You are standing in a field. To your east is a small white house with a boarded front door. There is a mailbox here. What do you do? To some of you, this is a familiar situation, it's the opening scene to the popular text adventure (AKA "interactive fiction") game Zork. These games were deep and interesting games in a time when most games struggled to match Space Invaders and Asteroids. How did they do this? By not having graphics and letting your imagination do the heavy lifting. You don't control your character with a joystick, you just type what you want to do and the game tells you what happens.
In this series of articles, we'll be making our own text adventure game in Ruby from scratch. This first part explains how the whole thing will be powered: from a single tree structure.