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<ol class="chapter"><li class="chapter-item expanded affix "><a href="../index.html">The Puck Programming Language</a></li><li class="chapter-item expanded "><a href="OVERVIEW.html"><strong aria-hidden="true">1.</strong> Basic Usage</a></li><li><ol class="section"><li class="chapter-item expanded "><div><strong aria-hidden="true">1.1.</strong> Variables and Comments</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">1.2.</strong> Basic Types</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">1.3.</strong> Functions and Calls</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">1.4.</strong> Boolean and Integer Operations</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">1.5.</strong> Conditionals and Control Flow</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">1.6.</strong> Error Handling</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">1.7.</strong> Loops and Iterators</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">1.8.</strong> Modules</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">1.9.</strong> Compile-time Programming</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">1.10.</strong> Async and Threading</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">1.11.</strong> Advanced Types</div></li></ol></li><li class="chapter-item expanded "><a href="SYNTAX.html"><strong aria-hidden="true">2.</strong> Syntax</a></li><li><ol class="section"><li class="chapter-item expanded "><div><strong aria-hidden="true">2.1.</strong> Indentation Rules [todo]</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">2.2.</strong> Reserved Keywords</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">2.3.</strong> A Formal Grammar</div></li></ol></li><li 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aria-hidden="true">4.2.</strong> Implicit Modules</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">4.3.</strong> Defining Module Interfaces [todo]</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">4.4.</strong> Defining an External API [todo]</div></li></ol></li><li class="chapter-item expanded "><a href="ERRORS.html"><strong aria-hidden="true">5.</strong> Error Handling</a></li><li><ol class="section"><li class="chapter-item expanded "><div><strong aria-hidden="true">5.1.</strong> Errors as Monads</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">5.2.</strong> Errors as Catchable Exceptions</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">5.3.</strong> Errors and Void Functions [todo]</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">5.4.</strong> Unrecoverable Exceptions</div></li></ol></li><li class="chapter-item expanded "><a href="ASYNC.html" class="active"><strong aria-hidden="true">6.</strong> Async System</a></li><li><ol class="section"><li class="chapter-item expanded "><div><strong aria-hidden="true">6.1.</strong> Threading [todo]</div></li></ol></li><li class="chapter-item expanded "><a href="METAPROGRAMMING.html"><strong aria-hidden="true">7.</strong> Metaprogramming</a></li><li class="chapter-item expanded "><div><strong aria-hidden="true">8.</strong> Memory Management [todo]</div></li><li><ol class="section"><li class="chapter-item expanded "><div><strong aria-hidden="true">8.1.</strong> Reference Counting Optimizations</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">8.2.</strong> Annotations and Ownership</div></li></ol></li><li class="chapter-item expanded "><a href="INTEROP.html"><strong aria-hidden="true">9.</strong> Language Interop [draft]</a></li><li><ol class="section"><li class="chapter-item expanded "><div><strong aria-hidden="true">9.1.</strong> Rust, Swift, Nim</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">9.2.</strong> Java, Kotlin</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">9.3.</strong> Python, Racket, C</div></li></ol></li><li class="chapter-item expanded "><div><strong aria-hidden="true">10.</strong> Refinement Types [draft]</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">11.</strong> Dependent Types [draft]</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">12.</strong> Effects System [draft]</div></li></ol>
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<h1 class="menu-title">The Puck Programming Language</h1>
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<h1 id="asynchronous-programming"><a class="header" href="#asynchronous-programming">Asynchronous Programming</a></h1>
<blockquote>
<p>! This section is a <strong>draft</strong>. Many important details have yet to be ironed out.</p>
</blockquote>
<p>Puck has <a href="https://journal.stuffwithstuff.com/2015/02/01/what-color-is-your-function/">colourless</a> async/await, heavily inspired by <a href="https://kristoff.it/blog/zig-colorblind-async-await/">Zig's implementation</a>.</p>
<pre><code class="language-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()
</code></pre>
<p>Puck's async implementation relies heavily on its metaprogramming system.</p>
<p>The <code>async</code> macro will wrap a call returning <code>T</code> in a <code>Future[T]</code> and compute it asynchronously. The <code>await</code> function takes in a <code>Future[T]</code> and will block until it returns a value (or error). The <code>Future[T]</code> type is opaque, containing internal information useful for the <code>async</code> and <code>await</code> routines.</p>
<pre><code class="language-puck">pub macro async(self): Future[T] =
... todo ...
</code></pre>
<pre><code class="language-puck">pub func await[T](self: Future[T]): T =
while not self.ready do
# block
self.value! # apply callbacks?
</code></pre>
<p>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.</p>
<p>This (packaging up blocks of code to suspend and resume arbitrarily) is <em>hard</em>, and requires particular portable intermediate structures out of the compiler. Luckily, Zig is doing all of the R&D here. Some design decisions to consider revolve around <em>APIs</em>. The Linux kernel interface (among other things) provides both synchronous and asynchronous versions of its API, and fast code will use one or the other, depending if it is in an async context. Zig works around this by way of a known global constant that low-level functions read at compile time to determine whether to operate on synchronous APIs or asynchronous APIs. This is... not great. But what's better?</p>
<!-- 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. -->
<h2 id="threading"><a class="header" href="#threading">Threading</a></h2>
<p>It should be noted that async is <em>not</em> the same as threading, <em>nor</em> is it solely useful in the presence of threads...</p>
<p>How threads work deserves somewhat of a mention...</p>
<p>References:</p>
<ul>
<li><a href="https://journal.stuffwithstuff.com/2015/02/01/what-color-is-your-function/">What color is your function?</a></li>
<li><a href="https://kristoff.it/blog/zig-colorblind-async-await/">What is Zig's "colorblind" async/await?</a></li>
<li><a href="https://ziglearn.org/chapter-5/">Zig Learn: Async</a></li>
<li><a href="https://morestina.net/blog/1686/rust-async-is-colored">Rust async is colored and that's not a big deal</a></li>
<li><a href="https://old.reddit.com/r/elixir/np688d/">Why is there no need for async/await in Elixir?</a></li>
<li><a href="https://en.wikipedia.org/wiki/Async/await">Async/await on Wikipedia</a></li>
<li><a href="https://github.com/status-im/nim-chronos">nim-chronos</a></li>
<li><a href="https://github.com/nim-works/cps">nim-cps</a></li>
<li><a href="https://tokio.rs/tokio/tutorial">tokio</a></li>
<li><a href="https://forum.nim-lang.org/t/7347">Zig-style async/await for Nim</a></li>
</ul>
<p>Is async worth having separate from effect handlers? I think so...</p>
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