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To give you a feel for what grammar specification looks like with parboiled for Scala consider the following classic "calculator" example, with these rules in a simple pseudo notation:

Expression ← Term ((‘+’ / ‘-’) Term)*
Term ← Factor ((‘*’ / ‘/’) Factor)*
Factor ← Number / ‘(’ Expression ‘)’
Number ← [0-9]+

A parboiled parser definition, complete and in ready-to-compile Scala code would look like this:

import org.parboiled.scala._

class SimpleCalculator extends Parser {

  def Expression: Rule0 = rule { Term ~ zeroOrMore(anyOf("+-") ~ Term) }

  def Term = rule { Factor ~ zeroOrMore(anyOf("*/") ~ Factor) }

  def Factor = rule { Number | "(" ~ Expression ~ ")" }

  def Number = rule { oneOrMore("0" - "9") }
}


Tags: library   jvm   language development  

Last modified 07 October 2024