Added dummy expression to check that with removed double negations, expressions are still correctly normalized.

include/plasp/pddl/Expression.h

@@ -81,6 +81,7 @@ class Expression
 			At,
 			Binary,
 			Constant,
+			Dummy,
 			Either,
 			Imply,
 			Not,
@@ -89,7 +90,7 @@ class Expression
 			Predicate,
 			PrimitiveType,
 			Unsupported,
-			Variable
+			Variable,
 		};
 
 	public:

include/plasp/pddl/expressions/Dummy.h

@@ -0,0 +1,38 @@
+#ifndef __PLASP__PDDL__EXPRESSIONS__DUMMY_H
+#define __PLASP__PDDL__EXPRESSIONS__DUMMY_H
+
+#include <plasp/pddl/Expression.h>
+
+namespace plasp
+{
+namespace pddl
+{
+namespace expressions
+{
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+//
+// Dummy
+//
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+class Dummy: public ExpressionCRTP<Dummy>
+{
+	public:
+		static const Expression::Type ExpressionType = Expression::Type::Dummy;
+
+		bool isNormalized() const;
+
+		ExpressionPointer normalize() override;
+
+	private:
+		bool m_isNormalized = false;
+};
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+}
+}
+}
+
+#endif