feat: add signal api

benches/mapped.luau

@@ -1,10 +1,10 @@
 local Charm = require("../packages/charm/src")
 local bench = require("./bench")
 
-local atom = Charm.atom
 local computed = Charm.computed
 local mapped = Charm.mapped
-local setCurrentSub = Charm.core.setCurrentSub
+local setActiveSub = Charm.core.setActiveSub
+local signal = Charm.signal
 
 type Entry = { number }
 
@@ -25,9 +25,9 @@ local function simpleMapped(source: () -> { Entry }, mapper: (Entry, number) ->
 		local nextState = {}
 
 		for index, value in state do
-			local currentSub = setCurrentSub(nil)
+			local currentSub = setActiveSub(nil)
 			local success, valueOut, keyOut = pcall(mapper, value, index)
-			setCurrentSub(currentSub)
+			setActiveSub(currentSub)
 
 			if success then
 				nextState[keyOut] = valueOut
@@ -52,26 +52,26 @@ end
 
 for _, percent in { 0.1, 0.5, 1 } do
 	bench.run(`mapped {percent}`, function()
-		local src = atom(initialState)
+		local src, setSrc = signal(initialState)
 		local out = mapped(src, mapper)
 
 		bench.profilebegin("init")
 		out()
 		bench.profileend()
-		src(updatePercentage(percent))
+		setSrc(updatePercentage(percent))
 		bench.profilebegin("update")
 		out()
 		bench.profileend()
 	end)
 
 	bench.run(`control {percent}`, function()
-		local src = atom(initialState)
+		local src, setSrc = signal(initialState)
 		local out = simpleMapped(src, mapper)
 
 		bench.profilebegin("init")
 		out()
 		bench.profileend()
-		src(updatePercentage(percent))
+		setSrc(updatePercentage(percent))
 		bench.profilebegin("update")
 		out()
 		bench.profileend()

benches/propagate.luau

@@ -1,15 +1,15 @@
 local Charm = require("../packages/charm/src")
 local bench = require("./bench")
 
-local atom = Charm.atom
 local computed = Charm.computed
 local effect = Charm.effect
 local listen = Charm.listen
+local signal = Charm.signal
 
 for _, w in { 10, 100 } do
 	for _, h in { 10, 100 } do
 		bench.run(`propagate {w}*{h}`, function()
-			local src = atom(1)
+			local src, setSrc = signal(1)
 			for _ = 1, w do
 				local last = src
 				for _ = 1, h do
@@ -22,7 +22,7 @@ for _, w in { 10, 100 } do
 					last()
 				end)
 			end
-			src(src() + 1)
+			setSrc(src() + 1)
 		end)
 	end
 end
@@ -30,7 +30,7 @@ end
 for _, w in { 10, 100 } do
 	for _, h in { 10, 100 } do
 		bench.run(`propagate (listen) {w}*{h}`, function()
-			local src = atom(1)
+			local src, setSrc = signal(1)
 			for _ = 1, w do
 				local last = src
 				for _ = 1, h do
@@ -41,7 +41,7 @@ for _, w in { 10, 100 } do
 				end
 				listen(last, function() end)
 			end
-			src(src() + 1)
+			setSrc(src() + 1)
 		end)
 	end
 end

packages/charm-sync/src/__tests__/patch.spec.luau

@@ -24,7 +24,7 @@ local function mockArraySerdes(object: { [any]: any }): { [any]: any }
 end
 
 afterEach(function()
-	config.autoSerialize = true
+	config.fixArrays = true
 	config.validatePatches = true
 end)
 
@@ -104,13 +104,13 @@ test("cannot preserve sparse arrays", function()
 end)
 
 test("optionally fixes sparse arrays", function()
-	config.autoSerialize = true
+	config.fixArrays = true
 
 	for index in next, patch.diff({ 1, 1, 1, 1, 1 }, { 2, 1, 1, 2 }) do
 		assert(type(index) == "string", `expected {type(index)} {index} to be string`)
 	end
 
-	config.autoSerialize = false
+	config.fixArrays = false
 
 	for index in next, patch.diff({ 1, 1, 1, 1, 1 }, { 2, 1, 1, 2 }) do
 		assert(type(index) == "number", `expected {type(index)} {index} to be number`)

packages/charm-sync/src/client.luau

@@ -16,7 +16,6 @@ local function syncAtoms(atoms: { [string]: Charm.Atom })
 			warn("[Charm] Attempted to sync different atoms with the same key:", key)
 			continue
 		end
-
 		atomRegister[key] = atom
 	end
 end

packages/charm-sync/src/config.luau

@@ -12,9 +12,9 @@ return {
 	--- to address remote event argument limitations. Defaults to `true`.
 	--- This option should be disabled if your network library uses a custom
 	--- serialization method (i.e. Zap, ByteNet) to prevent interference.
-	autoSerialize = true,
+	fixArrays = true,
 	--- When `true`, patches will be validated before being sent to clients to
 	--- enforce remote event limitations. Only checked in strict mode and if
-	--- `autoSerialize` is enabled. Defaults to `true`.
+	--- `fixArrays` is enabled. Defaults to `true`.
 	validatePatches = true,
 }

packages/charm-sync/src/index.d.ts

@@ -1,7 +1,5 @@
 import { Atom } from "@rbxts/charm";
 
-type Cleanup = () => void;
-
 type Key = string | number | symbol;
 
 /**
@@ -18,7 +16,7 @@ type SelectorMap = Record<string, () => any>;
 /**
  * Infers the type of the return values produced by a map of functions.
  */
-type StateOfMap<T> = {
+export type StateOfMap<T> = {
 	readonly [P in keyof T]: T[P] extends () => infer State ? State : never;
 };
 
@@ -88,11 +86,11 @@ export const config: {
 	 *
 	 * @server
 	 */
-	autoSerialize: boolean;
+	fixArrays: boolean;
 	/**
 	 * When `true`, patches will be validated before being sent to clients to
 	 * enforce remote event limitations. Only checked in strict mode and if
-	 * `autoSerialize` is enabled. Defaults to `true`.
+	 * `fixArrays` is enabled. Defaults to `true`.
 	 *
 	 * @server
 	 */
@@ -178,11 +176,10 @@ export namespace server {
 	 * be sent to clients whenever the atoms are updated.
 	 *
 	 * @param onSync The function to call when patches can be sent to a client.
-	 * @returns `stopSync()`
 	 */
 	export function startSync<Atoms extends { [key: string]: Atom<any> }, Serialize extends boolean = true>(
 		onSync: (client: Player, payloads: SyncPayload<Atoms, Serialize>[]) => void,
-	): Cleanup;
+	): void;
 
 	/**
 	 * Stops automatically syncing registered atoms to clients. Patches will

packages/charm-sync/src/patch.luau

@@ -3,7 +3,7 @@ local config = require("./config")
 local types = require("./types")
 local validate = require("./validate")
 
-local flags = Charm.flags
+local globals = Charm.globals
 
 export type None = types.None
 
@@ -73,13 +73,13 @@ local function diff(currentState: any, nextState: any): any
 		patches[key] = diff(previous, nextState[key])
 	end
 
-	if config.autoSerialize then
+	if config.fixArrays then
 		-- Coerce sparse array patches into dictionaries
 		if currentState[1] ~= nil or nextState[1] ~= nil then
 			patches = stringifySparseArray(patches)
 		end
 
-		if flags.strict and config.validatePatches then
+		if globals.strict and config.validatePatches then
 			for key, value in patches do
 				validate(value, key)
 			end

packages/charm-sync/src/server.luau

@@ -5,11 +5,13 @@ local types = require("./types")
 
 type SyncPayload = types.SyncPayload
 
+local globals = Charm.globals
+
 type RegisteredAtom<T = any> = {
-	atom: () -> T,
+	callback: () -> T,
-	value: T,
+	currentValue: T,
-	valueLastSynced: T,
+	previousValue: T,
-	stop: () -> (),
+	dispose: () -> (),
 }
 
 type SyncStatus = number
@@ -19,82 +21,82 @@ local LISTENING_FOR_CHANGES: SyncStatus = 1
 
 local atomRegister: { [string]: RegisteredAtom } = {}
 local clientRegister: { [any]: { [string]: SyncStatus } } = {}
-local globalUpdates: { { key: string, value: any, previousValue: any } } = {}
+local globalUpdates: { { key: string, currentValue: any, previousValue: any } } = {}
 
 local connection: RBXScriptConnection?
 local onSyncCallback: (client: any, payloads: { SyncPayload }) -> ()?
 
-local function registerAtom<T>(key: string, atom: () -> T)
+local function syncGlobalAtom<T>(key: string, callback: () -> T)
 	if atomRegister[key] then
-		if atomRegister[key].atom ~= atom then
+		if atomRegister[key].callback ~= callback then
 			warn("[Charm] Attempted to sync different atoms with the same key:", key)
 		end
 		return
 	end
 
 	local registeredAtom: RegisteredAtom<T> = {
-		atom = atom,
+		callback = callback,
-		value = atom(),
+		currentValue = callback(),
-		valueLastSynced = atom(),
+		previousValue = callback(),
-		stop = function() end,
+		dispose = function() end,
 	}
 
-	registeredAtom.stop = Charm.effect(function()
+	registeredAtom.dispose = Charm.effect(function()
-		local value = atom()
+		local newValue = callback()
 
 		-- When preserving history, we need to keep track of previous values
 		-- so we can create granular patches for each change.
-		if config.preserveHistory and registeredAtom.value ~= value then
+		if config.preserveHistory and registeredAtom.currentValue ~= newValue then
 			table.insert(globalUpdates, {
 				key = key,
-				value = value,
+				currentValue = newValue,
-				previousValue = registeredAtom.value,
+				previousValue = registeredAtom.currentValue,
 			})
 		end
 
-		registeredAtom.value = value
+		registeredAtom.currentValue = newValue
 	end)
 
 	atomRegister[key] = registeredAtom
 end
 
-local function unregisterAtom(key: string)
+local function unsyncGlobalAtom(key: string)
 	local registeredAtom = atomRegister[key]
 
 	if registeredAtom then
-		registeredAtom.stop()
+		registeredAtom.dispose()
 		atomRegister[key] = nil
 	end
 end
 
-local function unregisterUnusedAtoms()
+local function unsyncStaleGlobalAtoms()
-	local used: { [string]: boolean } = {}
+	local active: { [string]: boolean } = {}
 
 	for _, clientAtoms in clientRegister do
 		for key in clientAtoms do
-			used[key] = true
+			active[key] = true
 		end
 	end
 
 	for key in atomRegister do
-		if not used[key] then
+		if not active[key] then
-			unregisterAtom(key)
+			unsyncGlobalAtom(key)
 		end
 	end
 end
 
-local function createHistoricalPatches(): { any }
+local function createGlobalPatchHistory(): { any }
 	local patchCount = #globalUpdates
 	local patches = table.create(patchCount)
 
 	for index, update in globalUpdates do
-		patches[index] = patch.diff(update.previousValue, update.value)
+		patches[index] = patch.diff(update.previousValue, update.currentValue)
 	end
 
 	return patches
 end
 
-local function createHistoricalPayloadsForClient(client: any, patches: { any }): { SyncPayload }
+local function createPayloadHistoryForClient(client: any, patches: { any }): { SyncPayload }
 	local syncedAtoms = clientRegister[client]
 
 	if not syncedAtoms then
@@ -123,9 +125,8 @@ local function createHistoricalPayloadsForClient(client: any, patches: { any }):
 		elseif status == PENDING_INITIAL_STATE then
 			table.insert(payloads, {
 				type = "init",
-				data = { [key] = update.value },
+				data = { [key] = update.currentValue },
 			})
-
 			syncedAtoms[key] = LISTENING_FOR_CHANGES
 		end
 	end
@@ -138,7 +139,7 @@ local function createHistoricalPayloadsForClient(client: any, patches: { any }):
 		local registeredAtom = atomRegister[key]
 
 		if status == PENDING_INITIAL_STATE and registeredAtom then
-			initPayload[key] = registeredAtom.value
+			initPayload[key] = registeredAtom.currentValue
 			syncedAtoms[key] = LISTENING_FOR_CHANGES
 		end
 	end
@@ -150,20 +151,20 @@ local function createHistoricalPayloadsForClient(client: any, patches: { any }):
 	return payloads
 end
 
-local function createPatch(): any
+local function createGlobalPatch(): any
 	local current: { [string]: any } = {}
 	local previous: { [string]: any } = {}
 
 	for key, registeredAtom in atomRegister do
-		current[key] = registeredAtom.value
+		current[key] = registeredAtom.currentValue
-		previous[key] = registeredAtom.valueLastSynced
+		previous[key] = registeredAtom.previousValue
-		registeredAtom.valueLastSynced = registeredAtom.value
+		registeredAtom.previousValue = registeredAtom.currentValue
 	end
 
 	return patch.diff(previous, current)
 end
 
-local function createPayloadsForClient(client: any, patchData: any): { SyncPayload }
+local function createPayloadForClient(client: any, patchData: any): { SyncPayload }
 	local syncedAtoms = clientRegister[client]
 	local payloads: { SyncPayload } = {}
 
@@ -182,7 +183,7 @@ local function createPayloadsForClient(client: any, patchData: any): { SyncPaylo
 		if status == LISTENING_FOR_CHANGES then
 			patchPayload[key] = patchData[key]
 		elseif status == PENDING_INITIAL_STATE then
-			initPayload[key] = registeredAtom.value
+			initPayload[key] = registeredAtom.currentValue
 			syncedAtoms[key] = LISTENING_FOR_CHANGES
 		end
 	end
@@ -215,7 +216,7 @@ local function syncAtomsToClient(client: any, atoms: { [string]: () -> any })
 	local syncedAtoms = clientRegister[client]
 
 	for key, atom in atoms do
-		registerAtom(key, atom)
+		syncGlobalAtom(key, atom)
 
 		if not syncedAtoms[key] then
 			-- Mark the atom as pending initial state so we send its full value
@@ -263,18 +264,18 @@ local function flush()
 		return
 	end
 
-	local patches = if config.preserveHistory then createHistoricalPatches() else createPatch()
+	local patches = if config.preserveHistory then createGlobalPatchHistory() else createGlobalPatch()
 
 	-- While payload objects are technically mutable as they are unique to
 	-- each client, the data inside them is not safe to mutate.
-	if Charm.flags.frozen then
+	if globals.frozen then
 		Charm.deepFreeze(patches)
 	end
 
 	for client in clientRegister do
 		local payloads: { SyncPayload } = if config.preserveHistory
-			then createHistoricalPayloadsForClient(client, patches)
+			then createPayloadHistoryForClient(client, patches)
-			else createPayloadsForClient(client, patches)
+			else createPayloadForClient(client, patches)
 
 		if payloads[1] then
 			if task then
@@ -285,10 +286,43 @@ local function flush()
 		end
 	end
 
-	unregisterUnusedAtoms()
+	unsyncStaleGlobalAtoms()
 	table.clear(globalUpdates)
 end
 
+--- Starts automatically syncing registered atoms to clients. Patches will
+--- be sent to clients whenever the atoms are updated.
+---
+--- @param onSync The function to call when patches can be sent to a client.
+local function startSync(onSync: (client: any, payloads: { SyncPayload }) -> ())
+	if connection then
+		connection:Disconnect()
+	end
+
+	onSyncCallback = onSync
+
+	if not game then
+		return
+	end
+
+	local timer = 0
+
+	connection = game:GetService("RunService").Heartbeat:Connect(function(deltaTime)
+		if config.interval < 0 then
+			return
+		end
+
+		timer += deltaTime
+
+		if timer >= config.interval then
+			timer = 0
+			debug.profilebegin("CharmSync")
+			flush()
+			debug.profileend()
+		end
+	end)
+end
+
 --- Stops automatically syncing registered atoms to clients. Patches will
 --- no longer be sent to clients until `startSync` is called again.
 local function stopSync()
@@ -307,42 +341,6 @@ local function reset()
 	stopSync()
 end
 
---- Starts automatically syncing registered atoms to clients. Patches will
---- be sent to clients whenever the atoms are updated.
----
---- @param onSync The function to call when patches can be sent to a client.
---- @return `stopSync()`
-local function startSync(onSync: (client: any, payloads: { SyncPayload }) -> ()): () -> ()
-	if connection then
-		connection:Disconnect()
-	end
-
-	onSyncCallback = onSync
-
-	if not game then
-		return stopSync
-	end
-
-	local timer = 0
-
-	connection = game:GetService("RunService").Heartbeat:Connect(function(deltaTime)
-		if config.interval < 0 then
-			return
-		end
-
-		timer += deltaTime
-
-		if timer >= config.interval then
-			timer = 0
-			debug.profilebegin("CharmSync")
-			flush()
-			debug.profileend()
-		end
-	end)
-
-	return stopSync
-end
-
 return {
 	syncAtomsToClient = syncAtomsToClient,
 	unsyncClient = unsyncClient,

packages/charm/src/__tests__/core/signal.spec.luau

@@ -1,13 +1,13 @@
 local core = require("../../core")
 local suite = require("../../../../../test/suite")
 
-local atom = core.atom
+local signal = core.signal
 local effect = core.effect
 local test = suite.test
 
 test("should accept equality function", function()
 	local calls = {}
-	local src = atom(0, function(current, incoming)
+	local src, setSrc = signal(0, function(current, incoming)
 		return current == incoming or incoming % 2 == 1
 	end)
 
@@ -15,23 +15,23 @@ test("should accept equality function", function()
 		table.insert(calls, src())
 	end)
 
-	src(2)
+	setSrc(2)
-	src(3)
+	setSrc(3)
 	assert(src() == 2, "should skip odd value")
 
-	src(4)
+	setSrc(4)
-	src(5)
+	setSrc(5)
 	assert(src() == 4, "should skip odd value")
 	assert(table.concat(calls) == "024", `should only call on even updates, got {table.concat(calls)}`)
 end)
 
 test("should enforce immutability", function()
-	local src = atom({ nested = {} })
+	local src, setSrc = signal({ nested = {} })
 	assert(not pcall(function()
 		src().nested.a = 1
 	end), "should not allow mutation of initial value")
 
-	src({ nested = { a = 1 } })
+	setSrc({ nested = { a = 1 } })
 	assert(not pcall(function()
 		src().nested.a = 2
 	end), "should not allow mutation of new value")

packages/charm/src/__tests__/spec.luau

@@ -1,9 +1,6 @@
 local suite = require("../../../../test/suite")
 
 suite.describe("core", function()
-	suite.describe("atom", function()
-		require("./core/atom.spec")
-	end)
 	suite.describe("computed", function()
 		require("./core/computed.spec")
 	end)
@@ -16,6 +13,9 @@ suite.describe("core", function()
 	suite.describe("gc", function()
 		require("./core/gc.spec")
 	end)
+	suite.describe("signal", function()
+		require("./core/signal.spec")
+	end)
 	suite.describe("topology", function()
 		require("./core/topology.spec")
 	end)

packages/charm/src/core.luau

@@ -1,5 +1,5 @@
 local alien = require("./alien")
-local config = require("./flags")
+local globals = require("./globals")
 local utils = require("./utils")
 
 export type ReactiveFlags = alien.ReactiveFlags
@@ -74,7 +74,7 @@ end
 local function runCleanups(effect: EffectScope)
 	for _, cleanup in effect.cleanups do
 		local prevSub = setActiveSub(nil)
-		local success, result: any = (if config.strict then noYield else pcall)(cleanup)
+		local success, result: any = (if globals.strict then noYield else pcall)(cleanup)
 		activeSub = prevSub
 		if not success then
 			error(result)
@@ -87,18 +87,17 @@ local function setNotPending(sub: ReactiveNode, flags: ReactiveFlags)
 	sub.flags = bit32.band(flags, bit32.bnot(PENDING))
 end
 
-local function run(e: Effect | EffectScope, flags: ReactiveFlags): ()
+local function run(e: Effect, flags: ReactiveFlags): ()
 	if
 		bit32.btest(flags, DIRTY)
 		or (bit32.btest(flags, PENDING) and (checkDirty(e.deps :: Link, e) or setNotPending(e, flags)))
 	then
 		runCleanups(e)
-		local e = e :: Effect
 		cycle += 1
 		e.depsTail = nil
 		e.flags = bit32.bor(WATCHING, RECURSED_CHECK)
 		local prevSub = setActiveSub(e)
-		local success, result: (() -> ())? = (if config.strict then noYield else pcall)(e.fn, e.stop)
+		local success, result: (() -> ())? = (if globals.strict then noYield else pcall)(e.fn, e.stop)
 		activeSub = prevSub
 		e.flags = bit32.band(e.flags, bit32.bnot(RECURSED_CHECK))
 		purgeDeps(e)
@@ -155,7 +154,7 @@ local function updateComputed(c: Computed): boolean
 	c.flags = bit32.bor(MUTABLE, RECURSED_CHECK)
 	local prevSub = setActiveSub(c)
 	local oldValue = c.value
-	local success, result: unknown = (if config.strict then noYield else pcall)(c.getter, oldValue)
+	local success, result: unknown = (if globals.strict then noYield else pcall)(c.getter, oldValue)
 	activeSub = prevSub
 	c.flags = bit32.band(c.flags, bit32.bnot(RECURSED_CHECK))
 	purgeDeps(c)
@@ -163,7 +162,7 @@ local function updateComputed(c: Computed): boolean
 		error(result)
 	end
 	if oldValue ~= result then
-		if config.frozen then
+		if globals.frozen then
 			deepFreeze(result)
 		end
 		c.value = result
@@ -205,14 +204,15 @@ local function computedOper<T>(this: Computed<T>): () -> T
 	end
 end
 
-local function signalOper<T>(this: Signal<T>, equals: ((current: T, incoming: T) -> boolean)?): (...((T) -> T) | T) -> T
+local function signalOper<T>(
-	return function(...: ((T) -> T) | T): T
+	this: Signal<T>,
-		if select("#", ...) ~= 0 then
+	equals: ((current: T, incoming: T) -> boolean)?
-			local update = ...
+): (() -> T, (((T) -> T) | T) -> T)
+	local function setter(update: ((T) -> T) | T): T
 		local value: T
 		if type(update) == "function" then
 			local prevSub = setActiveSub(nil)
-				local success, result: T = (if config.strict then noYield else pcall)(update, this.currentValue)
+			local success, result: T = (if globals.strict then noYield else pcall)(update, this.currentValue)
 			activeSub = prevSub
 			if not success then
 				error(result)
@@ -222,7 +222,7 @@ local function signalOper<T>(this: Signal<T>, equals: ((current: T, incoming: T)
 			value = update
 		end
 		if if equals then not equals(this.pendingValue, value) else this.pendingValue ~= value then
-				if config.frozen then
+			if globals.frozen then
 				deepFreeze(value)
 			end
 			this.pendingValue = value
@@ -237,7 +237,9 @@ local function signalOper<T>(this: Signal<T>, equals: ((current: T, incoming: T)
 			return value
 		end
 		return this.currentValue
-		else
+	end
+
+	local function getter(): T
 		if bit32.btest(this.flags, DIRTY) then
 			if updateSignal(this) then
 				local subs = this.subs
@@ -259,7 +261,8 @@ local function signalOper<T>(this: Signal<T>, equals: ((current: T, incoming: T)
 		end
 		return this.currentValue
 	end
-	end
+
+	return getter, setter
 end
 
 local function effectScopeOper(this: EffectScope): () -> ()
@@ -279,15 +282,18 @@ local function effectOper(this: Effect): () -> ()
 	return effectScopeOper(this)
 end
 
---- Creates a reactive atom that acts as both a getter and setter. Calling the
+--- Creates a reactive signal that stores a value and notifies subscribers when
---- atom with an argument sets its value, while calling it with no arguments
+--- the value changes. The signal provides both a getter and a setter.
---- returns its current value.
 ---
---- @param value The initial value of the atom. If empty, the atom's value will be `undefined`.
+--- @param initialValue The initial value of the signal.
---- @param equals A comparator function to determine if the atom's value has changed.
+--- @param equals A comparator function to determine if the signal's value has changed.
---- @see https://github.com/littensy/charm?tab=readme-ov-file#atomstate-options
+--- @return A tuple containing the getter and setter functions for the signal.
-local function atom<T>(initialValue: T, equals: ((current: T, incoming: T) -> boolean)?): (...((T) -> T) | T) -> T
+--- @see https://github.com/littensy/charm?tab=readme-ov-file#signalstate-equals
-	if config.frozen then
+local function signal<T>(
+	initialValue: T,
+	equals: ((current: T, incoming: T) -> boolean)?
+): (() -> T, (((T) -> T) | T) -> T)
+	if globals.frozen then
 		deepFreeze(initialValue)
 	end
 	return signalOper({
@@ -297,6 +303,20 @@ local function atom<T>(initialValue: T, equals: ((current: T, incoming: T) -> bo
 	}, equals)
 end
 
+--- Creates a reactive atom that acts as both a getter and setter. Calling the
+--- atom with an argument sets its value, while calling it with no arguments
+--- returns its current value.
+---
+--- @param value The initial value of the atom. If empty, the atom's value will be `undefined`.
+--- @param equals A comparator function to determine if the atom's value has changed.
+--- @see https://github.com/littensy/charm?tab=readme-ov-file#atomstate-equals
+local function atom<T>(initialValue: T, equals: ((current: T, incoming: T) -> boolean)?): (...((T) -> T) | T) -> T
+	local getter, setter = signal(initialValue, equals)
+	return function(...: ((T) -> T) | T): T
+		return if select("#", ...) == 0 then getter() else setter((...))
+	end
+end
+
 --- Creates a new atom that is computed based on the values of other atoms.
 --- The returned atom is read-only, and its value is automatically updated when
 --- any atoms accessed from within the getter function change.
@@ -343,11 +363,11 @@ local function effect(fn: (stop: () -> ()) -> ()): () -> ()
 	}
 	e.stop = effectOper(e)
 	local prevSub = setActiveSub(e)
-	if prevSub and (config.trackInnerEffects or prevSub.flags == NONE) then
+	if prevSub and (globals.trackInnerEffects or prevSub.flags == NONE) then
 		link(e, prevSub, 0)
 	end
 	local stopped = false
-	local success, result: (() -> ())? = (if config.strict then noYield else pcall)(fn, function()
+	local success, result: (() -> ())? = (if globals.strict then noYield else pcall)(fn, function()
 		stopped = true
 	end)
 	activeSub = prevSub
@@ -379,7 +399,7 @@ local function effectScope(fn: () -> (), detached: boolean?): () -> ()
 	if prevSub and not detached then
 		link(e, prevSub, 0)
 	end
-	local success, result: (() -> ())? = (if config.strict then noYield else pcall)(fn)
+	local success, result: (() -> ())? = (if globals.strict then noYield else pcall)(fn)
 	activeSub = prevSub
 	if not success then
 		error(result)
@@ -456,7 +476,7 @@ end
 --- @return The return value of the callback.
 local function batched<Args..., Results...>(callback: (Args...) -> Results..., ...: Args...): Results...
 	startBatch()
-	local results: { any } = { (if config.strict then noYield else pcall)(callback, ...) }
+	local results: { any } = { (if globals.strict then noYield else pcall)(callback, ...) }
 	endBatch()
 	if not results[1] then
 		error(results[2])
@@ -464,6 +484,59 @@ local function batched<Args..., Results...>(callback: (Args...) -> Results..., .
 	return unpack(results, 2)
 end
 
+--- Creates an effect that only runs the callback when the value returned by the
+--- getter changes. The callback receives the new value and the previous value
+--- as arguments.
+---
+--- @param getter A function that returns the value to watch.
+--- @param callback The function to run when the value changes.
+--- @return A function for disposing the effect.
+--- @see https://github.com/littensy/charm?tab=readme-ov-file#subscribegetter-callback
+local function subscribe<T>(getter: () -> T, callback: (state: T, lastState: T) -> ()): () -> ()
+	local tracked = computed(function()
+		return getter()
+	end)
+	local current: T
+	local mounted = true
+	return effect(function()
+		local previous = current
+		current = tracked()
+		if mounted then
+			mounted = false
+		else
+			peek(callback, current, previous)
+		end
+	end)
+end
+
+--- Creates an effect that runs the callback one immediately, and then again
+--- when the value returned by the getter changes. The callback receives the new
+--- value, the previous value, and a cleanup function as arguments.
+---
+--- @param getter A function that returns the value to watch.
+--- @param callback The function to run when the value changes.
+--- @return A function for disposing the effect.
+--- @see https://github.com/littensy/charm?tab=readme-ov-file#listengetter-callback
+local function listen<T>(getter: () -> T, callback: (state: T, previous: T?, dispose: () -> ()) -> ()): () -> ()
+	local tracked = computed(function()
+		return getter()
+	end)
+	local current: T
+	local disposed = false
+	local dispose = function()
+		disposed = true
+	end
+	dispose = effect(function()
+		local previous = current
+		current = tracked()
+		peek(callback, current, previous, dispose)
+	end)
+	if disposed then
+		dispose()
+	end
+	return dispose
+end
+
 local function notify(e: ReactiveNode)
 	local flags = e.flags
 	if not bit32.btest(flags, QUEUED) then
@@ -513,6 +586,7 @@ return {
 	startBatch = startBatch,
 	endBatch = endBatch,
 	atom = atom,
+	signal = signal,
 	computed = computed,
 	effect = effect,
 	effectScope = effectScope,
@@ -520,4 +594,6 @@ return {
 	untracked = untracked,
 	peek = peek,
 	batched = batched,
+	subscribe = subscribe,
+	listen = listen,
 }

packages/charm/src/globals.luau

@@ -3,17 +3,18 @@ local function inlineTest(): string
 end
 
 local isO2 = inlineTest() ~= "inlineTest"
+local isDev = not isO2 or _G.__DEV__ == true
 
 return {
 	--- Enforces synchronous, non-yielding behavior in atoms and effects.
 	--- Also enables state validation in Charm Sync to catch sync errors early.
 	--- Enabled if the optimization level is below 2, which is true in studio.
-	strict = not isO2,
+	strict = isDev,
 	--- Enforces immutability of atoms by deep-freezing table values. Enabled
 	--- if the optimization level is below 2, which is true in studio.
-	frozen = not isO2,
+	frozen = isDev,
-	--- Whether inner effects should clean up after themselves when their
+	--- Whether parent effects should track inner effects and clean them up
-	--- parent effect re-runs. This is usually desirable, but can be disabled
+	--- when the parent effect re-runs. This is usually desirable, but can be
-	--- to revert to the old behavior. Defaults to `true`.
+	--- disabled to revert to the old behavior. Defaults to `true`.
 	trackInnerEffects = true,
 }

packages/charm/src/index.d.ts

@@ -7,7 +7,7 @@ type Cleanup = () => void;
  * current value.
  */
 export interface Atom<T> {
-	(value: T | ((value: T) => T)): T;
+	(newValue: T | ((currentValue: T) => T)): T;
 	(): T;
 }
 
@@ -18,7 +18,7 @@ export type Equals<T> = (current: T, incoming: T) => boolean;
 /**
  * Global flags that modify the behavior of Charm's reactive system.
  */
-export const flags: {
+export const globals: {
 	/**
 	 * Enforces synchronous, non-yielding behavior in atoms and effects.
 	 * Also enables state validation in Charm Sync to catch sync errors early.
@@ -31,13 +31,30 @@ export const flags: {
 	 */
 	frozen: boolean;
 	/**
-	 * Whether inner effects should clean up after themselves when their
+	 * Whether parent effects should track inner effects and clean them up
-	 * parent effect re-runs. This is usually desirable, but can be disabled
+	 * when the parent effect re-runs. This is usually desirable, but can be
-	 * to revert to the old behavior. Defaults to `true`.
+	 * disabled to revert to the old behavior. Defaults to `true`.
 	 */
 	trackInnerEffects: boolean;
 };
 
+/**
+ * Creates a reactive signal that stores a value and notifies subscribers when
+ * the value changes. The signal provides both a getter and a setter.
+ *
+ * @param initialValue The initial value of the signal.
+ * @param equals A comparator function to determine if the signal's value has changed.
+ * @return A tuple containing the getter and setter functions for the signal.
+ * @see https://github.com/littensy/charm?tab=readme-ov-file#signalstate-equals
+ */
+export function signal<T>(
+	value: T,
+	equals?: Equals<T>,
+): LuaTuple<[() => T, (newValue: T | ((currentValue: T) => T)) => T]>;
+export function signal<T>(): LuaTuple<
+	[() => T | undefined, (newValue: T | ((currentValue?: T) => T | undefined)) => T | undefined]
+>;
+
 /**
  * Creates a reactive atom that acts as both a getter and setter. Calling the
  * atom with an argument sets its value, while calling it with no arguments

packages/charm/src/init.luau

@@ -1,33 +1,33 @@
 local core = require("@self/core")
-local flags = require("@self/flags")
+local globals = require("@self/globals")
-local listen = require("@self/listen")
 local mapped = require("@self/mapped")
 local observe = require("@self/observe")
-local subscribe = require("@self/subscribe")
-local types = require("@self/types")
 local utils = require("@self/utils")
 
+type Update<T> = ((previous: T) -> T) | T
+
 --- A reactive atom that acts as both a getter and setter. Calling the atom with
 --- an argument sets its value, while calling it with no arguments returns its
 --- current value.
-export type Atom<T = any> = types.Atom<T>
+export type Atom<T = any> = (...Update<T>) -> T
 
-export type Selector<T = any> = types.Selector<T>
+export type Selector<T = any> = () -> T
 
 return {
 	core = core,
-	flags = flags,
+	globals = globals,
 	atom = core.atom,
 	batched = core.batched,
 	computed = core.computed,
 	effect = core.effect,
 	effectScope = core.effectScope,
+	listen = core.listen,
 	onCleanup = core.onCleanup,
 	peek = core.peek,
+	signal = core.signal,
+	subscribe = core.subscribe,
 	untracked = core.untracked,
-	listen = listen,
 	mapped = mapped,
 	observe = observe,
-	subscribe = subscribe,
 	deepFreeze = utils.deepFreeze,
 }

packages/charm/src/listen.luau

@@ -1,40 +0,0 @@
-local core = require("./core")
-
-local computed = core.computed
-local effect = core.effect
-local peek = core.peek
-
---- Creates an effect that runs the callback one immediately, and then again
---- when the value returned by the getter changes. The callback receives the new
---- value, the previous value, and a cleanup function as arguments.
----
---- @param getter A function that returns the value to watch.
---- @param callback The function to run when the value changes.
---- @return A function for disposing the effect.
---- @see https://github.com/littensy/charm?tab=readme-ov-file#listengetter-callback
-local function listen<T>(getter: () -> T, callback: (state: T, previous: T?, dispose: () -> ()) -> ()): () -> ()
-	local tracked = computed(function()
-		return getter()
-	end)
-
-	local current: T
-	local disposed = false
-
-	local function dispose()
-		disposed = true
-	end
-
-	dispose = effect(function()
-		local previous = current
-		current = tracked()
-		peek(callback, current, previous, dispose)
-	end)
-
-	if disposed then
-		dispose()
-	end
-
-	return dispose
-end
-
-return listen

packages/charm/src/observe.luau

@@ -1,11 +1,10 @@
 local core = require("./core")
-local flags = require("./flags")
+local globals = require("./globals")
 
+local batched = core.batched
 local effect = core.effect
 local effectScope = core.effectScope
 local onCleanup = core.onCleanup
-local startBatch = core.startBatch
-local endBatch = core.endBatch
 
 --- Calls the observer function for each unique key in the table returned by the
 --- getter. The observer is called once for each key, and again when a new key
@@ -51,13 +50,11 @@ local function observe<K, V>(getter: () -> { [K]: V }, observer: (item: V, key:
 		local previousItems = currentItems
 		currentItems = getter()
 		if currentItems ~= previousItems then
-			startBatch()
+			batched(updateScopes, currentItems, previousItems)
-			updateScopes(currentItems, previousItems)
-			endBatch()
 		end
 	end)
 
-	if flags.trackInnerEffects then
+	if globals.trackInnerEffects then
 		onCleanup(disposeScopes, true)
 	end
 

packages/charm/src/subscribe.luau

@@ -1,34 +0,0 @@
-local core = require("./core")
-
-local computed = core.computed
-local effect = core.effect
-local peek = core.peek
-
---- Creates an effect that only runs the callback when the value returned by the
---- getter changes. The callback receives the new value and the previous value
---- as arguments.
----
---- @param getter A function that returns the value to watch.
---- @param callback The function to run when the value changes.
---- @return A function for disposing the effect.
---- @see https://github.com/littensy/charm?tab=readme-ov-file#subscribegetter-callback
-local function subscribe<T>(getter: () -> T, callback: (state: T, lastState: T) -> ()): () -> ()
-	local tracked = computed(function()
-		return getter()
-	end)
-
-	local current: T
-	local mounted = true
-
-	return effect(function()
-		local previous = current
-		current = tracked()
-		if mounted then
-			mounted = false
-		else
-			peek(callback, current, previous)
-		end
-	end)
-end
-
-return subscribe

packages/charm/src/types.luau

@@ -1,7 +0,0 @@
-type Update<T> = ((previous: T) -> T) | T
-
-export type Atom<T> = (...Update<T>) -> T
-
-export type Selector<T> = () -> T
-
-return {}

packages/react-charm/src/init.luau

@@ -16,6 +16,7 @@ local function useAtom<T>(getter: () -> T, dependencies: { any }?): T
 
 	React.useLayoutEffect(function()
 		return Charm.effect(function()
+			-- Wrap in untracked to avoid tracking inner effect and atom calls
 			Charm.untracked(setState, getter())
 		end)
 	end, dependencies or {})
@@ -39,6 +40,7 @@ local function useAtomBinding<T>(getter: () -> T, dependencies: { any }?)
 
 	React.useLayoutEffect(function()
 		return Charm.effect(function()
+			-- Wrap in untracked to avoid tracking inner effect and atom calls
 			Charm.untracked(setBinding, getter())
 		end)
 	end, dependencies or {})

packages/vide-charm/src/init.luau

@@ -10,6 +10,7 @@ local function useAtom<State>(getter: () -> State): () -> State
 	local state = Vide.source(getter())
 
 	Vide.cleanup(Charm.effect(function()
+		-- Wrap in untracked to avoid tracking inner effect and atom calls
 		Charm.untracked(state :: (State) -> State, getter())
 	end))
 

test/spec.server.luau

@@ -1,8 +1,8 @@
 local Charm = require("../packages/charm/src")
 local suite = require("./suite")
 
-Charm.flags.strict = true
+Charm.globals.strict = true
-Charm.flags.frozen = true
+Charm.globals.frozen = true
 
 suite.describe("charm", function()
 	require("../packages/charm/src/__tests__/spec")