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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 class="chapter-item expanded "><a href="TYPES.html"><strong aria-hidden="true">3.</strong> Type System</a></li><li><ol class="section"><li class="chapter-item expanded "><div><strong aria-hidden="true">3.1.</strong> Basic Types</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">3.2.</strong> Parameter Types</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">3.3.</strong> Reference Types</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">3.4.</strong> Abstract Types</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">3.5.</strong> Advanced Types</div></li></ol></li><li class="chapter-item expanded "><a href="MODULES.html"><strong aria-hidden="true">4.</strong> Module System</a></li><li><ol class="section"><li class="chapter-item expanded "><div><strong aria-hidden="true">4.1.</strong> Using Modules</div></li><li class="chapter-item expanded "><div><strong 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" class="active"><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"><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 id="error-handling"><a class="header" href="#error-handling">Error Handling</a></h1>
+<p>Puck's error handling is shamelessly stolen from Swift. It uses a combination of <code>Option</code>/<code>Result</code> types and <code>try</code>/<code>catch</code> statements, and leans somewhat on Puck's metaprogramming capabilities.</p>
+<p>There are several ways to handle errors in Puck. If the error is encoded in the type, one can:</p>
+<ol>
+<li><code>match</code> on the error</li>
+<li>compactly match on the error with <code>if ... of</code></li>
+<li>propagate the error with <code>?</code></li>
+<li>throw the error with <code>!</code></li>
+</ol>
+<p>If an error is thrown, one <strong>must</strong> explicitly handle (or disregard) it with a <code>try/catch</code> block or risk runtime failure. This method of error handling may feel more familiar to Java programmers.</p>
+<h2 id="errors-as-monads"><a class="header" href="#errors-as-monads">Errors as Monads</a></h2>
+<p>Puck provides <a href="std/default/options.pk"><code>Option[T]</code></a> and a <a href="std/default/results.pk"><code>Result[T, E]</code></a> types, imported by default. These are <code>union</code> types and so must be pattern matched upon to be useful: but the standard library provides <a href="std/default/results.pk">a bevy of helper functions</a>.
+Two in particular are of note. The <code>?</code> operator unwraps a Result or propagates its error up a function call (and may only be used in type-appropriate contexts). The <code>!</code> operator unwraps an Option or Result directly or throws an exception in the case of None or Error.</p>
+<pre><code class="language-puck">pub macro `?`[T, E](self: Result[T, E]) =
+ quote:
+ match `self`
+ of Okay(x): x
+ of Error(e): return Error(e)
+</code></pre>
+<pre><code class="language-puck">pub func `!`[T](self: Option[T]): T =
+ match self
+ of Some(x): x
+ of None: raise EmptyValue
+
+pub func `!`[T, E](self: Result[T, E]): T =
+ of Okay(x): x
+ of Error(e): raise e
+</code></pre>
+<p>The utility of the provided helpers in <a href="std/default/options.pk"><code>std.options</code></a> and <a href="std/default/results.pk"><code>std.results</code></a> should not be understated. While encoding errors into the type system may appear restrictive at first glance, some syntactic sugar goes a long way in writing compact and idiomatic code. Java programmers in particular are urged to give type-first errors a try, before falling back on unwraps and <code>try</code>/<code>catch</code>.</p>
+<p>A notable helpful type is the aliasing of <code>Result[T]</code> to <code>Result[T, ref Err]</code>, for when the particular error does not matter. This breaks <code>try</code>/<code>catch</code> exhaustion (as <code>ref Err</code> denotes a reference to <em>any</em> Error), but is particularly useful when used in conjunction with the propagation operator.</p>
+<h2 id="errors-as-catchable-exceptions"><a class="header" href="#errors-as-catchable-exceptions">Errors as Catchable Exceptions</a></h2>
+<p>Errors raised by <code>raise</code>/<code>throw</code> (or subsequently the <code>!</code> operator) must be explicitly caught and handled via a <code>try</code>/<code>catch</code>/<code>finally</code> statement.
+If an exception is not handled within a function body, the function must be explicitly marked as a throwing function via the <code>yeet</code> prefix (name to be determined). The compiler will statically determine which exceptions in particular are thrown from any given function, and enforce them to be explicitly handled or explicitly ignored.</p>
+<p>Despite functioning here as exceptions: errors remain types. An error thrown from an unwrapped <code>Result[T, E]</code> is of type <code>E</code>. <code>catch</code> statements, then, may pattern match upon possible errors, behaving similarly to <code>of</code> branches.</p>
+<pre><code class="language-puck">try:
+ ...
+catch &quot;Error&quot;:
+ ...
+finally:
+ ...
+</code></pre>
+<p>This creates a distinction between two types of error handling, working in sync: functional error handling with <a href="https://en.wikipedia.org/wiki/Option_type">Option</a> and <a href="https://en.wikipedia.org/wiki/Result_type">Result</a> types, and object-oriented error handling with <a href="https://en.wikipedia.org/wiki/Exception_handling">catchable exceptions</a>. These styles may be swapped between with minimal syntactic overhead. Libraries, however, should universally use <code>Option</code>/<code>Result</code>, as this provides the best support for both styles.</p>
+<!-- [nullable types](https://en.wikipedia.org/wiki/Nullable_type)?? -->
+<h2 id="errors-and-void-functions"><a class="header" href="#errors-and-void-functions">Errors and Void Functions</a></h2>
+<p>Some functions do not return a value but can still fail: for example, setters.
+This can make it difficult to do monadic error handling elegantly: one could return a <code>Result[void, E]</code>, but...</p>
+<pre><code class="language-puck">pub func set[T](self: list[T], i: uint, val: T) =
+ if i &gt; self.length:
+ raise IndexOutOfBounds
+ self.data.raw_set(offset = i, val)
+</code></pre>
+<h2 id="unrecoverable-exceptions"><a class="header" href="#unrecoverable-exceptions">Unrecoverable Exceptions</a></h2>
+<p>There exist errors from which a program can not reasonably recover. These are the following:</p>
+<ul>
+<li><code>Assertation Failure</code>: a call to an <code>assert</code> function has returned false at runtime.</li>
+<li><code>Out of Memory</code>: the executable is out of memory.</li>
+<li><code>Stack Overflow</code>: the executable has overflowed the stack.</li>
+<li>any others?</li>
+</ul>
+<p>They are not recoverable, but the user should be aware of them as possible failure conditions.</p>
+<p>References: <a href="https://docs.swift.org/swift-book/documentation/the-swift-programming-language/errorhandling">Error Handling in Swift</a></p>
+
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