Adding a comparison combinator for pairs.

2 files changed, 10 insertions, 0 deletions

diff --git a/lib/util.ml b/lib/util.ml
index 38d73d3453..0389336258 100644
--- a/lib/util.ml
+++ b/lib/util.ml
@@ -20,6 +20,12 @@ let on_pi1 f (a,b,c) = (f a,b,c)
 let on_pi2 f (a,b,c) = (a,f b,c)
 let on_pi3 f (a,b,c) = (a,b,f c)
 
+(* Comparing pairs *)
+
+let pair_compare cmpx cmpy (x1,y1 as p1) (x2,y2 as p2) =
+  if p1 == p2 then 0 else
+  let c = cmpx x1 x2 in if c == 0 then cmpy y1 y2 else c
+
 (* Projections from triplets *)
 
 let pi1 (a,_,_) = a
diff --git a/lib/util.mli b/lib/util.mli
index 1eb60f509a..fa3b622621 100644
--- a/lib/util.mli
+++ b/lib/util.mli
@@ -17,6 +17,10 @@ val on_fst : ('a -> 'b) -> 'a * 'c -> 'b * 'c
 val on_snd : ('a -> 'b) -> 'c * 'a -> 'c * 'b
 val map_pair : ('a -> 'b) -> 'a * 'a -> 'b * 'b
 
+(** Comparing pairs *)
+
+val pair_compare : ('a -> 'a -> int) -> ('b -> 'b -> int) -> ('a * 'b -> 'a * 'b -> int)
+
 (** Mapping under triple *)
 
 val on_pi1 : ('a -> 'b) -> 'a * 'c * 'd -> 'b * 'c * 'd