(define-syntax my-delay
  (syntax-rules ()
    ((my-delay x) (lambda () x))))

(define-syntax cons-stream
  (syntax-rules ()
    ((cons-stream head tail)(cons head (delay tail)))))

(define empty-stream `())
(define (car-stream s)
  (car s))
(define (cdr-stream s)
  (force (cdr s)))

(define (nats-after n)
  (cons-stream n (nats-after (+ 1 n))))

(define nats (nats-after 0))

(define (pow-after n)
  (cons-stream (expt 2 n) (pow-after (+ n 1))))

(define pow2 (pow-after 0))

(define (fibs-after first second)
  (cons-stream (+ first second) (fibs-after second (+ first second))))

(define fibs (fibs-after 0 1))

(define (stream-take s n)
  (if (equal? n 0) `()
      (cons (car-stream s) (stream-take (cdr-stream s) (- n 1)))))

(define (stream-from-list l)
  (if (null? l) `()
      (cons-stream (car l) (stream-from-list (cdr l)))))
(define l `(1 2 3 4 5 6))

(define (stream-map f s)
  (if (null? s) `()
      (cons-stream (f (car-stream s)) (stream-map f (cdr-stream s)))))

(define (stream-filter p? s)
  (if (null? s) `()
      (if (p? (car-stream s)) (cons-stream (car-stream s) (stream-filter p? (cdr-stream s)))
          (stream-filter p? (cdr-stream s)))))