Games for Programmers: Zendo

In addition to teaching and programming, I also enjoy playing board games. This is the first in an irregular series of game recommendations for programmers. Of course, you don't have to be a programmer to enjoy these games, but if you are a programmer, then I think there's a pretty good chance that you'll like them.

Zendo is a game about debugging. Ok, it's not really about debugging, but you'll see what I mean in a moment.

Zendo is a logic game played with a bunch of Icehouse pieces (plastic pyramids in several different colors and sizes) and some markers.

(photo by Terraliptar)

During the game, pyramids will be placed in groups (called “koans”) that either satisfy or don't satisfy some secret rule. The players try to figure out the rule based on these examples. For example, consider the following group:

(photo by Ted Alspach)

This group might satisfy the rule “at least one piece off the table” or “exactly one tilted piece” or “fewer than two green pieces” or “contains pieces of three different sizes”. It would not satisfy the rule “no two pieces of the same color”.

One player is designated as the master, who chooses the secret rule and judges whether proposed groups satisfy the rule. The master initially sets out one group that satisfies the rule (marked with a white stone), and one that doesn't (marked with a black stone). The other players take turns proposing groups, which the master then marks with white or black stones. Later in the game, players try to guess the rule, based on the evidence they've seen. If a guess is correct, that player wins the round, and a new master is chosen for the next round. If a guess is incorrect, then the master creates a counter-example, either a group the satisfies the secret rule but not the player's rule, or a group that satisfies the player's rule but not the secret rule. Either way, the master marks the counter-example with the appropriately colored stone.

That's the basics of the game. There are a few more details that can be found in the complete Zendo rules. (That site also offers a fascinating design history of the game.)

As a player, you are constantly coming up with possible rules and checking whether they are consistent with the examples that are already on the table. Often you will have more than one possible rule in mind. When it's your turn, you try to design a group that will help narrow down the choices. Ideally, you want a make your group so that either a positive or a negative answer will support some possible rules and deny others.

The primary challenge as master is coming up with a good secret rule, one that is not too hard and not too easy. Of course, too hard and too easy will depend on who you are playing with. Looney Labs sells a pack of Zendo rule cards to get you started. These rules are fairly easy and are perfect for those new to the game. Eventually, you will want to start creating your own rules.

Debugging

Debugging is a fundamental skill of the programmer. When its your own bug or you're operating under severe time pressure, negative emotional reactions can make debugging quite stressful. But when you are helping somebody else debug their code, it can be quite fun, kind of like a logic puzzle.

There are two basic approaches to debugging; most debugging sessions combine both. In one approach, you step through the code, re-thinking each line and looking for something suspicious.

In the other approach, you look at the observable evidence—for this input, it's producing that output, when it should be producing this other output, or the web site crashes every day between 5pm and 6pm— and try to come up with a hypothesis for what might be going wrong. For example, you might hypothesize that something is going wrong when two clients happen to have the same name, or that somebody is mixing up row-column coordinates with X-Y coordinates. Often you try to come up with an experiment that might confirm or deny your hypothesis, or help select between several competing hypotheses. Once you have a fairly solid hypothesis, you can usually narrow down where in the code to go looking for the error.

It's this latter approach to debugging that Zendo captures so well, that of making and testing and refining and discarding hypotheses.

Of course, that's the perspective of a computer scientist. Other kinds of scientists might prefer to think of Zendo in terms of the scientific method.

How to get it

Zendo used to be sold in a nice boxed set, but that is long out of print. In fact, I didn't get my copy until after it was already out of print. I got it as a gift from my BoardGameGeek Secret Santa, a charming annual tradition where hundreds of boardgamers anonymously send Christmas presents (games, naturally) to other gamers around the world, usually gamers that the sender doesn't even know.

You can still buy the pyramids from Looney Labs, where they are sold as Treehouse sets. You would need at least four sets to play Zendo—five would be better. It's kind of expensive that way, but fortunately there are a whole bunch of other games you can play with the pieces. You would still need a set of markers, but poker chips or coins in several denominations work fine.

In fact, with only minor modifications, it's easy to improvise a set of pieces for Zendo out of common household objects, such as bottles of beer.