Scala example source code file (ControlContext.scala)

This example Scala source code file (ControlContext.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

a, a, a1, annotation, b, b, b1, controlcontext, controlcontext, exception, exception, staticannotation, throw, typeconstraint

The Scala ControlContext.scala source code

// $Id$

package scala.util.continuations
import annotation.{ Annotation, StaticAnnotation, TypeConstraint }

class cpsParam[-B,+C] extends StaticAnnotation with TypeConstraint

private class cpsSym[B] extends Annotation // implementation detail

private class cpsSynth extends Annotation // implementation detail

private class cpsPlus extends StaticAnnotation with TypeConstraint // implementation detail
private class cpsMinus extends Annotation // implementation detail



final class ControlContext[+A,-B,+C](val fun: (A => B, Exception => B) => C, val x: A) extends Serializable {
  
  /*  
    final def map[A1](f: A => A1): ControlContext[A1,B,C] = {
      new ControlContext((k:(A1 => B)) => fun((x:A) => k(f(x))), null.asInstanceOf[A1])
    }
  
    final def flatMap[A1,B1<:B](f: (A => ControlContext[A1,B1,B])): ControlContext[A1,B1,C] = {
      new ControlContext((k:(A1 => B1)) => fun((x:A) => f(x).fun(k)))
    }
  */


  @noinline final def map[A1](f: A => A1): ControlContext[A1,B,C] = {
    if (fun eq null)
      try {
        new ControlContext(null, f(x)) // TODO: only alloc if f(x) != x
      } catch {
        case ex: Exception => 
          new ControlContext((k: A1 => B, thr: Exception => B) => thr(ex).asInstanceOf[C], null.asInstanceOf[A1])
      }
    else
      new ControlContext({ (k: A1 => B, thr: Exception => B) =>
        fun( { (x:A) =>
          var done = false
          try {
            val res = f(x)
            done = true
            k(res)
          } catch {
            case ex: Exception if !done =>
              thr(ex)
          }
        }, thr)
      }, null.asInstanceOf[A1])
  }
  

  // it would be nice if @inline would turn the trivial path into a tail call.
  // unfortunately it doesn't, so we do it ourselves in SelectiveCPSTransform
  
  @noinline final def flatMap[A1,B1,C1<:B](f: (A => ControlContext[A1,B1,C1])): ControlContext[A1,B1,C] = {
    if (fun eq null)
      try {
        f(x).asInstanceOf[ControlContext[A1,B1,C]]
      } catch {
        case ex: Exception => 
          new ControlContext((k: A1 => B1, thr: Exception => B1) => thr(ex).asInstanceOf[C], null.asInstanceOf[A1])
      }
    else
      new ControlContext({ (k: A1 => B1, thr: Exception => B1) =>
        fun( { (x:A) =>
          var done = false
          try {
            val ctxR = f(x)
            done = true
            val res: C1 = ctxR.foreachFull(k, thr) // => B1
            res
          } catch {
            case ex: Exception if !done =>
              thr(ex).asInstanceOf[B] // => B NOTE: in general this is unsafe! 
          }                           // However, the plugin will not generate offending code
        }, thr.asInstanceOf[Exception=>B]) // => B
      }, null.asInstanceOf[A1])
  }

  final def foreach(f: A => B) = foreachFull(f, throw _)
  
  def foreachFull(f: A => B, g: Exception => B): C = {
    if (fun eq null)
      f(x).asInstanceOf[C]
    else
      fun(f, g)
  }
  

  final def isTrivial = fun eq null
  final def getTrivialValue = x.asInstanceOf[A]

  // need filter or other functions?

  final def flatMapCatch[A1>:A,B1<:B,C1>:C<:B1](pf: PartialFunction[Exception, ControlContext[A1,B1,C1]]): ControlContext[A1,B1,C1] = {
    if (fun eq null)
      this
    else {
      val fun1 = (ret1: A1 => B1, thr1: Exception => B1) => {
        val thr: Exception => B1 = { t: Exception =>
          var captureExceptions = true
          try {
            if (pf.isDefinedAt(t)) {
              val cc1 = pf(t)
              captureExceptions = false
              cc1.foreachFull(ret1, thr1) // Throw => B
            } else {
              captureExceptions = false
              thr1(t) // Throw => B1
            }
          } catch {
            case t1: Exception if captureExceptions => thr1(t1) // => E2
          }
        }
        fun(ret1, thr)// fun(ret1, thr)  // => B
      }
      new ControlContext(fun1, null.asInstanceOf[A1])
    }
  }

  final def mapFinally(f: () => Unit): ControlContext[A,B,C] = {
    if (fun eq null) {
      try {
        f()
        this
      } catch {
        case ex: Exception => 
          new ControlContext((k: A => B, thr: Exception => B) => thr(ex).asInstanceOf[C], null.asInstanceOf[A])
      }
    } else {
      val fun1 = (ret1: A => B, thr1: Exception => B) => {
        val ret: A => B = { x: A =>
          var captureExceptions = true
          try {
            f()
            captureExceptions = false
            ret1(x)
          } catch {
            case t1: Exception if captureExceptions => thr1(t1)
          }
        }
        val thr: Exception => B = { t: Exception =>
          var captureExceptions = true
          try {
            f()
            captureExceptions = false
            thr1(t)
          } catch {
            case t1: Exception if captureExceptions => thr1(t1)
          }
        }
        fun(ret, thr1)
      }
      new ControlContext(fun1, null.asInstanceOf[A])
    }
  }
  
}