diff --git a/resources/grammar/check_grammar.sh b/resources/grammar/check_grammar.sh
index eb48d5f84..30a057f76 100755
--- a/resources/grammar/check_grammar.sh
+++ b/resources/grammar/check_grammar.sh
@@ -1,4 +1,23 @@
-for fn in `find ../../../c3c -name '*.c3' | sort`
+echo "Testing lib"
+for fn in `find ../../../c3c/lib -name '*.c3' | sort`
+do
+     echo -n $fn
+     cat $fn | ./c3yacc
+done
+echo "Testing resources"
+for fn in `find ../../../c3c/resources -name '*.c3' | sort`
+do
+     echo -n $fn
+     cat $fn | ./c3yacc
+done
+echo "Testing unit tests"
+for fn in `find ../../../c3c/test/unit -name '*.c3' | sort`
+do
+     echo -n $fn
+     cat $fn | ./c3yacc
+done
+echo "Testing compiler tests"
+for fn in `find ../../../c3c/test/test_suite -name '*.c3t' | sort`
 do
      echo -n $fn
      cat $fn | ./c3yacc
diff --git a/resources/grammar/grammar.y b/resources/grammar/grammar.y
index df1ebf551..ae26b3797 100644
--- a/resources/grammar/grammar.y
+++ b/resources/grammar/grammar.y
@@ -557,8 +557,10 @@ type
 	| type '[' constant_expr ']'
 	| type '[' ']'
 	| type '[' '*' ']'
+	| type '[' '?' ']'
 	| type LVEC constant_expr RVEC
 	| type LVEC '*' RVEC
+	| type LVEC '?' RVEC
 	;
 
 optional_type
@@ -1094,6 +1096,7 @@ fn_parameter_list
 parameter_default
 	: parameter
 	| parameter '=' expr
+	| parameter '=' type
 	;
 
 parameters
@@ -1131,8 +1134,8 @@ func_definition
 
 const_declaration
 	: CONST CONST_IDENT opt_attributes '=' expr ';'
-	| CONST type CONST_IDENT opt_attributes '=' expr ';'
-	| CONST type CONST_IDENT opt_attributes ';'
+	| CONST optional_type CONST_IDENT opt_attributes '=' expr ';'
+	| CONST optional_type CONST_IDENT opt_attributes ';'
 	;
 
 func_typedef
@@ -1204,8 +1207,18 @@ interface_body
 	;
 
 interface_declaration
-	: INTERFACE TYPE_IDENT '{' '}'
-	| INTERFACE TYPE_IDENT '{' interface_body '}'
+	: INTERFACE interface_declaration_name '{' '}'
+	| INTERFACE interface_declaration_name '{' interface_body '}'
+	;
+
+interface_parents
+	: TYPE_IDENT
+	| interface_parents ',' TYPE_IDENT
+	;
+
+interface_declaration_name
+	: TYPE_IDENT
+	| TYPE_IDENT ':' interface_parents
 	;
 
 distinct_declaration