List size goal operator with core.logic

logic-sizeo.clj

;; These two goals taken from https://spin.atomicobject.com/2015/12/14/logic-programming-clojure-finite-domain-constraints/
(defn sumo [l sum]
  (fresh [head tail tail-sum]
         (conde
           [(== l ()) (== sum 0)]
           [(conso head tail l)
            (fd/+ head tail-sum sum)
            (sumo tail tail-sum)])))

(defn everyo [l f]
  (fresh [head tail]
         (conde
           [(== l ())]
           [(conso head tail l)
            (f head)
            (everyo tail f)])))

(defn sizeo [l size]
  (fresh [tail tail-size]
         (conde
           [(== l ()) (== size 0)]
           [(resto l tail)
            (fd/+ size -1 tail-size)
            (sizeo tail tail-size)])))

(run 1 [l]
     (fresh [size]
            (fd/in size (fd/interval 0 2))
            (everyo l #(fd/in % (fd/interval 1 10)))
            (sumo l 10)
            (sizeo l size)))