Represent natural number as a stream using lazy evaluation property

nat.rkt

#lang racket

;; natural number representation as a stream using lazy evaluation property
(define natural-number
  (letrec
      ([nat-stream
        (lambda (i)
          (cons (thunk i) (thunk (nat-stream (+ i 1)))))])
    (nat-stream 0)))

;; return the first n elements of the stream as a list
(define (first-n n stream)
  (if (equal? n 0)
      null
      (cons ((car stream))
            (first-n (- n 1) ((cdr stream))))))

;; return the first 10 natural number
(first-n 10 natural-number)