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<!DOCTYPE html>
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<title>Intro to Haskell for Erlangers</title>
<link rel="stylesheet" href="css/slides.css"/>
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<script src="js/slides.js"></script>
</head>
<body>
<div class="reveal">
<div class="slides">
<section id="title" class="slide level1">
<h1></h1>
<h1>
Intro to Haskell<br> for Erlangers
</h1>
<h3>
Bob Ippolito (<a href="https://twitter.com/etrepum"><span class="citation" data-cites="etrepum">@etrepum</span></a>)<br> Erlang Factory SF<br> March 7, 2014
</h3>
<h4>
<a href="http://bob.ippoli.to/haskell-for-erlangers-2014/">bob.ippoli.to/haskell-for-erlangers-2014</a>
</h4>
</section>
<section id="who-am-i" class="slide level1">
<h1>Who am I?</h1>
<ul>
<li>Not classically trained in CS</li>
<li>Erlang user since 2006 (Mochi Media, mochiweb, etc.)</li>
<li>Haskell user since 2012 (ported <a href="http://exercism.io">exercism.io</a> curriculum)</li>
<li>Currently teaching web technologies to teenagers with <a href="http://www.missionbit.com/">Mission Bit</a></li>
<li>Doing a bit of advising/investing in startups</li>
</ul>
</section>
<section id="why-learn-haskell" class="slide level1">
<h1>Why learn Haskell?</h1>
<ul>
<li>I learn a lot of from studying new languages</li>
<li>Types are supposed to help you write better software</li>
<li>I like QuickCheck and Dialyzer</li>
<li>Good support for parallelism and concurrency</li>
<li>Will help me understand more CS papers</li>
</ul>
</section>
<section id="cost-of-concurrency" class="slide level1">
<h1></h1>
<p>RAM footprint per unit of concurrency (approx)</p>
<table id="concurrency-table">
<tr class="haskell">
<td class="num">
1.3KB
</td>
<td class="name">
<div class="bar-ctr"><div class="bar"></div></div>
<span>Haskell ThreadId + MVar (GHC 7.6.3, 64-bit)</span>
</td>
</tr>
<tr class="erlang">
<td class="num">
2.6 KB
</td>
<td class="name">
<div class="bar-ctr"><div class="bar"></div></div>
<span>Erlang process (64-bit)</span>
</td>
</tr>
<tr class="go">
<td class="num">
8.0 KB
</td>
<td class="name">
<div class="bar-ctr"><div class="bar"></div></div>
<span>Go goroutine</span>
</td>
</tr>
<tr class="java-min">
<td class="num">
64.0 KB
</td>
<td class="name">
<div class="bar-ctr"><div class="bar"></div></div>
<span>Java thread stack (minimum)</span>
</td>
</tr>
<tr class="c-min">
<td class="num">
64.0 KB
</td>
<td class="name">
<div class="bar-ctr"><div class="bar"></div></div>
<span>C pthread stack (minimum)</span>
</td>
</tr>
<tr class="placeholder"><td colspan="2"><hr/></td></td>
<tr class="java">
<td class="num">
1 MB
</td>
<td class="name">
<div class="bar-ctr"><div class="bar"></div></div>
<span>Java thread stack (default)</span>
</td>
</tr>
<tr class="c">
<td class="num">
8 MB
</td>
<td class="name">
<div class="bar-ctr"><div class="bar"></div></div>
<span>C pthread stack (default, 64-bit Mac OS X)</span>
</td>
</tr>
</table>
</section>
<section id="starting-out" class="slide level1">
<h1>Starting out</h1>
<ul>
<li>Intimidated by Haskell for years</li>
<li>Took a class while at Facebook</li>
<li>Read several books</li>
<li>Deliberate practice</li>
</ul>
</section>
<section id="haskells-appeal" class="slide level1">
<h1>Haskell's Appeal</h1>
<ul>
<li>Abstractions can often be used without penalty</li>
<li>Efficient parallel and concurrent programming</li>
<li>Type system makes maintenance easier</li>
<li>Nice syntax (not too heavy or lightweight)</li>
<li>Fantastic community & ecosystem</li>
</ul>
</section>
<section id="haskell-history" class="slide level1">
<h1>Haskell</h1>
<!-- http://www.haskell.org/haskellwiki/Haskell_Brooks_Curry -->
<figure>
<img src="img/HaskellBCurry.jpg">
<figcaption>
<strong>Haskell</strong> B. Curry
</figcaption>
</figure>
</section>
<section id="early-history" class="slide level1">
<h1>Early History</h1>
<!-- http://www.haskell.org/onlinereport/preface-jfp.html
http://research.microsoft.com/en-us/um/people/simonpj/papers/history-of-haskell/history.pdf
-->
<dl>
<dt>1987</dt>
<dd>More than a dozen non-strict FP languages in use
</dd>
<dd>FCPA '87 meeting (Peyton Jones, Hudak, et. al.)
</dd>
<dd>Formed FPLang committee
</dd>
<dd>Wanted to base language on Miranda, but Turner declined
</dd>
<dt>1988</dt>
<dd>Chose the name Haskell
</dd>
<dd>Hudak and Wadler chosen to be editors of the report
</dd>
<dt>1990 (April 1st!)</dt>
<dd>Haskell 1.0 report published (125 pages)
</dd>
</dl>
</section>
<section id="ifip-1992" class="slide level1">
<h1></h1>
<!-- extracted from history.pdf -->
<figure>
<img src="img/ifip-1992.jpg" />
<figcaption>
IFIP 1992 Working Group
</figcaption>
</figure>
</section>
<section id="ifip-1992-erl" class="slide level1">
<h1></h1>
<!-- extracted from history.pdf -->
<figure>
<img src="img/ifip-1992-erl.jpg" />
<figcaption>
John Hughes (QuickCheck), Philip Wadler (Subtyping for Erlang)
</figcaption>
</figure>
</section>
<section id="evolution" class="slide level1">
<h1>Evolution</h1>
<dl>
<dt>1992</dt>
<dd>Glasgow Haskell Compiler (GHC)
</dd>
<dt>1996</dt>
<dd>Haskell 1.3 - Monadic I/O, seq, strictness annotations
</dd>
<dt>1999</dt>
<dd>Haskell 98 - Commitment to stability
</dd>
<dt>2002</dt>
<dd>Revised Haskell 98 (260 pages)
</dd>
<dt>2010</dt>
<dd>Haskell 2010 (300 pages)
</dd>
</dl>
</section>
<section id="domain" class="slide level1">
<h1>Domain</h1>
<p><strong>General Purpose</strong></p>
<ul>
<li>Very effective for parsing and compilation</li>
<li>Great for DSEL (Domain Specific Embedded Languages)</li>
<li>Has been popular in academia for some time</li>
<li>Becoming more popular in industry</li>
</ul>
</section>
<section id="commercial-use" class="slide level1">
<h1>Commercial Use</h1>
<!-- http://www.haskell.org/haskellwiki/Haskell_in_industry -->
<dl>
<dt>Internet</dt>
<dd><a href="https://skillsmatter.com/skillscasts/4429-simon-marlow">Facebook</a> - Haxl rule engine "fighting spam with pure functions"
</dd>
<dt>Biotech</dt>
<dd><a href="http://cufp.galois.com/2008/abstracts.html#BalabanDavid">Amgen</a> - informatics, simulation
</dd>
<dt>Finance</dt>
<dd><a href="http://cufp.galois.com/2006/abstracts.html#HowardMansell">Credit Suisse</a> - quantitative modeling
</dd>
<dd><a href="http://lambda-the-ultimate.org/node/3331">Barclays</a> - DSEL for exotic equity derivatives
</dd>
<dd><a href="http://cufp.galois.com/2008/abstracts.html#PolakowJeff">Deutsche Bank</a> - trading group infrastructure
</dd>
<dd><a href="http://haskell.org/communities/05-2010/html/report.html#sect7.6">Tsuru Capital</a> - trading platform
</dd>
<dd><a href="https://www.youtube.com/watch?v=o3m2NkusI9k">McGraw-Hill Financial</a> - report generation (with <a href="http://ermine-language.github.io/ermine/">ermine</a>)
</dd>
<dt>Semiconductor Design</dt>
<dd><a href="http://www.slideshare.net/mansu/bluespec-talk">Bluespec</a> - high-level language for chip design
</dd>
</dl>
</section>
<section id="consumer-apps" class="slide level1">
<h1>Consumer Apps</h1>
<!--
Bump:
* https://github.com/MichaelXavier/Angel
* http://devblog.bu.mp/post/40786229350/haskell-at-bump
* https://www.fpcomplete.com/wp-content/uploads/2013/05/Bump%20case%20study.pdf
Silk:
* http://engineering.silk.co/post/31920990633/why-we-use-haskell
* https://www.fpcomplete.com/wp-content/uploads/2013/05/Silk%20case%20study.pdf
-->
<dl>
<dt><a href="https://www.silk.co/">Silk</a></dt>
<dd>"A platform for sharing collections about anything"
</dd>
<dt><a href="http://chordify.net/">Chordify</a></dt>
<dd>"Chord transcription for the masses"
</dd>
<dt><a href="https://bu.mp/">Bump</a> (Google, Sep 2013)</dt>
<dd>"Send files, videos, everything!" Mobile + web.
</dd>
<dt><a href="http://www.mailrank.com/">MailRank</a> (Facebook, Nov 2011)</dt>
<dd>Email inbox prioritization. Shuttered post-acquisition.
</dd>
<dt><a href="https://bazqux.com/">Bazqux</a></dt>
<dd>"RSS reader that shows comments to posts"
</dd>
</dl>
</section>
<section id="commercial-services" class="slide level1">
<h1>Commercial Services</h1>
<!--
Janrain:
* https://www.fpcomplete.com/wp-content/uploads/2013/05/janrain%20case%20study.pdf
Scrive:
* https://www.fpcomplete.com/wp-content/uploads/Scrive-case-study.pdf
Spaceport:
* https://github.com/sibblingz/spaceport-sp-opensource
Skedge:
* http://www.youtube.com/watch?v=BveDrw9CwEg
* http://cufp.org/sites/all/files/slides/2013/trinkle.pdf
-->
<dl>
<dt><a href="http://janrain.com/">janrain</a></dt>
<dd>User management platform.
</dd>
<dt><a href="http://spaceport.io/">Spaceport</a> (Facebook, Aug 2013)</dt>
<dd>Mobile game framework using ActionScript 3
</dd>
<dt><a href="http://scrive.com/">scrive</a></dt>
<dd>E-signing service (nordic market)
</dd>
<dt><a href="http://www.openbrain.co.uk/">OpenBrain</a></dt>
<dd>Computing platform for scientific and business analytics
</dd>
<dt><a href="http://skedge.me/">skedge.me</a></dt>
<dd>Enterprise appointment scheduling
</dd>
</dl>
</section>
<section id="compilers" class="slide level1">
<h1>Compilers</h1>
<dl>
<dt>Haskell</dt>
<dd><a href="http://www.haskell.org/ghc/">GHC</a>, <a href="http://ajhc.metasepi.org/">Ajhc</a>, <a href="https://github.com/valderman/haste-compiler">Haste</a>, <a href="https://github.com/ghcjs/ghcjs">GHCJS</a>
</dd>
<dt>Dependently typed</dt>
<dd><a href="http://wiki.portal.chalmers.se/agda/">Agda</a> - also an interactive proof assistant!
</dd>
<dd><a href="http://www.idris-lang.org/">Idris</a> - general purpose
</dd>
<dt>Compile to JavaScript</dt>
<dd><a href="http://elm-lang.org/">Elm</a> - functional reactive in the browser
</dd>
<dd><a href="http://fay-lang.org/">Fay</a> - Haskell subset
</dd>
<dt>Imperative</dt>
<dd><a href="http://pugscode.org/">Pugs</a> - first Perl 6 implementation
</dd>
</dl>
</section>
<section id="standalone-apps" class="slide level1">
<h1>Standalone Apps</h1>
<dl>
<dt><a href="http://johnmacfarlane.net/pandoc/">Pandoc</a></dt>
<dd>Markup swiss-army knife (used to make these slides!)
</dd>
<dt><a href="http://darcs.net/">Darcs</a></dt>
<dd>Distributed revision control system (like Git or Mercurial)
</dd>
<dt><a href="http://xmonad.org/">xmonad</a></dt>
<dd>"the tiling window manager that rocks"
</dd>
<dt><a href="http://gitit.net/">Gitit</a></dt>
<dd>Wiki backed by Git, Darcs, or Mercurial
</dd>
<dt><a href="http://git-annex.branchable.com/">git-annex</a></dt>
<dd>Manage large files with git (similar to Dropbox)
</dd>
<dt><a href="http://www.implicitcad.org/">ImplicitCAD</a></dt>
<dd>Programmatic Solid 3D CAD modeler
</dd>
</dl>
</section>
<section id="haskell-platform" class="slide level1">
<h1>Haskell Platform</h1>
<h3>
Haskell: Batteries Included
</h3>
<ul>
<li><a href="http://www.haskell.org/platform">http://www.haskell.org/platform</a></li>
<li>GHC compiler and GHCi interpreter</li>
<li>Robust and stable set of vetted packages</li>
<li><a href="http://www.haskell.org/cabal/">Cabal</a>; easily fetch more packages from <a href="http://hackage.haskell.org/">Hackage</a></li>
</ul>
</section>
<section id="editor-support" class="slide level1">
<h1>Editor Support</h1>
<dl>
<dt>Emacs</dt>
<dd><a href="http://www.mew.org/~kazu/proj/ghc-mod/en/">ghc-mod</a> + <a href="http://community.haskell.org/~ndm/hlint/">HLint</a>
</dd>
<dt>Vim</dt>
<dd><a href="https://github.com/bitc/hdevtools">hdevtools</a> + <a href="https://github.com/scrooloose/syntastic">Syntastic</a> + <a href="https://github.com/bitc/vim-hdevtools">vim-hdevtools</a>
</dd>
<dt>Sublime Text</dt>
<dd><a href="https://github.com/bitc/hdevtools">hdevtools</a> + <a href="https://github.com/SublimeHaskell/SublimeHaskell">SublimeHaskell</a>
</dd>
<dt>Eclipse</dt>
<dd><a href="http://eclipsefp.github.io/">EclipseFP</a> + <a href="http://community.haskell.org/~ndm/hlint/">HLint</a>
</dd>
<dt>Web</dt>
<dd><a href="https://www.fpcomplete.com/business/haskell-center/overview/">FP Haskell Center</a>
</dd>
</dl>
</section>
<section id="haskell-syntax" class="slide level1">
<h1>Haskell Syntax</h1>
<dl>
<dt>Types</dt>
<dd>Defines types and typeclasses
</dd>
<dd><p>Constructors and record accessors become values</p>
</dd>
<dt>Values</dt>
<dd>Named bindings
</dd>
<dd>Instances of constructors
</dd>
<dd>Functions
</dd>
<dd><p>Control flow</p>
</dd>
</dl>
</section>
<section id="relative-to-erlang" class="slide level1">
<h1>Relative to Erlang</h1>
<ul>
<li>Syntax is minimal & familiar</li>
<li>Haskell's pattern matching is not as clever as Erlang's</li>
<li>Types are kinda like having Dialyzer for every compile<br> (although Dialyzer is really quite different!)</li>
<li>Typeclasses are nice, Erlang doesn't have them</li>
<li>Erlang is probably (much) better for long-running systems</li>
</ul>
</section>
<section id="listsmap2" class="slide level1 big-code">
<h1>lists:map/2</h1>
<pre class="sourceCode erlang"><code class="sourceCode erlang"><span class="fu">map(</span><span class="dt">F</span><span class="fu">,</span> <span class="fu">[</span><span class="dt">H</span><span class="fu">|</span><span class="dt">T</span><span class="fu">])</span> <span class="kw">-></span>
<span class="fu">[</span><span class="dt">F</span><span class="fu">(</span><span class="dt">H</span><span class="fu">)|map(</span><span class="dt">F</span><span class="fu">,</span> <span class="dt">T</span><span class="fu">)];</span>
<span class="fu">map(</span><span class="dt">F</span><span class="fu">,</span> <span class="fu">[])</span> <span class="ch">when</span> <span class="fu">is_function(</span><span class="dt">F</span><span class="fu">,</span> <span class="dv">1</span><span class="fu">)</span> <span class="kw">-></span> <span class="fu">[].</span></code></pre>
</section>
<section id="map" class="slide level1 big-code">
<h1>map</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell">map _ [] <span class="fu">=</span> []
map f (x<span class="fu">:</span>xs) <span class="fu">=</span> f x <span class="fu">:</span> map f xs</code></pre>
</section>
<section id="listsmap2-typed" class="slide level1 big-code">
<h1>lists:map/2 (typed)</h1>
<pre class="sourceCode erlang"><code class="sourceCode erlang"><span class="kw">-</span><span class="ch">spec</span> <span class="fu">map(</span><span class="dt">Fun</span><span class="fu">,</span> <span class="dt">List1</span><span class="fu">)</span> <span class="kw">-></span> <span class="dt">List2</span> <span class="ch">when</span>
<span class="dt">Fun</span> <span class="fu">::</span> <span class="kw">fun</span><span class="fu">((</span><span class="dt">A</span><span class="fu">)</span> <span class="kw">-></span> <span class="dt">B</span><span class="fu">),</span>
<span class="dt">List1</span> <span class="fu">::</span> <span class="fu">[</span><span class="dt">A</span><span class="fu">],</span>
<span class="dt">List2</span> <span class="fu">::</span> <span class="fu">[</span><span class="dt">B</span><span class="fu">],</span>
<span class="dt">A</span> <span class="fu">::</span> <span class="fu">term(),</span>
<span class="dt">B</span> <span class="fu">::</span> <span class="fu">term().</span>
<span class="fu">map(</span><span class="dt">F</span><span class="fu">,</span> <span class="fu">[</span><span class="dt">H</span><span class="fu">|</span><span class="dt">T</span><span class="fu">])</span> <span class="kw">-></span>
<span class="fu">[</span><span class="dt">F</span><span class="fu">(</span><span class="dt">H</span><span class="fu">)|map(</span><span class="dt">F</span><span class="fu">,</span> <span class="dt">T</span><span class="fu">)];</span>
<span class="fu">map(</span><span class="dt">F</span><span class="fu">,</span> <span class="fu">[])</span> <span class="ch">when</span> <span class="fu">is_function(</span><span class="dt">F</span><span class="fu">,</span> <span class="dv">1</span><span class="fu">)</span> <span class="kw">-></span> <span class="fu">[].</span></code></pre>
</section>
<section id="map-typed" class="slide level1 big-code">
<h1>map (typed)</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell">map<span class="ot"> ::</span> (a <span class="ot">-></span> b) <span class="ot">-></span> [a] <span class="ot">-></span> [b]
map _ [] <span class="fu">=</span> []
map f (x<span class="fu">:</span>xs) <span class="fu">=</span> f x <span class="fu">:</span> map f xs</code></pre>
</section>
<section id="listsfoldr3" class="slide level1 big-code">
<h1>lists:foldr/3</h1>
<pre class="sourceCode erlang"><code class="sourceCode erlang"><span class="kw">-</span><span class="ch">spec</span> <span class="fu">foldr(</span><span class="dt">Fun</span><span class="fu">,</span> <span class="dt">Acc0</span><span class="fu">,</span> <span class="dt">List</span><span class="fu">)</span> <span class="kw">-></span> <span class="dt">Acc1</span> <span class="ch">when</span>
<span class="dt">Fun</span> <span class="fu">::</span> <span class="kw">fun</span><span class="fu">((</span><span class="dt">Elem</span> <span class="fu">::</span> <span class="dt">T</span><span class="fu">,</span> <span class="dt">AccIn</span><span class="fu">)</span> <span class="kw">-></span> <span class="dt">AccOut</span><span class="fu">),</span>
<span class="dt">Acc0</span> <span class="fu">::</span> <span class="fu">term(),</span>
<span class="dt">Acc1</span> <span class="fu">::</span> <span class="fu">term(),</span>
<span class="dt">AccIn</span> <span class="fu">::</span> <span class="fu">term(),</span>
<span class="dt">AccOut</span> <span class="fu">::</span> <span class="fu">term(),</span>
<span class="dt">List</span> <span class="fu">::</span> <span class="fu">[</span><span class="dt">T</span><span class="fu">],</span>
<span class="dt">T</span> <span class="fu">::</span> <span class="fu">term().</span>
<span class="fu">foldr(</span><span class="dt">F</span><span class="fu">,</span> <span class="dt">Accu</span><span class="fu">,</span> <span class="fu">[</span><span class="dt">Hd</span><span class="fu">|</span><span class="dt">Tail</span><span class="fu">])</span> <span class="kw">-></span>
<span class="dt">F</span><span class="fu">(</span><span class="dt">Hd</span><span class="fu">,</span> <span class="fu">foldr(</span><span class="dt">F</span><span class="fu">,</span> <span class="dt">Accu</span><span class="fu">,</span> <span class="dt">Tail</span><span class="fu">));</span>
<span class="fu">foldr(</span><span class="dt">F</span><span class="fu">,</span> <span class="dt">Accu</span><span class="fu">,</span> <span class="fu">[])</span> <span class="ch">when</span> <span class="fu">is_function(</span><span class="dt">F</span><span class="fu">,</span> <span class="dv">2</span><span class="fu">)</span> <span class="kw">-></span> <span class="dt">Accu</span><span class="fu">.</span></code></pre>
</section>
<section id="foldr" class="slide level1 big-code">
<h1>foldr</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell">foldr<span class="ot"> ::</span> (a <span class="ot">-></span> b <span class="ot">-></span> b) <span class="ot">-></span> b <span class="ot">-></span> [a] <span class="ot">-></span> b
foldr k z <span class="fu">=</span> go
<span class="kw">where</span>
go [] <span class="fu">=</span> z
go (y<span class="fu">:</span>ys) <span class="fu">=</span> y <span class="ot">`k`</span> go ys</code></pre>
</section>
<section id="sum-type" class="slide level1 small-title big-code">
<h1>Sum Type</h1>
<pre class="sourceCode erlang"><code class="sourceCode erlang"><span class="co">%% sum type, 3 possible values</span>
<span class="kw">-</span><span class="ch">type</span> <span class="fu">choice()</span> <span class="fu">::</span> <span class="ch">definitely</span>
<span class="fu">|</span> <span class="ch">possibly</span>
<span class="fu">|</span> <span class="ch">no_way</span><span class="fu">.</span></code></pre>
</section>
<section id="sum-type-1" class="slide level1 small-title big-code">
<h1>Sum Type</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="co">-- sum type, 3 possible values</span>
<span class="kw">data</span> <span class="dt">Choice</span> <span class="fu">=</span> <span class="dt">Definitely</span>
<span class="fu">|</span> <span class="dt">Possibly</span>
<span class="fu">|</span> <span class="dt">NoWay</span></code></pre>
</section>
<section id="product-type" class="slide level1 small-title big-code">
<h1>Product Type</h1>
<pre class="sourceCode erlang"><code class="sourceCode erlang"><span class="co">%% product type, 9 possible values (3 * 3)</span>
<span class="kw">-</span><span class="ch">type</span> <span class="fu">choices()</span> <span class="fu">::</span> <span class="fu">{choice(),</span> <span class="fu">choice()}.</span></code></pre>
</section>
<section id="product-type-1" class="slide level1 small-title big-code">
<h1>Product Type</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="co">-- product type, 9 possible values (3 * 3)</span>
<span class="kw">data</span> <span class="dt">Choices</span> <span class="fu">=</span> <span class="dt">Choices</span> <span class="dt">Choice</span> <span class="dt">Choice</span>
<span class="co">-- as a tuple with a type alias</span>
<span class="co">-- NOT THE SAME AS ABOVE! :)</span>
<span class="kw">type</span> <span class="dt">Choices</span> <span class="fu">=</span> (<span class="dt">Choice</span>, <span class="dt">Choice</span>)</code></pre>
</section>
<section id="product-type-record" class="slide level1 small-title big-code">
<h1>Product Type (Record)</h1>
<pre class="sourceCode erlang"><code class="sourceCode erlang"><span class="co">%% record syntax</span>
<span class="kw">-</span><span class="fu">record(</span><span class="ch">choices</span><span class="fu">,</span>
<span class="ch">fst_choice</span> <span class="fu">::</span> <span class="fu">choice(),</span>
<span class="ch">snd_choice</span> <span class="fu">::</span> <span class="fu">choice()).</span>
<span class="co">%% getters need to be implemented manually</span>
<span class="kw">-</span><span class="ch">spec</span> <span class="fu">fst_choice(#</span><span class="ch">choices</span><span class="fu">{})</span> <span class="kw">-></span> <span class="fu">choice().</span>
<span class="fu">fst_choice(#</span><span class="ch">choices</span><span class="fu">{</span><span class="ch">fst_choices</span><span class="kw">=</span><span class="dt">X</span><span class="fu">})</span> <span class="kw">-></span> <span class="dt">X</span><span class="fu">.</span>
<span class="kw">-</span><span class="ch">spec</span> <span class="fu">snd_choice(#</span><span class="ch">choices</span><span class="fu">{})</span> <span class="kw">-></span> <span class="fu">choice().</span>
<span class="fu">snd_choice(#</span><span class="ch">choices</span><span class="fu">{</span><span class="ch">snd_choices</span><span class="kw">=</span><span class="dt">X</span><span class="fu">})</span> <span class="kw">-></span> <span class="dt">X</span><span class="fu">.</span></code></pre>
</section>
<section id="product-type-record-1" class="slide level1 small-title big-code">
<h1>Product Type (Record)</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="co">-- record syntax defines accessors automatically</span>
<span class="kw">data</span> <span class="dt">Choices</span> <span class="fu">=</span>
<span class="dt">Choices</span> {<span class="ot"> fstChoice ::</span> <span class="dt">Choice</span>
,<span class="ot"> sndChoice ::</span> <span class="dt">Choice</span>
}
<span class="co">-- these getters are automatically defined</span>
<span class="ot">fstChoice ::</span> <span class="dt">Choices</span> <span class="ot">-></span> <span class="dt">Choice</span>
fstChoice (<span class="dt">Choices</span> { fstChoice <span class="fu">=</span> x }) <span class="fu">=</span> x
<span class="ot">sndChoice ::</span> <span class="dt">Choices</span> <span class="ot">-></span> <span class="dt">Choice</span>
sndChoice (<span class="dt">Choices</span> { sndChoice <span class="fu">=</span> x }) <span class="fu">=</span> x</code></pre>
</section>
<section id="abstract-data-type" class="slide level1 small-title big-code">
<h1>Abstract Data Type</h1>
<pre class="sourceCode erlang"><code class="sourceCode erlang"><span class="co">%% abstract data type for a list</span>
<span class="kw">-</span><span class="ch">type</span> <span class="fu">cons(</span><span class="dt">A</span><span class="fu">)</span> <span class="fu">::</span> <span class="ch">nil</span>
<span class="fu">|</span> <span class="fu">{</span><span class="ch">cons</span><span class="fu">,</span> <span class="dt">A</span><span class="fu">,</span> <span class="fu">cons(</span><span class="dt">A</span><span class="fu">)}.</span></code></pre>
</section>
<section id="abstract-data-type-1" class="slide level1 small-title big-code">
<h1>Abstract Data Type</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="co">-- abstract data type for a list</span>
<span class="kw">data</span> <span class="dt">List</span> a <span class="fu">=</span> <span class="dt">Nil</span>
<span class="fu">|</span> <span class="dt">Cons</span> a (<span class="dt">List</span> a)</code></pre>
</section>
<section id="types-and-constructors-1" class="slide level1 small-title big-code highlight-type">
<h1></h1>
<h1>
<span class="hl-type">Types</span> and <span class="hl-constructor">Constructors</span>
</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="kw">data</span> <span class="dt hl-type">Choice</span> <span class="fu">=</span> <span class="dt hl-constructor">Definitely</span>
<span class="fu">|</span> <span class="dt hl-constructor">Possibly</span>
<span class="fu">|</span> <span class="dt hl-constructor">NoWay</span>
<span class="kw">data</span> <span class="dt hl-type">Choices</span> <span class="fu">=</span> <span class="dt hl-constructor">Choices</span> <span class="dt hl-type">Choice</span> <span class="dt hl-type">Choice</span>
<span class="ot">mkChoices ::</span> <span class="dt hl-type">Choice</span> <span class="ot">-></span> <span class="dt hl-type">Choice</span> <span class="ot">-></span> <span class="dt hl-type">Choices</span>
mkChoices a b <span class="fu">=</span> <span class="dt hl-constructor">Choices</span> a b
<span class="ot">fstChoice ::</span> <span class="dt hl-type">Choices</span> <span class="ot">-></span> <span class="dt hl-type">Choice</span>
fstChoice (<span class="dt hl-constructor">Choices</span> a _) <span class="fu">=</span> a</code></pre>
</section>
<section id="types-and-constructors-2" class="slide level1 small-title big-code highlight-constructor">
<h1></h1>
<h1>
<span class="hl-type">Types</span> and <span class="hl-constructor">Constructors</span>
</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="kw">data</span> <span class="dt hl-type">Choice</span> <span class="fu">=</span> <span class="dt hl-constructor">Definitely</span>
<span class="fu">|</span> <span class="dt hl-constructor">Possibly</span>
<span class="fu">|</span> <span class="dt hl-constructor">NoWay</span>
<span class="kw">data</span> <span class="dt hl-type">Choices</span> <span class="fu">=</span> <span class="dt hl-constructor">Choices</span> <span class="dt hl-type">Choice</span> <span class="dt hl-type">Choice</span>
<span class="ot">mkChoices ::</span> <span class="dt hl-type">Choice</span> <span class="ot">-></span> <span class="dt hl-type">Choice</span> <span class="ot">-></span> <span class="dt hl-type">Choices</span>
mkChoices a b <span class="fu">=</span> <span class="dt hl-constructor">Choices</span> a b
<span class="ot">fstChoice ::</span> <span class="dt hl-type">Choices</span> <span class="ot">-></span> <span class="dt hl-type">Choice</span>
fstChoice (<span class="dt hl-constructor">Choices</span> a _) <span class="fu">=</span> a</code></pre>
</section>
<section id="using-types" class="slide level1 big-code">
<h1>Using Types</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="co">-- Values can be annotated in-line</span>
<span class="dv">2</span> <span class="fu">^</span> (<span class="dv">1</span><span class="ot"> ::</span> <span class="dt">Int</span>)
<span class="co">-- Bindings can be annotated</span>
<span class="ot">success ::</span> a <span class="ot">-></span> <span class="dt">Maybe</span> a
<span class="co">-- Constructors are values</span>
<span class="co">-- (and product constructors are functions)</span>
success x <span class="fu">=</span> <span class="dt">Just</span> x
<span class="co">-- Constructors can be pattern matched</span>
<span class="co">-- _ is a wildcard</span>
<span class="kw">case</span> success <span class="dt">True</span> <span class="kw">of</span>
<span class="dt">Just</span> <span class="dt">True</span> <span class="ot">-></span> ()
_ <span class="ot">-></span> ()</code></pre>
</section>
<section id="pattern-matching" class="slide level1 big-code">
<h1>Pattern Matching</h1>
<pre class="sourceCode erlang"><code class="sourceCode erlang"><span class="kw">-</span><span class="ch">spec</span> <span class="fu">is_just({</span><span class="ch">just</span><span class="fu">,</span> <span class="dt">A</span><span class="fu">}</span> <span class="fu">|</span> <span class="ch">nothing</span><span class="fu">)</span> <span class="kw">-></span> <span class="fu">boolean().</span>
<span class="fu">is_just({</span><span class="ch">just</span><span class="fu">,</span> <span class="dt">_</span><span class="fu">})</span> <span class="kw">-></span>
<span class="ch">true</span><span class="fu">;</span>
<span class="fu">is_just(</span><span class="ch">nothing</span><span class="fu">)</span> <span class="kw">-></span>
<span class="ch">false</span><span class="fu">.</span></code></pre>
</section>
<section id="pattern-matching-1" class="slide level1 big-code">
<h1>Pattern Matching</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="ot">isJust ::</span> <span class="dt">Maybe</span> a <span class="ot">-></span> <span class="dt">Bool</span>
isJust (<span class="dt">Just</span> _) <span class="fu">=</span> <span class="dt">True</span>
isJust <span class="dt">Nothing</span> <span class="fu">=</span> <span class="dt">False</span></code></pre>
</section>
<section id="pattern-matching-2" class="slide level1 big-code">
<h1>Pattern Matching</h1>
<p>Erlang's pattern matching allows non-linear patterns.</p>
<pre class="sourceCode erlang"><code class="sourceCode erlang"><span class="kw">-</span><span class="ch">spec</span> <span class="fu">is_equal(</span><span class="dt">A</span><span class="fu">,</span> <span class="dt">A</span><span class="fu">)</span> <span class="kw">-></span> <span class="fu">boolean()</span> <span class="ch">when</span>
<span class="dt">A</span> <span class="fu">::</span> <span class="fu">term().</span>
<span class="fu">is_equal(</span><span class="dt">A</span><span class="fu">,</span> <span class="dt">A</span><span class="fu">)</span> <span class="kw">-></span> <span class="ch">true</span><span class="fu">;</span>
<span class="fu">is_equal(</span><span class="dt">_</span><span class="fu">,</span> <span class="dt">_</span><span class="fu">)</span> <span class="kw">-></span> <span class="ch">false</span><span class="fu">.</span></code></pre>
</section>
<section id="pattern-matching-3" class="slide level1 big-code">
<h1>Pattern Matching</h1>
<p>Haskell's... does not.</p>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="ot">isEqual ::</span> a <span class="ot">-></span> a <span class="ot">-></span> <span class="dt">Bool</span>
isEqual a b <span class="fu">=</span> undefined</code></pre>
<blockquote>
This isn't even possible! Only constructors can be pattern matched. Types have no built-in equality.
</blockquote>
</section>
<section id="infix-and-prefix" class="slide level1 big-code">
<h1>`Infix` and (Prefix)</h1>
<pre class="sourceCode erlang"><code class="sourceCode erlang"><span class="co">%% Symbolic operators can be used</span>
<span class="co">%% as functions from the erlang module</span>
<span class="ch">erlang</span><span class="fu">:</span><span class="ch">'+'</span><span class="fu">(</span><span class="dt">A</span><span class="fu">,</span> <span class="dt">B</span><span class="fu">).</span></code></pre>
<blockquote>
Erlang doesn't have user-defined infix operators
</blockquote>
</section>
<section id="infix-and-prefix-1" class="slide level1 big-code">
<h1>`Infix` and (Prefix)</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="co">-- Symbolic operators can be used</span>
<span class="co">-- prefix when in (parentheses)</span>
(<span class="fu">+</span>) a b
<span class="co">-- Named functions can be used</span>
<span class="co">-- infix when in `backticks`</span>
x <span class="ot">`elem`</span> xs
<span class="co">-- infixl, infixr define associativity</span>
<span class="co">-- and precedence (0 lowest, 9 highest)</span>
<span class="kw">infixr</span> <span class="dv">5</span> <span class="ot">`append`</span>
a <span class="ot">`append`</span> b <span class="fu">=</span> a <span class="fu">++</span> b</code></pre>
</section>
<section id="functions-lambdas" class="slide level1 big-code">
<h1>Functions & Lambdas</h1>
<pre class="sourceCode erlang"><code class="sourceCode erlang"><span class="kw">-</span><span class="ch">spec</span> <span class="fu">add(integer(),</span> <span class="fu">integer())</span> <span class="kw">-></span> <span class="fu">integer().</span>
<span class="fu">add(</span><span class="dt">X</span><span class="fu">,</span> <span class="dt">Acc</span><span class="fu">)</span> <span class="kw">-></span>
<span class="dt">X</span> <span class="kw">+</span> <span class="dt">Acc</span><span class="fu">.</span>
<span class="kw">-</span><span class="ch">spec</span> <span class="fu">sum_fun([integer()])</span> <span class="kw">-></span> <span class="fu">integer().</span>
<span class="fu">sum_fun(</span><span class="dt">Xs</span><span class="fu">)</span> <span class="kw">-></span>
<span class="fu">lists:foldl(</span><span class="kw">fun</span> <span class="ch">add</span><span class="kw">/</span><span class="dv">2</span><span class="fu">,</span> <span class="dv">0</span><span class="fu">,</span> <span class="dt">Xs</span><span class="fu">).</span>
<span class="kw">-</span><span class="ch">spec</span> <span class="fu">sum_lambda([integer()])</span> <span class="kw">-></span> <span class="fu">integer().</span>
<span class="fu">sum_lambda(</span><span class="dt">Xs</span><span class="fu">)</span> <span class="kw">-></span>
<span class="fu">lists:foldl(</span>
<span class="kw">fun</span> <span class="fu">(</span><span class="dt">X</span><span class="fu">,</span> <span class="dt">Acc</span><span class="fu">)</span> <span class="kw">-></span> <span class="dt">X</span> <span class="kw">+</span> <span class="dt">Acc</span> <span class="kw">end</span><span class="fu">,</span>
<span class="dv">0</span><span class="fu">,</span>
<span class="dt">Xs</span><span class="fu">).</span></code></pre>
</section>
<section id="functions-lambdas-1" class="slide level1 big-code">
<h1>Functions & Lambdas</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="ot">add ::</span> <span class="dt">Integer</span> <span class="ot">-></span> <span class="dt">Integer</span> <span class="ot">-></span> <span class="dt">Integer</span>
add acc x <span class="fu">=</span> acc <span class="fu">+</span> x
<span class="ot">sumFun ::</span> [<span class="dt">Integer</span>] <span class="ot">-></span> <span class="dt">Integer</span>
sumFun xs <span class="fu">=</span> foldl add <span class="dv">0</span> xs
<span class="ot">sumLambda ::</span> [<span class="dt">Integer</span>] <span class="ot">-></span> <span class="dt">Integer</span>
sumLambda xs <span class="fu">=</span> foldl (\acc x <span class="ot">-></span> acc <span class="fu">+</span> x) <span class="dv">0</span> xs</code></pre>
</section>
<section id="functions-lambdas-2" class="slide level1 big-code">
<h1>Functions & Lambdas</h1>
<ul>
<li>Haskell <em>only</em> has functions of one argument</li>
<li><code>a -> b -> c</code> is really <code>a -> (b -> c)</code></li>
<li><code>f a b</code> is really <code>(f a) b</code></li>
<li>Let's leverage that…</li>
</ul>
</section>
<section id="functions-lambdas-3" class="slide level1 big-code highlight">
<h1>Functions & Lambdas</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="ot">add ::</span> <span class="dt">Integer</span> <span class="ot">-></span> <span class="dt">Integer</span> <span class="ot">-></span> <span class="dt">Integer</span>
add acc x <span class="fu">=</span> acc <span class="fu">+</span> x
<span class="ot">sumFun ::</span> [<span class="dt">Integer</span>] <span class="ot">-></span> <span class="dt">Integer</span>
sumFun <span class="hl">xs</span> <span class="fu">=</span> foldl add <span class="dv">0</span> <span class="hl">xs</span>
<span class="ot">sumLambda ::</span> [<span class="dt">Integer</span>] <span class="ot">-></span> <span class="dt">Integer</span>
sumLambda <span class="hl">xs</span> <span class="fu">=</span> foldl (\acc x <span class="ot">-></span> acc <span class="fu">+</span> x) <span class="dv">0</span> <span class="hl">xs</span></code></pre>
</section>
<section id="functions-lambdas-4" class="slide level1 big-code highlight">
<h1>Functions & Lambdas</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="ot">add ::</span> <span class="dt">Integer</span> <span class="ot">-></span> <span class="dt">Integer</span> <span class="ot">-></span> <span class="dt">Integer</span>
add acc x <span class="fu">=</span> acc <span class="fu hl">+</span> x
<span class="ot">sumFun ::</span> [<span class="dt">Integer</span>] <span class="ot">-></span> <span class="dt">Integer</span>
sumFun <span class="fu">=</span> foldl add <span class="dv">0</span>
<span class="ot">sumLambda ::</span> [<span class="dt">Integer</span>] <span class="ot">-></span> <span class="dt">Integer</span>
sumLambda <span class="fu">=</span> foldl (\acc x <span class="ot">-></span> acc <span class="fu hl">+</span> x) <span class="dv">0</span></code></pre>
</section>
<section id="functions-lambdas-5" class="slide level1 big-code highlight">
<h1>Functions & Lambdas</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="ot">add ::</span> <span class="dt">Integer</span> <span class="ot">-></span> <span class="dt">Integer</span> <span class="ot">-></span> <span class="dt">Integer</span>
add acc <span class="hl">x</span> <span class="fu">=</span> <span class="fu">(+)</span> acc <span class="hl">x</span>
<span class="ot">sumFun ::</span> [<span class="dt">Integer</span>] <span class="ot">-></span> <span class="dt">Integer</span>
sumFun <span class="fu">=</span> foldl add <span class="dv">0</span>
<span class="ot">sumLambda ::</span> [<span class="dt">Integer</span>] <span class="ot">-></span> <span class="dt">Integer</span>
sumLambda <span class="fu">=</span> foldl (\acc <span class="hl">x</span> <span class="ot">-></span> <span class="fu">(+)</span> acc <span class="hl">x</span>) <span class="dv">0</span></code></pre>
</section>
<section id="functions-lambdas-6" class="slide level1 big-code highlight">
<h1>Functions & Lambdas</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="ot">add ::</span> <span class="dt">Integer</span> <span class="ot">-></span> <span class="dt">Integer</span> <span class="ot">-></span> <span class="dt">Integer</span>
add <span class="hl">acc</span> <span class="fu">=</span> <span class="fu">(+)</span> <span class="hl">acc</span>
<span class="ot">sumFun ::</span> [<span class="dt">Integer</span>] <span class="ot">-></span> <span class="dt">Integer</span>
sumFun <span class="fu">=</span> foldl add <span class="dv">0</span>
<span class="ot">sumLambda ::</span> [<span class="dt">Integer</span>] <span class="ot">-></span> <span class="dt">Integer</span>
sumLambda <span class="fu">=</span> foldl (\<span class="hl">acc</span> <span class="ot">-></span> <span class="fu">(+)</span> <span class="hl">acc</span>) <span class="dv">0</span></code></pre>
</section>
<section id="functions-lambdas-7" class="slide level1 big-code highlight">
<h1>Functions & Lambdas</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="ot">add ::</span> <span class="dt">Integer</span> <span class="ot">-></span> <span class="dt">Integer</span> <span class="ot">-></span> <span class="dt">Integer</span>
add <span class="fu">=</span> <span class="fu">(+)</span>
<span class="ot">sumFun ::</span> [<span class="dt">Integer</span>] <span class="ot">-></span> <span class="dt">Integer</span>
sumFun <span class="fu">=</span> foldl add <span class="dv">0</span>
<span class="ot">sumLambda ::</span> [<span class="dt">Integer</span>] <span class="ot">-></span> <span class="dt">Integer</span>
sumLambda <span class="fu">=</span> foldl <span class="fu">(+)</span> <span class="dv">0</span></code></pre>
</section>
<section id="guards" class="slide level1 big-code">
<h1>Guards</h1>
<pre class="sourceCode erlang"><code class="sourceCode erlang"><span class="kw">-</span><span class="ch">spec</span> <span class="fu">is_negative(number())</span> <span class="kw">-></span> <span class="fu">boolean().</span>
<span class="fu">is_negative(</span><span class="dt">X</span><span class="fu">)</span> <span class="ch">when</span> <span class="dt">X</span> <span class="kw"><</span> <span class="dv">0</span> <span class="kw">-></span>
<span class="ch">true</span><span class="fu">;</span>
<span class="fu">is_negative(</span><span class="dt">_</span><span class="fu">)</span> <span class="kw">-></span>
<span class="ch">false</span><span class="fu">.</span></code></pre>
</section>
<section id="guards-1" class="slide level1 big-code">
<h1>Guards</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="ot">isNegative ::</span> (<span class="dt">Num</span> a) <span class="ot">=></span> a <span class="ot">-></span> <span class="dt">Bool</span>
isNegative x
<span class="fu">|</span> x <span class="fu"><</span> <span class="dv">0</span> <span class="fu">=</span> <span class="dt">True</span>
<span class="fu">|</span> otherwise <span class="fu">=</span> <span class="dt">False</span></code></pre>
</section>
<section id="guards-2" class="slide level1 big-code">
<h1>Guards</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="ot">isNegative ::</span> (<span class="dt">Num</span> a) <span class="ot">=></span> a <span class="ot">-></span> <span class="dt">Bool</span>
isNegative x
<span class="fu">|</span> x <span class="fu"><</span> <span class="dv">0</span> <span class="fu">=</span> <span class="dt">True</span>
<span class="fu">|</span> otherwise <span class="fu">=</span> <span class="dt">False</span>
<span class="ot">absoluteValue ::</span> (<span class="dt">Num</span> a) <span class="ot">=></span> a <span class="ot">-></span> <span class="dt">Bool</span>
absoluteValue x
<span class="fu">|</span> isNegative x <span class="fu">=</span> <span class="fu">-</span>x
<span class="fu">|</span> otherwise <span class="fu">=</span> x</code></pre>
</section>
<section id="built-in-types" class="slide level1 big-code small-title">
<h1>Built-in types</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="co">-- (), pronounced "unit"</span>
<span class="ot">unit ::</span> ()
unit <span class="fu">=</span> ()
<span class="co">-- Char</span>
<span class="ot">someChar ::</span> <span class="dt">Char</span>
someChar <span class="fu">=</span> <span class="ch">'x'</span>
<span class="co">-- Instances of Num typeclass</span>
<span class="ot">someDouble ::</span> <span class="dt">Double</span>
someDouble <span class="fu">=</span> <span class="dv">1</span>
<span class="co">-- Instances of Fractional typeclass</span>
<span class="ot">someRatio ::</span> <span class="dt">Rational</span>
someRatio <span class="fu">=</span> <span class="dv">1</span><span class="fu">.</span><span class="dv">2345</span></code></pre>
</section>
<section id="lists-tuples" class="slide level1 big-code small-title">
<h1>Lists & Tuples</h1>
<pre class="sourceCode erlang"><code class="sourceCode erlang"><span class="fu">some_list()</span> <span class="kw">-></span>
<span class="fu">[</span><span class="dv">1</span><span class="fu">,</span> <span class="dv">2</span><span class="fu">,</span> <span class="dv">3</span><span class="fu">].</span>
<span class="fu">some_other_list()</span> <span class="kw">-></span>
<span class="fu">[</span><span class="dv">4</span> <span class="fu">|</span> <span class="fu">[</span><span class="dv">5</span> <span class="fu">|</span> <span class="fu">[</span><span class="dv">6</span> <span class="fu">|</span> <span class="fu">[]]]].</span>
<span class="fu">some_tuple()</span> <span class="kw">-></span>
<span class="fu">{</span><span class="dv">10</span><span class="fu">,</span> <span class="dv">$4</span><span class="fu">}.</span>
<span class="fu">some_string()</span> <span class="kw">-></span>
<span class="st">"foo"</span><span class="fu">.</span></code></pre>
</section>
<section id="lists-tuples-1" class="slide level1 big-code small-title">
<h1>Lists & Tuples</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="co">-- [a], type can be written prefix as `[] a`</span>
someList,<span class="ot"> someOtherList ::</span> [<span class="dt">Int</span>]
someList <span class="fu">=</span> [<span class="dv">1</span>, <span class="dv">2</span>, <span class="dv">3</span>]
someOtherList <span class="fu">=</span> <span class="dv">4</span> <span class="fu">:</span> <span class="dv">5</span> <span class="fu">:</span> <span class="dv">6</span> <span class="fu">:</span> []
dontWriteThis <span class="fu">=</span> (<span class="fu">:</span>) <span class="dv">4</span> (<span class="dv">5</span> <span class="fu">:</span> (<span class="fu">:</span>) <span class="dv">6</span> [])
<span class="co">-- (a, b), can be written prefix as `(,) a b`</span>
someTuple,<span class="ot"> someOtherTuple ::</span> (<span class="dt">Int</span>, <span class="dt">Char</span>)
someTuple <span class="fu">=</span> (<span class="dv">10</span>, <span class="ch">'4'</span>)
someOtherTuple <span class="fu">=</span> (,) <span class="dv">4</span> <span class="ch">'2'</span>
<span class="co">-- [Char], also known as String</span>
<span class="co">-- (also see the OverloadedStrings extension)</span>
<span class="ot">someString ::</span> <span class="dt">String</span>
someString <span class="fu">=</span> <span class="st">"foo"</span></code></pre>
</section>
<section id="typeclass-syntax" class="slide level1 big-code">
<h1>Typeclass Syntax</h1>
<ul>
<li><p>Erlang doesn't have typeclasses.</p></li>
<li><p>Elixir has Protocols, which are closer, but they are also not typeclasses.</p></li>
</ul>
</section>
<section id="typeclass-syntax-1" class="slide level1 big-code">
<h1>Typeclass Syntax</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="kw">class</span> <span class="dt">Equals</span> a <span class="kw">where</span>
<span class="ot"> isEqual ::</span> a <span class="ot">-></span> a <span class="ot">-></span> <span class="dt">Bool</span>
<span class="kw">instance</span> <span class="dt">Equals</span> <span class="dt">Choice</span> <span class="kw">where</span>
isEqual <span class="dt">Definitely</span> <span class="dt">Definitely</span> <span class="fu">=</span> <span class="dt">True</span>
isEqual <span class="dt">Possibly</span> <span class="dt">Possibly</span> <span class="fu">=</span> <span class="dt">True</span>
isEqual <span class="dt">NoWay</span> <span class="dt">NoWay</span> <span class="fu">=</span> <span class="dt">True</span>
isEqual _ _ <span class="fu">=</span> <span class="dt">False</span>
<span class="kw">instance</span> (<span class="dt">Equals</span> a) <span class="ot">=></span> <span class="dt">Equals</span> [a] <span class="kw">where</span>
isEqual (a<span class="fu">:</span>as) (b<span class="fu">:</span>bs) <span class="fu">=</span> isEqual a b <span class="fu">&&</span>
isEqual as bs
isEqual as bs <span class="fu">=</span> null as <span class="fu">&&</span> null bs</code></pre>
</section>
<section id="typeclass-syntax-2" class="slide level1 big-code">
<h1>Typeclass Syntax</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="co">{-</span>
<span class="co">class Eq a where</span>
<span class="co"> (==) :: a -> a -> Bool</span>
<span class="co">-}</span>
<span class="kw">instance</span> <span class="dt">Eq</span> <span class="dt">Choice</span> <span class="kw">where</span>
<span class="dt">Definitely</span> <span class="fu">==</span> <span class="dt">Definitely</span> <span class="fu">=</span> <span class="dt">True</span>
<span class="dt">Possibly</span> <span class="fu">==</span> <span class="dt">Possibly</span> <span class="fu">=</span> <span class="dt">True</span>
<span class="dt">NoWay</span> <span class="fu">==</span> <span class="dt">NoWay</span> <span class="fu">=</span> <span class="dt">True</span>
_ <span class="fu">==</span> _ <span class="fu">=</span> <span class="dt">False</span></code></pre>
</section>
<section id="typeclass-syntax-3" class="slide level1 big-code">
<h1>Typeclass Syntax</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="kw">data</span> <span class="dt">Choice</span> <span class="fu">=</span> <span class="dt">Definitely</span>
<span class="fu">|</span> <span class="dt">Possibly</span>
<span class="fu">|</span> <span class="dt">NoWay</span>
<span class="kw">deriving</span> (<span class="dt">Eq</span>)</code></pre>
</section>
<section id="typeclass-syntax-4" class="slide level1 big-code">
<h1>Typeclass Syntax</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="kw">data</span> <span class="dt">Choice</span> <span class="fu">=</span> <span class="dt">Definitely</span>
<span class="fu">|</span> <span class="dt">Possibly</span>
<span class="fu">|</span> <span class="dt">NoWay</span>
<span class="kw">deriving</span> ( <span class="dt">Eq</span>, <span class="dt">Ord</span>, <span class="dt">Enum</span>, <span class="dt">Bounded</span>
, <span class="dt">Show</span>, <span class="dt">Read</span> )</code></pre>
</section>
<section id="quickcheck" class="slide level1 big-code">
<h1>QuickCheck</h1>
<pre class="sourceCode erlang"><code class="sourceCode erlang"><span class="fu">prop_itsthere()</span> <span class="kw">-></span>
<span class="fu">?</span><span class="dt">FORALL</span><span class="fu">(</span><span class="dt">I</span><span class="fu">,int(),</span>
<span class="fu">[</span><span class="dt">I</span><span class="fu">]</span> <span class="kw">==</span> <span class="fu">queue:to_list(</span>
<span class="fu">queue:cons(</span><span class="dt">I</span><span class="fu">,</span>
<span class="fu">queue:new()))).</span></code></pre>
</section>
<section id="quickcheck-1" class="slide level1 big-code">
<h1>QuickCheck</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="kw">import</span> Data.Sequence ((|>), empty)
<span class="kw">import</span> Data.Foldable (toList)
<span class="ot">prop_itsthere ::</span> <span class="dt">Int</span> <span class="ot">-></span> <span class="dt">Bool</span>
prop_itsthere i <span class="fu">=</span> [i] <span class="fu">==</span> toList (empty <span class="fu">|></span> i)</code></pre>
</section>
<section id="quickcheck-2" class="slide level1 big-code">
<h1>QuickCheck</h1>
<pre class="sourceCode bash"><code class="sourceCode bash">$ <span class="kw">ghci</span></code></pre>
<pre class="sourceCode haskell"><code class="sourceCode haskell">λ> <span class="kw">import</span> Test.QuickCheck
λ> <span class="kw">import</span> Data.Foldable
λ> <span class="kw">import</span> Data.Sequence
λ> quickCheck (\i <span class="ot">-></span> [<span class="ot">i ::</span> <span class="dt">Int</span>] <span class="fu">==</span>
toList (empty <span class="fu">|></span> i))
<span class="fu">+++</span> <span class="dt">OK</span>, passed <span class="dv">100</span> tests<span class="fu">.</span></code></pre>
</section>
<section id="do-syntax" class="slide level1 big-code highlight">
<h1>Do syntax</h1>
<!--
```erlang
-spec main([string()]) -> ok.
main(_Args) ->
{ok, Secret} = file:read_file("/etc/passwd"),
file:write_file("/tmp/passwd", Secret),
ok.
```
-->
<pre class="sourceCode erlang"><code class="sourceCode erlang"><span class="kw">-</span><span class="ch">spec</span> <span class="fu">main([string()])</span> <span class="kw">-></span> <span class="ch">ok</span><span class="fu">.</span>
<span class="fu">main(</span><span class="dt">_Args</span><span class="fu">)</span> <span class="kw">-></span>
<span class="fu">{</span><span class="ch">ok</span><span class="fu">,</span> <span class="dt">Secret</span><span class="fu">}</span> <span class="kw">=</span> <span class="fu">file:read_file(</span><span class="st">"/etc/passwd"</span><span class="fu">)<span class="hl">,</span></span>
<span class="fu">file:write_file(</span><span class="st">"/tmp/passwd"</span><span class="fu">,</span> <span class="dt">Secret</span><span class="fu">)<span class="hl">,</span></span>
<span class="ch">ok</span><span class="fu"><span class="hl">.</span></span></code></pre>
</section>
<section id="do-syntax-io" class="slide level1 big-code">
<h1>Do syntax (IO)</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="ot">main ::</span> <span class="dt">IO</span> ()
main <span class="fu">=</span> <span class="kw">do</span>
secret <span class="ot"><-</span> readFile <span class="st">"/etc/passwd"</span>
writeFile <span class="st">"/tmp/passwd"</span> secret
return ()</code></pre>
</section>
<section id="do-syntax-1" class="slide level1 big-code">
<h1>Do syntax</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell">
<span class="kw">do</span> m
<span class="co">-- desugars to:</span>
m
<span class="kw">do</span> a <span class="ot"><-</span> m
return a
<span class="co">-- desugars to:</span>
m <span class="fu">>>=</span> \a <span class="ot">-></span> return a
<span class="kw">do</span> m
return ()
<span class="co">-- desugars to:</span>
m <span class="fu">>></span> return ()</code></pre>
</section>
<section id="do-syntax-io-1" class="slide level1 big-code highlight">
<h1>Do syntax (IO)</h1>
<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="ot">main ::</span> <span class="dt">IO</span> ()
main <span class="fu">=</span> <span class="hl"><span class="kw">do</span></span>
<span class="hl">secret <span class="ot"><-</span></span> readFile <span class="st">"/etc/passwd"</span>
writeFile <span class="st">"/tmp/passwd"</span> secret
return ()</code></pre>
</section>
<section id="do-syntax-io-2" class="slide level1 big-code highlight">
<h1>Do syntax (IO)</h1>