Scala example source code file (IMain.scala)

This example Scala source code file (IMain.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

bean, boolean, compiler, concurrent, left, list, name, nsc, reflection, request, right, string, symbol, t, type, utilities

The IMain.scala Scala example source code

/* NSC -- new Scala compiler
 * Copyright 2005-2013 LAMP/EPFL
 * @author  Martin Odersky
 */

package scala
package tools.nsc
package interpreter

import PartialFunction.cond
import scala.language.implicitConversions
import scala.beans.BeanProperty
import scala.collection.mutable
import scala.concurrent.{ Future, ExecutionContext }
import scala.reflect.runtime.{ universe => ru }
import scala.reflect.{ ClassTag, classTag }
import scala.reflect.internal.util.{ BatchSourceFile, SourceFile }
import scala.tools.util.PathResolver
import scala.tools.nsc.io.AbstractFile
import scala.tools.nsc.typechecker.{ TypeStrings, StructuredTypeStrings }
import scala.tools.nsc.util.{ ScalaClassLoader, stringFromReader, stringFromWriter, StackTraceOps }
import scala.tools.nsc.util.Exceptional.unwrap
import javax.script.{AbstractScriptEngine, Bindings, ScriptContext, ScriptEngine, ScriptEngineFactory, ScriptException, CompiledScript, Compilable}

/** An interpreter for Scala code.
 *
 *  The main public entry points are compile(), interpret(), and bind().
 *  The compile() method loads a complete Scala file.  The interpret() method
 *  executes one line of Scala code at the request of the user.  The bind()
 *  method binds an object to a variable that can then be used by later
 *  interpreted code.
 *
 *  The overall approach is based on compiling the requested code and then
 *  using a Java classloader and Java reflection to run the code
 *  and access its results.
 *
 *  In more detail, a single compiler instance is used
 *  to accumulate all successfully compiled or interpreted Scala code.  To
 *  "interpret" a line of code, the compiler generates a fresh object that
 *  includes the line of code and which has public member(s) to export
 *  all variables defined by that code.  To extract the result of an
 *  interpreted line to show the user, a second "result object" is created
 *  which imports the variables exported by the above object and then
 *  exports members called "$eval" and "$print". To accomodate user expressions
 *  that read from variables or methods defined in previous statements, "import"
 *  statements are used.
 *
 *  This interpreter shares the strengths and weaknesses of using the
 *  full compiler-to-Java.  The main strength is that interpreted code
 *  behaves exactly as does compiled code, including running at full speed.
 *  The main weakness is that redefining classes and methods is not handled
 *  properly, because rebinding at the Java level is technically difficult.
 *
 *  @author Moez A. Abdel-Gawad
 *  @author Lex Spoon
 */
class IMain(@BeanProperty val factory: ScriptEngineFactory, initialSettings: Settings, protected val out: JPrintWriter) extends AbstractScriptEngine with Compilable with Imports {
  imain =>

  setBindings(createBindings, ScriptContext.ENGINE_SCOPE)
  object replOutput extends ReplOutput(settings.Yreploutdir) { }

  @deprecated("Use replOutput.dir instead", "2.11.0")
  def virtualDirectory = replOutput.dir
  // Used in a test case.
  def showDirectory() = replOutput.show(out)

  private[nsc] var printResults               = true      // whether to print result lines
  private[nsc] var totalSilence               = false     // whether to print anything
  private var _initializeComplete             = false     // compiler is initialized
  private var _isInitialized: Future[Boolean] = null      // set up initialization future
  private var bindExceptions                  = true      // whether to bind the lastException variable
  private var _executionWrapper               = ""        // code to be wrapped around all lines

  /** We're going to go to some trouble to initialize the compiler asynchronously.
   *  It's critical that nothing call into it until it's been initialized or we will
   *  run into unrecoverable issues, but the perceived repl startup time goes
   *  through the roof if we wait for it.  So we initialize it with a future and
   *  use a lazy val to ensure that any attempt to use the compiler object waits
   *  on the future.
   */
  private var _classLoader: util.AbstractFileClassLoader = null                              // active classloader
  private val _compiler: ReplGlobal                 = newCompiler(settings, reporter)   // our private compiler

  def compilerClasspath: Seq[java.net.URL] = (
    if (isInitializeComplete) global.classPath.asURLs
    else new PathResolver(settings).result.asURLs  // the compiler's classpath
  )
  def settings = initialSettings
  // Run the code body with the given boolean settings flipped to true.
  def withoutWarnings[T](body: => T): T = beQuietDuring {
    val saved = settings.nowarn.value
    if (!saved)
      settings.nowarn.value = true

    try body
    finally if (!saved) settings.nowarn.value = false
  }

  /** construct an interpreter that reports to Console */
  def this(settings: Settings, out: JPrintWriter) = this(null, settings, out)
  def this(factory: ScriptEngineFactory, settings: Settings) = this(factory, settings, new NewLinePrintWriter(new ConsoleWriter, true))
  def this(settings: Settings) = this(settings, new NewLinePrintWriter(new ConsoleWriter, true))
  def this(factory: ScriptEngineFactory) = this(factory, new Settings())
  def this() = this(new Settings())

  lazy val formatting: Formatting = new Formatting {
    val prompt = Properties.shellPromptString
  }
  lazy val reporter: ReplReporter = new ReplReporter(this)

  import formatting._
  import reporter.{ printMessage, withoutTruncating }

  // This exists mostly because using the reporter too early leads to deadlock.
  private def echo(msg: String) { Console println msg }
  private def _initSources = List(new BatchSourceFile("<init>", "class $repl_$init { }"))
  private def _initialize() = {
    try {
      // if this crashes, REPL will hang its head in shame
      val run = new _compiler.Run()
      assert(run.typerPhase != NoPhase, "REPL requires a typer phase.")
      run compileSources _initSources
      _initializeComplete = true
      true
    }
    catch AbstractOrMissingHandler()
  }
  private def tquoted(s: String) = "\"\"\"" + s + "\"\"\""
  private val logScope = scala.sys.props contains "scala.repl.scope"
  private def scopelog(msg: String) = if (logScope) Console.err.println(msg)

  // argument is a thunk to execute after init is done
  def initialize(postInitSignal: => Unit) {
    synchronized {
      if (_isInitialized == null) {
        _isInitialized =
          Future(try _initialize() finally postInitSignal)(ExecutionContext.global)
      }
    }
  }
  def initializeSynchronous(): Unit = {
    if (!isInitializeComplete) {
      _initialize()
      assert(global != null, global)
    }
  }
  def isInitializeComplete = _initializeComplete

  lazy val global: Global = {
    if (!isInitializeComplete) _initialize()
    _compiler
  }

  import global._
  import definitions.{ ObjectClass, termMember, dropNullaryMethod}

  lazy val runtimeMirror = ru.runtimeMirror(classLoader)

  private def noFatal(body: => Symbol): Symbol = try body catch { case _: FatalError => NoSymbol }

  def getClassIfDefined(path: String)  = (
           noFatal(runtimeMirror staticClass path)
    orElse noFatal(rootMirror staticClass path)
  )
  def getModuleIfDefined(path: String) = (
           noFatal(runtimeMirror staticModule path)
    orElse noFatal(rootMirror staticModule path)
  )

  implicit class ReplTypeOps(tp: Type) {
    def andAlso(fn: Type => Type): Type = if (tp eq NoType) tp else fn(tp)
  }

  // TODO: If we try to make naming a lazy val, we run into big time
  // scalac unhappiness with what look like cycles.  It has not been easy to
  // reduce, but name resolution clearly takes different paths.
  object naming extends {
    val global: imain.global.type = imain.global
  } with Naming {
    // make sure we don't overwrite their unwisely named res3 etc.
    def freshUserTermName(): TermName = {
      val name = newTermName(freshUserVarName())
      if (replScope containsName name) freshUserTermName()
      else name
    }
    def isInternalTermName(name: Name) = isInternalVarName("" + name)
  }
  import naming._

  object deconstruct extends {
    val global: imain.global.type = imain.global
  } with StructuredTypeStrings

  lazy val memberHandlers = new {
    val intp: imain.type = imain
  } with MemberHandlers
  import memberHandlers._

  /** Temporarily be quiet */
  def beQuietDuring[T](body: => T): T = {
    val saved = printResults
    printResults = false
    try body
    finally printResults = saved
  }
  def beSilentDuring[T](operation: => T): T = {
    val saved = totalSilence
    totalSilence = true
    try operation
    finally totalSilence = saved
  }

  def quietRun[T](code: String) = beQuietDuring(interpret(code))

  /** takes AnyRef because it may be binding a Throwable or an Exceptional */
  private def withLastExceptionLock[T](body: => T, alt: => T): T = {
    assert(bindExceptions, "withLastExceptionLock called incorrectly.")
    bindExceptions = false

    try     beQuietDuring(body)
    catch   logAndDiscard("withLastExceptionLock", alt)
    finally bindExceptions = true
  }

  def executionWrapper = _executionWrapper
  def setExecutionWrapper(code: String) = _executionWrapper = code
  def clearExecutionWrapper() = _executionWrapper = ""

  /** interpreter settings */
  lazy val isettings = new ISettings(this)

  /** Instantiate a compiler.  Overridable. */
  protected def newCompiler(settings: Settings, reporter: reporters.Reporter): ReplGlobal = {
    settings.outputDirs setSingleOutput replOutput.dir
    settings.exposeEmptyPackage.value = true
    new Global(settings, reporter) with ReplGlobal { override def toString: String = "<global>" }
  }

  /** Parent classloader.  Overridable. */
  protected def parentClassLoader: ClassLoader =
    settings.explicitParentLoader.getOrElse( this.getClass.getClassLoader() )

  /* A single class loader is used for all commands interpreted by this Interpreter.
     It would also be possible to create a new class loader for each command
     to interpret.  The advantages of the current approach are:

       - Expressions are only evaluated one time.  This is especially
         significant for I/O, e.g. "val x = Console.readLine"

     The main disadvantage is:

       - Objects, classes, and methods cannot be rebound.  Instead, definitions
         shadow the old ones, and old code objects refer to the old
         definitions.
  */
  def resetClassLoader() = {
    repldbg("Setting new classloader: was " + _classLoader)
    _classLoader = null
    ensureClassLoader()
  }
  final def ensureClassLoader() {
    if (_classLoader == null)
      _classLoader = makeClassLoader()
  }
  def classLoader: util.AbstractFileClassLoader = {
    ensureClassLoader()
    _classLoader
  }

  def backticked(s: String): String = (
    (s split '.').toList map {
      case "_"                               => "_"
      case s if nme.keywords(newTermName(s)) => s"`$s`"
      case s                                 => s
    } mkString "."
  )
  def readRootPath(readPath: String) = getModuleIfDefined(readPath)

  abstract class PhaseDependentOps {
    def shift[T](op: => T): T

    def path(name: => Name): String = shift(path(symbolOfName(name)))
    def path(sym: Symbol): String = backticked(shift(sym.fullName))
    def sig(sym: Symbol): String  = shift(sym.defString)
  }
  object typerOp extends PhaseDependentOps {
    def shift[T](op: => T): T = exitingTyper(op)
  }
  object flatOp extends PhaseDependentOps {
    def shift[T](op: => T): T = exitingFlatten(op)
  }

  def originalPath(name: String): String = originalPath(name: TermName)
  def originalPath(name: Name): String   = typerOp path name
  def originalPath(sym: Symbol): String  = typerOp path sym
  def flatPath(sym: Symbol): String      = flatOp shift sym.javaClassName
  def translatePath(path: String) = {
    val sym = if (path endsWith "$") symbolOfTerm(path.init) else symbolOfIdent(path)
    sym.toOption map flatPath
  }
  def translateEnclosingClass(n: String) = symbolOfTerm(n).enclClass.toOption map flatPath

  private class TranslatingClassLoader(parent: ClassLoader) extends util.AbstractFileClassLoader(replOutput.dir, parent) {
    /** Overridden here to try translating a simple name to the generated
     *  class name if the original attempt fails.  This method is used by
     *  getResourceAsStream as well as findClass.
     */
    override protected def findAbstractFile(name: String): AbstractFile =
      super.findAbstractFile(name) match {
        case null if _initializeComplete => translatePath(name) map (super.findAbstractFile(_)) orNull
        case file => file
      }
  }
  private def makeClassLoader(): util.AbstractFileClassLoader =
    new TranslatingClassLoader(parentClassLoader match {
      case null   => ScalaClassLoader fromURLs compilerClasspath
      case p      => new ScalaClassLoader.URLClassLoader(compilerClasspath, p)
    })

  // Set the current Java "context" class loader to this interpreter's class loader
  def setContextClassLoader() = classLoader.setAsContext()

  def allDefinedNames: List[Name]  = exitingTyper(replScope.toList.map(_.name).sorted)
  def unqualifiedIds: List[String] = allDefinedNames map (_.decode) sorted

  /** Most recent tree handled which wasn't wholly synthetic. */
  private def mostRecentlyHandledTree: Option[Tree] = {
    prevRequests.reverse foreach { req =>
      req.handlers.reverse foreach {
        case x: MemberDefHandler if x.definesValue && !isInternalTermName(x.name) => return Some(x.member)
        case _ => ()
      }
    }
    None
  }

  private def updateReplScope(sym: Symbol, isDefined: Boolean) {
    def log(what: String) {
      val mark = if (sym.isType) "t " else "v "
      val name = exitingTyper(sym.nameString)
      val info = cleanTypeAfterTyper(sym)
      val defn = sym defStringSeenAs info

      scopelog(f"[$mark$what%6s] $name%-25s $defn%s")
    }
    if (ObjectClass isSubClass sym.owner) return
    // unlink previous
    replScope lookupAll sym.name foreach { sym =>
      log("unlink")
      replScope unlink sym
    }
    val what = if (isDefined) "define" else "import"
    log(what)
    replScope enter sym
  }

  def recordRequest(req: Request) {
    if (req == null)
      return

    prevRequests += req

    // warning about serially defining companions.  It'd be easy
    // enough to just redefine them together but that may not always
    // be what people want so I'm waiting until I can do it better.
    exitingTyper {
      req.defines filterNot (s => req.defines contains s.companionSymbol) foreach { newSym =>
        val oldSym = replScope lookup newSym.name.companionName
        if (Seq(oldSym, newSym).permutations exists { case Seq(s1, s2) => s1.isClass && s2.isModule }) {
          replwarn(s"warning: previously defined $oldSym is not a companion to $newSym.")
          replwarn("Companions must be defined together; you may wish to use :paste mode for this.")
        }
      }
    }
    exitingTyper {
      req.imports foreach (sym => updateReplScope(sym, isDefined = false))
      req.defines foreach (sym => updateReplScope(sym, isDefined = true))
    }
  }

  private[nsc] def replwarn(msg: => String) {
    if (!settings.nowarnings)
      printMessage(msg)
  }

  def compileSourcesKeepingRun(sources: SourceFile*) = {
    val run = new Run()
    assert(run.typerPhase != NoPhase, "REPL requires a typer phase.")
    reporter.reset()
    run compileSources sources.toList
    (!reporter.hasErrors, run)
  }

  /** Compile an nsc SourceFile.  Returns true if there are
   *  no compilation errors, or false otherwise.
   */
  def compileSources(sources: SourceFile*): Boolean =
    compileSourcesKeepingRun(sources: _*)._1

  /** Compile a string.  Returns true if there are no
   *  compilation errors, or false otherwise.
   */
  def compileString(code: String): Boolean =
    compileSources(new BatchSourceFile("<script>", code))

  /** Build a request from the user. `trees` is `line` after being parsed.
   */
  private def buildRequest(line: String, trees: List[Tree]): Request = {
    executingRequest = new Request(line, trees)
    executingRequest
  }

  private def safePos(t: Tree, alt: Int): Int =
    try t.pos.start
    catch { case _: UnsupportedOperationException => alt }

  // Given an expression like 10 * 10 * 10 we receive the parent tree positioned
  // at a '*'.  So look at each subtree and find the earliest of all positions.
  private def earliestPosition(tree: Tree): Int = {
    var pos = Int.MaxValue
    tree foreach { t =>
      pos = math.min(pos, safePos(t, Int.MaxValue))
    }
    pos
  }

  private def requestFromLine(line: String, synthetic: Boolean): Either[IR.Result, Request] = {
    val content = indentCode(line)
    val trees = parse(content) match {
      case parse.Incomplete     => return Left(IR.Incomplete)
      case parse.Error          => return Left(IR.Error)
      case parse.Success(trees) => trees
    }
    repltrace(
      trees map (t => {
        // [Eugene to Paul] previously it just said `t map ...`
        // because there was an implicit conversion from Tree to a list of Trees
        // however Martin and I have removed the conversion
        // (it was conflicting with the new reflection API),
        // so I had to rewrite this a bit
        val subs = t collect { case sub => sub }
        subs map (t0 =>
          "  " + safePos(t0, -1) + ": " + t0.shortClass + "\n"
        ) mkString ""
      }) mkString "\n"
    )
    // If the last tree is a bare expression, pinpoint where it begins using the
    // AST node position and snap the line off there.  Rewrite the code embodied
    // by the last tree as a ValDef instead, so we can access the value.
    val last = trees.lastOption.getOrElse(EmptyTree)
    last match {
      case _:Assign                        => // we don't want to include assignments
      case _:TermTree | _:Ident | _:Select => // ... but do want other unnamed terms.
        val varName  = if (synthetic) freshInternalVarName() else freshUserVarName()
        val rewrittenLine = (
          // In theory this would come out the same without the 1-specific test, but
          // it's a cushion against any more sneaky parse-tree position vs. code mismatches:
          // this way such issues will only arise on multiple-statement repl input lines,
          // which most people don't use.
          if (trees.size == 1) "val " + varName + " =\n" + content
          else {
            // The position of the last tree
            val lastpos0 = earliestPosition(last)
            // Oh boy, the parser throws away parens so "(2+2)" is mispositioned,
            // with increasingly hard to decipher positions as we move on to "() => 5",
            // (x: Int) => x + 1, and more.  So I abandon attempts to finesse and just
            // look for semicolons and newlines, which I'm sure is also buggy.
            val (raw1, raw2) = content splitAt lastpos0
            repldbg("[raw] " + raw1 + "   <--->   " + raw2)

            val adjustment = (raw1.reverse takeWhile (ch => (ch != ';') && (ch != '\n'))).size
            val lastpos = lastpos0 - adjustment

            // the source code split at the laboriously determined position.
            val (l1, l2) = content splitAt lastpos
            repldbg("[adj] " + l1 + "   <--->   " + l2)

            val prefix   = if (l1.trim == "") "" else l1 + ";\n"
            // Note to self: val source needs to have this precise structure so that
            // error messages print the user-submitted part without the "val res0 = " part.
            val combined   = prefix + "val " + varName + " =\n" + l2

            repldbg(List(
              "    line" -> line,
              " content" -> content,
              "     was" -> l2,
              "combined" -> combined) map {
                case (label, s) => label + ": '" + s + "'"
              } mkString "\n"
            )
            combined
          }
        )
        // Rewriting    "foo ; bar ; 123"
        // to           "foo ; bar ; val resXX = 123"
        requestFromLine(rewrittenLine, synthetic) match {
          case Right(req) => return Right(req withOriginalLine line)
          case x          => return x
        }
      case _ =>
    }
    Right(buildRequest(line, trees))
  }

  // dealias non-public types so we don't see protected aliases like Self
  def dealiasNonPublic(tp: Type) = tp match {
    case TypeRef(_, sym, _) if sym.isAliasType && !sym.isPublic => tp.dealias
    case _                                                      => tp
  }

  /**
   *  Interpret one line of input. All feedback, including parse errors
   *  and evaluation results, are printed via the supplied compiler's
   *  reporter. Values defined are available for future interpreted strings.
   *
   *  The return value is whether the line was interpreter successfully,
   *  e.g. that there were no parse errors.
   */
  def interpret(line: String): IR.Result = interpret(line, synthetic = false)
  def interpretSynthetic(line: String): IR.Result = interpret(line, synthetic = true)
  def interpret(line: String, synthetic: Boolean): IR.Result = compile(line, synthetic) match {
    case Left(result) => result
    case Right(req)   => new WrappedRequest(req).loadAndRunReq
  }

  private def compile(line: String, synthetic: Boolean): Either[IR.Result, Request] = {
    if (global == null) Left(IR.Error)
    else requestFromLine(line, synthetic) match {
      case Left(result) => Left(result)
      case Right(req)   =>
       // null indicates a disallowed statement type; otherwise compile and
       // fail if false (implying e.g. a type error)
       if (req == null || !req.compile) Left(IR.Error) else Right(req)
    }
  }

  var code = ""
  var bound = false
  def compiled(script: String): CompiledScript = {
    if (!bound) {
      quietBind("engine" -> this.asInstanceOf[ScriptEngine])
      bound = true
    }
    val cat = code + script
    compile(cat, false) match {
      case Left(result) => result match {
        case IR.Incomplete => {
          code = cat + "\n"
          new CompiledScript {
            def eval(context: ScriptContext): Object = null
            def getEngine: ScriptEngine = IMain.this
          }
        }
        case _ => {
          code = ""
          throw new ScriptException("compile-time error")
        }
      }
      case Right(req)   => {
        code = ""
        new WrappedRequest(req)
      }
    }
  }

  private class WrappedRequest(val req: Request) extends CompiledScript {
    var recorded = false

    /** In Java we would have to wrap any checked exception in the declared
     *  ScriptException. Runtime exceptions and errors would be ok and would
     *  not need to be caught. So let us do the same in Scala : catch and
     *  wrap any checked exception, and let runtime exceptions and errors
     *  escape. We could have wrapped runtime exceptions just like other
     *  exceptions in ScriptException, this is a choice.
     */
    @throws[ScriptException]
    def eval(context: ScriptContext): Object = {
      val result = req.lineRep.evalEither match {
        case Left(e: RuntimeException) => throw e
        case Left(e: Exception) => throw new ScriptException(e)
        case Left(e) => throw e
        case Right(result) => result.asInstanceOf[Object]
      }
      if (!recorded) {
        recordRequest(req)
        recorded = true
      }
      result
    }

    def loadAndRunReq = classLoader.asContext {
      val (result, succeeded) = req.loadAndRun

      /** To our displeasure, ConsoleReporter offers only printMessage,
       *  which tacks a newline on the end.  Since that breaks all the
       *  output checking, we have to take one off to balance.
       */
      if (succeeded) {
        if (printResults && result != "")
          printMessage(result stripSuffix "\n")
        else if (isReplDebug) // show quiet-mode activity
          printMessage(result.trim.lines map ("[quiet] " + _) mkString "\n")

        // Book-keeping.  Have to record synthetic requests too,
        // as they may have been issued for information, e.g. :type
        recordRequest(req)
        IR.Success
      }
      else {
        // don't truncate stack traces
        withoutTruncating(printMessage(result))
        IR.Error
      }
    }

    def getEngine: ScriptEngine = IMain.this
  }

  /** Bind a specified name to a specified value.  The name may
   *  later be used by expressions passed to interpret.
   *
   *  @param name      the variable name to bind
   *  @param boundType the type of the variable, as a string
   *  @param value     the object value to bind to it
   *  @return          an indication of whether the binding succeeded
   */
  def bind(name: String, boundType: String, value: Any, modifiers: List[String] = Nil): IR.Result = {
    val bindRep = new ReadEvalPrint()
    bindRep.compile("""
        |object %s {
        |  var value: %s = _
        |  def set(x: Any) = value = x.asInstanceOf[%s]
        |}
      """.stripMargin.format(bindRep.evalName, boundType, boundType)
      )
    bindRep.callEither("set", value) match {
      case Left(ex) =>
        repldbg("Set failed in bind(%s, %s, %s)".format(name, boundType, value))
        repldbg(util.stackTraceString(ex))
        IR.Error

      case Right(_) =>
        val line = "%sval %s = %s.value".format(modifiers map (_ + " ") mkString, name, bindRep.evalPath)
        repldbg("Interpreting: " + line)
        interpret(line)
    }
  }
  def directBind(name: String, boundType: String, value: Any): IR.Result = {
    val result = bind(name, boundType, value)
    if (result == IR.Success)
      directlyBoundNames += newTermName(name)
    result
  }
  def directBind(p: NamedParam): IR.Result                                    = directBind(p.name, p.tpe, p.value)
  def directBind[T: ru.TypeTag : ClassTag](name: String, value: T): IR.Result = directBind((name, value))

  def rebind(p: NamedParam): IR.Result = {
    val name     = p.name
    val newType  = p.tpe
    val tempName = freshInternalVarName()

    quietRun("val %s = %s".format(tempName, name))
    quietRun("val %s = %s.asInstanceOf[%s]".format(name, tempName, newType))
  }
  def quietBind(p: NamedParam): IR.Result                               = beQuietDuring(bind(p))
  def bind(p: NamedParam): IR.Result                                    = bind(p.name, p.tpe, p.value)
  def bind[T: ru.TypeTag : ClassTag](name: String, value: T): IR.Result = bind((name, value))

  /** Reset this interpreter, forgetting all user-specified requests. */
  def reset() {
    clearExecutionWrapper()
    resetClassLoader()
    resetAllCreators()
    prevRequests.clear()
    resetReplScope()
    replOutput.dir.clear()
  }

  /** This instance is no longer needed, so release any resources
   *  it is using.  The reporter's output gets flushed.
   */
  def close() {
    reporter.flush()
  }

  /** Here is where we:
   *
   *  1) Read some source code, and put it in the "read" object.
   *  2) Evaluate the read object, and put the result in the "eval" object.
   *  3) Create a String for human consumption, and put it in the "print" object.
   *
   *  Read! Eval! Print! Some of that not yet centralized here.
   */
  class ReadEvalPrint(val lineId: Int) {
    def this() = this(freshLineId())

    val packageName = sessionNames.line + lineId
    val readName    = sessionNames.read
    val evalName    = sessionNames.eval
    val printName   = sessionNames.print
    val resultName  = sessionNames.result

    def bindError(t: Throwable) = {
      if (!bindExceptions) // avoid looping if already binding
        throw t

      val unwrapped = unwrap(t)

      // Example input: $line3.$read$$iw$$iw$
      val classNameRegex = (naming.lineRegex + ".*").r
      def isWrapperInit(x: StackTraceElement) = cond(x.getClassName) {
        case classNameRegex() if x.getMethodName == nme.CONSTRUCTOR.decoded => true
      }
      val stackTrace = unwrapped stackTracePrefixString (!isWrapperInit(_))

      withLastExceptionLock[String]({
        directBind[Throwable]("lastException", unwrapped)(StdReplTags.tagOfThrowable, classTag[Throwable])
        stackTrace
      }, stackTrace)
    }

    // TODO: split it out into a package object and a regular
    // object and we can do that much less wrapping.
    def packageDecl = "package " + packageName

    def pathTo(name: String)   = packageName + "." + name
    def packaged(code: String) = packageDecl + "\n\n" + code

    def readPath  = pathTo(readName)
    def evalPath  = pathTo(evalName)

    def call(name: String, args: Any*): AnyRef = {
      val m = evalMethod(name)
      repldbg("Invoking: " + m)
      if (args.nonEmpty)
        repldbg("  with args: " + args.mkString(", "))

      m.invoke(evalClass, args.map(_.asInstanceOf[AnyRef]): _*)
    }

    def callEither(name: String, args: Any*): Either[Throwable, AnyRef] =
      try Right(call(name, args: _*))
      catch { case ex: Throwable => Left(ex) }

    class EvalException(msg: String, cause: Throwable) extends RuntimeException(msg, cause) { }

    private def evalError(path: String, ex: Throwable) =
      throw new EvalException("Failed to load '" + path + "': " + ex.getMessage, ex)

    private def load(path: String): Class[_] = {
      try Class.forName(path, true, classLoader)
      catch { case ex: Throwable => evalError(path, unwrap(ex)) }
    }

    lazy val evalClass = load(evalPath)

    def evalEither = callEither(resultName) match {
      case Left(ex) => ex match {
          case ex: NullPointerException => Right(null)
          case ex => Left(unwrap(ex))
      }
      case Right(result) => Right(result)
    }

    def compile(source: String): Boolean = compileAndSaveRun("<console>", source)

    /** The innermost object inside the wrapper, found by
      * following accessPath into the outer one.
      */
    def resolvePathToSymbol(accessPath: String): Symbol = {
      val readRoot = readRootPath(readPath) // the outermost wrapper
      (accessPath split '.').foldLeft(readRoot: Symbol) {
        case (sym, "")    => sym
        case (sym, name)  => exitingTyper(termMember(sym, name))
      }
    }
    /** We get a bunch of repeated warnings for reasons I haven't
     *  entirely figured out yet.  For now, squash.
     */
    private def updateRecentWarnings(run: Run) {
      def loop(xs: List[(Position, String)]): List[(Position, String)] = xs match {
        case Nil                  => Nil
        case ((pos, msg)) :: rest =>
          val filtered = rest filter { case (pos0, msg0) =>
            (msg != msg0) || (pos.lineContent.trim != pos0.lineContent.trim) || {
              // same messages and same line content after whitespace removal
              // but we want to let through multiple warnings on the same line
              // from the same run.  The untrimmed line will be the same since
              // there's no whitespace indenting blowing it.
              (pos.lineContent == pos0.lineContent)
            }
          }
          ((pos, msg)) :: loop(filtered)
      }
      val warnings = loop(run.allConditionalWarnings flatMap (_.warnings))
      if (warnings.nonEmpty)
        mostRecentWarnings = warnings
    }
    private def evalMethod(name: String) = evalClass.getMethods filter (_.getName == name) match {
      case Array()       => null
      case Array(method) => method
      case xs            => sys.error("Internal error: eval object " + evalClass + ", " + xs.mkString("\n", "\n", ""))
    }
    private def compileAndSaveRun(label: String, code: String) = {
      showCodeIfDebugging(code)
      val (success, run) = compileSourcesKeepingRun(new BatchSourceFile(label, packaged(code)))
      updateRecentWarnings(run)
      success
    }
  }

  /** One line of code submitted by the user for interpretation */
  class Request(val line: String, val trees: List[Tree]) {
    def defines    = defHandlers flatMap (_.definedSymbols)
    def imports    = importedSymbols
    def value      = Some(handlers.last) filter (h => h.definesValue) map (h => definedSymbols(h.definesTerm.get)) getOrElse NoSymbol

    val lineRep = new ReadEvalPrint()

    private var _originalLine: String = null
    def withOriginalLine(s: String): this.type = { _originalLine = s ; this }
    def originalLine = if (_originalLine == null) line else _originalLine

    /** handlers for each tree in this request */
    val handlers: List[MemberHandler] = trees map (memberHandlers chooseHandler _)
    def defHandlers = handlers collect { case x: MemberDefHandler => x }

    /** list of names used by this expression */
    val referencedNames: List[Name] = handlers flatMap (_.referencedNames)

    /** def and val names */
    def termNames = handlers flatMap (_.definesTerm)
    def typeNames = handlers flatMap (_.definesType)
    def importedSymbols = handlers flatMap {
      case x: ImportHandler => x.importedSymbols
      case _                => Nil
    }

    /** Code to import bound names from previous lines - accessPath is code to
      * append to objectName to access anything bound by request.
      */
    lazy val ComputedImports(importsPreamble, importsTrailer, accessPath) =
      exitingTyper(importsCode(referencedNames.toSet, ObjectSourceCode))

    /** the line of code to compute */
    def toCompute = line

    /** The path of the value that contains the user code. */
    def fullAccessPath = s"${lineRep.readPath}$accessPath"

    /** The path of the given member of the wrapping instance. */
    def fullPath(vname: String) = s"$fullAccessPath.`$vname`"

    /** generate the source code for the object that computes this request */
    abstract class Wrapper extends IMain.CodeAssembler[MemberHandler] {
      def path = originalPath("$intp")
      def envLines = {
        if (!isReplPower) Nil // power mode only for now
        else List("def %s = %s".format("$line", tquoted(originalLine)), "def %s = Nil".format("$trees"))
      }
      def preamble = s"""
        |$preambleHeader
        |%s%s%s
      """.stripMargin.format(lineRep.readName, envLines.map("  " + _ + ";\n").mkString,
        importsPreamble, indentCode(toCompute))

      val generate = (m: MemberHandler) => m extraCodeToEvaluate Request.this

      /** A format string with %s for $read, specifying the wrapper definition. */
      def preambleHeader: String

      /** Like preambleHeader for an import wrapper. */
      def prewrap: String = preambleHeader + "\n"

      /** Like postamble for an import wrapper. */
      def postwrap: String
    }

    private class ObjectBasedWrapper extends Wrapper {
      def preambleHeader = "object %s {"

      def postamble = importsTrailer + "\n}"

      def postwrap = "}\n"
    }

    private class ClassBasedWrapper extends Wrapper {
      def preambleHeader = "class %s extends Serializable {"

      /** Adds an object that instantiates the outer wrapping class. */
      def postamble  = s"""$importsTrailer
                          |}
                          |object ${lineRep.readName} extends ${lineRep.readName}
                          |""".stripMargin

      import nme.{ INTERPRETER_IMPORT_WRAPPER => iw }

      /** Adds a val that instantiates the wrapping class. */
      def postwrap = s"}\nval $iw = new $iw\n"
    }

    private lazy val ObjectSourceCode: Wrapper =
      if (settings.Yreplclassbased) new ClassBasedWrapper else new ObjectBasedWrapper

    private object ResultObjectSourceCode extends IMain.CodeAssembler[MemberHandler] {
      /** We only want to generate this code when the result
       *  is a value which can be referred to as-is.
       */
      val evalResult = Request.this.value match {
        case NoSymbol => ""
        case sym      => "lazy val %s = %s".format(lineRep.resultName, originalPath(sym))
      }
      // first line evaluates object to make sure constructor is run
      // initial "" so later code can uniformly be: + etc
      val preamble = """
      |object %s {
      |  %s
      |  lazy val %s: String = %s {
      |    %s
      |    (""
      """.stripMargin.format(
        lineRep.evalName, evalResult, lineRep.printName,
        executionWrapper, fullAccessPath
      )

      val postamble = """
      |    )
      |  }
      |}
      """.stripMargin
      val generate = (m: MemberHandler) => m resultExtractionCode Request.this
    }

    /** Compile the object file.  Returns whether the compilation succeeded.
     *  If all goes well, the "types" map is computed. */
    lazy val compile: Boolean = {
      // error counting is wrong, hence interpreter may overlook failure - so we reset
      reporter.reset()

      // compile the object containing the user's code
      lineRep.compile(ObjectSourceCode(handlers)) && {
        // extract and remember types
        typeOf
        typesOfDefinedTerms

        // Assign symbols to the original trees
        // TODO - just use the new trees.
        defHandlers foreach { dh =>
          val name = dh.member.name
          definedSymbols get name foreach { sym =>
            dh.member setSymbol sym
            repldbg("Set symbol of " + name + " to " + symbolDefString(sym))
          }
        }

        // compile the result-extraction object
        val handls = if (printResults) handlers else Nil
        withoutWarnings(lineRep compile ResultObjectSourceCode(handls))
      }
    }

    lazy val resultSymbol = lineRep.resolvePathToSymbol(accessPath)
    def applyToResultMember[T](name: Name, f: Symbol => T) = exitingTyper(f(resultSymbol.info.nonPrivateDecl(name)))

    /* typeOf lookup with encoding */
    def lookupTypeOf(name: Name) = typeOf.getOrElse(name, typeOf(global.encode(name.toString)))

    private def typeMap[T](f: Type => T) =
      mapFrom[Name, Name, T](termNames ++ typeNames)(x => f(cleanMemberDecl(resultSymbol, x)))

    /** Types of variables defined by this request. */
    lazy val compilerTypeOf = typeMap[Type](x => x) withDefaultValue NoType
    /** String representations of same. */
    lazy val typeOf         = typeMap[String](tp => exitingTyper(tp.toString))

    lazy val definedSymbols = (
      termNames.map(x => x -> applyToResultMember(x, x => x)) ++
      typeNames.map(x => x -> compilerTypeOf(x).typeSymbolDirect)
    ).toMap[Name, Symbol] withDefaultValue NoSymbol

    lazy val typesOfDefinedTerms = mapFrom[Name, Name, Type](termNames)(x => applyToResultMember(x, _.tpe))

    /** load and run the code using reflection */
    def loadAndRun: (String, Boolean) = {
      try   { ("" + (lineRep call sessionNames.print), true) }
      catch { case ex: Throwable => (lineRep.bindError(ex), false) }
    }

    override def toString = "Request(line=%s, %s trees)".format(line, trees.size)
  }

  def createBindings: Bindings = new IBindings {
    override def put(name: String, value: Object): Object = {
      val n = name.indexOf(":")
      val p: NamedParam = if (n < 0) (name, value) else {
        val nme = name.substring(0, n).trim
        val tpe = name.substring(n + 1).trim
        NamedParamClass(nme, tpe, value)
      }
      if (!p.name.startsWith("javax.script")) bind(p)
      null
    }
  }

  @throws[ScriptException]
  def compile(script: String): CompiledScript = eval("new javax.script.CompiledScript { def eval(context: javax.script.ScriptContext): Object = { " + script + " }.asInstanceOf[Object]; def getEngine: javax.script.ScriptEngine = engine }").asInstanceOf[CompiledScript]

  @throws[ScriptException]
  def compile(reader: java.io.Reader): CompiledScript = compile(stringFromReader(reader))

  @throws[ScriptException]
  def eval(script: String, context: ScriptContext): Object = compiled(script).eval(context)

  @throws[ScriptException]
  def eval(reader: java.io.Reader, context: ScriptContext): Object = eval(stringFromReader(reader), context)

  override def finalize = close

  /** Returns the name of the most recent interpreter result.
   *  Mostly this exists so you can conveniently invoke methods on
   *  the previous result.
   */
  def mostRecentVar: String =
    if (mostRecentlyHandledTree.isEmpty) ""
    else "" + (mostRecentlyHandledTree.get match {
      case x: ValOrDefDef           => x.name
      case Assign(Ident(name), _)   => name
      case ModuleDef(_, name, _)    => name
      case _                        => naming.mostRecentVar
    })

  private var mostRecentWarnings: List[(global.Position, String)] = Nil
  def lastWarnings = mostRecentWarnings

  private lazy val importToGlobal  = global mkImporter ru
  private lazy val importToRuntime = ru.internal createImporter global
  private lazy val javaMirror = ru.rootMirror match {
    case x: ru.JavaMirror => x
    case _                => null
  }
  private implicit def importFromRu(sym: ru.Symbol): Symbol = importToGlobal importSymbol sym
  private implicit def importToRu(sym: Symbol): ru.Symbol   = importToRuntime importSymbol sym

  def classOfTerm(id: String): Option[JClass] = symbolOfTerm(id) match {
    case NoSymbol => None
    case sym      => Some(javaMirror runtimeClass importToRu(sym).asClass)
  }

  def typeOfTerm(id: String): Type = symbolOfTerm(id).tpe

  def valueOfTerm(id: String): Option[Any] = exitingTyper {
    def value() = {
      val sym0    = symbolOfTerm(id)
      val sym     = (importToRuntime importSymbol sym0).asTerm
      val module  = runtimeMirror.reflectModule(sym.owner.companionSymbol.asModule).instance
      val module1 = runtimeMirror.reflect(module)
      val invoker = module1.reflectField(sym)

      invoker.get
    }

    try Some(value()) catch { case _: Exception => None }
  }

  /** It's a bit of a shotgun approach, but for now we will gain in
   *  robustness. Try a symbol-producing operation at phase typer, and
   *  if that is NoSymbol, try again at phase flatten. I'll be able to
   *  lose this and run only from exitingTyper as soon as I figure out
   *  exactly where a flat name is sneaking in when calculating imports.
   */
  def tryTwice(op: => Symbol): Symbol = exitingTyper(op) orElse exitingFlatten(op)

  def symbolOfIdent(id: String): Symbol  = symbolOfType(id) orElse symbolOfTerm(id)
  def symbolOfType(id: String): Symbol   = tryTwice(replScope lookup (id: TypeName))
  def symbolOfTerm(id: String): Symbol   = tryTwice(replScope lookup (id: TermName))
  def symbolOfName(id: Name): Symbol     = replScope lookup id

  def runtimeClassAndTypeOfTerm(id: String): Option[(JClass, Type)] = {
    classOfTerm(id) flatMap { clazz =>
      clazz.supers find (!_.isScalaAnonymous) map { nonAnon =>
        (nonAnon, runtimeTypeOfTerm(id))
      }
    }
  }

  def runtimeTypeOfTerm(id: String): Type = {
    typeOfTerm(id) andAlso { tpe =>
      val clazz      = classOfTerm(id) getOrElse { return NoType }
      val staticSym  = tpe.typeSymbol
      val runtimeSym = getClassIfDefined(clazz.getName)

      if ((runtimeSym != NoSymbol) && (runtimeSym != staticSym) && (runtimeSym isSubClass staticSym))
        runtimeSym.info
      else NoType
    }
  }

  def cleanTypeAfterTyper(sym: => Symbol): Type = {
    exitingTyper(
      dealiasNonPublic(
        dropNullaryMethod(
          sym.tpe_*
        )
      )
    )
  }
  def cleanMemberDecl(owner: Symbol, member: Name): Type =
    cleanTypeAfterTyper(owner.info nonPrivateDecl member)

  object exprTyper extends {
    val repl: IMain.this.type = imain
  } with ExprTyper { }

  /** Parse a line into and return parsing result (error, incomplete or success with list of trees) */
  object parse {
    abstract sealed class Result
    case object Error extends Result
    case object Incomplete extends Result
    case class Success(trees: List[Tree]) extends Result

    def apply(line: String): Result = debugging(s"""parse("$line")""")  {
      var isIncomplete = false
      reporter.withIncompleteHandler((_, _) => isIncomplete = true) {
        reporter.reset()
        val trees = newUnitParser(line).parseStats()
        if (reporter.hasErrors) Error
        else if (isIncomplete) Incomplete
        else Success(trees)
      }
    }
  }

  def symbolOfLine(code: String): Symbol =
    exprTyper.symbolOfLine(code)

  def typeOfExpression(expr: String, silent: Boolean = true): Type =
    exprTyper.typeOfExpression(expr, silent)

  protected def onlyTerms(xs: List[Name]): List[TermName] = xs collect { case x: TermName => x }
  protected def onlyTypes(xs: List[Name]): List[TypeName] = xs collect { case x: TypeName => x }

  def definedTerms      = onlyTerms(allDefinedNames) filterNot isInternalTermName
  def definedTypes      = onlyTypes(allDefinedNames)
  def definedSymbolList = prevRequestList flatMap (_.defines) filterNot (s => isInternalTermName(s.name))

  // Terms with user-given names (i.e. not res0 and not synthetic)
  def namedDefinedTerms = definedTerms filterNot (x => isUserVarName("" + x) || directlyBoundNames(x))

  private var _replScope: Scope = _
  private def resetReplScope() {
    _replScope = newScope
  }
  def replScope = {
    if (_replScope eq null)
      _replScope = newScope

    _replScope
  }

  private var executingRequest: Request = _
  private val prevRequests       = mutable.ListBuffer[Request]()
  private val directlyBoundNames = mutable.Set[Name]()

  def allHandlers     = prevRequestList flatMap (_.handlers)
  def lastRequest     = if (prevRequests.isEmpty) null else prevRequests.last
  def prevRequestList = prevRequests.toList
  def importHandlers  = allHandlers collect { case x: ImportHandler => x }

  def withoutUnwrapping(op: => Unit): Unit = {
    val saved = isettings.unwrapStrings
    isettings.unwrapStrings = false
    try op
    finally isettings.unwrapStrings = saved
  }

  def symbolDefString(sym: Symbol) = {
    TypeStrings.quieter(
      exitingTyper(sym.defString),
      sym.owner.name + ".this.",
      sym.owner.fullName + "."
    )
  }

  def showCodeIfDebugging(code: String) {
    /** Secret bookcase entrance for repl debuggers: end the line
     *  with "// show" and see what's going on.
     */
    def isShow = code.lines exists (_.trim endsWith "// show")
    if (isReplDebug || isShow) {
      beSilentDuring(parse(code)) match {
        case parse.Success(ts) =>
          ts foreach { t =>
            withoutUnwrapping(echo(asCompactString(t)))
          }
        case _ =>
      }
    }
  }

  // debugging
  def debugging[T](msg: String)(res: T) = {
    repldbg(msg + " " + res)
    res
  }
}

/** Utility methods for the Interpreter. */
object IMain {
  import java.util.Arrays.{ asList => asJavaList }

  class Factory extends ScriptEngineFactory {
    @BeanProperty
    val engineName = "Scala Interpreter"

    @BeanProperty
    val engineVersion = "1.0"

    @BeanProperty
    val extensions: JList[String] = asJavaList("scala")

    @BeanProperty
    val languageName = "Scala"

    @BeanProperty
    val languageVersion = scala.util.Properties.versionString

    def getMethodCallSyntax(obj: String, m: String, args: String*): String = null

    @BeanProperty
    val mimeTypes: JList[String] = asJavaList("application/x-scala")

    @BeanProperty
    val names: JList[String] = asJavaList("scala")

    def getOutputStatement(toDisplay: String): String = null

    def getParameter(key: String): Object = key match {
      case ScriptEngine.ENGINE => engineName
      case ScriptEngine.ENGINE_VERSION => engineVersion
      case ScriptEngine.LANGUAGE => languageName
      case ScriptEngine.LANGUAGE_VERSION => languageVersion
      case ScriptEngine.NAME => names.get(0)
      case _ => null
    }

    def getProgram(statements: String*): String = null

    def getScriptEngine: ScriptEngine = new IMain(this, new Settings() {
      usemanifestcp.value = true
    })
  }

  // The two name forms this is catching are the two sides of this assignment:
  //
  // $line3.$read.$iw.$iw.Bippy =
  //   $line3.$read$$iw$$iw$Bippy@4a6a00ca
  private def removeLineWrapper(s: String) = s.replaceAll("""\$line\d+[./]\$(read|eval|print)[$.]""", "")
  private def removeIWPackages(s: String)  = s.replaceAll("""\$(iw|read|eval|print)[$.]""", "")
  def stripString(s: String)               = removeIWPackages(removeLineWrapper(s))

  trait CodeAssembler[T] {
    def preamble: String
    def generate: T => String
    def postamble: String

    def apply(contributors: List[T]): String = stringFromWriter { code =>
      code println preamble
      contributors map generate foreach (code println _)
      code println postamble
    }
  }

  trait StrippingWriter {
    def isStripping: Boolean
    def stripImpl(str: String): String
    def strip(str: String): String = if (isStripping) stripImpl(str) else str
  }
  trait TruncatingWriter {
    def maxStringLength: Int
    def isTruncating: Boolean
    def truncate(str: String): String = {
      if (isTruncating && (maxStringLength != 0 && str.length > maxStringLength))
        (str take maxStringLength - 3) + "..."
      else str
    }
  }
  abstract class StrippingTruncatingWriter(out: JPrintWriter)
          extends JPrintWriter(out)
             with StrippingWriter
             with TruncatingWriter {
    self =>

    def clean(str: String): String = truncate(strip(str))
    override def write(str: String) = super.write(clean(str))
  }
  class ReplStrippingWriter(intp: IMain) extends StrippingTruncatingWriter(intp.out) {
    import intp._
    def maxStringLength    = isettings.maxPrintString
    def isStripping        = isettings.unwrapStrings
    def isTruncating       = reporter.truncationOK

    def stripImpl(str: String): String = naming.unmangle(str)
  }
}