logic-boys-girls.clj

(ns logical-boys-girls.core
  (:require            [clojure.core.logic :as logic]
                       [clojure.core.logic.fd :as fd]))
(logic/run*
 [q]
 (let [students-count (fd/interval 1 100)]
   (logic/fresh [boys girls h-girls q-girls h-boys q-boys]
                ;; boring part

                ;; every lvar belongs to number from interval
                (fd/in boys students-count)
                (fd/in girls students-count)
                (fd/in h-girls students-count)
                (fd/in q-girls students-count)
                (fd/in h-boys students-count)
                (fd/in q-boys students-count)

                ;; fun part
                (fd/+ boys girls 48) ;; number of students in class

                (fd/* 2 h-girls girls) ;; divide girls in two groups
                (fd/* 2 q-girls h-girls) ;; rest should seat with each other, so divide one more time
                (fd/>= boys h-girls) ;; there should be enough boys to sit with half of girls 

                (fd/* 2 h-boys boys) ;; same stuff for boys, see comments above
                (fd/* 2 q-boys h-boys)
                (fd/>= girls h-boys)

                (logic/== [boys girls] q))))