lazy.h

Go to the documentation of this file.

/**********************************************************************
 * LeechCraft - modular cross-platform feature rich internet client.
 * Copyright (C) 2006-2014  Georg Rudoy
 *
 * Boost Software License - Version 1.0 - August 17th, 2003
 *
 * Permission is hereby granted, free of charge, to any person or organization
 * obtaining a copy of the software and accompanying documentation covered by
 * this license (the "Software") to use, reproduce, display, distribute,
 * execute, and transmit the Software, and to prepare derivative works of the
 * Software, and to permit third-parties to whom the Software is furnished to
 * do so, all subject to the following:
 *
 * The copyright notices in the Software and this entire statement, including
 * the above license grant, this restriction and the following disclaimer,
 * must be included in all copies of the Software, in whole or in part, and
 * all derivative works of the Software, unless such copies or derivative
 * works are solely in the form of machine-executable object code generated by
 * a source language processor.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
 * SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
 * FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 **********************************************************************/
 
#pragma once
 
#include <functional>
#include "monadplus.h"
 
namespace LC
{
namespace Util
{
    template<typename T>
    using Lazy_t = std::function<T ()>;
 
    template<typename T>
    Lazy_t<T> MakeLazy (const T& t)
    {
        return [t] { return t; };
    }
 
    template<typename R, typename F>
    Lazy_t<R> MakeLazyF (const F& l)
    {
        return l;
    }
 
    template<typename T>
    struct InstanceMonadPlus<Lazy_t<T>, std::enable_if_t<IsMonadPlus<T> ()>>
    {
        static Lazy_t<T> Mzero ()
        {
            return [] { return Util::Mzero<T> (); };
        }
 
        static Lazy_t<T> Mplus (const Lazy_t<T>& t1, const Lazy_t<T>& t2)
        {
            return [=]
            {
                const auto rt1 = t1 ();
                return rt1 != Util::Mzero<T> () ? rt1 : t2 ();
            };
        }
    };
}
}