Scoped variables, single namespace variables and functions

Makefile

@@ -3,6 +3,7 @@ CXXFLAGS:=$(CXXFLAGS) -std=c++20 -Wall -Wextra -Werror=switch -Werror=return-typ
 CPPFLAGS:=$(CPPFLAGS) -Ilib/expected/ -Ilib/ut/ -Isrc/
 
 Obj=                     \
+		bin/environment.o    \
 		bin/errors.o         \
 		bin/interpreter.o    \
 		bin/lexer.o          \

examples/variables.mq

@@ -0,0 +1,2 @@
+var x = 10;
+say (x + 1)

src/environment.cc

@@ -0,0 +1,49 @@
+#include <musique.hh>
+
+std::vector<Env> *Env::pool = nullptr;
+
+Env& Env::force_define(std::string name, Value new_value)
+{
+	variables.insert_or_assign(std::move(name), std::move(new_value));
+	return *this;
+}
+
+Env& Env::parent()
+{
+	return (*pool)[parent_enviroment_id];
+}
+
+Value* Env::find(std::string const& name)
+{
+	for (Env *prev = nullptr, *env = this; env != prev; prev = std::exchange(env, &env->parent())) {
+		if (auto it = env->variables.find(name); it != env->variables.end()) {
+			return &it->second;
+		}
+	}
+	return nullptr;
+}
+
+usize Env::operator++() const
+{
+	auto const parent_id = this - pool->data();
+	auto const free = std::find_if(pool->begin(), pool->end(), [](Env const& env) { return env.parent_enviroment_id == Env::Unused; });
+	Env* next = free == pool->end()
+		? &pool->emplace_back()
+		: &*free;
+
+	next->parent_enviroment_id = parent_id;
+	return next - pool->data();
+}
+
+usize Env::operator--()
+{
+	if (this == pool->data())
+		return 0;
+	variables.clear();
+	return std::exchange(parent_enviroment_id, Unused);
+}
+
+Env& Env::global()
+{
+	return (*pool)[0];
+}

src/errors.cc

@@ -71,6 +71,7 @@ std::ostream& operator<<(std::ostream& os, Error const& err)
 
 	case errors::Expected_Keyword:
 	case errors::Function_Not_Defined:
+	case errors::Not_Callable:
 	case errors::Unexpected_Token_Type:
 	case errors::Unresolved_Operator:
 		return os << err.message << '\n';
@@ -173,6 +174,15 @@ Error errors::expected_keyword(Token const& unexpected, std::string_view keyword
 	return err;
 }
 
+Error errors::not_callable(std::optional<Location> location, Value::Type value_type)
+{
+	Error err;
+	err.type = errors::Not_Callable;
+	err.location = std::move(location);
+	err.message = format("Couldn't call value of type ", type_name(value_type));
+	return err;
+}
+
 void errors::all_tokens_were_not_parsed(std::span<Token> tokens)
 {
 	error_heading(std::cerr, std::nullopt, Error_Level::Bug);

src/interpreter.cc

@@ -4,7 +4,7 @@
 
 static auto numeric_binary_operator(auto binop)
 {
-	return [binop = std::move(binop)](std::vector<Value> args) {
+	return [binop = std::move(binop)](std::vector<Value> args) -> Result<Value> {
 		auto result = std::move(args.front());
 		for (auto &v : std::span(args).subspan(1)) {
 			assert(result.type == Value::Type::Number, "LHS should be a number");
@@ -20,20 +20,26 @@ Interpreter::Interpreter()
 {
 }
 
+Interpreter::~Interpreter()
+{
+	Env::pool = nullptr;
+}
+
 Interpreter::Interpreter(std::ostream& out)
 	: out(out)
 {
-	functions["typeof"] = [](std::vector<Value> args) -> Value {
+	assert(Env::pool == nullptr, "Only one instance of interpreter can be at one time");
-		assert(args.size() == 1, "typeof expects only one argument");
+	Env::pool = &env_pool;
-		switch (args.front().type) {
-		case Value::Type::Nil:    return Value::symbol("nil");
-		case Value::Type::Number: return Value::symbol("number");
-		case Value::Type::Symbol: return Value::symbol("symbol");
-		}
-		unreachable();
-	};
 
-	functions["say"] = [&out](std::vector<Value> args) -> Value {
+	auto &global = env_pool.emplace_back();
+	global.parent_enviroment_id = 0;
+
+	global.force_define("typeof", [](std::vector<Value> args) -> Value {
+		assert(args.size() == 1, "typeof expects only one argument");
+		return Value::symbol(std::string(type_name(args.front().type)));
+	});
+
+	global.force_define("say", [&out](std::vector<Value> args) -> Value {
 		for (auto it = args.begin(); it != args.end(); ++it) {
 			out << *it;
 			if (std::next(it) != args.end())
@@ -41,7 +47,7 @@ Interpreter::Interpreter(std::ostream& out)
 		}
 		out << '\n';
 		return {};
-	};
+	});
 
 	operators["+"] = numeric_binary_operator(std::plus<>{});
 	operators["-"] = numeric_binary_operator(std::minus<>{});
@@ -49,6 +55,16 @@ Interpreter::Interpreter(std::ostream& out)
 	operators["/"] = numeric_binary_operator(std::divides<>{});
 }
 
+Env& Interpreter::env()
+{
+	return env_pool[current_env];
+}
+
+Env const& Interpreter::env() const
+{
+	return env_pool[current_env];
+}
+
 Result<Value> Interpreter::eval(Ast &&ast)
 {
 	switch (ast.type) {
@@ -84,15 +100,18 @@ Result<Value> Interpreter::eval(Ast &&ast)
 
 	case Ast::Type::Call:
 		{
+			auto location = ast.arguments.front().location;
 			Value func = Try(eval(std::move(ast.arguments.front())));
-			assert(func.type == Value::Type::Symbol, "Currently only symbols can be called");
+			if (func.type != Value::Type::Symbol)
-			if (auto it = functions.find(func.s); it != functions.end()) {
+				return errors::not_callable(std::move(location), func.type);
+
+			if (auto body = env().find(func.s); body) {
 				std::vector<Value> values;
 				values.reserve(ast.arguments.size());
 				for (auto& a : std::span(ast.arguments).subspan(1)) {
 					values.push_back(Try(eval(std::move(a))));
 				}
-				return it->second(std::move(values));
+				return (*body)(std::move(values));
 			} else {
 				return errors::function_not_defined(func);
 			}

src/musique.hh

@@ -48,6 +48,7 @@ namespace errors
 		Function_Not_Defined,
 		Unresolved_Operator,
 		Expected_Keyword,
+		Not_Callable
 	};
 }
 
@@ -113,6 +114,15 @@ struct Error
 
 std::ostream& operator<<(std::ostream& os, Error const& err);
 
+template<template<typename ...> typename Template, typename>
+struct is_template : std::false_type {};
+
+template<template<typename ...> typename Template, typename ...T>
+struct is_template<Template, Template<T...>> : std::true_type {};
+
+template<template<typename ...> typename Template, typename T>
+constexpr auto is_template_v = is_template<Template, T>::value;
+
 template<typename T>
 struct [[nodiscard("This value may contain critical error, so it should NOT be ignored")]] Result : tl::expected<T, Error>
 {
@@ -149,6 +159,23 @@ struct [[nodiscard("This value may contain critical error, so it should NOT be i
 			return Storage::value();
 		}
 	}
+
+	inline tl::expected<T, Error> to_expected() &&
+	{
+		return *static_cast<Storage*>(this);
+	}
+
+	template<typename Map>
+	requires is_template_v<Result, std::invoke_result_t<Map, T&&>>
+	auto and_then(Map &&map) &&
+	{
+		return std::move(*static_cast<Storage*>(this)).and_then(
+			[map = std::forward<Map>(map)](T &&value) {
+				return std::move(map)(std::move(value)).to_expected();
+			});
+	}
+
+	using Storage::and_then;
 };
 
 // NOTE This implementation requires C++ language extension: statement expressions
@@ -390,22 +417,54 @@ struct Number
 
 std::ostream& operator<<(std::ostream& os, Number const& num);
 
+struct Value;
+
+using Function = std::function<Result<Value>(std::vector<Value>)>;
+
+template<typename T, typename ...XS>
+constexpr auto is_one_of = (std::is_same_v<T, XS> || ...);
+
 // TODO Add location
 struct Value
 {
 	static Result<Value> from(Token t);
 	static Value number(Number n);
 	static Value symbol(std::string s);
+	static Value lambda(Function f);
 
 	enum class Type
 	{
 		Nil,
 		Number,
 		Symbol,
+		Lambda,
 	};
 
+	Value() = default;
+	Value(Value const&) = default;
+	Value(Value &&) = default;
+	Value& operator=(Value const&) = default;
+	Value& operator=(Value &&) = default;
+
+	template<typename Callable>
+	requires (!std::is_same_v<std::remove_cvref_t<Callable>, Value>)
+		&& std::invocable<Callable, std::vector<Value>>
+		&& is_one_of<std::invoke_result_t<Callable, std::vector<Value>>, Value, Result<Value>>
+	inline Value(Callable &&callable)
+		: type{Type::Lambda}
+	{
+		if constexpr (std::is_same_v<Result<Value>, std::invoke_result_t<Callable, std::vector<Value>>>) {
+			f = std::move(callable);
+		} else {
+			f = [fun = std::move(callable)](std::vector<Value> args) -> Result<Value> {
+				return fun(std::move(args));
+			};
+		}
+	}
+
 	Type type = Type::Nil;
 	Number n{};
+	Function f{};
 
 	// TODO Most strings should not be allocated by Value, but reference to string allocated previously
 	// Wrapper for std::string is needed that will allocate only when needed, middle ground between:
@@ -413,24 +472,56 @@ struct Value
 	//   std::string_view - not-owning string type
 	std::string s{};
 
+	Result<Value> operator()(std::vector<Value> args);
+
 	bool operator==(Value const& other) const;
 };
 
+std::string_view type_name(Value::Type t);
+
 std::ostream& operator<<(std::ostream& os, Value const& v);
 
-using Function = std::function<Value(std::vector<Value>)>;
+struct Env
+{
+	static std::vector<Env> *pool;
+	std::unordered_map<std::string, Value> variables;
+	usize parent_enviroment_id;
+
+	Env() = default;
+	Env(Env const&) = delete;
+	Env(Env &&) = default;
+	Env& operator=(Env const&) = delete;
+	Env& operator=(Env &&) = default;
+
+	static Env& global();
+
+	/// Defines new variable regardless of it's current existance
+	Env& force_define(std::string name, Value new_value);
+	Env& parent();
+	Value* find(std::string const& name);
+
+	usize operator++() const;
+	usize operator--();
+
+	static constexpr decltype(Env::parent_enviroment_id) Unused = -1;
+};
 
 struct Interpreter
 {
 	std::ostream &out;
-	std::unordered_map<std::string, Function> functions;
 	std::unordered_map<std::string, Function> operators;
+	std::vector<Env> env_pool;
+	usize current_env = 0;
 
 	Interpreter();
+	~Interpreter();
 	Interpreter(std::ostream& out);
 	Interpreter(Interpreter const&) = delete;
 	Interpreter(Interpreter &&) = default;
 
+	Env& env();
+	Env const& env() const;
+
 	Result<Value> eval(Ast &&ast);
 };
 
@@ -449,6 +540,8 @@ namespace errors
 	Error unresolved_operator(Token const& op);
 	Error expected_keyword(Token const& unexpected, std::string_view keyword);
 
+	Error not_callable(std::optional<Location> location, Value::Type value_type);
+
 	[[noreturn]]
 	void all_tokens_were_not_parsed(std::span<Token>);
 }

src/parser.cc

@@ -110,23 +110,23 @@ Result<Ast> Parser::parse_atomic_expression()
 				token_id = start;
 			}
 
-			return parse_sequence().and_then([&](Ast ast) -> tl::expected<Ast, Error> {
+			return parse_sequence().and_then([&](Ast &&ast) -> Result<Ast> {
 				Try(ensure(Token::Type::Close_Block));
 				consume();
-				return Ast::block(opening.location, ast, std::move(parameters));
+				return Ast::block(opening.location, std::move(ast), std::move(parameters));
 			});
 		}
 
 	case Token::Type::Open_Paren:
 		consume();
-		return parse_expression().and_then([&](Ast ast) -> tl::expected<Ast, Error> {
+		return parse_expression().and_then([&](Ast ast) -> Result<Ast> {
 			Try(ensure(Token::Type::Close_Paren));
 			consume();
 			return ast;
 		});
 
 	default:
-		return peek().and_then([](auto const& token) -> tl::expected<Ast, Error> {
+		return peek().and_then([](auto const& token) -> Result<Ast> {
 			return tl::unexpected(errors::unexpected_token(token));
 		});
 	}

src/tests/environment.cc

@@ -0,0 +1,80 @@
+#include <boost/ut.hpp>
+#include <musique.hh>
+
+using namespace boost::ut;
+using namespace std::string_view_literals;
+
+static void equals(
+	Value *received,
+	Value expected,
+	reflection::source_location sl = reflection::source_location::current())
+{
+	expect(received != nullptr, sl) << "Value was not found";
+	expect(eq(*received, expected), sl);
+}
+
+suite environment_test = [] {
+	"Global enviroment exists"_test = [] {
+		Interpreter i;
+		expect(eq(&i.env_pool.front(), &Env::global()));
+	};
+
+	"Environment scoping"_test = [] {
+		should("nested scoping preserve outer scope") = [] {
+			Interpreter i;
+
+			i.env().force_define("x", Value::number(Number(10)));
+			i.env().force_define("y", Value::number(Number(20)));
+
+			equals(i.env().find("x"), Value::number(Number(10)));
+			equals(i.env().find("y"), Value::number(Number(20)));
+
+			i.current_env = ++i.env();
+			i.env().force_define("x", Value::number(Number(30)));
+			equals(i.env().find("x"), Value::number(Number(30)));
+			equals(i.env().find("y"), Value::number(Number(20)));
+
+			i.current_env = --i.env();
+			equals(i.env().find("x"), Value::number(Number(10)));
+			equals(i.env().find("y"), Value::number(Number(20)));
+		};
+
+		should("nested variables missing from outer scope") = [] {
+			Interpreter i;
+
+			i.current_env = ++i.env();
+			i.env().force_define("x", Value::number(Number(30)));
+			equals(i.env().find("x"), Value::number(Number(30)));
+
+			i.current_env = --i.env();
+			expect(eq(i.env().find("x"), nullptr));
+		};
+
+		should("stay at global scope when too much end of scope is applied") = [] {
+			Interpreter i;
+			i.current_env = --i.env();
+			expect(eq(&i.env(), &Env::global()));
+		};
+
+		should("reuse already allocated enviroments") = [] {
+			Interpreter i;
+
+			i.current_env = ++i.env();
+			auto const first_env = &i.env();
+			i.env().force_define("x", Value::number(Number(30)));
+			equals(i.env().find("x"), Value::number(Number(30)));
+
+			i.current_env = --i.env();
+			expect(eq(i.env().find("x"), nullptr));
+
+			i.current_env = ++i.env();
+			expect(eq(first_env, &i.env()));
+			expect(eq(i.env().find("x"), nullptr));
+			i.env().force_define("x", Value::number(Number(30)));
+			equals(i.env().find("x"), Value::number(Number(30)));
+
+			i.current_env = --i.env();
+			expect(eq(i.env().find("x"), nullptr));
+		};
+	};
+};

src/tests/interpreter.cc

@@ -59,5 +59,20 @@ suite intepreter_test = [] {
 			produces_output("say 1; say 2; say 3", "1\n2\n3\n");
 			produces_output("say 1 2 3", "1 2 3\n");
 		};
+
+		should("allows only for calling which is callable") = [] {
+			Interpreter i;
+			{
+				auto result = Parser::parse("10 20", "test").and_then([&](Ast &&ast) { return i.eval(std::move(ast)); });
+				expect(!result.has_value()) << "Expected code to have failed";
+				expect(eq(result.error().type, errors::Not_Callable));
+			}
+			{
+				i.env().force_define("call_me", Value::number(Number(10)));
+				auto result = Parser::parse("call_me 20", "test").and_then([&](Ast &&ast) { return i.eval(std::move(ast)); });
+				expect(!result.has_value()) << "Expected code to have failed";
+				expect(eq(result.error().type, errors::Not_Callable));
+			}
+		};
 	};
 };

src/tests/value.cc

@@ -0,0 +1,35 @@
+#include <boost/ut.hpp>
+#include <musique.hh>
+
+using namespace boost::ut;
+using namespace std::string_view_literals;
+
+static std::string str(auto const& printable)
+{
+	std::stringstream ss;
+	ss << printable;
+	return std::move(ss).str();
+}
+
+suite value_test = [] {
+	"Comparisons"_test = [] {
+		should("be always not equal for lambdas") = [] {
+			expect(neq(Value::lambda(nullptr), Value::lambda(nullptr)));
+		};
+
+		should("are always not equal when types differ") = [] {
+			expect(neq(Value::symbol("0"), Value::number(Number(0))));
+		};
+	};
+
+	"Value printing"_test = [] {
+		expect(eq("nil"sv, str(Value{})));
+
+		expect(eq("10"sv, str(Value::number(Number(10)))));
+		expect(eq("1/2"sv, str(Value::number(Number(2, 4)))));
+
+		expect(eq("foo"sv, str(Value::symbol("foo"))));
+
+		expect(eq("<lambda>"sv, str(Value::lambda(nullptr))));
+	};
+};

src/value.cc

@@ -20,7 +20,7 @@ Value Value::number(Number n)
 {
 	Value v;
 	v.type = Type::Number;
-	v.n = n;
+	v.n = std::move(n).simplify();
 	return v;
 }
 
@@ -28,10 +28,27 @@ Value Value::symbol(std::string s)
 {
 	Value v;
 	v.type = Type::Symbol;
-	v.s = s;
+	v.s = std::move(s);
 	return v;
 }
 
+Value Value::lambda(Function f)
+{
+	Value v;
+	v.type = Type::Lambda;
+	v.f = std::move(f);
+	return v;
+}
+
+Result<Value> Value::operator()(std::vector<Value> args)
+{
+	if (type == Type::Lambda) {
+		return f(std::move(args));
+	}
+	// TODO Fill location
+	return errors::not_callable(std::nullopt, type);
+}
+
 bool Value::operator==(Value const& other) const
 {
 	if (type != other.type)
@@ -41,6 +58,7 @@ bool Value::operator==(Value const& other) const
 	case Type::Nil:    return true;
 	case Type::Number: return n == other.n;
 	case Type::Symbol: return s == other.s;
+	case Type::Lambda: return false; // TODO Reconsider if functions are comparable
 	}
 
 	unreachable();
@@ -57,6 +75,20 @@ std::ostream& operator<<(std::ostream& os, Value const& v)
 
 	case Value::Type::Symbol:
 		return os << v.s;
+
+	case Value::Type::Lambda:
+		return os << "<lambda>";
+	}
+	unreachable();
+}
+
+std::string_view type_name(Value::Type t)
+{
+	switch (t) {
+	case Value::Type::Lambda: return "lambda";
+	case Value::Type::Nil:    return "nil";
+	case Value::Type::Number: return "number";
+	case Value::Type::Symbol: return "symbol";
 	}
 	unreachable();
 }