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.

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!

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/

$ 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

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

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.