// Three-state boolean logic library



// Copyright Douglas Gregor 2002-2004. Use, modification and

// distribution is subject to the Boost Software License, Version

// 1.0. (See accompanying file LICENSE_1_0.txt or copy at

// http://www.boost.org/LICENSE_1_0.txt)





// For more information, see http://www.boost.org

#ifndef BOOST_LOGIC_TRIBOOL_HPP

#define BOOST_LOGIC_TRIBOOL_HPP



#include <boost/logic/tribool_fwd.hpp>

#include <boost/config.hpp>

#include <boost/detail/workaround.hpp>



#if BOOST_WORKAROUND(_MSC_VER, >= 1200)

#  pragma once

#endif



namespace boost { namespace logic {



/// INTERNAL ONLY

namespace detail {

/**

 * INTERNAL ONLY

 *

 * \brief A type used only to uniquely identify the 'indeterminate'

 * function/keyword.

 */

struct indeterminate_t

{

#if BOOST_WORKAROUND(__BORLANDC__, < 0x0600)

  char dummy_; // BCB would use 8 bytes by default

#endif

};



} // end namespace detail



/**

 * INTERNAL ONLY

 * The type of the 'indeterminate' keyword. This has the same type as the

 * function 'indeterminate' so that we can recognize when the keyword is

 * used.

 */

typedef bool (*indeterminate_keyword_t)(tribool, detail::indeterminate_t);



/**

 * \brief Keyword and test function for the indeterminate tribool value

 *

 * The \c indeterminate function has a dual role. It's first role is

 * as a unary function that tells whether the tribool value is in the

 * "indeterminate" state. It's second role is as a keyword

 * representing the indeterminate (just like "true" and "false"

 * represent the true and false states). If you do not like the name

 * "indeterminate", and would prefer to use a different name, see the

 * macro \c BOOST_TRIBOOL_THIRD_STATE.

 *

 * \returns <tt>x.value == tribool::indeterminate_value</tt>

 * \throws nothrow

 */

inline bool

indeterminate(tribool x,

              detail::indeterminate_t dummy = detail::indeterminate_t());



/**

 * \brief A 3-state boolean type.

 *

 * 3-state boolean values are either true, false, or

 * indeterminate.

 */

class tribool

{

private:

  /// INTERNAL ONLY

  struct dummy {

    void nonnull() {};

  };



  typedef void (dummy::*safe_bool)();



public:

  /**

   * Construct a new 3-state boolean value with the value 'false'.

   *

   * \throws nothrow

   */

  tribool() : value(false_value) {}



  /**

   * Construct a new 3-state boolean value with the given boolean

   * value, which may be \c true or \c false.

   *

   * \throws nothrow

   */

  tribool(bool value) : value(value? true_value : false_value) {}



  /**

   * Construct a new 3-state boolean value with an indeterminate value.

   *

   * \throws nothrow

   */

  tribool(indeterminate_keyword_t) : value(indeterminate_value) {}



  /**

   * Use a 3-state boolean in a boolean context. Will evaluate true in a

   * boolean context only when the 3-state boolean is definitely true.

   *

   * \returns true if the 3-state boolean is true, false otherwise

   * \throws nothrow

   */

  operator safe_bool() const

  {

    return value == true_value? &dummy::nonnull : 0;

  }



  /**

   * The actual stored value in this 3-state boolean, which may be false, true,

   * or indeterminate.

   */

  enum value_t { false_value, true_value, indeterminate_value } value;

};



// Check if the given tribool has an indeterminate value. Also doubles as a

// keyword for the 'indeterminate' value

inline bool indeterminate(tribool x, detail::indeterminate_t)

{

  return x.value == tribool::indeterminate_value;

}



/** @defgroup logical Logical operations

 */

//@{

/**

 * \brief Computes the logical negation of a tribool

 *

 * \returns the logical negation of the tribool, according to the

 * table:

 *  <table border=1>

 *    <tr>

 *      <th><center><code>!</code></center></th>

 *      <th/>

 *    </tr>

 *    <tr>

 *      <th><center>false</center></th>

 *      <td><center>true</center></td>

 *    </tr>

 *    <tr>

 *      <th><center>true</center></th>

 *      <td><center>false</center></td>

 *    </tr>

 *    <tr>

 *      <th><center>indeterminate</center></th>

 *      <td><center>indeterminate</center></td>

 *    </tr>

 *  </table>

 * \throws nothrow

 */

inline tribool operator!(tribool x)

{

  return x.value == tribool::false_value? tribool(true)

        :x.value == tribool::true_value? tribool(false)

        :tribool(indeterminate);

}



/**

 * \brief Computes the logical conjuction of two tribools

 *

 * \returns the result of logically ANDing the two tribool values,

 * according to the following table:

 *       <table border=1>

 *           <tr>

 *             <th><center><code>&amp;&amp;</code></center></th>

 *             <th><center>false</center></th>

 *             <th><center>true</center></th>

 *             <th><center>indeterminate</center></th>

 *           </tr>

 *           <tr>

 *             <th><center>false</center></th>

 *             <td><center>false</center></td>

 *             <td><center>false</center></td>

 *             <td><center>false</center></td>

 *           </tr>

 *           <tr>

 *             <th><center>true</center></th>

 *             <td><center>false</center></td>

 *             <td><center>true</center></td>

 *             <td><center>indeterminate</center></td>

 *           </tr>

 *           <tr>

 *             <th><center>indeterminate</center></th>

 *             <td><center>false</center></td>

 *             <td><center>indeterminate</center></td>

 *             <td><center>indeterminate</center></td>

 *           </tr>

 *       </table>

 * \throws nothrow

 */

inline tribool operator&&(tribool x, tribool y)

{

  if (static_cast<bool>(!x) || static_cast<bool>(!y))

    return false;

  else if (static_cast<bool>(x) && static_cast<bool>(y))

    return true;

  else

    return indeterminate;

}



/**

 * \overload

 */

inline tribool operator&&(tribool x, bool y)

{ return y? x : tribool(false); }



/**

 * \overload

 */

inline tribool operator&&(bool x, tribool y)

{ return x? y : tribool(false); }



/**

 * \overload

 */

inline tribool operator&&(indeterminate_keyword_t, tribool x)

{ return !x? tribool(false) : tribool(indeterminate); }



/**

 * \overload

 */

inline tribool operator&&(tribool x, indeterminate_keyword_t)

{ return !x? tribool(false) : tribool(indeterminate); }



/**

 * \brief Computes the logical disjunction of two tribools

 *

 * \returns the result of logically ORing the two tribool values,

 * according to the following table:

 *       <table border=1>

 *           <tr>

 *             <th><center><code>||</code></center></th>

 *             <th><center>false</center></th>

 *             <th><center>true</center></th>

 *             <th><center>indeterminate</center></th>

 *           </tr>

 *           <tr>

 *             <th><center>false</center></th>

 *             <td><center>false</center></td>

 *             <td><center>true</center></td>

 *             <td><center>indeterminate</center></td>

 *           </tr>

 *           <tr>

 *             <th><center>true</center></th>

 *             <td><center>true</center></td>

 *             <td><center>true</center></td>

 *             <td><center>true</center></td>

 *           </tr>

 *           <tr>

 *             <th><center>indeterminate</center></th>

 *             <td><center>indeterminate</center></td>

 *             <td><center>true</center></td>

 *             <td><center>indeterminate</center></td>

 *           </tr>

 *       </table>

 *  \throws nothrow

 */

inline tribool operator||(tribool x, tribool y)

{

  if (static_cast<bool>(!x) && static_cast<bool>(!y))

    return false;

  else if (static_cast<bool>(x) || static_cast<bool>(y))

    return true;

  else

    return indeterminate;

}



/**

 * \overload

 */

inline tribool operator||(tribool x, bool y)

{ return y? tribool(true) : x; }



/**

 * \overload

 */

inline tribool operator||(bool x, tribool y)

{ return x? tribool(true) : y; }



/**

 * \overload

 */

inline tribool operator||(indeterminate_keyword_t, tribool x)

{ return x? tribool(true) : tribool(indeterminate); }



/**

 * \overload

 */

inline tribool operator||(tribool x, indeterminate_keyword_t)

{ return x? tribool(true) : tribool(indeterminate); }

//@}



/**

 * \brief Compare tribools for equality

 *

 * \returns the result of comparing two tribool values, according to

 * the following table:

 *       <table border=1>

 *          <tr>

 *            <th><center><code>==</code></center></th>

 *            <th><center>false</center></th>

 *            <th><center>true</center></th>

 *            <th><center>indeterminate</center></th>

 *          </tr>

 *          <tr>

 *            <th><center>false</center></th>

 *            <td><center>true</center></td>

 *            <td><center>false</center></td>

 *            <td><center>indeterminate</center></td>

 *          </tr>

 *          <tr>

 *            <th><center>true</center></th>

 *            <td><center>false</center></td>

 *            <td><center>true</center></td>

 *            <td><center>indeterminate</center></td>

 *          </tr>

 *          <tr>

 *            <th><center>indeterminate</center></th>

 *            <td><center>indeterminate</center></td>

 *            <td><center>indeterminate</center></td>

 *            <td><center>indeterminate</center></td>

 *          </tr>

 *      </table>

 * \throws nothrow

 */

inline tribool operator==(tribool x, tribool y)

{

  if (indeterminate(x) || indeterminate(y))

    return indeterminate;

  else

    return (x && y) || (!x && !y);

}



/**

 * \overload

 */

inline tribool operator==(tribool x, bool y) { return x == tribool(y); }



/**

 * \overload

 */

inline tribool operator==(bool x, tribool y) { return tribool(x) == y; }



/**

 * \overload

 */

inline tribool operator==(indeterminate_keyword_t, tribool x)

{ return tribool(indeterminate) == x; }



/**

 * \overload

 */

inline tribool operator==(tribool x, indeterminate_keyword_t)

{ return tribool(indeterminate) == x; }



/**

 * \brief Compare tribools for inequality

 *

 * \returns the result of comparing two tribool values for inequality,

 * according to the following table:

 *       <table border=1>

 *           <tr>

 *             <th><center><code>!=</code></center></th>

 *             <th><center>false</center></th>

 *             <th><center>true</center></th>

 *             <th><center>indeterminate</center></th>

 *           </tr>

 *           <tr>

 *             <th><center>false</center></th>

 *             <td><center>false</center></td>

 *             <td><center>true</center></td>

 *             <td><center>indeterminate</center></td>

 *           </tr>

 *           <tr>

 *             <th><center>true</center></th>

 *             <td><center>true</center></td>

 *             <td><center>false</center></td>

 *             <td><center>indeterminate</center></td>

 *           </tr>

 *           <tr>

 *             <th><center>indeterminate</center></th>

 *             <td><center>indeterminate</center></td>

 *             <td><center>indeterminate</center></td>

 *             <td><center>indeterminate</center></td>

 *           </tr>

 *       </table>

 * \throws nothrow

 */

inline tribool operator!=(tribool x, tribool y)

{

  if (indeterminate(x) || indeterminate(y))

    return indeterminate;

  else

    return !((x && y) || (!x && !y));

}



/**

 * \overload

 */

inline tribool operator!=(tribool x, bool y) { return x != tribool(y); }



/**

 * \overload

 */

inline tribool operator!=(bool x, tribool y) { return tribool(x) != y; }



/**

 * \overload

 */

inline tribool operator!=(indeterminate_keyword_t, tribool x)

{ return tribool(indeterminate) != x; }



/**

 * \overload

 */

inline tribool operator!=(tribool x, indeterminate_keyword_t)

{ return x != tribool(indeterminate); }



} } // end namespace boost::logic



// Pull tribool and indeterminate into namespace "boost"

namespace boost {

  using logic::tribool;

  using logic::indeterminate;

}



/**

 * \brief Declare a new name for the third state of a tribool

 *

 * Use this macro to declare a new name for the third state of a

 * tribool. This state can have any number of new names (in addition

 * to \c indeterminate), all of which will be equivalent. The new name will be

 * placed in the namespace in which the macro is expanded.

 *

 * Example:

 *   BOOST_TRIBOOL_THIRD_STATE(true_or_false)

 *

 *   tribool x(true_or_false);

 *   // potentially set x

 *   if (true_or_false(x)) {

 *     // don't know what x is

 *   }

 */

#define BOOST_TRIBOOL_THIRD_STATE(Name)                                 \

inline bool                                                             \

Name(boost::logic::tribool x,                                           \

     boost::logic::detail::indeterminate_t dummy =                      \

       boost::logic::detail::indeterminate_t())                         \

{ return x.value == boost::logic::tribool::indeterminate_value; }



#endif // BOOST_LOGIC_TRIBOOL_HPP



