A-M baby

Task/Hamming-numbers/Racket/hamming-numbers.rkt

@@ -0,0 +1,23 @@
+#lang racket
+(require racket/stream)
+(define first stream-first)
+(define rest  stream-rest)
+
+(define (merge s1 s2)
+  (define x1 (first s1))
+  (define x2 (first s2))
+  (cond [(= x1 x2) (merge s1 (rest s2))]
+        [(< x1 x2) (stream-cons x1 (merge (rest s1) s2))]
+        [else      (stream-cons x2 (merge s1 (rest s2)))]))
+
+(define (mult k) (λ(x) (* x k)))
+
+(define hamming
+  (stream-cons
+   1 (merge (stream-map (mult 2) hamming)
+            (merge (stream-map (mult 3) hamming)
+                   (stream-map (mult 5) hamming)))))
+
+(for/list ([i 20] [x hamming]) x)
+(stream-ref hamming 1690)
+(stream-ref hamming 999999)