Re: Mini-C example

Florian Klemme <[email protected]> wrote on 03.08.2016 17:34:21:

> From: Florian Klemme <[email protected]>
> To: [email protected], 
> Date: 03.08.2016 17:36
> Subject: [Spirit-general] Mini-C example
> 
> On 03.08.2016 01:59, Frank Hein wrote:
> Regarding your compiler implementation did you examine the mini-c 
> example provided with qi? Inspiring. 
> Oh, it is! I haven't seen it before. I see, there is a lot of 
> refactorization for me to do. ;-) 


> I've seen that Joel uses multiple grammars to parse the source, but 
> I can only find the instantiation of the function-parser in main(). 

You can understand grammars as a container for rules. You can use them
to give some structure (by topic, for example) to your rule set. 

A grammar is also a nonterminal parser. When you define a grammer, you
provide a start rule, which is one of the rules defined within the 
grammar.

That's not all about grammars but enough to get a basic understanding.

If you phrase_parse an input with a grammar provided as parser, then qi 
applies
the rules defined in the grammer starting with the defined start rule. 
This
may depend on other rules. 


> Where are the others instantiated? Or how does this chain of grammars 
work?
> Also, what does this "body" member do?
>     template <typename Iterator>
>     function<Iterator>::function(error_handler<Iterator>& error_handler)
>       : function::base_type(start), body(error_handler)

Above function::base_type(start) makes the rule named 'start' the start 
rule
of the grammar 'function'.

So if you would phrase_parse( x,y, function, skipper) rule evalution 
starts
at the 'start' rule.

> name =
>                 !body.expr.keywords
>             >>  raw[lexeme[(alpha | '_') >> *(alnum | '_')]]
>             ;

You can even make a grammar known from another grammar. Take a look at
the declaration of body. It's statement<Iterator> body. This is the 
statement
grammar declared in statement.hpp. The statement grammar again has a 
member, which is
the expression grammar. 

That way the mini-c grammars have a top-down knowledge of each other. In 
main only the 
top level grammar is explicitly, the others are instantiated as a (chain 
of) members of
the outer grammar.

Regards, Frank


> Florian
> 
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