I’ll start with generators, seeing as they’re the simplest case. As @zvolkov mentioned, they’re functions/objects that can be repeatedly called without returning, but when called will return (yield) a value and then suspend their execution. When they’re called again, they will start up from where they last suspended execution and do their thing again. A … Read more
Before we introduce continuations we need to build some infrastructure. Below is a trampoline that operates on Iteration objects. An iteration is a computation that can either Yield a new value or it can be Done. sealed trait Iteration[+R] case class Yield[+R](result: R, next: () => Iteration[R]) extends Iteration[R] case object Done extends Iteration[Nothing] def … Read more
It is concurrent, in the sense that many outstanding asychronous operations may be in progress at any time. It may or may not be multithreaded. By default, await will schedule the continuation back to the “current execution context”. The “current execution context” is defined as SynchronizationContext.Current if it is non-null, or TaskScheduler.Current if there’s no … Read more
I believe that continuations are a special case of callbacks. A function may callback any number of functions, any number of times. For example: var array = [1, 2, 3]; forEach(array, function (element, array, index) { array[index] = 2 * element; }); console.log(array); function forEach(array, callback) { var length = array.length; for (var i = … Read more
The general idea is correct – the remainder of the method is made into a continuation of sorts. The “fast path” blog post has details on how the async/await compiler transformation works. Differences, off the top of my head: The await keyword also makes use of a “scheduling context” concept. The scheduling context is SynchronizationContext.Current … Read more
tail calls first (part 1) First write the loop such that it recurs in tail position const foldr = (f, init, xs = []) => loop ( ( i = 0 , k = identity ) => i >= xs.length ? k (init) : recur ( i + 1 , r => k (f (r, … Read more