Value Members

1.  object cats

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

   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)

   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. 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")