Add a way to make a fully generally parser about cats-parse HOT 6 CLOSED

You might want to take a look at:

https://github.com/typelevel/cats-parse/blob/main/core/shared/src/main/scala/cats/parse/Numbers.scala

Also note the repAs method that can build the string in a more efficient manner than you do here.

Lastly, you can parse a signed int32 without parsing the string and maybe failing, but it is more work: you either parse a - or not. If you don't see a - you either see 0, or 1 followed by 0 to 8 digits, etc...

This is like building a regular expression for a limited integer. It's probably worth implementing and adding to Numbers so people don't have to struggle with it.

That said, I do question if a parse error is what you want here vs an error message that says the number is too large. That can be done by using Numbers + filter (or flatMap but filter can be more efficient).

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Suppose you have another parser you'd like to embed inside a cats parse parser, that would be one example.

A second example is supporting something we could support but don't (e.g. getting access to the whole String).

I don't think it is a great idea, but it is an escape hatch if someone gets in an unusual place.

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Do you have examples of when this is necessary?

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I've got a concrete example from something I'm working on at the moment.

Unless I'm missing a standard combinator, this is currently how to parse an integer:

final val integer: Parser[Int] =
  Parser
    .charIn('0' to '9')
    .rep
    .map { chars =>
      chars
        .foldLeft(new StringBuilder(chars.length))(_ append _)
        .mkString
    }
    .flatMap { input =>
      Either
        .catchNonFatal(input.toInt)
        .fold(
          _ => Parser.failWith(s"Invalid number: $input"),
          Parser.pure
        )
    }

from cats-parse.

I do this for unsigned ints:

  def safeToInt(value: String): Option[Int] =
    Try(value.toInt).toOption

  val uintP: Parser[Int] = Numbers.digits.mapFilter(safeToInt)

from cats-parse.

Thanks for pointing me towards Numbers. Aside from the direct stuff, it's got a lot of good examples.

In my case, a parse error is desirable because I'm using it to parse command line arguments, so an out of bounds number is going to be less common than a parse error caused by an extraneous quote.

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