giles
8a9168c8d5
- fix hk-eval-let: multi-clause where/let now uses hk-bind-decls! grouping (enables go 0 / go k pattern) - add concatMap/concat/abs/negate to Prelude (list comprehension support) - cache init env in hk-env0 (eval-expr-source 5x faster)
39 lines
998 B
Plaintext
39 lines
998 B
Plaintext
;; nqueens.hs — n-queens solver via list comprehension + where.
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;;
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;; Also exercises:
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;; - multi-clause let/where binding (go 0 = ...; go k = ...)
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;; - list comprehensions (desugared to concatMap)
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;; - abs (from Prelude)
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;; - [1..n] finite range
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;;
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;; n=8 is too slow for a 60s timeout; n=4 and n=5 run in ~17s combined.
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(define
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hk-prog-val
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(fn
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(src name)
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(hk-deep-force (get (hk-eval-program (hk-core src)) name))))
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(define
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hk-nq-base
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"queens n = go n
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where
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go 0 = [[]]
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go k = [q:qs | qs <- go (k - 1), q <- [1..n], safe q qs]
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safe q qs = check q qs 1
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check q [] _ = True
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check q (c:cs) d = q /= c && abs (q - c) /= d && check q cs (d + 1)
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")
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(hk-test
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"nqueens: queens 4 has 2 solutions"
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(hk-prog-val (str hk-nq-base "result = length (queens 4)\n") "result")
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2)
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(hk-test
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"nqueens: queens 5 has 10 solutions"
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(hk-prog-val (str hk-nq-base "result = length (queens 5)\n") "result")
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10)
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{:fails hk-test-fails :pass hk-test-pass :fail hk-test-fail}
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