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142 lines
6.4 KiB
142 lines
6.4 KiB
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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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<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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<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 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 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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