;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-intermediate-lambda-reader.ss" "lang")((modname streams) (read-case-sensitive #t) (teachpacks ((lib "docs.rkt" "teachpack" "htdp"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "docs.rkt" "teachpack" "htdp")) #f)))
(define (stream f x) (cons (f x) (list f)))

(stream (lambda(x)(* 2 x)) 5) ; stream w first element 10

(define (square x) (* x x))
;(square 2) ; returns 4
(stream square 2) ; returns stream w first element 4

(define ss (stream square 2)) 
(define (head str) (car str))
(head ss) ; unbounded list of squares of values starting with 4 = 2 squared


(head (stream (lambda(x)(* 2 x)) 5))

(define (tail str) (cons (apply (car (cdr str)) (list (car str))) (cdr str)))
(tail ss)
(head (tail ss))
(head (tail (tail ss)))
(tail (tail ss))