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(project (vars ...) goal ...) defmacro walks each named var via mk-walk*, rebinds them in the body's lexical scope, then mk-conjs the body goals on the same substitution. Hygienic — gensym'd s-param so user vars survive. Lets you reach into host SX for arithmetic, string ops, anything that needs a ground value: (project (n) (== q (* n n))), (project (s) (== q (str s \"!\"))), and so on. 6 new tests, 194/194 cumulative.
26 lines
1012 B
Plaintext
26 lines
1012 B
Plaintext
;; lib/minikanren/project.sx — Phase 5 piece B: `project`.
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;;
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;; (project (x y) g1 g2 ...)
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;; — rebinds each named var to (mk-walk* var s) within the body's
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;; lexical scope, then runs the conjunction of the body goals on
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;; the same substitution. Use to escape into regular SX (arithmetic,
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;; string ops, host predicates) when you need a ground value.
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;;
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;; If any of the projected vars is still unbound at this point, the body
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;; sees the raw `(:var NAME)` term — that is intentional and lets you
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;; mix project with `(== ground? var)` patterns or with conda guards.
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;;
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;; Hygiene: substitution parameter is gensym'd so it doesn't capture user
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;; vars (`s` is a popular relation parameter name).
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(defmacro
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project
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(vars &rest goals)
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(let
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((s-sym (gensym "proj-s-")))
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(quasiquote
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(fn
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((unquote s-sym))
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((let (unquote (map (fn (v) (list v (list (quote mk-walk*) v s-sym))) vars)) (mk-conj (splice-unquote goals)))
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(unquote s-sym))))))
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