Add stream type to frptools.

(prettier got ahold of this commit)

README.md

@@ -1,7 +1,7 @@
 # FRP tools
 
-Property, Container and Computed value stores designed to work together for storing discrete and
-derived state.
+Property, Container, Computed and Stream value stores designed to work together for storing discrete
+and derived state.
 
 # [property](./src/property.js)
 
@@ -153,6 +153,30 @@ const b = prop(new Set([2, 3]), hashSet);
 const intersection = computed(_intersection, [a, b], hashSet);
 ```
 
+# [stream](./src/stream.js)
+
+`stream` is a computed that works asynchronously. Dependencies can be synchronous or asynchronous
+functions but the hash function remains synchronous.
+
+## Usage
+
+### Creation
+
+```js
+const getToken = stream(
+	async tokenUrl => fetch(tokenUrl), // computation function
+	[getTokenUrl] // array of dependencies, can be a property, computed or stream
+);
+```
+
+### Read
+
+```js
+if (await getToken()) { /* do stuff with the token */ }
+```
+
+Call it to receive the stored value, recomputing if necessary.
+
 # [container](./src/container.js)
 
 `container` is a wrapper around any container type (Object, Set, Map, or Array) while monitoring

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "frptools",
-	"version": "3.1.1",
+	"version": "3.2.0",
 	"description": "Observable Property and Computed data streams",
 	"main": "src/index.js",
 	"files": ["src"],

spec/stream.spec.js

@@ -0,0 +1,100 @@
+import { prop, computed, stream } from '../src/index.js';
+import { dirtyMock, hashSet } from '../src/testUtil.js';
+
+describe('A stream', () => {
+	const add = (a, b) => a + b;
+	const square = a => a * a;
+
+	async function delayAdd(a, b) {
+		return new Promise(resolve =>
+			setTimeout(() => {
+				resolve(a + b);
+			}, 30)
+		);
+	}
+	async function delaySquare(a) {
+		return new Promise(resolve =>
+			setTimeout(() => {
+				resolve(a * a);
+			}, 30)
+		);
+	}
+
+	it('accepts prop, computed and stream dependencies', async done => {
+		const a = prop(0);
+		const b = computed(square, [a]);
+		const c = stream(delaySquare, [a]);
+		const d = stream(delayAdd, [a, c]);
+		const e = stream(delaySquare, [b]);
+
+		expect(await c()).toEqual(0);
+		expect(await d()).toEqual(0);
+		expect(await e()).toEqual(0);
+
+		a(1);
+		expect(await c()).toEqual(1);
+		expect(await d()).toEqual(2);
+		expect(await e()).toEqual(1);
+
+		a(2);
+		expect(await c()).toEqual(4);
+		expect(await d()).toEqual(6);
+		expect(await e()).toEqual(16);
+
+		a(3);
+		expect(await c()).toEqual(9);
+		expect(await d()).toEqual(12);
+		expect(await e()).toEqual(81);
+		done();
+	});
+
+	it('computes automatically when subscribed', async done => {
+		let runCount = 0;
+		let subRunCount = 0;
+		let currentValue = 1;
+		const a = prop(0);
+		const b = stream(
+			async val => {
+				runCount += 1;
+				expect(val).toEqual(currentValue);
+				return new Promise(resolve => setTimeout(() => resolve(val * val), 30));
+			},
+			[a]
+		);
+
+		// b does not evaluate
+		a(1);
+		expect(runCount).toEqual(0);
+		// b evaluates
+		expect(await b()).toEqual(1);
+		expect(runCount).toEqual(1);
+		// b does not evaluate
+		expect(await b()).toEqual(1);
+		expect(runCount).toEqual(1);
+
+		const cancelSubscription = b.subscribe(val => {
+			subRunCount += 1;
+			expect(val).toEqual(currentValue * currentValue);
+		});
+
+		currentValue = 3;
+		// b evaluates
+		a(3);
+
+		// b is triggered to update but hasn't yet
+		expect(runCount).toEqual(1);
+		expect(subRunCount).toEqual(0);
+
+		setTimeout(async () => {
+			// b should have updated now
+			expect(runCount).toEqual(2);
+			expect(subRunCount).toEqual(1);
+
+			// b does not evaluate
+			expect(await b()).toEqual(9);
+			expect(runCount).toEqual(2);
+			expect(subRunCount).toEqual(1);
+			done();
+		}, 40);
+	});
+});

src/index.js

@@ -1,4 +1,5 @@
 export { prop } from './property.js';
 export { computed } from './computed.js';
+export { stream } from './stream.js';
 export { container } from './container.js';
 export { call, id, pick } from './util.js';

src/stream.js

@@ -0,0 +1,51 @@
+import { id, registerFire, registerSubscriptions, call } from './util.js';
+
+export function stream(fn, dependencies = [], hash = id) {
+	let subscribers = [];
+	let isDirty = true;
+	let val;
+	let oldId;
+
+	// Compute new value, call subscribers if changed.
+	const accessor = async function _computed() {
+		if (isDirty) {
+			const newVal = await fn.apply(null, await Promise.all(dependencies.map(call)));
+			isDirty = false;
+			const newId = hash(newVal);
+			if (oldId !== newId) {
+				oldId = newId;
+				val = newVal;
+				accessor.fire(val);
+			}
+		}
+		return val;
+	};
+
+	// Add child nodes to the logic graph (value-based)
+	accessor.subscribe = registerSubscriptions(subscribers);
+	accessor.fire = registerFire(subscribers);
+
+	// Receive dirty flag from parent logic node (dependency).  Pass it down.
+	accessor.setDirty = function setDirty() {
+		if (!isDirty) {
+			isDirty = true;
+			subscribers.forEach(s => s.setDirty && s.setDirty());
+		}
+		return subscribers.length && accessor;
+	};
+
+	// Remove this node from the logic graph completely
+	accessor.detach = () => {
+		subscribers = [];
+		dependentSubscriptions.forEach(call);
+	};
+
+	// Remove child nodes from the logic graph
+	accessor.unsubscribeAll = () => {
+		subscribers = [];
+	};
+
+	const dependentSubscriptions = dependencies.map(d => d.subscribe(accessor.setDirty));
+
+	return accessor;
+}