Бесконечные списки

(use-syntax (ice-9 syncase))

(define-syntax lazy-cons
  (syntax-rules ()
    ((lazy-cons a b)
     (cons a (delay b)))))

(define (lazy-car p)
  (car p))

(define (lazy-cdr p)
  (force (cdr p)))

(define (lazy-head xs k)
  (define (iter i xs l)
    (if (= i k) l (iter (+ i 1) (lazy-cdr xs) (append l (list (lazy-car xs))))))
  (iter 0 xs '()))


(define (lazy-ref xs k)
  (define (iter i xs)
    (if (= i k) (lazy-car xs) (iter (+ i 1) (lazy-cdr xs))))
  (iter 0 xs))

(define (natural n)
  (lazy-cons n (natural (+ n 1))))

(define naturals
  (natural 0))

(define (lazy-map . args)
  (define (iter xs S)
    (if (null? xs) S (iter (cdr xs) (append S (list (lazy-cdr (car xs)))))))
  (let ((proc (car args))
        (xs (if (list? (cadr args))
                (cadr args)
                (cdr args))))
   (lazy-cons
    (eval (cons proc (map lazy-car xs)) (interaction-environment))
    (lazy-map proc  (iter xs '())))))

(define (lazy-filter pred? xs)
  (define (iter xs)
    (if (pred? (lazy-car xs)) xs (iter (lazy-cdr xs))))
  (let ((xs (iter xs)))
    (lazy-cons (lazy-car xs) (lazy-filter pred? (lazy-cdr xs)))))