Crabablanca: command-line chess in Rust

So named after legendary chess player José Raúl Capablanca and Ferris the Rust mascot, who is a crab.

How to play

After compilation, launching the executable in a terminal window will start the game. Default behaviour is that the player must input moves for both sides using standard algebraic chess notation (with some exceptions, noted below). A number of commands allow for different behaviour:

• white hands control of the black pieces to the engine, leaving the player as white
• black hands control of the white pieces to the engine, leaving the player as black
• play hands control of both sides to the engine, which will then play against itself
• showme and !showme toggle display of every possible move after each move is made
• preview briefly shows the top engine move in the current position
• next plays the top engine move
• quit and exit terminate the program

Exceptions to standard chess notation are as follows:

• Castling is performed by inputting a king move to the square it will end up on having castled (ie. Kc1/Kg1 for white, Kc8/Kg8 for black), instead of standard O-O/O-O-O.
• Pawns automatically promote to queens, no additional notation for promotion is currently supported.
• En passant is not implemented, so notation to attempt it will not be accepted.

The Crabablanca engine

Crabablanca is a from-scratch engine.

Board representation

Crabablanca is built on "bitboards", whereby each set of pieces of a certain type (eg. white rooks, black pawns, etc.) is represented by a 64-bit unsigned integer. Each bit represents a square of the chessboard, and is 1 if a piece is present in that square, and 0 otherwise. This allows for highly compact representation and efficient manipulation of the state of the board.

Evaluation

Crabablanca considers material balance, central pawns, piece mobility, king safety, doubled pawns, and possible checks when assessing static evaluation. The evaluation function has not been thoroughly tuned, and is a long way from complete.

Search

Crabablanca uses an alpha/beta depth-first search to a fixed depth. Currently that depth is set to 4 ply (ie. 2 moves from each side), which is not a lot - this is limited by the (currently!) rudimentary nature of the engine. Plans to improve search performance include implementing a transposition table and experimenting with multi-threaded search.