diff options
Diffstat (limited to 'coding-exercises/3/3.5.2/53.rkt')
| -rw-r--r-- | coding-exercises/3/3.5.2/53.rkt | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/coding-exercises/3/3.5.2/53.rkt b/coding-exercises/3/3.5.2/53.rkt new file mode 100644 index 0000000..776e619 --- /dev/null +++ b/coding-exercises/3/3.5.2/53.rkt @@ -0,0 +1,43 @@ +#lang racket +(require "../../../shared/sicp-stream.rkt") +(newline) (print "54") (newline) +(define (add-streams s1 s2) (stream-map + s1 s2)) +(define (scale-stream s factor) (stream-map (lambda (x) (* factor x)) s)) +(define (mul-streams s1 s2) (stream-map * s1 s2)) +(define ones (stream-cons 1 ones)) +(define integers (stream-cons 1 (add-streams ones integers))) +(define factorials (stream-cons 1 (mul-streams integers factorials))) +(stream-ref factorials 5) + +(newline) (print "55") (newline) +(define (partial-sums s) + (define me (stream-cons 0 (add-streams s me))) + me) +(stream-ref (partial-sums integers) 4) + +(newline) (print "56") (newline) +(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) + (stream-cons s1car (merge (stream-cdr s1) s2))) + ((> s1car s2car) + (stream-cons s2car (merge s1 (stream-cdr s2)))) + (else + (stream-cons s1car + (merge (stream-cdr s1) + (stream-cdr s2))))))))) +(define S (stream-cons 1 (merge (scale-stream S 2) (merge (scale-stream S 3) (scale-stream S 5))))) + +(newline) (print "57") (newline) +(define additions 0) +(define (add-streams-counted s1 s2) (stream-map (lambda (x y) (set! additions (+ additions 1)) (+ x y)) s1 s2)) +(define fibs (stream-cons 0 + (stream-cons 1 + (add-streams-counted (stream-cdr fibs) + fibs)))) +(stream-ref fibs 20) +(println additions) (newline) (println "Streams in racket are forced when car is called.") |