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Effect.scala
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Effect.scala
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/*
* Copyright 2017 Typelevel
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package cats
package effect
import simulacrum._
import cats.data.{EitherT, StateT, WriterT}
import scala.annotation.implicitNotFound
import scala.util.Either
/**
* A monad that can suspend side effects into the `F` context and
* that supports lazy and potentially asynchronous evaluation.
*/
@typeclass
@implicitNotFound("""Cannot find implicit value for Effect[${F}].
Building this implicit value might depend on having an implicit
s.c.ExecutionContext in scope, a Strategy or some equivalent type.""")
trait Effect[F[_]] extends Async[F] {
def runAsync[A](fa: F[A])(cb: Either[Throwable, A] => IO[Unit]): IO[Unit]
}
private[effect] trait EffectInstances {
implicit def catsEitherTEffect[F[_]: Effect]: Effect[EitherT[F, Throwable, ?]] =
new Effect[EitherT[F, Throwable, ?]] with Async.EitherTAsync[F, Throwable] {
protected def F = Effect[F]
def runAsync[A](fa: EitherT[F, Throwable, A])(cb: Either[Throwable, A] => IO[Unit]): IO[Unit] =
F.runAsync(fa.value)(cb.compose(_.right.flatMap(x => x)))
}
implicit def catsStateTEffect[F[_]: Effect, S: Monoid]: Effect[StateT[F, S, ?]] =
new Effect[StateT[F, S, ?]] with Async.StateTAsync[F, S] {
protected def F = Effect[F]
def runAsync[A](fa: StateT[F, S, A])(cb: Either[Throwable, A] => IO[Unit]): IO[Unit] =
F.runAsync(fa.runA(Monoid[S].empty))(cb)
}
implicit def catsWriterTEffect[F[_]: Effect, L: Monoid]: Effect[WriterT[F, L, ?]] =
new Effect[WriterT[F, L, ?]] with Async.WriterTAsync[F, L] {
protected def F = Effect[F]
protected def L = Monoid[L]
def runAsync[A](fa: WriterT[F, L, A])(cb: Either[Throwable, A] => IO[Unit]): IO[Unit] =
F.runAsync(fa.run)(cb.compose(_.right.map(_._2)))
}
}
object Effect extends EffectInstances