What is Crystal

Crystal is like Ruby but compiled, with types, and speed.

What you can make with Crystal

  • Fast webapps that look and feel like Ruby
  • Fast Ruby extensions
  • LISP implementations and your own languages
  • CLI Apps

How to get Crystal

On macOS run:

$ brew install crystal-lang

On Ubuntu run:

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

On Arch run:

$ sudo pacman -S crystal

How to make things with Crystal

First things first, let's run some code. Run the following to open a crystal playground:

$ crystal play

How to make Hello World with Crystal

Open it up and type out some code:

puts "Hello world!"

Tip: Strings in Crystal are always double quoted.

Everything in Crystal is an object:

# Strings are objects

"hello world".class #=> String Class

# Numbers are objects

1.class #=> Int32 Class

# Special values are objects
nil.class #=> Nil Class
true.class #=> Bool Class
false.class #=> Bool Class

Because everything is an object we get methods on every thing:

1.to_s #=> "1"
["cats", "dogs"].join(" ") #=> "cats dogs": String

How to make a Webapp With Crystal

We outputted a string, so now let's output that string on an http port, like a real developer.

First create a new Crystal project:

$ crystal init app cats_are_awesome
$ cd cats_are_awesome

Add Kemal (a Sinatra like web framework) to shard.yaml

    github: kemalcr/kemal
    branch: master

Now install Kemal using shards:

$ shards install

Once it finishes we can finish our app declaring the awesomeness of cats. Open src/cats_are_awesome.cr and change it to the following:

require "kemal"

get "/" do
  "Cats are awesome!"


Now you can run it like this:

$ crystal build --release src/cats_are_awesome.cr
$ ./cats_are_awesome

Congrats you are now a Crystal programmer! I knew you could do it! I believed in you!