Scala,树结构化数据的解析器组合

Question

如何使用解析器来解析跨越多行的记录？我需要解析树数据(并最终将其转换为树数据结构).我在下面的代码中遇到了难以跟踪的解析错误,但不清楚这是否是Scala解析器的最佳方法.问题更多的是解决问题的方法,而不是调试现有的代码.

EBNF-ish语法是:

SP          = " "
CRLF        = "\r\n"
level       = "0" | "1" | "2" | "3"
varName     = {alphanum}
varValue    = {alphnum}
recordBegin = "0", varName
recordItem  = level, varName, [varValue]
record      = recordBegin, {recordItem}
file        = {record}

试图实现和测试语法:

import util.parsing.combinator._
val input = """0 fruit
1 id 2
1 name apple
2 type red
3 size large
3 origin Texas, US
2 date 2 aug 2011
0 fruit
1 id 3
1 name apple
2 type green
3 size small
3 origin Florida, US
2 date 3 Aug 2011"""

object TreeParser extends JavaTokenParsers {
  override val skipWhitespace = false
  def CRLF = "\r\n" | "\n"
  def BOF = "\\A".r
  def EOF = "\\Z".r
  def TXT = "[^\r\n]*".r
  def TXTNOSP = "[^ \r\n]*".r
  def SP = "\\s".r
  def level: Parser[Int] = "[0-3]{1}".r ^^ {v => v.toInt}
  def varName: Parser[String] = SP ~> TXTNOSP
  def varValue: Parser[String] = SP ~> TXT
  def recordBegin: Parser[Any] =  "0" ~ SP ~ varName ~ CRLF
  def recordItem: Parser[(Int,String,String)] = level ~ varValue ~ opt(varValue) <~ CRLF ^^
    {case l ~ f ~ v => (l,f,v.map(_+"").getOrElse(""))}
  def record: Parser[List[(Int,String,String)]] = recordBegin ~> rep(recordItem)
  def file: Parser[List[List[(Int,String,String)]]] = rep(record) <~ EOF
  def parse(input: String) = parseAll(file, input)
}

val result = TreeParser.parse(input).get
result.foreach(println)

Answer 1

正如丹尼尔所说，你应该更好地让解析器处理空格跳过，以最小化你的代码。但是，您可能需要调整该whitespace值，以便可以显式匹配行尾。我在下面这样做是为了防止解析器在没有定义记录值的情况下移动到下一行。

如果您想匹配字母单词，请尽可能尝试使用JavaTokenParserslike中定义的解析器。ident

为了简化错误跟踪，请执行NoSuccess匹配，parseAll以便您可以看到解析器在哪个点失败。

import util.parsing.combinator._

val input = """0 fruit
1 id 2
1 name apple
2 type red
3 size large
3 origin Texas, US
2 var_without_value
2 date 2 aug 2011
0 fruit
1 id 3
1 name apple
2 type green
3 size small
3 origin Florida, US
2 date 3 Aug 2011"""

object TreeParser extends JavaTokenParsers {
  override val whiteSpace = """[ \t]+""".r

  val level = """[1-3]{1}""".r

  val value = """[a-zA-Z0-9_, ]*""".r
  val eol = """[\r?\n]+""".r

  def recordBegin = "0" ~ ident <~ eol

  def recordItem = level ~ ident ~ opt(value) <~ opt(eol) ^^ {
    case l ~ n ~ v => (l.toInt, n, v.getOrElse(""))
  }

  def record = recordBegin ~> rep1(recordItem)

  def file = rep1(record)

  def parse(input: String) = parseAll(file, input) match {
    case Success(result, _) => result
    case NoSuccess(msg, _) => throw new RuntimeException("Parsing Failed:" + msg)
  }
}

val result = TreeParser.parse(input)
result.foreach(println)