地图上的解析器组合器匹配

Question

I'm writing romanization tool using Scala's pattern combinators.

In one of the parsers I want to be able to match on some set of string values and transform them into corresponding values.

Namely, I use Map[String, String] to translate between these values, but I did not find a way to match on map's keys without using separate regular expression.

object Transliteration extends RegexParsers {
  private[text] val diphthongsMap = Map(
    "ай" -> "ay",
    "ей" -> "ey",
    "ий" -> "iy",
    "ой" -> "oy",
    "уй" -> "uy",
    "ый" -> "yi",
    "эй" -> "ey",
    "юй" -> "yuy",
    "яй" -> "yay"
  )

 def diphthong: Parser[String] =
    """ай|ей|ий|ой|уй|ый|эй|юй|яй""".r ^^ { diphthongsMap(_) }

 def text: Parser[String] =
    rep1(notSymbols, extendedWord) ^^ { _.mkString }

 [... bunch of other parsers ...]

  def translatePhrase(phrase: String): String =
    parseAll(text, phrase).get
}

Can I ditch explicit regular expression entirely? Maybe write custom Parser?

EDIT: I wasn't entirely clear that I just want more efficient way of coding diphthong method without hardcode, not rewriting the whole logic of the program.

Answer 1

A custom parser is probably not needed. One solution is to fold on the map:

def romanize(cyrillicString: String) = 
  diphthongsMap.foldLeft(cyrillicString) { 
    case (s, (from, to)) => s.replace(from, to) 
  }

although this solution isn't very efficient, with an approximate runtime of O(N^2) although could be okay to use for shorter text, as the cost of setting up a parser or a regex can be amortized.