5 files changed, 379 insertions, 1 deletions
diff --git a/nihil.core/CMakeLists.txt b/nihil.core/CMakeLists.txt
index e9998a3..d0713ce 100644
--- a/nihil.core/CMakeLists.txt
+++ b/nihil.core/CMakeLists.txt
@@ -14,6 +14,7 @@ target_sources(nihil.core
 	error.ccm
 	features.ccm
 	flagset.ccm
+	generator.ccm
 	guard.ccm
 	match.ccm
 	monad.ccm
@@ -25,3 +26,31 @@ target_sources(nihil.core
 	tabulate.ccm
 	uuid.ccm
 )
+
+if (NIHIL_TESTS)
+	add_executable(nihil.core.test
+		capture_stream.test.cc
+		ctype.test.cc
+		error.test.cc
+		flagset.test.cc
+		generator.test.cc
+		guard.test.cc
+		match.test.cc
+		monad.test.cc
+		next_word.test.cc
+		parse_size.test.cc
+		skipws.test.cc
+		tabulate.test.cc
+	)
+
+	target_link_libraries(nihil.core.test PRIVATE
+		nihil.std
+		nihil.core
+		Catch2::Catch2WithMain)
+
+	include(CTest)
+	include(Catch)
+	catch_discover_tests(nihil.core.test)
+
+	enable_testing()
+endif ()
diff --git a/nihil.core/error.test.cc b/nihil.core/error.test.cc
index f4ec1ee..7a923e4 100644
--- a/nihil.core/error.test.cc
+++ b/nihil.core/error.test.cc
@@ -4,7 +4,6 @@
 
 import nihil.std;
 import nihil.core;
-import nihil.util;
 
 namespace {
 inline constexpr auto *test_tags = "[nihil][nihil.error]";
diff --git a/nihil.core/generator.ccm b/nihil.core/generator.ccm
new file mode 100644
index 0000000..4d2bfe3
--- /dev/null
+++ b/nihil.core/generator.ccm
@@ -0,0 +1,240 @@
+// generator - Single-header, ranges-compatible generator type built
+// on C++20 coroutines
+// Written in 2021 by Sy Brand (tartanllama@gmail.com, @TartanLlama)
+//
+// Documentation available at https://tl.tartanllama.xyz/
+//
+// To the extent possible under law, the author(s) have dedicated all
+// copyright and related and neighboring rights to this software to the
+// public domain worldwide. This software is distributed without any warranty.
+//
+// You should have received a copy of the CC0 Public Domain Dedication
+// along with this software. If not, see
+// <http://creativecommons.org/publicdomain/zero/1.0/>.
+export module nihil.core:generator;
+
+import nihil.std;
+
+namespace nihil {
+
+export template <typename T>
+struct generator
+{
+private:
+	struct promise
+	{
+		using value_type = std::remove_reference_t<T>;
+		using reference_type =
+			std::conditional_t<std::is_pointer_v<value_type>, value_type, value_type &>;
+		using pointer_type =
+			std::conditional_t<std::is_pointer_v<value_type>, value_type, value_type *>;
+
+		promise() = default;
+
+		[[nodiscard]] auto get_return_object() -> generator
+		{
+			return generator(std::coroutine_handle<promise>::from_promise(*this));
+		}
+
+		[[nodiscard]] auto initial_suspend() const -> std::suspend_always
+		{
+			return {};
+		}
+
+		[[nodiscard]] auto final_suspend() const noexcept -> std::suspend_always
+		{
+			return {};
+		}
+
+		void return_void() const noexcept
+		{
+		}
+
+		void unhandled_exception() noexcept
+		{
+			exception_ = std::current_exception();
+		}
+
+		void rethrow_if_exception()
+		{
+			if (exception_) {
+				std::rethrow_exception(exception_);
+			}
+		}
+
+		std::suspend_always yield_value(value_type &&v) noexcept
+		{
+			value_ = std::move(v);
+			return {};
+		}
+
+		std::suspend_always yield_value(value_type const &v) noexcept
+		requires(!std::is_reference_v<T>)
+		{
+			value_ = v;
+			return {};
+		}
+
+		std::suspend_always yield_value(value_type &v) noexcept
+		requires(std::is_reference_v<T>)
+		{
+			value_ = &v;
+			return {};
+		}
+
+		std::exception_ptr                                     exception_;
+		std::variant<std::monostate, value_type, value_type *> value_;
+	};
+
+public:
+	using promise_type = promise;
+	class sentinel
+	{
+	};
+
+	class iterator
+	{
+		using handle_type = std::coroutine_handle<promise_type>;
+
+	public:
+		using value_type = typename promise_type::value_type;
+		using reference_type = typename promise_type::reference_type;
+		using pointer_type = typename promise_type::pointer_type;
+		using difference_type = std::ptrdiff_t;
+
+		iterator() = default;
+		~iterator()
+		{
+			if (handle_)
+				handle_.destroy();
+		}
+
+		// Non-copyable because coroutine handles point to a unique resource
+		iterator(iterator const &) = delete;
+		iterator(iterator &&rhs) noexcept
+			: handle_(std::exchange(rhs.handle_, nullptr))
+		{
+		}
+
+		auto operator=(iterator const &) -> iterator & = delete;
+
+		auto operator=(iterator &&rhs) noexcept -> iterator &
+		{
+			handle_ = std::exchange(rhs.handle_, nullptr);
+			return *this;
+		}
+
+		friend auto operator==(iterator const &it, sentinel) noexcept -> bool
+		{
+			return (!it.handle_ || it.handle_.done());
+		}
+
+		auto operator++() -> iterator &
+		{
+			handle_.resume();
+			if (handle_.done()) {
+				handle_.promise().rethrow_if_exception();
+			}
+			return *this;
+		}
+
+		void operator++(int)
+		{
+			(void)this->operator++();
+		}
+
+		reference_type operator*() const
+			noexcept(noexcept(std::is_nothrow_copy_constructible_v<reference_type>))
+		requires(std::is_reference_v<T>)
+		{
+			return *std::get<value_type *>(handle_.promise().value_);
+		}
+
+		reference_type operator*() const
+			noexcept(noexcept(std::is_nothrow_copy_constructible_v<reference_type>))
+		requires(!std::is_reference_v<T>)
+		{
+			return std::get<value_type>(handle_.promise().value_);
+		}
+
+		value_type *operator->() const
+			noexcept(noexcept(std::is_nothrow_copy_constructible_v<reference_type>))
+		requires(std::is_reference_v<T>)
+		{
+			return std::get<value_type *>(handle_.promise().value_);
+		}
+
+		value_type *operator->() const
+			noexcept(noexcept(std::is_nothrow_copy_constructible_v<reference_type>))
+		requires(!std::is_reference_v<T>)
+		{
+			return &std::get<value_type>(handle_.promise().value_);
+		}
+
+	private:
+		friend struct generator;
+
+		explicit iterator(handle_type handle)
+			: handle_(handle)
+		{
+		}
+
+		handle_type handle_;
+	};
+
+	using handle_type = std::coroutine_handle<promise_type>;
+
+	generator() noexcept = default;
+	~generator()
+	{
+		if (handle_)
+			handle_.destroy();
+	}
+
+	generator(generator const &) = delete;
+
+	generator(generator &&rhs) noexcept
+		: handle_(std::exchange(rhs.handle_, nullptr))
+	{
+	}
+
+	auto operator=(generator const &) -> generator & = delete;
+
+	auto operator=(generator &&rhs) noexcept -> generator &
+	{
+		swap(rhs);
+		return *this;
+	}
+
+	auto begin() -> iterator
+	{
+		handle_.resume();
+		if (handle_.done()) {
+			handle_.promise().rethrow_if_exception();
+		}
+		return iterator(std::exchange(handle_, nullptr));
+	}
+
+	auto end() const noexcept -> sentinel
+	{
+		return {};
+	}
+
+	void swap(generator &other) noexcept
+	{
+		std::swap(handle_, other.handle_);
+	}
+
+private:
+	friend class iterator;
+	explicit generator(handle_type handle) noexcept
+		: handle_(handle)
+	{
+	}
+
+	handle_type handle_ = nullptr;
+};
+} // namespace nihil
+
+export template <typename T>
+inline constexpr bool std::ranges::enable_view<nihil::generator<T>> = true;
diff --git a/nihil.core/generator.test.cc b/nihil.core/generator.test.cc
new file mode 100644
index 0000000..1fc0f22
--- /dev/null
+++ b/nihil.core/generator.test.cc
@@ -0,0 +1,109 @@
+// This source code is released into the public domain.
+
+#include <catch2/catch_test_macros.hpp>
+
+import nihil.std;
+import nihil.core;
+
+namespace {
+inline auto constexpr test_tags = "[nihil][nihil.generator]";
+
+SCENARIO("A generator that yields values", test_tags)
+{
+	GIVEN ("A generator that yields values") {
+		auto fn = [&]() -> nihil::generator<int> {
+			co_yield 1;
+			co_yield 2;
+		};
+
+		THEN ("The generator yields the original values") {
+			REQUIRE(std::ranges::equal(fn(), std::vector{1, 2}));
+		}
+	}
+}
+
+SCENARIO("A generator that yields references", test_tags)
+{
+	GIVEN ("A generator that yields references") {
+		auto one = 1, two = 2;
+		auto fn = [&]() -> nihil::generator<int &> {
+			co_yield one;
+			co_yield two;
+		};
+		auto range = fn();
+
+		THEN ("The references refer to the original values") {
+			auto it = std::ranges::begin(range);
+			REQUIRE(&*it == &one);
+			++it;
+			REQUIRE(&*it == &two);
+			++it;
+			REQUIRE(it == std::ranges::end(range));
+		}
+	}
+}
+
+SCENARIO("A generator that yields pointers", test_tags)
+{
+	GIVEN ("A generator that yields pointers") {
+		auto one = 1, two = 2;
+		auto fn = [&]() -> nihil::generator<int *> {
+			co_yield &one;
+			co_yield &two;
+		};
+
+		THEN ("The pointers point to the original values") {
+			REQUIRE(std::ranges::equal(fn(), std::vector{&one, &two}));
+		}
+	}
+}
+
+SCENARIO("A generator that yields lvalues", test_tags)
+{
+	GIVEN ("A generator that yields pointers") {
+		auto one = 1, two = 2;
+		auto fn = [&]() -> nihil::generator<int> {
+			co_yield one;
+			co_yield two;
+		};
+
+		THEN ("The pointers point to the original values") {
+			REQUIRE(std::ranges::equal(fn(), std::vector{1, 2}));
+		}
+	}
+}
+
+TEST_CASE("generator: exceptions", "[generator]")
+{
+	auto fn = []() -> nihil::generator<int> {
+		co_yield 1;
+		throw std::runtime_error("test");
+	};
+
+	auto range = fn();
+	auto it = std::ranges::begin(range);
+	REQUIRE(*it == 1);
+	REQUIRE_THROWS_AS(it++, std::runtime_error);
+}
+
+#if 0
+// TODO: Re-enable this test once we have a standard-compliant generator.
+TEST_CASE("generator: elements_of", "[generator]")
+{
+	auto fn1 = [] -> nihil::generator<int> {
+		co_yield 1;
+		co_yield 2;
+		co_yield 3;
+	};
+
+	auto fn2 = [&fn1] -> nihil::generator<int> {
+		co_yield nihil::elements_of(fn1());
+	};
+
+	auto values = std::vector<int>();
+	std::ranges::copy(fn2(), std::back_inserter(values));
+
+	REQUIRE(values == std::vector{1, 2, 3});
+}
+#endif
+} // anonymous namespace
diff --git a/nihil.core/nihil.core.ccm b/nihil.core/nihil.core.ccm
index 37ad032..7634026 100644
--- a/nihil.core/nihil.core.ccm
+++ b/nihil.core/nihil.core.ccm
@@ -8,6 +8,7 @@ export import :errc;
 export import :error;
 export import :features;
 export import :flagset;
+export import :generator;
 export import :guard;
 export import :match;
 export import :monad;