From 03d5cf5686e9ea5448ee5e4901792130d9527a74 Mon Sep 17 00:00:00 2001
From: Arnaud Spiwack
Date: Mon, 24 Feb 2014 16:23:04 +0100
Subject: A view type for IStream.

View types are better practice than option types for pattern-matching. (Plus, they save a minute amount of allocations)---
 lib/iStream.ml  | 10 +++++-----
 lib/iStream.mli |  7 ++++++-
 2 files changed, 11 insertions(+), 6 deletions(-)

(limited to 'lib')

diff --git a/lib/iStream.ml b/lib/iStream.ml
index f7d50612f9..ba08ffd24e 100644
--- a/lib/iStream.ml
+++ b/lib/iStream.ml
@@ -6,9 +6,11 @@
 (*         *       GNU Lesser General Public License Version 2.1        *)
 (************************************************************************)
 
-type 'a node =
+type ('a,'r) peek =
 | Nil
-| Cons of 'a * 'a t
+| Cons of 'a * 'r
+
+type 'a node = ('a,'a t) peek
 
 and 'a t = 'a node Lazy.t
 
@@ -32,9 +34,7 @@ let rec is_empty s = match Lazy.force s with
 | Nil -> true
 | Cons (_, _) -> false
 
-let peek s = match Lazy.force s with
-| Nil -> None
-| Cons (x, s) -> Some (x, s)
+let peek = Lazy.force
 
 let rec of_list = function
 | [] -> empty
diff --git a/lib/iStream.mli b/lib/iStream.mli
index caae0ad35a..fd3fa6c503 100644
--- a/lib/iStream.mli
+++ b/lib/iStream.mli
@@ -31,7 +31,12 @@ val thunk : 'a t Lazy.t -> 'a t
 val is_empty : 'a t -> bool
 (** Whethere a stream is empty. *)
 
-val peek : 'a t -> ('a * 'a t) option
+type ('a,'r) peek =
+| Nil
+| Cons of 'a * 'r
+(** View type for {!peek} *)
+
+val peek : 'a t -> ('a , 'a t) peek
 (** Return the head and the tail of a stream, if any. *)
 
 (** {6 Standard operations}
-- 
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