Play Zork while reading the 1980 code that makes it work

Type “open mailbox” in The Visible Zorker, and the game does what it always did: tells you the mailbox is open, with a leaflet inside. But on the same page, you also see the function that just ran, what variables it touched, and where every object in the room currently sits. Andrew Plotkin, the interactive fiction veteran behind the Obsessively Complete…