alist of query-variable bindings; ground success is nil, so “one ground proof” is (nil) and failure is ()
• :project nil returns raw proof environments instead
• :max-depth optionally bounds user-rule resolution (the default is NIL, meaning unbounded); exhaustion signals prolog-depth-limit-exceeded; 0 disables rule expansion entirely, facts still match
• :limit must be nil or a positive integer