applicative.h

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/**********************************************************************
 * LeechCraft - modular cross-platform feature rich internet client.
 * Copyright (C) 2006-2014  Georg Rudoy
 *
 * Distributed under the Boost Software License, Version 1.0.
 * (See accompanying file LICENSE or copy at https://www.boost.org/LICENSE_1_0.txt)
 **********************************************************************/
 
#pragma once
 
#include <optional>
#include "either.h"
 
namespace LC
{
namespace Util
{
    template<typename Applicative>
    struct InstanceApplicative;
 
    template<typename AF, typename AV>
    using GSLResult_t = typename InstanceApplicative<AF>::template GSLResult<AV>::Type_t;
 
    template<template<typename...> class Applicative, typename... Args, typename T>
    auto Pure (const T& v)
    {
        return InstanceApplicative<Applicative<Args..., T>>::Pure (v);
    }
 
    template<typename Applicative, typename T>
    auto Pure (const T& v) -> decltype (InstanceApplicative<Applicative>::Pure (v))
    {
        return InstanceApplicative<Applicative>::Pure (v);
    }
 
    template<typename AF, typename AV>
    GSLResult_t<AF, AV> GSL (const AF& af, const AV& av)
    {
        return InstanceApplicative<AF>::GSL (af, av);
    }
 
    template<typename AF, typename AV>
    auto operator* (const AF& af, const AV& av) -> decltype (GSL (af, av))
    {
        return GSL (af, av);
    }
 
    // Implementations
 
    template<typename T>
    struct InstanceApplicative<std::optional<T>>
    {
        using Type_t = std::optional<T>;
 
        template<typename>
        struct GSLResult;
 
        template<typename V>
        struct GSLResult<std::optional<V>>
        {
            using Type_t = std::optional<std::result_of_t<T (const V&)>>;
        };
 
        template<typename U>
        static std::optional<U> Pure (const U& v)
        {
            return { v };
        }
 
        template<typename AV>
        static GSLResult_t<Type_t, AV> GSL (const Type_t& f, const AV& v)
        {
            if (!f || !v)
                return {};
 
            return { (*f) (*v) };
        }
    };
 
    template<typename L, typename R>
    struct InstanceApplicative<Either<L, R>>
    {
        using Type_t = Either<L, R>;
 
        template<typename>
        struct GSLResult;
 
        template<typename V>
        struct GSLResult<Either<L, V>>
        {
            using Type_t = Either<L, std::result_of_t<R (const V&)>>;
        };
 
        template<typename RP>
        static Either<L, RP> Pure (const RP& v)
        {
            return Either<L, RP>::Right (v);
        }
 
        template<typename AV>
        static GSLResult_t<Type_t, AV> GSL (const Type_t& f, const AV& v)
        {
            using R_t = GSLResult_t<Type_t, AV>;
 
            if (f.IsLeft ())
                return R_t::Left (f.GetLeft ());
 
            if (v.IsLeft ())
                return R_t::Left (v.GetLeft ());
 
            return R_t::Right (f.GetRight () (v.GetRight ()));
        }
    };
 
}
}