Scala: Can I nudge a combinator parser to be locally greedy?
- by eed3si9n
Suppose I have an ambiguous language expressed in combinator parser. Is there a way to make certain expressions locally greedy? Here's an example of what I mean.
import scala.util.parsing.combinator._
object Example extends JavaTokenParsers {
def obj: Parser[Any] = (shortchain | longchain) ~ anyrep
def longchain: Parser[Any] = zero~zero~one~one
def shortchain: Parser[Any] = zero~zero
def anyrep: Parser[Any] = rep(any)
def any: Parser[Any] = zero | one
def zero: Parser[Any] = "0"
def one: Parser[Any] = "1"
def main(args: Array[String]) {
println(parseAll(obj, args(0) ))
}
}
After compiling, I can run it as follows:
$ scala Example 001111
[1.7] parsed: ((0~0)~List(1, 1, 1, 1))
I would like to somehow instruct the first part of obj to be locally greedy and match with longchain. If I switch the order around, it matches the longchain, but that's not because of the greediness.
def obj: Parser[Any] = (longchain | shortchain) ~ anyrep
