Support for predicate tests to indicate Success or Failure for parsers of T about fastparse

[lihaoyi]

Sounds reasonable. I'd just call it filter ^_^

On Mon, Jun 1, 2015 at 12:36 PM, Russ White [email protected]
wrote:

If this feature already exists I apologize for missing it.

It would be nice to have a built in construct for parsers with predicates
like this:
import fastparse._
object Parser {
def predicatedT(pred: T => Boolean): Parser[T] = P {
parser.flatMap(x => if (pred(x)) Pass.map(_ => x) else Fail)
}
val pDigits: Parser[Int] = P(CharIn('0' to '9').rep(1).!.map(_.toInt))
val pEven: Parser[Int] = predicated(pDigits)({x => x % 2 == 0})
val pOdd: Parser[Int] = predicated(pDigits)({x => x % 2 != 0})
}

object Run extends App {
import Parser._
println(pEven.parse("123"))
println(pEven.parse("124"))
println(pOdd.parse("123"))
println(pOdd.parse("124"))
}
Run...
Failure(predicated:0 / Fail:3 ..."", false)
Success(124, 3)
Success(123, 3)
Failure(predicated:0 / Fail:3 ..."", false)

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#23.

[russwyte]

That is precisely what I would suggest. :)

[lihaoyi]

Feel free to send a PR!

[russwyte]

I created PR #24 to add filter transformer.