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rev-acco is the standard tail-recursive reverse with an accumulator; rev-2o starts the accumulator at the empty list. Faster than the appendo-driven reverseo for forward queries because there is no nested appendo per element. Trade-off: rev-acco is asymmetric. The accumulator's initial-empty cannot be enumerated backwards the way reverseo does, so reverseo is still the right choice when both directions matter. A test verifies rev-2o and reverseo agree on forward queries. 6 new tests, 422/422 cumulative.
47 lines
1.0 KiB
Plaintext
47 lines
1.0 KiB
Plaintext
;; lib/minikanren/tests/rev-acco.sx — accumulator-style reverse.
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;;
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;; Faster than reverseo for forward queries (no quadratic appendos).
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;; Trade-off: rev-acco is asymmetric (acc=initial-empty for the public
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;; interface), so it does not cleanly run backwards in run* the way
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;; reverseo does.
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(mk-test "rev-2o-empty" (run* q (rev-2o (list) q)) (list (list)))
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(mk-test
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"rev-2o-singleton"
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(run* q (rev-2o (list 7) q))
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(list (list 7)))
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(mk-test
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"rev-2o-three"
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(run* q (rev-2o (list 1 2 3) q))
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(list (list 3 2 1)))
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(mk-test
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"rev-2o-five"
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(run*
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q
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(rev-2o (list 1 2 3 4 5) q))
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(list (list 5 4 3 2 1)))
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(mk-test
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"rev-2o-strings"
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(run* q (rev-2o (list "a" "b" "c") q))
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(list (list "c" "b" "a")))
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(mk-test
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"rev-2o-reverseo-agree"
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(let
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((via-reverseo (first (run* q (reverseo (list 1 2 3 4 5) q))))
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(via-rev-2o
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(first
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(run*
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q
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(rev-2o
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(list 1 2 3 4 5)
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q)))))
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(= via-reverseo via-rev-2o))
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true)
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(mk-tests-run!)
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