Alpha-beta pruning

3 files changed, 23 insertions, 7 deletions

diff --git a/ai/src/lib.rs b/ai/src/lib.rs
index 583c50b..405c88d 100644
--- a/ai/src/lib.rs
+++ b/ai/src/lib.rs
@@ -26,7 +26,7 @@ fn eval_position(board: CheckersBitBoard) -> f32 {
 	}
 }
 
-pub fn eval(depth: usize, board: CheckersBitBoard) -> f32 {
+pub fn eval(depth: usize, mut alpha: f32, beta: f32, board: CheckersBitBoard) -> f32 {
 	if depth == 0 {
 		eval_position(board)
 	} else {
@@ -35,14 +35,21 @@ pub fn eval(depth: usize, board: CheckersBitBoard) -> f32 {
 		for current_move in PossibleMoves::moves(board) {
 			let board = unsafe { current_move.apply_to(board) };
 			let current_eval = if board.turn() != turn {
-				1.0 - eval(depth - 1, board)
+				1.0 - eval(depth - 1, 1.0 - beta, 1.0 - alpha, board)
 			} else {
-				eval(depth - 1, board)
+				eval(depth - 1, alpha, beta, board)
 			};
 
+			if current_eval >= beta {
+				return beta;
+			}
+
 			if best_eval < current_eval {
 				best_eval = current_eval;
 			}
+			if alpha < best_eval {
+				alpha = best_eval;
+			}
 		}
 
 		best_eval
diff --git a/cli/src/eval.rs b/cli/src/eval.rs
index eaa2d41..d078c5f 100644
--- a/cli/src/eval.rs
+++ b/cli/src/eval.rs
@@ -1,4 +1,4 @@
 use ai::CheckersBitBoard;
-pub fn eval() -> f32 {
-	ai::eval(12, CheckersBitBoard::starting_position())
+pub fn eval(depth: usize) -> f32 {
+	ai::eval(depth, 0.0, 1.0, CheckersBitBoard::starting_position())
 }
diff --git a/cli/src/main.rs b/cli/src/main.rs
index 57991f0..a550092 100644
--- a/cli/src/main.rs
+++ b/cli/src/main.rs
@@ -47,7 +47,16 @@ fn main() {
 		);
 	}
 
-	if let Some(_matches) = matches.subcommand_matches("eval") {
-		println!("{}", eval::eval());
+	if let Some(matches) = matches.subcommand_matches("eval") {
+		println!(
+			"{}",
+			eval::eval(
+				matches
+					.value_of("depth")
+					.unwrap()
+					.parse::<usize>()
+					.expect("Error: not a valid number")
+			)
+		);
 	}
 }