CH04-Scala Example

首先是一个计算器的文法定义：

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Expression <- Term (('+' / '-') Term)*
Term <- Factor (('*' / '/') Factor)*
Factor <- Number / '(' Expression ')'
Number <- [0-9]+

然后是基于 Scala 代码的解析器定义：

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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") }
}

最后是对该解析器的应用：

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val input = "1+2"
val parser = new SimpleCalculator { override val buildParseTree = true }
val result = ReportingParseRunner(parser.Expression).run(input)
val parseTreePrintOut = org.parboiled.support.ParseTreeUtils.printNodeTree(result)
println(parseTreePrintOut)