1 files changed, 45 insertions, 0 deletions
diff --git a/project2/variables.cpp b/project2/variables.cpp
index b866165..9108889 100644
--- a/project2/variables.cpp
+++ b/project2/variables.cpp
@@ -18,6 +18,11 @@ SimpleMessageException(UnknownVariableType);
 SimpleMessageException(UnknownVariableSource);
 SimpleMessageException(NoVariableDefinition);
 
+bool Null::operator<(const Null &) const
+{
+	return false;
+}
+
 enum VT_typeID {
 	DefaultType,
 	String,
@@ -111,6 +116,46 @@ VariableType::operator=(const VariableType & vt)
 	_VT::operator=(*((const _VT *)&vt));
 }
 
+template <class S>
+class compi : public boost::static_visitor<bool> {
+	public:
+		compi(const S & s) : _s(s) { }
+		bool operator()(const S & t) const
+		{
+			return _s < t;
+		}
+		template <class T>
+		bool operator()(const T &) const
+		{
+			// should never be called
+			throw std::logic_error("Shouldn't ever be comparing variables of different type");
+		}
+	private:
+		const S & _s;
+};
+class comp : public boost::static_visitor<bool> {
+	public:
+		comp(const VariableType & a) : _a(a) { }
+		template <class T>
+		bool operator()(const T & t) const
+		{
+			return boost::apply_visitor(compi<T>(t), _a);
+		}
+	private:
+		const VariableType & _a;
+};
+bool
+VariableType::operator<(const VariableType & b) const
+{
+	if (this->which() < b.which()) {
+		return true;
+	}
+	if (this->which() == b.which()) {
+		return boost::apply_visitor(comp(*this), b);
+	}
+	return false;
+}
+
 /// Variable implementation whose value is a literal value of some known type
 class VariableLiteral : public VariableImpl {
 	public: