lambda

Synopsis

template <class Name1, ..., class Namen, class F>
struct lambda
{
  template <class T1, ..., class Tn>
  struct apply
    // unspecified
  ;
};

Description

Name1, ..., Namen are classes, F is a syntax. The lambda metafunction class takes classes, T1, ..., Tn as arguments and produces a new nullary metafunction. It binds T1, ..., Tn to the names Name1, ..., Namen in the body of F using let.

The arguments may be _, in which case the value of the argument is ignored and no substitution happens.

The metafunction classes support currying as well. Applying less arguments to the metafunction class as n produces a new metafunction class taking the missing arguments. F is evaluated only when all arguments are provided.

Header

#include <mpllibs/metamonad/lambda.hpp>

Expression semantics

For any k > 0, n1 ... nk and t1 ... tk classes and f nullary metafunction

lambda<n1, ..., nk, syntax<f>>::apply<t1, ..., tk>::type

is equivalent to

multi_let<
  mpl::map<
    mpl::pair<n1, t1>,
    // ...
    mpl::pair<nk, tk>
  >,
  syntax<f>
>::type::type

For any 0 < j < k

lambda<n1, ..., nk, syntax<f>>
  ::apply<t1, ..., tj>::type::apply<t(j+1), ..., tk>::type

is equivalent to

lambda<n1, ..., nk, syntax<f>>::apply<t1, ..., tk>::type

Example

using boost::mpl::plus;
using boost::mpl::int_;

using namespace mpllibs::metamonad::name;

typedef lambda<n, syntax<plus<int_<1>, n>>> plus_1;

Copyright Abel Sinkovics (abel at elte dot hu) 2011. Distributed under 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

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