ScalaTest/src/ExPackratParser.scala - main - EugenyCh7/JavaAndScalaLessons

ScalaTest/src/ExPackratParser.scala
70 строк2 KB
Eugeny Chekmarev
right whiteSpace
20 июн 2021, 21:00
20 июн 2021, 21:00b6ceb6c
import scala.util.matching.Regex
import scala.util.parsing.combinator.{PackratParsers, RegexParsers}
import scala.util.parsing.input.CharSequenceReader

object ExPackratParser extends App {
  class ExprParser extends RegexParsers with PackratParsers {
    val number: PackratParser[Double] = "[+-]?[0-9]+".r ^^ (_.toDouble)

    lazy val atom: PackratParser[Double] = {
      "(" ~> expr <~ ")" | number
    }

    lazy val power: PackratParser[Double] = {
      atom ~ rep("^" ~> atom) ^^ {
        case first ~ list =>
          (first :: list).foldRight(1.0)(Math.pow)
      }
    }

    lazy val mul: PackratParser[Double] = {
      power ~ rep(("*" | "/") ~ power) ^^ {
        case first ~ list =>
          list.foldLeft(first)((result, next) => {
            next match {
              case "*" ~ x => result * x
              case "/" ~ x => result / x
            }
          })
      }
    }

    lazy val expr: PackratParser[Double] = {
      mul ~ rep(("+" | "-") ~ mul) ^^ {
        case first ~ list =>
          list.foldLeft(first)((result, next) => {
            next match {
              case "+" ~ x => result + x
              case "-" ~ x => result - x
            }
          })
      }
    }

    def parseAll[T](p: Parser[T], input: String): ParseResult[T] = {
      phrase(p)(new PackratReader(new CharSequenceReader(input)))
    }

    override val whiteSpace: Regex = "[ \t]".r
  }

  List(
    "10 - 9 + 8 - 7 + 6 - 5",
    "2 * 3 * 4",
    "1 / 2 / 3",
    "100 + (2 + 3) - (12 + 13)",
    "(1 + 1 + 1) / (2 + 2 + 2) / (4)",
    "4 ^ 3 ^ 2",
    "(2 * 4 / 2) ^ ((1 + 1) / 2 * 3) ^ (1 * 1 + 0 + 1)",
    "-100",
    "-100 - 100"
  ).foreach(input => {
    val parser = new ExprParser
    val result = parser.parseAll(parser.expr, input)
    print(s"$input -> ")
    if (result.successful)
      println(result.get)
    else
      println("<fail>")
  })
}