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268 lines
9.7 KiB
268 lines
9.7 KiB
///////////////////////////////////////////////////////////////////////////////
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/// \file when.hpp
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/// Definition of when transform.
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//
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// Copyright 2008 Eric Niebler. Distributed under the Boost
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// Software License, Version 1.0. (See accompanying file
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// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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#ifndef BOOST_PROTO_TRANSFORM_WHEN_HPP_EAN_10_29_2007
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#define BOOST_PROTO_TRANSFORM_WHEN_HPP_EAN_10_29_2007
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#include <boost/preprocessor/cat.hpp>
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#include <boost/preprocessor/repetition/enum_params.hpp>
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#include <boost/preprocessor/repetition/enum_trailing_params.hpp>
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#include <boost/preprocessor/iteration/iterate.hpp>
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#include <boost/mpl/at.hpp>
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#include <boost/mpl/if.hpp>
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#include <boost/mpl/map.hpp>
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#include <boost/mpl/eval_if.hpp>
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#include <boost/proto/proto_fwd.hpp>
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#include <boost/proto/traits.hpp>
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#include <boost/proto/transform/call.hpp>
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#include <boost/proto/transform/make.hpp>
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#include <boost/proto/transform/impl.hpp>
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#include <boost/proto/transform/env.hpp>
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#if defined(_MSC_VER)
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# pragma warning(push)
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# pragma warning(disable : 4714) // function 'xxx' marked as __forceinline not inlined
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#endif
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namespace boost { namespace proto
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{
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namespace detail
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{
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template<typename Grammar, typename R, typename Fun>
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struct when_impl
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: transform<when<Grammar, Fun> >
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{
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typedef Grammar first;
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typedef Fun second;
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typedef typename Grammar::proto_grammar proto_grammar;
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// Note: do not evaluate is_callable<R> in this scope.
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// R may be an incomplete type at this point.
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template<typename Expr, typename State, typename Data>
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struct impl : transform_impl<Expr, State, Data>
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{
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// OK to evaluate is_callable<R> here. R should be compete by now.
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typedef
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typename mpl::if_c<
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is_callable<R>::value
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, proto::call<Fun> // "R" is a function to call
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, proto::make<Fun> // "R" is an object to construct
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>::type
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which;
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typedef typename which::template impl<Expr, State, Data>::result_type result_type;
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/// Evaluate <tt>R(A0,A1,...)</tt> as a transform either with
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/// <tt>call\<\></tt> or with <tt>make\<\></tt> depending on
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/// whether <tt>is_callable\<R\>::value</tt> is \c true or
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/// \c false.
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///
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/// \param e The current expression
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/// \param s The current state
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/// \param d An arbitrary data
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/// \pre <tt>matches\<Expr, Grammar\>::value</tt> is \c true
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/// \return <tt>which()(e, s, d)</tt>
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BOOST_FORCEINLINE
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result_type operator ()(
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typename impl::expr_param e
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, typename impl::state_param s
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, typename impl::data_param d
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) const
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{
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return typename which::template impl<Expr, State, Data>()(e, s, d);
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}
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};
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};
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}
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/// \brief A grammar element and a PrimitiveTransform that associates
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/// a transform with the grammar.
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///
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/// Use <tt>when\<\></tt> to override a grammar's default transform
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/// with a custom transform. It is for used when composing larger
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/// transforms by associating smaller transforms with individual
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/// rules in your grammar, as in the following transform which
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/// counts the number of terminals in an expression.
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///
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/// \code
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/// // Count the terminals in an expression tree.
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/// // Must be invoked with initial state == mpl::int_<0>().
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/// struct CountLeaves
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/// : or_<
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/// when<terminal<_>, mpl::next<_state>()>
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/// , otherwise<fold<_, _state, CountLeaves> >
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/// >
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/// {};
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/// \endcode
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///
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/// In <tt>when\<G, T\></tt>, when \c T is a class type it is a
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/// PrimitiveTransform and the following equivalencies hold:
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///
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/// <tt>boost::result_of\<when\<G,T\>(E,S,V)\>::type</tt> is the same as
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/// <tt>boost::result_of\<T(E,S,V)\>::type</tt>.
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///
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/// <tt>when\<G,T\>()(e,s,d)</tt> is the same as
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/// <tt>T()(e,s,d)</tt>.
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template<typename Grammar, typename PrimitiveTransform /*= Grammar*/>
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struct when
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: PrimitiveTransform
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{
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typedef Grammar first;
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typedef PrimitiveTransform second;
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typedef typename Grammar::proto_grammar proto_grammar;
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};
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/// \brief A specialization that treats function pointer Transforms as
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/// if they were function type Transforms.
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///
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/// This specialization requires that \c Fun is actually a function type.
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///
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/// This specialization is required for nested transforms such as
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/// <tt>when\<G, T0(T1(_))\></tt>. In C++, functions that are used as
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/// parameters to other functions automatically decay to funtion
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/// pointer types. In other words, the type <tt>T0(T1(_))</tt> is
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/// indistinguishable from <tt>T0(T1(*)(_))</tt>. This specialization
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/// is required to handle these nested function pointer type transforms
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/// properly.
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template<typename Grammar, typename Fun>
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struct when<Grammar, Fun *>
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: when<Grammar, Fun>
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{};
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/// \brief Syntactic sugar for <tt>when\<_, Fun\></tt>, for use
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/// in grammars to handle all the cases not yet handled.
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///
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/// Use <tt>otherwise\<T\></tt> in your grammars as a synonym for
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/// <tt>when\<_, T\></tt> as in the following transform which
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/// counts the number of terminals in an expression.
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///
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/// \code
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/// // Count the terminals in an expression tree.
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/// // Must be invoked with initial state == mpl::int_<0>().
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/// struct CountLeaves
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/// : or_<
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/// when<terminal<_>, mpl::next<_state>()>
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/// , otherwise<fold<_, _state, CountLeaves> >
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/// >
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/// {};
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/// \endcode
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template<typename Fun>
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struct otherwise
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: when<_, Fun>
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{};
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namespace envns_
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{
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// Define the transforms global
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BOOST_PROTO_DEFINE_ENV_VAR(transforms_type, transforms);
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}
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using envns_::transforms;
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/// \brief This specialization uses the Data parameter as a collection
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/// of transforms that can be indexed by the specified rule.
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///
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/// Use <tt>when\<T, external_transform\></tt> in your code when you would like
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/// to define a grammar once and use it to evaluate expressions with
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/// many different sets of transforms. The transforms are found by
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/// using the Data parameter as a map from rules to transforms.
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///
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/// See \c action_map for an example.
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template<typename Grammar>
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struct when<Grammar, external_transform>
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: proto::transform<when<Grammar, external_transform> >
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{
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typedef Grammar first;
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typedef external_transform second;
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typedef typename Grammar::proto_grammar proto_grammar;
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template<typename Expr, typename State, typename Data>
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struct impl
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: remove_reference<
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typename mpl::eval_if_c<
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proto::result_of::has_env_var<Data, transforms_type>::value
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, proto::result_of::env_var<Data, transforms_type>
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, proto::result_of::env_var<Data, data_type>
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>::type
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>::type::template when<Grammar>::template impl<Expr, State, Data>
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{};
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};
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/// \brief For defining a map of Rule/Transform pairs for use with
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/// <tt>when\<T, external_transform\></tt> to make transforms external to the grammar
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///
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/// The following code defines a grammar with a couple of external transforms.
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/// It also defines an action_map that maps from rules to transforms. It then
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/// passes that transforms map at the Data parameter to the grammar. In this way,
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/// the behavior of the grammar can be modified post-hoc by passing a different
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/// action_map.
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///
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/// \code
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/// struct int_terminal
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/// : proto::terminal<int>
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/// {};
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///
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/// struct char_terminal
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/// : proto::terminal<char>
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/// {};
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///
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/// struct my_grammar
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/// : proto::or_<
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/// proto::when< int_terminal, proto::external_transform >
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/// , proto::when< char_terminal, proto::external_transform >
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/// , proto::when<
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/// proto::plus< my_grammar, my_grammar >
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/// , proto::fold< _, int(), my_grammar >
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/// >
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/// >
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/// {};
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///
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/// struct my_transforms
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/// : proto::external_transforms<
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/// proto::when<int_terminal, print(proto::_value)>
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/// , proto::when<char_terminal, print(proto::_value)>
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/// >
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/// {};
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///
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/// proto::literal<int> i(1);
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/// proto::literal<char> c('a');
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/// my_transforms trx;
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///
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/// // Evaluate "i+c" using my_grammar with the specified transforms:
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/// my_grammar()(i + c, 0, trx);
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/// \endcode
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template<BOOST_PP_ENUM_PARAMS_WITH_A_DEFAULT(BOOST_MPL_LIMIT_MAP_SIZE, typename T, mpl::na)>
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struct external_transforms
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{
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typedef mpl::map<BOOST_PP_ENUM_PARAMS(BOOST_MPL_LIMIT_MAP_SIZE, T)> map_type;
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template<typename Rule>
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struct when
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: proto::when<_, typename mpl::at<map_type, Rule>::type>
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{};
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};
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// Other specializations of proto::when are generated by the preprocessor...
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#include <boost/proto/transform/detail/when.hpp>
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/// INTERNAL ONLY
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///
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template<typename Grammar, typename Transform>
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struct is_callable<when<Grammar, Transform> >
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: mpl::true_
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{};
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}} // namespace boost::proto
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#if defined(_MSC_VER)
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# pragma warning(pop)
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#endif
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#endif
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