add lecture 08

lectures/08/infstream.ml

@@ -0,0 +1,9 @@
+type 'a infstream = Cons of 'a * (unit -> 'a infstream)
+
+let hd (Cons (h, _)) = h
+let tl (Cons (_, t)) = t ()
+
+let rec from n = Cons (n, fun () -> from (n + 1))
+let rec take n (Cons (h, t)) =
+  if n <= 0 then []
+  else h :: take (n - 1) (t ())