Crystal is a programming language that aims to provide Ruby-like syntax with C-like performance. It compiles to efficient native code without needing to specify variable or argument types. Crystal installation is simple on Linux, macOS, and Windows. Programs can be run, built, and compiled directly from the command line. While still in pre-alpha, the language is designed and its compiler written in Crystal. Porting Ruby code to Crystal is easy with few needed modifications. Current limitations include a lack of incremental compilation and difficulty implementing a REPL due to Crystal not being dynamically typed.

1. Crystal
The Programming Language
@KamilLelonek

2. Language goals
Ruby-inspired syntax.
Ruby's efficiency for writing code.
C's efficiency for running code.
Compile to efficient native code.
Never have to specify the type of a variable
or method argument.
Have compile-time evaluation and
generation of code, to avoid boilerplate
code.

3. Installation
sudo apt-get install crystal
sudo yum install crystal
brew tap manastech/crystal && brew install crystal
➜ ~ crystal
Usage: crystal [command] [switches] [program file] [--] [arguments]
Command:
build compile program file
browser open an http server to browse program file
deps install project dependencies
docs generate documentation
eval eval code
hierarchy show type hierarchy
run (default) compile and run program file
spec compile and run specs (in spec directory)
types show type of main variables
--help show this help
--version show version

4. Run, Build, Compile
➜ ls
hello.cr
➜ crystal hello.cr
Hello World
➜ crystal build hello.cr
➜ crystal ls -l
-rwxr-xr-x hello
-rw-rw-r-- hello.cr
➜ crystal ./hello
Hello World
Execute on the fly:
Compile and run:

5. Current Status
The project is in pre-alpha stage: language is still
being designed.
The compiler is written in Crystal.
Includes conservative garbage collector, but this
will change in the future.

6. Crystal vs Ruby
Porting the code from Ruby to Crystal is very easy and most
of the time needs few modifications.
The ported code behaved exactly the same as in Ruby.
The ported code reveals bugs during compilation, which
means that, Crystal helps you have more robust and correct
code.

7. Limitations
● Incremental compilation is not possible
Because there are no type annotations, the compiler needs to
figure out the type of everything, each time, from scratch.
● It is hard to do a REPL
If code always had type annotations machine code could be
generated and not worry about a variable’s type possibly
changing, or even a type’s instance variables being created or
changed.
● Crystal is not a dynamic language
When it finishes compiling it assigns a type to every variable and
method that were used.

8. Resources
Documentation: http://bit.ly/crystal-docs
Source Code: http://bit.ly/crystal-source
Community: http://bit.ly/crystal-community
Examples:
• https://github.com/KamilLelonek/crystal-twitter-client
• https://github.com/KamilLelonek/crystal-examples

9. DEMO