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Doing sequence with effects
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| package habito.effects | |
| object EffSequence { | |
| import org.atnos.eff._ | |
| import Eff._ | |
| import Effects._ | |
| import EvalEffect._ | |
| import WriterCreation._ | |
| import cats.data._ | |
| import cats.syntax.all._ | |
| import Tag._ | |
| object HadoopStack { | |
| trait HadoopTag | |
| case class HadoopConf(mappers: Int) | |
| type HadoopReader[A] = Reader[HadoopConf, A] @@ HadoopTag | |
| type WriterString[A] = Writer[String, A] | |
| type Hadoop = HadoopReader |: WriterString |: Eval |: NoEffect | |
| object Hadoop { | |
| implicit val HadoopReaderMember: Member.Aux[HadoopReader, Hadoop, WriterString |: Eval |: NoEffect] = | |
| Member.first | |
| implicit val WriterStringMember: Member.Aux[WriterString, Hadoop, HadoopReader |: Eval |: NoEffect] = | |
| Member.successor | |
| implicit val EvalMember: Member.Aux[Eval, Hadoop, HadoopReader |: WriterString |: NoEffect] = | |
| Member.successor | |
| } | |
| import Hadoop._ | |
| def askHadoopConf: Eff[Hadoop, HadoopConf] = | |
| ReaderEffect.askTagged | |
| def readFile(path: String): Eff[Hadoop, String] = | |
| for { | |
| c <- askHadoopConf | |
| _ <- tell("Reading from "+path) | |
| } yield c.mappers.toString | |
| import ReaderImplicits._ | |
| def runHadoopReader[R <: Effects, A](conf: HadoopConf): Eff[HadoopReader |: R, A] => Eff[R, A] = | |
| (e: Eff[HadoopReader |: R, A]) => ReaderEffect.runReaderTagged(conf)(e) | |
| } | |
| // this imports the `into` and runXXX syntax | |
| import org.atnos.eff.syntax.all._ | |
| import HadoopStack._ | |
| val list = List(readFile("/tmp/data"), readFile("/tmp/data"), readFile("/tmp/data")) | |
| import cats.std.all._ | |
| val efs = list.sequence | |
| val action = for { | |
| // read a file from hadoop | |
| s <- readFile("/tmp/data") | |
| } yield () | |
| import org.atnos.eff.implicits._ | |
| // and we can run the composite action | |
| action.runReaderTagged(HadoopConf(10)).runWriter.runEval.run | |
| } |
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