GameState::reward_for_player is no longer a trait function

We need GameState::rewards_for_players implemented, the library
currently doesn't need to specify for a singular player.

benches/e2e.rs

@@ -125,6 +125,19 @@ impl TicTacToe {
 
         None
     }
+
+    fn reward_for_player(&self, player: &Player) -> RewardVal {
+        if let Some(winner) = self.get_winner() {
+            if winner == *player {
+                return 1.0; // Win
+            } else {
+                return 0.0; // Loss
+            }
+        }
+
+        // Draw
+        0.5
+    }
 }
 
 impl GameState for TicTacToe {
@@ -161,19 +174,6 @@ impl GameState for TicTacToe {
         self.get_winner().is_some() || self.moves_played == 9
     }
 
-    fn reward_for_player(&self, player: &Self::Player) -> RewardVal {
-        if let Some(winner) = self.get_winner() {
-            if winner == *player {
-                return 1.0; // Win
-            } else {
-                return 0.0; // Loss
-            }
-        }
-
-        // Draw
-        0.5
-    }
-
     fn rewards_for_players(&self) -> HashMap<Self::Player, RewardVal> {
         HashMap::from_iter(vec![
             (Player::X, self.reward_for_player(&Player::X)),

examples/auto_tic_tac_toe.rs

@@ -148,6 +148,19 @@ impl TicTacToe {
 
         None
     }
+
+    fn reward_for_player(&self, player: &Player) -> RewardVal {
+        if let Some(winner) = self.get_winner() {
+            if winner == *player {
+                return 1.0; // Win
+            } else {
+                return 0.0; // Loss
+            }
+        }
+
+        // Draw
+        0.5
+    }
 }
 
 impl GameState for TicTacToe {
@@ -184,19 +197,6 @@ impl GameState for TicTacToe {
         self.get_winner().is_some() || self.moves_played == 9
     }
 
-    fn reward_for_player(&self, player: &Self::Player) -> RewardVal {
-        if let Some(winner) = self.get_winner() {
-            if winner == *player {
-                return 1.0; // Win
-            } else {
-                return 0.0; // Loss
-            }
-        }
-
-        // Draw
-        0.5
-    }
-
     fn rewards_for_players(&self) -> HashMap<Self::Player, RewardVal> {
         HashMap::from_iter(vec![
             (Player::X, self.reward_for_player(&Player::X)),

examples/tic_tac_toe.rs

@@ -191,6 +191,19 @@ impl TicTacToe {
 
         None
     }
+
+    fn reward_for_player(&self, player: &Player) -> RewardVal {
+        if let Some(winner) = self.get_winner() {
+            if winner == *player {
+                return 1.0; // Win
+            } else {
+                return 0.0; // Loss
+            }
+        }
+
+        // Draw
+        0.5
+    }
 }
 
 impl GameState for TicTacToe {
@@ -227,19 +240,6 @@ impl GameState for TicTacToe {
         self.get_winner().is_some() || self.moves_played == 9
     }
 
-    fn reward_for_player(&self, player: &Self::Player) -> RewardVal {
-        if let Some(winner) = self.get_winner() {
-            if winner == *player {
-                return 1.0; // Win
-            } else {
-                return 0.0; // Loss
-            }
-        }
-
-        // Draw
-        0.5
-    }
-
     fn rewards_for_players(&self) -> HashMap<Self::Player, RewardVal> {
         HashMap::from_iter(vec![
             (Player::X, self.reward_for_player(&Player::X)),

src/state.rs

@@ -40,11 +40,11 @@ pub trait GameState: Clone + Debug {
     /// instead should modify a copy of the state and return that.
     fn state_after_action(&self, action: &Self::Action) -> Self;
 
-    /// Returns the reward from the perspective of the given player for the game state
+    /// Returns the rewards for all players from their perspective for the game state
     ///
-    /// This evaluates the current state from the perspective of the given player, and
+    /// This evaluates the current state from the perspective of each player, and
-    /// returns the reward indicating how good of a result the given state is for the
+    /// returns a HashMap mapping each player to the result of this evaluation, which
-    /// player.
+    /// we call the reward.
     ///
     /// This is used in the MCTS backpropagation and simulation phases to evaluate
     /// the value of a given node in the search tree.
@@ -55,9 +55,6 @@ pub trait GameState: Clone + Debug {
     /// - 0.0 => a loss for the player
     ///
     /// Other values can be used for relative wins or losses
-    fn reward_for_player(&self, player: &Self::Player) -> RewardVal;
-
-    /// Returns the rewards for all players at the current state
     fn rewards_for_players(&self) -> HashMap<Self::Player, RewardVal>;
 
     /// Returns the player whose turn it is for the game state