Move compiler and compiler tests to compiler dir

1 files changed, 966 insertions, 0 deletions

diff --git a/compiler/src/dotty/tools/dotc/repl/CompilingInterpreter.scala b/compiler/src/dotty/tools/dotc/repl/CompilingInterpreter.scala
new file mode 100644
index 000000000..5b3669d5e
--- /dev/null
+++ b/compiler/src/dotty/tools/dotc/repl/CompilingInterpreter.scala
@@ -0,0 +1,966 @@
+package dotty.tools
+package dotc
+package repl
+
+import java.io.{
+  File, PrintWriter, PrintStream, StringWriter, Writer, OutputStream,
+  ByteArrayOutputStream => ByteOutputStream
+}
+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 scala.reflect.io.{PlainDirectory, Directory}
+import reporting.{ConsoleReporter, Reporter}
+import core.Flags
+import util.{SourceFile, NameTransformer}
+import io.ClassPath
+import ast.Trees._
+import parsing.Parsers._
+import core._
+import dotty.tools.backend.jvm.GenBCode
+import Symbols._, Types._, Contexts._, StdNames._, Names._, NameOps._
+import Decorators._
+import scala.util.control.NonFatal
+import printing.SyntaxHighlighting
+
+/** An interpreter for Scala code which is based on the `dotc` compiler.
+ *
+ *  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 definition(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 definition named "result".  To accommodate 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
+ * @author Martin Odersky
+ *
+ * @param out   The output to use for diagnostics
+ * @param ictx  The context to use for initialization of the interpreter,
+ *              needed to access the current classpath.
+ */
+class CompilingInterpreter(
+  out: PrintWriter,
+  ictx: Context,
+  parentClassLoader: Option[ClassLoader]
+) extends Compiler with Interpreter {
+  import ast.untpd._
+  import CompilingInterpreter._
+
+  ictx.base.initialize()(ictx)
+
+  /** directory to save .class files to */
+  val virtualDirectory =
+    if (ictx.settings.d.isDefault(ictx)) new VirtualDirectory("(memory)", None)
+    else new PlainDirectory(new Directory(new java.io.File(ictx.settings.d.value(ictx)))) // for now, to help debugging
+
+  /** A GenBCode phase that uses `virtualDirectory` for its output */
+  private class REPLGenBCode extends GenBCode {
+    override def outputDir(implicit ctx: Context) = virtualDirectory
+  }
+
+  /** Phases of this compiler use `REPLGenBCode` instead of `GenBCode`. */
+  override def phases = Phases.replace(
+    classOf[GenBCode], _ => new REPLGenBCode :: Nil, super.phases)
+
+  /** whether to print out result lines */
+  private var printResults: Boolean = true
+  private var delayOutput: Boolean = false
+
+  val previousOutput = ListBuffer.empty[String]
+
+  override def lastOutput() = {
+    val prev = previousOutput.toList
+    previousOutput.clear()
+    prev
+  }
+
+  override def delayOutputDuring[T](operation: => T): T = {
+    val old = delayOutput
+    try {
+      delayOutput = true
+      operation
+    } finally {
+      delayOutput = old
+    }
+  }
+
+  /** Temporarily be quiet */
+  override def beQuietDuring[T](operation: => T): T = {
+    val wasPrinting = printResults
+    try {
+      printResults = false
+      operation
+    } finally {
+      printResults = wasPrinting
+    }
+  }
+
+  private def newReporter =
+    new ConsoleReporter(Console.in, out) {
+      override def printMessage(msg: String) =
+        if (!delayOutput) {
+          out.print(/*clean*/(msg) + "\n")
+          // Suppress clean for now for compiler messages
+          // Otherwise we will completely delete all references to
+          // line$object$ module classes. The previous interpreter did not
+          // have the project because the module class was written without the final `$'
+          // and therefore escaped the purge. We can turn this back on once
+          // we drop the final `$' from module classes.
+          out.flush()
+        } else {
+          previousOutput += (/*clean*/(msg) + "\n")
+        }
+    }
+
+  /** the previous requests this interpreter has processed */
+  private val prevRequests = new ArrayBuffer[Request]()
+
+  /** the compiler's classpath, as URL's */
+  val compilerClasspath: List[URL] = ictx.platform.classPath(ictx).asURLs
+
+  /* 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 */
+  val classLoader: ClassLoader = {
+    lazy val parent = new URLClassLoader(compilerClasspath.toArray,
+                                         classOf[Interpreter].getClassLoader)
+
+    new AbstractFileClassLoader(virtualDirectory, parentClassLoader.getOrElse(parent))
+  }
+
+  // Set the current Java "context" class loader to this interpreter's class loader
+  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)(implicit ctx: Context): List[Tree] = {
+        val source = new SourceFile("<console>", code.toCharArray())
+        val parser = new Parser(source)
+        val (selfDef, stats) = parser.templateStatSeq
+        stats
+      }
+      val trees = simpleParse(line)(ctx.fresh.setReporter(reporter))
+      if (reporter.hasErrors) {
+        Some(Nil) // the result did not parse, so stop
+      } else if (justNeedsMore) {
+        None
+      } else {
+        Some(trees)
+      }
+    }
+  }
+
+  /** Compile a SourceFile.  Returns the root context of the run that compiled the file.
+   */
+  def compileSources(sources: List[SourceFile])(implicit ctx: Context): Context = {
+    val reporter = newReporter
+    val run = newRun(ctx.fresh.setReporter(reporter))
+    run.compileSources(sources)
+    run.runContext
+  }
+
+  /** Compile a string.  Returns true if there are no
+   *  compilation errors, or false otherwise.
+   */
+  def compileString(code: String)(implicit ctx: Context): Boolean = {
+    val runCtx = compileSources(List(new SourceFile("<script>", code.toCharArray)))
+    !runCtx.reporter.hasErrors
+  }
+
+  override def interpret(line: String)(implicit ctx: Context): Interpreter.Result = {
+    // if (prevRequests.isEmpty)
+    //  new Run(this) // initialize the compiler // (not sure this is needed)
+    // parse
+    parse(line) match {
+      case None => Interpreter.Incomplete
+      case Some(Nil) => Interpreter.Error // parse error or empty input
+      case Some(tree :: Nil) if tree.isTerm && !tree.isInstanceOf[Assign] =>
+        previousOutput.clear() // clear previous error reporting
+        interpret(s"val $newVarName =\n$line")
+      case Some(trees) =>
+        previousOutput.clear() // clear previous error reporting
+        val req = new Request(line, newLineName)
+        if (!req.compile())
+          Interpreter.Error // an error happened during compilation, e.g. a type error
+        else {
+          val (resultStrings, succeeded) = req.loadAndRun()
+          if (delayOutput)
+            previousOutput ++= resultStrings.map(clean)
+          else if (printResults || !succeeded)
+            resultStrings.foreach(x => out.print(clean(x)))
+          if (succeeded) {
+            prevRequests += req
+            Interpreter.Success
+          }
+          else Interpreter.Error
+        }
+    }
+  }
+
+  private def loadAndSetValue(objectName: String, value: AnyRef) = {
+    /** This terrible string is the wrapped class's full name inside the
+     *  classloader:
+     *  lineX$object$$iw$$iw$list$object
+     */
+    val objName: String = List(
+      currentLineName + INTERPRETER_WRAPPER_SUFFIX,
+      INTERPRETER_IMPORT_WRAPPER,
+      INTERPRETER_IMPORT_WRAPPER,
+      objectName
+    ).mkString("$")
+
+    try {
+      val resObj: Class[_] = Class.forName(objName, true, classLoader)
+      val setMethod = resObj.getDeclaredMethods.find(_.getName == "set")
+
+      setMethod.fold(false) { method =>
+        method.invoke(resObj, value) == null
+      }
+    } catch {
+      case NonFatal(_) =>
+        // Unable to set value on object due to exception during reflection
+        false
+    }
+  }
+
+  /** This bind is implemented by creating an object with a set method and a
+   *  field `value`. The value is then set via Java reflection.
+   *
+   *  Example: We want to bind a value `List(1,2,3)` to identifier `list` from
+   *  sbt. The bind method accomplishes this by creating the following:
+   *  {{{
+   *    object ContainerObjectWithUniqueID {
+   *      var value: List[Int] = _
+   *      def set(x: Any) = value = x.asInstanceOf[List[Int]]
+   *    }
+   *    val list = ContainerObjectWithUniqueID.value
+   *  }}}
+   *
+   *  Between the object being created and the value being assigned, the value
+   *  inside the object is set via reflection.
+   */
+  override def bind(id: String, boundType: String, value: AnyRef)(implicit ctx: Context): Interpreter.Result =
+    interpret(
+      """
+        |object %s {
+        |  var value: %s = _
+        |  def set(x: Any) = value = x.asInstanceOf[%s]
+        |}
+      """.stripMargin.format(id + INTERPRETER_WRAPPER_SUFFIX, boundType, boundType)
+    ) match {
+      case Interpreter.Success if loadAndSetValue(id + INTERPRETER_WRAPPER_SUFFIX, value) =>
+        val line = "val %s = %s.value".format(id, id + INTERPRETER_WRAPPER_SUFFIX)
+        interpret(line)
+      case Interpreter.Error | Interpreter.Incomplete =>
+        out.println("Set failed in bind(%s, %s, %s)".format(id, boundType, value))
+        Interpreter.Error
+    }
+
+  /** Trait collecting info about one of the statements of an interpreter request */
+  private trait StatementInfo {
+    /** The statement */
+    def statement: Tree
+
+    /** The names defined previously and referred to in the statement */
+    def usedNames: List[Name]
+
+    /** The names defined in the statement */
+    val boundNames: List[Name]
+
+    /** Statement is an import that contains a wildcard */
+    val importsWildcard: Boolean
+
+    /** The names imported by the statement (if it is an import clause) */
+    val importedNames: Seq[Name]
+
+    /** Statement defines an implicit calue or method */
+    val definesImplicit: Boolean
+  }
+
+  /** One line of code submitted by the user for interpretation */
+  private class Request(val line: String, val lineName: String)(implicit ctx: Context) {
+    private val trees = {
+      val parsed = parse(line)
+      previousOutput.clear() // clear previous error reporting
+      parsed match {
+        case Some(ts) => ts
+        case None => Nil
+      }
+    }
+
+    /** name to use for the object that will compute "line" */
+    private def objectName = lineName + INTERPRETER_WRAPPER_SUFFIX
+
+    /** name of the object that retrieves the result from the above object */
+    private def resultObjectName = "RequestResult$" + objectName
+
+    private def chooseHandler(stat: Tree): StatementHandler = stat match {
+      case stat: DefDef => new DefHandler(stat)
+      case stat: ValDef => new ValHandler(stat)
+      case stat: PatDef => new PatHandler(stat)
+      case stat @ Assign(Ident(_), _) => new AssignHandler(stat)
+      case stat: ModuleDef => new ModuleHandler(stat)
+      case stat: TypeDef if stat.isClassDef => new ClassHandler(stat)
+      case stat: TypeDef => new TypeAliasHandler(stat)
+      case stat: Import => new ImportHandler(stat)
+//    case DocDef(_, documented) => chooseHandler(documented)
+      case stat => new GenericHandler(stat)
+    }
+
+    private val handlers: List[StatementHandler] = trees.map(chooseHandler)
+
+    /** all (public) names defined by these statements */
+    private val boundNames = ListSet(handlers.flatMap(_.boundNames): _*).toList
+
+    /** list of names used by this expression */
+    private val usedNames: List[Name] = handlers.flatMap(_.usedNames)
+
+    private val (importsPreamble, importsTrailer, accessPath) =
+      importsCode(usedNames.toSet)
+
+    /** Code to access a variable with the specified name */
+    private def fullPath(vname: String): String = s"$objectName$accessPath.`$vname`"
+
+    /** Code to access a variable with the specified name */
+    private def fullPath(vname: Name): String = fullPath(vname.toString)
+
+    /** the line of code to compute */
+    private def toCompute = line
+
+    /** generate the source code for the object that computes this request
+     *  TODO Reformulate in a functional way
+     */
+    private def objectSourceCode: String =
+      stringFrom { code =>
+        // header for the wrapper object
+        code.println(s"object $objectName{")
+        code.print(importsPreamble)
+        code.println(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 */
+    private var typeOf: Map[Name, String] = _
+
+    /** generate source code for the object that retrieves the result
+        from objectSourceCode */
+    private def resultObjectSourceCode: String =
+      stringFrom(code => {
+        code.println(s"object $resultObjectName")
+        code.println("{ val result: String = {")
+        code.println(s"$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 = {
+      val compileCtx = compileSources(
+        List(new SourceFile("<console>", objectSourceCode.toCharArray)))
+      !compileCtx.reporter.hasErrors && {
+        this.typeOf = findTypes(compileCtx)
+        val resultCtx = compileSources(
+          List(new SourceFile("<console>", resultObjectSourceCode.toCharArray)))
+        !resultCtx.reporter.hasErrors
+      }
+    }
+
+    /** Dig the types of all bound variables out of the compiler run.
+     *  TODO: Change the interface so that we typecheck, and then transform
+     *  directly. Treating the compiler as less of a blackbox will require
+     *  much less magic here.
+     */
+    private def findTypes(implicit ctx: Context): 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
+    }
+
+    /** Sets both System.{out,err} and Console.{out,err} to supplied
+     *  `os: OutputStream`
+     */
+    private def withOutput[T](os: ByteOutputStream)(op: ByteOutputStream => T) = {
+      val ps     = new PrintStream(os)
+      val oldOut = System.out
+      val oldErr = System.err
+      System.setOut(ps)
+      System.setErr(ps)
+
+      try {
+        Console.withOut(os)(Console.withErr(os)(op(os)))
+      } finally {
+        System.setOut(oldOut)
+        System.setErr(oldErr)
+      }
+    }
+
+    /** load and run the code using reflection.
+     *  @return  A pair consisting of the run's result as a `List[String]`, and
+     *           a boolean indicating whether the run succeeded without throwing
+     *           an exception.
+     */
+    def loadAndRun(): (List[String], Boolean) = {
+      val interpreterResultObject: Class[_] =
+        Class.forName(resultObjectName, true, classLoader)
+      val valMethodRes: java.lang.reflect.Method =
+        interpreterResultObject.getMethod("result")
+      try {
+        withOutput(new ByteOutputStream) { ps =>
+          val rawRes = valMethodRes.invoke(interpreterResultObject).toString
+          val res =
+            if (ictx.useColors) new String(SyntaxHighlighting(rawRes).toArray)
+            else rawRes
+          val prints = ps.toString("utf-8")
+          val printList = if (prints != "") prints :: Nil else Nil
+
+          if (!delayOutput) out.print(prints)
+
+          (printList :+ res, true)
+        }
+      } catch {
+        case NonFatal(ex) =>
+          def cause(ex: Throwable): Throwable =
+            if (ex.getCause eq null) ex else cause(ex.getCause)
+          val orig = cause(ex)
+          (stringFrom(str => orig.printStackTrace(str)) :: Nil, false)
+      }
+    }
+
+    /** Compute imports that allow definitions from previous
+     *  requests to be visible in a new request.  Returns
+     *  three pieces of related code as strings:
+     *
+     *  1. A _preamble_: An initial code fragment that should go before
+     *  the code of the new request.
+     *
+     *  2. A _trailer_: 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, StatementInfo)] = {
+        /** Loop through a list of StatementHandlers and select
+         *  which ones to keep.  'wanted' is the set of
+         *  names that need to be imported.
+         */
+        def select(reqs: List[(Request, StatementInfo)], wanted: Set[Name]): List[(Request, StatementInfo)] = {
+          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 preamble = new StringBuffer
+      val trailingBraces = new StringBuffer
+      val accessPath = new StringBuffer
+      val impname = INTERPRETER_IMPORT_WRAPPER
+      val currentImps = mutable.Set[Name]()
+
+      // add code for a new object to hold some imports
+      def addWrapper(): Unit = {
+        preamble.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.statement.isInstanceOf[Import])
+          preamble.append(handler.statement.show + ";\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()
+          preamble.append("import ")
+          preamble.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.
+
+      (preamble.toString, trailingBraces.toString, accessPath.toString)
+    }
+
+    // ------ Handlers ------------------------------------------
+
+    /** Class to handle one statement among all the statements included
+     *  in a single interpreter request.
+     */
+    private sealed abstract class StatementHandler(val statement: Tree) extends StatementInfo {
+      val usedNames: List[Name] = {
+        val ivt = new UntypedTreeAccumulator[mutable.Set[Name]] {
+          override def apply(ns: mutable.Set[Name], tree: Tree)(implicit ctx: Context) =
+            tree match {
+              case Ident(name) => ns += name
+              case _ => foldOver(ns, tree)
+            }
+        }
+        ivt.foldOver(HashSet(), statement).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 = statement 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(statement: Tree) extends StatementHandler(statement)
+
+    private abstract class ValOrPatHandler(statement: Tree)
+        extends StatementHandler(statement) {
+      override val boundNames: List[Name] = _boundNames
+      override def valAndVarNames = boundNames
+
+      override def resultExtractionCode(req: Request, code: PrintWriter): Unit = {
+        if (!shouldShowResult(req)) return
+        val resultExtractors = boundNames.map(name => resultExtractor(req, name))
+        code.print(resultExtractors.mkString(""))
+      }
+
+      private def resultExtractor(req: Request, varName: Name): String = {
+        val prettyName = varName.decode
+        val varType = string2code(req.typeOf(varName))
+        val fullPath = req.fullPath(varName)
+
+        s""" + "$prettyName: $varType = " + {
+           |  if ($fullPath.asInstanceOf[AnyRef] != null) {
+           |    (if ($fullPath.toString().contains('\\n')) "\\n" else "") +
+           |      $fullPath.toString() + "\\n"
+           |  } else {
+           |    "null\\n"
+           |  }
+           |}""".stripMargin
+      }
+
+      protected def _boundNames: List[Name]
+      protected def shouldShowResult(req: Request): Boolean
+    }
+
+    private class ValHandler(statement: ValDef) extends ValOrPatHandler(statement) {
+      override def _boundNames = List(statement.name)
+
+      override def shouldShowResult(req: Request): Boolean =
+        !statement.mods.is(Flags.AccessFlags) &&
+          !(isGeneratedVarName(statement.name.toString) &&
+            req.typeOf(statement.name.encode) == "Unit")
+    }
+
+
+    private class PatHandler(statement: PatDef) extends ValOrPatHandler(statement) {
+      override def _boundNames = statement.pats.flatMap(findVariableNames)
+
+      override def shouldShowResult(req: Request): Boolean =
+        !statement.mods.is(Flags.AccessFlags)
+
+      private def findVariableNames(tree: Tree): List[Name] = tree match {
+        case Ident(name) if name.toString != "_" => List(name)
+        case _ => VariableNameFinder(Nil, tree).reverse
+      }
+
+      private object VariableNameFinder extends UntypedDeepFolder[List[Name]](
+        (acc: List[Name], t: Tree) => t match {
+          case _: BackquotedIdent => acc
+          case Ident(name) if name.isVariableName && name.toString != "_" => name :: acc
+          case Bind(name, _) if name.isVariableName => name :: acc
+          case _ => acc
+        }
+      )
+    }
+
+    private class DefHandler(defDef: DefDef) extends StatementHandler(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(statement: Assign) extends StatementHandler(statement) {
+      val lhs = statement.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(i"val $helperName = ${statement.lhs};")
+      }
+
+      /** Print out lhs instead of the generated varName */
+      override def resultExtractionCode(req: Request, code: PrintWriter): Unit = {
+        code.print(" + \"" + lhs.show + ": " +
+          string2code(req.typeOf(helperName.encode)) +
+          " = \" + " +
+          string2code(req.fullPath(helperName))
+          + " + \"\\n\"")
+      }
+    }
+
+    private class ModuleHandler(module: ModuleDef) extends StatementHandler(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 StatementHandler(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 StatementHandler(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 StatementHandler(imp) {
+      override def resultExtractionCode(req: Request, code: PrintWriter): Unit = {
+        code.println("+ \"" + imp.show + "\\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
+  }
+
+  private def currentLineName =
+    INTERPRETER_LINE_PREFIX + (nextLineNo - 1)
+
+  /** 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)(implicit ctx: Context): String = {
+    val maxpr = ctx.settings.XreplLineWidth.value
+
+    if (maxpr <= 0)
+      return str
+
+    if (str.length <= maxpr)
+      return str
+
+    val trailer = "..."
+    if (maxpr >= trailer.length-1)
+      str.substring(0, maxpr-3) + trailer + "\n"
+    else
+      str.substring(0, maxpr-1)
+  }
+
+  /** Clean up a string for output */
+  private def clean(str: String)(implicit ctx: Context) =
+    truncPrintString(stripWrapperGunk(str))
+}
+
+/** Utility methods for the Interpreter. */
+object CompilingInterpreter {
+  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
+  }
+}