Pupil

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Overview

Pupil is a chess engine written in Go. The goal of writing this program was to create an engine capable of beating me in a 10 minute game.

Perft tests pass for the initial board state and for kiwipete up to depths 6 and 5 respectively.

Some of the major optimizations include: bitboard piece representation, magic bitboards for move generation, multi-threaded perft tests (for development speed), object pooling, and a transposition table keyed via zobrist hashes.

Although nowhere near as complete, the code is heavily inspired by the open-source Stockfish project, whose source code I dipped into heavily.

Note to anyone reading the code:

Apologies for the weird code style. I began this project before installing a linter in my editor/becoming familiar with the golang style guide. I haven't been able to find a good codemod/script to automatically clean it up. If you know of any, please let me know.

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Description

Feature	Implementation
Board representation	Bitboard
Square mapping	Little-endian Rank-file Mapping
Bitboard Serialization	Forward-scanning
Move encoding	16 bit From-to based
Move Generation	Magic Bitboard approach
Search	AlphaBeta search within the Negamax framework. Currently uses transposition tables to cache information about the different node types.
Evaluation	Simplified Evaluation Function: Material value and positional value based on precomputed arrays.

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History

This is my third attempt at a chess engine.

The predecessors:

1. Rhess - a command line game written in Ruby using a mailbox 8x8 board representation. Styled with 100% unicode and playable via keyboard.

2. Gogochess - a chess-move generator written in Go with a custom HashMap based move-list. Passing perft tests up to depth 5 and capable of solving Mate-in-Twos in less than a minute. Configured with HTTP API for browser integration and easy testing.

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Todo

• Test alpha-beta against negamax.
• Update transposition table for non-perft search
• Cache best move
• Update alpha-beta to search best move first
• Limit cache entry size
• Implement LRU/better cache clearing (simple array)
• Flesh out frontend for better UX
• Experiment compiling to WebAssembly
• Deploy (WebAssembly or no)

Nice to haves:

• Quiescence search
• Iterative deepening with time limit
• Concurrent alpha-beta
• Lint