Handling comments? about cpp-peglib HOT 4 CLOSED

HI Jerry, sorry for the late reply. I think the data source shouldn't have any 'parsing' logic like comment skipping, so that all rules can be seen in a PEG grammar file. I just wonder how difficult to specify your comment syntax in PEG grammar?

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@g40, thanks for the feedback. I actually handled the single line comment in my experimental programming language.

Here is the rule snippet that handles the line comment:

End                      <-  EndOfLine / EndOfFile
EndOfLine                <-  '\r\n' / '\n' / '\r'
EndOfFile                <-  !.
LineComment              <-  ('#' / '//') (!End .)* &End

This is a sample code that uses line comments.
https://github.com/yhirose/culebra/blob/master/samples/bug.cul

Does it work for you as well?

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Hi Yuji

Thanks. Yes, I saw that in the grammar grammar. My problem is that one now has to embed whitespace rules in the grammar which can be problematic, esp. in more complex cases. What I had in mind was abstracting the parser data source

template <typename T=char>
class data_source
{
// set up data source
data_source(const T* ps,size_t count) { ... }
//
T next() { // return next character }
// how many chars were matched?
size_t size() const { ... }
// reset data source if match failed
void reset() {... }
// once matched, i.e. '#' or '//' skips until eol
comment_mode(const char* ps) {...}
// multi-line, match start, continue to end ...
comment_mode(const T* ps,const T* pe) {...}
};

This is pretty non-invasive, just one level of indirection:

         std::string example("# hello world");
        data_source<> ds(example.data(),example.size()));
        ds.comment("#");
	std::shared_ptr<peg::Ast> ast;
	if (!parser.parse_n(ds.data(), ds.size(), ast))
             throw "an error!";

Thoughts?

BR

Jerry.

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Hi Yuji,

Sorry for the late reply here. On reflection, I think you are right. The lex style comment parsing mechanism does not work well with PEG parsers ...

Best.

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