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227 lines
8.9 KiB
227 lines
8.9 KiB
11 months ago
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<title>Julio Biason .Me 4.3</title>
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</head>
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<div class="sidebar-about">
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<a href="https://blog.juliobiason.me"><h1>Julio Biason .Me 4.3</h1></a>
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<p class="lead">Old school dev living in a 2.0 dev world</p>
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</div>
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<ul class="sidebar-nav">
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<li class="sidebar-nav-item"><a href="/">English</a></li>
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<li class="sidebar-nav-item"><a href="/pt">Português</a></li>
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<li class="sidebar-nav-item"><a href="/tags">Tags (EN)</a></li>
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<li class="sidebar-nav-item"><a href="/pt/tags">Tags (PT)</a></li>
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</ul>
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</div>
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<div class="content container">
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<div class="post">
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<h1 class="post-title"> Learn you some Erlang for great good! - Fred Hebert</h1>
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<span class="post-date">
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2020-10-25
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<a href="https://blog.juliobiason.me/tags/books/">#books</a>
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<a href="https://blog.juliobiason.me/tags/reviews/">#reviews</a>
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<a href="https://blog.juliobiason.me/tags/it/">#it</a>
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<a href="https://blog.juliobiason.me/tags/erlang/">#erlang</a>
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<a href="https://blog.juliobiason.me/tags/fred-hebert/">#fred hebert</a>
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<a href="https://blog.juliobiason.me/tags/stars-4/">#stars:4</a>
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<a href="https://blog.juliobiason.me/tags/books-2020/">#books:2020</a>
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<a href="https://blog.juliobiason.me/tags/published-2012/">#published:2012</a>
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</span>
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<p><a href="https://www.goodreads.com/book/show/6718693-learn-you-some-erlang-for-great-good">GoodReads Summary</a>:
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(No Summary)</p>
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<span id="continue-reading"></span><div>
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★★★★☆
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</div>
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<p>Another Erlang book for my collection.</p>
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<p>This one takes its time to explain every point. So if you like to go fast and
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furious, that's not it. Also, because I read some other books (ok, "book")
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about Erlang, some topics felt a little bit boring, 'cause I did get the point
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already.</p>
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<p>Also, it seems this books also suffer from the "let me use the shell to explain
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this point". It's not that bad when you want to show a point in the very
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beginning and then just drop it ('cause, you know, you won't use the shell as
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part of your application -- you may use as a helper to figure out when things
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go haywire, but not as a default tool) but not when you're near the middle of
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the book explaining some important topic, like supervisors.</p>
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<p>But, at the same time, some topics that the other books (ok, "book") completely
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ignored, like "how do you build, package and deploy an Erlang application".</p>
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<p>But yeah, the "using shell for important stuff" <em>really</em> annoyed me.</p>
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<h2 id="highlights">Highlights</h2>
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<blockquote>
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<p>The correct ordering of each element in a comparison is the following:
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number < atom < reference < fun < port < pid < tuple < list < bit string.</p>
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</blockquote>
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<blockquote>
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<p>A tuple that contains an atom with one element following it is called a
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tagged tuple.</p>
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</blockquote>
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<p><em>Note</em>: Example: <code>(tag, value, value)</code>, <code>(other_tag, value, value)</code>.</p>
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<blockquote>
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<p>port Erlang to the JVM, giving the Erjang.</p>
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</blockquote>
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<blockquote>
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<p>To compile to native code, you need to use the hipe module and call it the
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following way: hipe:c(Module,OptionsList). You could also use
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c(Module,[native]) </p>
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</blockquote>
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<blockquote>
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<p>There are also a few predefined macros, such as the following: </p>
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<ul>
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<li>?MODULE, which is replaced by the current module name as an atom </li>
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<li>?FILE, which is replaced by the filename as a string </li>
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<li>?LINE, which returns the line number of wherever the macro is placed </li>
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</ul>
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</blockquote>
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<blockquote>
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<p>-ifdef(DEBUGMODE).<br>
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-define(DEBUG(S), io:format("dbg: "++S)).<br>
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-else.<br>
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-define(DEBUG(S), ok).<br>
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-endif.</p>
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</blockquote>
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<p><em>Note</em>: This is how you define a function that exists only if the atom is
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defined.</p>
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<blockquote>
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<p>right_age(X) when X >= 16, X =< 104 -> true;
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right_age(_) -> false. </p>
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</blockquote>
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<p><em>Note</em>: The function for <code>right_age</code> returns true only when the guardian
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matches. Basically, we don't need <code>if</code>s in this kind of function.</p>
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<blockquote>
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<p>wrong_age(X) when X < 16; X > 104 -> true;<br>
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wrong_age(_) -> false </p>
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</blockquote>
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<p><em>Note</em>: Same thing.</p>
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<blockquote>
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<p>1> {ok, Binary} = file:read_file("road.txt").<br>
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{ok,<<"50\r\n10\r\n30\r\n5\r\n90\r\n20\r\n40\r\n2\r\n25\r\n10\r\n8\r\n0\r\n">>} <br>
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2> S = string:tokens(binary_to_list(Binary), "\r\n\t ").<br>
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["50","10","30","5","90","20","40","2","25","10","8","0"] </p>
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</blockquote>
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<p><em>Note</em>: the <code><<>></code> format denotes binary content (like bytes in Python, maybe?).</p>
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<blockquote>
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<p>main([FileName]) -> <br>
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{ok, Bin} = file:read_file(FileName),<br>
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Map = parse_map(Bin),<br>
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io:format("˜p˜n",[optimal_path(Map)]),<br>
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erlang:halt().</p>
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<p>The main function now has an arity of 1, needed to receive parameters from
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the command line. We’ve also added the function erlang:halt/0, which will
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shut down the Erlang VM after being called </p>
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</blockquote>
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<blockquote>
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<p>erlc road.erl <br>
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$ erl -noshell -run road main road.txt </p>
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</blockquote>
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<p><em>Note</em>: <code>erlc</code>, the Erlang Compiler. Still needs <code>erl</code> to run the thing,
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though.</p>
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<blockquote>
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<p>The Erlang escript command provides a simple way to run Erlang programs
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without starting the erl application directly.</p>
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</blockquote>
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<blockquote>
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<p>% This is a .hrl (header) file.<br>
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-record(included, {some_field, some_default = "yeah!", unimaginative_name}).</p>
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</blockquote>
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<p><em>Note</em>: Records are just tuples with added syntactic sugar.</p>
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<blockquote>
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<p>Because a single list doesn't allow efficiently adding and removing elements
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from both ends at once (it's only fast to add and remove the head), the idea
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behind the queue module is that if you have two lists, then you can use one
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to add elements and one to remove elements. One of the lists then behaves as
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one end of the queue, where you push values, and the other list acts as the
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other end, where you pop them. When the latter is empty, you take the former
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and reverse it </p>
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</blockquote>
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<blockquote>
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<p>Erlang directory structure, which looks like this:</p>
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<ul>
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<li>ebin/ </li>
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<li>include/ </li>
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<li>priv/ </li>
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<li>src/ </li>
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</ul>
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</blockquote>
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<blockquote>
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<p>Open a file named Emakefile.</p>
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</blockquote>
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<p><em>Note</em>: <code>Emakefile</code>s make file file.</p>
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<blockquote>
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<p>{'src/*', [debug_info, {i, "src"}, {i, "include"}, {outdir, "ebin"}]}. </p>
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</blockquote>
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<p><em>Note</em>: format of said Emakefile.</p>
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<blockquote>
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<p>erl -make </p>
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</blockquote>
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<p><em>Note</em>: How to build a project using the Emakefile.</p>
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<blockquote>
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<p>Start a shell to be a TCP server: </p>
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</blockquote>
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<p><em>Note</em>: This is the kind of stuff that drove me crazy: Why would I turn my
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shell into a TCP server? It makes no sense! Sure, it is simpler, but who the
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heck would do that in a normal way?</p>
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<blockquote>
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<p>Promises and futures are a bit like remote procedure calls </p>
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</blockquote>
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<p><em>Note</em>: WHAAAATTTTT?!?!?</p>
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</div>
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</div>
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</body>
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</html>
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