Real World OCaml v2

This is the source code for the Real World OCaml 2nd edition, which is still a work in progress. The original edition was written by Yaron Minsky, Anil Madhavapeddy and Jason Hickey, and the revised edition is being lead by Yaron Minsky and Anil Madhavapeddy. There have been significant contributions to the revised tooling from Ashish Agarwal, Jeremy Yallop, Frederic Bour, and Sander Spies.

An online snapshot of the development book is available from https://dev.realworldocaml.org. There is a Feedback pane on each chapter which leads to a dedicated section on the OCaml discussion forum where you can register broader feedback. More specific issues such as typos can be reported on the issue tracker.

Repository layout

Each chapter of the book sits in a separate subfolder of the book/ directory. The README.md file contains the text of the chapter, written in markdown. Each ocaml or shell code block in the chapter is validated using mdx. The more complex and structured examples live in an examples/ sub folder and mdx is used to keep the examples and the chapter's code block in sync.

The bin/ folder contains the OCaml scripts used to generate the books HTML and PDF versions.

All of the code and examples are built using OCaml 4.09.0.

Building

Here are the commands to build the website:

Installing Dependencies

You can install system dependencies by running:

make depext

All OCaml dependencies are vendored in the duniverse/ directory except for the dune build system itself. It's preferable to use an empty opam switch with only dune installed to avoid conflicts between the opam and local libraries. To set up your RWO development environment you can run:

opam switch create rwo 4.09.0
opam install dune=2.0.1

Generating the HTML

To generate the HTML pages:

make

The HTML pages are created in _build/default/static/. Open _build/default/static/index.html to start browsing the freshly built version of the book.

WIP Chapters

It is possible to mark a chapter as WIP so that it won't be included in the main website or PDF. To do so, you can wrap your chapter in a (wip <chapter-folder) in the table of content file, book/toc.scm, e.g.:

You can run dune build @site-wip or dune build @pdf-wip to generate the website or PDF versions of the book including all WIP chapters. You can find them respectivey in _build/default/static-wip/index.html and _build/default/static-wip/book.pdf.

Once the chapter is ready, you can simply replace (wip <chapter-folder) with <chapter-folder> in book/toc.scm.

Testing the code examples

It is possible to automatically test that the the code examples files work fine. To check that shell scripts and .ml files do what they are expected:

make test

This will run all the tests in "determinitic mode", which is suitable for the CI and it will display the diff between what is expected and what is produced.

To accept the changes:

make promote

Testing non-deterministic examples

A few code examples are not deterministic: for instance benchmarks. In this case, there is a specific dune profile to use:

dune runtest --profile non-deterministic ...

To accept the changes:

make promote

Standalone examples

Examples in each chapter's examples/ folder are split between correct/ and erroneous/. Each individual example is a valid dune-project that lives in its own sub folder. Examples that contain errors on purpose, for instance to showcase some specific compile errors, go into the latter. All other examples should go in correct/.

Examples in the correct/ folder are automatically built and tested in the CI. It's possible to build and test them individually using the dune alias corresponding to the example folder name. For instance, to build and test the example in book/imperative-programming/examples/correct/dictionary, one can run:

dune build @dictionary

Note that the runtest alias will also build and test examples so running make test will build all of the book's examples.

When adding a new chapter, the example folder should have the following structure:

examples/
├── correct/
├── dune
├── dune.inc
└── erroneous/

With the following dune file:

(data_only_dirs correct erroneous)

(rule
 (deps
  (source_tree ./))
 (action
  (with-stdout-to dune.gen
   (run rwo-examples-rules ./))))

(rule
 (alias runtest)
 (action (diff dune.inc dune.gen)))

(include dune.inc)

From that point forward, running dune runtest will generate the right dune rules for each folder in correct/. When the rules change, they must be accepted through promotion first.

Each example must explicitly define its external dependencies in a .rwo-example. For instance, if your example requires base and core, it must include the following .rwo-example file at its root:

(packages base core)

Upgrading or adding dependencies

RWO's dependencies are vendored using duniverse. If you want to upgrade them to their latest availbale opam version you can run:

make duniverse-upgrade

Additionally, if you're working on the book and need a new package vendored, you can simply add it to the $DEPS variable in the Makefile and run the above command again.

It's possible that after upgrading you get some errors because vendored dependencies use jbuild files instead of dune files and compatibility with those has been dropped in dune 2. You can upgrade those using the following command:

dune upgrade --root duniverse/<package_name>.<version>