51 lines
2.1 KiB
Racket
51 lines
2.1 KiB
Racket
#lang syndicate/hll ;; -*- racket -*-
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(actor (forever #:collect [(count 0)]
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(assert `(parent-count ,count))
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(on (asserted `(parent ,$p ,$c)) (+ count 1))
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(on (retracted `(parent ,$p ,$c)) (- count 1))))
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(define (insert-record record . monitors)
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(actor (until (or (retracted (assertion-set-union* monitors))
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(message `(retract ,record)))
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(assert record))))
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(insert-record `(parent john douglas))
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(insert-record `(parent bob john))
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(insert-record `(parent ebbon bob))
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(actor (forever (on (asserted `(parent ,$p ,$c))
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(insert-record `(ancestor ,p ,c)
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`(parent ,p ,c)))))
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(actor (forever (on (asserted `(parent ,$A ,$C))
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(actor (until (retracted `(parent ,A ,C))
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(on (asserted `(ancestor ,C ,$B))
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(insert-record `(ancestor ,A ,B)
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`(parent ,A ,C)
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`(ancestor ,C ,B))))))))
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(actor (forever (on (asserted `(ancestor ebbon douglas))
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(printf "Proved (ancestor ebbon douglas)\n"))
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(on (retracted `(ancestor ebbon douglas))
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(printf "Proof of (ancestor ebbon douglas) invalidated\n"))))
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(define (after msec thunk)
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(define id (gensym 'after))
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(if (zero? msec)
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(thunk)
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(actor (send! (set-timer id msec 'relative))
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(until (message (timer-expired id ?)))
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(thunk))))
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(define use-delays? #t)
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(after (if use-delays? 1000 0) (lambda ()
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(printf "----- Retracting\n")
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(message `(retract (parent bob john)))))
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(after (if use-delays? 2000 0) (lambda ()
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(printf "----- Asserting\n")
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(list (insert-record `(parent bob mary))
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(insert-record `(parent mary sue))
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(insert-record `(parent sue john)))))
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