Scala example source code file (TreeDSL.scala)

This example Scala source code file (TreeDSL.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

any_, apply, casestart, compiler, emptytree, if, lit, nsc, selectstart, symbol, tree, treemethods

The TreeDSL.scala Scala example source code

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

package scala.tools.nsc
package ast

import symtab.Flags
import scala.language.implicitConversions

/** A DSL for generating scala code.  The goal is that the
 *  code generating code should look a lot like the code it
 *  generates.
 */

trait TreeDSL {
  val global: Global

  import global._
  import definitions._

  object CODE {
    // Add a null check to a Tree => Tree function
    def nullSafe[T](f: Tree => Tree, ifNull: Tree): Tree => Tree =
      tree => IF (tree MEMBER_== NULL) THEN ifNull ELSE f(tree)

    def returning[T](x: T)(f: T => Unit): T = util.returning(x)(f)

    object LIT extends (Any => Literal) {
      def typed(x: Any)   = apply(x) setType ConstantType(Constant(x))
      def apply(x: Any)   = Literal(Constant(x))
    }

    // Boring, predictable trees.
    def TRUE  = LIT typed true
    def FALSE = LIT typed false
    def ZERO  = LIT(0)
    def NULL  = LIT(null)
    def UNIT  = LIT(())

    def fn(lhs: Tree, op:   Name, args: Tree*)  = Apply(Select(lhs, op), args.toList)
    def fn(lhs: Tree, op: Symbol, args: Tree*)  = Apply(Select(lhs, op), args.toList)

    class TreeMethods(target: Tree) {
      /** logical/comparison ops **/
      def OR(other: Tree) =
        if (target == EmptyTree) other
        else if (other == EmptyTree) target
        else gen.mkOr(target, other)

      def AND(other: Tree) =
        if (target == EmptyTree) other
        else if (other == EmptyTree) target
        else gen.mkAnd(target, other)

      /** Note - calling ANY_== in the matcher caused primitives to get boxed
       *  for the comparison, whereas looking up nme.EQ does not.  See #3570 for
       *  an example of how target.tpe can be non-null, yet it claims not to have
       *  a member called nme.EQ.  Not sure if that should happen, but we can be
       *  robust by dragging in Any regardless.
       */
      def MEMBER_== (other: Tree)   = {
        val opSym = if (target.tpe == null) NoSymbol else target.tpe member nme.EQ
        if (opSym == NoSymbol) ANY_==(other)
        else fn(target, opSym, other)
      }
      def ANY_EQ  (other: Tree)     = OBJ_EQ(other AS ObjectTpe)
      def ANY_==  (other: Tree)     = fn(target, Any_==, other)
      def ANY_!=  (other: Tree)     = fn(target, Any_!=, other)
      def OBJ_EQ  (other: Tree)     = fn(target, Object_eq, other)
      def OBJ_NE  (other: Tree)     = fn(target, Object_ne, other)

      def INT_>=  (other: Tree)     = fn(target, getMember(IntClass, nme.GE), other)
      def INT_==  (other: Tree)     = fn(target, getMember(IntClass, nme.EQ), other)
      def INT_-   (other: Tree)     = fn(target, getMember(IntClass, nme.MINUS), other)

      // generic operations on ByteClass, IntClass, LongClass
      def GEN_|   (other: Tree, kind: ClassSymbol)  = fn(target, getMember(kind, nme.OR), other)
      def GEN_&   (other: Tree, kind: ClassSymbol)  = fn(target, getMember(kind, nme.AND), other)
      def GEN_==  (other: Tree, kind: ClassSymbol)  = fn(target, getMember(kind, nme.EQ), other)
      def GEN_!=  (other: Tree, kind: ClassSymbol)  = fn(target, getMember(kind, nme.NE), other)

      /** Apply, Select, Match **/
      def APPLY(params: Tree*)      = Apply(target, params.toList)
      def APPLY(params: List[Tree]) = Apply(target, params)

      def DOT(member: Name)         = SelectStart(Select(target, member))
      def DOT(sym: Symbol)          = SelectStart(Select(target, sym))

      /** Assignment */
      // !!! This method is responsible for some tree sharing, but a diligent
      // reviewer pointed out that we shouldn't blindly duplicate these trees
      // as there might be DefTrees nested beneath them.  It's not entirely
      // clear how to proceed, so for now it retains the non-duplicating behavior.
      def ===(rhs: Tree)            = Assign(target, rhs)

      /** Casting & type tests -- working our way toward understanding exactly
       *  what differs between the different forms of IS and AS.
       *
       *  See ticket #2168 for one illustration of AS vs. AS_ANY.
       */
      def AS(tpe: Type)       = gen.mkAsInstanceOf(target, tpe, any = true, wrapInApply = false)
      def IS_OBJ(tpe: Type)   = gen.mkIsInstanceOf(target, tpe, any = false)

      def GETCLASS()          = fn(target, Object_getClass)
    }

    case class SelectStart(tree: Select) {
      def apply(args: Tree*) = Apply(tree, args.toList)
    }

    class CaseStart(pat: Tree, guard: Tree) {
      def IF(g: Tree): CaseStart    = new CaseStart(pat, g)
      def ==>(body: Tree): CaseDef  = CaseDef(pat, guard, body)
    }

    class IfStart(cond: Tree, thenp: Tree) {
      def THEN(x: Tree)     = new IfStart(cond, x)
      def ELSE(elsep: Tree) = If(cond, thenp, elsep)
      def ENDIF             = If(cond, thenp, EmptyTree)
    }
    class TryStart(body: Tree, catches: List[CaseDef], fin: Tree) {
      def CATCH(xs: CaseDef*) = new TryStart(body, xs.toList, fin)
      def ENDTRY              = Try(body, catches, fin)
    }

    def CASE(pat: Tree): CaseStart  = new CaseStart(pat, EmptyTree)
    def DEFAULT: CaseStart          = new CaseStart(Ident(nme.WILDCARD), EmptyTree)

    def NEW(tpt: Tree, args: Tree*): Tree   = New(tpt, List(args.toList))

    def NOT(tree: Tree)   = Select(tree, Boolean_not)
    def AND(guards: Tree*) = if (guards.isEmpty) EmptyTree else guards reduceLeft gen.mkAnd

    def IF(tree: Tree)    = new IfStart(tree, EmptyTree)
    def TRY(tree: Tree)   = new TryStart(tree, Nil, EmptyTree)
    def BLOCK(xs: Tree*)  = Block(xs.init.toList, xs.last)
    def SOME(xs: Tree*)   = Apply(SomeClass.companionSymbol, gen.mkTuple(xs.toList))

    /** Typed trees from symbols. */
    def REF(sym: Symbol)            = gen.mkAttributedRef(sym)
    def REF(pre: Type, sym: Symbol) = gen.mkAttributedRef(pre, sym)

    /** Implicits - some of these should probably disappear **/
    implicit def mkTreeMethods(target: Tree): TreeMethods = new TreeMethods(target)
    implicit def mkTreeMethodsFromSymbol(target: Symbol): TreeMethods = new TreeMethods(Ident(target))

    /** (foo DOT bar) might be simply a Select, but more likely it is to be immediately
     *  followed by an Apply.  We don't want to add an actual apply method to arbitrary
     *  trees, so SelectStart is created with an apply - and if apply is not the next
     *  thing called, the implicit from SelectStart -> Tree will provide the tree.
     */
    implicit def mkTreeFromSelectStart(ss: SelectStart): Select = ss.tree
    implicit def mkTreeMethodsFromSelectStart(ss: SelectStart): TreeMethods = mkTreeMethods(ss.tree)
  }
}