Question

我使用解析器组合器编写了一个scala解析器：

  case class KW(str: String) {

    val parser: Parser[String] = str
  }

  implicit class SymbolView(symbol: Symbol) {

    val $: KW = {
      KW(symbol.name.toLowerCase())
    }
  }

  implicit def ks2Parser(ks: KW): Parser[String] = ks.parser

  val _DELETE = 'delete $
  val _REMOVE = 'remove $
  val _DROP = 'drop $
  val DELETE = _DELETE | _REMOVE | _DROP

  lexical.reserved ++= Seq("delete", "remove", "drop")

  val scanner: lexical.Scanner = new lexical.Scanner("delete")

  phrase(DELETE).apply(scanner)

然而，scala解析器给我这个错误：

failure: You are trying to parse "drop", but it is neither contained in the delimiters list, nor in the reserved keyword list of your lexical object

我非常确定“删除”和“删除”都包含在词汇的保留关键字列表中（我在调试模式下都找到了）。所以这个错误信息显然是错误的。它是scala解析器组合器中的错误吗？我该怎么做才能解决它？

Answer 1

当您使用$时，StandardTokenParsers.keyword最终会在行val parser: Parser[String] = str中被隐含地调用。它在调用时使用lexical.reserved的内容。当您在_DELETE添加令牌之前创建_REMOVE / _DROP / lexical.reserved解析器时，会发生这些调用。

所以要么在创建解析器之前移动该行以添加保留标记：

lexical.reserved ++= Seq("delete", "remove", "drop")

val _DELETE = 'delete $
val _REMOVE = 'remove $
val _DROP = 'drop $
val DELETE = _DELETE | _REMOVE | _DROP

或者使解析器定义def s（或lazy val s）而不是val s：

def _DELETE = 'delete $
def _REMOVE = 'remove $
def _DROP = 'drop $
def DELETE = _DELETE | _REMOVE | _DROP

Scala Parser：但它既不包含在分隔符列表中，也不包含在lexical的保留关键字列表中

1 个答案: