Index: src/Parser/parser.yy
===================================================================
--- src/Parser/parser.yy	(revision 79caea8a12eb28a0abbd4a77f0bc23d32d991168)
+++ src/Parser/parser.yy	(revision 610194e1341d5e36cbe74f89330ac0d81feb73af)
@@ -2307,8 +2307,10 @@
 		{ $$ = new ExpressionNode( new TypeExpr( maybeMoveBuildType( $1 ) ) ); }
 	| assignment_expression
+		{ SemanticError( yylloc, toString("Expression generic parameters are currently unimplemented: ", $1->build()) ); $$ = nullptr; }
 	| type_list ',' type
 		{ $$ = (ExpressionNode *)( $1->set_last( new ExpressionNode( new TypeExpr( maybeMoveBuildType( $3 ) ) ) ) ); }
 	| type_list ',' assignment_expression
-		{ $$ = (ExpressionNode *)( $1->set_last( $3 )); }
+		{ SemanticError( yylloc, toString("Expression generic parameters are currently unimplemented: ", $3->build()) ); $$ = nullptr; }
+		// { $$ = (ExpressionNode *)( $1->set_last( $3 )); }
 	;