diff --git a/src/ast.cpp b/src/ast.cpp
index 1ea8548..02edd6f 100644
--- a/src/ast.cpp
+++ b/src/ast.cpp
@@ -5,6 +5,7 @@
  */
 
 #include <cstdint> // int64_t
+#include <memory>
 #include <string>
 
 #include "ast.h"
@@ -13,21 +14,14 @@
 
 namespace blaze {
 
-Collection::~Collection()
-{
-	for (auto node : m_nodes) {
-		delete node;
-	}
-}
-
-void Collection::addNode(ASTNode* node)
+void Collection::addNode(ASTNodePtr node)
 {
 	m_nodes.push_back(node);
 }
 
 // -----------------------------------------
 
-void HashMap::addElement(const std::string& key, ASTNode* value)
+void HashMap::addElement(const std::string& key, ASTNodePtr value)
 {
 	m_elements.emplace(key, value);
 }
@@ -78,7 +72,7 @@ Function::Function(Lambda lambda)
 
 // -----------------------------------------
 
-void Formatter<blaze::ASTNode*>::format(Builder& builder, blaze::ASTNode* value) const
+void Formatter<blaze::ASTNodePtr>::format(Builder& builder, blaze::ASTNodePtr value) const
 {
 	blaze::Printer printer;
 	return Formatter<std::string>::format(builder, printer.printNoErrorCheck(value));
diff --git a/src/ast.h b/src/ast.h
index f00e1a0..863cb15 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -8,6 +8,7 @@
 
 #include <cstdint>    // int64_t
 #include <functional> // std::function
+#include <memory>     // std::shared_ptr
 #include <span>
 #include <string>
 #include <string_view>
@@ -19,6 +20,9 @@
 
 namespace blaze {
 
+class ASTNode;
+typedef std::shared_ptr<ASTNode>  ASTNodePtr;
+
 class ASTNode {
 public:
 	virtual ~ASTNode() = default;
@@ -47,13 +51,13 @@ protected:
 
 class Collection : public ASTNode {
 public:
-	virtual ~Collection() override;
+	virtual ~Collection() = default;
 
 	virtual bool isCollection() const override { return true; }
 
-	void addNode(ASTNode* node);
+	void addNode(ASTNodePtr node);
 
-	const std::vector<ASTNode*>& nodes() const { return m_nodes; }
+	const std::vector<ASTNodePtr>& nodes() const { return m_nodes; }
 	size_t size() const { return m_nodes.size(); }
 	bool empty() const { return m_nodes.size() == 0; }
 
@@ -61,7 +65,7 @@ protected:
 	Collection() {}
 
 private:
-	std::vector<ASTNode*> m_nodes;
+	std::vector<ASTNodePtr> m_nodes;
 };
 
 // -----------------------------------------
@@ -98,14 +102,14 @@ public:
 
 	virtual bool isHashMap() const override { return true; }
 
-	void addElement(const std::string& key, ASTNode* value);
+	void addElement(const std::string& key, ASTNodePtr value);
 
-	const std::unordered_map<std::string, ASTNode*>& elements() const { return m_elements; }
+	const std::unordered_map<std::string, ASTNodePtr>& elements() const { return m_elements; }
 	size_t size() const { return m_elements.size(); }
 	bool empty() const { return m_elements.size() == 0; }
 
 private:
-	std::unordered_map<std::string, ASTNode*> m_elements;
+	std::unordered_map<std::string, ASTNodePtr> m_elements;
 };
 
 // -----------------------------------------
@@ -113,7 +117,7 @@ private:
 // "string"
 class String final : public ASTNode {
 public:
-	String(const std::string& data);
+	explicit String(const std::string& data);
 	virtual ~String() = default;
 
 	virtual bool isString() const override { return true; }
@@ -129,7 +133,7 @@ private:
 // :keyword
 class Keyword final : public ASTNode {
 public:
-	Keyword(const std::string& data);
+	explicit Keyword(const std::string& data);
 	virtual ~Keyword() = default;
 
 	virtual bool isKeyword() const override { return true; }
@@ -144,7 +148,7 @@ private:
 // 123
 class Number final : public ASTNode {
 public:
-	Number(int64_t number);
+	explicit Number(int64_t number);
 	virtual ~Number() = default;
 
 	virtual bool isNumber() const override { return true; }
@@ -160,7 +164,7 @@ private:
 // Symbols
 class Symbol final : public ASTNode {
 public:
-	Symbol(const std::string& symbol);
+	explicit Symbol(const std::string& symbol);
 	virtual ~Symbol() = default;
 
 	virtual bool isSymbol() const override { return true; }
@@ -176,7 +180,7 @@ private:
 // true, false, nil
 class Value final : public ASTNode {
 public:
-	Value(const std::string& value);
+	explicit Value(const std::string& value);
 	virtual ~Value() = default;
 
 	virtual bool isValue() const override { return true; }
@@ -189,11 +193,11 @@ private:
 
 // -----------------------------------------
 
-using Lambda = std::function<ASTNode*(std::span<ASTNode*>)>;
+using Lambda = std::function<ASTNodePtr(std::span<ASTNodePtr>)>;
 
 class Function final : public ASTNode {
 public:
-	Function(Lambda lambda);
+	explicit Function(Lambda lambda);
 	virtual ~Function() = default;
 
 	virtual bool isFunction() const override { return true; }
@@ -206,6 +210,14 @@ private:
 
 // -----------------------------------------
 
+template<typename T, typename... Args>
+std::shared_ptr<T> makePtr(Args&&... args)
+{
+	return std::make_shared<T>(std::forward<Args>(args)...);
+}
+
+// -----------------------------------------
+
 // clang-format off
 template<>
 inline bool ASTNode::fastIs<Collection>() const { return isCollection(); }
@@ -243,6 +255,6 @@ inline bool ASTNode::fastIs<Function>() const { return isFunction(); }
 // -----------------------------------------
 
 template<>
-struct ruc::format::Formatter<blaze::ASTNode*> : public Formatter<std::string> {
-	void format(Builder& builder, blaze::ASTNode* value) const;
+struct ruc::format::Formatter<blaze::ASTNodePtr> : public Formatter<std::string> {
+	void format(Builder& builder, blaze::ASTNodePtr value) const;
 };
diff --git a/src/environment.h b/src/environment.h
index 7674d6b..992f925 100644
--- a/src/environment.h
+++ b/src/environment.h
@@ -8,6 +8,7 @@
 
 #include <cstdint> // int64_t
 #include <iostream>
+#include <memory>
 #include <span>
 #include <string_view>
 #include <unordered_map>
@@ -27,7 +28,7 @@ public:
 	Environment() = default;
 	virtual ~Environment() = default;
 
-	ASTNode* lookup(const std::string& symbol)
+	ASTNodePtr lookup(const std::string& symbol)
 	{
 		m_current_key = symbol;
 		return m_values.find(symbol) != m_values.end() ? m_values[symbol] : nullptr;
@@ -35,7 +36,7 @@ public:
 
 protected:
 	std::string m_current_key;
-	std::unordered_map<std::string, ASTNode*> m_values;
+	std::unordered_map<std::string, ASTNodePtr> m_values;
 };
 
 class GlobalEnvironment final : public Environment {
@@ -44,62 +45,62 @@ public:
 	{
 		// TODO: Add more native functions
 		// TODO: Move the functions to their own file
-		auto add = [](std::span<ASTNode*> nodes) -> ASTNode* {
+		auto add = [](std::span<ASTNodePtr> nodes) -> ASTNodePtr {
 			int64_t result = 0;
 
 			for (auto node : nodes) {
-				if (!is<Number>(node)) {
+				if (!is<Number>(node.get())) {
 					Error::the().addError(format("wrong type argument: number-or-marker-p, '{}'", node));
 					return nullptr;
 				}
 
-				result += static_cast<Number*>(node)->number();
+				result += static_pointer_cast<Number>(node)->number();
 			}
 
-			return new Number(result);
+			return makePtr<Number>(result);
 		};
 
-		auto sub = [](std::span<ASTNode*> nodes) -> ASTNode* {
+		auto sub = [](std::span<ASTNodePtr> nodes) -> ASTNodePtr {
 			int64_t result = 0;
 
 			if (nodes.size() == 0) {
-				return new Number(0);
+				return makePtr<Number>(0);
 			}
 
 			for (auto node : nodes) {
-				if (!is<Number>(node)) {
+				if (!is<Number>(node.get())) {
 					Error::the().addError(format("wrong type argument: number-or-marker-p, '{}'", node));
 					return nullptr;
 				}
 			}
 
 			// Start with the first number
-			result += static_cast<Number*>(nodes[0])->number();
+			result += static_pointer_cast<Number>(nodes[0])->number();
 
 			// Skip the first node
 			for (auto it = std::next(nodes.begin()); it != nodes.end(); ++it) {
-				result -= static_cast<Number*>(*it)->number();
+				result -= static_pointer_cast<Number>(*it)->number();
 			}
 
-			return new Number(result);
+			return makePtr<Number>(result);
 		};
 
-		auto mul = [](std::span<ASTNode*> nodes) -> ASTNode* {
+		auto mul = [](std::span<ASTNodePtr> nodes) -> ASTNodePtr {
 			int64_t result = 1;
 
 			for (auto node : nodes) {
-				if (!is<Number>(node)) {
+				if (!is<Number>(node.get())) {
 					Error::the().addError(format("wrong type argument: number-or-marker-p, '{}'", node));
 					return nullptr;
 				}
 
-				result *= static_cast<Number*>(node)->number();
+				result *= static_pointer_cast<Number>(node)->number();
 			}
 
-			return new Number(result);
+			return makePtr<Number>(result);
 		};
 
-		auto div = [this](std::span<ASTNode*> nodes) -> ASTNode* {
+		auto div = [this](std::span<ASTNodePtr> nodes) -> ASTNodePtr {
 			double result = 0;
 
 			if (nodes.size() == 0) {
@@ -108,27 +109,27 @@ public:
 			}
 
 			for (auto node : nodes) {
-				if (!is<Number>(node)) {
+				if (!is<Number>(node.get())) {
 					Error::the().addError(format("wrong type argument: number-or-marker-p, '{}'", node));
 					return nullptr;
 				}
 			}
 
 			// Start with the first number
-			result += static_cast<Number*>(nodes[0])->number();
+			result += static_pointer_cast<Number>(nodes[0])->number();
 
 			// Skip the first node
 			for (auto it = std::next(nodes.begin()); it != nodes.end(); ++it) {
-				result /= static_cast<Number*>(*it)->number();
+				result /= static_pointer_cast<Number>(*it)->number();
 			}
 
-			return new Number((int64_t)result);
+			return makePtr<Number>((int64_t)result);
 		};
 
-		m_values.emplace("+", new Function(add));
-		m_values.emplace("-", new Function(sub));
-		m_values.emplace("*", new Function(mul));
-		m_values.emplace("/", new Function(div));
+		m_values.emplace("+", makePtr<Function>(add));
+		m_values.emplace("-", makePtr<Function>(sub));
+		m_values.emplace("*", makePtr<Function>(mul));
+		m_values.emplace("/", makePtr<Function>(div));
 	}
 	virtual ~GlobalEnvironment() = default;
 };
diff --git a/src/eval.cpp b/src/eval.cpp
index ff7cd48..e56ac5e 100644
--- a/src/eval.cpp
+++ b/src/eval.cpp
@@ -14,7 +14,7 @@
 
 namespace blaze {
 
-Eval::Eval(ASTNode* ast, Environment* env)
+Eval::Eval(ASTNodePtr ast, Environment* env)
 	: m_ast(ast)
 	, m_env(env)
 {
@@ -25,46 +25,53 @@ void Eval::eval()
 	m_ast = evalImpl(m_ast, m_env);
 }
 
-ASTNode* Eval::evalImpl(ASTNode* ast, Environment* env)
+ASTNodePtr Eval::evalImpl(ASTNodePtr ast, Environment* env)
 {
-	if (!is<List>(ast)) {
+	if (!is<List>(ast.get())) {
 		return evalAst(ast, env);
 	}
-	if (static_cast<List*>(ast)->empty()) {
+	if (static_cast<List*>(ast.get())->empty()) {
 		return ast;
 	}
 
-	return apply(static_cast<List*>(evalAst(ast, env)));
+	return apply(static_pointer_cast<List>(evalAst(ast, env)));
 }
 
-ASTNode* Eval::evalAst(ASTNode* ast, Environment* env)
+ASTNodePtr Eval::evalAst(ASTNodePtr ast, Environment* env)
 {
-	if (is<Symbol>(ast)) {
-		auto result = env->lookup(static_cast<Symbol*>(ast)->symbol());
+	ASTNode* ast_raw_ptr = ast.get();
+	if (is<Symbol>(ast_raw_ptr)) {
+		auto result = env->lookup(static_pointer_cast<Symbol>(ast)->symbol());
 		if (!result) {
-			Error::the().addError(format("symbol's function definition is void: {}", ast));
+			// TODO: Maybe add backlink to parent nodes?
+			if (is<List>(m_ast)) {
+				Error::the().addError(format("symbol's function definition is void: {}", ast_raw_ptr));
+			}
+			else {
+				Error::the().addError(format("symbol's value as variable is void: {}", ast_raw_ptr));
+			}
 		}
 		return result;
 	}
-	else if (is<List>(ast)) {
-		auto result = new List();
-		auto nodes = static_cast<List*>(ast)->nodes();
+	else if (is<List>(ast_raw_ptr)) {
+		auto result = makePtr<List>();
+		auto nodes = static_pointer_cast<List>(ast)->nodes();
 		for (auto node : nodes) {
 			result->addNode(evalImpl(node, env));
 		}
 		return result;
 	}
-	else if (is<Vector>(ast)) {
-		auto result = new Vector();
-		auto nodes = static_cast<Vector*>(ast)->nodes();
+	else if (is<Vector>(ast_raw_ptr)) {
+		auto result = makePtr<Vector>();
+		auto nodes = static_pointer_cast<Vector>(ast)->nodes();
 		for (auto node : nodes) {
 			result->addNode(evalImpl(node, env));
 		}
 		return result;
 	}
-	else if (is<HashMap>(ast)) {
-		auto result = new HashMap();
-		auto elements = static_cast<HashMap*>(ast)->elements();
+	else if (is<HashMap>(ast_raw_ptr)) {
+		auto result = makePtr<HashMap>();
+		auto elements = static_pointer_cast<HashMap>(ast)->elements();
 		for (auto& element : elements) {
 			result->addElement(element.first, evalImpl(element.second, env));
 		}
@@ -74,19 +81,19 @@ ASTNode* Eval::evalAst(ASTNode* ast, Environment* env)
 	return ast;
 }
 
-ASTNode* Eval::apply(List* evaluated_list)
+ASTNodePtr Eval::apply(std::shared_ptr<List> evaluated_list)
 {
 	auto nodes = evaluated_list->nodes();
 
-	if (!is<Function>(nodes[0])) {
+	if (!is<Function>(nodes[0].get())) {
 		Error::the().addError(format("invalid function: {}", nodes[0]));
 		return nullptr;
 	}
 
 	// car
-	auto lambda = static_cast<Function*>(nodes[0])->lambda();
+	auto lambda = static_pointer_cast<Function>(nodes[0])->lambda();
 	// cdr
-	std::span<ASTNode*> span { nodes.data() + 1, nodes.size() - 1 };
+	std::span<ASTNodePtr> span { nodes.data() + 1, nodes.size() - 1 };
 
 	return lambda(span);
 }
diff --git a/src/eval.h b/src/eval.h
index dcc9ace..06dcd2d 100644
--- a/src/eval.h
+++ b/src/eval.h
@@ -13,19 +13,19 @@ namespace blaze {
 
 class Eval {
 public:
-	Eval(ASTNode* ast, Environment* env);
+	Eval(ASTNodePtr ast, Environment* env);
 	virtual ~Eval() = default;
 
 	void eval();
 
-	ASTNode* ast() const { return m_ast; }
+	ASTNodePtr ast() const { return m_ast; }
 
 private:
-	ASTNode* evalImpl(ASTNode* ast, Environment* env);
-	ASTNode* evalAst(ASTNode* ast, Environment* env);
-	ASTNode* apply(List* evaluated_list);
+	ASTNodePtr evalImpl(ASTNodePtr ast, Environment* env);
+	ASTNodePtr evalAst(ASTNodePtr ast, Environment* env);
+	ASTNodePtr apply(std::shared_ptr<List> evaluated_list);
 
-	ASTNode* m_ast { nullptr };
+	ASTNodePtr m_ast { nullptr };
 	Environment* m_env { nullptr };
 };
 
diff --git a/src/printer.cpp b/src/printer.cpp
index aaa01b8..b10cfb7 100644
--- a/src/printer.cpp
+++ b/src/printer.cpp
@@ -27,7 +27,7 @@ Printer::~Printer()
 
 // -----------------------------------------
 
-std::string Printer::print(ASTNode* node)
+std::string Printer::print(ASTNodePtr node)
 {
 	if (Error::the().hasAnyError()) {
 		init();
@@ -38,7 +38,7 @@ std::string Printer::print(ASTNode* node)
 	return printNoErrorCheck(node);
 }
 
-std::string Printer::printNoErrorCheck(ASTNode* node)
+std::string Printer::printNoErrorCheck(ASTNodePtr node)
 {
 	init();
 
@@ -60,7 +60,7 @@ void Printer::init()
 	m_print = "";
 }
 
-void Printer::printImpl(ASTNode* node)
+void Printer::printImpl(ASTNodePtr node)
 {
 	auto printSpacing = [this]() -> void {
 		if (!m_first_node && !m_previous_node_is_list) {
@@ -68,36 +68,37 @@ void Printer::printImpl(ASTNode* node)
 		}
 	};
 
-	if (is<List>(node)) {
+	ASTNode* node_raw_ptr = node.get();
+	if (is<List>(node_raw_ptr)) {
 		printSpacing();
 		m_print += '(';
 		m_first_node = false;
 		m_previous_node_is_list = true;
-		auto nodes = static_cast<List*>(node)->nodes();
+		auto nodes = static_pointer_cast<List>(node)->nodes();
 		for (size_t i = 0; i < nodes.size(); ++i) {
 			printImpl(nodes[i]);
 			m_previous_node_is_list = false;
 		}
 		m_print += ')';
 	}
-	else if (is<Vector>(node)) {
+	else if (is<Vector>(node_raw_ptr)) {
 		printSpacing();
 		m_print += '[';
 		m_first_node = false;
 		m_previous_node_is_list = true;
-		auto nodes = static_cast<Vector*>(node)->nodes();
+		auto nodes = static_pointer_cast<Vector>(node)->nodes();
 		for (size_t i = 0; i < nodes.size(); ++i) {
 			printImpl(nodes[i]);
 			m_previous_node_is_list = false;
 		}
 		m_print += ']';
 	}
-	else if (is<HashMap>(node)) {
+	else if (is<HashMap>(node_raw_ptr)) {
 		printSpacing();
 		m_print += "{";
 		m_first_node = false;
 		m_previous_node_is_list = true;
-		auto elements = static_cast<HashMap*>(node)->elements();
+		auto elements = static_pointer_cast<HashMap>(node)->elements();
 		for (auto it = elements.begin(); it != elements.end(); ++it) {
 			m_print += format("{} ", it->first.front() == 0x7f ? ":" + it->first.substr(1) : it->first); // 127
 			printImpl(it->second);
@@ -109,22 +110,22 @@ void Printer::printImpl(ASTNode* node)
 		m_previous_node_is_list = false;
 		m_print += '}';
 	}
-	else if (is<String>(node)) {
+	else if (is<String>(node_raw_ptr)) {
 		// TODO: Implement string readably printing
 		printSpacing();
-		m_print += format("{}", static_cast<String*>(node)->data());
+		m_print += format("{}", static_pointer_cast<String>(node)->data());
 	}
-	else if (is<Keyword>(node)) {
+	else if (is<Keyword>(node_raw_ptr)) {
 		printSpacing();
-		m_print += format(":{}", static_cast<Keyword*>(node)->keyword().substr(1));
+		m_print += format(":{}", static_pointer_cast<Keyword>(node)->keyword().substr(1));
 	}
-	else if (is<Number>(node)) {
+	else if (is<Number>(node_raw_ptr)) {
 		printSpacing();
-		m_print += format("{}", static_cast<Number*>(node)->number());
+		m_print += format("{}", static_pointer_cast<Number>(node)->number());
 	}
-	else if (is<Symbol>(node)) {
+	else if (is<Symbol>(node_raw_ptr)) {
 		printSpacing();
-		m_print += format("{}", static_cast<Symbol*>(node)->symbol());
+		m_print += format("{}", static_pointer_cast<Symbol>(node)->symbol());
 	}
 }
 
diff --git a/src/printer.h b/src/printer.h
index 388ed03..e8ae6eb 100644
--- a/src/printer.h
+++ b/src/printer.h
@@ -17,12 +17,12 @@ public:
 	Printer();
 	virtual ~Printer();
 
-	std::string print(ASTNode* node);
-	std::string printNoErrorCheck(ASTNode* node);
+	std::string print(ASTNodePtr node);
+	std::string printNoErrorCheck(ASTNodePtr node);
 
 private:
 	void init();
-	void printImpl(ASTNode* node);
+	void printImpl(ASTNodePtr node);
 	void printError();
 
 	bool m_first_node { true };
diff --git a/src/reader.cpp b/src/reader.cpp
index d74fe19..cb8ea8a 100644
--- a/src/reader.cpp
+++ b/src/reader.cpp
@@ -7,6 +7,7 @@
 #include <cstddef> // size_t
 #include <cstdint> // uint64_t
 #include <cstdlib> // std::strtoll
+#include <memory>  // makePtr, std::shared_ptr
 #include <utility> // std::move
 
 #include "error.h"
@@ -55,7 +56,7 @@ void Reader::read()
 	}
 }
 
-ASTNode* Reader::readImpl()
+ASTNodePtr Reader::readImpl()
 {
 	if (m_tokens.size() == 0) {
 		return nullptr;
@@ -123,7 +124,7 @@ ASTNode* Reader::readImpl()
 	return nullptr;
 }
 
-ASTNode* Reader::readSpliceUnquote()
+ASTNodePtr Reader::readSpliceUnquote()
 {
 	ignore(); // ~@
 
@@ -132,18 +133,18 @@ ASTNode* Reader::readSpliceUnquote()
 		return nullptr;
 	}
 
-	List* list = new List();
-	list->addNode(new Symbol("splice-unquote"));
+	auto list = makePtr<List>();
+	list->addNode(makePtr<Symbol>("splice-unquote"));
 	list->addNode(readImpl());
 
 	return list;
 }
 
-ASTNode* Reader::readList()
+ASTNodePtr Reader::readList()
 {
 	ignore(); // (
 
-	List* list = new List();
+	auto list = makePtr<List>();
 	while (!isEOF() && peek().type != Token::Type::ParenClose) {
 		list->addNode(readImpl());
 	}
@@ -156,11 +157,11 @@ ASTNode* Reader::readList()
 	return list;
 }
 
-ASTNode* Reader::readVector()
+ASTNodePtr Reader::readVector()
 {
 	ignore(); // [
 
-	Vector* vector = new Vector();
+	auto vector = makePtr<Vector>();
 	while (!isEOF() && peek().type != Token::Type::BracketClose) {
 		vector->addNode(readImpl());
 	}
@@ -172,30 +173,30 @@ ASTNode* Reader::readVector()
 	return vector;
 }
 
-ASTNode* Reader::readHashMap()
+ASTNodePtr Reader::readHashMap()
 {
 	ignore(); // {
 
-	HashMap* hash_map = new HashMap();
+	auto hash_map = makePtr<HashMap>();
 	while (!isEOF() && peek().type != Token::Type::BraceClose) {
-		ASTNode* key = readImpl();
-		ASTNode* value = readImpl();
+		auto key = readImpl();
+		auto value = readImpl();
 
-		if (!key && !value) {
+		if (key == nullptr && value == nullptr) {
 			break;
 		}
 
-		if (!key || !value) {
+		if (key == nullptr || value == nullptr) {
 			Error::the().addError("hash-map requires an even-sized list");
 			return nullptr;
 		}
 
-		if (!is<String>(key) && !is<Keyword>(key)) {
+		if (!is<String>(key.get()) && !is<Keyword>(key.get())) {
 			Error::the().addError(format("{} is not a string or keyword", key));
 			return nullptr;
 		}
 
-		std::string keyString = is<String>(key) ? static_cast<String*>(key)->data() : static_cast<Keyword*>(key)->keyword();
+		std::string keyString = is<String>(key.get()) ? static_pointer_cast<String>(key)->data() : static_pointer_cast<Keyword>(key)->keyword();
 		hash_map->addElement(keyString, value);
 	}
 
@@ -206,7 +207,7 @@ ASTNode* Reader::readHashMap()
 	return hash_map;
 }
 
-ASTNode* Reader::readQuote()
+ASTNodePtr Reader::readQuote()
 {
 	ignore(); // '
 
@@ -215,14 +216,14 @@ ASTNode* Reader::readQuote()
 		return nullptr;
 	}
 
-	List* list = new List();
-	list->addNode(new Symbol("quote"));
+	auto list = makePtr<List>();
+	list->addNode(makePtr<Symbol>("quote"));
 	list->addNode(readImpl());
 
 	return list;
 }
 
-ASTNode* Reader::readQuasiQuote()
+ASTNodePtr Reader::readQuasiQuote()
 {
 	ignore(); // `
 
@@ -231,14 +232,14 @@ ASTNode* Reader::readQuasiQuote()
 		return nullptr;
 	}
 
-	List* list = new List();
-	list->addNode(new Symbol("quasiquote"));
+	auto list = makePtr<List>();
+	list->addNode(makePtr<Symbol>("quasiquote"));
 	list->addNode(readImpl());
 
 	return list;
 }
 
-ASTNode* Reader::readUnquote()
+ASTNodePtr Reader::readUnquote()
 {
 	ignore(); // ~
 
@@ -247,14 +248,14 @@ ASTNode* Reader::readUnquote()
 		return nullptr;
 	}
 
-	List* list = new List();
-	list->addNode(new Symbol("unquote"));
+	auto list = makePtr<List>();
+	list->addNode(makePtr<Symbol>("unquote"));
 	list->addNode(readImpl());
 
 	return list;
 }
 
-ASTNode* Reader::readWithMeta()
+ASTNodePtr Reader::readWithMeta()
 {
 	ignore(); // ^
 
@@ -265,17 +266,17 @@ ASTNode* Reader::readWithMeta()
 	}
 	retreat();
 
-	List* list = new List();
-	list->addNode(new Symbol("with-meta"));
-	ASTNode* first = readImpl();
-	ASTNode* second = readImpl();
+	auto list = makePtr<List>();
+	list->addNode(makePtr<Symbol>("with-meta"));
+	ASTNodePtr first = readImpl();
+	ASTNodePtr second = readImpl();
 	list->addNode(second);
 	list->addNode(first);
 
 	return list;
 }
 
-ASTNode* Reader::readDeref()
+ASTNodePtr Reader::readDeref()
 {
 	ignore(); // @
 
@@ -284,14 +285,14 @@ ASTNode* Reader::readDeref()
 		return nullptr;
 	}
 
-	List* list = new List();
-	list->addNode(new Symbol("deref"));
+	auto list = makePtr<List>();
+	list->addNode(makePtr<Symbol>("deref"));
 	list->addNode(readImpl());
 
 	return list;
 }
 
-ASTNode* Reader::readString()
+ASTNodePtr Reader::readString()
 {
 	std::string symbol = consume().symbol;
 
@@ -300,24 +301,24 @@ ASTNode* Reader::readString()
 		Error::the().addError("expected '\"', got EOF");
 	}
 
-	return new String(symbol);
+	return makePtr<String>(symbol);
 }
 
-ASTNode* Reader::readKeyword()
+ASTNodePtr Reader::readKeyword()
 {
-	return new Keyword(consume().symbol);
+	return makePtr<Keyword>(consume().symbol);
 }
 
-ASTNode* Reader::readValue()
+ASTNodePtr Reader::readValue()
 {
 	Token token = consume();
 	char* end_ptr = nullptr;
 	int64_t result = std::strtoll(token.symbol.c_str(), &end_ptr, 10);
 	if (end_ptr == token.symbol.c_str() + token.symbol.size()) {
-		return new Number(result);
+		return makePtr<Number>(result);
 	}
 
-	return new Symbol(token.symbol);
+	return makePtr<Symbol>(token.symbol);
 }
 
 // -----------------------------------------
@@ -366,12 +367,13 @@ void Reader::dump()
 	dumpImpl(m_node);
 }
 
-void Reader::dumpImpl(ASTNode* node)
+void Reader::dumpImpl(ASTNodePtr node)
 {
 	std::string indentation = std::string(m_indentation * 2, ' ');
 
-	if (is<List>(node)) {
-		List* list = static_cast<List*>(node);
+	ASTNode* node_raw_ptr = node.get();
+	if (is<List>(node_raw_ptr)) {
+		List* list = static_cast<List*>(node_raw_ptr);
 		print("{}", indentation);
 		print(fg(ruc::format::TerminalColor::Blue), "ListContainer");
 		print(" <");
@@ -384,20 +386,25 @@ void Reader::dumpImpl(ASTNode* node)
 		m_indentation--;
 		return;
 	}
-	else if (is<String>(node)) {
+	else if (is<String>(node_raw_ptr)) {
 		print("{}", indentation);
 		print(fg(ruc::format::TerminalColor::Yellow), "StringNode");
-		print(" <{}>", static_cast<String*>(node)->data());
+		print(" <{}>", static_cast<String*>(node_raw_ptr)->data());
 	}
-	else if (is<Number>(node)) {
+	else if (is<Keyword>(node_raw_ptr)) {
+		print("{}", indentation);
+		print(fg(ruc::format::TerminalColor::Yellow), "KeywordNode");
+		print(" <{}>", static_cast<Keyword*>(node_raw_ptr)->keyword());
+	}
+	else if (is<Number>(node_raw_ptr)) {
 		print("{}", indentation);
 		print(fg(ruc::format::TerminalColor::Yellow), "NumberNode");
-		print(" <{}>", static_cast<Number*>(node)->number());
+		print(" <{}>", static_cast<Number*>(node_raw_ptr)->number());
 	}
-	else if (is<Symbol>(node)) {
+	else if (is<Symbol>(node_raw_ptr)) {
 		print("{}", indentation);
 		print(fg(ruc::format::TerminalColor::Yellow), "SymbolNode");
-		print(" <{}>", static_cast<Symbol*>(node)->symbol());
+		print(" <{}>", static_cast<Symbol*>(node_raw_ptr)->symbol());
 	}
 	print("\n");
 }
diff --git a/src/reader.h b/src/reader.h
index 91dfb44..981fcd5 100644
--- a/src/reader.h
+++ b/src/reader.h
@@ -7,6 +7,7 @@
 #pragma once
 
 #include <cstddef> // size_t
+#include <memory>  // std::shared_ptr
 #include <vector>
 
 #include "ast.h"
@@ -24,7 +25,7 @@ public:
 
 	void dump();
 
-	ASTNode* node() { return m_node; }
+	ASTNodePtr node() { return m_node; }
 
 private:
 	bool isEOF() const;
@@ -34,21 +35,21 @@ private:
 	void ignore();
 	void retreat();
 
-	ASTNode* readImpl();
-	ASTNode* readSpliceUnquote(); // ~@
-	ASTNode* readList();          // ()
-	ASTNode* readVector();        // []
-	ASTNode* readHashMap();       // {}
-	ASTNode* readQuote();         // '
-	ASTNode* readQuasiQuote();    // `
-	ASTNode* readUnquote();       // ~
-	ASTNode* readWithMeta();      // ^
-	ASTNode* readDeref();         // @
-	ASTNode* readString();        // "foobar"
-	ASTNode* readKeyword();       // :keyword
-	ASTNode* readValue();         // number, "true", "false", "nil", symbol
+	ASTNodePtr readImpl();
+	ASTNodePtr readSpliceUnquote(); // ~@
+	ASTNodePtr readList();          // ()
+	ASTNodePtr readVector();        // []
+	ASTNodePtr readHashMap();       // {}
+	ASTNodePtr readQuote();         // '
+	ASTNodePtr readQuasiQuote();    // `
+	ASTNodePtr readUnquote();       // ~
+	ASTNodePtr readWithMeta();      // ^
+	ASTNodePtr readDeref();         // @
+	ASTNodePtr readString();        // "foobar"
+	ASTNodePtr readKeyword();       // :keyword
+	ASTNodePtr readValue();         // number, "true", "false", "nil", symbol
 
-	void dumpImpl(ASTNode* node);
+	void dumpImpl(ASTNodePtr node);
 
 	size_t m_index { 0 };
 	size_t m_indentation { 0 };
@@ -58,7 +59,7 @@ private:
 	bool m_invalid_syntax { false };
 	bool m_is_unbalanced { false };
 
-	ASTNode* m_node { nullptr };
+	ASTNodePtr m_node { nullptr };
 };
 
 } // namespace blaze
diff --git a/src/step1_read_print.cpp b/src/step1_read_print.cpp
index d28840d..479607d 100644
--- a/src/step1_read_print.cpp
+++ b/src/step1_read_print.cpp
@@ -15,7 +15,7 @@
 #include "settings.h"
 
 #if 0
-auto read(std::string_view input) -> blaze::ASTNode*
+auto read(std::string_view input) -> blaze::ASTNodePtr
 {
 	blaze::Lexer lexer(input);
 	lexer.tokenize();
@@ -32,15 +32,15 @@ auto read(std::string_view input) -> blaze::ASTNode*
 	return reader.node();
 }
 
-auto eval(blaze::ASTNode* ast) -> blaze::ASTNode*
+auto eval(blaze::ASTNodePtr ast) -> blaze::ASTNodePtr
 {
 	return ast;
 }
 
-auto print(blaze::ASTNode* exp) -> void
+auto print(blaze::ASTNodePtr exp) -> std::string
 {
-	blaze::Printer printer(exp);
-	printer.dump();
+	blaze::Printer printer;
+	return printer.print(exp);
 }
 
 auto rep(std::string_view input) -> void
@@ -48,7 +48,7 @@ auto rep(std::string_view input) -> void
 	blaze::Error::the().clearErrors();
 	blaze::Error::the().setInput(input);
 
-	print(eval(read(input)));
+	print("{}\n", print(eval(read(input))).c_str());
 }
 
 static auto cleanup(int signal) -> void
diff --git a/src/step2_eval.cpp b/src/step2_eval.cpp
index b6657eb..4efffa1 100644
--- a/src/step2_eval.cpp
+++ b/src/step2_eval.cpp
@@ -16,7 +16,7 @@
 #include "settings.h"
 
 #if 1
-auto read(std::string_view input) -> blaze::ASTNode*
+auto read(std::string_view input) -> blaze::ASTNodePtr
 {
 	blaze::Lexer lexer(input);
 	lexer.tokenize();
@@ -33,7 +33,7 @@ auto read(std::string_view input) -> blaze::ASTNode*
 	return reader.node();
 }
 
-auto eval(blaze::ASTNode* ast) -> blaze::ASTNode*
+auto eval(blaze::ASTNodePtr ast) -> blaze::ASTNodePtr
 {
 	blaze::GlobalEnvironment env;
 	blaze::Eval eval(ast, &env);
@@ -42,7 +42,7 @@ auto eval(blaze::ASTNode* ast) -> blaze::ASTNode*
 	return eval.ast();
 }
 
-auto print(blaze::ASTNode* exp) -> std::string
+auto print(blaze::ASTNodePtr exp) -> std::string
 {
 	blaze::Printer printer;