解析带有转义单引号的字符串

Question

我想解析一个字符串，该字符串包含单引号之间的 ASCII 字符，并且可以包含连续两个 ' 的转义单引号。

'string value contained between single quotes -> '' and so on...'

结果应该是：

string value contained between single quotes -> ' and so on...

use nom::{
    bytes::complete::{tag, take_while},
    error::{ErrorKind, ParseError},
    sequence::delimited,
    IResult,
};

fn main() {
    let res = string_value::<(&str, ErrorKind)>("'abc''def'");

    assert_eq!(res, Ok(("", "abc\'def")));
}

pub fn is_ascii_char(chr: char) -> bool {
    chr.is_ascii()
}

fn string_value<'a, E: ParseError<&'a str>>(i: &'a str) -> IResult<&'a str, &'a str, E> {
    delimited(tag("'"), take_while(is_ascii_char), tag("'"))(i)
}

如何检测转义引号而不是字符串结尾？

Answer 1

这很棘手，但以下是可行的：

//# nom = "5.0.1"
use nom::{
    bytes::complete::{escaped_transform, tag},
    character::complete::none_of,
    combinator::{recognize, map_parser},
    multi::{many0, separated_list},
    sequence::delimited,
    IResult,
};

fn main() {
    let (_, res) = parse_quoted("'abc''def'").unwrap();
    assert_eq!(res, "abc'def");
    let (_, res) = parse_quoted("'xy@$%!z'").unwrap();
    assert_eq!(res, "xy@$%!z");
    let (_, res) = parse_quoted("'single quotes -> '' and so on...'").unwrap();
    assert_eq!(res, "single quotes -> ' and so on...");
}

fn parse_quoted(input: &str) -> IResult<&str, String> {
    let seq = recognize(separated_list(tag("''"), many0(none_of("'"))));
    let unquote = escaped_transform(none_of("'"), '\'', tag("'"));
    let res = delimited(tag("'"), map_parser(seq, unquote), tag("'"))(input)?;

    Ok(res)
}

一些解释：

解析器 seq 可以识别在双引号和其他任何内容之间交替出现的任何序列；
unquote 将任何双引号转换为单引号；
map_parser 然后将两者组合在一起以产生所需的结果。

请注意，由于使用了escaped_transform组合子，解析结果是String而不是&str。即，有额外的分配。

Answer 2

我正在学习 nom，以下是我的尝试。

let a = r###"'string value contained between single quotes -> '' and so on...'"###;

fn parser(input: &str) -> IResult<&str, &str> {
    let len = input.chars().count() - 2;
    delimited(tag("'"), take(len), tag("'"))(input)
}

let (remaining, mut matched) = parser(a).unwrap_or_default();

let sss = matched.replace("''", "'");
matched = &sss;
println!("remaining: {:#?}", remaining);
println!("matched: {:#?}", matched);

它打印出这个结果：

remaining: ""
matched: "string value contained between single quotes -> ' and so on..."

我的测试基于 nom 6.2.1。

解析带有转义单引号的字符串

Parse string with escaped single quotes

parsing

rust

nom