;; lib/hyperscript/plugins/prolog.sx — Prolog plugin
;;
;; Provides the `prolog` HS-level function. Replaces the ad-hoc
;; hs-prolog-hook / hs-set-prolog-hook! slots that previously lived in
;; lib/hyperscript/runtime.sx (nodes 140–142 of the plugin design doc).
;;
;; Two-step wiring preserves the original API:
;;   1. lib/prolog/runtime.sx loaded → defines pl-query-one
;;   2. lib/prolog/hs-bridge.sx (or this file's auto-wire) calls
;;      (hs-set-prolog-hook! (fn (db goal) (not (= nil (pl-query-one db goal)))))
;; If neither is loaded, calling (prolog db goal) raises a clear error.

(define hs-prolog-hook nil)

(define hs-set-prolog-hook! (fn (f) (set! hs-prolog-hook f)))

(define
  prolog
  (fn
    (db goal)
    (if
      (nil? hs-prolog-hook)
      (raise "prolog hook not installed")
      (hs-prolog-hook db goal))))