#ifndef METAL_LAMBDA_LAMBDA_HPP
#define METAL_LAMBDA_LAMBDA_HPP

#include "../config.hpp"

namespace metal {
/// \cond
namespace detail {
    template <class val>
    struct _is_lambda;

    template <class val>
    struct _as_lambda;
}
/// \endcond

/// \ingroup lambda
///
/// ### Description
/// Checks whether some \value is a \lambda.
///
/// ### Usage
/// For any \value `val`
/// \code
///     using result = metal::is_lambda<val>;
/// \endcode
///
/// \returns: \number
/// \semantics:
///     If `val` is a \lambda, then
///     \code
///         using result = metal::true_;
///     \endcode
///     otherwise
///     \code
///         using result = metal::false_;
///     \endcode
///
/// ### Example
/// \snippet lambda.cpp is_lambda
///
/// ### See Also
/// \see lambda, is_value, is_number, is_pair, is_list, is_map
template <class val>
using is_lambda = typename detail::_is_lambda<val>::type;

/// \ingroup lambda
///
/// ### Description
/// Given any \value that is a specialization of a template class or union
/// whose template parameters are all themselves \values, constructs a
/// \lambda that contains that template.
///
/// ### Usage
/// For any \value `val`
/// \code
///     using result = metal::as_lambda<val>;
/// \endcode
///
/// \returns: \lambda
///
/// ### Example
/// \snippet lambda.cpp as_lambda
///
/// ### See Also
/// \see lambda, as_list
template <class val>
using as_lambda = typename detail::_as_lambda<val>::type;

/// \ingroup lambda
///
/// ### Description
/// Constructs a \lambda out of an \expression.
///
/// ### Usage
/// For any \expression `expr`
/// \code
///     using result = metal::lambda<expr>;
/// \endcode
///
/// \returns: \lambda
///
/// ### See Also
/// \see is_lambda
template <template <class...> class expr>
#if defined(METAL_DOXYGENATING)
using lambda = struct {
};
#else
struct lambda {
};
#endif
}

#include "../number/number.hpp"

namespace metal {
/// \cond
namespace detail {
    template <class val>
    struct _is_lambda : false_ {
    };

    template <template <class...> class expr>
    struct _is_lambda<lambda<expr>> : true_ {
    };

    template <class val>
    struct _as_lambda {
    };

    template <template <class...> class expr, class... vals>
    struct _as_lambda<expr<vals...>> {
        using type = lambda<expr>;
    };
}
/// \endcond
}

#endif