Merge pull request herd#1731 from herd/upgrade-mymap

[lib] Modernise a few functions of the `MyMap`module

Use `Map` stdlib `update` and `union` functions.

Author: maranget

lib/myMap.ml

@@ -76,7 +76,6 @@ module Make(O:Set.OrderedType) : S with type key = O.t =
 
     let pp_str pp_bind m = pp_str_delim ";" pp_bind m
 
-
     let pp chan pp_bind m =
       iter
         (fun k v -> pp_bind chan k v ; fprintf chan ";")
@@ -86,14 +85,7 @@ module Make(O:Set.OrderedType) : S with type key = O.t =
 
     let union_std = union
 
-    let union u m1 m2 =
-      fold
-        (fun k v1 m ->
-          try
-            let v2 = find k m2 in
-            add k (u v1 v2) m
-          with Not_found -> add k v1 m)
-        m1 m2
+    let union u m1 m2 = union_std (fun _ v1 v2 -> Some (u v1 v2)) m1 m2
 
     let unions u ms = match ms with
     | [] -> empty
@@ -111,7 +103,10 @@ module Make(O:Set.OrderedType) : S with type key = O.t =
       fun t acc -> fold fold_binding t acc
 
     let accumulate k v m =
-      let vs = safe_find [] k m in
-      add k (v::vs) m
+      update k
+        (function
+         | None -> Some [v]
+         | Some vs -> Some (v::vs))
+        m
 
   end