正则表达式 – scala中的表达式求值程序(可能有占位符？)

scala类库中内置了一个解析器组合器.由于scala库已经模块化,现在它是一个独立的项目,生活在https://github.com/scala/scala-parser-combinators.

更新：每个人都在寻找一个与scala-parser-combinators概念相似的解析器组合库,应该看看fastparse.它非常快,并且不使用宏.因此它可以作为scala-parser-combinators的替代品.

有关如何在Programming in Scala第33章“组合器解析”中使用它的一些示例.

这里有一个小语法,ast和评估员,可以帮助你入门.这缺少很多东西,如空格处理,操作符优先级等.您也不应该使用字符串来编码不同的比较运算符.但是我认为,通过这个以及Scala编程中的章节,您应该能够提出适合您需求的内容.

import scala.util.parsing.combinator.{JavaTokenParsers,PackratParsers}

sealed abstract class AST
sealed abstract class BooleanExpression extends AST
case class BooleanOperation(op: String,lhs: BooleanExpression,rhs:BooleanExpression) extends BooleanExpression
case class Comparison(op:String,rhs:Constant) extends BooleanExpression
case class Constant(value: Double) extends AST

object ConditionParser extends JavaTokenParsers with PackratParsers {

  val booleanOperator : PackratParser[String] = literal("||") | literal("&&")
  val comparisonOperator : PackratParser[String] = literal("<=") | literal(">=") | literal("==") | literal("!=") | literal("<") | literal(">")
  val constant : PackratParser[Constant] = floatingPointNumber.^^ { x => Constant(x.toDouble) }
  val comparison : PackratParser[Comparison] = (comparisonOperator ~ constant) ^^ { case op ~ rhs => Comparison(op,rhs) }
  lazy val p1 : PackratParser[BooleanExpression] = booleanOperation | comparison
  val booleanOperation = (p1 ~ booleanOperator ~ p1) ^^ { case lhs ~ op ~ rhs => BooleanOperation(op,lhs,rhs) }
}

object Evaluator {

  def evaluate(expression:BooleanExpression,value:Double) : Boolean = expression match {
    case Comparison("<=",Constant(c)) => value <= c
    case Comparison(">=",Constant(c)) => value >= c
    case Comparison("==",Constant(c)) => value == c
    case Comparison("!=",Constant(c)) => value != c
    case Comparison("<",Constant(c)) => value < c
    case Comparison(">",Constant(c)) => value > c
    case BooleanOperation("||",a,b) => evaluate(a,value) || evaluate(b,value)
    case BooleanOperation("&&",value) && evaluate(b,value)
  }
}

object Test extends App {

  def parse(text:String) : BooleanExpression = ConditionParser.parseAll(ConditionParser.p1,text).get

  val texts = Seq(
    "<2000","<2000||>20000","==1","<=3000",">0.9&&<1.1")

  val xs = Seq(0.0,1.0,100000.0)

  for {
    text <- texts
    expression = parse(text)
    x <- xs
    result = Evaluator.evaluate(expression,x)
  } {
    println(s"$text $expression $x $result")
  }
}