trying to fix this shit :(

Cargo.toml

@@ -6,5 +6,5 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-bumpalo = { version = "3.9.1", features = [] }
+bumpalo = { version = "3.9.1" }
 rand = "0.8.4"

src/lib.rs

@@ -11,35 +11,44 @@ pub enum Status<P> {
     Winner(P),
 }
 
+pub trait PlayerState: Eq + Copy {
+    fn next(self) -> Self;
+}
+
 pub trait GameState: Clone + std::fmt::Debug {
-    type Player: Eq + Copy + std::fmt::Debug;
+    type Player: PlayerState + std::fmt::Debug;
 
     fn next_states(&self) -> Box<dyn ExactSizeIterator<Item = Self>>;
 
     fn status(&self) -> Status<Self::Player>;
 
+    fn toggle_player(&mut self);
+
     fn next_random_play(&mut self);
 }
 
 mod mcts {
-    use crate::{GameState, Status};
+    use crate::{GameState, PlayerState, Status};
     use bumpalo::Bump;
     use rand::Rng;
     use std::cell::Cell;
 
     #[derive(Debug, Clone)]
-    struct Node<'tree, S> {
+    struct Node<'tree, S: GameState> {
         state: S,
+        // todo: don't have this field and let the GameState handle this all
+        player: S::Player,
         visited: Cell<u32>,
         score: Cell<i32>,
         parent: Option<&'tree Node<'tree, S>>,
         children: Cell<&'tree [Node<'tree, S>]>,
     }
 
-    impl<'tree, S> Node<'tree, S> {
-        fn new(state: S, alloc: &'tree Bump) -> Node<S> {
+    impl<'tree, S: GameState> Node<'tree, S> {
+        fn new(state: S, player: S::Player, alloc: &'tree Bump) -> Node<'tree, S> {
             Node {
                 state,
+                player,
                 visited: Cell::new(0),
                 score: Cell::new(0),
                 parent: None,
@@ -64,26 +73,31 @@ mod mcts {
 
     const MAX_TRIES: u64 = 10_000;
 
-    pub fn find_next_move<S: GameState>(current_state: S, opponent: S::Player) -> S {
+    pub fn find_next_move<S: GameState>(current_state: S, own_player: S::Player) -> S {
         let alloc = Bump::new();
+        let opponent = own_player.next();
 
-        let root_node = alloc.alloc(Node::new(current_state, &alloc));
+        let root_node = alloc.alloc(Node::new(current_state, opponent, &alloc));
 
         for _ in 0..MAX_TRIES {
+            // Phase 1 - Selection
             let promising_node = select_promising_node(root_node);
 
+            // Phase 2 - Expansion
             if promising_node.state.status() == Status::InProgress {
                 expand_node(&alloc, promising_node);
             }
 
-            if !promising_node.children.get().is_empty() {
-                let child = promising_node.random_child();
-                let playout_result = simulate_random_playout(child, opponent);
-                back_propagation(child, playout_result);
+            // Phase 3 - Simulation
+            let promising_node = if !promising_node.children.get().is_empty() {
+                promising_node.random_child()
             } else {
-                let playout_result = simulate_random_playout(promising_node, opponent);
-                back_propagation(promising_node, playout_result);
+                promising_node
             };
+            let playout_result = simulate_random_playout(promising_node, opponent);
+
+            // Phase 4 - Update
+            back_propagation(promising_node, playout_result);
         }
 
         let winner_node = root_node.child_with_max_score();
@@ -92,7 +106,9 @@ mod mcts {
         node.state.clone()
     }
 
-    fn select_promising_node<'tree, S>(root_node: &'tree Node<'tree, S>) -> &'tree Node<'tree, S> {
+    fn select_promising_node<'tree, S: GameState>(
+        root_node: &'tree Node<'tree, S>,
+    ) -> &'tree Node<'tree, S> {
         let mut node = root_node;
 
         while !node.children.get().is_empty() {
@@ -107,6 +123,7 @@ mod mcts {
 
         let new_nodes = possible_states.map(|state| Node {
             state,
+            player: node.player.next(),
             visited: Cell::new(0),
             score: Cell::new(0),
             parent: Some(node),
@@ -148,6 +165,7 @@ mod mcts {
         }
 
         while board_status == Status::InProgress {
+            state.toggle_player();
             state.next_random_play();
             board_status = state.status();
         }
@@ -157,6 +175,7 @@ mod mcts {
 
     mod uct {
         use crate::mcts::Node;
+        use crate::GameState;
 
         pub fn uct(total_visit: u32, win_score: i32, node_visit: i32) -> u32 {
             if node_visit == 0 {
@@ -170,7 +189,7 @@ mod mcts {
             num as u32
         }
 
-        pub(super) fn find_best_node_with_uct<'tree, S>(
+        pub(super) fn find_best_node_with_uct<'tree, S: GameState>(
             node: &'tree Node<'tree, S>,
         ) -> Option<&'tree Node<'tree, S>> {
             let parent_visit_count = node.visited.get();
@@ -184,7 +203,7 @@ mod mcts {
 }
 
 pub mod tic_tac_toe {
-    use crate::{GameState, Status};
+    use crate::{GameState, PlayerState, Status};
     use rand::Rng;
     use std::fmt::{Display, Formatter, Write};
 
@@ -194,10 +213,8 @@ pub mod tic_tac_toe {
         X,
     }
 
-    impl std::ops::Not for Player {
-        type Output = Self;
-
-        fn not(self) -> Self::Output {
+    impl crate::PlayerState for Player {
+        fn next(self) -> Self {
             match self {
                 Self::O => Self::X,
                 Self::X => Self::O,
@@ -265,7 +282,7 @@ pub mod tic_tac_toe {
                 .map(|(i, _)| {
                     let mut new_state = *self;
 
-                    new_state.active_player = !self.active_player;
+                    new_state.active_player = self.active_player.next();
                     new_state.board[i] = new_state.active_player.into();
 
                     new_state
@@ -306,9 +323,11 @@ pub mod tic_tac_toe {
             Status::InProgress
         }
 
-        fn next_random_play(&mut self) {
-            self.active_player = !self.active_player;
+        fn toggle_player(&mut self) {
+            self.active_player = self.active_player.next();
+        }
 
+        fn next_random_play(&mut self) {
             let free_fields = self.free_fields();
             let random_field = rand::thread_rng().gen_range(0..free_fields);
 
@@ -352,6 +371,7 @@ pub mod tic_tac_toe {
         use std::io::Write;
 
         const PLAYING_PLAYER: Player = Player::O;
+        const AI_PLAYER: Player = Player::X;
 
         pub fn main() {
             let mut board = Board::new(PLAYING_PLAYER);
@@ -364,7 +384,7 @@ pub mod tic_tac_toe {
                     break result;
                 }
 
-                let ai_play = mcts::find_next_move(board, PLAYING_PLAYER);
+                let ai_play = mcts::find_next_move(board, AI_PLAYER);
                 board = ai_play;
 
                 if let Some(result) = is_finished(&board) {