From 6e67d8ab7ccef5e1513427fadce7487ffbe3991d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Julien=20Valverd=C3=A9?= <julien.valverde@mailo.com>
Date: Mon, 18 May 2026 14:12:48 +0200
Subject: [PATCH] Add provide

---
 packages/effect-lens/README.md        | 14 -------
 packages/effect-lens/src/Lens.test.ts |  5 +--
 packages/effect-lens/src/Lens.ts      | 54 ++++++++++++++++++++++++++-
 3 files changed, 55 insertions(+), 18 deletions(-)

diff --git a/packages/effect-lens/README.md b/packages/effect-lens/README.md
index d177c27..c976d80 100644
--- a/packages/effect-lens/README.md
+++ b/packages/effect-lens/README.md
@@ -95,20 +95,6 @@ const lens = Effect.all([
 
 Note: while Lens supports asynchronous effects for the proxy logic, we would recommend keeping them synchronous to preserve atomicity.
 
-If a `Lens` depends on a service in its environment, you can provide that service directly to the lens:
-```typescript
-class Offset extends Context.Tag("Offset")<Offset, { readonly value: number }>() {}
-
-const root = Lens.fromSubscriptionRef(ref)
-const offsetLens = Lens.mapEffect(
-    root,
-    n => Effect.map(Offset, ({ value }) => n + value),
-    (_n, next) => Effect.map(Offset, ({ value }) => next - value),
-)
-
-const runnableLens = Lens.provide(offsetLens, Offset, { value: 5 })
-```
-
 
 ### Focusing
 
diff --git a/packages/effect-lens/src/Lens.test.ts b/packages/effect-lens/src/Lens.test.ts
index e417b42..c0707c3 100644
--- a/packages/effect-lens/src/Lens.test.ts
+++ b/packages/effect-lens/src/Lens.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect, test } from "bun:test"
-import { Chunk, Context, Effect, Option, SubscriptionRef } from "effect"
+import { Chunk, Context, Effect, Layer, Option, SubscriptionRef } from "effect"
 import * as Lens from "./Lens.js"
 
 
@@ -67,8 +67,7 @@ describe("Lens", () => {
                             n => Effect.map(Offset, ({ value }) => n + value),
                             (_n, next) => Effect.map(Offset, ({ value }) => next - value),
                         ),
-                        Offset,
-                        { value: 5 },
+                        Layer.succeed(Offset, { value: 5 }),
                     )
 
                     return Effect.flatMap(
diff --git a/packages/effect-lens/src/Lens.ts b/packages/effect-lens/src/Lens.ts
index 9c6663b..7ad71fe 100644
--- a/packages/effect-lens/src/Lens.ts
+++ b/packages/effect-lens/src/Lens.ts
@@ -1,4 +1,4 @@
-import { Array, Chunk, type Context, Effect, Function, identity, Option, Pipeable, Predicate, Readable, Stream, type SubscriptionRef, type SynchronizedRef } from "effect"
+import { Array, Chunk, Effect, Function, identity, type Layer, Option, Pipeable, Predicate, Readable, Stream, type Context, type SubscriptionRef, type SynchronizedRef } from "effect"
 import type { NoSuchElementException } from "effect/Cause"
 import * as Subscribable from "./Subscribable.js"
 
@@ -273,6 +273,58 @@ export const mapStream: {
  * Provides a single service to a `Lens`, removing it from both the read and write environments.
  */
 export const provide: {
+    <const Layers extends readonly [Layer.Layer.Any, ...Array<Layer.Layer.Any>]>(
+        layers: Layers,
+    ): <A, ER, EW, RR, RW>(self: Lens<A, ER, EW, RR, RW>) => Lens<
+        A,
+        ER | { [k in keyof Layers]: Layer.Layer.Error<Layers[k]> }[number],
+        EW | { [k in keyof Layers]: Layer.Layer.Error<Layers[k]> }[number],
+        { [k in keyof Layers]: Layer.Layer.Context<Layers[k]> }[number] | Exclude<RR, { [k in keyof Layers]: Layer.Layer.Success<Layers[k]> }[number]>,
+        { [k in keyof Layers]: Layer.Layer.Context<Layers[k]> }[number] | Exclude<RW, { [k in keyof Layers]: Layer.Layer.Success<Layers[k]> }[number]>
+    >
+    <ROut, E2, RIn>(
+        layer: Layer.Layer<ROut, E2, RIn>,
+    ): <A, ER, EW, RR, RW>(self: Lens<A, ER, EW, RR, RW>) => Lens<A, ER | E2, EW | E2, RIn | Exclude<RR, ROut>, RIn | Exclude<RW, ROut>>
+    <R2>(
+        context: Context.Context<R2>,
+    ): <A, ER, EW, RR, RW>(self: Lens<A, ER, EW, RR, RW>) => Lens<A, ER, EW, Exclude<RR, R2>, Exclude<RW, R2>>
+    <A, ER, EW, RR, RW, const Layers extends readonly [Layer.Layer.Any, ...Array<Layer.Layer.Any>]>(
+        self: Lens<A, ER, EW, RR, RW>,
+        layers: Layers,
+    ): Lens<
+        A,
+        ER | { [k in keyof Layers]: Layer.Layer.Error<Layers[k]> }[number],
+        EW | { [k in keyof Layers]: Layer.Layer.Error<Layers[k]> }[number],
+        { [k in keyof Layers]: Layer.Layer.Context<Layers[k]> }[number] | Exclude<RR, { [k in keyof Layers]: Layer.Layer.Success<Layers[k]> }[number]>,
+        { [k in keyof Layers]: Layer.Layer.Context<Layers[k]> }[number] | Exclude<RW, { [k in keyof Layers]: Layer.Layer.Success<Layers[k]> }[number]>
+    >
+    <A, ER, EW, RR, RW, ROut, E2, RIn>(
+        self: Lens<A, ER, EW, RR, RW>,
+        layer: Layer.Layer<ROut, E2, RIn>,
+    ): Lens<A, ER | E2, EW | E2, RIn | Exclude<RR, ROut>, RIn | Exclude<RW, ROut>>
+    <A, ER, EW, RR, RW, R2>(
+        self: Lens<A, ER, EW, RR, RW>,
+        context: Context.Context<R2>,
+    ): Lens<A, ER, EW, Exclude<RR, R2>, Exclude<RW, R2>>
+} = Function.dual(2, <A, ER, EW, RR, RW>(
+    self: Lens<A, ER, EW, RR, RW>,
+    provider: unknown,
+): Lens<A, any, any, any, any> => make({
+    get get() { return Effect.provide(self.get, provider as any) },
+    get changes() {
+        return Stream.unwrapScoped(
+            Effect.map(
+                Effect.provide(Effect.context<RR>(), provider as any),
+                (context) => Stream.provideContext(self.changes as Stream.Stream<A, ER, RR>, context),
+            ),
+        )
+    },
+    modify: <B, E1 = never, R1 = never>(
+        f: (a: A) => Effect.Effect<readonly [B, A], E1, R1>
+    ) => Effect.provide(self.modify(f), provider as any),
+}))
+
+export const provideService: {
     <A, ER, EW, RR, RW, I, S>(
         self: Lens<A, ER, EW, RR, RW>,
         tag: Context.Tag<I, S>,