Scheme streams

gistfile1.scm

(define (delay x)
  (lambda () x)
  )

(define (force x)
  (x)
)

(define (cons-stream x y)
  (cons x (delay y))
)

(define (head stream)
  (car stream)
)

(define (tail stream)
  (force (cdr stream))
)

(define empty-stream '())

(define empty-stream? null?)


(define (append-streams str1 str2)
  (if (empty-stream? s1)s2
    (cons-stream (head str1) (append-stream (tail str1)str2))
  )
)

(define (map-streams proc stream)
  (if(empty-stram? stream)the-empty-stream
     (cons-stream (proc (head stream)(map-stream proc (tail stream))))
   )
)

(define (filter-stream pred? stream)
  (cond ((empty-stream? stream) the-empty-stream)
        ((pred? (head stream))
        (cons-stream (head stream)(filter-stream pred? (tail stream))))
       (else (filter-stream pred? (tail stream))) 
  )
)

(define (add-streams str1 str2)
  (cons-stream (+ (head str1 )(head str2))
               (add-stream (tail str1)
                           (tail str2))
  )
)