From e703a3f65530070c02e657b5ae313e6be5ff929a Mon Sep 17 00:00:00 2001
From: Simon Cruanes <simon.cruanes.2007@m4x.org>
Date: Thu, 7 Aug 2014 13:14:23 +0200
Subject: [PATCH] CCOrd.map

---
 core/CCOrd.ml  | 2 ++
 core/CCOrd.mli | 8 ++++++++
 2 files changed, 10 insertions(+)

diff --git a/core/CCOrd.ml b/core/CCOrd.ml
index 8474e12e..7e05bf3f 100644
--- a/core/CCOrd.ml
+++ b/core/CCOrd.ml
@@ -89,3 +89,5 @@ let array_ ord a1 a2 =
           then aux (i+1) else c
   in
   aux 0
+
+let map f ord a b = ord (f a) (f b)
diff --git a/core/CCOrd.mli b/core/CCOrd.mli
index 90e929d8..45d24259 100644
--- a/core/CCOrd.mli
+++ b/core/CCOrd.mli
@@ -64,3 +64,11 @@ val list_ : 'a t -> 'a list t
 (** Lexicographic combination on lists *)
 
 val array_ : 'a t -> 'a array t
+
+val map : ('a -> 'b) -> 'b t -> 'a t
+(** [map f ord] is the comparison function that, given objects [x] and [y],
+    projects [x] and [y] using [f] (e.g. using a record field) and then
+    compares those projections with [ord].
+    Example:
+    [map fst CCInt.compare] compares values of type [(int * 'a)]  by their
+      first component. *)