Moved from Result<void> to std::optional<Error>

include/musique.hh

@@ -2,7 +2,6 @@
 #define Musique_Header_HH
 
 #include <chrono>
-#include <concepts>
 #include <cstdint>
 #include <cstring>
 #include <functional>
@@ -390,6 +389,73 @@ struct [[nodiscard("This value may contain critical error, so it should NOT be i
 	}
 };
 
+/// Abstraction over any value that are either value or error
+///
+/// Inspired by P2561R0
+template<typename = void>
+struct Try_Traits
+{
+	template<typename T>
+	static constexpr bool is_ok(T const& v) { return Try_Traits<T>::is_ok(v); }
+
+	template<typename T>
+	static constexpr auto yield_value(T&& v) { return Try_Traits<T>::yield_value(std::forward<T>(v)); }
+
+	template<typename T>
+	static constexpr auto yield_error(T&& v) { return Try_Traits<T>::yield_error(std::forward<T>(v)); }
+};
+
+template<>
+struct Try_Traits<std::optional<Error>>
+{
+	using Value_Type = std::nullopt_t;
+	using Error_Type = Error;
+
+	static constexpr bool is_ok(std::optional<Error> const& o)
+	{
+		return not o.has_value();
+	}
+
+	static std::nullopt_t yield_value(std::optional<Error>&& err)
+	{
+		assert(not err.has_value(), "Trying to yield value from optional that contains error");
+		return std::nullopt;
+	}
+
+	static Error yield_error(std::optional<Error>&& err)
+	{
+		assert(err.has_value(), "Trying to yield value from optional that NOT constains error");
+		return std::move(*err);
+	}
+};
+
+template<typename T>
+struct Try_Traits<Result<T>>
+{
+	using Value_Type = T;
+	using Error_Type = Error;
+
+	static constexpr bool is_ok(Result<T> const& o)
+	{
+		return o.has_value();
+	}
+
+	static auto yield_value(Result<T> val)
+	{
+		assert(val.has_value(), "Trying to yield value from expected that contains error");
+		if constexpr (std::is_void_v<T>) {
+		} else {
+			return std::move(*val);
+		}
+	}
+
+	static Error yield_error(Result<T>&& val)
+	{
+		assert(not val.has_value(), "Trying to yield error from expected with value");
+		return std::move(val.error());
+	}
+};
+
 /// Shorthand for forwarding error values with Result type family.
 ///
 /// This implementation requires C++ language extension: statement expressions
@@ -398,9 +464,10 @@ struct [[nodiscard("This value may contain critical error, so it should NOT be i
 #define Try(Value)                                             \
 	({                                                           \
 		auto try_value = (Value);                                  \
-		if (not try_value.has_value()) [[unlikely]]  \
+	 	using Trait [[maybe_unused]] = Try_Traits<std::decay_t<decltype(try_value)>>; \
-			return tl::unexpected(try_value.error());  \
+		if (not Trait::is_ok(try_value)) [[unlikely]]                \
-		std::move(try_value).value();                \
+			return Trait::yield_error(std::move(try_value));                \
+		Trait::yield_value(std::move(try_value));                              \
 	})
 
 /// Drop in replacement for bool when C++ implcit conversions stand in your way
@@ -1035,7 +1102,7 @@ struct Interpreter
 	/// There is always at least one context
 	std::vector<Context> context_stack;
 
-	std::function<Result<void>(Interpreter&, Value)> default_action;
+	std::function<std::optional<Error>(Interpreter&, Value)> default_action;
 
 	struct Incoming_Midi_Callbacks;
 	std::unique_ptr<Incoming_Midi_Callbacks> callbacks;
@@ -1056,7 +1123,7 @@ struct Interpreter
 	void leave_scope();
 
 	/// Play note resolving any missing parameters with context via `midi_connection` member.
-	Result<void> play(Chord);
+	std::optional<Error> play(Chord);
 
 	/// Add to global interpreter scope all builtin function definitions
 	///
@@ -1150,7 +1217,7 @@ struct Value_Formatter
 
 	Value_Formatter nest(Context nested = Free) const;
 
-	Result<void> format(std::ostream& os, Interpreter &interpreter, Value const& value);
+	std::optional<Error> format(std::ostream& os, Interpreter &interpreter, Value const& value);
 };
 
 Result<std::string> format(Interpreter &i, Value const& value);

include/musique_internal.hh

@@ -27,14 +27,14 @@ struct Guard
 		return Error { std::move(error) };
 	}
 
-	inline Result<void> yield_result() const
+	inline std::optional<Error> yield_result() const
 	{
 		return yield_error();
 	}
 
-	inline Result<void> operator()(bool(*predicate)(Value::Type), Value const& v) const
+	inline std::optional<Error> operator()(bool(*predicate)(Value::Type), Value const& v) const
 	{
-		return predicate(v.type) ? Result<void>{} : yield_result();
+		return predicate(v.type) ? std::optional<Error>{} : yield_result();
 	}
 };
 
@@ -98,7 +98,7 @@ struct Interpreter::Incoming_Midi_Callbacks
 };
 
 enum class Midi_Connection_Type { Output, Input };
-Result<void> ensure_midi_connection_available(Interpreter&, Midi_Connection_Type, std::string_view operation_name);
+std::optional<Error> ensure_midi_connection_available(Interpreter&, Midi_Connection_Type, std::string_view operation_name);
 
 constexpr std::size_t hash_combine(std::size_t lhs, std::size_t rhs) {
 	return lhs ^= rhs + 0x9e3779b9 + (lhs << 6) + (lhs >> 2);

src/builtin_functions.cc

@@ -35,7 +35,7 @@ concept Iterable = (With_Index_Method<T> || With_Index_Operator<T>) && requires
 
 /// Create chord out of given notes
 template<Iterable T>
-static inline Result<void> create_chord(std::vector<Note> &chord, Interpreter &interpreter, T args)
+static inline std::optional<Error> create_chord(std::vector<Note> &chord, Interpreter &interpreter, T args)
 {
 	for (auto i = 0u; i < args.size(); ++i) {
 		Value arg;
@@ -229,7 +229,7 @@ static auto builtin_program_change(Interpreter &i, std::vector<Value> args) -> R
 /// Plays sequentialy notes walking into arrays and evaluation blocks
 ///
 /// @invariant default_action is play one
-static inline Result<void> sequential_play(Interpreter &i, Value v)
+static inline std::optional<Error> sequential_play(Interpreter &i, Value v)
 {
 	switch (v.type) {
 	break; case Value::Type::Array:
@@ -250,7 +250,7 @@ static inline Result<void> sequential_play(Interpreter &i, Value v)
 }
 
 /// Play what's given
-static Result<void> action_play(Interpreter &i, Value v)
+static std::optional<Error> action_play(Interpreter &i, Value v)
 {
 	Try(sequential_play(i, std::move(v)));
 	return {};
@@ -335,7 +335,7 @@ static Result<Value> builtin_sim(Interpreter &interpreter, std::vector<Value> ar
 	struct {
 		Interpreter &interpreter;
 
-		Result<void> operator()(std::vector<Chord> &track, Value &arg)
+		std::optional<Error> operator()(std::vector<Chord> &track, Value &arg)
 		{
 			if (arg.type == Value::Type::Music) {
 				track.push_back(std::move(arg).chord);
@@ -351,13 +351,13 @@ static Result<Value> builtin_sim(Interpreter &interpreter, std::vector<Value> ar
 			}
 
 			// Invalid type for sim function
-			return errors::Unsupported_Types_For {
+			return Error{errors::Unsupported_Types_For {
 				.type = errors::Unsupported_Types_For::Function,
 				.name = "sim",
 				.possibilities = {
 					"(music | array of music)+"
 				},
-			};
+			}};
 		}
 	} append { interpreter };
 

src/interpreter.cc

@@ -217,7 +217,7 @@ void Interpreter::leave_scope()
 	env = env->leave();
 }
 
-Result<void> Interpreter::play(Chord chord)
+std::optional<Error> Interpreter::play(Chord chord)
 {
 	Try(ensure_midi_connection_available(*this, Midi_Connection_Type::Output, "play"));
 	auto &ctx = context_stack.back();
@@ -256,7 +256,7 @@ Result<void> Interpreter::play(Chord chord)
 	return {};
 }
 
-Result<void> ensure_midi_connection_available(Interpreter &i, Midi_Connection_Type m, std::string_view operation_name)
+std::optional<Error> ensure_midi_connection_available(Interpreter &i, Midi_Connection_Type m, std::string_view operation_name)
 {
 	switch (m) {
 	break; case Midi_Connection_Type::Output:

src/main.cc

@@ -153,7 +153,7 @@ struct Runner
 	}
 
 	/// Run given source
-	Result<void> run(std::string_view source, std::string_view filename, bool output = false)
+	std::optional<Error> run(std::string_view source, std::string_view filename, bool output = false)
 	{
 		auto ast = Try(Parser::parse(source, filename, repl_line_number));
 
@@ -326,9 +326,10 @@ static Result<void> Main(std::span<char const*> args)
 
 			Lines::the.add_line("<repl>", raw, repl_line_number);
 			auto result = runner.run(raw, "<repl>", true);
-			if (not result.has_value()) {
+			using Traits = Try_Traits<std::decay_t<decltype(result)>>;
+			if (not Traits::is_ok(result)) {
 				std::cout << std::flush;
-				std::cerr << result.error() << std::flush;
+				std::cerr << Traits::yield_error(std::move(result)) << std::flush;
 			}
 			repl_line_number++;
 			// We don't free input line since there could be values that still relay on it