Chess

An experiment on chess-playing, using actors as underlaying computational model.

Overview

Interaction with a front-end

In modern chess engines, the user interface is not catered for by the engine. Instead of that, a standard protocol is implemented, and used to interact with specialised, front-end programs, such as Arena and PyChess.

There are several standards, of which two are outstanding:

• Chess Engine Communication Protocol
• Universal Chess Interface

This program implements UCI, because it's more modern and better supported by front-end programs than CECP.

UCI implementation

For details of the protocol, see the UCI specification.

In this program the UCI is implemented as a finite-state machine, supported by Akka's FSM actors.

A FSM can be described as a set of relations of the form: State(S) x Event(E) -> Actions (A), State(S’). In a given state S, receiving an event E from the front-end triggers a set of actions (effects) and sets the machine to a new state S´.

States: Idle (the engine is doing nothing), Ready (initialised, can receive the uci command), Waiting (waiting to receive commands), Dead (operation is finished), GameResetting (reset game information), Thinking (calculating).

Events that can be sent by the GUI: UCI, Debug, IsReady, SetOption, Register, UCINewGame, Position, Go, Stop, PonderHit, Quit.

Internally generated events: GameReset, ThinkingStopped.

State	Event	Actions	New state
Idle	Start	Initialise	Ready
Ready	UCI	Send id..., send option..., send uciok	Waiting
Waiting	Debug	Set debug on/off	Waiting
Waiting	IsReady	Send readyok	Waiting
Waiting	SetOption	Change an option	Waiting
Waiting	Register	Send successful registration strings	Waiting
Waiting	UCINewGame	Reset game information	GameResetting
GameResetting	IsReady	Set readyok as pending	GameResetting
GameResetting	GameReset	Send readyok if pending	Waiting
GameResetting	Debug	Set debug on/off	GameResetting
GameResetting	Quit	Exit	Dead
Waiting	Position	Set internal board	Waiting
Waiting	Go	Start evaluating	Thinking
Thinking	IsReady	Send readyok	Thinking
Thinking	PonderHit	Deactivate pondering	Thinking
Thinking	ThinkingStopped	Stop evaluating, send info+bestmove+ponder	Waiting
Thinking	Stop	Stop evaluating, send info+bestmove+ponder	Waiting
Thinking	Debug	Set debug on/off	Thinking
Thinking	Quit	Exit	Dead
Waiting	Quit	Exit	Dead
Dead	-	-	Dead

The licensing model of this program makes the use of the copyprotection response irrelevant. Also, the registration process is always instantaneously successful.

Currently, the only options supported by the program are UCI_EngineAbout (for which there is no equivalent SetOption command) and Ponder.

Computational model

References

The Chess Programming Wiki contains a lot of useful information about many aspects of the challenge, including notational alternatives, AI, testing and tuning.

The Portable Game Notation site describes with detail and clarity notational aspects of the game.