Initial Commit

2018-02-08 21:28:33 -05:00
commit 678c1d3966
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+/*=============================================================================
+    Copyright (c) 1998-2003 Joel de Guzman
+    Copyright (c) 2001 Daniel Nuffer
+    Copyright (c) 2002 Hartmut Kaiser
+    http://spirit.sourceforge.net/
+
+  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(BOOST_SPIRIT_OPTIONAL_HPP)
+#define BOOST_SPIRIT_OPTIONAL_HPP
+
+#include <boost/spirit/home/classic/namespace.hpp>
+#include <boost/spirit/home/classic/core/parser.hpp>
+#include <boost/spirit/home/classic/core/primitives/primitives.hpp>
+#include <boost/spirit/home/classic/core/composite/composite.hpp>
+#include <boost/spirit/home/classic/meta/as_parser.hpp>
+
+namespace boost { namespace spirit {
+
+BOOST_SPIRIT_CLASSIC_NAMESPACE_BEGIN
+
+    ///////////////////////////////////////////////////////////////////////////
+    //
+    //  optional class
+    //
+    //      Handles expressions of the form:
+    //
+    //          !a
+    //
+    //      where a is a parser. The expression returns a composite
+    //      parser that matches its subject zero (0) or one (1) time.
+    //
+    ///////////////////////////////////////////////////////////////////////////
+    struct optional_parser_gen;
+    
+    template <typename S>
+    struct optional
+    :   public unary<S, parser<optional<S> > >
+    {
+        typedef optional<S>                 self_t;
+        typedef unary_parser_category       parser_category_t;
+        typedef optional_parser_gen         parser_generator_t;
+        typedef unary<S, parser<self_t> >   base_t;
+    
+        optional(S const& a)
+        : base_t(a) {}
+    
+        template <typename ScannerT>
+        typename parser_result<self_t, ScannerT>::type
+        parse(ScannerT const& scan) const
+        {
+            typedef typename parser_result<self_t, ScannerT>::type result_t;
+            typedef typename ScannerT::iterator_t iterator_t;
+            iterator_t save = scan.first;
+            if (result_t r = this->subject().parse(scan))
+            {
+                return r;
+            }
+            else
+            {
+                scan.first = save;
+                return scan.empty_match();
+            }
+        }
+    };
+    
+    struct optional_parser_gen
+    {
+        template <typename S>
+        struct result 
+        {
+            typedef optional<S> type;
+        };
+    
+        template <typename S>
+        static optional<S>
+        generate(parser<S> const& a)
+        {
+            return optional<S>(a.derived());
+        }
+    };
+    
+    template <typename S>
+    optional<S>
+    operator!(parser<S> const& a);
+
+BOOST_SPIRIT_CLASSIC_NAMESPACE_END
+
+}} // namespace BOOST_SPIRIT_CLASSIC_NS
+
+#endif
+
+#include <boost/spirit/home/classic/core/composite/impl/optional.ipp>