# Asynchronous Programming

Puck has [colourless](https://journal.stuffwithstuff.com/2015/02/01/what-color-is-your-function/) async/await, heavily inspired by [Zig's implementation](https://kristoff.it/blog/zig-colorblind-async-await/).

```puck
pub func fetch(url: str): str = ...

let a: Future[T] = async fetch_html()
let b: T = a.await
let c: T = await async fetch_html()
```

Puck's async implementation relies heavily on its metaprogramming system.

The `async` macro will wrap a call returning `T` in a `Future[T]` and compute it asynchronously. The `await` function takes in a `Future[T]` and will block until it returns a value (or error). The `Future[T]` type is opaque, containing internal information useful for the `async` and `await` routines.

```puck
pub macro async(self): Future[T] =
  ... todo ...
```

```puck
pub func await[T](self: Future[T]): T =
  while not self.ready:
    block
  self.value! # apply callbacks?
```

This implementation differs from standard async/await implementations quite a bit.
In particular, this means there is no concept of an "async function" - any block of computation that resolves to a value can be made asynchronous. This allows for "anonymous" async functions, among other things.

<!-- Asynchronous programming is hard to design and hard to use. Even Rust doesn't do a great job. It *shouldn't* need built-in language support - we should be able to encode it as a type and provide any special syntax via macros. Note that async is not just threading! threading is solved well by Rust's rayon and Go's (blugh) goroutines. -->

## Threading

How threads work deserves somewhat of a mention. todo

References:
- [What color is your function?](https://journal.stuffwithstuff.com/2015/02/01/what-color-is-your-function/)
- [What is Zig's "colorblind" async/await?](https://kristoff.it/blog/zig-colorblind-async-await/)
- [Zig Learn: Async](https://ziglearn.org/chapter-5/)
- [Rust async is colored and that's not a big deal](https://morestina.net/blog/1686/rust-async-is-colored)
- [Why is there no need for async/await in Elixir?](https://old.reddit.com/r/elixir/np688d/)
- [Async/await on Wikipedia](https://en.wikipedia.org/wiki/Async/await)
- [nim-chronos](https://github.com/status-im/nim-chronos)
- [nim-cps](https://github.com/nim-works/cps)
- [tokio](https://tokio.rs/tokio/tutorial)
- [Zig-style async/await for Nim](https://forum.nim-lang.org/t/7347)

Is async worth having separate from effect handlers? I think so...