Scala example source code file (Pasted.scala)

This example Scala source code file (Pasted.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

boolean, compiler, continuestring, list, nsc, pasteanalyzer, pasted, promptstring, replaying, string, traversableonce, unit

The Pasted.scala Scala example source code

/* NSC -- new Scala compiler
 * Copyright 2005-2013 LAMP/EPFL
 * @author Paul Phillips
 */

package scala.tools.nsc
package interpreter

/** If it looks like they're pasting in a scala interpreter
 *  transcript, remove all the formatting we inserted so we
 *  can make some sense of it.
 *
 *  Most of the interesting code in here is due to my goal of
 *  "paste idempotence" i.e. the transcript resulting from pasting
 *  a transcript should itself be pasteable and should achieve
 *  the same result.
 */
abstract class Pasted {
  def ContinueString: String
  def PromptString: String
  def interpret(line: String): Unit

  def matchesPrompt(line: String) = matchesString(line, PromptString)
  def matchesContinue(line: String) = matchesString(line, ContinueString)
  def running = isRunning

  private def matchesString(line: String, target: String): Boolean = (
    (line startsWith target) ||
    (line.nonEmpty && " \t".toSet(line.head) && matchesString(line.tail, target))
  )
  private def stripString(line: String, target: String) = line indexOf target match {
    case -1   => line
    case idx  => line drop (idx + target.length)
  }
  private var isRunning    = false
  private val resReference = """(?<!^)(res\d+)""".r
  private val resCreation  = """^\s*(res\d+):.*""".r
  private val resAssign    = """^val (res\d+).*""".r

  private class PasteAnalyzer(val lines: List[String]) {
    val referenced = lines flatMap (resReference findAllIn _.trim.stripPrefix("res")) toSet
    val cmds       = lines reduceLeft append split PromptString filterNot (_.trim == "") toList

    /** If it's a prompt or continuation line, strip the formatting bits and
     *  assemble the code.  Otherwise ship it off to be analyzed for res references
     *  and discarded.
     */
    def append(code: String, line: String): String =
      if (matchesPrompt(line)) code + "\n" + line
      else if (matchesContinue(line)) code + "\n" + stripString(line, ContinueString)
      else fixResRefs(code, line)

    /** If the line looks like
     *    res15: Int
     *
     *  and the additional conditions hold that:
     *    1) res15 is referenced from elsewhere in the transcript
     *    2) the preceding repl line is not "val res15 = ..." because that
     *    indicates it has already been "val-ified" on a previous paste
     *
     *  then we go back in time to the preceding scala> prompt and
     *  rewrite the line containing <expr> as
     *    val res15 = { <expr> }
     *  and the rest as they say is rewritten history.
     *
     *  In all other cases, discard the line.
     */
    def fixResRefs(code: String, line: String) = line match {
      case resCreation(resName) if referenced(resName) =>
        code.lastIndexOf(PromptString) match {
          case -1   => code
          case idx  =>
            val (str1, str2) = code splitAt (idx + PromptString.length)
            str2 match {
              case resAssign(`resName`) => code
              case _                    => "%sval %s = { %s }".format(str1, resName, str2)
            }
        }
      case _ => code
    }

    def run() {
      println("// Replaying %d commands from transcript.\n" format cmds.size)
      cmds foreach { cmd =>
        print(PromptString)
        interpret(cmd)
      }
    }
  }

  /** Commands start on lines beginning with "scala>" and each successive
   *  line which begins with the continuation string is appended to that command.
   *  Everything else is discarded.  When the end of the transcript is spotted,
   *  all the commands are replayed.
   */
  def apply(lines: TraversableOnce[String]) = {
    isRunning = true
    try new PasteAnalyzer(lines.toList) run()
    finally isRunning = false
  }
}