From c3e0f81f7ebab9d3843dafd40f23de938494c73a Mon Sep 17 00:00:00 2001
From: Simon Cruanes <simon.cruanes.2007@m4x.org>
Date: Mon, 25 Apr 2016 20:39:08 +0200
Subject: [PATCH] add `CCLazy_list.take`

---
 src/iter/CCLazy_list.ml  | 9 +++++++++
 src/iter/CCLazy_list.mli | 6 +++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/iter/CCLazy_list.ml b/src/iter/CCLazy_list.ml
index a1d94cf0..a258f372 100644
--- a/src/iter/CCLazy_list.ml
+++ b/src/iter/CCLazy_list.ml
@@ -50,8 +50,17 @@ let filter ~f l =
 
 (*$=
   [2;4;6] (of_list [1;2;3;4;5;6;7] |> filter ~f:(fun x -> x mod 2=0) |> to_list)
+  [2;4;6] (of_gen Gen.(1 -- max_int) |> filter ~f:(fun x -> x mod 2=0) |> take 3 |> to_list)
 *)
 
+let rec take n l =
+  lazy (
+    match l with
+      | _ when n=0 -> Nil
+      | lazy Nil -> Nil
+      | lazy (Cons (x,tl)) -> Cons (x, take (n-1) tl)
+  )
+
 let rec append a b =
   lazy (
     match a with
diff --git a/src/iter/CCLazy_list.mli b/src/iter/CCLazy_list.mli
index 77c7870d..613be3fe 100644
--- a/src/iter/CCLazy_list.mli
+++ b/src/iter/CCLazy_list.mli
@@ -32,7 +32,11 @@ val map : f:('a -> 'b) -> 'a t -> 'b t
 (** Lazy map *)
 
 val filter : f:('a -> bool) -> 'a t -> 'a t
-(** Filter values
+(** Filter values.
+    @since NEXT_RELEASE *)
+
+val take : int -> 'a t -> 'a t
+(** Take at most n values.
     @since NEXT_RELEASE *)
 
 val append : 'a t -> 'a t -> 'a t