Once a month, web developers from across the Mozilla Project get together to design user-friendly advertisements. When we’re not deciding which police alarm we want to auto-play, we find time to talk about our side projects and drink, an occurrence we like to call “Beer and Tell”.

There’s a wiki page available with a list of the presenters, as well as links to their presentation materials. There’s also a recording available courtesy of Air Mozilla.

Erik Rose: Whitespace-significant Meta-grammar for Homoiconic Languages

The only presenter this week was ErikRose, who shared a prototype grammar for a class of whitespace-significant programming languages. The goal was to represent the nested-list structure of homoiconic languages like Lisp while keeping redundant bracing out of the way like Python.

if is_yak then
    shave yak
    bathe yak
  else
    do productive_work

--> (if is_yak then
        ((shave yak)
         (bathe yak))
     else
        ((do productive_work))
    )

Normally, when the else statement in code similar to the sample above isn’t indented and is at the same level as the if statement, the parser must know that else statements may follow after if statements and are related to them. To get around this, ErikRose suggests using a partial outdent. This way, the parser can recognize that the else statement is separate from the shave and bathe lines but should still be grouped with the if statement, even if the parser doesn’t know what an if statement is.

Erik’s gist contains a few more samples and a possible grammar for parsing a language like this using Parsimonious, his parsing library.

Our focus group of QVC customers has given us great insight in to just what the average internet user is looking for in their sponsored content. Early retirement, here we come!

If you’re interested in attending the next Beer and Tell, sign up for the dev-webdev@lists.mozilla.org mailing list. An email is sent out a week beforehand with connection details. You could even add yourself to the wiki and show off your side-project!

See you next month!