Packages

final case class EitherT[F[_], A, B](value: F[Either[A, B]]) extends Product with Serializable

Transformer for Either, allowing the effect of an arbitrary type constructor F to be combined with the fail-fast effect of Either.

EitherT[F, A, B] wraps a value of type F[Either[A, B]]. An F[C] can be lifted in to EitherT[F, A, C] via EitherT.right, and lifted in to a EitherT[F, C, B] via EitherT.left.

Source
EitherT.scala
Linear Supertypes
Serializable, Serializable, Product, Equals, AnyRef, Any
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  1. EitherT
  2. Serializable
  3. Serializable
  4. Product
  5. Equals
  6. AnyRef
  7. Any
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Visibility
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Instance Constructors

  1. new EitherT(value: F[Either[A, B]])

Value Members

  1. final def !=(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  2. final def ##(): Int
    Definition Classes
    AnyRef → Any
  3. final def ==(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  4. def ===(that: EitherT[F, A, B])(implicit eq: Eq[F[Either[A, B]]]): Boolean
  5. def applyAlt[D](ff: EitherT[F, A, (B) ⇒ D])(implicit F: Apply[F]): EitherT[F, A, D]
  6. final def asInstanceOf[T0]: T0
    Definition Classes
    Any
  7. def biSemiflatMap[C, D](fa: (A) ⇒ F[C], fb: (B) ⇒ F[D])(implicit F: Monad[F]): EitherT[F, C, D]

    Combine leftSemiflatMap and semiflatMap together.

    Combine leftSemiflatMap and semiflatMap together.

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List, String, Int] = EitherT[List, String, Int](List(Left("abc"), Right(123)))
scala> eitherT.biSemiflatMap(string => List(string.length), int => List(int.toFloat))
res0: cats.data.EitherT[List,Int,Float] = EitherT(List(Left(3), Right(123.0)))
  8. def biflatMap[C, D](fa: (A) ⇒ EitherT[F, C, D], fb: (B) ⇒ EitherT[F, C, D])(implicit F: FlatMap[F]): EitherT[F, C, D]
  9. def bimap[C, D](fa: (A) ⇒ C, fb: (B) ⇒ D)(implicit F: Functor[F]): EitherT[F, C, D]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List, String, Int] =
     |   EitherT[List, String, Int](List(Right(123), Left("abc")))
scala> eitherT.bimap(string => string.length, int => int % 100)
res0: EitherT[List, Int, Int] = EitherT(List(Right(23), Left(3)))
  10. def bitraverse[G[_], C, D](f: (A) ⇒ G[C], g: (B) ⇒ G[D])(implicit traverseF: Traverse[F], applicativeG: Applicative[G]): G[EitherT[F, C, D]]
  11. def clone(): AnyRef
    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( ... ) @native() @IntrinsicCandidate()
  12. def collectRight(implicit FA: Alternative[F], FM: Monad[F]): F[B]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List, String, Int] =
     |   EitherT[List, String, Int](List(Right(123), Left("abc")))
scala> eitherT.collectRight
res0: List[Int] = List(123)
  13. def combine(that: EitherT[F, A, B])(implicit F: Apply[F], B: Semigroup[B]): EitherT[F, A, B]

    Similar to Either#combine but mapped over an F context.

    Similar to Either#combine but mapped over an F context.

    Examples:

    scala> import cats.data.EitherT
scala> import cats.implicits._
scala> val l1: EitherT[Option, String, Int] = EitherT.left(Some("error 1"))
scala> val l2: EitherT[Option, String, Int] = EitherT.left(Some("error 2"))
scala> val r3: EitherT[Option, String, Int] = EitherT.right(Some(3))
scala> val r4: EitherT[Option, String, Int] = EitherT.right(Some(4))
scala> val noneEitherT: EitherT[Option, String, Int] = EitherT.left(None)

scala> l1 combine l2
res0: EitherT[Option, String, Int] = EitherT(Some(Left(error 1)))

scala> l1 combine r3
res1: EitherT[Option, String, Int] = EitherT(Some(Left(error 1)))

scala> r3 combine l1
res2: EitherT[Option, String, Int] = EitherT(Some(Left(error 1)))

scala> r3 combine r4
res3: EitherT[Option, String, Int] = EitherT(Some(Right(7)))

scala> l1 combine noneEitherT
res4: EitherT[Option, String, Int] = EitherT(None)

scala> noneEitherT combine l1
res5: EitherT[Option, String, Int] = EitherT(None)

scala> r3 combine noneEitherT
res6: EitherT[Option, String, Int] = EitherT(None)

scala> noneEitherT combine r4
res7: EitherT[Option, String, Int] = EitherT(None)
  14. def compare(that: EitherT[F, A, B])(implicit o: Order[F[Either[A, B]]]): Int
  15. def ensure[AA >: A](onFailure: ⇒ AA)(f: (B) ⇒ Boolean)(implicit F: Functor[F]): EitherT[F, AA, B]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val e1: EitherT[List, String, Int] = EitherT[List, String, Int](List(Right(123), Left("abc")))
scala> e1.ensure("error")(_ > 150)
res0: EitherT[List, String, Int] = EitherT(List(Left(error), Left(abc)))

scala> val e2: EitherT[List, String, Int] = EitherT[List, String, Int](List(Right(123), Left("abc")))
scala> e2.ensure("error")(_ > 100)
res1: EitherT[List, String, Int] = EitherT(List(Right(123), Left(abc)))
  16. def ensureOr[AA >: A](onFailure: (B) ⇒ AA)(f: (B) ⇒ Boolean)(implicit F: Functor[F]): EitherT[F, AA, B]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val e1: EitherT[List, String, Int] = EitherT[List, String, Int](List(Right(123), Left("abc")))
scala> e1.ensureOr(_ => "error")(_ > 100)
res0: EitherT[List, String, Int] = EitherT(List(Right(123), Left(abc)))

scala> val e2: EitherT[List, String, Int] = EitherT[List, String, Int](List(Right(123), Left("abc")))
scala> e2.ensureOr(_ => "error")(_ > 150)
res1: EitherT[List, String, Int] = EitherT(List(Left(error), Left(abc)))
  17. final def eq(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  18. def exists(f: (B) ⇒ Boolean)(implicit F: Functor[F]): F[Boolean]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List, String, Int] = EitherT[List, String, Int](List(Right(123), Left("abc")))
scala> eitherT.exists(_ > 100)
res0: List[Boolean] = List(true, false)
  19. def flatMap[AA >: A, D](f: (B) ⇒ EitherT[F, AA, D])(implicit F: Monad[F]): EitherT[F, AA, D]
  20. def flatMapF[AA >: A, D](f: (B) ⇒ F[Either[AA, D]])(implicit F: Monad[F]): EitherT[F, AA, D]
  21. def fold[C](fa: (A) ⇒ C, fb: (B) ⇒ C)(implicit F: Functor[F]): F[C]

    Transform this EitherT[F, A, B] into a F[C].

    Transform this EitherT[F, A, B] into a F[C].

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List, String, Int] = EitherT[List, String, Int](List(Left("456"), Right(123)))
scala> eitherT.fold(string => string.toInt, int => int)
res0: List[Int] = List(456, 123)
  22. def foldF[C](fa: (A) ⇒ F[C], fb: (B) ⇒ F[C])(implicit F: FlatMap[F]): F[C]

    Transform this EitherT[F, A, B] into a F[C].

    Transform this EitherT[F, A, B] into a F[C].

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List, String, Int] = EitherT[List, String, Int](List(Right(123),Left("abc")))
scala> eitherT.foldF(string => string.split("").toList, _ => List("123"))
res0: List[String] = List(123, a, b, c)
  23. def foldLeft[C](c: C)(f: (C, B) ⇒ C)(implicit F: Foldable[F]): C
  24. def foldRight[C](lc: Eval[C])(f: (B, Eval[C]) ⇒ Eval[C])(implicit F: Foldable[F]): Eval[C]
  25. def forall(f: (B) ⇒ Boolean)(implicit F: Functor[F]): F[Boolean]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List, String, Int] = EitherT[List, String, Int](List(Right(123), Left("abc")))
scala> eitherT.forall(_ > 100)
res0: List[Boolean] = List(true, true)
  26. final def getClass(): Class[_]
    Definition Classes
    AnyRef → Any
    Annotations
    @native() @IntrinsicCandidate()
  27. def getOrElse[BB >: B](default: ⇒ BB)(implicit F: Functor[F]): F[BB]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List,String,Int] = EitherT[List, String,Int](List(Right(123),Left("abc")))
scala> eitherT.getOrElse(456)
res0: List[Int] = List(123, 456)
  28. def getOrElseF[BB >: B](default: ⇒ F[BB])(implicit F: Monad[F]): F[BB]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List,String,Int] = EitherT[List, String,Int](List(Right(123),Left("abc")))
scala> eitherT.getOrElseF(List(456))
res0: List[Int] = List(123, 456)
  29. final def isInstanceOf[T0]: Boolean
    Definition Classes
    Any
  30. def isLeft(implicit F: Functor[F]): F[Boolean]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List,String,Int] = EitherT[List, String,Int](List(Right(123),Left("abc")))
scala> eitherT.isLeft
res0: List[Boolean] = List(false, true)
  31. def isRight(implicit F: Functor[F]): F[Boolean]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List,String,Int] = EitherT[List, String,Int](List(Right(123),Left("abc")))
scala> eitherT.isRight
res0: List[Boolean] = List(true, false)
  32. def leftFlatMap[BB >: B, C](f: (A) ⇒ EitherT[F, C, BB])(implicit F: Monad[F]): EitherT[F, C, BB]
  33. def leftMap[C](f: (A) ⇒ C)(implicit F: Functor[F]): EitherT[F, C, B]
  34. def leftSemiflatMap[D](f: (A) ⇒ F[D])(implicit F: Monad[F]): EitherT[F, D, B]
  35. def leftSemiflatTap[C](f: (A) ⇒ F[C])(implicit F: Monad[F]): EitherT[F, A, B]
  36. def map[D](f: (B) ⇒ D)(implicit F: Functor[F]): EitherT[F, A, D]
  37. def mapK[G[_]](f: ~>[F, G]): EitherT[G, A, B]

    Modify the context F using transformation f.

  38. def merge[AA >: A](implicit ev: <:<[B, AA], F: Functor[F]): F[AA]
  39. final def ne(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  40. final def notify(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native() @IntrinsicCandidate()
  41. final def notifyAll(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native() @IntrinsicCandidate()
  42. def orElse[C, BB >: B](default: ⇒ EitherT[F, C, BB])(implicit F: Monad[F]): EitherT[F, C, BB]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val e1: EitherT[Option,String,Int] = EitherT[Option, String,Int](Some(Right(123)))
scala> e1.orElse(EitherT[Option,Boolean,Int](Some(Right(456))))
res0: EitherT[Option, Boolean, Int] = EitherT(Some(Right(123)))

scala> val e2: EitherT[Option,String,Int] = EitherT[Option, String,Int](Some(Left("abc")))
scala> e2.orElse(EitherT[Option,Boolean,Int](Some(Left(true))))
res1: EitherT[Option, Boolean, Int] = EitherT(Some(Left(true)))
  43. def partialCompare(that: EitherT[F, A, B])(implicit p: PartialOrder[F[Either[A, B]]]): Double
  44. def recover(pf: PartialFunction[A, B])(implicit F: Functor[F]): EitherT[F, A, B]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List,String,Int] =
     |   EitherT[List, String,Int](List(Right(123),Left("abc")))
scala> val pf: PartialFunction[String, Int] = {case "abc" => 456}
scala> eitherT.recover(pf)
res0: EitherT[List, String, Int] = EitherT(List(Right(123), Right(456)))
  45. def recoverWith(pf: PartialFunction[A, EitherT[F, A, B]])(implicit F: Monad[F]): EitherT[F, A, B]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List,String,Int] =
     |   EitherT[List, String,Int](List(Right(123),Left("abc")))
scala> val pf: PartialFunction[String, EitherT[List, String, Int]] =
     |   {case "abc" => EitherT[List, String, Int](List(Right(456)))}
scala> eitherT.recoverWith(pf)
res0: EitherT[List, String, Int] = EitherT(List(Right(123), Right(456)))
  46. def rethrowT(implicit F: MonadError[F, _ >: A]): F[B]

    Inverse of MonadError#attemptT Given MonadError[F, E :> A] transforms Either[F, A, B] to F[B] If the value was B, F[B] is successful If the value was A, F[B] is failed with E

    Inverse of MonadError#attemptT Given MonadError[F, E :> A] transforms Either[F, A, B] to F[B] If the value was B, F[B] is successful If the value was A, F[B] is failed with E

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val e1: EitherT[Option, Unit, Int] = EitherT[Option, Unit, Int](Some(Right(123)))
scala> e1.rethrowT
res0: Option[Int] = Some(123)

scala> val e2: EitherT[Option, Unit, Int] = EitherT[Option, Unit, Int](Some(Left(())))
scala> e2.rethrowT
res1: Option[Int] = None

scala> import scala.util.Try
scala> import java.lang.Exception

scala> val e3: EitherT[Try, Throwable, String] = EitherT[Try, Throwable, String](Try(Right("happy cats")))
scala> e3.rethrowT
res2: util.Try[String] = Success(happy cats)

scala> val e4: EitherT[Try, Throwable, String] = EitherT[Try, Throwable, String](Try(Left(new Exception("sad cats"))))
scala> e4.rethrowT
res3: util.Try[String] = Failure(java.lang.Exception: sad cats)
  47. def semiflatMap[D](f: (B) ⇒ F[D])(implicit F: Monad[F]): EitherT[F, A, D]
  48. def semiflatTap[C](f: (B) ⇒ F[C])(implicit F: Monad[F]): EitherT[F, A, B]
  49. def show(implicit show: Show[F[Either[A, B]]]): String
  50. def subflatMap[AA >: A, D](f: (B) ⇒ Either[AA, D])(implicit F: Functor[F]): EitherT[F, AA, D]
  51. def swap(implicit F: Functor[F]): EitherT[F, B, A]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List,String,Int] = EitherT[List, String,Int](List(Right(123),Left("abc")))
scala> eitherT.swap
res0: EitherT[List,Int,String] = EitherT(List(Left(123), Right(abc)))
  52. final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
    AnyRef
  53. def to[G[_]](implicit F: Functor[F], G: Alternative[G]): F[G[B]]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List, String, Int] = EitherT[List, String, Int](List(Right(123), Left("abc")))
scala> eitherT.to[Option]
res0: List[Option[Int]] = List(Some(123), None)
  54. def toNested: Nested[F, [β$2$]Either[A, β$2$], B]

    Transform this EitherT[F, A, B] into a Nested[F, Either[A, *], B].

    Transform this EitherT[F, A, B] into a Nested[F, Either[A, *], B].

    An example where toNested can be used, is to get the Apply.ap function with the behavior from the composed Apply instances from F and Either[A, *], which is inconsistent with the behavior of the ap from Monad of EitherT.

    scala> import cats.data.EitherT
scala> import cats.implicits._
scala> val ff: EitherT[List, String, Int => String] =
     |   EitherT(List(Either.right(_.toString), Either.left("error")))
scala> val fa: EitherT[List, String, Int] =
     |   EitherT(List(Either.right(1), Either.right(2)))
scala> ff.ap(fa)
res0: EitherT[List,String,String] = EitherT(List(Right(1), Right(2), Left(error)))
scala> EitherT((ff.toNested).ap(fa.toNested).value)
res1: EitherT[List,String,String] = EitherT(List(Right(1), Right(2), Left(error), Left(error)))
  55. def toNestedValidated(implicit F: Functor[F]): Nested[F, [β$4$]Validated[A, β$4$], B]

    Transform this EitherT[F, A, B] into a Nested[F, Validated[A, *], B].

    Transform this EitherT[F, A, B] into a Nested[F, Validated[A, *], B].

    Example:

    scala> import cats.data.{EitherT, Validated}
scala> import cats.implicits._
scala> val f: Int => String = i => (i*2).toString
scala> val r1: EitherT[Option, String, Int => String] = EitherT.right(Some(f))
r1: cats.data.EitherT[Option,String,Int => String] = EitherT(Some(Right(<function1>)))
scala> val r2: EitherT[Option, String, Int] = EitherT.right(Some(10))
r2: cats.data.EitherT[Option,String,Int] = EitherT(Some(Right(10)))
scala> type ErrorOr[A] = Validated[String, A]
scala> (r1.toNestedValidated).ap(r2.toNestedValidated)
res0: cats.data.Nested[Option,ErrorOr,String] = Nested(Some(Valid(20)))
  56. def toNestedValidatedNec(implicit F: Functor[F]): Nested[F, [β$8$]Validated[Type[A], β$8$], B]

    Transform this EitherT[F, A, B] into a Nested[F, ValidatedNec[A, *], B].

  57. def toNestedValidatedNel(implicit F: Functor[F]): Nested[F, [β$6$]Validated[NonEmptyList[A], β$6$], B]

    Transform this EitherT[F, A, B] into a Nested[F, ValidatedNel[A, *], B].

  58. def toOption(implicit F: Functor[F]): OptionT[F, B]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List, String, Int] = EitherT[List, String, Int](List(Right(123), Left("abc")))
scala> eitherT.toOption
res0: OptionT[List, Int] = OptionT(List(Some(123), None))
  59. def toValidated(implicit F: Functor[F]): F[Validated[A, B]]
  60. def toValidatedNec(implicit F: Functor[F]): F[ValidatedNec[A, B]]
  61. def toValidatedNel(implicit F: Functor[F]): F[ValidatedNel[A, B]]
  62. def transform[C, D](f: (Either[A, B]) ⇒ Either[C, D])(implicit F: Functor[F]): EitherT[F, C, D]
  63. def traverse[G[_], D](f: (B) ⇒ G[D])(implicit traverseF: Traverse[F], applicativeG: Applicative[G]): G[EitherT[F, A, D]]
  64. val value: F[Either[A, B]]
  65. def valueOr[BB >: B](f: (A) ⇒ BB)(implicit F: Functor[F]): F[BB]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List, String, Int] = EitherT[List, String, Int](List(Right(123), Left("abc")))
scala> eitherT.valueOr(_.length)
res0: List[Int] = List(123, 3)
  66. def valueOrF[BB >: B](f: (A) ⇒ F[BB])(implicit F: Monad[F]): F[BB]

    Example:

    Example:

    scala> import cats.implicits._
scala> import cats.data.EitherT

scala> val eitherT: EitherT[List, String, Int] = EitherT[List, String, Int](List(Right(123), Left("abc")))
scala> eitherT.valueOrF(string => List(string.length))
res0: List[Int] = List(123, 3)
  67. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  68. final def wait(arg0: Long): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... ) @native()
  69. final def wait(): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  70. def withValidated[C, D](f: (Validated[A, B]) ⇒ Validated[C, D])(implicit F: Functor[F]): EitherT[F, C, D]

    Run this value as a Validated against the function and convert it back to an EitherT.

    Run this value as a Validated against the function and convert it back to an EitherT.

    The Applicative instance for EitherT "fails fast" - it is often useful to "momentarily" have it accumulate errors instead, which is what the Validated data type gives us.

    Example:

    scala> import cats.implicits._
scala> type Error = String
scala> val v1: Validated[NonEmptyList[Error], Int] = Validated.invalidNel("error 1")
scala> val v2: Validated[NonEmptyList[Error], Int] = Validated.invalidNel("error 2")
scala> val eithert: EitherT[Option, Error, Int] = EitherT.leftT[Option, Int]("error 3")
scala> eithert.withValidated { v3 => (v1, v2, v3.toValidatedNel).mapN { case (i, j, k) => i + j + k } }
res0: EitherT[Option, NonEmptyList[Error], Int] = EitherT(Some(Left(NonEmptyList(error 1, error 2, error 3))))

Deprecated Value Members

  1. def finalize(): Unit
    Attributes
    protected[lang]
    Definition Classes
    AnyRef
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    @throws( classOf[java.lang.Throwable] ) @Deprecated
    Deprecated

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Inherited from Serializable

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