Trait alcibiades::Evaluator [−] [src]

pub trait Evaluator: Clone + SetOption + Send + 'static {
    fn new(position: &Board) -> Self;
    fn evaluate(&self, position: &Board) -> Value;
    fn is_zugzwangy(&self, position: &Board) -> bool;

    fn will_do_move(&mut self, position: &Board, m: Move) { ... }
    fn done_move(&mut self, position: &Board, m: Move) { ... }
    fn will_undo_move(&mut self, position: &Board, m: Move) { ... }
    fn undone_move(&mut self, position: &Board, m: Move) { ... }
}

A trait used to statically evaluate positions.

An evaluation function is used to heuristically determine the relative value of a position, i.e. the chances of winning. If we could see to the end of the game in every line, the evaluation would only have values of "loss", "draw", and "win". In practice, however, we do not know the exact value of a position, so we must make an approximation. Beginning chess players learn to do this starting with the value of the pieces themselves. Computer evaluation functions also use the value of the material as the most significant aspect and then add other considerations.

Static evaluation is an evaluation that considers only the static material and positional properties of the current position, without analyzing any tactical variations. Therefore, if the position has pending tactical threats, the static evaluation will be grossly incorrect. To implement your own static evaluator, you must define a type that implements the Evaluator trait.

Required Methods

Creates a new instance bound to a given position.

When a new evaluator is created it is bound to a particular chess position (given by the position parameter), and for the moment, this is the only position that it can evaluate. The evaluator then can be re-bound to the next (or the previous) position in the current line of play by issuing a pair of calls to the will_do_move and done_move methods (or respectively, will_undo_move and undone_move methods). Thus, evaluator's state can be kept up-to-date, following the current line of play.

Evaluates the the position to which the evaluator is currently bound.

position points to the position to which the evaluator is currently bound.

The returned value must be between VALUE_EVAL_MIN and VALUE_EVAL_MAX.

Returns whether the position to which the evaluator is currently bound is "zugzwangy".

position points to the position to which the evaluator is currently bound.

In many endgame positions there is a relatively high probability of zugzwang occurring. For such positions, this method returns true. This is useful when we want to decide whether it is safe to try a null move.

Provided Methods

Updates evaluator's state to keep up with a move that will be played.

position points to the position to which the evaluator is currently bound (that is: before m is played).

m is a legal move, or (if not in check) a "null move".

Updates evaluator's state to keep up with a move that was played.

position points to the new position to which the evaluator is bound (that is: after m was played).

Updates evaluator's state to keep up with a move that will be taken back.

position points to the position to which the evaluator is currently bound (that is: before m is taken back).

Updates evaluator's state in accordance with a move that was taken back.

position points to the new position to which the evaluator is bound (that is: after m was taken back).

Implementors