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added leftT and improved existing lift API for EitherT #1614

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merged 2 commits into from
Apr 24, 2017
Merged

added leftT and improved existing lift API for EitherT #1614

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5940e27
added leftT and improved existing creation API for EitherT
kailuowang Apr 18, 2017
5e67748
added fromOptionF
kailuowang Apr 20, 2017
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13 changes: 13 additions & 0 deletions core/src/main/scala/cats/data/EitherT.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -362,6 +362,19 @@ private[data] trait EitherTFunctions {
EitherT(F.pure(Either.fromOption(opt, ifNone)))
}

/** Transforms an `F[Option]` into an `EitherT`, using the second argument if the `Option` is a `None`.
* {{{
* scala> import cats.implicits._
* scala> val o: Option[Int] = None
* scala> EitherT.fromOptionF(List(o), "Answer not known.")
* res0: EitherT[List, String, Int] = EitherT(List(Left(Answer not known.)))
* scala> EitherT.fromOptionF(List(Option(42)), "Answer not known.")
* res1: EitherT[List, String, Int] = EitherT(List(Right(42)))
* }}}
*/
final def fromOptionF[F[_], E, A](fopt: F[Option[A]], ifNone: => E)(implicit F: Functor[F]): EitherT[F, E, A] =
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Just wondering, is this better than OptionT(fopt).toRight(ifNone) ?

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Didn't know about the OptionT.toRight, Looks like this one has slightly less function calls and an allocation to OptionT?

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@peterneyens anything else in this PR?

EitherT(F.map(fopt)(opt => Either.fromOption(opt, ifNone)))

/** If the condition is satisfied, return the given `A` in `Right`
* lifted into the specified `Applicative`, otherwise, return the
* given `E` in `Left` lifted into the specified `Applicative`.
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