lab 07

labs/07/primes.ml

@@ -0,0 +1,21 @@
+type 'a infstream = Cons of 'a * (unit -> 'a infstream)
+
+let rec take n (Cons (h, t)) =
+  if n <= 0 then []
+  else h :: take (n - 1) (t ())
+
+let rec from n = Cons (n, fun () -> from (n + 1))
+
+let rec filter f (Cons (h, t)) =
+  if f h then Cons (h, fun () -> filter f (t ()))
+  else filter f (t ())
+
+let primes =
+  let rec sieve (Cons (h, t)) =
+    Cons (h, fun () ->
+      sieve (filter (fun x -> x mod h <> 0) (t ()))
+    )
+  in
+  sieve @@ from 2;;
+
+take 100 primes;;