Merge pull request #159 from orbifx/master

Add `CCImmutArray.sub`, which creates a copy

src/data/CCImmutArray.ml

@@ -27,6 +27,8 @@ let set a n x =
   a'.(n) <- x;
   a'
 
+let sub = Array.sub (* Would this not be better implemented with CCArray_slice *)
+
 let map = Array.map
 
 let mapi = Array.mapi

src/data/CCImmutArray.mli

@@ -36,6 +36,15 @@ val get : 'a t -> int -> 'a
 val set : 'a t -> int -> 'a -> 'a t
 (** Copy the array and modify its copy *)
 
+val sub : 'a t -> int -> int -> 'a t
+(** [sub a start len] returns a fresh array of length len, containing the elements
+    from [start] to pstart + len - 1] of array a.
+
+    Raises [Invalid_argument "Array.sub"] if [start] and [len] do not designate a
+    valid subarray of a; that is, if start < 0, or len < 0, or start + len > Array.length a.
+
+    @since NEXT_RELEASE *)
+
 val map : ('a -> 'b) -> 'a t -> 'b t
 
 val mapi : (int -> 'a -> 'b) -> 'a t -> 'b t