Crystal Programming Language

This is the language reference for the Crystal programming language.

Crystal is a programming language with the following goals:

Have a syntax similar to Ruby (but compatibility with it is not a goal).
Be statically type-checked, but without having to specify the type of variables or method parameters.
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.

Crystal's standard library is documented in the API docs.

Contributing to the Language Reference

Do you consider yourself a helpful person? If you find bugs or sections which need more clarification you're welcome to contribute to this language reference. You can submit a pull request to this repository: https://github.com/crystal-lang/crystal-book

Thank you very much!

Branches

There is a separate branch for every minor Crystal release, all deployed alongside each other on https://crystal-lang.org/reference/ Typically, only branches of maintained releases receive updates, i.e. the branch for the most recent Crystal release.

Changes that apply to the current Crystal release should go into the most recent release/* branch.
Changes that apply to yet unreleased features should go into master. They'll be part of the release/* branch for the next release. The master branch is deployed at https://crystal-lang.org/reference/master/

Building and Serving Locally

$ git clone https://github.com/crystal-lang/crystal-book
$ cd crystal-book
$ pip install -r requirements.txt

Live preview (at http://127.0.0.1:8000):

$ make serve
INFO    -  Building documentation...
INFO    -  Cleaning site directory
INFO    -  Documentation built in 3.02 seconds
INFO    -  Serving on http://127.0.0.1:8000
...

Build into the site directory (some functionality won't work if opening the files locally):

$ make build

devenv environment

This project includes configuration for a reproducible environment via devenv.sh with integrated pre-commit checks.

Live preview (at http://127.0.0.1:8000):

$ devenv up
Building shell ...
pre-commit-hooks.nix: hooks up to date
17:37:13 system  | serve.1 started (pid=6507)
17:37:13 serve.1 | INFO     -  Building documentation...
17:37:13 serve.1 | INFO     -  Cleaning site directory
17:37:16 serve.1 | INFO     -  Documentation built in 2.64 seconds
17:37:16 serve.1 | INFO     -  [17:37:16] Watching paths for changes: 'docs', 'mkdocs.yml'
17:37:16 serve.1 | INFO     -  [17:37:16] Serving on http://127.0.0.1:8000/reference/latest/

Build the site:

$ devenv shell build
Building shell ...
pre-commit-hooks.nix: hooks up to date
rm -rf ./site
mkdocs build -d ./site  --strict
INFO     -  Cleaning site directory
INFO     -  Building documentation to directory: ./site
INFO     -  Documentation built in 2.43 seconds

Enter the development shell and build the site from there:

$ devenv shell
Building shell ...
Entering shell ...

pre-commit-hooks.nix: hooks up to date
$(devenv) make build
mkdocs build -d ./site  --strict
INFO     -  Cleaning site directory
INFO     -  Building documentation to directory: ./site
INFO     -  Documentation built in 2.43 seconds

Run pre-commit checks on the entire repository:

$ devenv ci

Adding a page

To add a page, create a Markdown file in the desired location. Then, add a link in the SUMMARY.md file which acts as the navigation for the language reference.