Day 1: The Call to Adventure

When we first built our system, we found writing configuration files burdensome. The file formats we could use to describe test inputs and outputs just weren’t that expressive.

Take comma-separated values (CSV), for instance. Say you wanted to describe characters and vehicles for a video game. Your CSV configuration file might start like this:

 name, treasure1, treasure2, treasure3, treasure4, treasure5
 knight, -1000, +200, --, --, --

Now, say you wanted to add a square vehicle to the in-game world, and make it so you can’t accidentally change the width without also changing the height:

 name, width, height
 mine cart, $cube_size, $cube_size

Here’s the problem: CSV doesn’t support collections or constraints. You’d ...

Get Seven More Languages in Seven Weeks now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.