Sieve of Eratosthenes

1 files changed, 37 insertions, 0 deletions

diff --git a/sieve/eratosthenes.scm b/sieve/eratosthenes.scm
new file mode 100644
index 0000000..d9da30d
--- /dev/null
+++ b/sieve/eratosthenes.scm
@@ -0,0 +1,37 @@
+
+
+
+(add-to-load-path (dirname (current-filename)))
+
+(import
+    (srfi srfi-41)
+    (extra-functional)
+    (my-streams))
+
+
+
+(define base (stream-from 2))
+
+
+
+(define (mark n item)
+    (if (eq? (remainder (car item) n) 0)
+        (cons (car item) #f)
+        item))
+
+
+
+(define-stream (sieve input)
+    (stream-let loop ((strm (stream-map (part (flip cons) #t) input)))
+        (stream-match strm ((item . rest)
+            (if (cdr item)
+                (stream-cons
+                    (car item)
+                    (loop (stream-map (part mark (car item)) rest)))
+                (loop rest))))))
+
+
+
+(define eratosthenes (sieve base))
+
+