diff --git a/CMakeLists.txt b/CMakeLists.txt
index 015e32e..4f1d93b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -87,3 +87,7 @@ add_dependencies(test0 ${PROJECT})
 add_custom_target(test1
     COMMAND env STEP=step1_read_print MAL_IMPL=js ../vendor/mal/runtest.py --deferrable --optional ../vendor/mal/tests/step1_read_print.mal -- ./${PROJECT})
 add_dependencies(test1 ${PROJECT})
+
+add_custom_target(test2
+    COMMAND env STEP=step_eval MAL_IMPL=js ../vendor/mal/runtest.py --deferrable --optional ../vendor/mal/tests/step2_eval.mal -- ./${PROJECT})
+add_dependencies(test2 ${PROJECT})
diff --git a/src/ast.cpp b/src/ast.cpp
index 47da97e..803a627 100644
--- a/src/ast.cpp
+++ b/src/ast.cpp
@@ -59,6 +59,13 @@ Value::Value(const std::string& value)
 {
 }
 
+// -----------------------------------------
+
+Function::Function(Lambda lambda)
+	: m_lambda(lambda)
+{
+}
+
 } // namespace blaze
 
 // -----------------------------------------
diff --git a/src/ast.h b/src/ast.h
index cafa549..6cf3134 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -6,7 +6,9 @@
 
 #pragma once
 
-#include <cstdint> // int64_t
+#include <cstdint>    // int64_t
+#include <functional> // std::function
+#include <span>
 #include <string>
 #include <string_view>
 #include <typeinfo> // typeid
@@ -51,6 +53,8 @@ public:
 	void addNode(ASTNode* node);
 
 	const std::vector<ASTNode*>& nodes() const { return m_nodes; }
+	size_t size() const { return m_nodes.size(); }
+	bool empty() const { return m_nodes.size() == 0; }
 
 protected:
 	Collection() {}
@@ -173,6 +177,22 @@ public:
 private:
 	std::string m_value;
 };
+
+// -----------------------------------------
+
+using Lambda = std::function<ASTNode*(std::span<ASTNode*>)>;
+
+class Function final : public ASTNode {
+public:
+	Function(Lambda lambda);
+	virtual ~Function() = default;
+
+	virtual bool isFunction() const override { return true; }
+
+	Lambda lambda() const { return m_lambda; }
+
+private:
+	Lambda m_lambda;
 };
 
 // -----------------------------------------
@@ -204,6 +224,9 @@ inline bool ASTNode::fastIs<Symbol>() const { return isSymbol(); }
 
 template<>
 inline bool ASTNode::fastIs<Value>() const { return isValue(); }
+
+template<>
+inline bool ASTNode::fastIs<Function>() const { return isFunction(); }
 // clang-format on
 
 } // namespace blaze
diff --git a/src/environment.h b/src/environment.h
new file mode 100644
index 0000000..8131626
--- /dev/null
+++ b/src/environment.h
@@ -0,0 +1,148 @@
+/*
+ * Copyright (C) 2023 Riyyi
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#pragma once
+
+#include <cstdint> // int64_t
+#include <iostream>
+#include <span>
+#include <string_view>
+#include <unordered_map>
+#include <vector>
+
+#include "error.h"
+#include "ruc/format/color.h"
+#include "ruc/singleton.h"
+
+#include "ast.h"
+#include "types.h"
+
+namespace blaze {
+
+class Environment {
+public:
+	Environment() = default;
+	virtual ~Environment() = default;
+
+	ASTNode* lookup(const std::string& symbol)
+	{
+		m_current_key = symbol;
+		return m_values.find(symbol) != m_values.end() ? m_values[symbol] : nullptr;
+	}
+
+protected:
+	std::string m_current_key;
+	std::unordered_map<std::string, ASTNode*> m_values;
+};
+
+class GlobalEnvironment final : public Environment {
+public:
+	GlobalEnvironment()
+	{
+		auto add = [](std::span<ASTNode*> nodes) -> ASTNode* {
+			int64_t result = 0;
+
+			for (auto node : nodes) {
+				if (!is<Number>(node)) {
+					Error::the().addError(format("wrong type argument: number-or-marker-p, '{}'", node));
+					return nullptr;
+				}
+
+				result += static_cast<Number*>(node)->number();
+			}
+
+			return new Number(result);
+		};
+
+		auto sub = [](std::span<ASTNode*> nodes) -> ASTNode* {
+			int64_t result = 0;
+
+			if (nodes.size() == 0) {
+				return new Number(0);
+			}
+
+			for (auto node : nodes) {
+				if (!is<Number>(node)) {
+					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();
+
+			// Skip the first node
+			for (auto it = std::next(nodes.begin()); it != nodes.end(); ++it) {
+				result -= static_cast<Number*>(*it)->number();
+			}
+
+			return new Number(result);
+		};
+
+		auto mul = [](std::span<ASTNode*> nodes) -> ASTNode* {
+			int64_t result = 1;
+
+			for (auto node : nodes) {
+				if (!is<Number>(node)) {
+					Error::the().addError(format("wrong type argument: number-or-marker-p, '{}'", node));
+					return nullptr;
+				}
+
+				result *= static_cast<Number*>(node)->number();
+			}
+
+			return new Number(result);
+		};
+
+		auto div = [this](std::span<ASTNode*> nodes) -> ASTNode* {
+			double result = 0;
+
+			if (nodes.size() == 0) {
+				Error::the().addError(format("wrong number of arguments: {}, 0", m_current_key));
+				return nullptr;
+			}
+
+			for (auto node : nodes) {
+				if (!is<Number>(node)) {
+					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();
+
+			// Skip the first node
+			for (auto it = std::next(nodes.begin()); it != nodes.end(); ++it) {
+				result /= static_cast<Number*>(*it)->number();
+			}
+
+			return new 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));
+	}
+	virtual ~GlobalEnvironment() = default;
+};
+
+} // namespace blaze
+
+// associative data structure that maps symbols (the keys) to values
+
+// values = anything, including other symbols.
+// an environment is like a hash table
+
+// value can map to:
+// list
+// vector
+// hash-map
+// symbol
+// number
+// string
+// function
diff --git a/src/eval.cpp b/src/eval.cpp
new file mode 100644
index 0000000..85a43f0
--- /dev/null
+++ b/src/eval.cpp
@@ -0,0 +1,90 @@
+/*
+ * Copyright (C) 2023 Riyyi
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <span> // std::span
+
+#include "ast.h"
+#include "environment.h"
+#include "eval.h"
+#include "ruc/meta/assert.h"
+#include "types.h"
+
+namespace blaze {
+
+Eval::Eval(ASTNode* ast, Environment* env)
+	: m_ast(ast)
+	, m_env(env)
+{
+}
+
+void Eval::eval()
+{
+	m_ast = evalImpl(m_ast, m_env);
+}
+
+ASTNode* Eval::evalImpl(ASTNode* ast, Environment* env)
+{
+	if (!is<List>(ast)) {
+		return evalAst(ast, env);
+	}
+	if (static_cast<List*>(ast)->empty()) {
+		return ast;
+	}
+
+	return apply(static_cast<List*>(evalAst(ast, env)));
+}
+
+ASTNode* Eval::evalAst(ASTNode* ast, Environment* env)
+{
+	if (is<Symbol>(ast)) {
+		auto result = env->lookup(static_cast<Symbol*>(ast)->symbol());
+		if (!result) {
+			Error::the().addError(format("'{}' not found", ast));
+		}
+		return result;
+	}
+	else if (is<List>(ast)) {
+		auto result = new List();
+		auto nodes = static_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();
+		for (auto node : nodes) {
+			result->addNode(evalImpl(node, env));
+		}
+		return result;
+	}
+	else if (is<HashMap>(ast)) {
+		// TODO
+		VERIFY_NOT_REACHED();
+		return nullptr;
+	}
+
+	return ast;
+}
+
+ASTNode* Eval::apply(List* evaluated_list)
+{
+	auto nodes = evaluated_list->nodes();
+
+	if (!is<Function>(nodes[0])) {
+		return nullptr;
+	}
+
+	// car
+	auto lambda = static_cast<Function*>(nodes[0])->lambda();
+	// cdr
+	std::span<ASTNode*> span { nodes.data() + 1, nodes.size() - 1 };
+
+	return lambda(span);
+}
+
+} // namespace blaze
diff --git a/src/eval.h b/src/eval.h
new file mode 100644
index 0000000..dcc9ace
--- /dev/null
+++ b/src/eval.h
@@ -0,0 +1,32 @@
+/*
+ * Copyright (C) 2023 Riyyi
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#pragma once
+
+#include "ast.h"
+#include "environment.h"
+
+namespace blaze {
+
+class Eval {
+public:
+	Eval(ASTNode* ast, Environment* env);
+	virtual ~Eval() = default;
+
+	void eval();
+
+	ASTNode* ast() const { return m_ast; }
+
+private:
+	ASTNode* evalImpl(ASTNode* ast, Environment* env);
+	ASTNode* evalAst(ASTNode* ast, Environment* env);
+	ASTNode* apply(List* evaluated_list);
+
+	ASTNode* m_ast { nullptr };
+	Environment* m_env { nullptr };
+};
+
+} // namespace blaze
diff --git a/src/step1_read_print.cpp b/src/step1_read_print.cpp
index e901b2e..d28840d 100644
--- a/src/step1_read_print.cpp
+++ b/src/step1_read_print.cpp
@@ -14,7 +14,7 @@
 #include "reader.h"
 #include "settings.h"
 
-#if 1
+#if 0
 auto read(std::string_view input) -> blaze::ASTNode*
 {
 	blaze::Lexer lexer(input);
diff --git a/src/step2_eval.cpp b/src/step2_eval.cpp
new file mode 100644
index 0000000..e0a546c
--- /dev/null
+++ b/src/step2_eval.cpp
@@ -0,0 +1,113 @@
+#include <csignal>  // std::signal
+#include <cstdlib>  // std::exit
+#include <iostream> // std::cin
+#include <string>   // std::getline
+#include <string_view>
+
+#include "environment.h"
+#include "eval.h"
+#include "ruc/argparser.h"
+#include "ruc/format/color.h"
+
+#include "ast.h"
+#include "error.h"
+#include "lexer.h"
+#include "printer.h"
+#include "reader.h"
+#include "settings.h"
+
+#if 1
+auto read(std::string_view input) -> blaze::ASTNode*
+{
+	blaze::Lexer lexer(input);
+	lexer.tokenize();
+	if (blaze::Settings::the().get("dump-lexer") == "1") {
+		lexer.dump();
+	}
+
+	blaze::Reader reader(std::move(lexer.tokens()));
+	reader.read();
+	if (blaze::Settings::the().get("dump-reader") == "1") {
+		reader.dump();
+	}
+
+	return reader.node();
+}
+
+auto eval(blaze::ASTNode* ast) -> blaze::ASTNode*
+{
+	blaze::GlobalEnvironment env;
+	blaze::Eval eval(ast, &env);
+	eval.eval();
+	return eval.ast();
+}
+
+auto print(blaze::ASTNode* exp) -> void
+{
+	blaze::Printer printer(exp);
+	printer.dump();
+}
+
+auto rep(std::string_view input) -> void
+{
+	blaze::Error::the().clearErrors();
+	blaze::Error::the().setInput(input);
+
+	print(eval(read(input)));
+}
+
+static auto cleanup(int signal) -> void
+{
+	print("\033[0m");
+	std::exit(signal);
+}
+
+auto main(int argc, char* argv[]) -> int
+{
+	bool dump_lexer = false;
+	bool dump_reader = false;
+	bool pretty_print = false;
+
+	// CLI arguments
+	ruc::ArgParser arg_parser;
+	arg_parser.addOption(dump_lexer, 'l', "dump-lexer", nullptr, nullptr);
+	arg_parser.addOption(dump_reader, 'r', "dump-reader", nullptr, nullptr);
+	arg_parser.addOption(pretty_print, 'c', "color", nullptr, nullptr);
+	arg_parser.parse(argc, argv);
+
+	// Set settings
+	blaze::Settings::the().set("dump-lexer", dump_lexer ? "1" : "0");
+	blaze::Settings::the().set("dump-reader", dump_reader ? "1" : "0");
+	blaze::Settings::the().set("pretty-print", pretty_print ? "1" : "0");
+
+	// Signal callbacks
+	std::signal(SIGINT, cleanup);
+	std::signal(SIGTERM, cleanup);
+
+	while (true) {
+		if (!pretty_print) {
+			print("user> ");
+		}
+		else {
+			print(fg(ruc::format::TerminalColor::Blue), "user>");
+			print(" \033[1m");
+		}
+		std::string line;
+		std::getline(std::cin, line);
+		if (pretty_print) {
+			print("\033[0m");
+		}
+
+		// Exit with Ctrl-D
+		if (std::cin.eof() || std::cin.fail()) {
+			break;
+		}
+
+		rep(line);
+	}
+
+	return 0;
+}
+#endif
+
+// - Add AST node printing support to ruc::format