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Hands-on Scala Programming Build Pipeline

This repository contains the book rendering pipeline for the book It contains the full contents of the first 5 chapters, with the subsequent 15 chapters replaced by stubs. This repo contains markdown sources and can generate "sample" (5 chapter) and "dist" (20 chapter) versions of the book in PDF, EPub and Mobi formats, along with a static website containing a Web/HTML sample of the book. Page numbers, table of contents, etc. are all handled programmatically and can be tweaked as desired. The generated PDFs can easily be fed into IngramSpark to produce paperback editions.

This repo can perform parallel and incremental builds of the book, re-rendering a full PDF in less than 60 seconds and individual chapters in about 1 second. It comes with a -w flag to watch inputs, allowing an extremely fast turnaround time between editing a chapter and viewing the rendered PDF.

This repo contains a test suite that validates all the book's standalone code examples and exercises, and does further validation on the book's internal and external links to make sure that no links are broken.

This build pipeline is designed to support the book Hands-on Scala Programming, and will likely need to be modified to support any other book. There are no opaque libraries or opaque helper code: all the code necessary is included, except for a small set of dependencies below. It is expected you will need to fork this repository if you want to render your own e-books. Code quality is at a level suitable for such a one-off use case, with some amount of messiness, duplication, and cheap hacks that are correct enough for Hands-on Scala to look as it does.

All versions of the book are generated using HTML/CSS rendered via Chromium (via Google's Puppeteer library) giving ultimate flexibility in how you want the book to look. Modifying the book is similar to modifying a HTML website, allowing you to fully customize the styling and layout however you see fit. The principles behind the build system are explored in Hands-on Scala's Chapter 10: Static Build Pipelines, which ends with an exercise to build a minimal version of such a pipeline rendering HTML/CSS to PDFs using the same techniques used in this repository to render the book itself.

As Hands-on Scala Programming is complete, I do not expected to be updating these repository going forward. This repo is purely mean to serve as a template for people to copy and modify, or as a reference, in case anyone else wants to undertake a similar project in future.


This repo assumes you are running on Mac OS-X, but can probably be updated to run on Linux and other operating systems without too much difficulty. This repo requires the following dependencies to be pre-installed on the system:

  • The bash shell
  • The java runtime
  • The dot graphviz executable
  • The node Javascript runtime and npm package manager

In the process, this repo also makes use of the following dependencies which will be automatically downloaded as necessary:

  • The Mill build tool, to manage the build pipeline
  • Commonmark-Java to handle markdown parsing
  • The Scalatags templating engine, to render the HTML version of the book
  • Bootstrap CSS for styling
  • The Puppeteer Javascript library, which uses Chromium to convert HTML web pages to PDFs
  • Apache PDFBox, for general PDF-manipulating utilities
  • EPubLib, to handle construction of EPub files
  • Kindlegen for generating Mobi files


You can compile various formats of the book via the following command-line commands:

./mill -i show dist.print.pdf # print-ready PDF, with tweaked colors and gutter margin
./mill -i show dist.color.pdf # normal color PDF
./mill -i show dist.compact.pdf # thin-margin color PDF, for easy reading on ipads etc.
./mill -i show dist.epub.epub # epub, for use in iBooks etc.
./mill -i show # Physical kindle version (doesnt look good on kindle app)

This repo also can generate 5-chapter preview versions of each format:

./mill -i show sample.print.pdf
./mill -i show sample.color.pdf
./mill -i show sample.compact.pdf
./mill -i show sample.epub.epub
./mill -i show

Note that the first time you run a command, it may take a while to download all the necessary dependencies. Subsequent runs will be much faster, and changes made to the book's sources will only result in the necessary parts of the book being re-built.

The online website and web preview can be built via

./mill -i show site.local

Note that the website bundles sample copies of the book in each format, and thus may take quite a while to build the first time or after any change that affects the book contents. After the first build, the sample copies are cached and building is relatively fast-ish.

The github repo of snippets, exectable example code, and exercise solutions can be updated via:

./mill -i show uploadGithub


To run the pipeline in parallel over multiple cores, you can use:

./mill -i -j 8 dist.color.pdf

This spans 8 threads to run different parts of the pipeline in parallel

Individual Chapters

Individual chapter PDFs can be rendered via

./mill -i show dist.color.part[1].chapter[5].pdf

If you need to debug the raw HTML before they get converted into PDFs, the HTML for an individual chapter can be rendered via

./mill -i show dist.color.part[1].chapter[5].body.html
./mill -i show dist.color.part[1].chapter[5].cover.html

Watch and Rebuild

When iterating on a particular chapter, you can speed up the turnaround time by using the -w flag:

./mill -i -w  dist.color.part[1].chapter[5].pdf

This watches the input files and automatically incrementally re-builds that chapter's PDF when any input file changes. You can use the same -w flag on any of the other commands we saw above.


The repository's test suite can be run via

./mill -i dist.test
./mill -i example[_].test

The first command above does some sanity checks (all external links return 200s, epubcheck passes, internal-links refer to a page with the linked text), while the second command runs the individual test suites for all the examples. Note that the test suites aren't particularly hermetic, and some fiddling may be necessary to get all the tests to pass. Note that the examples' test suites are cached, so if one fails you can fix the issue and re-run the above command to pick up where it left off.


The book's text is stored as markdown files, in 20 chapters split over 4 parts:

  • 1 - Introduction to Scala/
  • 2 - Local Development/
  • 3 - Web Services/
  • 4 - Program Design/

Each part has a file contains the introductory page or that part of the book, as well as 5 chapters each with a file containing the chapter contents. The chapters also have folders containing the working code examples, each of which has a file with a short description as well as a bash command that can be used to test and exercise the example.

The markdown is enhanced with the following features:

Inline Macros

`%Part I Introduction to Scala`

`%O(log n)`

Block Macros

> `%example 2 - Transforms`
> ...

> `%horizontal-50`
> ...

Custom Highlighters




These special forms are recognized at parse time and expanded into larger HTML templates. The implementation of these can be found in the


Source code and build system used to generate the book Hands-on Scala Programming