From 55ff51f2cbde21bf7b1fce9c6284291b77fe81bf Mon Sep 17 00:00:00 2001
From: Simon Cruanes <simon.cruanes.2007@m4x.org>
Date: Fri, 15 Feb 2013 17:35:00 +0100
Subject: [PATCH] more combinators (iterate and forever); some sequences of
 random elements

---
 sequence.ml  | 30 ++++++++++++++++++++++++++++++
 sequence.mli | 19 +++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/sequence.ml b/sequence.ml
index 869fe24..632fab9 100644
--- a/sequence.ml
+++ b/sequence.ml
@@ -36,6 +36,16 @@ let singleton x = fun k -> k x
 (** Infinite sequence of the same element *)
 let repeat x = fun k -> while true do k x done
 
+(** [iterate f x] is the infinite sequence (x, f(x), f(f(x)), ...) *)
+let iterate f x =
+  let rec iterate k x = k x; iterate k (f x) in
+  from_iter (fun k -> iterate k x)
+
+(** Sequence that calls the given function to produce elements *)
+let forever f =
+  let rec forever k = k (f ()); forever k in
+  from_iter forever
+
 (** Cycle forever through the given sequence. O(n). *)
 let cycle s = fun k -> while true do s k; done
 
@@ -320,6 +330,26 @@ module Map = struct
   end
 end
 
+(** {2 Infinite sequences of random values} *)
+
+let random_int bound = forever (fun () -> Random.int bound)
+
+let random_bool = forever Random.bool
+
+let random_float bound = forever (fun () -> Random.float bound)
+
+(** Sequence of choices of an element in the array *)
+let random_array a =
+  assert (Array.length a > 0);
+  let seq k =
+    while true do
+      let i = Random.int (Array.length a) in
+      k a.(i);
+    done in
+  from_iter seq
+
+let random_list l = random_array (Array.of_list l)
+
 (** {2 Pretty printing of sequences} *)
 
 (** Pretty print a sequence of ['a], using the given pretty printer
diff --git a/sequence.mli b/sequence.mli
index bc7267f..ed1a640 100644
--- a/sequence.mli
+++ b/sequence.mli
@@ -42,6 +42,12 @@ val singleton : 'a -> 'a t
 val repeat : 'a -> 'a t
   (** Infinite sequence of the same element *)
 
+val iterate : ('a -> 'a) -> 'a -> 'a t
+  (** [iterate f x] is the infinite sequence (x, f(x), f(f(x)), ...) *)
+
+val forever : (unit -> 'b) -> 'b t
+  (** Sequence that calls the given function to produce elements *)
+
 val cycle : 'a t -> 'a t
   (** Cycle forever through the given sequence. Assume the
       given sequence can be traversed any amount of times (not transient). *)
@@ -204,6 +210,19 @@ module Map : sig
   module Make(V : Map.OrderedType) : S with type key = V.t
 end
 
+(** {2 Infinite sequences of random values} *)
+
+val random_int : int -> int t
+
+val random_bool : bool t
+
+val random_float : float -> float t
+
+val random_array : 'a array -> 'a t
+  (** Sequence of choices of an element in the array *)
+
+val random_list : 'a list -> 'a t
+
 (** {2 Pretty printing of sequences} *)
 
 val pp_seq : ?sep:string -> (Format.formatter -> 'a -> unit) ->