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cats.scala
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cats.scala
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package com.thoughtworks.dsl
package domains
import _root_.cats.{Applicative, FlatMap}
import com.thoughtworks.dsl.Dsl
import com.thoughtworks.dsl.Dsl.!!
import _root_.cats.MonadError
import com.thoughtworks.Extractor._
import com.thoughtworks.dsl.keywords.Catch.CatchDsl
import com.thoughtworks.dsl.keywords.{Monadic, Return}
import scala.language.higherKinds
import scala.language.implicitConversions
import scala.util.control.Exception.Catcher
/** Contains interpreters to enable [[Dsl.Keyword#unary_$bang !-notation]]
* for [[keywords.Monadic]] and other keywords
* in code blocks whose type support [[cats.FlatMap]] and [[cats.MonadError]].
*
* @example [[cats.free.Trampoline Trampoline]] is a monadic data type that performs tail call optimization.
* It can be built from a `@[[Dsl.reset reset]]` code block within some [[Dsl.Keyword#unary_$bang !-notation]],
* similar to the [[com.thoughtworks.each.Monadic.EachOps#each each]] method in
* [[https://github.com/ThoughtWorksInc/each 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")
* }}}
* @example A `@[[Dsl.reset 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 `@[[Dsl.reset 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")
* }}}
* @author 杨博 (Yang Bo)
*/
object cats {
protected type MonadThrowable[F[_]] = MonadError[F, Throwable]
implicit def catsReturnDsl[F[_], A, B](implicit applicative: Applicative[F],
restReturnDsl: Dsl[Return[A], B, Nothing]): Dsl[Return[A], F[B], Nothing] = {
(keyword: Return[A], handler: Nothing => F[B]) =>
applicative.pure(restReturnDsl.cpsApply(keyword, identity))
}
implicit def catsCatchDsl[F[_], A, B](implicit monadError: MonadThrowable[F]): CatchDsl[F[A], F[B], A] = {
(block: F[A] !! A, catcher: Catcher[F[A] !! A], handler: A => F[B]) =>
val fa = monadError.flatMap(monadError.pure(block))(_(monadError.pure))
val protectedFa = monadError.handleErrorWith(fa) {
case catcher.extract(recovered) =>
recovered(monadError.pure)
case e =>
monadError.raiseError[A](e)
}
monadError.flatMap(protectedFa)(handler)
}
implicit def catsMonadicDsl[F[_], A, B](implicit flatMap: FlatMap[F]): Dsl[Monadic[F, A], F[B], A] = {
(keyword: Monadic[F, A], handler: A => F[B]) =>
flatMap.flatMap(keyword.fa)(handler)
}
}