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I often see the claim that AE generalizes control flow, so you can (for example) implement coroutines. But the most obvious way I would implement AE in a language runtime is with coroutines, where effects are just syntactic sugar around yield/resume.

What am I missing?

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One thing AE provides but not coroutines is type safety. More concretely AE can specify what a function can do and cannot do lexically in code. A generator/coroutine cannot.

For example, a function annotated with say `query_db(): User can Datebase` means the function can call database and the caller must provide a `Database` handler to call the `query_db`.

The constraint of what can do and not is pretty popular in other programming fields, most notably, NextJS. A server component CANNOT use client feature and a client component CANNOt access server db.

Coroutines don't take away type safety any more than function calls do.

But this gets back to what I was saying about generalization - the way I would implement what you're talking about is with coroutines and dynamic scoping. I'm still missing how AE is more general and not something you implement on top of other building blocks.

I think the idea is that you can use it like async/await, except that a function must statically declare which interfaces it is allowed to await on, and the implementations are passed in through an implicit context. I'd be a bit worried that using it widely for capabilities, etc., would just multiply the number of function colors.

> would just multiply the number of function colors.

Would there really be colors?

I mean sure, the caller of an effectful function will either have to handle the effect or become effectful itself, so in this sense effectfulness is infectious.

However, while a function might use the `await` effect, when calling the function you could also just define the effect handler so as to block, instead of defering the task and jumping back to the event loop. In other words, wouldn't this solve the issue of colors? One would simply define all possibly blocking functions as await-effectful. Whether or not they actually await / run asynchronously would be up to the caller.

The problem is, if you're using them for capabilities, it wouldn't just be an 'Await' effect: it would be an 'AwaitDatabase' effect and an 'AwaitFilesystem' effect and an 'AwaitNetwork' effect and an 'AwaitSubprocess' effect and....

And everything working with generic function objects would have to lug around all these effects, unless the language has a very solid 'effect polymorphism' story.

> unless the language has a very solid 'effect polymorphism' story.

That seems to be the premise, yeah. (See also the comment by the Ante author on polymorphism somewhere here in the thread.)

> The problem is, if you're using them for capabilities, it wouldn't just be an 'Await' effect: it would be an 'AwaitDatabase' effect and an 'AwaitFilesystem' effect and an 'AwaitNetwork' effect and an 'AwaitSubprocess' effect and....

I have to admit I will have to think about this a bit. It's already late over here and my brain is no longer working. :)

Yes, this is what Effect-TS is doing for JavaScript, minus the syntactic sugar, but I don't know if this is a good idea in the end. It reminds me of the Spring framework, DI is also a form of AE, but it spreads like cancer through the code. The other day I was watching this talk[1] from EffectDays on how to use effects on the frontend and the entire talk was a dude showing boilerplate that did nothing. I think that AE is a beguiling idea, it lets you express imperative code in a functional language, but in a language like JS the added work of wrapping everything in a function feel like a step down from writing the simples JS you can imagine. Just as a counter example, there is also canvasmotion[2] which also uses coroutines to express scenarios for 2D graphics and this feels like it is making something hard easier.

[1] https://www.youtube.com/watch?v=G_jp87gxILE [2] https://motioncanvas.io/

I'm not sure I follow, JS doesn't have coroutines (generator functions can be used kind of like coroutines, but for example you can't resume them with an argument).

Yes it does:

  function* greeter() {
    const name = yield "What's your name?"
    yield `Hello, ${name}!`
  }
  const gen = greeter()
  
  console.log(gen.next().value)
  console.log(gen.next("Alice").value)

TIL!

Other people in this thread have claimed that AE handlers can resume the code multiple times, as in call/cc, as opposed to resuming a coroutine, which can only be done once for each time it yields.

Personally, I don't see a whole lot of value in that, with how unpredictable execution could get. I'd rather write a function that explicitly returns another function to be called multiple times. (Or some equivalent, e.g., a function that returns an iterator.)

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