Basic Recursive Parser

Parser.kt

class Parser(private val rules: List<Rule>) {

  fun parse(source: CharSequence): List<Node> {
    val ast = ArrayList<Node>()
    var mutableSource = source

    while (mutableSource.isNotEmpty()) {      
      
      // Find a rule that matches the source.
      for (rule in rules) {
       
        val matcher = rule.pattern.matcher(mutableSource)
        if (matcher.find()) {
          // Grab the text that matched the rule.
          // This looks like **...text...** for the bold rule.
          val match = matcher.group()
          
          // Trim off the part of the source that matches the rule.
          // This step is why Rules must only match the beginning of the source!
          mutableSource = mutableSource.subSequence(match.length, mutableSource.length)

          // Pass the matched text to the rule for further processing.
          // Then add the generated node to the result.
          val node = rule.parse(matcher, this)
          ast.add(node)
          
          // We have matched a rule and modified the source.
          // Start our search for a matching rule from the beginning.
          break
        }
      }
    }

    return ast
  }
}