From 9f3eb956d3f24c490680fe89d570bf6eda19a7a9 Mon Sep 17 00:00:00 2001
From: Rudi Grinberg <rudi.grinberg@gmail.com>
Date: Thu, 22 Mar 2018 22:42:42 +0800
Subject: [PATCH] Add Env.update

---
 src/env.ml  | 3 +++
 src/env.mli | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/src/env.ml b/src/env.ml
index 69a9ab75..4546584f 100644
--- a/src/env.ml
+++ b/src/env.ml
@@ -77,3 +77,6 @@ let diff x y =
     | Some _ -> None
     | None -> vx)
   |> make
+
+let update t ~var ~f =
+  make (Map.update t.vars var ~f)
diff --git a/src/env.mli b/src/env.mli
index 37cd5fe1..904a8d15 100644
--- a/src/env.mli
+++ b/src/env.mli
@@ -23,4 +23,7 @@ val add : t -> var:Var.t -> value:string -> t
 
 val diff : t -> t -> t
 
+val update : t -> var:string -> f:(string option -> string option) -> t
+
 val sexp_of_t : t -> Sexp.t
+