diff -r d726e4b46c33 -r 0cedda2544da src/chess/rules.h
--- a/src/chess/rules.h	Wed May 28 15:47:57 2014 +0200
+++ b/src/chess/rules.h	Wed Jun 11 15:38:01 2014 +0200
@@ -33,13 +33,16 @@
 #include <stdint.h>
 #include <sys/time.h>
 
-#define VALID_MOVE_SYNTAX   0
-#define INVALID_MOVE_SYNTAX 1
-#define INVALID_POSITION    2
-#define AMBIGUOUS_MOVE      3
-#define NEED_PROMOTION      4
-#define PIECE_PINNED        5
-#define KING_IN_CHECK       6
+#define VALID_MOVE_SYNTAX      0
+#define VALID_MOVE_SEMANTICS   0 /* use same code for a success */
+#define INVALID_MOVE_SYNTAX    1
+#define INVALID_POSITION       2
+#define AMBIGUOUS_MOVE         3
+#define NEED_PROMOTION         4
+#define PIECE_PINNED           5
+#define KING_IN_CHECK          6
+#define KING_MOVES_INTO_CHECK  7
+#define RULES_VIOLATED        10
 
 
 #define PIECE_MASK       0x0F
@@ -268,7 +271,7 @@
  * @param gamestate the current game state
  * @param mstr the input string to parse
  * @param move a pointer to object where the move data shall be stored
- * @return status code (see rules/rules.h for the list of codes)
+ * @return status code (see macros in this file for the list of codes)
  */
 int eval_move(GameState *gamestate, char *mstr, Move *move);
 
@@ -276,9 +279,9 @@
  * Validates move by applying chess rules.
  * @param gamestate the current game state
  * @param move the move to validate
- * @return TRUE, if the move complies to chess rules, FALSE otherwise
+ * @return status code (see macros in this file for the list of codes)
  */
-_Bool validate_move(GameState *gamestate, Move *move);
+int validate_move(GameState *gamestate, Move *move);
 
 /**
  * Applies a move and deletes captured pieces.