com.thoughtworks.dsl.domains
Type members
Classlikes
Contains interpreters to enable !-notation for Monadic and other keywords in code blocks whose type support scalaz.Bind, scalaz.MonadError and scalaz.MonadTrans.
Contains interpreters to enable !-notation for Monadic and other keywords in code blocks whose type support scalaz.Bind, scalaz.MonadError and scalaz.MonadTrans.
- Authors
杨博 (Yang Bo)
- Example
scalaz.Free.Trampoline is a monadic data type that performs tail call optimization. It can be built from a
@[[Dsl.reset reset]]
code block within some !-notation, similar to the each method in ThoughtWorks Each.import _root_.scalaz.Trampoline import _root_.scalaz.Free.Trampoline import com.thoughtworks.dsl.keywords.Monadic import com.thoughtworks.dsl.keywords.Monadic.given import com.thoughtworks.dsl.domains.scalaz.given import com.thoughtworks.dsl.bangnotation._ val trampoline3 = Trampoline.done(3) def dslSquare = reset(Trampoline.delay { s"This string is produced by a trampoline: ${!trampoline3 * !trampoline3}" }) dslSquare.run should be("This string is produced by a trampoline: 9")
`!trampoline3` is a shortcut of `!Monadic(trampoline3)`, enabled by `import com.thoughtworks.dsl.keywords.Monadic.given`, which will be converted to `flatMap` calls by our DSL interpreter. Thus, the method `dslSquare` is equivalent to the following code in [[scalaz.syntax]]:
def scalazSyntaxSquare = trampoline3.flatMap { tmp1 => trampoline3.flatMap { tmp2 => Trampoline.delay { s"This string is produced by a trampoline: ${tmp1 * tmp2}" } } } scalazSyntaxSquare.run should be("This string is produced by a trampoline: 9")
<hr/> A `@[[Dsl.reset reset]]` code block can contain `try` / `catch` / `finally` if the monadic data type supports [[scalaz.MonadError]]. [[https://github.com/ThoughtWorksInc/tryt.scala tryt.scala]] is a monad transformer that provides [[scalaz.MonadError]], therefore `try` / `catch` / `finally` expressions can be used inside a `@[[Dsl.reset reset]]` code block whose return type is `TryT[Trampoline, ?]`.
import com.thoughtworks.tryt.invariant.TryT, TryT.given import scala.util.{Try, Success} type TryTTransfomredTrampoline[A] = TryT[Trampoline, A] val trampolineSuccess0: TryTTransfomredTrampoline[Int] = TryT(Trampoline.done(Try(0))) def dslTryCatch: TryTTransfomredTrampoline[String] = reset(TryT(Trampoline.delay(Try { try { s"Division result: ${!trampoline3 / !trampolineSuccess0}" } catch { case e: ArithmeticException => s"Cannot divide ${!trampoline3} by ${!trampolineSuccess0}" } }))) inside(dslTryCatch) { case TryT(trampoline) => trampoline.run should be(Success("Cannot divide 3 by 0")) }
Note that [[Dsl.Keyword#unary_$bang !-notation]] can be used on both `trampoline3` and `trampolineSuccess0` even when they are different types, i.e. `trampoline3` is a vanilla [[scalaz.Free.Trampoline Trampoline]], while `trampolineSuccess0` is a [[com.thoughtworks.tryt.invariant.TryT TryT]]-transfomred [[scalaz.Free.Trampoline Trampoline]]. It is possible because the interpreters of the [[keywords.Monadic]] invoke [[scalaz.MonadTrans.liftM]] automatically. The above `dslTryCatch` method is equivalent to the following code in [[scalaz.syntax]]:
import _root_.scalaz.syntax.monad._ def scalazSyntaxTryCatch: TryTTransfomredTrampoline[String] = { import _root_.scalaz.syntax.monadError._ trampoline3.liftM[TryT].flatMap { tmp0 => trampolineSuccess0.flatMap { tmp1 => TryT(Trampoline.delay(Try(s"Division result: ${tmp0 / tmp1}"))) } }.handleError { case e: ArithmeticException => trampoline3.liftM[TryT].flatMap { tmp2 => trampolineSuccess0.flatMap { tmp3 => TryT(Trampoline.delay(Try(s"Cannot divide ${tmp2} by ${tmp3}"))) } } case e => e.raiseError[TryTTransfomredTrampoline, String] } } inside(scalazSyntaxTryCatch) { case TryT(trampoline) => trampoline.run should be(Success("Cannot divide 3 by 0")) }
Types
The asynchronous task that supports exception handling, resource management, and is stack-safe.
The asynchronous task that supports exception handling, resource management, and is stack-safe.
- Example
A Task can be created from
for
-comprehension, where keywords.Each and keywords.Fork can be used together to asynchronously iterate collections. For example, the aboveconcatenateRemoteData
downloads and concatenates data from multiple URLs.import com.thoughtworks.dsl.bangnotation._ import com.thoughtworks.dsl._ import com.thoughtworks.dsl.keywords._ import com.thoughtworks.dsl.keywords.Shift._ import com.thoughtworks.dsl.domains.Task import java.net.URL def concatenateRemoteData(urls: List[URL], downloader: URL => Task[Vector[Byte]]): Task[Vector[Byte]] = { for { url <- Fork(urls) data <- Shift(downloader(url)) byte <- Each(data) } yield byte }.as[Task[Vector[Byte]]]
A [[Task]] can be also created from [[Task.apply]]
def mockDownloader(url: URL) = Task { "mock data\n".getBytes.toVector }
A [[Task]] can be then converted to [[scala.concurrent.Future]] via [[Task.toFuture]], in order to integrate into other frameworks. In this example, it's a `Future[Assertion]` required by [[org.scalatest.freespec.AsyncFreeSpec]].
val mockUrls = List(new URL("http://example.com/file1"), new URL("http://example.com/file2")) import org.scalatest.Assertion def assertion: Task[Assertion] = *[Task] { !Shift(concatenateRemoteData(mockUrls, mockDownloader)) should be("mock data\nmock data\n".getBytes.toVector) } Task.toFuture(assertion)