Package

com.thoughtworks.dsl

keywords

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package keywords

Contains built-in domain-specific Keywords and their corresponding interpreters.

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package.scala
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Type Members

  1. trait AsynchronousIo[Value] extends Keyword[AsynchronousIo[Value], Value]

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  2. final case class Await[Value](future: Future[Value]) extends AnyVal with Keyword[Await[Value], Value] with Product with Serializable

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    Await is a Keyword to extract value from a scala.concurrent.Future.

    Await is a Keyword to extract value from a scala.concurrent.Future.

    This keyword is available in functions whose return types are Future, domains.task.Task, or any exception aware continuations as (_ !! Throwable !! _).

    Author:

    杨博 (Yang Bo)

    Example:
    1. Given a Future:

      import scala.concurrent.Future
      val myFuture40 = Future {
        40
      }

      It can be Await in another Future

      import scala.concurrent.Future
      def myFuture42 = Future {
        !Await(myFuture40) + 2
      }

      It can be converted to a domains.task.Task with the help of Await.

      import com.thoughtworks.dsl.domains.task._
      import com.thoughtworks.dsl.keywords._
      val myTask = Task {
        !Await(myFuture42)
      }

      Then a domains.task.Task can be converted back to a scala.concurrent.Future via domains.task.Task.toFuture.

      val myAssertionTask = Task {
        !Shift(myTask) should be(42)
      }
      Task.toFuture(myAssertionTask)
  3. final case class Catch[Domain, Value](block: !![Domain, Value], catcher: Catcher[!![Domain, Value]]) extends Keyword[Catch[Domain, Value], Value] with Product with Serializable

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    Author:

    杨博 (Yang Bo)

  4. sealed class Continue extends AnyRef

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    The base type of Continue keyword.

    The base type of Continue keyword.

    See also

    The Continue object, which is the only instance of this Continue class.

  5. final case class Each[Element](elements: Traversable[Element]) extends Keyword[Each[Element], Element] with Product with Serializable

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    Author:

    杨博 (Yang Bo)

  6. final case class Fork[Element](elements: Traversable[Element]) extends AnyVal with Keyword[Fork[Element], Element] with Product with Serializable

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  7. final case class Get[S]() extends Keyword[Get[S], S] with Product with Serializable

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    Author:

    杨博 (Yang Bo)

    See also

    Put

  8. final case class Monadic[F[_], A](fa: F[A]) extends Keyword[Monadic[F, A], A] with Product with Serializable

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    A keyword for extracting monadic value from the monadic expression fa.

    A keyword for extracting monadic value from the monadic expression fa.

    To do

    Monadic should be a scala.AnyVal after https://github.com/scala/bug/issues/10595 is resolved.

    See also

    com.thoughtworks.dsl.domains.scalaz for using this Monadic keyword with scalaz.Monad.

    com.thoughtworks.dsl.domains.cats for using this Monadic keyword with cats.Monad.

  9. final case class NoneSafe[A](option: Option[A]) extends AnyVal with Keyword[NoneSafe[A], A] with Product with Serializable

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  10. final case class NullSafe[A <: AnyRef](nullable: A @com.thoughtworks.dsl.Dsl.reset) extends AnyVal with Product with Serializable

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    NullSafe is a keyword to perform null check.

    NullSafe is a keyword to perform null check.

    Author:

    杨博 (Yang Bo)

    Examples:
    1. The ? operator usually works with Java libraries that may produce null.

      import com.thoughtworks.dsl.keywords.NullSafe._
      val myMap = new java.util.HashMap[String, String]();
      ((myMap.get("key1").? + myMap.get("key2").?): @ ?) should be(null)
    2. ,
    3. You can use ? annotation to represent a nullable value.

      import com.thoughtworks.dsl.keywords.NullSafe._
      case class Tree(left: Tree @ ? = null, right: Tree @ ? = null, value: String @ ? = null)
      val root: Tree @ ? = Tree(
        left = Tree(
          left = Tree(value = "left-left"),
          right = Tree(value = "left-right")
        ),
        right = Tree(value = "right")
      )

      A normal . is not null safe, when selecting left, right or value on a null value.

      a[NullPointerException] should be thrownBy {
        root.right.left.right.value
      }

      The above code throws an exception because root.right.left is null. The exception can be avoided by using ? on a nullable value:

      root.?.right.?.left.?.right.?.value should be(null)

      The entire expression will be null if one of ? is performed on a null value.


      The boundary of a null safe operator ? is the nearest enclosing expression whose type is annotated as @ ?.

      ("Hello " + ("world " + root.?.right.?.left.?.value)) should be("Hello world null")
      ("Hello " + (("world " + root.?.right.?.left.?.value.?): @ ?)) should be("Hello null")
      (("Hello " + ("world " + root.?.right.?.left.?.value.?)): @ ?) should be(null)
    Note

    The ? operator is only available on nullable values. A type is considered as nullable if it is a reference type, no matter it is annotated as @ ? or not.

    import com.thoughtworks.dsl.keywords.NullSafe._
    val explicitNullable: String @ ? = null
    ((explicitNullable.? + " Doe") : @ ?) should be(null)
    val implicitNullable: String = null
    ((implicitNullable.? + " Doe") : @ ?) should be(null)

    A type is considered as not nullable if it is a value type.

    val implicitNotNullable: Int = 0
    "(implicitNotNullable.? + 42) : @ ?" shouldNot compile

    Alternatively, a type can be considered as not nullable by explicitly converting it to NotNull.

    val explicitNotNullable: NotNull[String] = NotNull("John")
    """(explicitNotNullable.? + " Doe") : @ ?""" shouldNot compile
    See also

    NoneSafe for similar checks on scala.Options.

  11. final case class Put[S](value: S) extends AnyVal with Keyword[Put[S], Unit] with Product with Serializable

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    Put is a Keyword to put the value to the context.

    Put is a Keyword to put the value to the context.

    Purely functional programming languages usually do not support native first-class mutable variables. In those languages, mutable states can be implemented in state monads.

    Put and Get are the Dsl-based replacements of state monads.

    We use unary function as the domain of mutable state. The parameter of the unary function can be read from the Get keyword, and changed by the Put keyword.

    Author:

    杨博 (Yang Bo)

    Examples:
    1. Put and Get support multiple states. The following code creates a formatter that Put parts of content into a Vector[Any] of string buffers.

      def formatter: Double => Int => Vector[Any] => String = {
        !Put(!Get[Vector[Any]] :+ "x=")
        !Put(!Get[Vector[Any]] :+ !Get[Double])
        !Put(!Get[Vector[Any]] :+ ",y=")
        !Put(!Get[Vector[Any]] :+ !Get[Int])
        !Return((!Get[Vector[Any]]).mkString)
      }
      formatter(0.5)(42)(Vector.empty) should be("x=0.5,y=42")
    2. ,
    3. The following example creates a function that accepts a string parameter and returns the upper-cased last character of the parameter.

      def upperCasedLastCharacter: String => Char = {
        val initialValue = !Get[String]()
        !Put(initialValue.toUpperCase)
        val upperCased = !Get[String]()
        Function.const(upperCased.last)
      }

      For example, given a string of foo, the upper-cased last character should be O.

      // Output: O
      upperCasedLastCharacter("foo") should be('O')
    See also

    Get

  12. final case class Return[ReturnValue](returnValue: ReturnValue) extends AnyVal with Keyword[Return[ReturnValue], Nothing] with Product with Serializable

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    A Dsl.Keyword to early return a lifted value from the enclosing function.

    A Dsl.Keyword to early return a lifted value from the enclosing function.

    Author:

    杨博 (Yang Bo)

    Examples:
    1. Since this Return keyword can automatically lift the return type, TailCalls.done can be omitted.

      import scala.util.Random
      import scala.util.control.TailCalls
      import scala.util.control.TailCalls.TailRec
      def randomInt(): TailRec[Int] = {
        while (true) {
          val r = Random.nextInt(100)
          if (r % 10 != r / 10) {
            !Return(r)
          }
        }
        throw new AssertionError("Unreachable code");
      }
      val r = randomInt().result
      r should be < 100
      r % 10 should not be r / 10
    2. ,
    3. Suppose you are generating a random integer less than 100, whose first digit and second digit is different. A solution is generating integers in an infinite loop, and Return from the loop when the generated integer conforms with requirements.

      import scala.util.Random
      import scala.util.control.TailCalls
      import scala.util.control.TailCalls.TailRec
      def randomInt(): TailRec[Int] = {
        while (true) {
          val r = Random.nextInt(100)
          if (r % 10 != r / 10) {
            !Return(TailCalls.done(r))
          }
        }
        throw new AssertionError("Unreachable code");
      }
      val r = randomInt().result
      r should be < 100
      r % 10 should not be r / 10
  13. final case class Shift[Domain, Value](continuation: !![Domain, Value]) extends AnyVal with Keyword[Shift[Domain, Value], Value] with Product with Serializable

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    Author:

    杨博 (Yang Bo)

  14. final case class Using[R <: AutoCloseable](open: () ⇒ R) extends AnyVal with Keyword[Using[R], R] with Product with Serializable

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    Author:

    杨博 (Yang Bo)

  15. final case class Yield[Element](element: Element) extends AnyVal with Keyword[Yield[Element], Unit] with Product with Serializable

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    Author:

    杨博 (Yang Bo)

    Example:
    1. This Yield keyword must be put inside a function that returns Seq[Element] or Seq[Element] !! ..., or it will not compile.

      "def f(): Int = !Yield(1)" shouldNot compile

Value Members

  1. object AsynchronousIo

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  2. object Await extends Serializable

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  3. object Catch extends LowPriorityCatch0 with Serializable

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  4. object Continue extends Continue with Keyword[Continue, Nothing] with Product with Serializable

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    A keyword to skip the current iteration in a collection comprehension block.

    A keyword to skip the current iteration in a collection comprehension block.

    Author:

    杨博 (Yang Bo)

    Example:
    1. Each and Continue can be used to calculate composite numbers and prime numbers.

      def compositeNumbersBelow(maxNumber: Int) = collection.immutable.HashSet {
        val factor = !Each(2 until math.ceil(math.sqrt(maxNumber)).toInt)
        !Each(2 * factor until maxNumber by factor)
      }
      compositeNumbersBelow(13) should be(Set(4, 6, 8, 9, 10, 12))
      def primeNumbersBelow(maxNumber: Int) = Seq {
        val compositeNumbers = compositeNumbersBelow(maxNumber)
        val i = !Each(2 until maxNumber)
        if (compositeNumbers(i)) !Continue
        i
      }
      primeNumbersBelow(13) should be(Array(2, 3, 5, 7, 11))
    Note

    This Continue keyword is usually used with Each, to skip an element in the loop.

    See also

    Each for creating collection comprehensions.

  5. object Each extends Serializable

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  6. object Fork extends Serializable

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  7. object Get extends Serializable

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  8. object Monadic extends Serializable

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  9. object NoneSafe extends Serializable

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  10. object NullSafe extends Serializable

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  11. object Put extends Serializable

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  12. object Return extends Serializable

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  13. object Shift extends LowPriorityShift0 with Serializable

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  14. object Using extends Serializable

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  15. object Yield extends LowPriorityYield0 with Serializable

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