在StandardTokenParsers中使用正则表达式

Question

我正在尝试在基于StandardTokenParsers的解析器中使用正则表达式.为此,我将StdLexical子类化如下:

class CustomLexical extends StdLexical{
  def regex(r: Regex): Parser[String] = new Parser[String] {
    def apply(in:Input) = r.findPrefixMatchOf(in.source.subSequence(in.offset, in.source.length)) match {
      case Some(matched) => Success(in.source.subSequence(in.offset, in.offset + matched.end).toString,
        in.drop(matched.end))
      case None => Failure("string matching regex `" + r + "' expected but " + in.first + " found", in)
    }
  }

  override def token: Parser[Token] =
    (   regex("[a-zA-Z]:\\\\[\\w\\\\?]* | /[\\w/]*".r)     ^^ { StringLit(_) }
      | identChar ~ rep( identChar | digit )               ^^ { case first ~ rest => processIdent(first :: rest mkString "") }
      | ...

但是我对如何定义利用这个的Parser有点困惑.我有一个解析器定义为:

def mTargetFolder: Parser[String] = "TargetFolder" ~> "=" ~> mFilePath

应该用于识别有效的文件路径.我试过了:

def mFilePath: Parser[String] = "[a-zA-Z]:\\\\[\\w\\\\?]* | /[\\w/]*".r

但这显然是不对的.我收到一个错误:

scala: type mismatch;
 found   : scala.util.matching.Regex
 required: McfpDSL.this.Parser[String]
    def mFilePath: Parser[String] = "[a-zA-Z]:\\\\[\\w\\\\?]* | /[\\w/]*".r
                                                                          ^

在我的StdLexical子类上使用扩展的正确方法是什么？

Answer 1

如果你真的想使用基于令牌的解析,并重用StdLexical,我建议更新"TargetFolder"的语法,以便等号后的值是一个正确的字符串文字.或者换句话说,使路径应该用引号括起来.从那时起,您不再需要扩展StdLexical.

然后是将正则表达式转换为解析器的问题.Scala已经RegexParsers为此(隐式地将正则表达式转换为a Parser[String]),但不幸的是,这不是你想要的,因为它在你处理令牌的sttream时工作在Char(type Elem = Charin RegexParsers)的流上.所以我们确实必须定义我们自己从Regex到Parser[String](但是在句法级别而不是词汇级别,或者换句话说在令牌解析器中)的转换.

import scala.util.parsing.combinator.syntactical._
import scala.util.matching.Regex
import scala.util.parsing.input._

object MyParser extends StandardTokenParsers {
  import lexical.StringLit
  def regexStringLit(r: Regex): Parser[String] = acceptMatch( 
    "string literal matching regex " + r, 
    { case StringLit( s ) if r.unapplySeq(s).isDefined => s }
  )
  lexical.delimiters += "="
  lexical.reserved += "TargetFolder"
  lazy val mTargetFolder: Parser[String] = "TargetFolder" ~> "=" ~> mFilePath
  lazy val mFilePath: Parser[String] = regexStringLit("([a-zA-Z]:\\\\[\\w\\\\?]*)|(/[\\w/]*)".r)  
  def parseTargetFolder( s: String ) = { mTargetFolder( new lexical.Scanner( s ) ) }
}

例:

scala> MyParser.parseTargetFolder("""TargetFolder = "c:\Dir1\Dir2" """)
res12: MyParser.ParseResult[String] = [1.31] parsed: c:\Dir1\Dir2

scala> MyParser.parseTargetFolder("""TargetFolder = "/Dir1/Dir2" """)
res13: MyParser.ParseResult[String] = [1.29] parsed: /Dir1/Dir2

scala> MyParser.parseTargetFolder("""TargetFolder = "Hello world" """)
res14: MyParser.ParseResult[String] =
[1.16] failure: identifier matching regex ([a-zA-Z]:\\[\w\\?]*)|(/[\w/]*) expected
TargetFolder = "Hello world"
           ^

请注意,这里也修复了你的"目标文件夹"regexp,你在两个替代方案中缺少了parens,加上不需要的空格.