1 files changed, 139 insertions, 0 deletions
diff --git a/nihil/error.cc b/nihil/error.cc
new file mode 100644
index 0000000..de05855
--- /dev/null
+++ b/nihil/error.cc
@@ -0,0 +1,139 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+module;
+
+#include <memory>
+#include <optional>
+#include <string>
+#include <system_error>
+#include <variant>
+
+module nihil;
+
+namespace nihil {
+
+error::error()
+{
+}
+
+error::error(std::string_view what, error cause)
+	: m_error(std::string(what))
+	, m_cause(std::make_shared<error>(std::move(cause)))
+{
+}
+error::error(std::string_view what)
+	: m_error(std::string(what))
+{
+}
+
+error::error(std::error_condition what, error cause)
+	: m_error(what)
+	, m_cause(std::make_shared<error>(std::move(cause)))
+{
+}
+
+error::error(std::error_condition what)
+	: m_error(what)
+{
+}
+
+error::error(std::error_code what, error cause)
+	: m_error(what)
+	, m_cause(std::make_shared<error>(std::move(cause)))
+{
+}
+
+error::error(std::error_code what)
+	: m_error(what)
+{
+}
+
+error::error(error const &) = default;
+error::error(error &&) noexcept = default;
+auto error::operator=(this error &, error const &) -> error & = default;
+auto error::operator=(this error &, error &&) noexcept -> error & = default;
+
+auto error::cause(this error const &self) -> std::optional<error>
+{
+	if (self.m_cause)
+		return *self.m_cause;
+	return {};
+}
+
+auto error::str(this error const &self) -> std::string
+{
+	return self.m_error | match {
+		[] (std::monostate) -> std::string {
+			return "No error";
+		},
+		[] (std::error_code const &m) {
+			return m.message();
+		},
+		[] (std::error_condition const &m) {
+			return m.message();
+		},
+		[] (std::string const &m) {
+			return m;
+		}
+	};
+}
+
+auto error::what(this error const &self) -> std::string
+{
+	auto ret = self.str();
+
+	auto cause = self.m_cause;
+	while (cause) {
+		ret += ": " + cause->str();
+		cause = cause->m_cause;
+	}
+
+	return ret;
+}
+
+auto error::code(this error const &self) -> std::optional<std::error_code>
+{
+	auto const *code = std::get_if<std::error_code>(&self.m_error);
+	if (code)
+		return {*code};
+	return {};
+}
+
+auto error::condition(this error const &self)
+	-> std::optional<std::error_condition>
+{
+	auto const *condition = std::get_if<std::error_condition>(&self.m_error);
+	if (condition)
+		return {*condition};
+	return {};
+}
+
+auto operator==(error const &lhs, error const &rhs) -> bool
+{
+	return lhs.m_error == rhs.m_error;
+}
+
+auto operator<=>(error const &lhs, error const &rhs) -> std::strong_ordering
+{
+	return lhs.m_error <=> rhs.m_error;
+}
+
+auto operator==(error const &lhs, std::error_code const &rhs) -> bool
+{
+	return lhs.code() == rhs;
+}
+
+// Compare an error to an std::error_condition.
+auto operator==(error const &lhs, std::error_condition const &rhs) -> bool
+{
+	return lhs.condition() == rhs;
+}
+
+auto operator<<(std::ostream &strm, error const &e) -> std::ostream &
+{
+	return strm << e.what();
+}
+
+} // namespace nihil