Implement 4.76
parent
751e20229c
commit
66726a21f8
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@ -108,7 +108,7 @@
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(lambda (x1) (stream-map (lambda (x2) (append x1 x2)) s2))
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s1))
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(define (conjoin conjuncts frame-stream)
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(define (conjoin-efficient conjuncts frame-stream)
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(define (unify-bindings bindings)
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(define (go-unify bindings frame)
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(if (null? bindings)
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@ -120,42 +120,65 @@
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(go-unify bindings '()))
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(define (unify-frame-streams frame-stream-1 frame-stream-2)
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(display "UNIFY-FRAME-STREAMS\n")
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(let ((potential-bindings (stream-combinations frame-stream-1 frame-stream-2)))
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(stream-filter
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(lambda (f) (not (eq? f 'failed)))
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(stream-map unify-bindings potential-bindings))))
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(define (unify-frame-stream-list frame-stream-list)
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(if (null? (cdr frame-stream-list))
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(car frame-stream-list)
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(let ((frame-stream (unify-frame-streams (car frame-stream-list)
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(cadr frame-stream-list))))
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(display frame-stream) (newline)
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(unify-frame-stream-list (cons frame-stream (cddr frame-stream-list))))))
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(define (conjoin-single conjunct frame-stream-1)
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(if (not (tagged-list? conjunct 'not))
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(unify-frame-streams
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frame-stream-1
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(qeval conjunct frame-stream)) ; process separately
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(qeval conjunct frame-stream-1))) ; cannot process not separately
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(define (qeval-conjunction conjunction)
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(qeval conjunction frame-stream))
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(define (conjoin-inner conjuncts frame-stream)
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(if (null? conjuncts)
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frame-stream
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(let ((new-frame-stream (conjoin-single (car conjuncts) frame-stream)))
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(conjoin-inner (cdr conjuncts) new-frame-stream))))
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(let ((frame-stream-list (map qeval-conjunction conjuncts)))
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(unify-frame-stream-list frame-stream-list)))
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(conjoin-inner conjuncts frame-stream))
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(put 'and 'qeval conjoin)
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(put 'and2 'qeval conjoin-efficient)
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(eval-query
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'(rule (big-shot ?p)
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(and (job ?p (?div1 . ?rest1))
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(supervisor ?p ?boss)
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(job ?boss (?div2 . ?rest2))
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(not (same ?div1 ?div2)))))
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(and2 (job ?p (?div1 . ?rest1))
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(supervisor ?p ?boss)
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(job ?boss (?div2 . ?rest2))
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(not (same ?div1 ?div2)))))
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(eval-query '(big-shot ?x))
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(newline)
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(display "\nex-4.77 - improved-not\n")
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; Exercise 4.77. In section 4.4.3 we saw that not and lisp-value can cause the
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; query language to give ``wrong'' answers if these filtering operations are
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; applied to frames in which variables are unbound. Devise a way to fix this
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; shortcoming.
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; One idea is to perform the filtering in a ``delayed'' manner by
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; appending to the frame a ``promise'' to filter that is fulfilled only when
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; enough variables have been bound to make the operation possible. We could
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; wait to perform filtering until all other operations have been performed.
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; However, for efficiency's sake, we would like to perform filtering as soon as
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; possible so as to cut down on the number of intermediate frames generated.
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(display "--")
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(eval-query
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'(and (supervisor ?x ?y)
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(not (job ?x (computer programmer)))))
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(display "\n--\n")
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(display "\nex-4.77\n")
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(display "--")
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(eval-query
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'(and (not (job ?x (computer programmer)))
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(supervisor ?x ?y)))
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(display "\n--\n")
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;(display "\nex-4.78\n")
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;(display "\nex-4.79\n")
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(display "\nex-4.78\n")
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(display "\nex-4.79\n")
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