findall.clj

(ns pettomato.findall
  (:refer-clojure :exclude [==])
  (:use
   [clojure.core.logic.protocols])
  (:require
   [clojure.core.logic :refer :all]))

(defn findall
  "A goal that unifies l with a lazy sequence containing all possible
  instantiations of v that could be generated by applying the goal g
  to the current substitution."
  [v g l]
  (fn [a]
    (let [xs (map #(walk* % v) (take* (g a)))
          ;; The following line is necessary to remove the ::unbound
          ;; metadata flag from any fresh lvars, otherwise we will
          ;; have problems if we try to unify it later.
          xs (map #(if (meta %) (with-meta % {}) %) xs)
          g2 (== l xs)]
      (g2 a))))

(run* [q]
  (fresh [x y]
    (findall x (membero x [1 2 y]) q)
    (== y 3)
    (== q [1 2 3])))