package.json

@@ -1,6 +1,6 @@
 {
   "name": "@effect-fc/monorepo",
-  "packageManager": "bun@1.3.6",
+  "packageManager": "bun@1.3.11",
   "private": true,
   "workspaces": [
     "./packages/*"
@@ -15,12 +15,12 @@
     "clean:modules": "turbo clean:modules && rm -rf node_modules"
   },
   "devDependencies": {
-    "@biomejs/biome": "^2.3.11",
-    "@effect/language-service": "^0.75.0",
-    "@types/bun": "^1.3.6",
-    "npm-check-updates": "^19.3.1",
+    "@biomejs/biome": "^2.4.8",
+    "@effect/language-service": "^0.84.0",
+    "@types/bun": "^1.3.11",
+    "npm-check-updates": "^19.6.5",
     "npm-sort": "^0.0.4",
-    "turbo": "^2.7.5",
-    "typescript": "^5.9.3"
+    "turbo": "^2.8.20",
+    "typescript": "^6.0.2"
   }
 }

packages/docs/package.json

@@ -27,7 +27,7 @@
     "@docusaurus/module-type-aliases": "3.9.2",
     "@docusaurus/tsconfig": "3.9.2",
     "@docusaurus/types": "3.9.2",
-    "typescript": "~5.6.2"
+    "typescript": "~5.9.0"
   },
   "browserslist": {
     "production": [

packages/effect-fc/package.json

@@ -38,11 +38,14 @@
     "clean:modules": "rm -rf node_modules"
   },
   "devDependencies": {
-    "@effect/platform-browser": "^0.74.0"
+    "@effect/platform-browser": "^0.76.0"
   },
   "peerDependencies": {
     "@types/react": "^19.2.0",
-    "effect": "^3.19.0",
+    "effect": "^3.21.0",
     "react": "^19.2.0"
+  },
+  "dependencies": {
+    "effect-lens": "^0.1.1"
   }
 }

packages/effect-fc/src/Form.ts

@@ -1,12 +1,12 @@
 import { Array, Cause, Chunk, type Context, type Duration, Effect, Equal, Exit, Fiber, flow, Hash, HashMap, identity, Option, ParseResult, Pipeable, Predicate, Ref, Schema, type Scope, Stream } from "effect"
 import type * as React from "react"
 import * as Component from "./Component.js"
+import * as Lens from "./Lens.js"
 import * as Mutation from "./Mutation.js"
 import * as PropertyPath from "./PropertyPath.js"
 import * as Result from "./Result.js"
 import * as Subscribable from "./Subscribable.js"
 import * as SubscriptionRef from "./SubscriptionRef.js"
-import * as SubscriptionSubRef from "./SubscriptionSubRef.js"
 
 
 export const FormTypeId: unique symbol = Symbol.for("@effect-fc/Form/Form")
@@ -26,7 +26,7 @@ extends Pipeable.Pipeable {
     readonly debounce: Option.Option<Duration.DurationInput>
 
     readonly value: Subscribable.Subscribable<Option.Option<A>>
-    readonly encodedValue: SubscriptionRef.SubscriptionRef<I>
+    readonly encodedValue: Lens.Lens<I>
     readonly error: Subscribable.Subscribable<Option.Option<ParseResult.ParseError>>
     readonly validationFiber: Subscribable.Subscribable<Option.Option<Fiber.Fiber<A, ParseResult.ParseError>>>
 
@@ -54,10 +54,10 @@ extends Pipeable.Class() implements Form<A, I, R, MA, ME, MR, MP> {
         readonly autosubmit: boolean,
         readonly debounce: Option.Option<Duration.DurationInput>,
 
-        readonly value: SubscriptionRef.SubscriptionRef<Option.Option<A>>,
-        readonly encodedValue: SubscriptionRef.SubscriptionRef<I>,
-        readonly error: SubscriptionRef.SubscriptionRef<Option.Option<ParseResult.ParseError>>,
-        readonly validationFiber: SubscriptionRef.SubscriptionRef<Option.Option<Fiber.Fiber<A, ParseResult.ParseError>>>,
+        readonly value: Lens.Lens<Option.Option<A>>,
+        readonly encodedValue: Lens.Lens<I>,
+        readonly error: Lens.Lens<Option.Option<ParseResult.ParseError>>,
+        readonly validationFiber: Lens.Lens<Option.Option<Fiber.Fiber<A, ParseResult.ParseError>>>,
 
         readonly runSemaphore: Effect.Semaphore,
         readonly fieldCache: Ref.Ref<HashMap.HashMap<FormFieldKey, FormField<unknown, unknown>>>,
@@ -99,7 +99,7 @@ extends Pipeable.Class() implements Form<A, I, R, MA, ME, MR, MP> {
                 Option.isSome(this.debounce) ? Stream.debounce(this.debounce.value) : identity
             ),
 
-            encodedValue => this.validationFiber.pipe(
+            encodedValue => Lens.get(this.validationFiber).pipe(
                 Effect.andThen(Option.match({
                     onSome: Fiber.interrupt,
                     onNone: () => Effect.void,
@@ -110,18 +110,18 @@ extends Pipeable.Class() implements Form<A, I, R, MA, ME, MR, MP> {
                         exit => Effect.andThen(
                             Exit.matchEffect(exit, {
                                 onSuccess: v => Effect.andThen(
-                                    Ref.set(this.value, Option.some(v)),
-                                    Ref.set(this.error, Option.none()),
+                                    Lens.set(this.value, Option.some(v)),
+                                    Lens.set(this.error, Option.none()),
                                 ),
                                 onFailure: c => Option.match(Chunk.findFirst(Cause.failures(c), e => e._tag === "ParseError"), {
-                                    onSome: e => Ref.set(this.error, Option.some(e)),
+                                    onSome: e => Lens.set(this.error, Option.some(e)),
                                     onNone: () => Effect.void,
                                 }),
                             }),
-                            Ref.set(this.validationFiber, Option.none()),
+                            Lens.set(this.validationFiber, Option.none()),
                         ),
                     )).pipe(
-                        Effect.tap(fiber => Ref.set(this.validationFiber, Option.some(fiber))),
+                        Effect.tap(fiber => Lens.set(this.validationFiber, Option.some(fiber))),
                         Effect.andThen(Fiber.join),
                         Effect.andThen(value => this.autosubmit
                             ? Effect.asVoid(Effect.forkScoped(this.submitValue(value)))
@@ -136,7 +136,7 @@ extends Pipeable.Class() implements Form<A, I, R, MA, ME, MR, MP> {
     }
 
     get submit(): Effect.Effect<Option.Option<Result.Final<MA, ME, MP>>, Cause.NoSuchElementException> {
-        return this.value.pipe(
+        return Lens.get(this.value).pipe(
             Effect.andThen(identity),
             Effect.andThen(value => this.submitValue(value)),
         )
@@ -153,7 +153,7 @@ extends Pipeable.Class() implements Form<A, I, R, MA, ME, MR, MP> {
                             e => e._tag === "ParseError",
                         ),
                         {
-                            onSome: e => Ref.set(this.error, Option.some(e)),
+                            onSome: e => Lens.set(this.error, Option.some(e)),
                             onNone: () => Effect.void,
                         },
                     )
@@ -193,10 +193,10 @@ export const make = Effect.fnUntraced(function* <A, I = A, R = never, MA = void,
         options.autosubmit ?? false,
         Option.fromNullable(options.debounce),
 
-        yield* SubscriptionRef.make(Option.none<A>()),
-        yield* SubscriptionRef.make(options.initialEncodedValue),
-        yield* SubscriptionRef.make(Option.none<ParseResult.ParseError>()),
-        yield* SubscriptionRef.make(Option.none<Fiber.Fiber<A, ParseResult.ParseError>>()),
+        Lens.fromSubscriptionRef(yield* SubscriptionRef.make(Option.none<A>())),
+        Lens.fromSubscriptionRef(yield* SubscriptionRef.make(options.initialEncodedValue)),
+        Lens.fromSubscriptionRef(yield* SubscriptionRef.make(Option.none<ParseResult.ParseError>())),
+        Lens.fromSubscriptionRef(yield* SubscriptionRef.make(Option.none<Fiber.Fiber<A, ParseResult.ParseError>>())),
 
         yield* Effect.makeSemaphore(1),
         yield* Ref.make(HashMap.empty<FormFieldKey, FormField<unknown, unknown>>()),
@@ -228,7 +228,7 @@ extends Pipeable.Pipeable {
     readonly [FormFieldTypeId]: FormFieldTypeId
 
     readonly value: Subscribable.Subscribable<Option.Option<A>, Cause.NoSuchElementException>
-    readonly encodedValue: SubscriptionRef.SubscriptionRef<I>
+    readonly encodedValue: Lens.Lens<I>
     readonly issues: Subscribable.Subscribable<readonly ParseResult.ArrayFormatterIssue[]>
     readonly isValidating: Subscribable.Subscribable<boolean>
     readonly isSubmitting: Subscribable.Subscribable<boolean>
@@ -240,7 +240,7 @@ extends Pipeable.Class() implements FormField<A, I> {
 
     constructor(
         readonly value: Subscribable.Subscribable<Option.Option<A>, Cause.NoSuchElementException>,
-        readonly encodedValue: SubscriptionRef.SubscriptionRef<I>,
+        readonly encodedValue: Lens.Lens<I>,
         readonly issues: Subscribable.Subscribable<readonly ParseResult.ArrayFormatterIssue[]>,
         readonly isValidating: Subscribable.Subscribable<boolean>,
         readonly isSubmitting: Subscribable.Subscribable<boolean>,
@@ -276,7 +276,7 @@ export const makeFormField = <A, I, R, MA, ME, MR, MP, const P extends PropertyP
             onSome: v => Option.map(PropertyPath.get(v, path), Option.some),
             onNone: () => Option.some(Option.none()),
         })),
-        SubscriptionSubRef.makeFromPath(self.encodedValue, path),
+        Lens.map(self.encodedValue, a => Option.getOrThrow(PropertyPath.get(a, path)), (a, b) => Option.getOrThrow(PropertyPath.immutableSet(a, path, b))),
         Subscribable.mapEffect(self.error, Option.match({
             onSome: flow(
                 ParseResult.ArrayFormatter.formatError,
@@ -305,29 +305,35 @@ export const useInput = Effect.fnUntraced(function* <A, I>(
     field: FormField<A, I>,
     options?: useInput.Options,
 ): Effect.fn.Return<useInput.Success<I>, Cause.NoSuchElementException, Scope.Scope> {
-    const internalValueRef = yield* Component.useOnChange(() => Effect.tap(
-        Effect.andThen(field.encodedValue, SubscriptionRef.make),
-        internalValueRef => Effect.forkScoped(Effect.all([
+    const internalValueLens = yield* Component.useOnChange(() => Effect.gen(function*() {
+        const internalValueLens = yield* Lens.get(field.encodedValue).pipe(
+            Effect.flatMap(SubscriptionRef.make),
+            Effect.map(Lens.fromSubscriptionRef),
+        )
+
+        yield* Effect.forkScoped(Effect.all([
             Stream.runForEach(
-                Stream.drop(field.encodedValue, 1),
+                Stream.drop(field.encodedValue.changes, 1),
                 upstreamEncodedValue => Effect.whenEffect(
-                    Ref.set(internalValueRef, upstreamEncodedValue),
-                    Effect.andThen(internalValueRef, internalValue => !Equal.equals(upstreamEncodedValue, internalValue)),
+                    Lens.set(internalValueLens, upstreamEncodedValue),
+                    Effect.andThen(Lens.get(internalValueLens), internalValue => !Equal.equals(upstreamEncodedValue, internalValue)),
                 ),
             ),
 
             Stream.runForEach(
-                internalValueRef.changes.pipe(
+                internalValueLens.changes.pipe(
                     Stream.drop(1),
                     Stream.changesWith(Equal.equivalence()),
                     options?.debounce ? Stream.debounce(options.debounce) : identity,
                 ),
-                internalValue => Ref.set(field.encodedValue, internalValue),
+                internalValue => Lens.set(field.encodedValue, internalValue),
             ),
-        ], { concurrency: "unbounded" })),
-    ), [field, options?.debounce])
+        ], { concurrency: "unbounded" }))
 
-    const [value, setValue] = yield* SubscriptionRef.useSubscriptionRefState(internalValueRef)
+        return internalValueLens
+    }), [field, options?.debounce])
+
+    const [value, setValue] = yield* Lens.useState(internalValueLens)
     return { value, setValue }
 })
 
@@ -346,51 +352,59 @@ export const useOptionalInput = Effect.fnUntraced(function* <A, I>(
     field: FormField<A, Option.Option<I>>,
     options: useOptionalInput.Options<I>,
 ): Effect.fn.Return<useOptionalInput.Success<I>, Cause.NoSuchElementException, Scope.Scope> {
-    const [enabledRef, internalValueRef] = yield* Component.useOnChange(() => Effect.tap(
-        Effect.andThen(
-            field.encodedValue,
+    const [enabledLens, internalValueLens] = yield* Component.useOnChange(() => Effect.gen(function*() {
+        const [enabledLens, internalValueLens] = yield* Effect.flatMap(
+            Lens.get(field.encodedValue),
             Option.match({
-                onSome: v => Effect.all([SubscriptionRef.make(true), SubscriptionRef.make(v)]),
-                onNone: () => Effect.all([SubscriptionRef.make(false), SubscriptionRef.make(options.defaultValue)]),
+                onSome: v => Effect.all([
+                    Effect.map(SubscriptionRef.make(true), Lens.fromSubscriptionRef),
+                    Effect.map(SubscriptionRef.make(v), Lens.fromSubscriptionRef),
+                ]),
+                onNone: () => Effect.all([
+                    Effect.map(SubscriptionRef.make(false), Lens.fromSubscriptionRef),
+                    Effect.map(SubscriptionRef.make(options.defaultValue), Lens.fromSubscriptionRef),
+                ]),
             }),
-        ),
+        )
 
-        ([enabledRef, internalValueRef]) => Effect.forkScoped(Effect.all([
+        yield* Effect.forkScoped(Effect.all([
             Stream.runForEach(
-                Stream.drop(field.encodedValue, 1),
+                Stream.drop(field.encodedValue.changes, 1),
 
                 upstreamEncodedValue => Effect.whenEffect(
                     Option.match(upstreamEncodedValue, {
                         onSome: v => Effect.andThen(
-                            Ref.set(enabledRef, true),
-                            Ref.set(internalValueRef, v),
+                            Lens.set(enabledLens, true),
+                            Lens.set(internalValueLens, v),
                         ),
                         onNone: () => Effect.andThen(
-                            Ref.set(enabledRef, false),
-                            Ref.set(internalValueRef, options.defaultValue),
+                            Lens.set(enabledLens, false),
+                            Lens.set(internalValueLens, options.defaultValue),
                         ),
                     }),
 
                     Effect.andThen(
-                        Effect.all([enabledRef, internalValueRef]),
+                        Effect.all([Lens.get(enabledLens), Lens.get(internalValueLens)]),
                         ([enabled, internalValue]) => !Equal.equals(upstreamEncodedValue, enabled ? Option.some(internalValue) : Option.none()),
                     ),
                 ),
             ),
 
             Stream.runForEach(
-                enabledRef.changes.pipe(
-                    Stream.zipLatest(internalValueRef.changes),
+                enabledLens.changes.pipe(
+                    Stream.zipLatest(internalValueLens.changes),
                     Stream.drop(1),
                     Stream.changesWith(Equal.equivalence()),
                     options?.debounce ? Stream.debounce(options.debounce) : identity,
                 ),
-                ([enabled, internalValue]) => Ref.set(field.encodedValue, enabled ? Option.some(internalValue) : Option.none()),
+                ([enabled, internalValue]) => Lens.set(field.encodedValue, enabled ? Option.some(internalValue) : Option.none()),
             ),
-        ], { concurrency: "unbounded" })),
-    ), [field, options.debounce])
+        ], { concurrency: "unbounded" }))
 
-    const [enabled, setEnabled] = yield* SubscriptionRef.useSubscriptionRefState(enabledRef)
-    const [value, setValue] = yield* SubscriptionRef.useSubscriptionRefState(internalValueRef)
+        return [enabledLens, internalValueLens] as const
+    }), [field, options.debounce])
+
+    const [enabled, setEnabled] = yield* Lens.useState(enabledLens)
+    const [value, setValue] = yield* Lens.useState(internalValueLens)
     return { enabled, setEnabled, value, setValue }
 })

packages/effect-fc/src/Lens.ts

@@ -0,0 +1,63 @@
+import { Effect, Equivalence, Stream } from "effect"
+import { Lens } from "effect-lens"
+import * as React from "react"
+import * as Component from "./Component.js"
+import * as SetStateAction from "./SetStateAction.js"
+import * as SubscriptionRef from "./SubscriptionRef.js"
+
+
+export declare namespace useState {
+    export interface Options<A> {
+        readonly equivalence?: Equivalence.Equivalence<A>
+    }
+}
+
+export const useState = Effect.fnUntraced(function* <A, ER, EW, RR, RW>(
+    lens: Lens.Lens<A, ER, EW, RR, RW>,
+    options?: useState.Options<NoInfer<A>>,
+): Effect.fn.Return<readonly [A, React.Dispatch<React.SetStateAction<A>>], ER, RR | RW> {
+    const [reactStateValue, setReactStateValue] = React.useState(yield* Component.useOnMount(() => Lens.get(lens)))
+
+    yield* Component.useReactEffect(() => Effect.forkScoped(
+        Stream.runForEach(
+            Stream.changesWith(lens.changes, options?.equivalence ?? Equivalence.strict()),
+            v => Effect.sync(() => setReactStateValue(v)),
+        )
+    ), [lens])
+
+    const setValue = yield* Component.useCallbackSync(
+        (setStateAction: React.SetStateAction<A>) => Effect.andThen(
+            Lens.updateAndGet(lens, prevState => SetStateAction.value(setStateAction, prevState)),
+            v => setReactStateValue(v),
+        ),
+        [lens],
+    )
+
+    return [reactStateValue, setValue]
+})
+
+export declare namespace useFromState {
+    export interface Options<A> {
+        readonly equivalence?: Equivalence.Equivalence<A>
+    }
+}
+
+export const useFromState = Effect.fnUntraced(function* <A>(
+    [value, setValue]: readonly [A, React.Dispatch<React.SetStateAction<A>>],
+    options?: useFromState.Options<NoInfer<A>>,
+): Effect.fn.Return<Lens.Lens<A, never, never, never, never>> {
+    const lens = yield* Component.useOnMount(() => Effect.map(
+        SubscriptionRef.make(value),
+        Lens.fromSubscriptionRef,
+    ))
+
+    yield* Component.useReactEffect(() => Effect.forkScoped(Stream.runForEach(
+        Stream.changesWith(lens.changes, options?.equivalence ?? Equivalence.strict()),
+        v => Effect.sync(() => setValue(v)),
+    )), [setValue])
+    yield* Component.useReactEffect(() => Lens.set(lens, value), [value])
+
+    return lens
+})
+
+export * from "effect-lens/Lens"

packages/effect-fc/src/PropertyPath.test.ts

@@ -0,0 +1,67 @@
+import { describe, expect, test } from "bun:test"
+import { Option } from "effect"
+import * as PropertyPath from "./PropertyPath.js"
+
+
+describe("immutableSet with arrays", () => {
+    test("sets a top-level array element", () => {
+        const arr = [1, 2, 3]
+        const result = PropertyPath.immutableSet(arr, [1], 99)
+        expect(result).toEqual(Option.some([1, 99, 3]))
+    })
+
+    test("does not mutate the original array", () => {
+        const arr = [1, 2, 3]
+        PropertyPath.immutableSet(arr, [0], 42)
+        expect(arr).toEqual([1, 2, 3])
+    })
+
+    test("sets the first element of an array", () => {
+        const arr = ["a", "b", "c"]
+        const result = PropertyPath.immutableSet(arr, [0], "z")
+        expect(result).toEqual(Option.some(["z", "b", "c"]))
+    })
+
+    test("sets the last element of an array", () => {
+        const arr = [10, 20, 30]
+        const result = PropertyPath.immutableSet(arr, [2], 99)
+        expect(result).toEqual(Option.some([10, 20, 99]))
+    })
+
+    test("sets a nested array element inside an object", () => {
+        const obj = { tags: ["foo", "bar", "baz"] }
+        const result = PropertyPath.immutableSet(obj, ["tags", 1], "qux")
+        expect(result).toEqual(Option.some({ tags: ["foo", "qux", "baz"] }))
+    })
+
+    test("sets a deeply nested value inside an array of objects", () => {
+        const obj = { items: [{ name: "alice" }, { name: "bob" }] }
+        const result = PropertyPath.immutableSet(obj, ["items", 0, "name"], "charlie")
+        expect(result).toEqual(Option.some({ items: [{ name: "charlie" }, { name: "bob" }] }))
+    })
+
+    test("sets a value in a nested array", () => {
+        const matrix = [[1, 2], [3, 4]]
+        const result = PropertyPath.immutableSet(matrix, [1, 0], 99)
+        expect(result).toEqual(Option.some([[1, 2], [99, 4]]))
+    })
+
+    test("returns Option.none() for an out-of-bounds index", () => {
+        const arr = [1, 2, 3]
+        const result = PropertyPath.immutableSet(arr, [5], 99)
+        expect(result).toEqual(Option.none())
+    })
+
+    test("returns Option.none() for a non-numeric key on an array", () => {
+        const arr = [1, 2, 3]
+        // @ts-expect-error intentionally wrong key type
+        const result = PropertyPath.immutableSet(arr, ["length"], 0)
+        expect(result).toEqual(Option.none())
+    })
+
+    test("empty path returns Option.some of the value itself", () => {
+        const arr = [1, 2, 3]
+        const result = PropertyPath.immutableSet(arr, [], [9, 9, 9] as any)
+        expect(result).toEqual(Option.some([9, 9, 9]))
+    })
+})

packages/effect-fc/src/SubscriptionSubRef.test.ts

@@ -0,0 +1,183 @@
+import { describe, expect, test } from "bun:test"
+import { Chunk, Effect, Ref, SubscriptionRef } from "effect"
+import * as SubscriptionSubRef from "./SubscriptionSubRef.js"
+
+
+describe("SubscriptionSubRef with array refs", () => {
+    test("creates a subref for a single array element using path", async () => {
+        const value = await Effect.runPromise(
+            Effect.flatMap(
+                SubscriptionRef.make([{ name: "alice" }, { name: "bob" }, { name: "charlie" }]),
+                parent => {
+                    const subref = SubscriptionSubRef.makeFromPath(parent, [1, "name"])
+                    return subref.get
+                },
+            ),
+        )
+
+        expect(value).toBe("bob")
+    })
+
+    test("modifies a single array element via subref", async () => {
+        const result = await Effect.runPromise(
+            Effect.flatMap(
+                SubscriptionRef.make([{ name: "alice" }, { name: "bob" }, { name: "charlie" }]),
+                parent => {
+                    const subref = SubscriptionSubRef.makeFromPath(parent, [1, "name"])
+                    return Effect.flatMap(
+                        Ref.set(subref, "bob-updated"),
+                        () => Ref.get(parent),
+                    )
+                },
+            ),
+        )
+
+        expect(result).toEqual([{ name: "alice" }, { name: "bob-updated" }, { name: "charlie" }])
+    })
+
+    test("modifies array element at index 0", async () => {
+        const result = await Effect.runPromise(
+            Effect.flatMap(
+                SubscriptionRef.make([10, 20, 30]),
+                parent => {
+                    const subref = SubscriptionSubRef.makeFromPath(parent, [0])
+                    return Effect.flatMap(
+                        Ref.set(subref, 99),
+                        () => Ref.get(parent),
+                    )
+                },
+            ),
+        )
+
+        expect(result).toEqual([99, 20, 30])
+    })
+
+    test("modifies array element at last index", async () => {
+        const result = await Effect.runPromise(
+            Effect.flatMap(
+                SubscriptionRef.make(["a", "b", "c"]),
+                parent => {
+                    const subref = SubscriptionSubRef.makeFromPath(parent, [2])
+                    return Effect.flatMap(
+                        Ref.set(subref, "z"),
+                        () => Ref.get(parent),
+                    )
+                },
+            ),
+        )
+
+        expect(result).toEqual(["a", "b", "z"])
+    })
+
+    test("modifies nested array element", async () => {
+        const result = await Effect.runPromise(
+            Effect.flatMap(
+                SubscriptionRef.make([[1, 2], [3, 4], [5, 6]]),
+                parent => {
+                    const subref = SubscriptionSubRef.makeFromPath(parent, [1, 0])
+                    return Effect.flatMap(
+                        Ref.set(subref, 99),
+                        () => Ref.get(parent),
+                    )
+                },
+            ),
+        )
+
+        expect(result).toEqual([[1, 2], [99, 4], [5, 6]])
+    })
+
+    test("uses modifyEffect to transform array element", async () => {
+        const result = await Effect.runPromise(
+            Effect.flatMap(
+                SubscriptionRef.make([{ count: 1 }, { count: 2 }, { count: 3 }]),
+                parent => {
+                    const subref = SubscriptionSubRef.makeFromPath(parent, [1, "count"])
+                    return Effect.flatMap(
+                        Ref.update(subref, count => count + 100),
+                        () => Effect.map(Ref.get(parent), parentValue => ({ result: 102, parentValue })),
+                    )
+                },
+            ),
+        )
+
+        expect(result.result).toBe(102) // count + 100
+        expect(result.parentValue).toEqual([{ count: 1 }, { count: 102 }, { count: 3 }]) // count + 100
+    })
+
+    test("uses modify to transform array element", async () => {
+        const result = await Effect.runPromise(
+            Effect.flatMap(
+                SubscriptionRef.make([10, 20, 30]),
+                parent => {
+                    const subref = SubscriptionSubRef.makeFromPath(parent, [1])
+                    return Effect.flatMap(
+                        Ref.update(subref, x => x + 5),
+                        () => Effect.map(Ref.get(parent), parentValue => ({ result: 25, parentValue })),
+                    )
+                },
+            ),
+        )
+
+        expect(result.result).toBe(25) // 20 + 5
+        expect(result.parentValue).toEqual([10, 25, 30]) // 20 + 5
+    })
+
+    test("makeFromChunkIndex modifies chunk element", async () => {
+        const result = await Effect.runPromise(
+            Effect.flatMap(
+                SubscriptionRef.make(Chunk.make(100, 200, 300)),
+                parent => {
+                    const subref = SubscriptionSubRef.makeFromChunkIndex(parent, 1)
+                    return Effect.flatMap(
+                        Ref.set(subref, 999),
+                        () => Ref.get(parent),
+                    )
+                },
+            ),
+        )
+
+        expect(Chunk.toReadonlyArray(result)).toEqual([100, 999, 300])
+    })
+
+    test("makeFromGetSet with custom getter/setter for array element", async () => {
+        const result = await Effect.runPromise(
+            Effect.flatMap(
+                SubscriptionRef.make([{ id: 1, value: "a" }, { id: 2, value: "b" }]),
+                parent => {
+                    const subref = SubscriptionSubRef.makeFromGetSet(parent, {
+                        get: arr => arr[0].value,
+                        set: (arr, newValue) => [
+                            { ...arr[0], value: newValue },
+                            ...arr.slice(1),
+                        ],
+                    })
+                    return Effect.flatMap(
+                        Ref.set(subref, "updated"),
+                        () => Ref.get(parent),
+                    )
+                },
+            ),
+        )
+
+        expect(result).toEqual([{ id: 1, value: "updated" }, { id: 2, value: "b" }])
+    })
+
+    test("does not mutate original array when modifying via subref", async () => {
+        const original = [{ name: "alice" }, { name: "bob" }]
+        const result = await Effect.runPromise(
+            Effect.flatMap(
+                SubscriptionRef.make(original),
+                parent => {
+                    const subref = SubscriptionSubRef.makeFromPath(parent, [0, "name"])
+                    return Effect.flatMap(
+                        Ref.set(subref, "alice-updated"),
+                        () => Ref.get(parent),
+                    )
+                },
+            ),
+        )
+
+        expect(original).toEqual([{ name: "alice" }, { name: "bob" }]) // original unchanged
+        expect(result).toEqual([{ name: "alice-updated" }, { name: "bob" }]) // new value in ref
+    })
+})

packages/effect-fc/src/index.ts

@@ -2,6 +2,7 @@ export * as Async from "./Async.js"
 export * as Component from "./Component.js"
 export * as ErrorObserver from "./ErrorObserver.js"
 export * as Form from "./Form.js"
+export * as Lens from "./Lens.js"
 export * as Memoized from "./Memoized.js"
 export * as Mutation from "./Mutation.js"
 export * as PropertyPath from "./PropertyPath.js"

packages/effect-fc/tsconfig.json

@@ -34,5 +34,6 @@
     ]
   },
 
-  "include": ["./src"]
+  "include": ["./src"],
+  "exclude": ["**/*.test.ts", "**/*.spec.ts"]
 }

packages/example/package.json

@@ -13,30 +13,30 @@
     "clean:modules": "rm -rf node_modules"
   },
   "devDependencies": {
-    "@tanstack/react-router": "^1.154.12",
-    "@tanstack/react-router-devtools": "^1.154.12",
-    "@tanstack/router-plugin": "^1.154.12",
-    "@types/react": "^19.2.9",
+    "@tanstack/react-router": "^1.168.3",
+    "@tanstack/react-router-devtools": "^1.166.11",
+    "@tanstack/router-plugin": "^1.167.4",
+    "@types/react": "^19.2.14",
     "@types/react-dom": "^19.2.3",
-    "@vitejs/plugin-react": "^5.1.2",
-    "globals": "^17.0.0",
-    "react": "^19.2.3",
-    "react-dom": "^19.2.3",
-    "type-fest": "^5.4.1",
-    "vite": "^7.3.1"
+    "@vitejs/plugin-react": "^6.0.1",
+    "globals": "^17.4.0",
+    "react": "^19.2.4",
+    "react-dom": "^19.2.4",
+    "type-fest": "^5.5.0",
+    "vite": "^8.0.2"
   },
   "dependencies": {
-    "@effect/platform": "^0.94.2",
-    "@effect/platform-browser": "^0.74.0",
-    "@radix-ui/themes": "^3.2.1",
+    "@effect/platform": "^0.96.0",
+    "@effect/platform-browser": "^0.76.0",
+    "@radix-ui/themes": "^3.3.0",
     "@typed/id": "^0.17.2",
-    "effect": "^3.19.15",
+    "effect": "^3.21.0",
     "effect-fc": "workspace:*",
-    "react-icons": "^5.5.0"
+    "react-icons": "^5.6.0"
   },
   "overrides": {
-    "@types/react": "^19.2.9",
-    "effect": "^3.19.15",
-    "react": "^19.2.3"
+    "@types/react": "^19.2.14",
+    "effect": "^3.21.0",
+    "react": "^19.2.4"
   }
 }