I have an application which has two separate mini-languages. What the languages are, doesn't really matter, so I'll use surrogates that people are familiar with.

I wrote the first parser already, and it works well. It's a complicated grammar that reads a single entity. You could think of it like "how to parse a single database query." (It's not SQL but it's roughly the same complexity.) Call the parser on a string, and it returns an entity.

I was then going to write the other parser, which sometimes needs to parse entities of the first kind. Think of it like "how to parse a user interface template" like web or gui or something. Call the parser, and read the whole template.

In several circumstances, the template could include a full "query" type entity. The question is how to parse both mini-languages which can be interlaced, without using just one huge grammar. 

# query example
query:[ select foo from table X where foo.whatever is acceptable ]

[download]
# template example
identifier TEMPLATE
{
  code; code; code;
  query:[....];
  more code that uses query results; etc.
}

[download]
Now, I'm sure that technically, I *could* just write one huge massive grammar that handles both cases, where the query is just one possible sub-rule.

However, I don't want to go that route, since templates and queries are not really the same thing, and I want to maintain and/or release them separately. 

$TemplateParser = new Parse::RecDescent(<<'__GRAMMAR__');

   template:  identifier 'TEMPLATE' '{' statement(s) '}'

   statement: expression
            | conditional
            | loopcontrol
            | <do-this-other-parser: $QueryParser->query() >

__GRAMMAR__

[download]
What I'd like to see is a Parse::RecDescent way of calling a different parser to accomplish a subrule. Is there any such mechanism that I've missed in the documentation and examples?

--
[ e d @ h a l l e y . c c ]

In reply to using two Parse::RecDescent parsers together by halley

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