Scala Parser Combinator

Question

I am trying to write a Scala Parser combinator for the following input.

The input can be

10
(10)
((10)))
(((10)))

Here the number of brackets can keep on growing. but they should always match. So parsing should fail for ((((10)))

The result of parsing should always be the number at the center

I wrote the following parser

import scala.util.parsing.combinator._
class MyParser extends RegexParsers {
  def i = "[0-9]+".r ^^ (_.toInt)
  def n = "(" ~ i ~ ")" ^^ {case _ ~ b ~ _ => b.toInt}
  def expr = i | n
}
val parser = new MyParser
parser.parseAll(parser.expr, "10")
parser.parseAll(parser.expr, "(10)")

but now how do I handle the case where the number of brackets keep growing but matched?

Alexey Romanov · Accepted Answer · 2019-09-17 07:34:20Z

4

Easy, just make the parser recursive:

class MyParser extends RegexParsers {
  def i = "[0-9]+".r ^^ (_.toInt)
  def expr: Parser[Int] = i | "(" ~ expr ~ ")" ^^ {case _ ~ b ~ _ => b.toInt}
}

(but note that scala-parser-combinators has trouble with left-recursive definitions: Recursive definitions with scala-parser-combinators)

answered Sep 17, 2019 at 7:34

Alexey Romanov

172k38 gold badges329 silver badges509 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Scala Parser Combinator

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related