Update of /cvsroot/boost/boost/libs/xpressive/proto/example
In directory sc8-pr-cvs3.sourceforge.net:/tmp/cvs-serv7179
Modified Files:
vec3.cpp
Log Message:
use new function2 transform in CountLeaves transform
Index: vec3.cpp
===================================================================
RCS file: /cvsroot/boost/boost/libs/xpressive/proto/example/vec3.cpp,v
retrieving revision 1.1
retrieving revision 1.2
diff -u -d -r1.1 -r1.2
--- vec3.cpp 23 Jun 2007 06:32:01 -0000 1.1
+++ vec3.cpp 23 Jun 2007 07:42:23 -0000 1.2
@@ -9,10 +9,16 @@
// from PETE (http://www.codesourcery.com/pooma/download.html).
#include <iostream>
+#include <functional>
+#include <boost/mpl/int.hpp>
#include <boost/xpressive/proto/proto.hpp>
#include <boost/xpressive/proto/context.hpp>
#include <boost/xpressive/proto/proto_typeof.hpp>
+#include <boost/xpressive/proto/transform/arg.hpp>
+#include <boost/xpressive/proto/transform/fold.hpp>
+#include <boost/xpressive/proto/transform/function.hpp>
using namespace boost::proto;
+namespace mpl = boost::mpl;
// Here is an evaluation context that indexes into a Vec3
// expression, and combines the result.
@@ -35,25 +41,24 @@
int i_;
};
-// Here is an evaluation context that counts the number of
-// Vec3 terminals in an expression.
-struct CountLeavesCtx
- : callable_context< CountLeavesCtx >
-{
- typedef int result_type;
-
- CountLeavesCtx()
- : count(0)
- {}
-
- int operator()(tag::terminal, int const (&)[3])
- {
- ++this->count;
- return 0; // not used
- }
-
- int count;
-};
+// This transform counts the number of int[3] terminals in an expression.
+// It accumulates a runtime value, rather than computing a compile-time
+// value, just to demonstrate the use of the std::plus<> function object
+// as a transform.
+struct CountLeaves
+ : or_<
+ // match a Vec3 terminal, return 1
+ transform::always<terminal<int[3]>, mpl::int_<1> >
+ // match a terminal, return int() (which is 0)
+ , transform::always<terminal<_>, int>
+ // fold everything else, using std::plus<> to add
+ // the leaf count of each child to the accumulated state.
+ , transform::fold<
+ nary_expr<_, vararg<transform::function2<CountLeaves,
std::plus<int> > > >
+ , int // initial state of the fold is int() (which is 0)
+ >
+ >
+{};
// Here is the Vec3 struct, which is a vector of 3 integers.
struct Vec3
@@ -97,14 +102,13 @@
}
};
-// The count_leaves() function uses the CountLeavesCtx and
-// proto::eval() to count the number of leaves in an expression.
+// The count_leaves() function uses the CountLeaves transform and
+// to count the number of leaves in an expression.
template<typename Expr>
int count_leaves(Expr const &expr)
{
- CountLeavesCtx ctx;
- eval(expr, ctx);
- return ctx.count;
+ int i = 0;
+ return CountLeaves::call(expr, i, i);
}
int main()
-------------------------------------------------------------------------
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