Added back reference expressions to make the expression tree structure simpler.

include/plasp/pddl/Expression.h

@@ -62,6 +62,11 @@ class PrimitiveType;
 using PrimitiveTypePointer = std::unique_ptr<PrimitiveType>;
 using PrimitiveTypes = std::vector<PrimitiveTypePointer>;
 
+template<class Type>
+class Reference;
+template<class Type>
+using ReferencePointer = std::unique_ptr<Reference<Type>>;
+
 class Unsupported;
 using UnsupportedPointer = std::unique_ptr<Unsupported>;
 
@@ -89,6 +94,7 @@ class Expression
 			PredicateDeclaration,
 			Predicate,
 			PrimitiveType,
+			Reference,
 			Unsupported,
 			Variable,
 		};

include/plasp/pddl/expressions/Reference.h

@@ -0,0 +1,75 @@
+#ifndef __PLASP__PDDL__EXPRESSIONS__REFERENCE_H
+#define __PLASP__PDDL__EXPRESSIONS__REFERENCE_H
+
+#include <plasp/pddl/Expression.h>
+
+namespace plasp
+{
+namespace pddl
+{
+namespace expressions
+{
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+//
+// Reference
+//
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+template<class Type>
+class Reference: public ExpressionCRTP<Reference<Type>>
+{
+	public:
+		static const Expression::Type ExpressionType = Expression::Type::Reference;
+
+	public:
+		Reference(Type *value);
+
+		Type *get();
+		const Type *get() const;
+
+		ExpressionPointer normalize();
+
+	protected:
+		Type *m_value = nullptr;
+};
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+template<class Type>
+Reference<Type>::Reference(Type *value)
+:	m_value{value}
+{
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+template<class Type>
+Type *Reference<Type>::get()
+{
+	return m_value;
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+template<class Type>
+const Type *Reference<Type>::get() const
+{
+	return m_value;
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+template<class Type>
+ExpressionPointer Reference<Type>::normalize()
+{
+	return nullptr;
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+}
+}
+}
+
+#endif