I’ve pulled the plug on Code Quarterly. To read about why, please see this blog post. Thanks for your interest. —Peter Seibel

Code Challenge: Markup

These are the instructions for the first Code Quarterly Code Challenge. You can read more about the purpose of these Code Challenges if you don’t know what this is all about. Or, if you’ve already read these instructions and written your code, you can submit it.

The code challenge for our inaugural issue is to implement a parser for Markup, a lightweight markup language similar to Markdown and reStructuredText. Markup is designed to be editable in a plain text editor1 and to allow for arbitrary logical markup.2

A complete Markup processor consists of a parser that parses text files into some generic tree data structure representing the logical structure of the document and then one or more back-ends that given such a data structure can render it in some way, e.g. HTML, PDF, TeX, RTF, etc. For this challenge you need to implement only the parser, the data structure it returns, and a simple XML backend.

Like many real-world programming tasks, there are lots of ways to write code that meets the spec but there are enough corner cases that a lot of those ways turn into fairly ugly messes pretty quickly.3

The task

Your challenge, should you choose to accept it, is to provide:

  1. The source code to a parser that, given the contents of a file in whatever form is natural for your language of choice—perhaps as an open stream or a string—returns a data structure representing the document tree as described in the Markup specification if the file is syntactically correct.

  2. English language documentation for the data structure returned by the parser sufficient to allow a programmer familiar with your implementation language to write a back-end that generates some kind of output from the results returned by the parser.

  3. The source code to a sample back-end that generates well-formed XML according to the “Trivial XML backend” section of the spec.4

  4. The source code to a driver program that, given the name of a file, parses the file and then generates a corresponding XML file.

  5. Any libraries you use beyond those that are normally part of an installation of your chosen programming language.

  6. Any build instructions or scripts are needed to build the driver program or instructions how to run it if it requires no separate building.

  7. Optionally, any notes about your experience implementing this code: how you came up with your design, blind alleys you went up, or surprising problems you ran into. Or anything else you want to share.

You may implement your program in whatever programming language you want for whatever hardware platform and OS you like. However, all other things being equal, we’d rather get code that we can run on GNU/Linux, OS X, or Windows on x86 or x86-64 hardware unless there is a very compelling reason to choose a different platform.

The driver program can be a command line program, a GUI, or—for languages that provide some kind of interactive environment—a function that can be called with the name of the file to parse.

Issues with the spec

Like many real-world specs, this task specification as well as the Markup specification itself are almost certainly not perfect. As this is not life-critical software, you are free to use your best judgement to fill in any gaps that you discover. Or you may send queries to code@codequarterly.com and we’ll try to answer your questions as quickly as we can. Or you can leave a comment.

One notable gap in the spec is the omission of anything about what to do if you are asked to parse a file that is not syntactically correct Markup. It wouldn’t be unreasonable—mostly in order to keep this challenge from being too much work—to simply treat being asked to parse malformed input as an unspecified, anything-can-happen, demons-will-probably-come-out-of-your-nose situation. But if you want to write production quality code and come up with clever ways of giving precise and useful error messages or otherwise deal more gracefully with bad input, more power to you.

Okay, I accept your challenge

Great! There are two ways to get started. You can download an archive containing these instructions, as well as all the specification files and test cases you’ll need. The archive is available in tar.gz and zip. Or, if you have a GitHub account and don’t mind operating somewhat in public, you fork our project at:


It contains the same files you would get if you downloaded the challenge archive. You can then track the history of your development using git, which may be just as interesting as your final result.

When you’re ready to submit your code, you’ll need to create either a tar.gz, or a zip archive containing all your files and upload it here or submit the URL of a GitHub commit containing the code you want to submit.

In the meantime you can leave a question or comment or discuss this challenge with other participants on our comments page.

Submissions are due midnight Coordinated Universal Time, October 15th, 2010.

The fine print

Since we intend to publish the code on our web site and will discuss some of the code in our article we need sufficient rights to republish your code in its entirety. When you are ready to submit your code, you will need to agree to some terms giving us the rights we need. Beyond that, your code is yours to do with as you see fit.

Good luck and happy coding!

1 At least to the extent that Emacs can be considered a plain text editor.

2 The focus on logical markup is the main difference between Markup and Markdown and reStructuredText. There doesn’t seem to be any way to do that kind of logical markup in Markdown. In reStructuredText you can use “Interpreted Text” for logical markup. However unlike reStructuredText, Markup uses the same syntax for all character-level markup, minimizing the number of characters that have to be escaped otherwise.

Markup also differs from Markdown in that it is defined as a syntax that maps to an abstract tree rather than as a text format that maps to HTML. Thus Markup can be used for things other than generating HTML. In this respect it is more like reStructuredText.

3 Trust me, I’ve written enough ugly versions to be pretty sure about this —Editor

4 We don’t use XML because we have any great love for it but because it is a reasonable lowest-common-denominator format.