Monad prsing inspired parsing in JS / copy from codesandbox just not to lose it

index.js

const skip = (parser) => (text) => {
  const parsed = parser(text);
  if (parsed.length === 0) {
    return parsed;
  }
  return [{ parsed: [], text: parsed[0].text }];
};
const chain = (f) => (parser1) => (parser2) => (text) => {
  const parsed = parser1(text);
  if (parsed.length === 0) {
    return parsed;
  }
  const parsedNext = parser2(parsed[0].text);
  return parsedNext.length === 0
    ? parsedNext
    : [
        {
          parsed: f(parsed[0].parsed)(parsedNext[0].parsed),
          text: parsedNext[0].text
        }
      ];
};

const both = chain((x) => (y) => x.concat(y));
const bothsep = chain((x) => (y) => [x, y].flat());
const any = (parser1) => (parser2) => (text) => {
  const parsed = parser1(text);
  return parsed.length === 0 ? parser2(text) : parsed;
};
const parse = (parser) => (text) => {
  const parsed = parser(text);
  return parsed.length === 0 ? null : parsed[0].parsed;
};
const parserNothing = (text) => (text.length > 0 ? [{ parsed: [], text }] : []);
const parserItem = (text) =>
  text.length > 0 ? [{ parsed: text[0], text: text.slice(1) }] : [];
const parserSat = (p) => (text) => {
  const parsed = parserItem(text);
  return parsed.length === 0 || !p(parsed[0].parsed) ? [] : parsed;
};
const parserChar = (c) => parserSat((x) => x === c);
const parserMany = (parser) => (text) =>
  text.length === 0
    ? [{ parsed: [], text }]
    : any(parserSome(parser))(parserNothing)(text);
const parserSome = (parser) => (text) =>
  text.length === 0 ? [] : both(parser)(parserMany(parser))(text);
const parserWS = parserSat((x) => /\s/.test(x));
const parserSpace = parserSat((x) => /[ \t]/.test(x));
const parserNL = parserSat((x) => /[\r\n]/.test(x));
const parserSomeLine = both(parserMany(parserSat((x) => !/[\r\n]/.test(x))))(
  parserNL
);
// const parserEmptyLine = both(parserMany(parserSpace))(parserNL);
const parserDigit = parserSat((x) => /[0-9]/.test(x));
const parserLetter = parserSat((x) => /[a-zA-Z]/.test(x));
const parserString = (s) => (text) => {
  if (s.length === 0) {
    return [{ parsed: [], text }];
  }
  const parsed = both(parserChar(s[0]))(parserString(s.slice(1)))(text);
  if (parsed.length === 0) {
    return parsed;
  }
  return [{ parsed: parsed[0].parsed, text: parsed[0].text }];
};
const parserNumber = (text) => {
  const parsed = parserSome(parserDigit)(text);
  if (parsed.length === 0) {
    return parsed;
  }
  return [{ parsed: parseInt(parsed[0].parsed, 10), text: parsed[0].text }];
};
const parserSomeString = parserMany(any(parserLetter)(parserDigit));
const parserLabel = (text) => {
  const parsed = bothsep(skip(parserChar("[")))(
    bothsep(parserMany(parserLetter))(
      skip(both(parserChar("]"))(parserMany(parserWS)))
    )
  )(text);
  return parsed.length === 0
    ? parsed
    : [{ parsed: parsed[0].parsed[0], text: parsed[0].text }];
};
const parserKey = (k) => (text) => {
  const parsed = bothsep(skip(parserMany(parserSpace)))(
    bothsep(skip(parserString(k)))(
      bothsep(skip(both(parserChar(":"))(parserMany(parserSpace))))(
        bothsep(parserNumber)(skip(parserSomeLine))
      )
    )
  )(text);
  return parsed.length === 0
    ? parsed
    : [{ parsed: [{ [k]: parsed[0].parsed[0] }], text: parsed[0].text }];
};
const parserAnyKey = both(parserMany(parserSpace))(
  both(parserSomeString)(
    both(parserChar(":"))(
      both(parserMany(parserSpace))(both(parserSomeString)(parserSomeLine))
    )
  )
);
const parserAmount = parserKey("amount");
const parserPrice = parserKey("price");
const parserComment = both(skip(parserMany(parserSpace)))(
  both(skip(parserChar("#")))(parserSomeLine)
);
const parserSection = (text) => {
  const parsed = bothsep(skip(parserMany(any(parserWS)(parserComment))))(
    bothsep(parserLabel)(
      parserMany(
        any(any(parserAmount)(parserPrice))(
          skip(any(any(parserComment)(parserAnyKey))(parserSome(parserWS)))
        )
      )
    )
  )(text);
  return parsed.length === 0
    ? parsed
    : [
        {
          parsed: [
            Object.assign(
              { name: parsed[0].parsed[0] },
              ...parsed[0].parsed.slice(1)
            )
          ],
          text: parsed[0].text
        }
      ];
};
const parserConfig = parserMany(parserSection);

const main = () => {
  const text = `


# our products
[qwer]
    price: 30
    # something 
    something: other
    amount: 5
[asdf]
    price: 700
    # somethingelse 
    somethingelse: other-31
    amount: 1

#other products
[fdfd]
  # one more comment
      amount: 7
[vbnm]
  amount: 42
    price: 55
`;
  console.log(JSON.stringify(parse(parserConfig)(text), null, "  "));
};
main();