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retronym/eithert-sequence.scala

Created February 5, 2012 17:51
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EitherT sequence
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eithert-sequence.scala
scala> import scalaz._, Scalaz._, effect._
import scalaz._
import Scalaz._
import effect._
scala> val listIoEither = List(EitherT[IO, Int, String](IO(Right("r"))))
listIoEither: List[scalaz.EitherT[scalaz.effect.IO,Int,String]] = List(scalaz.EitherTFunctions$$anon$20@49ab1824)
scala> val ioEitherList = listIoEither.sequenceU
ioEitherList: scalaz.EitherT[scalaz.effect.IO,Int,List[java.lang.String]] = scalaz.EitherTFunctions$$anon$20@5d38a346
scala> ioEitherList.run.unsafePerformIO
res13: Either[Int,List[java.lang.String]] = Right(List(r))
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retronym commented Feb 5, 2012

This uses Traverse[List] and Applicative[[a]EitherT[IO, Int, a]].

See:

https://github.com/scalaz/scalaz/blob/scalaz-seven/core/src/main/scala/scalaz/std/List.scala#L28

https://github.com/scalaz/scalaz/blob/scalaz-seven/core/src/main/scala/scalaz/EitherT.scala#L258

https://github.com/scalaz/scalaz/blob/scalaz-seven/core/src/main/scala/scalaz/EitherT.scala#L83

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