Overview of Nilatac

You can browse Nilatac's opening book online here.

NEW: I've finally taken the time to apply the GPL to the source code. You can browse it here. So now it's truly free software. Of course, that doesn't make it any better :) And I'm still too lazy to make a tar.gz archive.

I'm a FICS user and I'm playing Nilatac. What features does it have?

• Nilatac accepts draws after 7 reversible moves. Please note the word reversible: 7 moves have to pass without any captures or pawn pushes before Nilatac will accept draws. This is an uncommon feature. Most computers ignore or decline all draw offers, which can be a real nuisance, because you have to keep playing a game that is an obvious draw until the 50 move rule or the 3rd repetition rule take effect.
  
  
• Nilatac will keep your seat warm. After you play a game, Nilatac will give you priority and decline match offers from anybody else for 5 seconds. This should give you time to hit rematch if you want to play some more. I added this feature because I know how frustrating it feels when someone comes and steals your computer just when you were having a good time with it :)
  
  
• Nilatac has a noescape policy. For the first 10 games you play against Nilatac, you will have to set noescape 1 before Nilatac will accept your invitation. The effect of this setting is that if you disconnect during the game, you will lose the game. I am really not too happy to enforce this policy, but without it people constantly disconnect on Nilatac and I have very little time to adjudicate its games. Once you play 10 or more games, you become a trusted opponent and Nilatac no longer requires you to set noescape to 1.
  
  
• Nilatac will not play rated against you if (a) you have a rating above 2000, (b) you are human and (c) you would exceed your best rating in case you won. I have had several complaints from good suicide players that people are exploting weaknesses in Nilatac to boost up their ratings, and I can see why that is disturbing. I do not want Nilatac to cause an instability in the ratings pool.

Ummm... suicide what?

• The goal is to lose all your pieces, even your king.
• Captures are mandatory. If you can capture, then you must do so. If you have multiple possibilities to capture, you can execute any of them.
• The king is not a special piece. You can leave it in check and it can be captured (thus, the term "check" becomes meaningless).
• Pawns can be promoted to kings as well.
• In case of stalemate, the side with fewer pieces wins (if the two sides have an equal number of pieces then the game ends in a draw).
• Castling is not allowed.

What's a chess server?

However, chess servers provide what you cannot always find in real life: a huge diversity of opponents with various styles and temperaments (and vocabulary, for that matter). You can play chess and variants, simultaneous matches, blind matches, bughouse, or you can sit back and watch lectures or other people's games (you can kibitz on those games too).

My favorite chess server is FICS (the Free Internet Chess Server). You can connect to FICS right off their webpage, although you probably want to follow these instructions in order to install a more friendly interface.

What's a chess engine?

I began work on Nilatac simply because a friend of mine from MIT had to write a suicide chess program as the final project for a programming lab. The idea sounded nice and I started coding my own suicide chess program. Shortly afterwards, I decided to connect it to a chess server.

Nilatac has no graphic interface. It does have a user-interactive mode, but you have to type in commands from the keyboard, for example "move e2e3" to make a move, or "think 20" to let Nilatac think for 20 seconds and then make a move. Nilatac was never designed as a stand-alone program; my focus was to connect it to a server.

The first version of Nilatac (this section to be continued)

What about the driver?

To make things more complicated, different servers have different output formats. Since I wanted the ability to connect Nilatac to multiple servers, I had to make the driver general enough to understand multiple syntaxes.

A good driver, therefore, is almost as important as a good engine. I decided to implement my own driver, although I've heard it's simple to connect your program using one of the consecrated clients like xboard. My driver simply spawns a telnet process to connect to the server, then captures the process' output. The driver then acts as a mediator between the server and the chess engine. For example, when it receives a board, the driver:

1. tells the engine what the board is;
2. decides for how long the engine should be allowed to think;
3. waits for the engine to make a move;
4. forwards that move to the server

• Accept or decline draw offers. Nilatac accepts draws after 7 reversible moves (i.e., 7 moves without any captures or pawn pushes). The server sends the number of reversible moves with each board.
• Message people who disconnect during the game. This is somewhat abusive, but most of the people who disconnect do so because they realize they're in a lost position.
• Send offers to resume the game to people who have an adjourned game with Nilatac when they return on the server.
• Remember who our last partner was. After finishing a game, Nilatac gives priority to its last opponent for a rematch, and declines invitations from any other players for 5 seconds. This is to allow people to play long streaks of games if they want that.
• Obey the commands of a designated player on the server (myself). If I tell Nilatac to quit, offer a draw or place a seek, it will do so. This is useful when Nilatac is running from my home computer and I am watching it from another place.
• When the game is finished, examine the move list and learn an opening. Nilatac has a self-generated opening book that it improves by examining its past games. In suicide, openings are crucial as one mistake can lead to a forced loss. We do not learn an opening if our last game was against a weak player, because we might have played a bad opening, but got away with it due to our opponent's weakness.
• Maintain a list of the best suiciders. Nilatac "trusts" these players and periodically examines their history games to learn more openings. This is done by simply issuing a sequence of "history" and "smoves" commands. Nilatac examines hundreds of games every day and its opening book is rapidly improving.
• Respond to tells. For now, we only respond to the "features" tell: if somebody tells us "features", we send them back a summary of our features. A nice idea would be to hook up Nilatac with Eliza so we could make it chat :-)

What algorithms is nilatac using?