Add mem function to SortedList.Map

types/sortedList.ml

@@ -243,6 +243,12 @@ module Make(X : Custom.T) = struct
 
     let add x v = union_disj [(x,v)]
 
+    let rec mem x l =
+      match l with
+        | [] -> false
+        | (t,_)::q -> 
+            let c = X.compare x t in
+            (c = 0) || ((c > 0) && (mem x q))
 
     let rec diff l1 l2 =
       match (l1,l2) with

types/sortedList.mli

@@ -33,6 +33,7 @@ sig
     type 'a map
     external get: 'a map -> (X.t * 'a) list = "%identity"
     val add: X.t -> 'a -> 'a map -> 'a map
+    val mem: X.t -> 'a map -> bool
     val length: 'a map -> int
     val domain: 'a map -> t
     val restrict: 'a map -> t -> 'a map