Scala example source code file (Printers.scala)

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

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

Scala tags/keywords

boolean, compiler, ident, if, isfalse, istrue, list, nsc, printwriter, string, tree, treeprinter

The Printers.scala Scala example source code

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

package scala.tools.nsc
package ast

import java.io.{ OutputStream, PrintWriter, StringWriter, Writer }

trait Printers extends scala.reflect.internal.Printers { this: Global =>

  import treeInfo.{ IsTrue, IsFalse }

  class TreePrinter(out: PrintWriter) extends super.TreePrinter(out) {

    override def print(args: Any*): Unit = args foreach {
      case tree: Tree =>
        printPosition(tree)
        printTree(
            if (tree.isDef && tree.symbol != NoSymbol && tree.symbol.isInitialized) {
              tree match {
                case ClassDef(_, _, _, impl @ Template(ps, noSelfType, body))
                if (tree.symbol.thisSym != tree.symbol) =>
                  ClassDef(tree.symbol, Template(ps, ValDef(tree.symbol.thisSym), body))
                case ClassDef(_, _, _, impl)           => ClassDef(tree.symbol, impl)
                case ModuleDef(_, _, impl)             => ModuleDef(tree.symbol, impl)
                case ValDef(_, _, _, rhs)              => ValDef(tree.symbol, rhs)
                case DefDef(_, _, _, vparamss, _, rhs) => DefDef(tree.symbol, vparamss, rhs)
                case TypeDef(_, _, _, rhs)             => TypeDef(tree.symbol, rhs)
                case _ => tree
              }
            } else tree)
      case unit: CompilationUnit =>
        print("// Scala source: " + unit.source + "\n")
        if (unit.body == null) print("<null>")
        else { print(unit.body); println() }
        println()
        out.flush()
      case arg =>
        super.print(arg)
    }
  }

  // overflow cases missing from TreePrinter in scala.reflect.api
  override def xprintTree(treePrinter: super.TreePrinter, tree: Tree) = tree match {
    case DocDef(comment, definition) =>
      treePrinter.print(comment.raw)
      treePrinter.println()
      treePrinter.print(definition)

    case TypeTreeWithDeferredRefCheck() =>
      treePrinter.print("<tree with deferred refcheck>")

    case SelectFromArray(qualifier, name, _) =>
      treePrinter.print(qualifier, ".<arr>", symName(tree, name))

    case _ =>
      super.xprintTree(treePrinter, tree)
  }

  /** A tree printer which is stingier about vertical whitespace and unnecessary
   *  punctuation than the standard one.
   */
  class CompactTreePrinter(out: PrintWriter) extends TreePrinter(out) {
    override def printRow(ts: List[Tree], start: String, sep: String, end: String) {
      print(start)
      printSeq(ts)(print(_))(print(sep))
      print(end)
    }

    // drill down through Blocks and pull out the real statements.
    def allStatements(t: Tree): List[Tree] = t match {
      case Block(stmts, expr) => (stmts flatMap allStatements) ::: List(expr)
      case _                  => List(t)
    }

    def printLogicalOr(t1: (Tree, Boolean), t2: (Tree, Boolean)) =
      printLogicalOp(t1, t2, "||")

    def printLogicalAnd(t1: (Tree, Boolean), t2: (Tree, Boolean)) =
      printLogicalOp(t1, t2, "&&")

    def printLogicalOp(t1: (Tree, Boolean), t2: (Tree, Boolean), op: String) = {
      def maybenot(tvalue: Boolean) = if (tvalue) "" else "!"

      print("%s(" format maybenot(t1._2))
      printTree(t1._1)
      print(") %s %s(".format(op, maybenot(t2._2)))
      printTree(t2._1)
      print(")")
    }

    override def printTree(tree: Tree): Unit = {
      // routing supercalls through this for debugging ease
      def s() = super.printTree(tree)

      tree match {
        // labels used for jumps - does not map to valid scala code
        case LabelDef(name, params, rhs) =>
          print("labeldef %s(%s) = ".format(name, params mkString ","))
          printTree(rhs)

        case Ident(name) =>
          print(decodedSymName(tree, name))

        // target.method(arg) ==> target method arg
        case Apply(Select(target, method), List(arg)) =>
          if (method.decode.toString == "||")
            printLogicalOr(target -> true, arg -> true)
          else if (method.decode.toString == "&&")
            printLogicalAnd(target -> true, arg -> true)
          else (target, arg) match {
            case (_: Ident, _: Literal | _: Ident)  =>
              printTree(target)
              print(" ")
              printTree(Ident(method))
              print(" ")
              printTree(arg)
            case _                        => s()
          }

        // target.unary_! ==> !target
        case Select(qualifier, name) if (name.decode startsWith "unary_") =>
          print(name.decode drop 6)
          printTree(qualifier)

        case Select(qualifier, name) =>
          printTree(qualifier)
          print(".")
          print(quotedName(name, decode = true))

        // target.toString() ==> target.toString
        case Apply(fn, Nil)   => printTree(fn)

        // if a Block only continues one actual statement, just print it.
        case Block(stats, expr) =>
          allStatements(tree) match {
            case List(x)            => printTree(x)
            case xs                 => s()
          }

        // We get a lot of this stuff
        case If( IsTrue(), x, _)        => printTree(x)
        case If(IsFalse(), _, x)        => printTree(x)

        case If(cond,  IsTrue(), elsep)   =>  printLogicalOr(cond -> true, elsep -> true)
        case If(cond, IsFalse(), elsep)   => printLogicalAnd(cond -> false, elsep -> true)
        case If(cond,  thenp, IsTrue())   =>  printLogicalOr(cond -> false, thenp -> true)
        case If(cond,  thenp, IsFalse())  => printLogicalAnd(cond -> true, thenp -> true)

        // If thenp or elsep has only one statement, it doesn't need more than one line.
        case If(cond, thenp, elsep) =>
          def ifIndented(x: Tree) = {
            indent() ; println() ; printTree(x) ; undent()
          }

          val List(thenStmts, elseStmts) = List(thenp, elsep) map allStatements
          print("if ("); print(cond); print(") ")

          thenStmts match {
            case List(x: If)  => ifIndented(x)
            case List(x)      => printTree(x)
            case _            => printTree(thenp)
          }

          if (elseStmts.nonEmpty) {
            print(" else")
            indent() ; println()
            elseStmts match {
              case List(x)  => printTree(x)
              case _        => printTree(elsep)
            }
            undent() ; println()
          }
        case _        => s()
      }
    }
  }

  def asString(t: Tree): String = render(t, newStandardTreePrinter, settings.printtypes, settings.uniqid, settings.Yshowsymowners, settings.Yshowsymkinds)
  def asCompactString(t: Tree): String = render(t, newCompactTreePrinter, settings.printtypes, settings.uniqid, settings.Yshowsymowners, settings.Yshowsymkinds)
  def asCompactDebugString(t: Tree): String = render(t, newCompactTreePrinter, true, true, true, true)

  def newStandardTreePrinter(writer: PrintWriter): TreePrinter = new TreePrinter(writer)
  def newCompactTreePrinter(writer: PrintWriter): CompactTreePrinter = new CompactTreePrinter(writer)

  override def newTreePrinter(writer: PrintWriter): TreePrinter =
    if (settings.Ycompacttrees) newCompactTreePrinter(writer)
    else newStandardTreePrinter(writer)
  override def newTreePrinter(stream: OutputStream): TreePrinter = newTreePrinter(new PrintWriter(stream))
  override def newTreePrinter(): TreePrinter = newTreePrinter(new PrintWriter(ConsoleWriter))
}