2 files changed, 22 insertions, 14 deletions

diff --git a/src/tree.cc b/src/tree.cc
index 77d9f4e..8ccb108 100644
--- a/src/tree.cc
+++ b/src/tree.cc
@@ -28,17 +28,23 @@ namespace {
 
 namespace SimpleParser {
 
-Tree::Tree(std::string term, const ConstantMap* constants):
+Tree::Tree(
+	const std::string& term,
+	const ConstantMap* constants
+):
 	term_(term),
-	constants_(constants) {
-	this->root_node_ = this->buildTree(term);
-}
+	constants_(constants),
+	node_collection_(),
+	root_node_{ this->buildTree(term) } { }
+
+Tree::Tree(const std::string& term):
+	Tree(term, nullptr) { }
 
-double Tree::solve() {
+double Tree::solve() const {
 	return this->root_node_->solve();
 }
 
-std::string Tree::print() {
+std::string Tree::print() const {
 	std::stringstream out;
 	out.precision(std::numeric_limits<double>::digits10);
 
@@ -60,7 +66,8 @@ std::string Tree::print() {
 		    << "\"];"
 		    << std::endl;
 
-		if ( node->type() == NodeType::OPERATOR ) {
+		if ( node->rightChild != nullptr &&
+		     node->leftChild  != nullptr ) {
 			size_t j{};
 
 			for ( auto&& child : this->node_collection_ ) {
diff --git a/src/tree.h b/src/tree.h
index 9dfc4a3..186f162 100644
--- a/src/tree.h
+++ b/src/tree.h
@@ -11,21 +11,22 @@ namespace SimpleParser {
 
 class Tree {
 	public:
-		explicit Tree(std::string);
-		Tree(std::string, const ConstantMap*);
+		Tree(const std::string&, const ConstantMap*);
+		explicit Tree(const std::string&);
 
-		double solve();
-		std::string print();
+		double solve()      const;
+		std::string print() const;
 
 	private:
 		template <class NType, typename... Args>
 		Node* addNode(Node**, Args&&... args);
 		Node* buildTree(std::string);
 
-		std::string term_;
-		Node* root_node_;
-		std::vector<std::unique_ptr<Node>> node_collection_;
+		const std::string  term_;
 		const ConstantMap* constants_;
+
+		std::vector<std::unique_ptr<Node>> node_collection_;
+		Node* const root_node_;
 };
 
 }