datalog example

gistfile1.txt

#lang racket

(require datalog)

(define corporate-chain
  (make-theory))

(datalog corporate-chain
         ;; shareholders
         (! (shareholder "Jorge"    "pf"))
         (! (shareholder "Bob"      "pf"))
         (! (shareholder "Googly"   "pj"))
         (! (shareholder "Megasoft" "pj"))
         ;; ownership
         (! (owns-a-share "Jorge"  "Construction SA" 60.8 "shareholder"))
         (! (owns-a-share "Bob"    "Construction SA" 39.2 "shareholder"))
         (! (owns-a-share "Googly" "Toys SA"         100 "shareholder")))

(define (majority? percent)
  ;; should return every owner who owns more than 50%
  (> percent 50))

(datalog corporate-chain
         (! (:- (major-stockholder SHAREHOLDER)
                (shareholder SHAREHOLDER KIND)
                (owns-a-share SHAREHOLDER COMPANY PERCENT RELATIONSHIP)
                (majority? PERCENT :- X)
                (= X true)))
         (? (major-stockholder X)))