Add union in Map interface

2 files changed, 10 insertions, 0 deletions

diff --git a/clib/cSig.mli b/clib/cSig.mli
index 859018ca4b..0012bcef17 100644
--- a/clib/cSig.mli
+++ b/clib/cSig.mli
@@ -68,6 +68,8 @@ sig
     val remove: key -> 'a t -> 'a t
     val merge:
          (key -> 'a option -> 'b option -> 'c option) -> 'a t -> 'b t -> 'c t
+    val union:
+      (key -> 'a -> 'a -> 'a option) -> 'a t -> 'a t -> 'a t
     val compare: ('a -> 'a -> int) -> 'a t -> 'a t -> int
     val equal: ('a -> 'a -> bool) -> 'a t -> 'a t -> bool
     val iter: (key -> 'a -> unit) -> 'a t -> unit
diff --git a/clib/hMap.ml b/clib/hMap.ml
index 09ffb39c21..db59ef47b0 100644
--- a/clib/hMap.ml
+++ b/clib/hMap.ml
@@ -290,6 +290,14 @@ struct
     in
     Int.Map.merge fm s1 s2
 
+  let union f s1 s2 =
+    let fm h m1 m2 =
+      let m = Map.union f m1 m2 in
+      if Map.is_empty m then None
+      else Some m
+    in
+    Int.Map.union fm s1 s2
+
   let compare f s1 s2 =
     let fc m1 m2 = Map.compare f m1 m2 in
     Int.Map.compare fc s1 s2