我需要从文本中解析占位符,例如abc $$FOO$$ cba
. 我用 Scala 的解析器组合器破解了一些东西,但我对这个解决方案并不满意。
特别是,我在正则表达式中使用了零宽度匹配器(?=(\$\$|\z))
来停止解析文本并开始解析占位符。这听起来非常接近于在scala 邮件列表中讨论的恶作剧和色彩缤纷的恶作剧(这激发了这个问题的标题。)
所以,挑战:修复我的解析器在没有这个黑客的情况下工作。我希望看到从问题到您的解决方案的清晰进展,因此我可以替换随机组装组合器直到测试通过的策略。
import scala.util.parsing.combinator.RegexParsers
object PlaceholderParser extends RegexParsers {
sealed abstract class Element
case class Text(text: String) extends Element
case class Placeholder(key: String) extends Element
override def skipWhitespace = false
def parseElements(text: String): List[Element] = parseAll(elements, text) match {
case Success(es, _) => es
case NoSuccess(msg, _) => error("Could not parse: [%s]. Error: %s".format(text, msg))
}
def parseElementsOpt(text: String): ParseResult[List[Element]] = parseAll(elements, text)
lazy val elements: Parser[List[Element]] = rep(element)
lazy val element: Parser[Element] = placeholder ||| text
lazy val text: Parser[Text] = """(?ims).+?(?=(\$\$|\z))""".r ^^ Text.apply
lazy val placeholder: Parser[Placeholder] = delimiter ~> """[\w. ]+""".r <~ delimiter ^^ Placeholder.apply
lazy val delimiter: Parser[String] = literal("$$")
}
import org.junit.{Assert, Test}
class PlaceholderParserTest {
@Test
def parse1 = check("a quick brown $$FOX$$ jumped over the lazy $$DOG$$")(Text("a quick brown "), Placeholder("FOX"), Text(" jumped over the lazy "), Placeholder("DOG"))
@Test
def parse2 = check("a quick brown $$FOX$$!")(Text("a quick brown "), Placeholder("FOX"), Text("!"))
@Test
def parse3 = check("a quick brown $$FOX$$!\n!")(Text("a quick brown "), Placeholder("FOX"), Text("!\n!"))
@Test
def parse4 = check("a quick brown $$F.O X$$")(Text("a quick brown "), Placeholder("F.O X"))
def check(text: String)(expected: Element*) = Assert.assertEquals(expected.toList, parseElements(text))
}