Class Either<A,B>

java.lang.Object
fj.data.Either<A,B>
Direct Known Subclasses:
Either.Left, Either.Right
public abstract class Either<A,B> extends Object
The Either type represents a value of one of two possible types (a disjoint union). The data constructors; Left and Right represent the two possible values. The Either type is often used as an alternative to scala.Option where Left represents failure (by convention) and Right is akin to Some.
Version:
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  • Constructor Details

    • Either

      private Either()

  • Method Details

    • left

      public final Either.LeftProjection<A,B> left()
      Projects this either as a left.
      Returns:
      A left projection of this either.

    • right

      public final Either.RightProjection<A,B> right()
      Projects this either as a right.
      Returns:
      A right projection of this either.

    • isLeft

      public abstract boolean isLeft()
      Returns true if this either is a left, false otherwise.
      Returns:
      true if this either is a left, false otherwise.

    • isRight

      public abstract boolean isRight()
      Returns true if this either is a right, false otherwise.
      Returns:
      true if this either is a right, false otherwise.

    • either

      public abstract <X> X either(F<A,X> left, F<B,X> right)
      The catamorphism for either. Folds over this either breaking into left or right.
      Parameters:
      left - The function to call if this is left.
      right - The function to call if this is right.
      Returns:
      The reduced value.

    • bimap

      public final <X,Y> Either<X,Y> bimap(F<A,X> left, F<B,Y> right)
      Map the given functions across the appropriate side.
      Parameters:
      left - The function to map if this is left.
      right - The function to map if this is right.
      Returns:
      A new either value after mapping with the appropriate function applied.

    • equals

      public final boolean equals(Object other)
      Overrides:
      equals in class Object

    • hashCode

      public final int hashCode()
      Overrides:
      hashCode in class Object

    • swap

      public final Either<B,A> swap()
      If this is a left, then return the left value in right, or vice versa.
      Returns:
      The value of this either swapped to the opposing side.

    • left

      public static <A,B> Either<A,B> left(A a)
      Construct a left value of either.
      Parameters:
      a - The value underlying the either.
      Returns:
      A left value of either.

    • left_

      public static <A,B> F<A, Either<A,B>> left_()
      A function that constructs a left value of either.
      Returns:
      A function that constructs a left value of either.

    • right_

      public static <A,B> F<B, Either<A,B>> right_()
      A function that constructs a right value of either.
      Returns:
      A function that constructs a right value of either.

    • right

      public static <A,B> Either<A,B> right(B b)
      Construct a right value of either.
      Parameters:
      b - The value underlying the either.
      Returns:
      A right value of either.

    • either_

      public static <A,B,X> F<Either<A,B>, X> either_(F<A,X> left, F<B,X> right)
      First class catamorphism for either. Folds over this either breaking into left or right.
      Parameters:
      left - The function to call if this is left.
      right - The function to call if this is right.
      Returns:
      The reducing function.

    • leftMap

      public final <X> Either<X,B> leftMap(F<A,X> f)
      Map the given function across this either's left projection.
      Type Parameters:
      X - the type of the function output
      Parameters:
      f - the given function
      Returns:
      the either

    • leftMap_

      public static <A,B,X> F<F<A,X>, F<Either<A,B>, Either<X,B>>> leftMap_()
      Return a function that maps a given function across this either's left projection.
      Type Parameters:
      A - the type of the right value
      B - the type of the left value
      X - the type of the function output
      Returns:
      A function that maps another function across an either's left projection.

    • rightMap

      public final <X> Either<A,X> rightMap(F<B,X> f)
      Map the given function across this either's right.
      Type Parameters:
      X - the type of the function output
      Parameters:
      f - the given function
      Returns:
      the either

    • rightMap_

      public static <A,B,X> F<F<B,X>, F<Either<A,B>, Either<A,X>>> rightMap_()
      Return a function that maps a given function across this either's right projection.
      Type Parameters:
      A - the type of the right value
      B - the type of the left value
      X - the type of the function output
      Returns:
      A function that maps another function across an either's right projection.

    • joinLeft

      public static <A,B> Either<A,B> joinLeft(Either<Either<A,B>, B> e)
      Joins an either through left.
      Parameters:
      e - The either of either to join.
      Returns:
      An either after joining.

    • joinRight

      public static <A,B> Either<A,B> joinRight(Either<A, Either<A,B>> e)
      Joins an either through right.
      Parameters:
      e - The either of either to join.
      Returns:
      An either after joining.

    • sequenceLeft

      public static <A,X> Either<List<A>,X> sequenceLeft(List<Either<A,X>> a)
      Sequences through the left side of the either monad with a list of values.
      Parameters:
      a - The list of values to sequence with the either monad.
      Returns:
      A sequenced value.
      See Also:

    • sequenceRight

      public static <B,X> Either<X,List<B>> sequenceRight(List<Either<X,B>> a)
      Sequences through the right side of the either monad with a list of values.
      Parameters:
      a - The list of values to sequence with the either monad.
      Returns:
      A sequenced value.
      See Also:

    • traverseListRight

      public final <C> List<Either<A,C>> traverseListRight(F<B,List<C>> f)
      Traversable instance of RightProjection of Either for List.
      Returns:
      traversed value

    • traverseListLeft

      public final <C> List<Either<C,B>> traverseListLeft(F<A,List<C>> f)
      Traversable instance of LeftProjection of Either for List.
      Returns:
      traversed value

    • traverseIORight

      public final <C> IO<Either<A,C>> traverseIORight(F<B,IO<C>> f)
      Traversable instance of RightProjection of Either for IO.
      Returns:
      traversed value

    • traverseIOLeft

      public final <C> IO<Either<C,B>> traverseIOLeft(F<A,IO<C>> f)
      Traversable instance of LeftProjection of Either for IO.
      Returns:
      traversed value

    • traverseOptionRight

      public final <C> Option<Either<A,C>> traverseOptionRight(F<B, Option<C>> f)
      Traversable instance of RightProjection of Either for Option.
      Returns:
      traversed value

    • traverseOptionLeft

      public final <C> Option<Either<C,B>> traverseOptionLeft(F<A, Option<C>> f)
      Traversable instance of LeftProjection of Either for Option.
      Returns:
      traversed value

    • traverseStreamRight

      public final <C> Stream<Either<A,C>> traverseStreamRight(F<B, Stream<C>> f)
      Traversable instance of RightProjection of Either for Stream.
      Returns:
      traversed value

    • traverseStreamLeft

      public final <C> Stream<Either<C,B>> traverseStreamLeft(F<A, Stream<C>> f)
      Traversable instance of LeftProjection of Either for Stream.
      Returns:
      traversed value

    • reduce

      public static <A> A reduce(Either<A,A> e)
      Takes an Either to its contained value within left or right.
      Parameters:
      e - The either to reduce.
      Returns:
      An Either to its contained value within left or right.

    • iif

      public static <A,B> Either<A,B> iif(boolean c, F0<B> right, F0<A> left)
      If the condition satisfies, return the given B in right, otherwise, return the given A in left.
      Parameters:
      c - The condition to test.
      right - The right value to use if the condition satisfies.
      left - The left value to use if the condition does not satisfy.
      Returns:
      A constructed either based on the given condition.

    • lefts

      public static <A,B> List<A> lefts(List<Either<A,B>> es)
      Returns all the left values in the given list.
      Parameters:
      es - The list of possible left values.
      Returns:
      All the left values in the given list.

    • rights

      public static <A,B> List<B> rights(List<Either<A,B>> es)
      Returns all the right values in the given list.
      Parameters:
      es - The list of possible right values.
      Returns:
      All the right values in the given list.

    • toString

      public final String toString()
      Overrides:
      toString in class Object