Imported existing code

libraries/include/boost/spirit/home/qi/operator/difference.hpp

@@ -0,0 +1,93 @@
+/*=============================================================================
+    Copyright (c) 2001-2007 Joel de Guzman
+
+    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)
+=============================================================================*/
+#if !defined(SPIRIT_DIFFERENCE_FEB_11_2007_1250PM)
+#define SPIRIT_DIFFERENCE_FEB_11_2007_1250PM
+
+#include <boost/spirit/home/qi/domain.hpp>
+#include <boost/spirit/home/support/component.hpp>
+#include <boost/spirit/home/support/attribute_of.hpp>
+#include <vector>
+
+namespace boost { namespace spirit { namespace qi
+{
+    struct difference
+    {
+        template <typename Component, typename Context, typename Iterator>
+        struct attribute
+        {
+            typedef typename
+                result_of::left<Component>::type
+            left_type;
+
+            typedef typename
+                traits::attribute_of<
+                    qi::domain, left_type, Context, Iterator>::type
+            type;
+        };
+
+        template <
+            typename Component
+          , typename Iterator, typename Context
+          , typename Skipper, typename Attribute>
+        static bool parse(
+            Component const& component
+          , Iterator& first, Iterator const& last
+          , Context& context, Skipper const& skipper
+          , Attribute& attr)
+        {
+            typedef typename
+                result_of::left<Component>::type::director
+            ldirector;
+
+            typedef typename
+                result_of::right<Component>::type::director
+            rdirector;
+
+            // Unlike classic Spirit, with this version of difference, the rule
+            // lit("policeman") - "police" will always fail to match.
+
+            // Spirit2 does not count the matching chars while parsing and
+            // there is no reliable and fast way to check if the LHS matches
+            // more than the RHS.
+
+            // Try RHS first
+            Iterator start = first;
+            if (rdirector::parse(spirit::right(component), first, last, context, 
+                skipper, unused))
+            {
+                // RHS succeeds, we fail.
+                first = start;
+                return false;
+            }
+            // RHS fails, now try LHS
+            return ldirector::parse(spirit::left(component), first, last, 
+                context, skipper, attr);
+        }
+
+        template <typename Component, typename Context>
+        static std::string what(Component const& component, Context const& ctx)
+        {
+            std::string result = "difference[";
+
+            typedef typename
+                result_of::left<Component>::type::director
+            ldirector;
+
+            typedef typename
+                result_of::right<Component>::type::director
+            rdirector;
+
+            result += ldirector::what(spirit::left(component), ctx);
+            result += ", ";
+            result += rdirector::what(spirit::right(component), ctx);
+            result += "]";
+            return result;
+        }
+    };
+}}}
+
+#endif