Talk on Generators

Useful ideas on generators

Prerequisites

Global installation of Typescript, with tsc command.

Build and Run

npm install
npm start

Note: Nothing useful will happen when you run the code, until you have pasted in the demo code.

Elements of the Talk

Generic iteration

const gloriousStateful = function*(seed = 10) {
	let state = seed

	while (true) {
		yield ++state
	}
}

	// Using it
	const gen = gloriousStateful()

	for (const i of Iterable.range(0, 4)) {
		const {value, done} = gen.next()
		console.log(`Got value: ${value} done: ${done}`)
	}

Passing Values to the Generator

const communicative = function*() {
	let value = 99
	while (true) {
		value = yield value + 10
	}
}

	const gen = communicative()

	for (const i of Iterable.range(0, 4)) {
		const {value, done} = gen.next(i)
		console.log(`Got value: ${value} done: ${done}`)
	}

Issue Note the inconsitency in the first iteration. Issue Mutable state

Recursive

const recursive = function*(seed = 10) {
	yield seed
	yield* recursive(seed + 1)
}

Spreading finite gen into array

const finite = function*(seed = 10) {
	yield seed
	if (seed < 12) {
		yield* finite(seed + 1)
	}
}

	const gen = finite()

	const arr = [...gen]
	console.log(arr)

Iterating in for loop

	const gen = finite()

	for (const val of gen) {
		console.log(val)
	}

Using Ixjs to Achieving Gloriousness

	const gen = finite()
	const iter = Iterable.from(gen)

	for (const val of iter.filter(x => x > 10).take(1)) {
		console.log(val)
	}

	// Tip: add a log statement to the inner loop of `finite` to see how many times it actually runs.

init.ts - Sagas and Listen

	const {store, sagaMiddleware} = setupShop()
	sagaMiddleware.run(greetingLoop)
	const router = createRouter(store)

	listen(app => {
		app.use("/", router)
	})

	// Look at `greetingLoop` for the actual content.

Usage

CURLing Greets

curl -X POST http://127.0.0.1:3000/greeting --data '{"greeting":"Heisann"}' --header "Content-Type: application/json" -w "\n"