{"id":929,"date":"2010-01-28T03:27:29","date_gmt":"2010-01-28T11:27:29","guid":{"rendered":"http:\/\/boost-spirit.com\/home\/?p=929"},"modified":"2010-01-28T04:09:23","modified_gmt":"2010-01-28T12:09:23","slug":"can-the-classic-dynamic-parsers-be-ported-to-qi","status":"publish","type":"post","link":"https:\/\/boost-spirit.com\/home\/2010\/01\/28\/can-the-classic-dynamic-parsers-be-ported-to-qi\/","title":{"rendered":"Can the Classic Dynamic Parsers be Ported to Qi?"},"content":{"rendered":"

After writing about local variables for rules here<\/a> I would like to get back to some information I have had lying around for some time already. Today’s topic seems to be a nice fit as porting the dynamic parsers from Spirit.Classic<\/em> requires to utilize local variables. This allows me to give you some more examples for this facility.<\/p>\n

Previous versions of Spirit<\/em>, which are the versions we refer to as Spirit.Classic<\/em> today, implemented special dynamic parsers allowing to insert control statements into the parsing process (such as if_p<\/span>, while_p<\/span>, and for_p<\/span>). These dynamic parsers are not available anymore in Qi<\/em>. But it is easy enough to achieve the same behavior using existing Qi<\/em> components. This ‘Tip of the Day’ describes those techniques, which have been developed and contributed by Carl Barron. Thanks Carl!<\/p>\n

<\/p>\n

Generally, Spirit.Classic<\/em> allowed to employ the dynamic parser in two ways. The condition to check could be either a function or function object, or a parser expression. Functions or function objects are expected to return values convertible to bool<\/span>. When the evaluation of the function or function object yields true it will be considered as meeting the condition. When the parser matches the condition is met as well.<\/p>\n

General Notation<\/h5>\n

In the tables below we use the following notation:<\/p>\n