Object

com.thoughtworks.dsl

annotations

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object annotations

The namespace that contains annotations of control operators for delimited continuation.

All annotations defined here requires the Scala compiler plugin, which can be added in build.sbt: 

addCompilerPlugin("com.thoughtworks.dsl" %% "compilerplugin" % "latest.release")

Example of definition of shift control operator

Given a class that contains a doShift method, which is marked as @shift

import com.thoughtworks.dsl.annotations.{reset, shift}
implicit class ShiftOps[R, A](f: (A => R) => R) {
  def cpsApply(handler: A => R): R = f(handler)
  @shift def doShift: A = sys.error("Calls to this method should have been translated to `cpsApply`")
}
Source
annotations.scala
Example:

  1. When creating a @reset block that contains the doShift method, then the doShift method should be translated to cpsApply with a handler of captured rest code in the method,

    val explicitResetResult = {
  val i: Int = { (handler: Int => Int) =>
    handler(4) + 2
  }.doShift
  i * 10
}: @reset
explicitResetResult should be {
  ShiftOps { (handler: Int => Int) =>
    handler(4) + 2
  }.cpsApply { i =>
    i * 10
  }
}
explicitResetResult should be(42)

    and the result differs if you move the reset annotation.

    val explicitResetResult2 = {
  val i: Int = { (handler: Int => Int) =>
    handler(4) + 2
  }.doShift : @reset
  i * 10
}
explicitResetResult2 should be {
  val i = ShiftOps { (handler: Int => Int) =>
    handler(4) + 2
  }.cpsApply(identity)
  i * 10
}
explicitResetResult2 should be(60)
Note

If you omit an explicit reset annotation,

def automaticallyReset: Int = {
  val i: Int = { (handler: Int => Int) =>
    handler(4) + 2
  }.doShift
  i * 10
}

then the reset operation will be performed on the enclosing method or function automatically.

automaticallyReset should be {
  ShiftOps { (handler: Int => Int) =>
    handler(4) + 2
  }.cpsApply { i =>
    i * 10
  }
}
automaticallyReset should be(42)
See also

Dsl.Instruction for a sophisticated implementation of cpsApply.

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Type Members

  1. final class reset extends Annotation with StaticAnnotation

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    An annotation to explicitly perform reset control operator on a code block.

  2. final class shift extends Annotation with StaticAnnotation

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    An annotation to mark a method is a shift control operator.

Value Members

  1. final def !=(arg0: Any): Boolean

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  17. final def wait(): Unit

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  18. final def wait(arg0: Long, arg1: Int): Unit

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