Cacti Chess

A small chess engine written in go that isn't terrible. Written with help from the chess programming wiki, and loosely modeled after the vice engine written in c.

Project Goals

Cacti Chess isn't meant to be a serious engine, rather a way to learn a bit more go and understand how chess engines work in general.

With an opening book provided from a UCI compatible program, I'd estimate it's elo to be ~800-1000. It will usually avoid small blunders, but still suffers from strategic weaknesses. There are also a few features not implemented which would speed up the search and eval functions, allowing it to compute to deeper depths. Currently it can generate ~1 mil moves/sec in perft testing. Similarly it can evaluate a position to depth 5 in ~1 second.

There are some features not implemented that would help improve performance and evaluation.

• Move Ordering - Impacts Alpha/Beta move speed
• Transposition Tables - If we reach the same position two different ways, avoid duplicate computations after.
• Quiescence Function - If the last move of a line was a capture, look a little farther than normal to avoid tactical tricks. Wait for things to 'Quiet' down.
• Opening Books - Not needed for UCI GUIs, but makes the CLI version quite weak.

Packages

• cmd - A CLI wrapper around the engine
• engine
  • eval - Basic Material + Piece Square Evaluations
  • perft - Unit tests for millions and millions of chess positions to ensure move generation is working properly.
  • position - Models for the board/pieces/moves
  • search - AlphaBeta implementation to find the best line.
• lichess-bot - Slightly modified version of https://github.com/dolegi/lichess-bot
• uci - A UCI wrapper around the engine

CLI

You can play against the engine using a CLI. It will show a small terminal board where you can input moves. The move format matches UCI specs, where it is starting square, ending square, optional promote.

• e2e4
• e7e5
• h7h8q // move and promote

go run ./cmd play
...

rnbqkbnr
pppp.ppp
........
....p...
....P...
........
PPPP.PPP
RNBQKBNR
--------
side: 0
enPas: 75
castle: KQkq
posKey: a4db34adbeab59f6

UCI Engine

The uci package implements a (semi) UCI compatible interface to the engine. The main commands of position and go work without issue, though it doesn't understand all time control params. It is far enough along that you can play it using a chess GUI. I recommend the area gui. You can compile the uci package, and install it using arena. From there, it will be used to play games.

Lichess Bot

The lichess-bot package is a copy of https://github.com/dolegi/lichess-bot, which serves as a bridge between the UCI interface and Lichess API. It can be used to play games against the engine over lichess. A Lichess Bot API token is required to run.