How to parse dot's HTML-like strings?

[NeverGivinUp]

Parsing dot-files is generally straight forward. I don't know how to implement HTML-like strings, though. An HTML-like string is separated by an opening and closing angular bracket <...>. An attribute looks something like this

label=<<a href="somewhere"><b>That</b> place</a>>

For a test from graphviz see here.

It seems, like a parser, that would like to recognize, would need to hold state, so as to be able to detect, if a matching number of opening and closing brackets have been found. The repeating combinators, like take_while, only allow Fn tests (not FnMut), and ContainsToken::contains_token only allows &self, not &mut self.

Is there a way to parse HTML-Like strings?

[epage]

We will likely need a delimiter matching parser for #96 but not feeling ready to define that quite yet.

You could write this imperatively, something roughly like

• while unbalanced:
  • `(take_until(['<', '>']), any)``
  • Modify balance check according to the the any value (either < or >)
• Return O=()
• .recognize() the above

[NeverGivinUp]

Thanks @epage!

I imagine, the parsing would look like this

fn p_html_inner(input: &str) -> IResult<&str, ()> {
    let (mut input, bracket) = '<'.parse_peek(input)?;
    let mut balance = 1;
    while balance != 0 {
        let (remaining_input, (before_bracket, bracket)) =
            (take_until0(['<', '>']), any).parse_peek(input)?;
        match bracket {
            '<' => balance += 1,
            '>' => balance -= 1,
            _ => unreachable!("angular bracket is not a bracket"),
        }
        input = remaining_input;
    }
    Ok((input, ()))
}

However, I don't know what to call the recognize method on. Do I need to create a struct that implements Parser instead of writing a function?

[epage]

unpeek(p_html_inner).recognize()

unpeek takes the old nom-like purely functional function signature and turns it into an impl Parser<I, O, E>.

You could also do

fn p_html_inner(input: &mut &str) -> PResult<()> {
    let bracket = '<'.parse_next(input)?;
    let mut balance = 1;
    while balance != 0 {
        let (before_bracket, bracket) =
            (take_until0(['<', '>']), any).parse_next(input)?;
        match bracket {
            '<' => balance += 1,
            '>' => balance -= 1,
            _ => unreachable!("angular bracket is not a bracket"),
        }
    }
    Ok(())
}

and then you could do p_html_inner.recognize() since we have impl Parser for FnMut... for that signature.

[epage]

btw cargo add winnow -F simd to use simd to accelerate take_until0