A brief introduction

The Crystal programming language aims to be the following:

• Have a syntax similar to Ruby (but compatibility with it is not a goal)
• Statically type-checked but without having to specify the type of variables or method arguments.
• Be able to call C code by writing bindings to it in Crystal.
• Have compile-time evaluation and generation of code, to avoid boilerplate code.
• Compile to efficient native code.

The reason for my interest in Crystal is mainly the similarities to Ruby syntax, as my professional career started at a company that used Ruby on Rails for most of its applications I couldn’t end up doing anythin but loving Ruby, while being as efficiently run as a C program.

Hello World!

puts "Hello World!"

That’s it, that’s how you write a Hello World program in Crystal. Pretty neat huh? But how do I run it? You might ask, well, come along and I’ll show you! Note: I am writing this guide as I am learning Crystal myself. So I reserve the right to change and edit as much as I want as I learn more. Also, my primary resources are the official documentation and the official API if nothing else is stated. The version I’m using is 0.24.2, the latest version as of date.

Installing the Crystal Compiler

There are distributions available for a wide range of operating systems, below I shall list instructions for Debian and Ubuntu. For a complete list, or more installation details, please refer to this page.

Debian and Ubuntu

First, add the repository to your APT config.

curl https://dist.crystal-lang.org/apt/setup.sh | sudo bash

And second, install the Crystal compiler.

sudo apt-get install build-essential -y // This command is not always needed, but better safe than sorry I guess
sudo apt-get install crystal -y

Done! You can check if your installation was successful by running:

crystal -v

It should display something along the lines of:

Crystal 0.24.2 [4f9ed8d03] (2018-03-08)

If you want to upgrade your Crystal version, run the following.

sudo apt-get update
sudo apt-get install crystal

Crystal Box

I’ve created a Vagrant box with a Crystal installation for the ones, including myself, who are into that sort of thing. Which can be found here.

Using the Crystal Compiler

A Crystal file ends with .cr, and there are two ways to compile and run a Crystal program.

$ crystal hello_world.cr

and

$ crystal run hello_world.cr

The difference in result between these two are unbeknownst to me as of date. For more details on the compiler and what it is capable of, read this section!

Hello World pt.2

So, utilizing the information we’ve gathered up until now, we should now be able to create our Hello World program and run it! Start by creating a file named hello_world.cr. Write puts "Hello World!" to the file and save it. Then, in your terminal, go to the directory where you saved the file, type $ crystal hello_world.cr and press enter. After the compiler has done its magic, the text Hello World! should be visible in the terminal window. Good job! You’ve just created and run your first Crystal program.

Want more?

• An analysis of the simple server example.
• Requiring files.
• Local variables.
• Classes and methods.
• Literals
• Type Inference
• Compiler details