From 7c1612d9c2452f7451e9ca76a62c940a876ffe86 Mon Sep 17 00:00:00 2001
From: John Stefanelli <jpsdzn@gmail.com>
Date: Sat, 31 May 2025 19:43:46 +0200
Subject: [PATCH] [libjlx] First successful "execution"

---
 jlx/src/main.cpp                 |  10 +-
 libjlx/CMakeLists.txt            |   1 +
 libjlx/modules/ast.cppm          |   3 +-
 libjlx/modules/interpreter.cppm  | 859 +++++++++++++++++++++++++++++++
 libjlx/modules/main.cppm         |   1 +
 libjlx/modules/type_checker.cppm |  28 +-
 6 files changed, 881 insertions(+), 21 deletions(-)
 create mode 100644 libjlx/modules/interpreter.cppm

diff --git a/jlx/src/main.cpp b/jlx/src/main.cpp
index e68997f..82feaf4 100644
--- a/jlx/src/main.cpp
+++ b/jlx/src/main.cpp
@@ -12,7 +12,6 @@ int main(int argc, char** argv) {
 	std::istreambuf_iterator<char> start, end;
 	if (argc > 1) {
 		if (std::filesystem::is_regular_file(argv[1])) {
-			std::cout << "Opening: " << argv[1] << std::endl;
 			file = std::ifstream(argv[1]);
 			start = std::istreambuf_iterator<char>(file);
 		} else {
@@ -37,8 +36,6 @@ int main(int argc, char** argv) {
 		}
 	} while (res.has_value());
 
-	std::cout << "Read " << tokens.size() << " tokens\n";
-
 	auto last = std::string();
 	while(res.has_value()) {
 		const auto& t = res.value();
@@ -61,8 +58,6 @@ int main(int argc, char** argv) {
 		return 1;
 	}
 
-	std::cout << "Parsed " << rt->statements.size() << " statements" << std::endl;
-
 	auto type_checker = jlx::type_checker(rt->statements.begin(), rt->statements.end());
 	type_checker.include_stdlib();
 	try {
@@ -72,7 +67,10 @@ int main(int argc, char** argv) {
 		return 1;
 	}
 
-	std::cout << "Type checking OK." << std::endl;
+	auto interpreter = jlx::interpreter(rt->statements.begin(), rt->statements.end());
+	interpreter.add_stdlib();
+
+	interpreter.run();
 
 	return 0;
 }
diff --git a/libjlx/CMakeLists.txt b/libjlx/CMakeLists.txt
index da8ce16..a31a378 100644
--- a/libjlx/CMakeLists.txt
+++ b/libjlx/CMakeLists.txt
@@ -7,6 +7,7 @@ target_sources(libjlx PUBLIC FILE_SET libjlx_modules TYPE CXX_MODULES FILES
 	"${CMAKE_CURRENT_SOURCE_DIR}/modules/ast.cppm"
 	"${CMAKE_CURRENT_SOURCE_DIR}/modules/utils.cppm"
 	"${CMAKE_CURRENT_SOURCE_DIR}/modules/type_checker.cppm"
+	"${CMAKE_CURRENT_SOURCE_DIR}/modules/interpreter.cppm"
 )
 target_compile_options(libjlx PRIVATE $<IF:$<CXX_COMPILER_ID:Msvc>,/W4 /WX,-Wall -Wextra -Werror>)
 target_include_directories(libjlx PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/include") 
diff --git a/libjlx/modules/ast.cppm b/libjlx/modules/ast.cppm
index 1abcf4c..1db0d81 100644
--- a/libjlx/modules/ast.cppm
+++ b/libjlx/modules/ast.cppm
@@ -409,7 +409,6 @@ namespace jlx {
 
 			auto start = *current;
 
-
 			switch(current->type) {
 				case Identifier:
 					if (previous != nullptr) {
@@ -512,6 +511,8 @@ namespace jlx {
 					fail_invalid_token(*current);
 					break;
 			}
+
+			fail_invalid_token(*current);
 		}
 
 		std::unique_ptr<function_declaration> parse_function() {
diff --git a/libjlx/modules/interpreter.cppm b/libjlx/modules/interpreter.cppm
new file mode 100644
index 0000000..00644f8
--- /dev/null
+++ b/libjlx/modules/interpreter.cppm
@@ -0,0 +1,859 @@
+module;
+
+#include <charconv>
+#include <iterator>
+#include <variant>
+#include <optional>
+#include <unordered_map>
+#include <string_view>
+#include <ranges>
+#include <format>
+#include <iostream>
+
+export module jlx:interpreter;
+import :ast;
+import :type_checker;
+
+namespace jlx {
+	using runtime_value = std::variant<std::string, int8_t, int16_t, int32_t, int64_t, uint8_t, uint16_t, uint32_t, uint64_t, float, double, bool>;
+
+	struct interpreter_variable {
+		std::string type;
+		bool writable;
+		runtime_value value;
+	};
+
+	struct interpreter_variable_scope {
+		std::unordered_map<std::string, interpreter_variable> variables;
+	};
+
+	struct interpreter_function_scope {
+		std::optional<runtime_value> return_value;
+		bool returned = false;
+	};
+
+	struct interpreter_error : public std::runtime_error {
+		interpreter_error(std::string_view msg, const token& t) :
+		std::runtime_error(std::format("Interpreter error: {} at {}:{}:{}", msg, t.source_file, t.line, t.col).c_str()) {
+
+		}
+	};
+
+	template<class... Ts>
+	struct overload : Ts... { using Ts::operator()...; };
+
+	struct base_interpreter {
+		virtual std::optional<runtime_value> execute_statement(const statement&) = 0;
+		virtual void push_function_scope() = 0;
+		virtual void pop_function_scope() = 0;
+		virtual void push_variable_scope() = 0;
+		virtual void pop_variable_scope() = 0;
+		virtual interpreter_function_scope& current_function_scope() = 0;
+		virtual interpreter_variable_scope& current_variable_scope() = 0;
+		virtual bool is_in_function() = 0;
+		virtual void inject_value(const std::string_view&, runtime_value) = 0;
+
+		virtual ~base_interpreter() = default;
+	};
+
+	struct interpreter_function {
+		virtual std::optional<runtime_value> call(const std::vector<runtime_value>&, base_interpreter&) = 0;
+
+		virtual ~interpreter_function() = default;
+	};
+
+	template<typename A, typename B>
+	concept Operable = requires(A a, B b)
+	{
+		requires sizeof(A) >= sizeof(B);
+		{ a + b };
+		{ a - b };
+		{ a * b };
+		{ a / b };
+		{ a % b };
+		std::numeric_limits<A>::is_specialized;
+		std::numeric_limits<B>::is_specialized;
+		std::numeric_limits<A>::is_integer == std::numeric_limits<B>::is_integer;
+		std::numeric_limits<A>::is_signed == std::numeric_limits<B>::is_signed;
+	};
+
+	template<typename A, typename B>
+	concept Comparable = requires {
+		requires std::is_same_v<A, B> ||
+		requires (A a, B b)
+		{
+			requires std::numeric_limits<A>::is_signed == std::numeric_limits<B>::is_signed;
+			{ a == b } -> std::convertible_to<bool>;
+			{ a != b } -> std::convertible_to<bool>;
+		};
+	};
+
+	template<typename A, typename B>
+	concept Orderable = requires
+	{
+		requires std::is_same_v<A, B> || requires (A a, B b){
+			requires std::numeric_limits<std::remove_cvref_t<A>>::is_signed == std::numeric_limits<std::remove_cvref_t<B>>::is_signed;
+			{ a < b } -> std::convertible_to<bool>;
+			{ a > b } -> std::convertible_to<bool>;
+			{ a >= b } -> std::convertible_to<bool>;
+			{ a <= b } -> std::convertible_to<bool>;
+		};
+	};
+
+	static_assert(!Operable<std::string, uint32_t>);
+	static_assert(Operable<uint32_t, uint16_t>);
+	static_assert(!Operable<uint16_t, uint32_t>);
+	static_assert(!Comparable<std::string, signed char>);
+	static_assert(!Comparable<uint32_t, int32_t>);
+	static_assert(!Orderable<std::string, int32_t>);
+	static_assert(!Orderable<int8_t, uint32_t>);
+
+	template<typename A, typename B>
+	struct arithmetic_evaluator {
+		std::remove_cvref_t<A> sum(A a, B b) requires Operable<A, B> {
+			return a + b;
+		}
+
+		std::remove_cvref_t<A> mul(A a, B b) requires Operable<A, B> {
+			return a * b;
+		}
+
+		std::remove_cvref_t<A> div(A a, B b) requires Operable<A, B> {
+			return a / b;
+		}
+
+		std::remove_cvref_t<A> sub(A a, B b) requires Operable<A, B> {
+			return a - b;
+		}
+
+		std::remove_cvref_t<A> mod(A a, B b) requires Operable<A, B> {
+			return a % b;
+		}
+
+		std::remove_cvref_t<B> sum(A a, B b) requires Operable<B, A> && (!Operable<A, B>) {
+			return a + b;
+		}
+
+		std::remove_cvref_t<B> mul(A a, B b) requires Operable<B, A> && (!Operable<A, B>) {
+			return a * b;
+		}
+
+		std::remove_cvref_t<B> div(A a, B b) requires Operable<B, A> && (!Operable<A, B>) {
+			return a / b;
+		}
+
+		std::remove_cvref_t<B> sub(A a, B b) requires Operable<B, A> && (!Operable<A, B>) {
+			return a - b;
+		}
+
+		std::remove_cvref_t<B> mod(A a, B b) requires Operable<B, A> && (!Operable<A, B>) {
+			return a % b;
+		}
+
+		std::string sum(std::string a, B b) requires (!std::is_same_v<std::remove_cvref_t<B>, std::string>) {
+			return a + std::to_string(b);
+		}
+
+		std::string sum(std::string a, std::string b) {
+			return a + b;
+		}
+
+		[[noreturn]] A sum(A, B) requires (!std::is_same_v<std::remove_cvref_t<A>, std::string> && !Operable<A, B> && !Operable<B, A>) {
+			throw std::runtime_error("Arithmetically-incompatible types");
+		}
+
+		[[noreturn]] A mul(A, B) {
+			throw std::runtime_error("Arithmetically-incompatible types");
+		}
+
+		[[noreturn]] A div(A, B) {
+			throw std::runtime_error("Arithmetically-incompatible types");
+		}
+
+		[[noreturn]] A sub(A, B) {
+			throw std::runtime_error("Arithmetically-incompatible types");
+		}
+
+		[[noreturn]] A mod(A, B) {
+			throw std::runtime_error("Arithmetically-incompatible types");
+		}
+	};
+
+
+	template<typename A, typename B> requires Comparable<A, B>
+	bool are_equal(A a, B b) {
+		return a == b;
+	}
+
+	template<typename A, typename B>
+	[[noreturn]] bool are_equal(A, B) {
+		throw std::runtime_error("Non-comparable types");
+	}
+
+	template<typename A, typename B>
+	struct comparator {
+		bool more_than(A a, B b) requires Orderable<A, B> {
+			return a > b;
+		}
+
+		bool less_than(A a, B b) requires Orderable<A, B> {
+			return a < b;
+		}
+
+		bool more_equal_than(A a, B b) requires Orderable<A, B> {
+			return a >= b;
+		}
+
+		bool less_equal_than(A a, B b) requires Orderable<A, B> {
+			return a <= b;
+		}
+
+		bool more_than(A, B) {
+			throw std::runtime_error("Non-orderable types");
+		}
+
+		bool less_than(A, B) {
+			throw std::runtime_error("Non-orderable types");
+		}
+
+		bool more_equal_than(A, B) {
+			throw std::runtime_error("Non-orderable types");
+		}
+
+		bool less_equal_than(A, B) {
+			throw std::runtime_error("Non-orderable types");
+		}
+	};
+
+
+	template<typename T>
+	struct lambda_function : public interpreter_function {
+		std::function<T(const std::vector<runtime_value>&)> f;
+
+		explicit lambda_function(std::function<T(const std::vector<runtime_value>&)> f) : f(f) {
+
+		}
+
+		virtual std::optional<runtime_value> call(const std::vector<runtime_value>& args, base_interpreter&) {
+			return f(args);
+		}
+	};
+
+
+	template<>
+	struct lambda_function<void> : public interpreter_function {
+		std::function<void(const std::vector<runtime_value>&)> f;
+
+		explicit lambda_function(std::function<void(const std::vector<runtime_value>&)> f) : f(f) {
+
+		}
+
+		std::optional<runtime_value> call(const std::vector<runtime_value>& args, base_interpreter&) override {
+			f(args);
+
+			return std::nullopt;
+		}
+	};
+
+
+	struct basic_function : public interpreter_function {
+		const function_declaration* declaration;
+
+		explicit basic_function(const function_declaration* declaration) : declaration(declaration) {
+
+		}
+
+		std::optional<runtime_value> call(const std::vector<runtime_value>& args, base_interpreter& i) override {
+			if (args.size() != declaration->parameters.size()) {
+				throw interpreter_error("Wrong number of arguments for function call", declaration->t);
+			}
+
+			i.push_function_scope();
+			i.push_variable_scope();
+			for (auto a_id = 1ULL; a_id < args.size(); a_id++) {
+				auto param = declaration->parameters[a_id];
+				auto arg = args[a_id];
+
+				//TODO: Check argument type
+				i.inject_value(param.name, arg);
+			}
+
+			i.execute_statement(*declaration->body);
+
+			std::optional<runtime_value> return_value;
+			auto& func_scope = i.current_function_scope();
+			if (func_scope.returned) {
+				return_value = func_scope.return_value;
+			}
+
+			i.pop_variable_scope();
+			i.pop_function_scope();
+
+			//TODO: Check type of RVL?
+			return return_value;
+		}
+	};
+
+	export template<statement_iterator T, std::sentinel_for<T> E>
+	class interpreter : public base_interpreter {
+		T current;
+		E end;
+		std::vector<interpreter_variable_scope> scopes;
+		std::unordered_map<std::string, std::unique_ptr<interpreter_function>> functions;
+		std::vector<interpreter_function_scope> function_scopes;
+	public:
+		constexpr std::string_view get_type_for_value(const runtime_value& v) {
+			auto id = v.index();
+			switch (id) {
+				case 0:
+					return "string";
+				case 1:
+					return "i8";
+				case 2:
+					return "i16";
+				case 3:
+					return "i32";
+				case 4:
+					return "i64";
+				case 5:
+					return "u8";
+				case 6:
+					return "u16";
+				case 7:
+					return "u32";
+				case 8:
+					return "u64";
+				case 9:
+					return "f32";
+				case 10:
+					return "f64";
+				case 11:
+					return "boolean";
+				default:
+					return "i64";
+			}
+		}
+
+		interpreter(T start, E end) : current(start), end(end) {
+			scopes.emplace_back();
+		}
+
+		void add_stdlib() {
+			functions.try_emplace("print", std::make_unique<lambda_function<void>>([](const auto& args) {
+				if (args.size() != 1) {
+					throw std::runtime_error("No arguments to print()");
+				}
+
+				const auto& arg0 = args[0];
+
+				if (arg0.index() != 0) {
+					throw std::runtime_error("Invalid argument to print()");
+				}
+
+				const auto& str = std::get<0>(arg0);
+
+				std::cout << str << std::endl;
+			}));
+
+			functions.insert_or_assign("boolean_to_string", std::make_unique<lambda_function<std::string>>([](const auto& args) {
+				if (args.size() != 1) {
+					throw std::runtime_error("No arguments to boolean_to_string()");
+				}
+
+				const auto& arg0 = args[0];
+
+				if (arg0.index() != 11) {
+					throw std::runtime_error("Invalid argument to boolean_to_string()");
+				}
+
+				bool b = std::get<11>(arg0);
+
+				return b ? "true" : "false";
+			}));
+		}
+
+		void run() {
+			while (current != end) {
+				execute_statement(**current);
+				++current;
+			}
+		}
+
+		static runtime_value parse_literal(const expression& e) {
+			auto* lv = dynamic_cast<const literal_value*>(&e);
+
+			if (lv == nullptr) {
+				throw interpreter_error("Internal interpreter error", e.t);
+			}
+
+			auto& content = lv->t.content;
+
+			const auto* begin = content.data();
+			const auto* end = begin + content.size();
+			switch (lv->t.type) {
+				case Number:
+					if (content.find('.') != std::string::npos) {
+						double d{};
+
+						auto v = std::from_chars(begin, end, d, std::chars_format::scientific);
+
+						if (v.ec == std::errc()) {
+							return d;
+						} else {
+							throw interpreter_error("Failed to parse float/double value", lv->t);
+						}
+					} else {
+						uint64_t i{};
+
+						auto v = std::from_chars(begin, end, i);
+
+						if (v.ec == std::errc()) {
+							return i;
+						} else {
+							throw interpreter_error("Failed to parse integer value", lv->t);
+						}
+					}
+					break;
+				case String:
+					return content;
+					break;
+				case Boolean:
+					if (content == "true") {
+						return true;
+					} else if (content == "false") {
+						return false;
+					} else {
+						throw interpreter_error("Invalid boolean value", lv->t);
+					}
+					break;
+				default:
+					throw interpreter_error("Invalid literal value", lv->t);
+			}
+		}
+
+		static runtime_value negate(runtime_value v) {
+			if (v.index() == 0 || v.index() == 11) {
+				throw std::runtime_error("Invalid literal value");
+			}
+
+			return std::visit(overload {
+				[](std::string&) -> runtime_value { throw std::runtime_error("Invalid negation value"); },
+				[](bool) -> runtime_value { throw std::runtime_error("Invalid boolean value"); },
+				[]<typename X>(X a) -> runtime_value { return -a; }
+			}, v);
+		}
+
+		bool logical_or(const dual_operation* dvo) {
+			auto v0 = eval_expression(*dvo->first_operand);
+
+			if (v0->index() != 11) {
+				throw std::runtime_error("Invalid operand type");
+			}
+
+			bool b0 = std::get<11>(*v0);
+
+			if (!b0) {
+				auto v1 = eval_expression(*dvo->second_operand);
+
+				if (v1->index() != 11) {
+					throw std::runtime_error("Invalid operand type");
+				}
+
+				bool b1 = std::get<11>(*v1);
+
+				return b1;
+			}
+
+			return true;
+		}
+
+		bool logical_and(const dual_operation* dvo) {
+			auto v0 = eval_expression(*dvo->first_operand);
+
+			if (!v0.has_value()) {
+				throw interpreter_error("Invalid operand value", dvo->first_operand->t);
+			}
+
+			if (v0->index() != 11) {
+				throw interpreter_error("Invalid operand type", dvo->first_operand->t);
+			}
+
+			bool b0 = std::get<11>(*v0);
+
+			if (b0) {
+				auto v1 = eval_expression(*dvo->second_operand);
+
+				if (!v1.has_value()) {
+					throw interpreter_error("Invalid operand value", dvo->second_operand->t);
+				}
+
+				if (v1->index() != 11) {
+					throw interpreter_error("Invalid operand type", dvo->second_operand->t);
+				}
+
+				bool b1 = std::get<11>(*v1);
+
+				return b1;
+			}
+
+			return false;
+		}
+
+		runtime_value arithmetic_op(const dual_operation* dvo) {
+			auto v0 = eval_expression(*dvo->first_operand);
+			auto v1 = eval_expression(*dvo->second_operand);
+
+			if (!v0.has_value() || !v1.has_value()) {
+				throw interpreter_error("Invalid operand value", dvo->t);
+			}
+
+			return std::visit([&dvo]<typename A, typename B>(A&& a, B&& b) {
+				if (dvo->operator_token.content == "+") {
+					return runtime_value(arithmetic_evaluator<A, B>().sum(a, b));
+				} else if (dvo->operator_token.content == "-") {
+					return runtime_value(arithmetic_evaluator<A, B>().sub(a, b));
+				} else if (dvo->operator_token.content == "*") {
+					return runtime_value(arithmetic_evaluator<A, B>().mul(a, b));
+				} else if (dvo->operator_token.content == "/") {
+					return runtime_value(arithmetic_evaluator<A, B>().div(a, b));
+				} else if (dvo->operator_token.content == "%") {
+					return runtime_value(arithmetic_evaluator<A, B>().mod(a, b));
+				} else {
+					throw interpreter_error("Invalid arithmetic operand", dvo->operator_token);
+				}
+			}, v0.value(), v1.value());
+		}
+
+		runtime_value compare_op(const dual_operation* dvo) {
+			auto v0 = eval_expression(*dvo->first_operand);
+			auto v1 = eval_expression(*dvo->second_operand);
+
+			if (!v0.has_value() || !v1.has_value()) {
+				throw interpreter_error("Invalid operand value", dvo->t);
+			}
+
+			return std::visit([&dvo]<typename A, typename B>(A&& a, B&& b) {
+				if (dvo->operator_token.content == "==") {
+					return are_equal(a, b);
+				} else if (dvo->operator_token.content == "!=") {
+					return !are_equal(a, b);
+				} else {
+					throw interpreter_error("Invalid comparator operator", dvo->operator_token);
+				}
+			}, v0.value(), v1.value());
+		}
+
+		runtime_value order_op(const dual_operation* dvo) {
+			auto v0 = eval_expression(*dvo->first_operand);
+			auto v1 = eval_expression(*dvo->second_operand);
+
+			if (!v0.has_value() || !v1.has_value()) {
+				throw interpreter_error("Invalid operand value", dvo->t);
+			}
+
+			return std::visit([&dvo]<typename A, typename B>(A&& a, B&& b) {
+				if (dvo->operator_token.content == ">") {
+					return comparator<A, B>().more_than(a, b);
+				} else if (dvo->operator_token.content == "<") {
+					return comparator<A, B>().less_than(a, b);
+				} else if (dvo->operator_token.content == ">=") {
+					return comparator<A, B>().more_equal_than(a, b);
+				} else if (dvo->operator_token.content == "<=") {
+					return comparator<A, B>().less_equal_than(a, b);
+				} else {
+					throw interpreter_error("Invalid comparator operator", dvo->operator_token);
+				}
+			}, v0.value(), v1.value());
+		}
+
+		std::optional<runtime_value> eval_expression(const expression& e) {
+			switch (e.et) {
+				case EtInvalid:
+					throw interpreter_error("Invalid expression", e.t);
+				case EtLiteralValue:
+					return parse_literal(e);
+				case EtSingleValueOperation: {
+						auto* svo = dynamic_cast<const single_operation*>(&e);
+
+						if (svo == nullptr) {
+							throw interpreter_error("Internal interpreter error", e.t);
+						}
+
+						auto val = eval_expression(*svo->operand);
+
+						if (!val.has_value()) {
+							throw interpreter_error("Invalid operand value", svo->operand->t);
+						}
+
+						if (svo->operator_token.content == "+") {
+							return val;
+						} else if (svo->operator_token.content == "-") {
+							return negate (val.value());
+						} else if (svo->operator_token.content == "!") {
+							if (val->index() != 11) {
+								throw interpreter_error("Invalid operand type", svo->operand->t);
+							} else {
+								return !std::get<11>(val.value());
+							}
+						} else {
+							throw interpreter_error("Invalid operator", svo->operator_token);
+						}
+					}
+					break;
+				case EtDualValueOperation: {
+						auto* dvo = dynamic_cast<const dual_operation*>(&e);
+
+						if (dvo == nullptr) {
+							throw interpreter_error("Internal interpreter error", e.t);
+						}
+
+						if (dvo->operator_token.content == "||") {
+							return logical_or(dvo);
+						}
+
+						if (dvo->operator_token.content == "&&") {
+							return logical_and(dvo);
+						}
+
+						if (dvo->operator_token.content == "+" || dvo->operator_token.content == "-"
+							|| dvo->operator_token.content == "*" || dvo->operator_token.content == "/"
+							|| dvo->operator_token.content == "%") {
+							return arithmetic_op(dvo);
+						}
+
+						if (dvo->operator_token.content == "==" || dvo->operator_token.content == "!=") {
+							return compare_op(dvo);
+						}
+
+						if (dvo->operator_token.content == ">" || dvo->operator_token.content == "<" ||
+							dvo->operator_token.content == "<=" || dvo->operator_token.content == ">=") {
+							return order_op(dvo);
+						}
+
+						throw interpreter_error("Invalid operator", dvo->operator_token);
+					}
+					break;
+				case EtFunctionCall: {
+						auto* call = dynamic_cast<const function_call*>(&e);
+
+						if (call == nullptr) {
+							throw interpreter_error("Internal interpreter error", e.t);
+						}
+
+						auto it = functions.find(call->function_name);
+
+						if (it == functions.end()) {
+							throw interpreter_error(std::format("Function {} not found", call->function_name), call->t);
+						}
+
+						std::vector<runtime_value> args;
+
+						for (auto& a : call->arguments) {
+							auto arg = eval_expression(*a);
+
+							if (!arg.has_value()) {
+								throw interpreter_error("Internal interpreter error", a->t);
+							}
+							args.emplace_back(arg.value());
+						}
+
+						return it->second->call(args, *this);
+					}
+					break;
+				case EtIdentifier: {
+						auto* id = dynamic_cast<const identifier_expression*>(&e);
+
+						if (id == nullptr) {
+							throw interpreter_error("Internal interpreter error", e.t);
+						}
+
+						for (auto& s : std::ranges::reverse_view(scopes)) {
+							if (s.variables.contains(id->name)) {
+								auto& v = s.variables.at(id->name).value;
+								return v;
+							}
+						}
+
+						throw interpreter_error("Variable not found", e.t);
+					}
+					break;
+			}
+		}
+
+		std::optional<runtime_value> execute_statement(const statement& s) override {
+			switch (s.type) {
+				case Expression: {
+						auto* ex = dynamic_cast<const expression*>(&s);
+
+						if (ex == nullptr) {
+							throw interpreter_error("Internal interpreter error", s.t);
+						}
+
+						return eval_expression(*ex);
+					}
+					break;
+				case Block: {
+						auto* b = dynamic_cast<const block*>(&s);
+
+						if (b == nullptr) {
+							throw interpreter_error("Internal interpreter error", s.t);
+						}
+
+						push_variable_scope();
+
+						for (auto& st : b->statements) {
+							execute_statement(*st);
+
+							if (is_in_function()) {
+								auto& sc = current_function_scope();
+								if (sc.returned) {
+									break;
+								}
+							}
+						}
+
+						pop_variable_scope();
+
+						return std::nullopt;
+					}
+					break;
+				case ReturnStatement: {
+						auto* r = dynamic_cast<const return_statement*>(&s);
+
+						if (r == nullptr) {
+							throw interpreter_error("Internal interpreter error", s.t);
+						}
+
+						auto val = r->expression != nullptr ? eval_expression(*r->expression) : std::nullopt;
+
+						auto& sc = current_function_scope();
+						sc.return_value = val;
+						sc.returned = true;
+					}
+					break;
+				case Root: {
+						auto* r = dynamic_cast<const root_statement*>(&s);
+
+						if (r == nullptr) {
+							throw interpreter_error("Internal interpreter error", s.t);
+						}
+
+						for (auto& st : r->statements) {
+							execute_statement(*st);
+						}
+					}
+					break;
+				case FunctionDeclaration: {
+						auto* d = dynamic_cast<const function_declaration*>(&s);
+
+						if (d == nullptr) {
+							throw interpreter_error("Internal interpreter error", s.t);
+						}
+
+						if (functions.find(d->name) != functions.end()) {
+							throw interpreter_error("Duplicate function name", s.t);
+						}
+
+						functions.emplace(d->name, std::make_unique<basic_function>(d));
+
+						return std::nullopt;
+					}
+					break;
+				case VariableDeclaration: {
+						auto* d = dynamic_cast<const variable_declaration*>(&s);
+
+						if (d == nullptr) {
+							throw interpreter_error("Internal interpreter error", s.t);
+						}
+
+						auto& sc = current_variable_scope();
+
+						if (sc.variables.find(d->name) != sc.variables.end()) {
+							throw interpreter_error("Duplicate variable name", s.t);
+						}
+
+						auto val = d->initial_expression != nullptr ? eval_expression(*d->initial_expression) : throw std::runtime_error("Non-initialized variables are not supported yet."); //TODO: This
+
+						sc.variables.insert_or_assign(d->name, interpreter_variable {
+							d->type.has_value() ? d->type.value() : "void",
+							!d->constant,
+							val.has_value() ? val.value() : runtime_value(0),
+						});
+
+						return std::nullopt;
+					}
+					break;
+				case IfStatement: {
+					auto* is = dynamic_cast<const if_statement*>(&s);
+
+					if (is == nullptr) {
+						throw interpreter_error("Internal interpreter error", s.t);
+					}
+
+					auto condition = eval_expression(*is->condition);
+
+					if (!condition.has_value()) {
+						throw interpreter_error("No condition for if statement", is->condition->t);
+					}
+
+					if (condition->index() != 11) {
+						throw interpreter_error("If condition is not boolean", is->condition->t);
+					}
+
+					if (std::get<11>(condition.value())) {
+						execute_statement(*is->block);
+					}
+				} break;
+			}
+			throw interpreter_error("Internal interpreter error", s.t);
+		}
+
+		void push_variable_scope() override {
+			scopes.emplace_back();
+		}
+
+		void pop_variable_scope() override {
+			scopes.pop_back();
+		}
+
+		void push_function_scope() override {
+			function_scopes.emplace_back();
+		}
+
+		void pop_function_scope() override {
+			function_scopes.pop_back();
+		}
+
+		void inject_value(const std::string_view& name, runtime_value val) override {
+			auto& s = scopes.back();
+
+			auto type = get_type_for_value(val);
+
+			if (s.variables.contains(std::string(name))) {
+				throw std::runtime_error("Injection failed: Variable already exists");
+			}
+
+			s.variables.insert_or_assign(std::string(name), interpreter_variable {
+				std::string(type),
+				false,
+				std::move(val)
+			});
+		}
+
+		interpreter_function_scope& current_function_scope() override {
+			if (function_scopes.empty()) {
+				throw std::runtime_error("Internal interpreter error");
+			}
+
+			return function_scopes.back();
+		}
+
+		interpreter_variable_scope& current_variable_scope() override {
+			return scopes.back();
+		}
+
+		bool is_in_function() override {
+			return !function_scopes.empty();
+		}
+	};
+}
\ No newline at end of file
diff --git a/libjlx/modules/main.cppm b/libjlx/modules/main.cppm
index 4bd9954..a075631 100644
--- a/libjlx/modules/main.cppm
+++ b/libjlx/modules/main.cppm
@@ -5,3 +5,4 @@ export import :source_stream;
 export import :tokenizer;
 export import :ast;
 export import :type_checker;
+export import :interpreter;
\ No newline at end of file
diff --git a/libjlx/modules/type_checker.cppm b/libjlx/modules/type_checker.cppm
index 14f5771..1722614 100644
--- a/libjlx/modules/type_checker.cppm
+++ b/libjlx/modules/type_checker.cppm
@@ -33,6 +33,20 @@ namespace jlx {
 		}
 	};
 
+	export constexpr std::array<std::string_view, 11> stringable_types = {
+		"i8",
+		"i16",
+		"i32",
+		"i64",
+		"u8",
+		"u16",
+		"u32",
+		"u64",
+		"f32",
+		"f64",
+		"boolean"
+	};
+
 	class type_checker_utils {
 		static std::size_t size_of(const std::string_view& type) {
 			if (type == "u8" || type == "i8" || type == "char") {
@@ -583,20 +597,6 @@ namespace jlx {
 		void include_stdlib() {
 			auto& glob = get_global_scope();
 
-			constexpr std::array<std::string_view, 11> stringable_types = {
-				"i8",
-				"i16",
-				"i32",
-				"i64",
-				"u8",
-				"u16",
-				"u32",
-				"u64",
-				"f32",
-				"f64",
-				"boolean"
-			};
-
 			for (const auto& type : stringable_types) {
 				glob.functions.insert_or_assign(std::format("{}_to_string", type), runtime_function{
 					"string",