In parboiled2, how should I report an error in a parser action?

Question

What's the best way to report an error in a parser action in parboiled2 (I'm using v 2.1.4)?

For example, say I want to read an integer value and report an error if its not within the expected range? I tried calling fail, but that doesn't appear to be valid within a parser action. Also, I can't tell how I should provide the stack value to the test rule. Do I simply throw a ParseError exception?

To be a little more specific, consider the following rule:

def Index = rule {
  capture(oneOrMore(CharPredicate.Digit)) ~> {s => // s is a String
    val i = s.toInt
    if(i > SomeMaxIndexValue) ??? // What do I put here?
    else i
  }
}

Answer 1

You can use test for that. The trick is that actions can also return a Rule.

def Index = rule {
  capture(oneOrMore(CharPredicate.Digit)) ~> {s =>
    val i = s.toInt
    test(i <= SomeMaxIndexValue) ~ push(i)
  }
}