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Three coupled fixes plus a new relations module land together because
each is required for the next: appendo can't terminate without all
three.
1. unify.sx — added (:cons h t) tagged cons-cell shape because SX has no
improper pairs. The unifier treats (:cons h t) and the native list
(h . t) as equivalent. mk-walk* re-flattens cons cells back to flat
lists for clean reification.
2. stream.sx — switched mature stream cells from plain SX lists to a
(:s head tail) tagged shape so a mature head can have a thunk tail.
With the old representation, mk-mplus had to (cons head thunk) which
SX rejects (cons requires a list cdr).
3. conde.sx — wraps each clause in Zzz (inverse-eta delay) for laziness.
Zzz uses (gensym "zzz-s-") for the substitution parameter so it does
not capture user goals that follow the (l s ls) convention. Without
gensym, every relation that uses `s` as a list parameter silently
binds it to the substitution dict.
relations.sx is the new module: nullo, pairo, caro, cdro, conso,
firsto, resto, listo, appendo, membero. 25 new tests.
Canary green:
(run* q (appendo (list 1 2) (list 3 4) q))
→ ((1 2 3 4))
(run* q (fresh (l s) (appendo l s (list 1 2 3)) (== q (list l s))))
→ ((() (1 2 3)) ((1) (2 3)) ((1 2) (3)) ((1 2 3) ()))
(run 3 q (listo q))
→ (() (_.0) (_.0 _.1))
152/152 cumulative.
83 lines
2.6 KiB
Plaintext
83 lines
2.6 KiB
Plaintext
;; lib/minikanren/unify.sx — Phase 1 + cons-cell extension.
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;;
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;; miniKanren-on-SX, built on lib/guest/match.sx. The kit ships the heavy
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;; lifting (walk-with, unify-with, occurs-with, extend, empty-subst,
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;; mk-var/is-var?/var-name); this file supplies a miniKanren-shaped cfg
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;; and a thin public API.
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;;
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;; Term shapes:
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;; logic var : (:var NAME) — kit's mk-var
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;; cons cell : (:cons HEAD TAIL) — for relational programming
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;; (built by mk-cons; lets relations decompose lists by
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;; head/tail without proper improper pairs in the host)
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;; native list : SX list (a b c) — also unifies pair-style:
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;; args = (head, tail) so (1 2 3) ≡ (:cons 1 (:cons 2 (:cons 3 ())))
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;; atom : number / string / symbol / boolean / nil / ()
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;;
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;; Substitution: SX dict mapping VAR-NAME → term. Empty = (empty-subst).
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(define mk-cons (fn (h t) (list :cons h t)))
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(define
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mk-cons-cell?
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(fn (t) (and (list? t) (not (empty? t)) (= (first t) :cons))))
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(define mk-cons-head (fn (t) (nth t 1)))
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(define mk-cons-tail (fn (t) (nth t 2)))
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(define
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mk-list-pair?
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(fn (t) (and (list? t) (not (empty? t)) (not (is-var? t)))))
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(define mk-list-pair-head (fn (t) :pair))
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(define
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mk-list-pair-args
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(fn
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(t)
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(cond
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((mk-cons-cell? t) (list (mk-cons-head t) (mk-cons-tail t)))
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(:else (list (first t) (rest t))))))
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(define mk-cfg {:ctor-head mk-list-pair-head :var? is-var? :ctor? mk-list-pair? :occurs-check? false :var-name var-name :ctor-args mk-list-pair-args})
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(define mk-cfg-occurs {:ctor-head mk-list-pair-head :var? is-var? :ctor? mk-list-pair? :occurs-check? true :var-name var-name :ctor-args mk-list-pair-args})
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(define empty-s (empty-subst))
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(define mk-fresh-counter 0)
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(define
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make-var
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(fn
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()
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(begin
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(set! mk-fresh-counter (+ mk-fresh-counter 1))
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(mk-var (str "_." mk-fresh-counter)))))
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(define mk-var? is-var?)
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(define mk-walk (fn (t s) (walk-with mk-cfg t s)))
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(define
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mk-walk*
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(fn
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(t s)
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(let
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((w (mk-walk t s)))
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(cond
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((mk-cons-cell? w)
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(let
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((h (mk-walk* (mk-cons-head w) s))
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(tl (mk-walk* (mk-cons-tail w) s)))
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(cond
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((empty? tl) (list h))
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((mk-cons-cell? tl) tl)
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((list? tl) (cons h tl))
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(:else (mk-cons h tl)))))
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((mk-list-pair? w) (map (fn (a) (mk-walk* a s)) w))
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(:else w)))))
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(define mk-unify (fn (u v s) (unify-with mk-cfg u v s)))
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(define mk-unify-check (fn (u v s) (unify-with mk-cfg-occurs u v s)))
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