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143 lines
6.4 KiB
143 lines
6.4 KiB
11 months ago
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<!DOCTYPE html>
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<html lang="en">
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<title>Julio Biason .Me 4.3</title>
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<link rel="stylesheet" href="https://blog.juliobiason.me/print.css" media="print">
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<link rel="stylesheet" href="https://blog.juliobiason.me/poole.css">
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</head>
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<body class=" ">
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<div class="sidebar">
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<div class="container sidebar-sticky">
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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 class="content container">
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<div class="post">
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<h1 class="post-title">Things I Learnt The Hard Way - Learn The Basics of Functional Programming</h1>
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<span class="post-date">
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2019-06-26
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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/things-i-learnt/">#things i learnt</a>
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<a href="https://blog.juliobiason.me/tags/functional-programming/">#functional programming</a>
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</span>
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<p>At this point, you should at least have heard about how cool functional
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programming is. There are a lot of concepts here, but at least the very basic
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ones you should keep in mind.</p>
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<span id="continue-reading"></span>
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<p>A lot of talks about functional programming come with weird words like
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"functors" and "monads". It doesn't hurt to know what they really mean
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(disclaimer: I still don't). But some other stuff coming from functional
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programming is actually easy to understand and grasp.</p>
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<p>For example, immutability. This means that all your data can't change once
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it's created. Do you have a record with user information and the user changed
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their password? No, do not change the password field, create a new user record
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with the updated password and discard the old one. Sure, it does a lot of
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"create and destroy" sequences which makes absolutely no sense (why would you
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allocate memory for a new user, copy everything from the old one to the new
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one, update one field, and "deallocate" the memory from the old one? It makes
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no sense!) but, in the long run, it would prevent weird results, specially
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when you understand and start use threads.</p>
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<p>(Basically, you're avoiding a shared state -- the memory -- between parts of
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your code.)</p>
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<p>Another useful concept is pure functions. Pure functions are functions that,
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called with the same parameters, always return the same result, no matter how
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many times you call them. One example of a <em>non</em> pure function is <code>random()</code>:
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each time you call <code>random()</code>, you get a different number<sup class="footnote-reference"><a href="#1">1</a></sup>. An example of a
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pure function would be something like this in Python:</p>
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<pre data-lang="python" style="background-color:#2b303b;color:#c0c5ce;" class="language-python "><code class="language-python" data-lang="python"><span style="color:#b48ead;">def </span><span style="color:#8fa1b3;">mult</span><span>(</span><span style="color:#bf616a;">x</span><span>):
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</span><span> </span><span style="color:#b48ead;">return </span><span>x * </span><span style="color:#d08770;">4
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</span></code></pre>
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<p>No matter how many times you call <code>mult(2)</code>, it will always return 8. Another
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example could be our immutable password change above: You could easily write a
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function that receives a user record and returns a new user record with the
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password changed. You could call with the same record over and over again and
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it will always return the same resulting record.</p>
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<p>Pure functions are useful 'cause they are, first most, easy to test.</p>
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<p>Second, they are easy to chain, specially in a <a href="/books/things-i-learnt/data-flow">data
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flow</a> design: Because they don't have an
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internal state (which is the real reason they are called pure functions), you
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can easily call one after the other and no matter how many times you pass
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things around, they still produce the same result. And because each function,
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given the same input, produce the same result, chaining them all <em>also</em>
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produces the same result given the same inputs.</p>
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<p>Just those two concepts can make code longer (again, you're creating a new
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user record instead of simply changing one field), but the final result is a
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more robust code.</p>
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<div class="footnote-definition" id="1"><sup class="footnote-definition-label">1</sup>
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<p>Except in Haskell, but it does require sending the seed every time, so
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you end up with random values based on the seed, so even there it is a pure
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function.</p>
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</div>
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<div>
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<div style="float:left">
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<< <a href="/books/things-i-learnt/cognitive-cost">Cognitive Cost Is The Readability Killer</a>
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</div>
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<div style="float:right">
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<a href="/books/things-i-learnt/understand-shortcuts">Shortcuts Are Nice, But Only In The Short Run</a> >>
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</div>
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</div>
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</body>
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</html>
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