This change builds on several previous changes to implement Zobrist hashing of the
board. This hash can be updated incrementally as changes are made to the board.
In order to do that, various properties of the Board struct had to made internal.
In the setters and various mutating members of Board, the hash is updated as
state changes.
The entire hashing mechanism is optional. If no ZobristState is provided when the
Board is created, the hash is never computed.
Plumb the Zobrist state through Position as well so that clients of Position (the
ultimate interface for interacting with the chess engine) can provide global
state to the whole engine.
The explorer crate gives an example of how this works. Some global state is
computed during initialization and then passed to the Position when it's created.
Make the struct attribute private, and export two new methods. A getter, active_color(),
and a setter, set_active_color().
Update all references to the attribute to use the methods.
Instead of inheriting the MakeMove and UnmakeMove traits by being a BoardProvider,
implement bespoke versions of these two methods. This gives Position a chance to
do some of its own work (tracking captures, move records, etc) when making a move.
Pass the move record by reference to the unmake_move() method. Saves a copy.
Export the Result types for MakeMove and UnmakeMove.
The moves command writes all possible moves to the terminal.
Move the previous implementation of the moves command, which marked squares that
a piece could move to, to a 'movement' command.
Implement thiserror::Error for a bunch of error types, and remove string errors
from the implementation of the command handler in explorer.
Clean up parsing of basic types all over the place.
Update Cargo files to include thiserror and anyhow.
Clean up the implementation of the place command.
Track state with a State struct that contains a position and a builder. The place
command will place a new piece and then regenerate the position.
The make command makes a move. The syntax is:
make [color:w|b] [shape] [from square] [to square]
The fen command prints a FEN string representing the position.
