tribool.hpp

#ifndef TRIBOOL_HPP
#define TRIBOOL_HPP

#include <boost/config.hpp>

namespace logic {
	struct indeterminate_t;
	struct tribool {
		enum tribool_value_t {
			false_value = false,
			true_value = true,
			indeterminate_value = static_cast<int>(true) + 1
		};

		tribool(): value(false_value) { }
		tribool(bool b): value(static_cast<tribool_value_t>(b)) { }
		tribool(tribool_value_t b): value(b) { }
		tribool(const indeterminate_t &): value(indeterminate_value) { }

		tribool_value_t value;

		bool false_p() const { return value == false_value; }
		bool true_p() const { return value == true_value; }
		bool indeterminate_p() const { return value == indeterminate_value; }

		tribool operator !() const {
			return false_p() ? tribool(true) : true_p() ? tribool(false) : tribool(indeterminate_value);
		}
#ifdef BOOST_NO_EXPLICIT_CONVERSION_OPERATORS
	private:
		struct dummy { void nonnull() {}; };
		typedef void (dummy::*safe_bool)();
	public:
		operator safe_bool() const { return value == true_value ? &dummy::nonnull : 0; }
#else
		explicit operator bool() const { return value == true_value; }
#endif
	};
	static const struct indeterminate_t {
		operator bool() const { return false; }
		tribool operator !() const { return tribool(indeterminate_t()); }
		bool operator ()(indeterminate_t) const { return true; }
		bool operator ()(tribool b) const { return b.value == tribool::indeterminate_value; }
	} indeterminate = { };

	inline tribool operator ==(tribool x, tribool y) {
		return (x.indeterminate_p() || y.indeterminate_p()) ? indeterminate : tribool(x.value == y.value) ;
	}
	inline tribool operator ==(tribool x, bool y) { return x == tribool(y); }
	inline tribool operator ==(bool x, tribool y) { return y == x; }
	inline tribool operator ==(tribool, indeterminate_t) { return indeterminate; }
	inline tribool operator ==(indeterminate_t, tribool) { return indeterminate; }
	inline tribool operator ==(bool, indeterminate_t) { return indeterminate; }
	inline tribool operator ==(indeterminate_t, bool) { return indeterminate; }

	inline tribool operator !=(tribool x, tribool y) {
		return (x.indeterminate_p() || y.indeterminate_p()) ? indeterminate : tribool(x.value != y.value) ;
	}
	inline tribool operator !=(tribool x, bool y) { return x != tribool(y); }
	inline tribool operator !=(bool x, tribool y) { return y != x; }
	inline tribool operator !=(tribool, indeterminate_t) { return indeterminate; }
	inline tribool operator !=(indeterminate_t, tribool) { return indeterminate; }
	inline tribool operator !=(bool, indeterminate_t) { return indeterminate; }
	inline tribool operator !=(indeterminate_t, bool) { return indeterminate; }

	inline tribool operator &&(tribool x, tribool y) {
		return (x.false_p() || y.false_p()) ? tribool(false)
			: (x.indeterminate_p() || y.indeterminate_p()) ? indeterminate
				: tribool(true);
	}
	inline tribool operator &&(tribool x, bool y) { return y ? x : tribool(false); }
	inline tribool operator &&(bool x, tribool y) { return y && x; }
	inline tribool operator &&(tribool x, indeterminate_t) { return x.false_p() ? tribool(false) : indeterminate; }
	inline tribool operator &&(indeterminate_t, tribool x) { return x && indeterminate; }
	inline tribool operator &&(bool x, indeterminate_t) { return tribool(x) && indeterminate; }
	inline tribool operator &&(indeterminate_t, bool x) { return x && indeterminate; }

	inline tribool operator ||(tribool x, tribool y) {
		return (x.true_p() || y.true_p()) ? tribool(true)
			: (x.indeterminate_p() || y.indeterminate_p()) ? indeterminate
				: tribool(false);
	}
	inline tribool operator ||(tribool x, bool y) { return y ? tribool(true) : x; }
	inline tribool operator ||(bool x, tribool y) { return y || x; }
	inline tribool operator ||(tribool x, indeterminate_t) { return x.true_p() ? tribool(true) : indeterminate; }
	inline tribool operator ||(indeterminate_t, tribool x) { return x || indeterminate; }
	inline tribool operator ||(bool x, indeterminate_t) { return tribool(x) || indeterminate; }
	inline tribool operator ||(indeterminate_t, bool x) { return x || indeterminate; }

}

#endif