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queens.sx encodes a queen in row i at column ci. ino-each constrains
each ci to {1..n}; all-distincto handles the row/column distinct
property; safe-diag uses project to escape into host arithmetic for the
|c_i - c_j| != |i - j| diagonal guard. all-cells-safe iterates pairs at
goal-construction time so the constraint set is materialised once,
then driven by the search.
(run* q (fresh (a b c d) (== q (list a b c d))
(queens-cols (list a b c d) 4)))
-> ((2 4 1 3) (3 1 4 2))
Both valid 4-queens placements found. 6 new tests including the
two-solution invariant; 243/243 cumulative.
46 lines
923 B
Plaintext
46 lines
923 B
Plaintext
;; lib/minikanren/tests/queens.sx — N-queens, the classic miniKanren benchmark.
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;; --- safe-diag (helper) ---
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(mk-test
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"safe-diag-different-cols-different-distance"
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(run* q (safe-diag 1 4 2))
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(list (make-symbol "_.0")))
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(mk-test
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"safe-diag-same-distance-fails"
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(run* q (safe-diag 1 4 3))
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(list))
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(mk-test
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"safe-diag-same-distance-other-direction-fails"
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(run* q (safe-diag 4 1 3))
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(list))
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;; --- ino-each / range ---
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(mk-test
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"range-1-to-4"
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(range-1-to-n 4)
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(list 1 2 3 4))
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(mk-test "range-empty" (range-1-to-n 0) (list))
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;; --- 4-queens: two solutions ---
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(mk-test
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"queens-4"
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(let
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((sols (run* q (fresh (a b c d) (== q (list a b c d)) (queens-cols (list a b c d) 4)))))
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(and
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(= (len sols) 2)
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(and
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(some
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(fn (s) (= s (list 2 4 1 3)))
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sols)
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(some
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(fn (s) (= s (list 3 1 4 2)))
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sols))))
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true)
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(mk-tests-run!)
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