IStream: change type of thunk, spare allocations.

Two changes:
- 'a Lazy.t  becomes unit -> 'a
- 'a t becomes 'a u (the view type)

This spares two Lazy.force, and leverages Lazy.lazy_from_fun. Considering Lazy.force is fairly slow, in particular because of the write-barrier, this should be beneficial.

2 files changed, 10 insertions, 10 deletions

diff --git a/lib/iStream.ml b/lib/iStream.ml
index 65a336dafd..1d9f55998e 100644
--- a/lib/iStream.ml
+++ b/lib/iStream.ml
@@ -6,11 +6,11 @@
 (*         *       GNU Lesser General Public License Version 2.1        *)
 (************************************************************************)
 
-type ('a,'r) peek =
+type ('a,'r) u =
 | Nil
 | Cons of 'a * 'r
 
-type 'a node = ('a,'a t) peek
+type 'a node = ('a,'a t) u
 
 and 'a t = 'a node Lazy.t
 
@@ -18,7 +18,7 @@ let empty = Lazy.lazy_from_val Nil
 
 let cons x s = Lazy.lazy_from_val (Cons (x, s))
 
-let thunk s = lazy (Lazy.force (Lazy.force s))
+let thunk = Lazy.lazy_from_fun
 
 let rec force s = match Lazy.force s with
 | Nil -> ()
diff --git a/lib/iStream.mli b/lib/iStream.mli
index fd3fa6c503..9e4dec415a 100644
--- a/lib/iStream.mli
+++ b/lib/iStream.mli
@@ -15,6 +15,11 @@
 type +'a t
 (** Type of pure streams. *)
 
+type ('a,'r) u =
+| Nil
+| Cons of 'a * 'r
+(** View type to decompose and build streams. *)
+
 (** {6 Constructors} *)
 
 val empty : 'a t
@@ -23,7 +28,7 @@ val empty : 'a t
 val cons : 'a -> 'a t -> 'a t
 (** Append an element in front of a stream. *)
 
-val thunk : 'a t Lazy.t -> 'a t
+val thunk : (unit -> ('a,'a t) u) -> 'a t
 (** Internalize the lazyness of a stream. *)
 
 (** {6 Destructors} *)
@@ -31,12 +36,7 @@ val thunk : 'a t Lazy.t -> 'a t
 val is_empty : 'a t -> bool
 (** Whethere a stream is empty. *)
 
-type ('a,'r) peek =
-| Nil
-| Cons of 'a * 'r
-(** View type for {!peek} *)
-
-val peek : 'a t -> ('a , 'a t) peek
+val peek : 'a t -> ('a , 'a t) u
 (** Return the head and the tail of a stream, if any. *)
 
 (** {6 Standard operations}