`// C++/EOL-style comments` recipe does not seem to work

[nyurik]

The // C++/EOL-style comments recipe seems to not match the expected content. The expected parser here should accept //...\n, whereas the example for some reason works with a single char '%'. Moreover, ideally I would like an example that requires a newline with an optional end-of-line comment before that. Am I misreading it?

/// This version uses % to start a comment, does not consume the newline character, and returns an output of ().
pub fn peol_comment<'a, E: ParseError<&'a str>>(i: &'a str) -> IResult<&'a str, (), E>
{
  value(
    (), // Output is thrown away.
    pair(char('%'), is_not("\n\r"))
  ).parse(i)
}

[Just-Helpful]

There's every chance that this recipe might've been updated since you last saw it...
The description above the recipe now mentions that it uses a '%' character to start a single line comment:

This version uses % to start a comment, does not consume the newline character, and returns an output of ().

If you did want to use the //...\n format you mentioned, you could replace the char parsers being used as so:

use nom::{
  IResult,
  Parser,
  error::ParseError,
  combinator::value,
  sequence::pair,
  bytes::complete::is_not,
  character::complete::char,
};

pub fn seol_comment<'a, E: ParseError<&'a str>>(i: &'a str) -> IResult<&'a str, (), E>
{
  value(
    (), // Output is thrown away.
    pair(tag("//"), is_not("\n\r"))
  ).parse(i)
}

---

Similarly, there's also now a multiline recipe also available, which can be made to match the C-style with:

use nom::{
  IResult,
  Parser,
  error::ParseError,
  combinator::value,
  bytes::complete::{tag, take_until},
};

pub fn sinline_comment<'a, E: ParseError<&'a str>>(i: &'a str) -> IResult<&'a str, (), E> {
  value(
    (), // Output is thrown away.
    (
      tag("/*"),
      take_until("*/"),
      tag("*/")
    )
  ).parse(i)
}