From 2aa4e4eb97b44966e4afa91a3e9006adf3bd08bf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Julien=20Valverd=C3=A9?= <julien.valverde@mailo.com>
Date: Thu, 28 May 2026 02:14:52 +0200
Subject: [PATCH] Fix

---
 packages/effect-lens/src/Lens.ts | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/packages/effect-lens/src/Lens.ts b/packages/effect-lens/src/Lens.ts
index 2f8ac7f..9355e9b 100644
--- a/packages/effect-lens/src/Lens.ts
+++ b/packages/effect-lens/src/Lens.ts
@@ -294,11 +294,16 @@ export const map: {
     self: Lens<A, ER, EW, RR, RW>,
     get: (a: NoInfer<A>) => B,
     update: (a: NoInfer<A>, b: B) => NoInfer<A>,
-): Lens<B, ER, EW, RR, RW> => mapEffect(
-    self,
-    a => Effect.succeed(get(a)),
-    (a, b) => Effect.succeed(update(a, b)),
-))
+): Lens<B, ER, EW, RR, RW> => derive(self, {
+    resolve: parent => Effect.map(
+        parent,
+        frame => ({
+            value: get(frame.value),
+            commit: next => frame.commit(Effect.map(next, b => update(frame.value, b))),
+        }),
+    ),
+    transformStream: Stream.map(get),
+}))
 
 /**
  * Derives a new `Lens` by applying effectful getters and setters over the focused value.
@@ -307,16 +312,16 @@ export const mapEffect: {
     <A, ER, EW, RR, RW, B, EGet = never, RGet = never, ESet = never, RSet = never>(
         self: Lens<A, ER, EW, RR, RW>,
         get: (a: NoInfer<A>) => Effect.Effect<B, EGet, RGet>,
-        set: (a: NoInfer<A>, b: B) => Effect.Effect<NoInfer<A>, ESet, RSet>,
+        update: (a: NoInfer<A>, b: B) => Effect.Effect<NoInfer<A>, ESet, RSet>,
     ): Lens<B, ER | EGet, EW | ESet, RR | RGet, RW | RSet>
     <A, ER, EW, RR, RW, B, EGet = never, RGet = never, ESet = never, RSet = never>(
         get: (a: NoInfer<A>) => Effect.Effect<B, EGet, RGet>,
-        set: (a: NoInfer<A>, b: B) => Effect.Effect<NoInfer<A>, ESet, RSet>,
+        update: (a: NoInfer<A>, b: B) => Effect.Effect<NoInfer<A>, ESet, RSet>,
     ): (self: Lens<A, ER, EW, RR, RW>) => Lens<B, ER | EGet, EW | ESet, RR | RGet, RW | RSet>
 } = Function.dual(3, <A, ER, EW, RR, RW, B, EGet = never, RGet = never, ESet = never, RSet = never>(
     self: Lens<A, ER, EW, RR, RW>,
     get: (a: NoInfer<A>) => Effect.Effect<B, EGet, RGet>,
-    set: (a: NoInfer<A>, b: B) => Effect.Effect<NoInfer<A>, ESet, RSet>,
+    update: (a: NoInfer<A>, b: B) => Effect.Effect<NoInfer<A>, ESet, RSet>,
 ): Lens<B, ER | EGet, EW | ESet, RR | RGet, RW | RSet> => derive(self, {
     resolve: parent => Effect.flatMap(
         parent,
@@ -324,7 +329,7 @@ export const mapEffect: {
             get(frame.value),
             value => ({
                 value,
-                commit: next => frame.commit(Effect.flatMap(next, b => set(frame.value, b))),
+                commit: next => frame.commit(Effect.flatMap(next, b => update(frame.value, b))),
             }),
         ),
     ),