This is the repo used for the in-progress book "Crafting Interpreters". It contains the Markdown text of the book, full implementations of both interpreters, as well as the build system to weave the two together into the final site.

If you find an error or have a suggestion, please do file an issue here. Thank you!

Contributing

One of the absolute best things about writing a book online and putting it out there before it's done is that people like you have been kind enough to give me feedback, point out typos, and find other errors or unclear text.

If you'd like to do that, great! You can just file bugs here on the repo, or send a pull request if you're so inclined. If you want to send a pull request, but don't want to get the build system set up to regenerate the HTML too, don't worry about it. I'll do that when I pull it in.

Ports and implementations

Another way to get involved is by sharing your own implementation of Lox. Ports to other langauges are particularly useful since not every reader likes Java and C. Feel free to add your Lox port or implementation to the wiki:

• Lox implementations

Building Stuff

I am a terribly forgetful, error-prone mammal, so I automated as much as I could.

Prerequisites

I develop on an OS X machine, but any POSIX system should work too. With a little extra effort, you should be able to get this working on Windows as well, though I can't help you out much.

Most of the work is orchestrated by make. The build scripts, test runner, and other utilities are all written in Python 3. The makefile assumes python3 is on your PATH, but it only uses that to set up a Python venv environement which it then uses for everything else:

$ make setup

This creates the Python environment at util/env and installs the required packages into it. All other Python scripts in the repo invoke Python from this environment.

You also need Sass installed and on your PATH. Follow the instructions there to install it for your OS.

In order to compile the two interpreters, you need some C compiler on your path as well as javac.

Building

Once you've got that setup, try:

$ make

If everything is working, that will generate the site for the book as well as compiling the two interpreters clox and jlox. You can run either interpreter right from the root of the repo:

$ ./clox
$ ./jlox

Hacking on the book

The Markdown and snippets of source code are woven together into the final HTML using a hand-written little static site generator, util/build.py. It's a fairly simple static site generator. The generated HTML is committed in the repo under site/. It is built from a combination of Markdown for prose, which lives in book/, and snippets of code that are weaved in from the Java and C implementations in java/ and c/. (All of those funny looking comments in the source code are how it knows which snippet goes where.)

The script that does all the magic is util/build.py. You can run that directly, or run:

$ make book

That generates the entire site in one batch. If you are incrementally working on it, you'll want to run the development server:

$ make serve

This runs a little HTTP server on localhost rooted at the site/ directory. Any time you request a page, it regenerates any files whose sources have been changed, including Markdown files, interpreter source files, templates, and assets. Just let that keep running, edit files locally, and refresh your browser to see the changes.

Building the interpreters

You can build each interpreter like so:

$ make clox
$ make jlox

This builds the final version of each interpreter as it appears at the end of its part in the book.

You can also see what the interpreters look like at the end of each chapter. (I use this to make sure they are working even in the middle of the book.) This is driven by a script, util/split_chapters.py that uses the same comment markers for the code snippets to determine which chunks of code are present in each chapter. It takes only the snippets that have been seen by the end of each chapter and produces a new copy of the source in gen/, one directory for each chapter's code. (These are also an easier way to view the source code since they have all of the distracting marker comments stripped out.)

Then, each of those can be built separately. Run:

$ make c_chapters

And in the build/ directory, you'll get an executable for each chapter, like chap14_chunks, etc. Likewise:

$ make java_chapters

This compiles the Java code to classfiles in build/gen/ in a subdirectory for each chapter.

Repository Layout

• asset/ – Sass files and jinja2 templates used to generate the site.
• book/ - Markdown files for the text of each chapter.
• build/ - Intermediate files and other build output (except for the site) itself go here. Not committed to Git.
• c/ – Source code of clox, the interpreter written in C. Also contains an XCode project, if that's your thing.
• gen/ – Java source files generated by GenerateAst.java go here. Not committed.
• java/ – Source code of jlox, the interpreter written in Java.
• note/ – Various research, notes, TODOs, and other miscellanea.
• note/answers – Sample answers for the challenges. No cheating!
• site/ – The final generated site. The contents of this directory directly mirror craftinginterpreters.com. Most content here is generated by build.py, but fonts, images, and JS only live here. Everything is committed, even the generated content.
• test/ – Test cases for the Lox implementations.
• util/ – Tools and build scripts. The test runner and build system that generate the site from the Markdown and source files live here.