Scala example source code file (PatternBindings.scala)

This example Scala source code file (PatternBindings.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

bind, bindings, equalspatternclass, list, list, nil, pattern, pattern, symbol, tree, tree, type, type, typeref

The Scala PatternBindings.scala source code

/* NSC -- new Scala compiler
 * Copyright 2005-2011 LAMP/EPFL
 * Author: Paul Phillips
 */

package scala.tools.nsc
package matching

import transform.ExplicitOuter
import collection.immutable.TreeMap
import PartialFunction._

trait PatternBindings extends ast.TreeDSL
{ 
  self: ExplicitOuter with ParallelMatching =>
  
  import global.{ typer => _, _ }
  import definitions.{ EqualsPatternClass }
  import CODE._
  import Debug._
  
  /** EqualsPattern **/
  def isEquals(tpe: Type)             = cond(tpe) { case TypeRef(_, EqualsPatternClass, _) => true }
  def mkEqualsRef(tpe: Type)          = typeRef(NoPrefix, EqualsPatternClass, List(tpe))
  def decodedEqualsType(tpe: Type)    = condOpt(tpe) { case TypeRef(_, EqualsPatternClass, List(arg)) => arg } getOrElse (tpe)
  
  // A subtype test which creates fresh existentials for type
  // parameters on the right hand side.
  def matches(arg1: Type, arg2: Type) = decodedEqualsType(arg1) matchesPattern decodedEqualsType(arg2)

  // For spotting duplicate unapplies
  def isEquivalentTree(t1: Tree, t2: Tree) = (t1.symbol == t2.symbol) && (t1 equalsStructure t2)
  
  // Reproduce the Bind trees wrapping oldTree around newTree
  def moveBindings(oldTree: Tree, newTree: Tree): Tree = oldTree match {
    case b @ Bind(x, body)  => Bind(b.symbol, moveBindings(body, newTree))
    case _                  => newTree
  }
  
  // used as argument to `EqualsPatternClass'
  case class PseudoType(o: Tree) extends SimpleTypeProxy {
    override def underlying: Type = o.tpe
    override def safeToString: String = "PseudoType("+o+")"
  }

  // If the given pattern contains alternatives, return it as a list of patterns.
  // Makes typed copies of any bindings found so all alternatives point to final state.
  def extractBindings(p: Pattern): List[Pattern] =
    toPats(_extractBindings(p.boundTree, identity))
  
  private def _extractBindings(p: Tree, prevBindings: Tree => Tree): List[Tree] = {
    def newPrev(b: Bind) = (x: Tree) => treeCopy.Bind(b, b.name, x) setType x.tpe

    p match {
      case b @ Bind(_, body)  => _extractBindings(body, newPrev(b))
      case Alternative(ps)    => ps map prevBindings
    }
  }
  
  trait PatternBindingLogic {
    self: Pattern =>
    
    // This is for traversing the pattern tree - pattern types which might have
    // bound variables beneath them return a list of said patterns for flatMapping.
    def subpatternsForVars: List[Pattern] = Nil

    // The outermost Bind(x1, Bind(x2, ...)) surrounding the tree.
    private var _boundTree: Tree = tree
    def boundTree = _boundTree
    def setBound(x: Bind): Pattern = {
      _boundTree = x
      this
    }
    def boundVariables = strip(boundTree)
    
    // If a tree has bindings, boundTree looks something like
    //   Bind(v3, Bind(v2, Bind(v1, tree)))
    // This takes the given tree and creates a new pattern
    //   using the same bindings.
    def rebindTo(t: Tree): Pattern = Pattern(moveBindings(boundTree, t))

    // Wrap this pattern's bindings around (_: Type)
    def rebindToType(tpe: Type, ascription: Type = null): Pattern = {
      val aType = if (ascription == null) tpe else ascription
      rebindTo(Typed(WILD(tpe), TypeTree(aType)) setType tpe)
    }
    
    // Wrap them around _
    def rebindToEmpty(tpe: Type): Pattern =
      rebindTo(Typed(EmptyTree, TypeTree(tpe)) setType tpe)
    
    // Wrap them around a singleton type for an EqualsPattern check.
    def rebindToEqualsCheck(): Pattern =
      rebindToType(equalsCheck)
    
    // Like rebindToEqualsCheck, but subtly different.  Not trying to be
    // mysterious -- I haven't sorted it all out yet.
    def rebindToObjectCheck(): Pattern =
      rebindToType(mkEqualsRef(sufficientType), sufficientType)
       
    /** Helpers **/    
    private def wrapBindings(vs: List[Symbol], pat: Tree): Tree = vs match {
      case Nil      => pat
      case x :: xs  => Bind(x, wrapBindings(xs, pat)) setType pat.tpe
    }
    private def strip(t: Tree): List[Symbol] = t match {
      case b @ Bind(_, pat) => b.symbol :: strip(pat)
      case _                => Nil
    }
    private def deepstrip(t: Tree): List[Symbol] =
      treeCollect(t, { case x: Bind => x.symbol })
  }

  case class Binding(pvar: Symbol, tvar: Symbol) {
    override def toString() = pvar.name + " -> " + tvar.name
  }

  class Bindings(private val vlist: List[Binding]) {
    // if (!vlist.isEmpty)
    //   traceCategory("Bindings", this.toString)

    def get() = vlist
    def toMap = vlist map (x => (x.pvar, x.tvar)) toMap
    
    def add(vs: Iterable[Symbol], tvar: Symbol): Bindings = {
      val newBindings = vs.toList map (v => Binding(v, tvar))
      new Bindings(newBindings ++ vlist)
    }

    override def toString() = 
      if (vlist.isEmpty) "<none>"
      else vlist.mkString(", ")
  }

  val NoBinding: Bindings = new Bindings(Nil)
}