First PoC of REPL

Adaptation of REPL by Spoon from ca 2007. Compiles OK, but
not yet tested.

1 files changed, 920 insertions, 0 deletions

diff --git a/src/dotty/tools/dotc/repl/Interpreter.scala b/src/dotty/tools/dotc/repl/Interpreter.scala
new file mode 100644
index 000000000..b9853e18b
--- /dev/null
+++ b/src/dotty/tools/dotc/repl/Interpreter.scala
@@ -0,0 +1,920 @@
+package dotty.tools
+package dotc
+package repl
+
+import java.io.{File, PrintWriter, StringWriter, Writer}
+import java.lang.{Class, ClassLoader}
+import java.net.{URL, URLClassLoader}
+
+import scala.collection.immutable.ListSet
+import scala.collection.mutable
+import scala.collection.mutable.{ListBuffer, HashSet, ArrayBuffer}
+
+//import ast.parser.SyntaxAnalyzer
+import io.{PlainFile, VirtualDirectory}
+import reporting.{ConsoleReporter, Reporter}
+import core.Flags
+import util.{SourceFile, NameTransformer}
+import io.ClassPath
+import repl.{InterpreterResults=>IR}
+import ast.Trees._
+import parsing.Parsers._
+import core._
+import dotty.tools.backend.jvm.GenBCode
+import Symbols._, Types._, Contexts._, StdNames._, Names._, NameOps._
+import Decorators._
+import Interpreter._
+
+/** <p>
+ *    An interpreter for Scala code.
+ *  </p>
+ *  <p>
+ *    The main public entry points are <code>compile()</code> and
+ *    <code>interpret()</code>. The <code>compile()</code> method loads a
+ *    complete Scala file.  The <code>interpret()</code> method executes one
+ *    line of Scala code at the request of the user.
+ *  </p>
+ *  <p>
+ *    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.
+ *  </p>
+ *  <p>
+ *    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 a single member named "result".  To accomodate user expressions
+ *    that read from variables or methods defined in previous statements, "import"
+ *    statements are used.
+ *  </p>
+ *  <p>
+ *    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.
+ *  </p>
+ *
+ * @author Moez A. Abdel-Gawad
+ * @author Lex Spoon
+ */
+class Interpreter(out: PrintWriter) extends Compiler {
+
+  import ast.untpd._
+  import Interpreter._
+
+  /** directory to save .class files to */
+  val virtualDirectory = new VirtualDirectory("(memory)", None)
+
+  class REPLGenBCode extends GenBCode {
+    override def outputDir(implicit ctx: Context) = virtualDirectory
+  }
+
+  override def phases = Phases.replace(
+      classOf[GenBCode], _ => new REPLGenBCode :: Nil, super.phases)
+
+  /** whether to print out result lines */
+  private var printResults: Boolean = true
+
+  /** Be quiet.  Do not print out the results of each
+    * submitted command unless an exception is thrown.  */
+  def beQuiet = { printResults = false }
+
+  /** Temporarily be quiet */
+  def beQuietDuring[T](operation: => T): T = {
+    val wasPrinting = printResults
+    try {
+      printResults = false
+      operation
+    } finally {
+      printResults = wasPrinting
+    }
+  }
+
+  /** interpreter settings */
+  val isettings = new InterpreterSettings
+
+  def newReporter = new ConsoleReporter(Console.in, writer = out) {
+    //override def printMessage(msg: String) { out.println(clean(msg)) }
+    override def printMessage(msg: String) = {
+      out.print(clean(msg) + "\n")
+      out.flush()
+    }
+  }
+
+  /** the previous requests this interpreter has processed */
+  private val prevRequests = new ArrayBuffer[Request]()
+
+  /** the compiler's classpath, as URL's */
+  var compilerClasspath: List[URL] = _
+
+  /* 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.
+  */
+  /** class loader used to load compiled code */
+  var classLoader: ClassLoader = _
+
+  protected def parentClassLoader: ClassLoader = classOf[Interpreter].getClassLoader
+
+  def init()(implicit ctx: Context) = {
+    compilerClasspath = ctx.platform.classPath.asURLs
+    classLoader = {
+      val parent = new URLClassLoader(compilerClasspath.toArray, parentClassLoader)
+      new AbstractFileClassLoader(virtualDirectory, parent)
+    }
+  }
+
+  /** Set the current Java "context" class loader to this
+   *  interpreter's class loader
+   */
+  def setContextClassLoader(): Unit = {
+    Thread.currentThread.setContextClassLoader(classLoader)
+  }
+
+  /** Parse a line into a sequence of trees. Returns None if the input
+   *  is incomplete.
+   */
+  private def parse(line: String)(implicit ctx: Context): Option[List[Tree]] = {
+    var justNeedsMore = false
+    val reporter = newReporter
+    reporter.withIncompleteHandler { _ => _ => justNeedsMore = true } {
+      // simple parse: just parse it, nothing else
+      def simpleParse(code: String): List[Tree] = {
+        val source = new SourceFile("<console>", code.toCharArray())
+        val parser = new Parser(source)
+        val (selfDef, stats) = parser.templateStatSeq
+        stats
+      }
+      val trees = simpleParse(line)
+      if (reporter.hasErrors) {
+        Some(Nil) // the result did not parse, so stop
+      } else if (justNeedsMore) {
+        None
+      } else {
+        Some(trees)
+      }
+    }
+  }
+
+  /** Compile a SourceFile.  Returns true if there are
+   *  no compilation errors, or false othrewise.
+   */
+  def compileSources(sources: List[SourceFile])(implicit ctx: Context): Boolean = {
+    val reporter = newReporter
+    val run = new Run(this)(ctx.fresh.setReporter(reporter))
+    run.compileSources(sources)
+    !reporter.hasErrors
+  }
+
+  /** Compile a string.  Returns true if there are no
+   *  compilation errors, or false otherwise.
+   */
+  def compileString(code: String)(implicit ctx: Context): Boolean =
+    compileSources(List(new SourceFile("<script>", code.toCharArray)))
+
+  /** <p>
+   *    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.
+   *  </p>
+   *  <p>
+   *    The return value is whether the line was interpreter successfully,
+   *    e.g. that there were no parse errors.
+   *  </p>
+   *
+   *  @param line ...
+   *  @return     ...
+   */
+  def interpret(line: String)(implicit ctx: Context): IR.Result = {
+    if (prevRequests.isEmpty)
+      new Run(this) // initialize the compiler
+
+    // parse
+    val trees = parse(indentCode(line)) match {
+      case None => return IR.Incomplete
+      case Some(Nil) => return IR.Error // parse error or empty input
+      case Some(trees) => trees
+    }
+
+    trees match {
+      case List(_: Assign) => ()
+
+      case List(_: TermTree) | List(_: Ident) | List(_: Select) =>
+        // Treat a single expression specially.
+        // This is necessary due to it being hard to modify
+        // code at a textual level, and it being hard to
+        // submit an AST to the compiler.
+        return interpret("val " + newVarName() + " = \n" + line)
+
+      case _ => ()
+    }
+
+    val lineName = newLineName
+
+    // figure out what kind of request
+    val req = buildRequest(trees, line, lineName)
+    if (req eq null) return IR.Error // a disallowed statement type
+
+    if (!req.compile)
+      return IR.Error // an error happened during compilation, e.g. a type error
+
+    val (interpreterResultString, succeeded) = req.loadAndRun
+
+    if (printResults || !succeeded) {
+      // print the result
+      out.print(clean(interpreterResultString))
+    }
+
+    // book-keeping
+    if (succeeded)
+      prevRequests += req
+
+    if (succeeded) IR.Success else IR.Error
+  }
+
+  /** A counter used for numbering objects created by <code>bind()</code>. */
+  private var binderNum = 0
+
+  /** 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)(implicit ctx: Context): IR.Result = {
+    val binderName = "binder" + binderNum
+    binderNum += 1
+
+    compileString(
+      "object " + binderName +
+        "{ var value: " + boundType + " = _; " +
+        " def set(x: Any) = value=x.asInstanceOf[" + boundType + "]; }")
+
+    val binderObject =
+      Class.forName(binderName, true, classLoader)
+    val setterMethod =
+      (binderObject
+        .getDeclaredMethods
+        .toList
+        .find(meth => meth.getName == "set")
+        .get)
+    var argsHolder: Array[Any] = null // this roundabout approach is to try and
+    // make sure the value is boxed
+    argsHolder = List(value).toArray
+    setterMethod.invoke(null, argsHolder.asInstanceOf[Array[AnyRef]])
+
+    interpret("val " + name + " = " + binderName + ".value")
+  }
+
+  /** Class to handle one member among all the members included
+   *  in a single interpreter request.
+   */
+  private trait Handler {
+    def member: Tree
+    def usedNames: List[Name]
+    val boundNames: List[Name]
+    def valAndVarNames: List[Name]
+    def defNames: List[Name]
+    val importsWildcard: Boolean
+    val importedNames: Seq[Name]
+    val definesImplicit: Boolean
+    def extraCodeToEvaluate(req: Request, code: PrintWriter): Unit
+    def resultExtractionCode(req: Request, code: PrintWriter): Unit
+  }
+
+  /** Build a request from the user. <code>trees</code> is <code>line</code>
+   *  after being parsed.
+   */
+  private def buildRequest(trees: List[Tree], line: String, lineName: String)(implicit ctx: Context): Request =
+    new Request(line, lineName)
+
+  /** One line of code submitted by the user for interpretation */
+  private class Request(val line: String, val lineName: String)(implicit ctx: Context) {
+    val trees = parse(line) match {
+      case Some(ts) => ts
+      case None => Nil
+    }
+
+    /** name to use for the object that will compute "line" */
+    def objectName = lineName + INTERPRETER_WRAPPER_SUFFIX
+
+    /** name of the object that retrieves the result from the above object */
+    def resultObjectName = "RequestResult$" + objectName
+
+    private val handlers: List[MemberHandler] = trees.flatMap(chooseHandler(_))
+
+    /** all (public) names defined by these statements */
+    val boundNames = (ListSet() ++ handlers.flatMap(_.boundNames)).toList
+
+    /** list of names used by this expression */
+    val usedNames: List[Name] = handlers.flatMap(_.usedNames)
+
+    def myImportsCode = importsCode(Set.empty ++ usedNames)
+
+    /** Code to append to objectName to access anything that
+     *  the request binds.  */
+    val accessPath = myImportsCode._3
+
+
+    /** Code to access a variable with the specified name */
+    def fullPath(vname: String): String =
+      objectName + accessPath + ".`" + vname + "`"
+
+    /** Code to access a variable with the specified name */
+    def fullPath(vname: Name): String = fullPath(vname.toString)
+
+    /** the line of code to compute */
+    def toCompute = line
+
+    /** generate the source code for the object that computes this request */
+    def objectSourceCode: String =
+      stringFrom { code =>
+        // header for the wrapper object
+        code.println("object " + objectName + " {")
+
+        val (importsPreamble, importsTrailer, _) = myImportsCode
+
+        code.print(importsPreamble)
+
+        code.println(indentCode(toCompute))
+
+        handlers.foreach(_.extraCodeToEvaluate(this,code))
+
+        code.println(importsTrailer)
+
+        //end the wrapper object
+        code.println(";}")
+      }
+
+    /** Types of variables defined by this request.  They are computed
+        after compilation of the main object */
+    var typeOf: Map[Name, String] = _
+
+    /** generate source code for the object that retrieves the result
+        from objectSourceCode */
+    def resultObjectSourceCode: String =
+      stringFrom(code => {
+        code.println("object " + resultObjectName)
+        code.println("{ val result: String = {")
+        code.println(objectName + accessPath + ";")  // evaluate the object, to make sure its constructor is run
+        code.print("(\"\"")  // print an initial empty string, so later code can
+                            // uniformly be: + morestuff
+        handlers.foreach(_.resultExtractionCode(this, code))
+        code.println("\n)}")
+        code.println(";}")
+      })
+
+
+    /** Compile the object file.  Returns whether the compilation succeeded.
+     *  If all goes well, the "types" map is computed. */
+    def compile(): Boolean =
+      compileSources(
+        List(new SourceFile("<console>", objectSourceCode.toCharArray))) && {
+        // extract and remember types
+        this.typeOf = findTypes()
+        compileSources(
+          List(new SourceFile("<console>", resultObjectSourceCode.toCharArray)))
+      }
+
+    /** Dig the types of all bound variables out of the compiler run.
+     *
+     *  @param objRun ...
+     *  @return       ...
+     */
+    def findTypes(): Map[Name, String] = {
+      def valAndVarNames = handlers.flatMap(_.valAndVarNames)
+      def defNames = handlers.flatMap(_.defNames)
+
+      def getTypes(names: List[Name], nameMap: Name=>Name): Map[Name, String] = {
+        /** the outermost wrapper object */
+        val outerResObjSym: Symbol =
+          defn.EmptyPackageClass.info.decl(objectName.toTermName).symbol
+
+        /** the innermost object inside the wrapper, found by
+          * following accessPath into the outer one. */
+        val resObjSym =
+          (accessPath.split("\\.")).foldLeft(outerResObjSym) { (sym,str) =>
+            if (str.isEmpty) sym
+            else
+              ctx.atPhase(ctx.typerPhase.next) { implicit ctx =>
+                sym.info.member(str.toTermName).symbol
+              }
+          }
+
+        names.foldLeft(Map.empty[Name,String]) { (map, name) =>
+          val rawType =
+            ctx.atPhase(ctx.typerPhase.next) { implicit ctx =>
+              resObjSym.info.member(name).info
+            }
+
+          // the types are all =>T; remove the =>
+          val cleanedType = rawType.widenExpr
+
+          map + (name ->
+            ctx.atPhase(ctx.typerPhase.next) { implicit ctx =>
+              cleanedType.show
+            })
+        }
+      }
+
+      val names1 = getTypes(valAndVarNames, n => n.toTermName.fieldName)
+      val names2 = getTypes(defNames, identity)
+      names1 ++ names2
+    }
+
+    /** load and run the code using reflection */
+    def loadAndRun: (String, Boolean) = {
+      val interpreterResultObject: Class[_] =
+        Class.forName(resultObjectName, true, classLoader)
+      val resultValMethod: java.lang.reflect.Method =
+        interpreterResultObject.getMethod("result", null)
+      try {
+        (resultValMethod.invoke(interpreterResultObject, null).toString(),
+             true)
+      } catch {
+        case e =>
+          def caus(e: Throwable): Throwable =
+            if (e.getCause eq null) e else caus(e.getCause)
+          val orig = caus(e)
+          (stringFrom(str => orig.printStackTrace(str)), false)
+      }
+    }
+
+    /** Compute imports that allow definitions from previous
+     *  requests to be visible in a new request.  Returns
+     *  three pieces of related code:
+     *
+     *  1. An initial code fragment that should go before
+     *  the code of the new request.
+     *
+     *  2. A code fragment that should go after the code
+     *  of the new request.
+     *
+     *  3. An access path which can be traversed to access
+     *  any bindings inside code wrapped by #1 and #2 .
+     *
+     *  The argument is a set of Names that need to be imported.
+     *
+     *  Limitations: This method is not as precise as it could be.
+     *  (1) It does not process wildcard imports to see what exactly
+     *  they import.
+     *  (2) If it imports any names from a request, it imports all
+     *  of them, which is not really necessary.
+     *  (3) It imports multiple same-named implicits, but only the
+     *  last one imported is actually usable.
+     */
+    private def importsCode(wanted: Set[Name]): (String, String, String) = {
+      /** Narrow down the list of requests from which imports
+       *  should be taken.  Removes requests which cannot contribute
+       *  useful imports for the specified set of wanted names.
+       */
+      def reqsToUse: List[(Request, Handler)] = {
+        /** Loop through a list of MemberHandlers and select
+         *  which ones to keep.  'wanted' is the set of
+         *  names that need to be imported, and
+         *  'shadowed' is the list of names useless to import
+         *  because a later request will re-import it anyway.
+         */
+        def select(reqs: List[(Request, Handler)], wanted: Set[Name]): List[(Request, Handler)] = {
+          reqs match {
+            case Nil => Nil
+
+            case (req, handler) :: rest =>
+              val keepit =
+                (handler.definesImplicit ||
+                  handler.importsWildcard ||
+                  handler.importedNames.exists(wanted.contains(_)) ||
+                  handler.boundNames.exists(wanted.contains(_)))
+
+              val newWanted =
+                if (keepit) {
+                  (wanted
+                    ++ handler.usedNames
+                    -- handler.boundNames
+                    -- handler.importedNames)
+                } else {
+                  wanted
+                }
+
+              val restToKeep = select(rest, newWanted)
+
+              if (keepit)
+                (req, handler) :: restToKeep
+              else
+                restToKeep
+          }
+        }
+
+        val rhpairs = for {
+          req <- prevRequests.toList.reverse
+          handler <- req.handlers
+        } yield (req, handler)
+
+        select(rhpairs, wanted).reverse
+      }
+
+      val code = new StringBuffer
+      val trailingBraces = new StringBuffer
+      val accessPath = new StringBuffer
+      val impname = INTERPRETER_IMPORT_WRAPPER
+      val currentImps = mutable.Set.empty[Name]
+
+      // add code for a new object to hold some imports
+      def addWrapper(): Unit = {
+        code.append("object " + impname + "{\n")
+        trailingBraces.append("}\n")
+        accessPath.append("." + impname)
+        currentImps.clear
+      }
+
+      addWrapper()
+
+      // loop through previous requests, adding imports
+      // for each one
+      for ((req, handler) <- reqsToUse) {
+        // If the user entered an import, then just use it
+
+        // add an import wrapping level if the import might
+        // conflict with some other import
+        if (handler.importsWildcard ||
+          currentImps.exists(handler.importedNames.contains))
+          if (!currentImps.isEmpty)
+            addWrapper()
+
+        if (handler.member.isInstanceOf[Import])
+          code.append(handler.member.toString + ";\n")
+
+        // give wildcard imports a import wrapper all to their own
+        if (handler.importsWildcard)
+          addWrapper()
+        else
+          currentImps ++= handler.importedNames
+
+        // For other requests, import each bound variable.
+        // import them explicitly instead of with _, so that
+        // ambiguity errors will not be generated. Also, quote
+        // the name of the variable, so that we don't need to
+        // handle quoting keywords separately.
+        for (imv <- handler.boundNames) {
+          if (currentImps.contains(imv))
+            addWrapper()
+          code.append("import ")
+          code.append(req.objectName + req.accessPath + ".`" + imv + "`;\n")
+          currentImps += imv
+        }
+      }
+
+      addWrapper() // Add one extra wrapper, to prevent warnings
+      // in the frequent case of redefining
+      // the value bound in the last interpreter
+      // request.
+
+      (code.toString, trailingBraces.toString, accessPath.toString)
+    }
+
+    // ------ Handlers ------------------------------------------
+
+    private def chooseHandler(member: Tree): Option[MemberHandler] =
+      member match {
+        case member: DefDef =>
+          Some(new DefHandler(member))
+        case member: ValDef =>
+          Some(new ValHandler(member))
+        case member @ Assign(Ident(_), _) => Some(new AssignHandler(member))
+        case member: ModuleDef => Some(new ModuleHandler(member))
+        case member: TypeDef =>
+          Some(if (member.isClassDef) new ClassHandler(member)
+          else new TypeAliasHandler(member))
+        case member: Import => Some(new ImportHandler(member))
+        //      case DocDef(_, documented) => chooseHandler(documented)
+        case member => Some(new GenericHandler(member))
+      }
+
+    /** A traverser that finds all mentioned identifiers, i.e. things
+     *  that need to be imported.
+     *  It might return extra names.
+     */
+    private class ImportVarsTraverser(definedVars: List[Name]) extends TreeTraverser {
+      val importVars = new HashSet[Name]()
+
+      override def traverse(ast: Tree)(implicit ctx: Context): Unit = {
+        ast match {
+          case Ident(name) => importVars += name
+          case _ => traverseChildren(ast)
+        }
+      }
+    }
+
+    /** Class to handle one member among all the members included
+     *  in a single interpreter request.
+     */
+    private sealed abstract class MemberHandler(val member: Tree) extends Handler {
+      val usedNames: List[Name] = {
+        val ivt = new ImportVarsTraverser(boundNames)
+        ivt.traverse(member)
+        ivt.importVars.toList
+      }
+      val boundNames: List[Name] = Nil
+      def valAndVarNames: List[Name] = Nil
+      def defNames: List[Name] = Nil
+      val importsWildcard = false
+      val importedNames: Seq[Name] = Nil
+      val definesImplicit =
+        member match {
+          case tree: MemberDef => tree.mods.is(Flags.Implicit)
+          case _ => false
+        }
+
+      def extraCodeToEvaluate(req: Request, code: PrintWriter) = {}
+      def resultExtractionCode(req: Request, code: PrintWriter) = {}
+    }
+
+    private class GenericHandler(member: Tree) extends MemberHandler(member)
+
+    private class ValHandler(member: ValDef) extends MemberHandler(member) {
+      override val boundNames = List(member.name)
+      override def valAndVarNames = boundNames
+
+      override def resultExtractionCode(req: Request, code: PrintWriter): Unit = {
+        val vname = member.name
+        if (!member.mods.is(Flags.AccessFlags) &&
+          !(isGeneratedVarName(vname.toString) &&
+            req.typeOf(vname.encode) == "Unit")) {
+          val prettyName = vname.decode
+          code.print(" + \"" + prettyName + ": " +
+            string2code(req.typeOf(vname)) +
+            " = \" + " +
+            " (if(" +
+            req.fullPath(vname) +
+            ".asInstanceOf[AnyRef] != null) " +
+            " ((if(" +
+            req.fullPath(vname) +
+            ".toString().contains('\\n')) " +
+            " \"\\n\" else \"\") + " +
+            req.fullPath(vname) + ".toString() + \"\\n\") else \"null\\n\") ")
+        }
+      }
+    }
+
+    private class DefHandler(defDef: DefDef) extends MemberHandler(defDef) {
+      override val boundNames = List(defDef.name)
+      override def defNames = boundNames
+
+      override def resultExtractionCode(req: Request, code: PrintWriter): Unit = {
+        if (!defDef.mods.is(Flags.AccessFlags))
+          code.print("+\"" + string2code(defDef.name.toString) + ": " +
+            string2code(req.typeOf(defDef.name)) + "\\n\"")
+      }
+    }
+
+    private class AssignHandler(member: Assign) extends MemberHandler(member) {
+      val lhs = member.lhs.asInstanceOf[Ident] // an unfortunate limitation
+
+      val helperName = newInternalVarName().toTermName
+      override val valAndVarNames = List(helperName)
+
+      override def extraCodeToEvaluate(req: Request, code: PrintWriter): Unit = {
+        code.println("val " + helperName + " = " + member.lhs + ";")
+      }
+
+      /** Print out lhs instead of the generated varName */
+      override def resultExtractionCode(req: Request, code: PrintWriter): Unit = {
+        code.print(" + \"" + lhs + ": " +
+          string2code(req.typeOf(helperName.encode)) +
+          " = \" + " +
+          string2code(req.fullPath(helperName))
+          + " + \"\\n\"")
+      }
+    }
+
+    private class ModuleHandler(module: ModuleDef) extends MemberHandler(module) {
+      override val boundNames = List(module.name)
+
+      override def resultExtractionCode(req: Request, code: PrintWriter): Unit = {
+        code.println(" + \"defined module " +
+          string2code(module.name.toString)
+          + "\\n\"")
+      }
+    }
+
+    private class ClassHandler(classdef: TypeDef)
+      extends MemberHandler(classdef) {
+      override val boundNames =
+        List(classdef.name) :::
+          (if (classdef.mods.is(Flags.Case))
+            List(classdef.name.toTermName)
+          else
+            Nil)
+
+      // TODO: MemberDef.keyword does not include "trait";
+      // otherwise it could be used here
+      def keyword: String =
+        if (classdef.mods.is(Flags.Trait)) "trait" else "class"
+
+      override def resultExtractionCode(req: Request, code: PrintWriter): Unit = {
+        code.print(
+          " + \"defined " +
+            keyword +
+            " " +
+            string2code(classdef.name.toString) +
+            "\\n\"")
+      }
+    }
+
+    private class TypeAliasHandler(typeDef: TypeDef)
+      extends MemberHandler(typeDef) {
+      override val boundNames =
+        if (!typeDef.mods.is(Flags.AccessFlags) && !typeDef.rhs.isInstanceOf[TypeBoundsTree])
+          List(typeDef.name)
+        else
+          Nil
+
+      override def resultExtractionCode(req: Request, code: PrintWriter): Unit = {
+        code.println(" + \"defined type alias " +
+          string2code(typeDef.name.toString) + "\\n\"")
+      }
+    }
+
+    private class ImportHandler(imp: Import) extends MemberHandler(imp) {
+      override def resultExtractionCode(req: Request, code: PrintWriter): Unit = {
+        code.println("+ \"" + imp.toString + "\\n\"")
+      }
+
+      def isWildcardSelector(tree: Tree) = tree match {
+        case Ident(nme.USCOREkw) => true
+        case _ => false
+      }
+
+      /** Whether this import includes a wildcard import */
+      override val importsWildcard = imp.selectors.exists(isWildcardSelector)
+
+      /** The individual names imported by this statement */
+      override val importedNames: Seq[Name] =
+        imp.selectors.filterNot(isWildcardSelector).flatMap {
+          case sel: RefTree => List(sel.name.toTypeName, sel.name.toTermName)
+          case _ => Nil
+        }
+    }
+
+  } // end Request
+
+  // ------- String handling ----------------------------------
+
+  /** next line number to use */
+  private var nextLineNo = 0
+
+  /** allocate a fresh line name */
+  private def newLineName = {
+    val num = nextLineNo
+    nextLineNo += 1
+    INTERPRETER_LINE_PREFIX + num
+  }
+
+  /** next result variable number to use */
+  private var nextVarNameNo = 0
+
+  /** allocate a fresh variable name */
+  private def newVarName() = {
+    val num = nextVarNameNo
+    nextVarNameNo += 1
+    INTERPRETER_VAR_PREFIX + num
+  }
+
+  /** next internal variable number to use */
+  private var nextInternalVarNo = 0
+
+  /** allocate a fresh internal variable name */
+  private def newInternalVarName() = {
+    val num = nextVarNameNo
+    nextVarNameNo += 1
+    INTERPRETER_SYNTHVAR_PREFIX + num
+  }
+
+  /** Check if a name looks like it was generated by newVarName */
+  private def isGeneratedVarName(name: String): Boolean =
+    name.startsWith(INTERPRETER_VAR_PREFIX) && {
+      val suffix = name.drop(INTERPRETER_VAR_PREFIX.length)
+      suffix.forall(_.isDigit)
+    }
+
+  /** generate a string using a routine that wants to write on a stream */
+  private def stringFrom(writer: PrintWriter => Unit): String = {
+    val stringWriter = new StringWriter()
+    val stream = new NewLinePrintWriter(stringWriter)
+    writer(stream)
+    stream.close
+    stringWriter.toString
+  }
+
+  /** Truncate a string if it is longer than settings.maxPrintString */
+  private def truncPrintString(str: String): String = {
+    val maxpr = isettings.maxPrintString
+
+    if (maxpr <= 0)
+      return str
+
+    if (str.length <= maxpr)
+      return str
+
+    val trailer = "..."
+    if (maxpr >= trailer.length+1)
+      return str.substring(0, maxpr-3) + trailer
+
+    str.substring(0, maxpr)
+  }
+
+  /** Clean up a string for output */
+  private def clean(str: String) =
+    truncPrintString(Interpreter.stripWrapperGunk(str))
+
+  /** Indent some code by the width of the scala> prompt.
+   *  This way, compiler error messages read better.
+   */
+  def indentCode(code: String) = {
+    val spaces = "       "
+
+    stringFrom(str =>
+      for (line <- code.lines) {
+        str.print(spaces)
+        str.print(line + "\n")
+        str.flush()
+      })
+  }
+}
+
+/** Utility methods for the Interpreter. */
+object Interpreter {
+  val INTERPRETER_WRAPPER_SUFFIX = "$object"
+  val INTERPRETER_LINE_PREFIX = "line"
+  val INTERPRETER_VAR_PREFIX = "res"
+  val INTERPRETER_IMPORT_WRAPPER = "$iw"
+  val INTERPRETER_SYNTHVAR_PREFIX = "synthvar$"
+
+  /** Delete a directory tree recursively.  Use with care!
+   */
+  private[repl] def deleteRecursively(path: File): Unit = {
+    path match  {
+      case _ if !path.exists =>
+        ()
+      case _ if path.isDirectory =>
+        for (p <- path.listFiles)
+          deleteRecursively(p)
+        path.delete
+      case _ =>
+        path.delete
+    }
+  }
+
+  /** Heuristically strip interpreter wrapper prefixes
+   *  from an interpreter output string.
+   */
+  def stripWrapperGunk(str: String): String = {
+    val wrapregex = "(line[0-9]+\\$object[$.])?(\\$iw[$.])*"
+    str.replaceAll(wrapregex, "")
+  }
+
+  /** Convert a string into code that can recreate the string.
+   *  This requires replacing all special characters by escape
+   *  codes. It does not add the surrounding " marks.  */
+  def string2code(str: String): String = {
+    /** Convert a character to a backslash-u escape */
+    def char2uescape(c: Char): String = {
+      var rest = c.toInt
+      val buf = new StringBuilder
+      for (i <- 1 to 4) {
+	      buf ++= (rest % 16).toHexString
+	      rest = rest / 16
+      }
+      "\\" + "u" + buf.toString.reverse
+    }
+    val res = new StringBuilder
+    for (c <- str) {
+      if ("'\"\\" contains c) {
+	      res += '\\'
+	      res += c
+      } else if (!c.isControl) {
+	      res += c
+      } else {
+	      res ++= char2uescape(c)
+      }
+    }
+    res.toString
+  }
+}