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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="generator" content="pandoc">
<meta name="author" content="Malte Neuss">
<title>Algebraic Data Types (ADT)</title>
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</head>
<body>
<div class="reveal">
<div class="slides">
<section id="title-slide">
<h1 class="title">Algebraic Data Types (ADT)</h1>
<p class="author">Malte Neuss</p>
</section>
<section id="algebra" class="slide level2">
<h2>Algebra</h2>
<p>Numbers:</p>
<div class="sourceCode" id="cb1"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="dv">2</span> <span class="op">+</span> <span class="dv">2</span> <span class="op">+</span> <span class="dv">2</span> <span class="op">=</span> <span class="dv">3</span> <span class="op">*</span> <span class="dv">2</span></span></code></pre></div>
<div class="fragment">
<p>Types:</p>
<div class="sourceCode" id="cb2"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="kw">class</span> User </span>
<span id="cb2-2"><a href="#cb2-2" aria-hidden="true" tabindex="-1"></a> verified: Bool</span>
<span id="cb2-3"><a href="#cb2-3" aria-hidden="true" tabindex="-1"></a> email: String</span></code></pre></div>
<aside class="notes">
<p>Algebra = Lehre von Symbol-Konstellation und Manipulation</p>
</aside>
</div>
</section>
<section id="content" class="slide level2">
<h2>Content</h2>
<div>
<ul>
<li class="fragment">Product Type</li>
<li class="fragment">Sum Type</li>
<li class="fragment">Examples</li>
</ul>
</div>
<div class="fragment">
<blockquote>
<p><em>Make illegal state unrepresentable</em></p>
</blockquote>
</div>
</section>
<section id="basic-types" class="slide level2">
<h2>Basic Types</h2>
<pre><code>type Void: // 0
type Unit: unit // 1
type Bool: true, false // 2
...
type String: "", "a", "b" ... // infty</code></pre>
</section>
<section id="product-type" class="slide level2">
<h2>Product Type</h2>
<pre><code>type ProductType = Type x Type</code></pre>
<div class="fragment">
<div class="sourceCode" id="cb5"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb5-1"><a href="#cb5-1" aria-hidden="true" tabindex="-1"></a><span class="bu">type</span> User <span class="op">=</span> Bool x String</span></code></pre></div>
</div>
<div class="fragment">
<div class="sourceCode" id="cb6"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb6-1"><a href="#cb6-1" aria-hidden="true" tabindex="-1"></a><span class="kw">class</span> User </span>
<span id="cb6-2"><a href="#cb6-2" aria-hidden="true" tabindex="-1"></a> verified: Bool</span>
<span id="cb6-3"><a href="#cb6-3" aria-hidden="true" tabindex="-1"></a> email: String</span></code></pre></div>
</div>
</section>
<section id="product-type-1" class="slide level2">
<h2>Product Type</h2>
<div class="columns">
<div class="column" style="width:50%;">
<p>Type:</p>
<div class="sourceCode" id="cb7"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb7-1"><a href="#cb7-1" aria-hidden="true" tabindex="-1"></a><span class="bu">type</span> User <span class="op">=</span> Bool x String</span></code></pre></div>
<p>Values:</p>
<div class="sourceCode" id="cb8"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb8-1"><a href="#cb8-1" aria-hidden="true" tabindex="-1"></a>User(true, <span class="st">"[email protected]"</span>)</span>
<span id="cb8-2"><a href="#cb8-2" aria-hidden="true" tabindex="-1"></a>User(false, <span class="st">"[email protected]"</span>)</span>
<span id="cb8-3"><a href="#cb8-3" aria-hidden="true" tabindex="-1"></a>User(true, <span class="st">"[email protected]"</span>)</span>
<span id="cb8-4"><a href="#cb8-4" aria-hidden="true" tabindex="-1"></a>User(false, <span class="st">"[email protected]"</span>)</span>
<span id="cb8-5"><a href="#cb8-5" aria-hidden="true" tabindex="-1"></a>...</span></code></pre></div>
</div><div class="column" style="width:50%;">
<p><img data-src="img/cartesian-product.svg" style="width:90.0%" /></p>
<p><small style="font-size: 9pt"> By Quartl - Own work, CC BY-SA 3.0,
https://commons.wikimedia.org/w/index.php?curid=22436861 </small></p>
</div>
</div>
</section>
<section id="algebra-1" class="slide level2">
<h2>Algebra</h2>
<div class="sourceCode" id="cb9"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb9-1"><a href="#cb9-1" aria-hidden="true" tabindex="-1"></a>Bool x Bool: (true,true) (false,false) (true,false) (false,true)</span>
<span id="cb9-2"><a href="#cb9-2" aria-hidden="true" tabindex="-1"></a> <span class="dv">2</span> x <span class="dv">2</span> <span class="op">=</span> <span class="dv">4</span></span></code></pre></div>
<div class="fragment">
<div class="sourceCode" id="cb10"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb10-1"><a href="#cb10-1" aria-hidden="true" tabindex="-1"></a>Bool x Unit: (true,unit) (false,unit) <span class="op">~</span> Boolean</span>
<span id="cb10-2"><a href="#cb10-2" aria-hidden="true" tabindex="-1"></a> <span class="dv">2</span> x <span class="dv">1</span> <span class="op">=</span> <span class="dv">2</span> </span></code></pre></div>
</div>
<div class="fragment">
<div class="sourceCode" id="cb11"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb11-1"><a href="#cb11-1" aria-hidden="true" tabindex="-1"></a>Bool x Void: (true,???) <span class="op">~</span> Void</span>
<span id="cb11-2"><a href="#cb11-2" aria-hidden="true" tabindex="-1"></a> <span class="dv">2</span> x <span class="dv">0</span> <span class="op">=</span> <span class="dv">0</span></span></code></pre></div>
</div>
</section>
<section id="sum-type" class="slide level2">
<h2>Sum Type</h2>
<div class="sourceCode" id="cb12"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb12-1"><a href="#cb12-1" aria-hidden="true" tabindex="-1"></a><span class="bu">type</span> SumType <span class="op">=</span> Type <span class="op">+</span> Type</span></code></pre></div>
<div class="fragment">
<div class="sourceCode" id="cb13"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb13-1"><a href="#cb13-1" aria-hidden="true" tabindex="-1"></a><span class="bu">type</span> ID <span class="op">=</span> Int <span class="op">+</span> String</span></code></pre></div>
</div>
<div class="fragment">
<div class="sourceCode" id="cb14"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb14-1"><a href="#cb14-1" aria-hidden="true" tabindex="-1"></a><span class="bu">type</span> ID <span class="op">=</span> Int <span class="op">|</span> String Typescript</span></code></pre></div>
</div>
<div class="fragment">
<div class="sourceCode" id="cb15"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb15-1"><a href="#cb15-1" aria-hidden="true" tabindex="-1"></a> ID <span class="op">=</span> Union[<span class="bu">int</span>, <span class="bu">str</span>] Python</span></code></pre></div>
</div>
<div class="fragment">
<div class="sourceCode" id="cb16"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb16-1"><a href="#cb16-1" aria-hidden="true" tabindex="-1"></a>sealed trait ID Scala</span>
<span id="cb16-2"><a href="#cb16-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb16-3"><a href="#cb16-3" aria-hidden="true" tabindex="-1"></a><span class="cf">case</span> <span class="kw">class</span> IntID(Int) extends ID</span>
<span id="cb16-4"><a href="#cb16-4" aria-hidden="true" tabindex="-1"></a><span class="cf">case</span> <span class="kw">class</span> StringID(String) extends ID</span></code></pre></div>
</div>
</section>
<section id="sum-type-1" class="slide level2">
<h2>Sum Type</h2>
<div class="columns">
<div class="column" style="width:50%;">
<p>Type:</p>
<div class="sourceCode" id="cb17"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb17-1"><a href="#cb17-1" aria-hidden="true" tabindex="-1"></a><span class="bu">type</span> ID <span class="op">=</span> Int <span class="op">|</span> String</span></code></pre></div>
<p>Values:</p>
<div class="sourceCode" id="cb18"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb18-1"><a href="#cb18-1" aria-hidden="true" tabindex="-1"></a>myID: ID <span class="op">=</span> <span class="dv">1</span> ✓</span>
<span id="cb18-2"><a href="#cb18-2" aria-hidden="true" tabindex="-1"></a>myID: ID <span class="op">=</span> <span class="st">"123e4567-e89b..."</span> ✓</span>
<span id="cb18-3"><a href="#cb18-3" aria-hidden="true" tabindex="-1"></a>...</span></code></pre></div>
</div><div class="column" style="width:50%;">
<p><img data-src="img/disjoint-sets.svg" style="width:40.0%" /></p>
<p><small style="font-size: 9pt"> By Stephan Kulla (User:Stephan Kulla)
- Own work, CC BY 3.0,
https://commons.wikimedia.org/w/index.php?curid=14978640 </small></p>
</div>
</div>
</section>
<section id="algebra-2" class="slide level2">
<h2>Algebra</h2>
<div class="sourceCode" id="cb19"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb19-1"><a href="#cb19-1" aria-hidden="true" tabindex="-1"></a>Bool <span class="op">|</span> Unit: true, false, unit</span>
<span id="cb19-2"><a href="#cb19-2" aria-hidden="true" tabindex="-1"></a> <span class="dv">2</span> <span class="op">+</span> <span class="dv">1</span> <span class="op">=</span> <span class="dv">3</span> </span></code></pre></div>
<div class="fragment">
<div class="sourceCode" id="cb20"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb20-1"><a href="#cb20-1" aria-hidden="true" tabindex="-1"></a>Bool <span class="op">|</span> Void: true, false <span class="op">~</span> Bool</span>
<span id="cb20-2"><a href="#cb20-2" aria-hidden="true" tabindex="-1"></a> <span class="dv">2</span> <span class="op">+</span> <span class="dv">0</span> <span class="op">=</span> <span class="dv">2</span> <span class="dv">2</span></span></code></pre></div>
</div>
<div class="fragment">
<div class="sourceCode" id="cb21"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb21-1"><a href="#cb21-1" aria-hidden="true" tabindex="-1"></a>Bool <span class="op">|</span> Int: true, false, <span class="dv">1</span>, <span class="dv">2</span>, <span class="dv">3</span>, ...</span>
<span id="cb21-2"><a href="#cb21-2" aria-hidden="true" tabindex="-1"></a> <span class="dv">2</span> <span class="op">+</span> <span class="dv">2</span><span class="op">^</span><span class="dv">64</span> </span></code></pre></div>
</div>
</section>
<section id="unit-type" class="slide level2">
<h2>Unit Type</h2>
<div class="sourceCode" id="cb22"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb22-1"><a href="#cb22-1" aria-hidden="true" tabindex="-1"></a><span class="bu">type</span> BoolOpt <span class="op">=</span> Bool <span class="op">|</span> Unit </span>
<span id="cb22-2"><a href="#cb22-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb22-3"><a href="#cb22-3" aria-hidden="true" tabindex="-1"></a><span class="bu">type</span> Optional[T] <span class="op">=</span> T <span class="op">|</span> Unit </span></code></pre></div>
<div class="fragment">
<div class="sourceCode" id="cb23"><pre
class="sourceCode typescript"><code class="sourceCode typescript"><span id="cb23-1"><a href="#cb23-1" aria-hidden="true" tabindex="-1"></a><span class="kw">type</span> Optional[T] <span class="op">=</span> T <span class="op">|</span> <span class="dt">undefined</span> Typescript</span></code></pre></div>
</div>
<div class="fragment">
<div class="sourceCode" id="cb24"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb24-1"><a href="#cb24-1" aria-hidden="true" tabindex="-1"></a> Optional[T] <span class="op">=</span> Union[T, NoneType] Python</span></code></pre></div>
</div>
<div class="fragment">
<div class="sourceCode" id="cb25"><pre
class="sourceCode scala"><code class="sourceCode scala"><span id="cb25-1"><a href="#cb25-1" aria-hidden="true" tabindex="-1"></a><span class="kw">sealed</span> <span class="kw">trait</span> <span class="ex">Option</span><span class="op">[</span>A<span class="op">]</span> Scala</span>
<span id="cb25-2"><a href="#cb25-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb25-3"><a href="#cb25-3" aria-hidden="true" tabindex="-1"></a><span class="cf">case</span> <span class="kw">class</span> <span class="bu">Some</span><span class="op">[</span>A<span class="op">]</span> <span class="kw">extends</span> <span class="ex">Option</span><span class="op">[</span>A<span class="op">]</span></span>
<span id="cb25-4"><a href="#cb25-4" aria-hidden="true" tabindex="-1"></a><span class="cf">case</span> <span class="kw">object</span> <span class="bu">None</span> <span class="kw">extends</span> <span class="ex">Option</span><span class="op">[</span>A<span class="op">]</span></span></code></pre></div>
</div>
</section>
<section id="examples" class="slide level2">
<h2>Examples</h2>
<p>Modelling Data</p>
<blockquote>
<p>Make illegal state unrepresentable</p>
</blockquote>
</section>
<section id="no-adt-error-codes" class="slide level2">
<h2>No ADT: Error codes</h2>
<div class="sourceCode" id="cb26"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb26-1"><a href="#cb26-1" aria-hidden="true" tabindex="-1"></a><span class="kw">class</span> UserResult:</span>
<span id="cb26-2"><a href="#cb26-2" aria-hidden="true" tabindex="-1"></a> error_code: <span class="bu">int</span> <span class="co"># 0 means ok</span></span>
<span id="cb26-3"><a href="#cb26-3" aria-hidden="true" tabindex="-1"></a> user: User <span class="co"># contains dummy data on error</span></span>
<span id="cb26-4"><a href="#cb26-4" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb26-5"><a href="#cb26-5" aria-hidden="true" tabindex="-1"></a><span class="kw">def</span> fetchUser() <span class="op">-></span> UserResult:</span>
<span id="cb26-6"><a href="#cb26-6" aria-hidden="true" tabindex="-1"></a> <span class="co"># network call</span></span></code></pre></div>
<div class="fragment">
<div class="sourceCode" id="cb27"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb27-1"><a href="#cb27-1" aria-hidden="true" tabindex="-1"></a>myUser <span class="op">=</span> fetchUser()</span>
<span id="cb27-2"><a href="#cb27-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb27-3"><a href="#cb27-3" aria-hidden="true" tabindex="-1"></a><span class="cf">if</span> myUser.error_code <span class="op">==</span> <span class="dv">0</span>:</span>
<span id="cb27-4"><a href="#cb27-4" aria-hidden="true" tabindex="-1"></a> <span class="co"># do sth.</span></span>
<span id="cb27-5"><a href="#cb27-5" aria-hidden="true" tabindex="-1"></a> <span class="co"># what if myUser.user still has dummy data?</span></span>
<span id="cb27-6"><a href="#cb27-6" aria-hidden="true" tabindex="-1"></a><span class="cf">else</span></span>
<span id="cb27-7"><a href="#cb27-7" aria-hidden="true" tabindex="-1"></a> <span class="co"># do fallback</span></span></code></pre></div>
</div>
</section>
<section id="no-adt-error-codes-1" class="slide level2">
<h2>No ADT: Error codes</h2>
<div class="sourceCode" id="cb28"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb28-1"><a href="#cb28-1" aria-hidden="true" tabindex="-1"></a><span class="kw">class</span> UserResult:</span>
<span id="cb28-2"><a href="#cb28-2" aria-hidden="true" tabindex="-1"></a> error_code: <span class="bu">int</span> <span class="co"># 0 means ok</span></span>
<span id="cb28-3"><a href="#cb28-3" aria-hidden="true" tabindex="-1"></a> user: User <span class="co"># contains dummy data on error</span></span></code></pre></div>
<div class="fragment">
<p>Representable valid values:</p>
<div class="sourceCode" id="cb29"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb29-1"><a href="#cb29-1" aria-hidden="true" tabindex="-1"></a>UserResult(<span class="dv">0</span>, User(<span class="st">"John"</span>))</span>
<span id="cb29-2"><a href="#cb29-2" aria-hidden="true" tabindex="-1"></a>UserResult(<span class="dv">0</span>, User(<span class="st">"Jane"</span>))</span>
<span id="cb29-3"><a href="#cb29-3" aria-hidden="true" tabindex="-1"></a>UserResult(<span class="dv">1</span>, User(<span class="st">"dummy"</span>))</span>
<span id="cb29-4"><a href="#cb29-4" aria-hidden="true" tabindex="-1"></a>...</span></code></pre></div>
</div>
<div class="fragment">
<p>Representable invalid values:</p>
<pre><code>UserResult(1, User("John"))
UserResult(0, User("dummy"))</code></pre>
</div>
</section>
<section id="no-adt-exceptions" class="slide level2">
<h2>No ADT: Exceptions</h2>
<div class="sourceCode" id="cb31"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb31-1"><a href="#cb31-1" aria-hidden="true" tabindex="-1"></a><span class="kw">def</span> fetchUser() <span class="op">-></span> User:</span>
<span id="cb31-2"><a href="#cb31-2" aria-hidden="true" tabindex="-1"></a> <span class="co"># raise Exception on error</span></span></code></pre></div>
<div class="fragment">
<div class="sourceCode" id="cb32"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb32-1"><a href="#cb32-1" aria-hidden="true" tabindex="-1"></a>myUser <span class="op">=</span> fetchUser()</span>
<span id="cb32-2"><a href="#cb32-2" aria-hidden="true" tabindex="-1"></a><span class="co"># do sth.</span></span></code></pre></div>
</div>
<div class="fragment">
<div class="sourceCode" id="cb33"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb33-1"><a href="#cb33-1" aria-hidden="true" tabindex="-1"></a><span class="cf">try</span>:</span>
<span id="cb33-2"><a href="#cb33-2" aria-hidden="true" tabindex="-1"></a> myUser <span class="op">=</span> fetchUser()</span>
<span id="cb33-3"><a href="#cb33-3" aria-hidden="true" tabindex="-1"></a> <span class="co"># do sth.</span></span>
<span id="cb33-4"><a href="#cb33-4" aria-hidden="true" tabindex="-1"></a><span class="cf">except</span> ...</span></code></pre></div>
</div>
</section>
<section id="adt-optional" class="slide level2">
<h2>ADT: Optional</h2>
<div class="sourceCode" id="cb34"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb34-1"><a href="#cb34-1" aria-hidden="true" tabindex="-1"></a><span class="bu">type</span> Optional[T] <span class="op">=</span> NoneType <span class="op">|</span> T</span>
<span id="cb34-2"><a href="#cb34-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb34-3"><a href="#cb34-3" aria-hidden="true" tabindex="-1"></a><span class="kw">def</span> fetchUser() <span class="op">-></span> Optional[User]:</span>
<span id="cb34-4"><a href="#cb34-4" aria-hidden="true" tabindex="-1"></a> <span class="co"># return None on error</span></span></code></pre></div>
<div class="fragment">
<div class="sourceCode" id="cb35"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb35-1"><a href="#cb35-1" aria-hidden="true" tabindex="-1"></a>myUser <span class="op">=</span> fetchUser()</span>
<span id="cb35-2"><a href="#cb35-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb35-3"><a href="#cb35-3" aria-hidden="true" tabindex="-1"></a><span class="cf">if</span> <span class="bu">isinstance</span>(myUser, User):</span>
<span id="cb35-4"><a href="#cb35-4" aria-hidden="true" tabindex="-1"></a> <span class="co"># do sth.</span></span>
<span id="cb35-5"><a href="#cb35-5" aria-hidden="true" tabindex="-1"></a><span class="cf">elif</span> <span class="bu">isinstance</span>(myUser, NoneType):</span>
<span id="cb35-6"><a href="#cb35-6" aria-hidden="true" tabindex="-1"></a> <span class="co"># do fallback</span></span></code></pre></div>
</div>
</section>
<section id="adt-either" class="slide level2">
<h2>ADT: Either</h2>
<div class="sourceCode" id="cb36"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb36-1"><a href="#cb36-1" aria-hidden="true" tabindex="-1"></a><span class="bu">type</span> Either[E,T] <span class="op">=</span> E <span class="op">|</span> T</span>
<span id="cb36-2"><a href="#cb36-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb36-3"><a href="#cb36-3" aria-hidden="true" tabindex="-1"></a><span class="kw">def</span> fetchUser() <span class="op">-></span> Either[Error, User]:</span>
<span id="cb36-4"><a href="#cb36-4" aria-hidden="true" tabindex="-1"></a> <span class="co"># return Error value on error</span></span></code></pre></div>
<div class="fragment">
<div class="sourceCode" id="cb37"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb37-1"><a href="#cb37-1" aria-hidden="true" tabindex="-1"></a>myUser <span class="op">=</span> fetchUser()</span>
<span id="cb37-2"><a href="#cb37-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb37-3"><a href="#cb37-3" aria-hidden="true" tabindex="-1"></a><span class="cf">if</span> <span class="bu">isinstance</span>(myUser, User):</span>
<span id="cb37-4"><a href="#cb37-4" aria-hidden="true" tabindex="-1"></a> <span class="co"># do sth.</span></span>
<span id="cb37-5"><a href="#cb37-5" aria-hidden="true" tabindex="-1"></a><span class="cf">elif</span> <span class="bu">isinstance</span>(myUser, Error):</span>
<span id="cb37-6"><a href="#cb37-6" aria-hidden="true" tabindex="-1"></a> <span class="co"># analyze reason</span></span></code></pre></div>
</div>
</section>
<section id="adt-custom" class="slide level2">
<h2>ADT: Custom</h2>
<div class="sourceCode" id="cb38"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb38-1"><a href="#cb38-1" aria-hidden="true" tabindex="-1"></a><span class="bu">type</span> User <span class="op">=</span> Anonymous <span class="op">|</span> LoggedIn</span>
<span id="cb38-2"><a href="#cb38-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb38-3"><a href="#cb38-3" aria-hidden="true" tabindex="-1"></a><span class="kw">def</span> fetchUser() <span class="op">-></span> User:</span></code></pre></div>
<div class="fragment">
<div class="sourceCode" id="cb39"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb39-1"><a href="#cb39-1" aria-hidden="true" tabindex="-1"></a>myUser <span class="op">=</span> fetchUser()</span>
<span id="cb39-2"><a href="#cb39-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb39-3"><a href="#cb39-3" aria-hidden="true" tabindex="-1"></a><span class="cf">if</span> <span class="bu">isinstance</span>(myUser, Anonymous):</span>
<span id="cb39-4"><a href="#cb39-4" aria-hidden="true" tabindex="-1"></a> <span class="co"># do anonymous stuff.</span></span>
<span id="cb39-5"><a href="#cb39-5" aria-hidden="true" tabindex="-1"></a><span class="cf">elif</span> <span class="bu">isinstance</span>(myUser, LoggedIn):</span>
<span id="cb39-6"><a href="#cb39-6" aria-hidden="true" tabindex="-1"></a> <span class="co"># do logged-in stuff.</span></span></code></pre></div>
</div>
</section>
<section id="adt-custom-extended" class="slide level2">
<h2>ADT: Custom extended</h2>
<div class="sourceCode" id="cb40"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb40-1"><a href="#cb40-1" aria-hidden="true" tabindex="-1"></a><span class="bu">type</span> User <span class="op">=</span> Anonymous <span class="op">|</span> LoggedIn <span class="op">|</span> Admin</span>
<span id="cb40-2"><a href="#cb40-2" aria-hidden="true" tabindex="-1"></a> <span class="co"># !new!</span></span>
<span id="cb40-3"><a href="#cb40-3" aria-hidden="true" tabindex="-1"></a><span class="kw">def</span> fetchUser() <span class="op">-></span> User:</span></code></pre></div>
<div class="fragment">
<div class="sourceCode" id="cb41"><pre
class="sourceCode python"><code class="sourceCode python"><span id="cb41-1"><a href="#cb41-1" aria-hidden="true" tabindex="-1"></a>myUser <span class="op">=</span> fetchUser()</span>
<span id="cb41-2"><a href="#cb41-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb41-3"><a href="#cb41-3" aria-hidden="true" tabindex="-1"></a><span class="cf">if</span> <span class="bu">isinstance</span>(myUser, Anonymous):</span>
<span id="cb41-4"><a href="#cb41-4" aria-hidden="true" tabindex="-1"></a> <span class="co"># do anonymous stuff.</span></span>
<span id="cb41-5"><a href="#cb41-5" aria-hidden="true" tabindex="-1"></a><span class="cf">elif</span> <span class="bu">isinstance</span>(myUser, LoggedIn):</span>
<span id="cb41-6"><a href="#cb41-6" aria-hidden="true" tabindex="-1"></a> <span class="co"># do logged-in stuff.</span></span>
<span id="cb41-7"><a href="#cb41-7" aria-hidden="true" tabindex="-1"></a><span class="op">!!!</span> Compiler error: forgot Admin case <span class="op">!!!</span></span></code></pre></div>
</div>
</section>
<section id="further-topics" class="slide level2">
<h2>Further Topics</h2>
<div class="columns">
<div class="column" style="width:50%;">
<ul>
<li>Scala</li>
<li>Haskell</li>
<li>Rust</li>
<li>Dependent Types</li>
<li>Linear Types</li>
</ul>
</div><div class="column" style="width:50%;">
<p><small> Category Theory </small></p>
<p><img data-src="img/category_theory.svg" style="width:50.0%" /></p>
<ul>
<li>Functor (map)</li>
<li>Monad (flatMap)</li>
<li>…</li>
</ul>
</div>
</div>
<aside class="notes">
<p>Image is public domain</p>
</aside>
</section>
<section id="section" class="slide level2">
<h2></h2>
<p>Thanks</p>
</section>
</div>
</div>
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