Index: src/Parser/parser.yy
===================================================================
--- src/Parser/parser.yy	(revision c744563a070c9d4616eebd7603fd513964d395ab)
+++ src/Parser/parser.yy	(revision aeb5d0df40d6c1725a4d281a07385c12b9694732)
@@ -10,6 +10,6 @@
 // Created On       : Sat Sep  1 20:22:55 2001
 // Last Modified By : Peter A. Buhr
-// Last Modified On : Fri Feb 21 14:47:29 2020
-// Update Count     : 4468
+// Last Modified On : Wed Feb 26 14:27:39 2020
+// Update Count     : 4472
 //
 
@@ -2077,11 +2077,17 @@
 aggregate_control:										// CFA
 	GENERATOR
-		{ yyy = true; $$ = AggregateDecl::Coroutine; }
+		{ SemanticError( yylloc, "generator is currently unimplemented." ); $$ = AggregateDecl::NoAggregate; }
+	| MONITOR GENERATOR
+		{ SemanticError( yylloc, "monitor generator is currently unimplemented." ); $$ = AggregateDecl::NoAggregate; }
 	| COROUTINE
 		{ yyy = true; $$ = AggregateDecl::Coroutine; }
 	| MONITOR
 		{ yyy = true; $$ = AggregateDecl::Monitor; }
+	| MONITOR COROUTINE
+		{ SemanticError( yylloc, "monitor coroutine is currently unimplemented." ); $$ = AggregateDecl::NoAggregate; }
 	| THREAD
 		{ yyy = true; $$ = AggregateDecl::Thread; }
+	| MONITOR THREAD
+		{ SemanticError( yylloc, "monitor thread is currently unimplemented." ); $$ = AggregateDecl::NoAggregate; }
 	;