diff --git a/syntaxique/lang.y b/syntaxique/lang.y
index a3eb550..b7ff205 100644
--- a/syntaxique/lang.y
+++ b/syntaxique/lang.y
@@ -18,7 +18,7 @@ void yyerror(char *s)
 typedef struct var	// a variable
 {
 	char *name;
-	int type;
+	int class;
 	int value;	// 0 = bool, 1 = int
 	struct var *next;
 } var;
@@ -32,6 +32,7 @@ typedef struct varlist	// variable reference (used for print statement)
 typedef struct expr	// boolean expression
 {
 	int type;	// TRUE, FALSE, OR, AND, EQUIV, NOT, 0 (variable), PLUS, TIMES, INT, EQUALS, LT
+	int class;	// 0 = bool, 1 = int, 2 = both
 	var *var;
 	struct expr *left, *right;
 } expr;
@@ -55,11 +56,11 @@ stmt *program_stmts;
 /****************************************************************************/
 /* Functions for settting up data structures at parse time.                 */
 
-var* make_ident (char *s, int type)	// type = 0 for a boolean var, type = 1 for an int var
+var* make_ident (char *s, int class)	// type = 0 for a boolean var, type = 1 for an int var
 {
 	var *v = malloc(sizeof(var));
 	v->name = s;
-	v->type = type;
+	v->class = class;
 	v->value = 0;	// make variable false initially
 	v->next = NULL;
 	return v;
@@ -87,7 +88,7 @@ var* make_int(int val)
 {
 	var *v = malloc(sizeof(var));
 	v->name = NULL;
-	v->type = 1;	// int
+	v->class = 1;	// int
 	v->value = val;
 	v->next = NULL;
 	return v;
@@ -102,10 +103,11 @@ varlist* make_varlist (char *s)
 	return l;
 }
 
-expr* make_expr (int type, var *var, expr *left, expr *right)
+expr* make_expr (int type, int class, var *var, expr *left, expr *right)
 {
 	expr *e = malloc(sizeof(expr));
 	e->type = type;
+	e->class = class;
 	e->var = var;
 	e->left = left;
 	e->right = right;
@@ -197,20 +199,20 @@ assign	: IDENT ASSIGN expr
 varlist	: IDENT			{ $$ = make_varlist($1); }
 	| varlist ',' IDENT	{ ($$ = make_varlist($3))->next = $1; }
 
-expr	: IDENT		{ $$ = make_expr(0,find_ident($1),NULL,NULL); }
-	| expr XOR expr	{ $$ = make_expr(XOR,NULL,$1,$3); }
-	| expr OR expr	{ $$ = make_expr(OR,NULL,$1,$3); }
-	| expr AND expr	{ $$ = make_expr(AND,NULL,$1,$3); }
-	| expr EQUIV expr 	{ $$ = make_expr(EQUIV,NULL,$1,$3); }
-	| NOT expr	{ $$ = make_expr(NOT,NULL,$2,NULL); }
-	| TRUE		{ $$ = make_expr(TRUE,NULL,NULL,NULL); }
-	| FALSE		{ $$ = make_expr(FALSE,NULL,NULL,NULL); }
+expr	: IDENT		{ $$ = make_expr(0, 2, find_ident($1), NULL, NULL); }
+	| expr XOR expr	{ $$ = make_expr(XOR, 0, NULL, $1, $3); }
+	| expr OR expr	{ $$ = make_expr(OR, 0, NULL, $1, $3); }
+	| expr AND expr	{ $$ = make_expr(AND, 0, NULL, $1, $3); }
+	| expr EQUIV expr 	{ $$ = make_expr(EQUIV, 0, NULL, $1, $3); }
+	| NOT expr	{ $$ = make_expr(NOT, 0, NULL, $2, NULL); }
+	| TRUE		{ $$ = make_expr(TRUE, 0, NULL, NULL, NULL); }
+	| FALSE		{ $$ = make_expr(FALSE, 0, NULL, NULL, NULL); }
 	| '(' expr ')'	{ $$ = $2; }
-	| INT		{ $$ = make_expr(INT, make_int($1), NULL, NULL); }
-	| expr TIMES expr	{ $$ = make_expr(TIMES, NULL, $1, $3); }
-	| expr PLUS expr	{ $$ = make_expr(PLUS, NULL, $1, $3); }
-	| expr EQUALS expr	{ $$ = make_expr(EQUALS, NULL, $1, $3); }
-	| expr LT expr		{ $$ = make_expr(LT, NULL, $1, $3); }
+	| INT		{ $$ = make_expr(INT, 1, make_int($1), NULL, NULL); }
+	| expr TIMES expr	{ $$ = make_expr(TIMES, 1, NULL, $1, $3); }
+	| expr PLUS expr	{ $$ = make_expr(PLUS, 1, NULL, $1, $3); }
+	| expr LT expr		{ $$ = make_expr(LT, 0, NULL, $1, $3); }
+	| expr EQUALS expr	{ $$ = make_expr(EQUALS, 0, NULL, $1, $3); }
 
 
 %%
@@ -226,25 +228,74 @@ int eval (expr *e)
 	{
 		case TRUE: return 1;
 		case FALSE: return 0;
-		case XOR: return eval(e->left) ^ eval(e->right);
-		case OR: return eval(e->left) || eval(e->right);
-		case AND: return eval(e->left) && eval(e->right);
+		case XOR: {
+			if (e->left->class != 0 || e->right->class != 0) {
+				yyerror("An expression has wrong types");
+				exit(-1);
+			}
+			return eval(e->left) ^ eval(e->right);
+		}
+		case OR: {
+			if (e->left->class != 0 || e->right != NULL && e->right->class != 0) {
+				yyerror("An expression has wrong types");
+				exit(-1);
+			}
+			return eval(e->left) || eval(e->right);
+		}
+		case AND: {
+			if (e->left->class != 0 || e->right->class != 0) {
+				yyerror("An expression has wrong types");
+				exit(-1);
+			}
+			return eval(e->left) && eval(e->right);
+		}
 		case EQUIV: {
+			if (e->left->class != 0 || e->right->class != 0) {
+				yyerror("An expression has wrong types");
+				exit(-1);
+			}
 			int right = eval(e->right);
 			int left = eval(e->left);
 			return (right && left) || (!right && !left);  // Équivalent avec left == right avec la définition.
-														  // Toutefois, on privilégie cette forme car faux = 0 et vrai = tout entier non nul.
+														  // Toutefois, on privilégie cette forme car faux = 0 et vrai = tout entier non nul
 		}
-		case NOT: return !eval(e->left);
-		case PLUS:
+		case NOT: {
+			if (e->left->class != 0) {
+				yyerror("An expression has wrong types");
+				exit(-1);
+			}
+			return !eval(e->left);
+		}
+		case PLUS: {
+			if (e->left->class != 1 || e->right->class != 1) {
+				yyerror("An expression has wrong types");
+				exit(-1);
+			}
 			return eval(e->left) + eval(e->right);
-		case TIMES:
+		}
+		case TIMES: {
+			if (e->left->class != 1 || e->right->class != 1) {
+				yyerror("An expression has wrong types");
+				exit(-1);
+			}
 			return eval(e->left) * eval(e->right);
-		case EQUALS:
+		}
+		case EQUALS: {
+			if (e->left->class != 1 || e->right->class != 1) {
+				yyerror("An expression has wrong types");
+				exit(-1);
+			}
+
 			printf("%d, %d\n", eval(e->left), eval(e->right));
 			return eval(e->left) == eval(e->right) ? 1 : 0;
-		case LT:
+		}
+		case LT: {
+			if (e->left->class != 1 || e->right->class != 1) {
+				yyerror("An expression has wrong types");
+				exit(-1);
+			}
 			return eval(e->left) < eval(e->right) ? 1 : 0;
+		}
 		case INT:
 		case 0:
 			return e->var->value;
@@ -258,9 +309,9 @@ void print_vars (varlist *l)
 
 	if (!l) return;
 	print_vars(l->next);
-	if (l->var->type == 0)
+	if (l->var->class == 0)
 		printf("%s = %c  ", l->var->name, l->var->value ? 'T' : 'F');
-	else if (l->var->type == 1)
+	else if (l->var->class == 1)
 		printf("%s = %d  ", l->var->name, l->var->value);
 	else
 		fprintf(stderr, "The type of the var %s is unknown", l->var->name);
@@ -271,6 +322,10 @@ void execute (stmt *s)
 	switch(s->type)
 	{
 		case ASSIGN:
+			if (s->var->class != s->expr->class) {
+				yyerror("An assignment has the wrong type");
+				exit(-1);
+			}
 			s->var->value = eval(s->expr);
 			break;
 		case ';':
diff --git a/syntaxique/test2.my b/syntaxique/test2.my
index 6a2460c..d22beb4 100644
--- a/syntaxique/test2.my
+++ b/syntaxique/test2.my
@@ -1,5 +1,5 @@
 bool y;
 int x;
-x := 42 + 21;
-y := x == (7 * (5 + 4));
+x := 6 * (4 + 3);
+y := (0 < 1) || 19 + 23 == x;
 print x,y,x