From 151785335d5f5a318a0f1b0816fa67918ce93ba4 Mon Sep 17 00:00:00 2001
From: Olivier Nicole <olivier@chnik.fr>
Date: Mon, 20 Nov 2023 14:14:47 +0100
Subject: [PATCH] Add Lwd.map_and_set

---
 lib/lwd/lwd.ml  | 2 ++
 lib/lwd/lwd.mli | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/lib/lwd/lwd.ml b/lib/lwd/lwd.ml
index 57925d1..22e503c 100644
--- a/lib/lwd/lwd.ml
+++ b/lib/lwd/lwd.ml
@@ -308,6 +308,8 @@ let peek = function
   | Operator ({desc = Var v; _}) -> v.binding
   | _ -> assert false
 
+let map_and_set f v = set v (f (peek v))
+
 (* Primitives *)
 type 'a prim = 'a t
 let prim ~acquire ~release =
diff --git a/lib/lwd/lwd.mli b/lib/lwd/lwd.mli
index 386dde3..77ff1d3 100644
--- a/lib/lwd/lwd.mli
+++ b/lib/lwd/lwd.mli
@@ -67,6 +67,9 @@ val peek : 'a var -> 'a
 (** Observe the current value of the variable, without any dependency
     tracking. *)
 
+val map_and_set : ('a -> 'a) -> 'a var -> unit
+(** Modify a variable based on its currently observed value. *)
+
 type +'a prim
 (** A primitive document. It can correspond, for example, to
     a primitive UI element.