syndicate-2017/racket/doc/forward-chaining-hll.rkt.txt

60 lines
2.6 KiB
Racket

#lang prospect/hll ;; -*- racket -*-
(actor (forever #:collect [(count 0)]
(assert `(parent-count ,count))
(on (asserted `(parent ,$p ,$c)) (+ count 1))
(on (retracted `(parent ,$p ,$c)) (- count 1))))
(define (insert-record record . monitors)
(printf "Record ~v inserted, depending on ~v\n" record monitors)
(actor (state [(assert record)]
[(retracted (BIND-TO-PATCH-REMOVED removed (assertion-set-union* monitors)))
(printf "Retracting ~v because dependencies ~v vanished\n"
record
(assertion-set->list removed))]
[(message `(retract ,record))
(printf "Retracting ~v because we were told to explicitly\n" record)])))
(insert-record `(parent john douglas))
(insert-record `(parent bob john))
(insert-record `(parent ebbon bob))
(actor (forever (on (asserted `(parent ,$p ,$c))
(insert-record `(ancestor ,p ,c)
`(parent ,p ,c)))))
(actor (forever (on (asserted `(parent ,$A ,$C))
(printf "Inductive step for ~v asserted\n" `(parent ,A ,C))
(actor (state [(on (asserted `(ancestor ,C ,$B))
(insert-record `(ancestor ,A ,B)
`(parent ,A ,C)
`(ancestor ,C ,B)))]
[(retracted `(parent ,A ,C))
(printf
"Inductive step for ~v retracted because of removal\n"
`(parent ,A ,C))])))))
(actor (forever (on (asserted `(ancestor ebbon douglas))
(printf "Proved (ancestor ebbon douglas)\n"))
(on (retracted `(ancestor ebbon douglas))
(printf "Proof of (ancestor ebbon douglas) invalidated\n"))))
(define (after msec thunk)
(define id (gensym 'after))
(if (zero? msec)
(thunk)
(actor (send! (set-timer id msec 'relative))
(until (message (timer-expired id ?)))
(thunk))))
(define use-delays? #t)
(after (if use-delays? 1000 0) (lambda ()
(printf "----- Retracting\n")
(message `(retract (parent bob john)))))
(after (if use-delays? 2000 0) (lambda ()
(printf "----- Asserting\n")
(list (insert-record `(parent bob mary))
(insert-record `(parent mary sue))
(insert-record `(parent sue john)))))