Note duration calculation in current BPM context

Makefile

@@ -8,6 +8,7 @@ LDFLAGS=-L./lib/midi/
 LDLIBS=-lmidi-alsa -lasound
 
 Obj=                 \
+		context.o        \
 		environment.o    \
 		errors.o         \
 		interpreter.o    \

src/context.cc

@@ -0,0 +1,14 @@
+#include <musique.hh>
+
+Note Context::fill(Note note) const
+{
+	if (not note.octave) note.octave = octave;
+	if (not note.length) note.length = length;
+	return note;
+}
+
+std::chrono::duration<float> Context::length_to_duration(std::optional<Number> length) const
+{
+	auto const len = length ? *length : this->length;
+	return std::chrono::duration<float>(float(len.num * (60.f / (float(bpm) / 4))) / len.den);
+}

src/interpreter.cc

@@ -64,11 +64,16 @@ Interpreter::~Interpreter()
 Interpreter::Interpreter(std::ostream& out)
 	: out(out)
 {
+	{ // Context initialization
+		context_stack.emplace_back();
+	}
+	{ // Environment initlialization
 		assert(!bool(Env::global), "Only one instance of interpreter can be at one time");
-
 		env = Env::global = Env::make();
+	}
+	{ // Global default functions initialization
+		// TODO move `say` to `src/main.cc` since it's platform depdendent
 		auto &global = *Env::global;
-
 		global.force_define("typeof", +[](Interpreter&, std::vector<Value> args) -> Result<Value> {
 			assert(args.size() == 1, "typeof expects only one argument");
 			return Value::symbol(std::string(type_name(args.front().type)));
@@ -124,6 +129,7 @@ Interpreter::Interpreter(std::ostream& out)
 			assert(args.back().type == Value::Type::Number, "Only numbers can be used for indexing"); // TODO(assert)
 			return std::move(args.front()).blk.index(i, std::move(args.back()).n.as_int());
 		};
+	}
 }
 
 Result<Value> Interpreter::eval(Ast &&ast)

src/musique.hh

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <chrono>
 #include <concepts>
 #include <cstdint>
 #include <cstring>
@@ -557,6 +558,25 @@ private:
 	Env() = default;
 };
 
+/// Context holds default values for music related actions
+struct Context
+{
+	/// Default note octave
+	i8 octave = 4;
+
+	/// Default note length
+	Number length = Number(1, 4);
+
+	/// Default BPM
+	unsigned bpm = 120;
+
+	/// Fills empty places in Note like octave and length with default values from context
+	Note fill(Note) const;
+
+	/// Converts length to seconds with current bpm
+	std::chrono::duration<float> length_to_duration(std::optional<Number> length) const;
+};
+
 struct Interpreter
 {
 	/// Output of IO builtins like `say`
@@ -568,6 +588,10 @@ struct Interpreter
 	/// Current environment (current scope)
 	std::shared_ptr<Env> env;
 
+	/// Context stack. `constext_stack.back()` is a current context.
+	/// There is always at least one context
+	std::vector<Context> context_stack;
+
 	Interpreter();
 	~Interpreter();
 	explicit Interpreter(std::ostream& out);

src/tests/context.cc

@@ -0,0 +1,39 @@
+#include <boost/ut.hpp>
+#include <musique.hh>
+
+using namespace boost::ut;
+using namespace std::string_view_literals;
+
+void test_seconds_compute(
+	unsigned bpm,
+	Number length,
+	float value,
+	reflection::source_location const& sl = reflection::source_location::current())
+{
+	Context const ctx { .bpm = bpm };
+	auto const dur = ctx.length_to_duration(length);
+
+	static_assert(std::same_as<decltype(dur)::period, std::ratio<1, 1>>,
+		"tests provided by this function expects Context::length_to_duration to return seconds");
+
+	expect(dur.count() == _f(value), sl);
+}
+
+suite context_suite = [] {
+	"Context duration resolution"_test = [] {
+		test_seconds_compute(60, Number(2,1), 8);
+		test_seconds_compute(60, Number(1,1), 4);
+		test_seconds_compute(60, Number(1,2), 2);
+		test_seconds_compute(60, Number(1,4), 1);
+
+		test_seconds_compute(96, Number(2,1), 5);
+		test_seconds_compute(96, Number(1,1), 2.5);
+		test_seconds_compute(96, Number(1,2), 1.25);
+		test_seconds_compute(96, Number(1,4), 0.625);
+
+		test_seconds_compute(120, Number(2,1), 4);
+		test_seconds_compute(120, Number(1,1), 2);
+		test_seconds_compute(120, Number(1,2), 1);
+		test_seconds_compute(120, Number(1,4), 0.5);
+	};
+};