From 2646e295d9eb4811a41bff61168d7c9ef854e84c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Julien=20Valverd=C3=A9?= <julien.valverde@mailo.com>
Date: Tue, 24 Mar 2026 11:48:01 +0100
Subject: [PATCH] Add mapStream

---
 packages/effect-fc/src/Lens.ts | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/packages/effect-fc/src/Lens.ts b/packages/effect-fc/src/Lens.ts
index bce74e0..3c8e23f 100644
--- a/packages/effect-fc/src/Lens.ts
+++ b/packages/effect-fc/src/Lens.ts
@@ -139,6 +139,24 @@ export const mapEffect: {
     )),
 }))
 
+export const mapStream: {
+    <A, ER, EW, RR, RW>(
+        self: Lens<A, ER, EW, RR, RW>,
+        f: (changes: Stream.Stream<NoInfer<A>, NoInfer<ER>, NoInfer<RR>>) => Stream.Stream<NoInfer<A>, NoInfer<ER>, NoInfer<RR>>,
+    ): Lens<A, ER, EW, RR, RW>
+    <A, ER, EW, RR, RW>(
+        f: (changes: Stream.Stream<NoInfer<A>, NoInfer<ER>, NoInfer<RR>>) => Stream.Stream<NoInfer<A>, NoInfer<ER>, NoInfer<RR>>,
+    ): (self: Lens<A, ER, EW, RR, RW>) => Lens<A, ER, EW, RR, RW>
+} = Function.dual(2, <A, ER, EW, RR, RW>(
+    self: Lens<A, ER, EW, RR, RW>,
+    f: (changes: Stream.Stream<NoInfer<A>, NoInfer<ER>, NoInfer<RR>>) => Stream.Stream<NoInfer<A>, NoInfer<ER>, NoInfer<RR>>,
+): Lens<A, ER, EW, RR, RW> => make({
+    get get() { return self.get },
+    get changes() { return f(self.changes) },
+    modify: self.modify,
+}))
+
+
 export const mapField: {
     <A extends object, K extends keyof A, ER, EW, RR, RW>(
         self: Lens<A, ER, EW, RR, RW>,