interleaved streams and expand/run utilities.

scm/mukanren.scm

@@ -78,4 +78,31 @@
((call/fresh fives) empty-state)
;; 4.3 interleaved streams
;; 4.3 interleaved streams
(define (mplus $1 $2)
  (cond
    ((null? $1) $2)
    ((procedure? $1) (lambda () (mplus $2 ($1))))
    (else (cons (car $1) (mplus (cdr $1) $2)))))
(define (sixes x)
  (disj (≡ x 6) (lambda (s/c) (lambda () ((sixes x) s/c)))))
(define fives-and-sixes
  (call/fresh (lambda (x) (disj (fives x) (sixes x)))))
;; 5 utilities
(define (expand n s)
  (if (> n 1)
    (cond
      ((null? s) s)
      ((procedure? (cdr s)) `(,(car s) . ,(expand (- n 1) ((cdr s)))))
      (else `(,(car s) . ,(expand (- n 1) (cdr s)))))
    s))
(expand 5 (fives-and-sixes empty-state))
(define (run n g)
  (expand n (g empty-state)))