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conda-try mirrors condu-try but on the chosen clause it (mk-bind (head-goal s) (rest-conj)) — all head answers flow through. condu by contrast applies rest-conj to (first peek), keeping only one head answer. 7 new tests covering: first-non-failing-wins, skip-failing-head, all-fail, no-clauses, the conda-vs-condu divergence (`(1 2)` vs `(1)`), rest-goals running on every head answer, and the soft-cut no-fallthrough property. 169/169 cumulative.
43 lines
1.2 KiB
Plaintext
43 lines
1.2 KiB
Plaintext
;; lib/minikanren/conda.sx — Phase 5 piece A: `conda`, the soft-cut.
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;;
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;; (conda (g0 g ...) (h0 h ...) ...)
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;; — first clause whose head g0 produces ANY answer wins; ALL of g0's
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;; answers are then conj'd with the rest of that clause; later
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;; clauses are NOT tried.
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;; — differs from condu only in not wrapping g0 in onceo: condu
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;; commits to the SINGLE first answer, conda lets the head's full
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;; answer-set flow into the rest of the clause.
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;; (Reasoned Schemer chapter 10; Byrd 5.3.)
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(define
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conda-try
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(fn
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(clauses s)
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(cond
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((empty? clauses) mzero)
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(:else
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(let
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((cl (first clauses)))
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(let
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((head-goal (first cl)) (rest-goals (rest cl)))
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(let
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((peek (stream-take 1 (head-goal s))))
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(if
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(empty? peek)
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(conda-try (rest clauses) s)
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(mk-bind (head-goal s) (mk-conj-list rest-goals))))))))))
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(defmacro
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conda
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(&rest clauses)
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(quasiquote
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(fn
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(s)
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(conda-try
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(list
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(splice-unquote
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(map
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(fn (cl) (quasiquote (list (splice-unquote cl))))
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clauses)))
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s))))
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