Chapter 4, Metalinguistic Abstraction

Exercise 4.72


If a rule evaluation results in an infinite stream, then without interleave in an or, we will never see the results from the other parts of the or.

For example, consider the following rules:

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(assert! (ones ()))
(assert! (rule (ones (1 . ?x)) (ones ?x)))

(assert! (twos ()))
(assert! (rule (twos (2 . ?x)) (twos ?x)))

With interleave:

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;;; Query input:
(or (ones ?x) (twos ?y))

;;; Query results:
(or (ones ()) (twos ?y))
(or (ones ?x) (twos ()))
(or (ones (1)) (twos ?y))
(or (ones ?x) (twos (2)))
(or (ones (1 1)) (twos ?y))
(or (ones ?x) (twos (2 2)))
(or (ones (1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2)))
(or (ones (1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2)))
(or (ones (1 1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2 2)))
(or (ones (1 1 1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2 2 2)))
(or (ones (1 1 1 1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2 2 2 2)))
(or (ones (1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2 2 2 2 2)))
(or (ones (1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2 2 2 2 2 2)))
(or (ones (1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2 2 2 2 2 2 2)))
(or (ones (1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2 2 2 2 2 2 2 2)))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2 2 2 2 2 2 2 2 2)))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2 2 2 2 2 2 2 2 2 2)))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2 2 2 2 2 2 2 2 2 2 2)))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2 2 2 2 2 2 2 2 2 2 2 2)))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2)))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2)))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2)))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2)))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2)))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones ?x) (twos (2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2)))
...

Without interleave(replaced interleave-delayed in disjoin with stream-append-delayed):

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;;; Query input:
(or (ones ?x) (twos ?y))

;;; Query results:
(or (ones ()) (twos ?y))
(or (ones (1)) (twos ?y))
(or (ones (1 1)) (twos ?y))
(or (ones (1 1 1)) (twos ?y))
(or (ones (1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
(or (ones (1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1)) (twos ?y))
...