; #lang racket

; (require (except-in (planet neil/sicp)

; make-frame

; cons-stream

; the-empty-stream

; stream-null?))

; (provide (all-defined-out))

(define-syntax cons-stream

(syntax-rules ()

((_ A B) (cons A (delay B)))))

(define (stream-car stream) (car stream))

(define (stream-cdr stream) (force (cdr stream)))

(define the-empty-stream null)

(define (stream-null? s) (equal? s the-empty-stream))

(define (list->stream l)

(if (null? l)

the-empty-stream

(cons-stream (car l) (list->stream (cdr l)))))

(define (stream-ref s n)

(if (= n 0)

(stream-car s)

(stream-ref (stream-cdr s) (- n 1))))

(define (stream-for-each proc s)

(if (stream-null? s)

(display-line "")

(begin (proc (stream-car s))

(stream-for-each proc (stream-cdr s)))))

(define (display-stream s)

(stream-for-each display-line s))

(define (show-stream s n)

(cond ((or (zero? n)

(stream-null? s)) (display-line "done"))

(else

(show (stream-car s))

(show-stream (stream-cdr s) (- n 1) ))))

(define (display-line x)

(newline)

(display x))

(define (stream-enumerate-interval low high)

(if (> low high)

the-empty-stream

(cons-stream

low

(stream-enumerate-interval (+ low 1) high))))

(define (stream-filter pred stream)

(cond ((stream-null? stream) the-empty-stream)

((pred (stream-car stream))

(cons-stream (stream-car stream)

(stream-filter pred

(stream-cdr stream))))

(else (stream-filter pred (stream-cdr stream)))))

(define (stream-append s1 s2)

(if (stream-null? s1)

s2

(cons-stream (stream-car s1)

(stream-append (stream-cdr s1) s2))))

(define (stream-map proc s)

(if (stream-null? s)

the-empty-stream

(cons-stream (proc (stream-car s))

(stream-map proc (stream-cdr s)))))

(define (merge s1 s2)

(cond ((stream-null? s1) s2)

((stream-null? s2) s1)

(else

(let ((s1car (stream-car s1))

(s2car (stream-car s2)))

(cond ((< s1car s2car)

(cons-stream s1car (merge (stream-cdr s1) s2)))

((> s1car s2car)

(cons-stream s2car (merge s1 (stream-cdr s2))))

(else

(cons-stream s1car

(merge (stream-cdr s1)

(stream-cdr s2)))))))))

(define (show x)

(newline)

(display x))