Subject: [Boost-commit] svn:boost r64721 - sandbox/metagraph/libs/metagraph/example
From: gordon_at_[hidden]
Date: 2010-08-10 03:42:45
Author: gordon.woodhull
Date: 2010-08-10 03:42:39 EDT (Tue, 10 Aug 2010)
New Revision: 64721
URL: http://svn.boost.org/trac/boost/changeset/64721
Log:
add proto compile-time traversal example
Added:
sandbox/metagraph/libs/metagraph/example/proto_adaptor.cpp (contents, props changed)
Added: sandbox/metagraph/libs/metagraph/example/proto_adaptor.cpp
==============================================================================
--- (empty file)
+++ sandbox/metagraph/libs/metagraph/example/proto_adaptor.cpp 2010-08-10 03:42:39 EDT (Tue, 10 Aug 2010)
@@ -0,0 +1,136 @@
+// Example of adapting Proto trees into MPGL (aka mpl_graph) graphs
+// Copyright 2010 Gordon Woodhull.
+// Based on Proto example Calc1
+// Copyright 2008 Eric Niebler. 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)
+//
+// Start with the simple example of how to build an arithmetic expression
+// evaluator with placeholders, and then traverse the ASTs using DFS & BFS
+
+// This does compile-time traversal of the AST, which is not really the whole
+// problem. Instead it should be a Fusion/BGL hybrid
+
+#include <iostream>
+#include <boost/mpl/int.hpp>
+#include <boost/proto/core.hpp>
+#include <boost/proto/context.hpp>
+
+#include <boost/metagraph/mpl_graph/depth_first_search.hpp>
+#include <boost/mpl/pair.hpp>
+#include <boost/mpl/range_c.hpp>
+#include <boost/mpl/equal.hpp>
+#include <boost/typeof/typeof.hpp>
+
+
+namespace mpl = boost::mpl;
+namespace proto = boost::proto;
+namespace mpgl = boost::metagraph::mpl_graph;
+using proto::_;
+
+template<int I> struct placeholder {};
+
+// Define some placeholders
+proto::terminal< placeholder< 1 > >::type const _1 = {{}};
+proto::terminal< placeholder< 2 > >::type const _2 = {{}};
+
+// Define a calculator context, for evaluating arithmetic expressions
+struct calculator_context
+ : proto::callable_context< calculator_context const >
+{
+ // The values bound to the placeholders
+ double d[2];
+
+ // The result of evaluating arithmetic expressions
+ typedef double result_type;
+
+ explicit calculator_context(double d1 = 0., double d2 = 0.)
+ {
+ d[0] = d1;
+ d[1] = d2;
+ }
+
+ // Handle the evaluation of the placeholder terminals
+ template<int I>
+ double operator ()(proto::tag::terminal, placeholder<I>) const
+ {
+ return d[ I - 1 ];
+ }
+};
+
+template<typename Expr>
+double evaluate( Expr const &expr, double d1 = 0., double d2 = 0. )
+{
+ // Create a calculator context with d1 and d2 substituted for _1 and _2
+ calculator_context const ctx(d1, d2);
+
+ // Evaluate the calculator expression with the calculator_context
+ return proto::eval(expr, ctx);
+}
+
+// implement the MPGL IncidenceGraph concept on the Proto API
+// Vertex is Expr; Edge is mpl::pair<Expr, ChildNum>
+// Graph is unused
+
+// dummy graph telling mpgl to use these specializations
+struct proto_graph_rep;
+struct ProtoGraph {
+ typedef proto_graph_rep representation;
+};
+
+namespace boost {
+namespace metagraph {
+namespace mpl_graph {
+
+// this probably is not the most awesome way to specialize the mpgl metafunctions
+// mpl_graph.hpp should probably be opened up to rely more on the representation tag
+// instead of assuming that every impl will have giant maps in it
+
+template<typename Edge>
+struct source<Edge, ProtoGraph> :
+ mpl::first<Edge>
+{};
+template<typename Edge>
+struct target<Edge, ProtoGraph> :
+ proto::result_of::child_c<typename mpl::first<Edge>::type, mpl::second<Edge>::type::value>
+{};
+template<typename Vertex>
+struct out_edges<Vertex, ProtoGraph> :
+ mpl::fold<mpl::range_c<long,0,proto::arity_of<Vertex>::value>,
+ mpl::vector<>,
+ mpl::push_back<mpl::_1, mpl::pair<Vertex, mpl::_2> > >
+{};
+template<typename Vertex>
+struct out_degree<Vertex, ProtoGraph> :
+ proto::arity_of<Vertex>
+{};
+
+}
+}
+}
+
+struct preordering_visitor : mpgl::dfs_default_visitor_operations {
+ template<typename Node, typename Graph, typename State>
+ struct discover_vertex :
+ mpl::push_back<State, Node>
+ {};
+};
+
+// dummy Graph (unneeded)
+struct None {};
+
+template<typename Expr>
+struct proto_preorder_dfs :
+ mpl::first<typename mpgl::depth_first_search<ProtoGraph, preordering_visitor, mpl::vector<>, Expr>::type >
+{};
+
+typedef BOOST_TYPEOF(_1*12/_2) expr_type;
+typedef proto_preorder_dfs<expr_type>::type pre_expr_travs;
+
+BOOST_MPL_ASSERT(( mpl::equal<pre_expr_travs, void > ));
+
+int main()
+{
+
+ return 0;
+}