Regular expression

Kotlin introduces additional types like Regex for working with regular expressions. It uses kotlin.text.MatchResult that may be confused with java.util.regex.MatchResult.

// parse text with java library
val src = "123 23 45 67"

val patterns = arrayOf(
      Pattern.compile("\\d+"),
      Pattern.compile("\\s+"))

val matcher: Matcher = patterns[0].matcher(src).apply{
      region(0, src.length)
}

var foundMatch = false

with(matcher) {
    while (regionStart() < regionEnd()) {
        foundMatch = false
        patterns.forEachIndexed { index, pattern ->
            usePattern(pattern)

            if (lookingAt()) {
                // do something
                println("found match for ${patterns[index]} : ${src.substring(start(), end())}")
                
                foundMatch = true
                region(end(), regionEnd())
                return@forEachIndexed
            }
        }

       if (!foundMatch) throw IllegalStateException("Unknown token at ${regionStart()}")
    }
}


if (!foundMatch) 
    throw IllegalStateException("Unknown token at ${matcher.regionStart()}")
}

Follow link to read common regular expression syntax.