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if, unless, and cond

Here's something weird to think about: in a high-level functional language such as Elixir, writing conditional code is not exactly idiomatic. Using a combination of pattern matching and syntax rules we can write extremely clean code free of if statements and conditionals in general

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One thing I dislike about most code books is they tell you about syntax rules, but not about how people actually write the code in the wild. I need you to write solid code here at Red:4, so let’s take a second to talk about style.

If You Need “if”

Let’s revisit our Solar module’s power function. When I first wrote it, I did what most programmers would do:

defmodule Solar do
  def power(flare) do
    factor = 1
    if(flare.classification == :M) do
      factor = 10
    if(flare.classification == :X) do
      factor = 1000
    factor * flare.scale

This code isn’t bad, necessarily, but you’ll notice the lack of else if here. Which is OK, as that’s basically the same thing as a bunch of if statements.

The interesting thing about if (and unless) in Elixir is that they’re not really a part of the language - they’re macros:

An interesting note regarding if/2 and unless/2 is that they are implemented as macros in the language; they aren’t special language constructs as they would be in many languages. You can check the documentation and the source of if/2 in the Kernel module docs…

An if (or unless) statement is generally only used when you have a single condition you want to evaluate and they aren’t used very often. In fact, I’ve written a number of Elixir libraries (some quite large) as well as a pretty large ecommerce application. I have, perhaps, two if statements (if that) in all of the Elixir code I’ve ever written.

You just don’t need them when you have pattern matching and smaller, isolated functions.


The Code

Code for this video (and for the entire series) can be found in the production GitHub repo.

  • Welcome to Red:4

    Welcome to Red:4 - Where the Future Starts Yesterday. Blah blah blah we hope you like it here blah blah… We don't have a lot of time so let's just get to it shall we?

  • Letting Elixir Soak In

    Elixir syntax can be familiar and weird at the same time, especially if you're coming from Ruby. To prepare for this section, let's clear our minds - let go of familiar syntax cues and 'the way it's done' in the languages you already know.

  • Functional Programming Primer

    Functional programming has been around forever; it's nothing new. Elixir is a functional language, as is its progenitor, Erlang. If you're coming from an Object-oriented language like Java, Ruby, C#, Python or JavaScript, functional programming will take some getting used to.

  • I need you to setup a project

    You can think of Mix as your Elixir Utility Belt. It builds your projects, runs tasks for you, runs your tests, installs packages - a fascinating tool. That comes later - right now open up your terminal and navigate to a directory where you can save your work.

  • Calculating Escape Velocity

    I hope you're prepared to learn on the job. I'm about to ramp things up on you and it's for the simple reason that I'm under the gun - and to be honest *so are you*. We just got a new CTO, she arrived a few weeks after I got the job. She doesn't like me... which I guess isn't all that surprising.

  • Pattern Matching Basics

    Pattern Matching in Elixir is one of those things that can be vexxing, interesting, or obvious. Ultimately, however, it will be confusing if you have never dealt with it before.

  • Calculating Orbital Distance

    In this part we tidy things up, plugging in Authentication and hooking our download service into Firebase Storage.Nice work so far! The Science Team loves what we're doing and, as you might expect, have given us more work.

  • Debugging

    I'm always amazed when I manage to write Elixir code that compiles correctly the first time. It almost never happens! Let's have a look at a normal sequence you might stumble through, and I'll see if I can save you some time.

  • Solar Flare Project Setup

    We need to get rolling which means we need to setup a project and start cranking out some code! In this video we'll structure our project with tests and get to know the difference between Elixir script files and compilable executables.

  • List and Enumeration Basics

    Functional programming is all about transforming data and if we're going to work with Solar Flares, we need to understand how Lists work - how we query, slice, dice, add and remove. That's what we're going to do now.

  • Recursion and Refactoring Our Solar Flares

    Most developers know about recursion and have used it once or twice in their careers; perhaps more. It can be quite difficult to get right - this is not the case with Elixir. With a combination of pattern matching and the head/tail functionality of Lists, recursively iterating over lists is straightforward.

  • if, unless, and cond

    Here's something weird to think about: in a high-level functional language such as Elixir, writing conditional code is not exactly idiomatic. Using a combination of pattern matching and syntax rules we can write extremely clean code free of if statements and conditionals in general

  • A Quick Look at OTP

    You've seen a lot of Elixir so far and have learned some new concepts, especially if you're new to functional programming. No doubt that along the way you've probably been wondering, however: *how is this all supposed to work together? how can I actually build something?*. I've showed you a few little hints, but it's time to get explicit on this

  • Working With Ecto and PostgreSQL

    You have to store data somewhere and Elixir (and Erlang in general) give you quite a few tools to do so. In this video we'll see how to push data into PostgreSQL using Ecto, the ORM created by the Elixir team.

  • Troubleshooting OTP Errors

    We're in the weeds now! Sorry for the pain, but hey, backing over a cliff is what we do as developers isn't it? You *will find yourself completely stuck* when working with Elixir and I need you to be able to reason your way out of this mess.

  • Bombs Away!

    Developers often confuse *asynchronous* execution with *concurrent* or parallel execution. I do this often! It's something I learn and unlearn, all the time. Let's take a small tangent and discuss the difference.

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