The BOOST_PP_LIST_FOLD_LEFT_d macro folds (or accumulates) the elements of a list left-to-right.  It reenters BOOST_PP_WHILE with maximum efficiency.

Usage

BOOST_PP_LIST_FOLD_LEFT_ ## d(op, state, list)

Arguments

d
The next available BOOST_PP_WHILE iteration.
op
A ternary operation of the form op(d, state, elem).  This macro is called for each element in list--each time returning a new state.  This operation is expanded by BOOST_PP_LIST_FOLD_LEFT with the next available BOOST_PP_WHILE iteration, the current state, and the current element.
state
The initial state of the fold.
list
The list to be folded.

Remarks

For the list, (0, (1, (2, BOOST_PP_NIL))), this macro expands to:
op(d, op(d, op(d, state, 0), 1), 2)

See Also

Requirements

Header:  <boost/preprocessor/list/fold_left.hpp>

Sample Code

#include <boost/preprocessor/cat.hpp>
#include <boost/preprocessor/list/fold_left.hpp>

#define L1 (a, (b, (c, BOOST_PP_NIL)))
#define L2 (L1, (L1, (L1, BOOST_PP_NIL)))

#define OP(d, state, x) (BOOST_PP_LIST_FOLD_LEFT_ ## d(OP_2, _, x), state)
#define OP_2(d, state, x) BOOST_PP_CAT(state, x)

BOOST_PP_LIST_FOLD_LEFT(OP, BOOST_PP_NIL, L2)
/*
   expands to:
   (_abc, (_abc, (_abc, BOOST_PP_NIL)))
*/

Copyright Housemarque Oy 2002
Copyright Paul Mensonides 2002

Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at www.boost.org/LICENSE_1_0.txt)