Packages

object cats

Contains interpreters to enable !-notation for keywords.Monadic and other keywords in code blocks whose type support cats.FlatMap and cats.MonadError.

Author:

杨博 (Yang Bo)

Source
cats.scala
Examples:
  1. Trampoline is a monadic data type that performs tail call optimization. It can be built from a @reset code block within some !-notation, similar to the each method in ThoughtWorks Each.

    import _root_.cats.free.Trampoline
    import _root_.cats.instances.function._
    import com.thoughtworks.dsl.keywords.Monadic._
    import com.thoughtworks.dsl.domains.cats._
    import com.thoughtworks.dsl.Dsl.reset
    
    val trampoline3 = Trampoline.done(3)
    
    def dslSquare = Trampoline.delay {
      s"This string is produced by a trampoline: ${!trampoline3 * !trampoline3}"
    }: @reset
    
    dslSquare.run should be("This string is produced by a trampoline: 9")

    !trampoline3 is a shortcut of !Monadic(trampoline3), which will be converted to flatMap calls by our DSL interpreter. Thus, the method dslSquare is equivalent to the following code in cats.syntax:

    def catsSyntaxSquare = trampoline3.flatMap { tmp1 =>
      trampoline3.flatMap { tmp2 =>
        Trampoline.delay {
          s"This string is produced by a trampoline: ${tmp1 * tmp2}"
        }
      }
    }
    
    catsSyntaxSquare.run should be("This string is produced by a trampoline: 9")
  2. ,
  3. A @reset code block can contain try / catch / finally if the monadic data type supports cats.MonadError. For example, cats.effect.IO is a monadic data type that supports cats.MonadError, therefore try / catch / finally expressions can be used inside a @reset code block whose return type is cats.effect.IO.

    import com.thoughtworks.dsl.keywords.Monadic._
    import com.thoughtworks.dsl.domains.cats._
    import _root_.cats.effect.IO
    import com.thoughtworks.dsl.Dsl.reset
    
    val io0 = IO(0)
    
    def dslTryCatch: IO[String] = IO {
      try {
        s"Division result: ${!io0 / !io0}"
      } catch {
        case e: ArithmeticException =>
          s"Cannot divide ${!io0} by itself"
      }
    }: @reset
    
    dslTryCatch.unsafeRunSync() should be("Cannot divide 0 by itself")

    The above dslTryCatch method is equivalent to the following code in cats.syntax:

    def catsSyntaxTryCatch: IO[String] = {
      import _root_.cats.syntax.applicativeError._
      io0.flatMap { tmp0 =>
        io0.flatMap { tmp1 =>
           IO(s"Division result: ${tmp0 / tmp1}")
        }
      }.handleErrorWith {
        case e: ArithmeticException =>
          io0.flatMap { tmp2 =>
             IO(s"Cannot divide ${tmp2} by itself")
          }
        case e =>
          e.raiseError[IO, String]
      }
    }
    
    catsSyntaxTryCatch.unsafeRunSync() should be("Cannot divide 0 by itself")
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Type Members

  1. type MonadThrowable[F[_]] = MonadError[F, Throwable]
    Attributes
    protected

Value Members

  1. final def !=(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  2. final def ##(): Int
    Definition Classes
    AnyRef → Any
  3. final def ==(arg0: Any): Boolean
    Definition Classes
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  4. final def asInstanceOf[T0]: T0
    Definition Classes
    Any
  5. implicit def catsMonadicDsl[F[_], A, B](implicit flatMap: FlatMap[F]): Dsl[Monadic[F, A], F[B], A]
  6. implicit def catsReturnDsl[F[_], A, B](implicit applicative: Applicative[F], restReturnDsl: Dsl[Return[A], B, Nothing]): Dsl[Return[A], F[B], Nothing]
  7. implicit def catsTryCatch[F[_], A, B](implicit monadError: MonadThrowable[F]): TryCatch[A, F[B], F[A]]
  8. implicit def catsTryFinally[F[_], A, B](implicit monadError: MonadThrowable[F]): TryFinally[A, F[B], F[A], F[Unit]]
  9. def clone(): AnyRef
    Attributes
    protected[java.lang]
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    @native() @throws( ... )
  10. final def eq(arg0: AnyRef): Boolean
    Definition Classes
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  11. def equals(arg0: Any): Boolean
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  12. def finalize(): Unit
    Attributes
    protected[java.lang]
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    @throws( classOf[java.lang.Throwable] )
  13. final def getClass(): Class[_]
    Definition Classes
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    @native()
  14. def hashCode(): Int
    Definition Classes
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    @native()
  15. final def isInstanceOf[T0]: Boolean
    Definition Classes
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  16. final def ne(arg0: AnyRef): Boolean
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  17. final def notify(): Unit
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    @native()
  18. final def notifyAll(): Unit
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    @native()
  19. final def synchronized[T0](arg0: ⇒ T0): T0
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  20. def toString(): String
    Definition Classes
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  21. final def wait(): Unit
    Definition Classes
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    @throws( ... )
  22. final def wait(arg0: Long, arg1: Int): Unit
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    @throws( ... )
  23. final def wait(arg0: Long): Unit
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