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<title>Wissenswertes über Erlang</title>
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<section>
<h1 class="title">Wissenswertes über Erlang</h1>
<h2 class="author">Guido Günther</h2>
<h3 class="date">2016-05-09</h3>
</section>
<section id="who-am-i" class="slide level1">
<h1>Who am I</h1>
<ul>
<li>Free Software Hacker (Freelancing Software Developer)</li>
<li>Debian Developer since 2000</li>
<li>Contributed to libvirt-*, X11, Linux Kernel, GNOME, Calypso, …</li>
<li>FSFE Fellow and GNOME Foundation member</li>
<li>Rather new to Erlang</li>
</ul>
</section>
<section id="erl-what" class="slide level1">
<h1>Erl-what?</h1>
<ul>
<li>Developed at Ericsson in 1986</li>
<li>Open sourced 1998</li>
<li>Ericsson Language or Agner Krarup Erlang?</li>
<li><p>For telephone systems</p></li>
<li>Functional, concurrent programming language</li>
<li>Garbage collected runtime system</li>
<li><p>Erlang/OTP</p></li>
</ul>
</section>
<section id="erlang-features" class="slide level1">
<h1>Erlang, Features</h1>
<ul>
<li>Fault tolerant</li>
<li>Hot code replacements</li>
<li>Distributed</li>
<li>highly available - 12 years of uptime - nine 9s (30 ms / a)</li>
</ul>
</section>
<section id="projects" class="slide level1">
<h1>Projects</h1>
<ul>
<li>ejabberd, Riak, CouchDB, RabbitMQ</li>
<li>WhatsApp, GitHub, Facebook, …</li>
</ul>
</section>
<section id="you-lack-style---no-state" class="slide level1">
<h1>You lack style - no, state!</h1>
</section>
<section class="slide level1">
<h2 id="functional-language">Functional language</h2>
<p>f(x) = y</p>
</section>
<section class="slide level1">
<p>i = i + 3</p>
</section>
<section class="slide level1">
<p><del>i = i + 3</del></p>
</section>
<section class="slide level1">
<p>for (int i=0; i < 3; i++) do_something(i);</p>
</section>
<section class="slide level1">
<p><del>for (int i=0; i < 3; i++) do_something(i);</del></p>
</section>
<section class="slide level1">
<pre><code>1> A=3.
3
2> A=4.
** exception error: no match of right hand side value 4</code></pre>
</section>
<section class="slide level1">
<h2 id="no-means-no">No means No</h2>
<ul>
<li>No imperative programming</li>
<li>No global variables and state</li>
<li>No pointers</li>
<li>No variable reassignments</li>
</ul>
</section>
<section class="slide level1">
<ul>
<li>Yes, Higher Order Functions</li>
<li>Yes, Pattern Matching</li>
<li>Yes, Code Reloads</li>
<li>Yes, Lots of independent Processes</li>
</ul>
</section>
<section class="slide level1">
<h2 id="recursion-to-the-rescue">Recursion to the Rescue</h2>
<pre><code>loop(X) -> loop(X, 0).
loop(X=0, Sum) -> Sum;
loop(X, Sum) -> loop(X-1, Sum+X).</code></pre>
</section>
<section class="slide level1">
<h2 id="recursion-in-detail">Recursion in Detail</h2>
<pre><code>loop(3) -> loop(3, 0)
loop(3,0) -> loop(3-1, 0+3)
loop(2,3) -> loop(2-1, 3+2)
loop(1,5) -> loop(1-1, 5+1)
loop(0,6) -> 6
3 + 2 + 1 = 6</code></pre>
</section>
<section class="slide level1">
<h2 id="head-to-wall-tail">Head to <del>Wall</del> Tail</h2>
<pre><code>A = [this, is, a, list].
[H|T] = A.</code></pre>
</section>
<section class="slide level1">
<pre><code>rev(L) -> rev(L, []).
rev([], N) -> N;
rev([H|T], N) -> rev(T, [H] ++ N).</code></pre>
</section>
<section class="slide level1">
<pre><code>rev([a,b,c,d]) -> rev([a,b,c,d], [])
rev([a|[b,c,d]], []) -> rev([b,c,d], [a] ++ [])
rev([b|[c,d]], [a]) -> rev([c,d], [b] ++ [a])
rev([c|[d]], [b,a]) -> rev([d], [c] ++ [b,a])
rev([d|[], [c,b,a]) -> rev([], [d] ++ [c,b,a])
rev([], [d,c,b,a]) -> [d,c,b,a]</code></pre>
</section>
<section class="slide level1">
<h2 id="more-pattern-matching">More pattern matching</h2>
<pre><code>A = {this, is, a, tuple}.
{_, _, _, B} = A.</code></pre>
</section>
<section class="slide level1">
<pre><code>> B.
tuple
> _.
* 1: variable '_' is unbound</code></pre>
</section>
<section class="slide level1">
<h3 id="fun-with-funs">Fun with Funs</h3>
<pre><code>F = fun (X) -> X*X end.
> F(3).
> F(ok).</code></pre>
</section>
<section class="slide level1">
<pre><code>> F(3).
9
> F(ok).
** exception error: an error occurred when evaluating an arithmetic expression
in operator */2
called as ok * ok</code></pre>
</section>
<section class="slide level1">
<h2 id="success-typing">Success, Typing!</h2>
<p>Dialyzer</p>
<pre><code>-spec foobar(atom()) -> [atom()].
foobar(App) -> …</code></pre>
</section>
<section id="processes-which-processes" class="slide level1">
<h1>Processes, which Processes</h1>
</section>
<section class="slide level1">
<h2 id="spawning-a-process">Spawning a process</h2>
<pre><code>F = fun(X) -> io:format("~p~n", [X]) end.
times(X, Args, C) -> ...
spawn(l, times, [F, "I'm a process", 3]).</code></pre>
</section>
<section class="slide level1">
<pre><code>spawn(l, times, [F, "I'm a process", 3]),
spawn(l, times, [F, "I'm a process too", 3]).</code></pre>
</section>
<section class="slide level1">
<h2 id="concurrency-for-free">Concurrency for free!</h2>
<pre><code>"I'm a process"
"I'm a process too"
"I'm a process"
"I'm a process too"
<0.53.0>
"I'm a process"
"I'm a process too"</code></pre>
</section>
<section class="slide level1">
<h2 id="shared-nothing">Share(d) nothing</h2>
<pre><code>start_pong(Pid) -> …
pong(Pid) -> …
> P = l:start_pong(self()).
> P ! { ping, "foo" }.
> P ! giveup.</code></pre>
</section>
<section class="slide level1">
<pre><code>> R = fun () -> receive M -> M end end.</code></pre>
</section>
<section class="slide level1">
<pre><code>> R().
{pong,"hallo1"}
> R().
{pong,"hallo2"}</code></pre>
</section>
<section class="slide level1">
<h2 id="let-it-crash">Let it crash</h2>
<pre><code>2> P ! {ping, 3}.
{ping,3}
3>
=ERROR REPORT==== 8-May-2016::15:13:30 ===
Error in process <0.34.0> with exit value:
{badarg,[{io,format,[<0.25.0>,"pong: Received ping '~s'~n",[3]],[]},
{l,pong,1,[{file,"l.erl"},{line,57}]}]}</code></pre>
</section>
<section class="slide level1">
<pre><code>2> P ! whatever
Unknwown message asfasdf, giving up</code></pre>
</section>
<section class="slide level1">
<h2 id="linking-processes">Linking processes</h2>
<pre><code>> process_flag(trap_exit, true).
> P = l:start_pong2(self()).
3> P ! sadfsadf.
Unknwown message sadfsadf, giving upsadfsadf
4> receive X -> X end.
{'EXIT',<0.35.0>,reason}</code></pre>
</section>
<section class="slide level1">
<h2 id="distributed-nodes">Distributed nodes</h2>
<pre><code>$ erl -sname ping
$ erl -sname pong
register(spawn(...))</code></pre>
</section>
<section class="slide level1">
<p>On pong</p>
<pre><code>> P = l:start_pong3().</code></pre>
<p>On ping</p>
<pre><code>> {pong, pong@bogon} ! {ping, "hello", self()}.
> {pong, pong@bogon} ! {ping, "hello", self()}.
> receive X -> X end.
{pong,"hello"}</code></pre>
</section>
<section class="slide level1">
<pre><code>erlang:node().
erlang:nodes().</code></pre>
</section>
<section class="slide level1">
<h2 id="hot-code-replacements">Hot code replacements</h2>
<pre><code>version() -> …
c(l).</code></pre>
</section>
<section id="otp" class="slide level1">
<h1>OTP</h1>
<p>Open Telecommunication Platform</p>
</section>
<section class="slide level1">
<h2 id="batteries-inclued">Batteries inclued</h2>
<ul>
<li>EUnit</li>
<li>Mnesia</li>
<li>HTTP/SNMP/…</li>
<li>…</li>
</ul>
</section>
<section class="slide level1">
<h2 id="behaviours">Behaviours</h2>
<ul>
<li>gen_{server,fsm,event}</li>
<li>supervisor</li>
<li>application</li>
</ul>
</section>
<section id="debugging" class="slide level1">
<h1>Debugging</h1>
</section>
<section class="slide level1">
<h2 id="tracing-processes-messges">Tracing Processes, Messges, …</h2>
<pre><code>erl -sname observer -hidden -run observer</code></pre>
</section>
<section class="slide level1">
<h2 id="tracing-functions">Tracing functions</h2>
<pre><code>dbg:start().
dbg:tracer().
% trace messages (m)
dbg:p(pong, m). </code></pre>
</section>
<section id="the-greater-erlang-universe" class="slide level1">
<h1>The greater Erlang Universe</h1>
<ul>
<li>REST: <a href="https://github.com/webmachine/webmachine">Webmachine</a></li>
<li>JSON: <a href="https://github.com/davisp/jiffy">jiffy</a></li>
<li>YAML: <a href="https://github.com/processone/p1_yaml">p1_yaml</a></li>
<li>Build, run, test: <a href="https://github.com/erlang/rebar3">Rebar3</a></li>
<li>… your favorite erlang app goes here …</li>
</ul>
</section>
<section id="extending-erlang" class="slide level1">
<h1>Extending Erlang</h1>
</section>
<section class="slide level1">
<h2 id="nifs---gesundheit">NIFs - Gesundheit!</h2>
<p>Native Implemented Functions</p>
</section>
<section class="slide level1">
<h2 id="c-nodes">C-Nodes</h2>
</section>
<section id="see-also" class="slide level1">
<h1>See also</h1>
<ul>
<li><a href="http://elixir-lang.org/">Elixir</a></li>
<li><a href="http://lfe.io/">LFE(Lisp flavored Erlang)</a></li>
<li><a href="http://erlangonxen.org/">Erlang on Xen</a></li>
</ul>
</section>
<section id="further-reading" class="slide level1">
<h1>Further Reading</h1>
<ul>
<li><a href="http://learnyousomeerlang.com/">Learn you some erlang</a> - buy the book!</li>
<li>On Debian <a href="">/usr/share/doc/erlang-doc</a></li>
<li>Everywhere else: https://www.erlang.org/docs</li>
</ul>
</section>
<section id="questions" class="slide level1">
<h1>Questions?</h1>
</section>
</div>
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