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lib/minikanren/stream.sx: mzero/unit/mk-mplus/mk-bind/stream-take. Three stream shapes (empty, mature list, immature thunk). mk-mplus suspends and swaps on a paused-left for fair interleaving (Reasoned Schemer style). lib/minikanren/goals.sx: succeed/fail/==/==-check + conj2/disj2 + variadic mk-conj/mk-disj. ==-check is the opt-in occurs-checked variant. Forced-rename note: SX has a host primitive `bind` that silently shadows user-level defines, so all stream/goal operators are mk-prefixed. Recorded in feedback memory. 82/82 tests cumulative (48 unify + 34 goals).
59 lines
1.8 KiB
Plaintext
59 lines
1.8 KiB
Plaintext
;; lib/minikanren/stream.sx — Phase 2 piece A: lazy streams of substitutions.
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;;
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;; Three stream shapes per The Reasoned Schemer (chapter 9):
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;; mzero — empty stream (the SX empty list)
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;; mature — '(s . rest) (a proper SX list of substitutions)
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;; immature — a thunk (an SX lambda taking zero args, returns a stream)
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;;
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;; Immature thunks are how miniKanren keeps search lazy and supports
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;; interleaved disjunction without diverging on left-recursive relations.
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;; SX has plain function closures, so a thunk is just (fn () body).
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;;
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;; Names are mk-prefixed: SX has a host primitive `bind` that would shadow
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;; a user-level definition.
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(define mzero (list))
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(define unit (fn (s) (list s)))
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(define stream-pause? (fn (s) (and (not (list? s)) (callable? s))))
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;; mk-mplus — interleave two streams. If the first is mature/empty we use it
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;; directly; if it is paused, we suspend and swap so the other stream gets
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;; explored fairly (Reasoned Schemer "interleave").
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(define
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mk-mplus
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(fn
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(s1 s2)
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(cond
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((empty? s1) s2)
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((stream-pause? s1) (fn () (mk-mplus s2 (s1))))
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(:else (cons (first s1) (mk-mplus (rest s1) s2))))))
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;; mk-bind — apply goal g to every substitution in stream s, mk-mplus-ing results.
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(define
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mk-bind
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(fn
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(s g)
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(cond
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((empty? s) mzero)
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((stream-pause? s) (fn () (mk-bind (s) g)))
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(:else (mk-mplus (g (first s)) (mk-bind (rest s) g))))))
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;; stream-take — force up to n results out of a (possibly lazy) stream.
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;; n = -1 to take all (used by run*).
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(define
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stream-take
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(fn
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(n s)
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(cond
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((= n 0) (list))
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((empty? s) (list))
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((stream-pause? s) (stream-take n (s)))
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(:else
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(cons
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(first s)
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(stream-take
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(if (= n -1) -1 (- n 1))
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(rest s)))))))
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