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scalaz
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.
Author:
杨博 (Yang Bo)
scalaz.Free.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_.scalaz.Trampoline import _root_.scalaz.Free.Trampoline import com.thoughtworks.dsl.keywords.Monadic._ import com.thoughtworks.dsl.domains.scalaz._ 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 toflatMap
calls by our DSL interpreter. Thus, the methoddslSquare
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")
A@reset
code block can containtry
/catch
/finally
if the monadic data type supports scalaz.MonadError. tryt.scala is a monad transformer that provides scalaz.MonadError, thereforetry
/catch
/finally
expressions can be used inside a@reset
code block whose return type isTryT[Trampoline, ?]
.import com.thoughtworks.tryt.invariant.TryT, TryT._ import scala.util.{Try, Success} type TryTTransfomredTrampoline[A] = TryT[Trampoline, A] val trampolineSuccess0: TryTTransfomredTrampoline[Int] = TryT(Trampoline.done(Try(0))) def dslTryCatch: TryTTransfomredTrampoline[String] = TryT(Trampoline.delay(Try { try { s"Division result: ${!trampoline3 / !trampolineSuccess0}" } catch { case e: ArithmeticException => s"Cannot divide ${!trampoline3} by ${!trampolineSuccess0}" } })): @reset inside(dslTryCatch) { case TryT(trampoline) => trampoline.run should be(Success("Cannot divide 3 by 0")) }
Note that !-notation can be used on both
trampoline3
andtrampolineSuccess0
even when they are different types, i.e.trampoline3
is a vanilla Trampoline, whiletrampolineSuccess0
is a TryT-transfomred Trampoline. It is possible because the interpreters of the keywords.Monadic invoke scalaz.MonadTrans.liftM automatically. The abovedslTryCatch
method is equivalent to the following code in scalaz.syntax: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")) }
Example: -
object
task
Author:
杨博 (Yang Bo)