trait Traverse[F[_]] extends Functor[F] with Foldable[F] with UnorderedTraverse[F] with Serializable
Traverse, also known as Traversable.
Traversal over a structure with an effect.
Traversing with the cats.Id effect is equivalent to cats.Functor#map. Traversing with the cats.data.Const effect where the first type parameter has a cats.Monoid instance is equivalent to cats.Foldable#fold.
- Self Type
- Traverse[F]
- Alphabetic
- By Inheritance
- Traverse
- UnorderedTraverse
- Foldable
- UnorderedFoldable
- Functor
- Invariant
- Serializable
- Serializable
- AnyRef
- Any
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Abstract Value Members
-
abstract
def
foldLeft[A, B](fa: F[A], b: B)(f: (B, A) ⇒ B): B
Left associative fold on 'F' using the function 'f'.
Left associative fold on 'F' using the function 'f'.
Example:
scala> import cats.Foldable, cats.implicits._ scala> val fa = Option(1) Folding by addition to zero: scala> Foldable[Option].foldLeft(fa, Option(0))((a, n) => a.map(_ + n)) res0: Option[Int] = Some(1)
With syntax extensions,
foldLeft
can be used like:Folding `Option` with addition from zero: scala> fa.foldLeft(Option(0))((a, n) => a.map(_ + n)) res1: Option[Int] = Some(1) There's also an alias `foldl` which is equivalent: scala> fa.foldl(Option(0))((a, n) => a.map(_ + n)) res2: Option[Int] = Some(1)
- Definition Classes
- Foldable
-
abstract
def
foldRight[A, B](fa: F[A], lb: Eval[B])(f: (A, Eval[B]) ⇒ Eval[B]): Eval[B]
Right associative lazy fold on
F
using the folding function 'f'.Right associative lazy fold on
F
using the folding function 'f'.This method evaluates
lb
lazily (in some cases it will not be needed), and returns a lazy value. We are using(A, Eval[B]) => Eval[B]
to support laziness in a stack-safe way. Chained computation should be performed via .map and .flatMap.For more detailed information about how this method works see the documentation for
Eval[_]
.Example:
scala> import cats.Foldable, cats.Eval, cats.implicits._ scala> val fa = Option(1) Folding by addition to zero: scala> val folded1 = Foldable[Option].foldRight(fa, Eval.now(0))((n, a) => a.map(_ + n)) Since `foldRight` yields a lazy computation, we need to force it to inspect the result: scala> folded1.value res0: Int = 1 With syntax extensions, we can write the same thing like this: scala> val folded2 = fa.foldRight(Eval.now(0))((n, a) => a.map(_ + n)) scala> folded2.value res1: Int = 1 Unfortunately, since `foldRight` is defined on many collections - this extension clashes with the operation defined in `Foldable`. To get past this and make sure you're getting the lazy `foldRight` defined in `Foldable`, there's an alias `foldr`: scala> val folded3 = fa.foldr(Eval.now(0))((n, a) => a.map(_ + n)) scala> folded3.value res1: Int = 1
- Definition Classes
- Foldable
-
abstract
def
traverse[G[_], A, B](fa: F[A])(f: (A) ⇒ G[B])(implicit arg0: Applicative[G]): G[F[B]]
Given a function which returns a G effect, thread this effect through the running of this function on all the values in F, returning an F[B] in a G context.
Given a function which returns a G effect, thread this effect through the running of this function on all the values in F, returning an F[B] in a G context.
Example:
scala> import cats.implicits._ scala> def parseInt(s: String): Option[Int] = Either.catchOnly[NumberFormatException](s.toInt).toOption scala> List("1", "2", "3").traverse(parseInt) res0: Option[List[Int]] = Some(List(1, 2, 3)) scala> List("1", "two", "3").traverse(parseInt) res1: Option[List[Int]] = None
Concrete Value Members
-
final
def
!=(arg0: Any): Boolean
- Definition Classes
- AnyRef → Any
-
final
def
##(): Int
- Definition Classes
- AnyRef → Any
-
final
def
==(arg0: Any): Boolean
- Definition Classes
- AnyRef → Any
-
def
as[A, B](fa: F[A], b: B): F[B]
Replaces the
A
value inF[A]
with the supplied value.Replaces the
A
value inF[A]
with the supplied value.Example:
scala> import cats.Functor scala> import cats.implicits.catsStdInstancesForList scala> Functor[List].as(List(1,2,3), "hello") res0: List[String] = List(hello, hello, hello)
- Definition Classes
- Functor
-
final
def
asInstanceOf[T0]: T0
- Definition Classes
- Any
-
def
clone(): AnyRef
- Attributes
- protected[java.lang]
- Definition Classes
- AnyRef
- Annotations
- @native() @throws( ... )
-
def
collectFirst[A, B](fa: F[A])(pf: PartialFunction[A, B]): Option[B]
- Definition Classes
- Foldable
-
def
collectFirstSome[A, B](fa: F[A])(f: (A) ⇒ Option[B]): Option[B]
Like
collectFirst
fromscala.collection.Traversable
but takesA => Option[B]
instead ofPartialFunction
s.Like
collectFirst
fromscala.collection.Traversable
but takesA => Option[B]
instead ofPartialFunction
s.scala> import cats.implicits._ scala> val keys = List(1, 2, 4, 5) scala> val map = Map(4 -> "Four", 5 -> "Five") scala> keys.collectFirstSome(map.get) res0: Option[String] = Some(Four) scala> val map2 = Map(6 -> "Six", 7 -> "Seven") scala> keys.collectFirstSome(map2.get) res1: Option[String] = None
- Definition Classes
- Foldable
-
def
combineAll[A](fa: F[A])(implicit arg0: Monoid[A]): A
Alias for fold.
- def compose[G[_]](implicit arg0: Traverse[G]): Traverse[[α]F[G[α]]]
-
def
compose[G[_]](implicit arg0: Foldable[G]): Foldable[[α]F[G[α]]]
- Definition Classes
- Foldable
-
def
compose[G[_]](implicit arg0: Functor[G]): Functor[[α]F[G[α]]]
- Definition Classes
- Functor
-
def
compose[G[_]](implicit arg0: Invariant[G]): Invariant[[α]F[G[α]]]
- Definition Classes
- Invariant
- def composeContravariant[G[_]](implicit arg0: Contravariant[G]): Contravariant[[α]F[G[α]]]
-
def
composeFunctor[G[_]](implicit arg0: Functor[G]): Invariant[[α]F[G[α]]]
- Definition Classes
- Invariant
-
def
dropWhile_[A](fa: F[A])(p: (A) ⇒ Boolean): List[A]
Convert F[A] to a List[A], dropping all initial elements which match
p
.Convert F[A] to a List[A], dropping all initial elements which match
p
.- Definition Classes
- Foldable
-
final
def
eq(arg0: AnyRef): Boolean
- Definition Classes
- AnyRef
-
def
equals(arg0: Any): Boolean
- Definition Classes
- AnyRef → Any
-
def
exists[A](fa: F[A])(p: (A) ⇒ Boolean): Boolean
Check whether at least one element satisfies the predicate.
Check whether at least one element satisfies the predicate.
If there are no elements, the result is
false
.- Definition Classes
- Foldable → UnorderedFoldable
-
def
existsM[G[_], A](fa: F[A])(p: (A) ⇒ G[Boolean])(implicit G: Monad[G]): G[Boolean]
Check whether at least one element satisfies the effectful predicate.
Check whether at least one element satisfies the effectful predicate.
If there are no elements, the result is
false
.existsM
short-circuits, i.e. once atrue
result is encountered, no further effects are produced.For example:
scala> import cats.implicits._ scala> val F = Foldable[List] scala> F.existsM(List(1,2,3,4))(n => Option(n <= 4)) res0: Option[Boolean] = Some(true) scala> F.existsM(List(1,2,3,4))(n => Option(n > 4)) res1: Option[Boolean] = Some(false) scala> F.existsM(List(1,2,3,4))(n => if (n <= 2) Option(true) else Option(false)) res2: Option[Boolean] = Some(true) scala> F.existsM(List(1,2,3,4))(n => if (n <= 2) Option(true) else None) res3: Option[Boolean] = Some(true) scala> F.existsM(List(1,2,3,4))(n => if (n <= 2) None else Option(true)) res4: Option[Boolean] = None
- Definition Classes
- Foldable
-
def
filter_[A](fa: F[A])(p: (A) ⇒ Boolean): List[A]
Convert F[A] to a List[A], only including elements which match
p
.Convert F[A] to a List[A], only including elements which match
p
.- Definition Classes
- Foldable
-
def
finalize(): Unit
- Attributes
- protected[java.lang]
- Definition Classes
- AnyRef
- Annotations
- @throws( classOf[java.lang.Throwable] )
-
def
find[A](fa: F[A])(f: (A) ⇒ Boolean): Option[A]
Find the first element matching the predicate, if one exists.
Find the first element matching the predicate, if one exists.
- Definition Classes
- Foldable
-
def
flatSequence[G[_], A](fgfa: F[G[F[A]]])(implicit G: Applicative[G], F: FlatMap[F]): G[F[A]]
Thread all the G effects through the F structure and flatten to invert the structure from F[G[F[A]]] to G[F[A]].
Thread all the G effects through the F structure and flatten to invert the structure from F[G[F[A]]] to G[F[A]].
Example:
scala> import cats.implicits._ scala> val x: List[Option[List[Int]]] = List(Some(List(1, 2)), Some(List(3))) scala> val y: List[Option[List[Int]]] = List(None, Some(List(3))) scala> x.flatSequence res0: Option[List[Int]] = Some(List(1, 2, 3)) scala> y.flatSequence res1: Option[List[Int]] = None
-
def
flatTraverse[G[_], A, B](fa: F[A])(f: (A) ⇒ G[F[B]])(implicit G: Applicative[G], F: FlatMap[F]): G[F[B]]
A traverse followed by flattening the inner result.
A traverse followed by flattening the inner result.
Example:
scala> import cats.implicits._ scala> def parseInt(s: String): Option[Int] = Either.catchOnly[NumberFormatException](s.toInt).toOption scala> val x = Option(List("1", "two", "3")) scala> x.flatTraverse(_.map(parseInt)) res0: List[Option[Int]] = List(Some(1), None, Some(3))
-
final
def
fmap[A, B](fa: F[A])(f: (A) ⇒ B): F[B]
Alias for map, since map can't be injected as syntax if the implementing type already had a built-in
.map
method.Alias for map, since map can't be injected as syntax if the implementing type already had a built-in
.map
method.Example:
scala> import cats.implicits._ scala> val m: Map[Int, String] = Map(1 -> "hi", 2 -> "there", 3 -> "you") scala> m.fmap(_ ++ "!") res0: Map[Int,String] = Map(1 -> hi!, 2 -> there!, 3 -> you!)
- Definition Classes
- Functor
-
def
fold[A](fa: F[A])(implicit A: Monoid[A]): A
Fold implemented using the given Monoid[A] instance.
Fold implemented using the given Monoid[A] instance.
- Definition Classes
- Foldable
-
def
foldK[G[_], A](fga: F[G[A]])(implicit G: MonoidK[G]): G[A]
Fold implemented using the given
MonoidK[G]
instance.Fold implemented using the given
MonoidK[G]
instance.This method is identical to fold, except that we use the universal monoid (
MonoidK[G]
) to get aMonoid[G[A]]
instance.For example:
scala> import cats.implicits._ scala> val F = Foldable[List] scala> F.foldK(List(1 :: 2 :: Nil, 3 :: 4 :: 5 :: Nil)) res0: List[Int] = List(1, 2, 3, 4, 5)
- Definition Classes
- Foldable
-
final
def
foldLeftM[G[_], A, B](fa: F[A], z: B)(f: (B, A) ⇒ G[B])(implicit G: Monad[G]): G[B]
Alias for foldM.
-
def
foldM[G[_], A, B](fa: F[A], z: B)(f: (B, A) ⇒ G[B])(implicit G: Monad[G]): G[B]
Perform a stack-safe monadic left fold from the source context
F
into the target monadG
.Perform a stack-safe monadic left fold from the source context
F
into the target monadG
.This method can express short-circuiting semantics. Even when
fa
is an infinite structure, this method can potentially terminate if thefoldRight
implementation forF
and thetailRecM
implementation forG
are sufficiently lazy.Instances for concrete structures (e.g.
List
) will often have a more efficient implementation than the default one in terms offoldRight
.- Definition Classes
- Foldable
-
def
foldMap[A, B](fa: F[A])(f: (A) ⇒ B)(implicit B: Monoid[B]): B
Fold implemented by mapping
A
values intoB
and then combining them using the givenMonoid[B]
instance.Fold implemented by mapping
A
values intoB
and then combining them using the givenMonoid[B]
instance.- Definition Classes
- Foldable
-
def
foldMapM[G[_], A, B](fa: F[A])(f: (A) ⇒ G[B])(implicit G: Monad[G], B: Monoid[B]): G[B]
Monadic folding on
F
by mappingA
values toG[B]
, combining theB
values using the givenMonoid[B]
instance.Monadic folding on
F
by mappingA
values toG[B]
, combining theB
values using the givenMonoid[B]
instance.Similar to foldM, but using a
Monoid[B]
.scala> import cats.Foldable scala> import cats.implicits._ scala> val evenNumbers = List(2,4,6,8,10) scala> val evenOpt: Int => Option[Int] = | i => if (i % 2 == 0) Some(i) else None scala> Foldable[List].foldMapM(evenNumbers)(evenOpt) res0: Option[Int] = Some(30) scala> Foldable[List].foldMapM(evenNumbers :+ 11)(evenOpt) res1: Option[Int] = None
- Definition Classes
- Foldable
-
def
forall[A](fa: F[A])(p: (A) ⇒ Boolean): Boolean
Check whether all elements satisfy the predicate.
Check whether all elements satisfy the predicate.
If there are no elements, the result is
true
.- Definition Classes
- Foldable → UnorderedFoldable
-
def
forallM[G[_], A](fa: F[A])(p: (A) ⇒ G[Boolean])(implicit G: Monad[G]): G[Boolean]
Check whether all elements satisfy the effectful predicate.
Check whether all elements satisfy the effectful predicate.
If there are no elements, the result is
true
.forallM
short-circuits, i.e. once afalse
result is encountered, no further effects are produced.For example:
scala> import cats.implicits._ scala> val F = Foldable[List] scala> F.forallM(List(1,2,3,4))(n => Option(n <= 4)) res0: Option[Boolean] = Some(true) scala> F.forallM(List(1,2,3,4))(n => Option(n <= 1)) res1: Option[Boolean] = Some(false) scala> F.forallM(List(1,2,3,4))(n => if (n <= 2) Option(true) else Option(false)) res2: Option[Boolean] = Some(false) scala> F.forallM(List(1,2,3,4))(n => if (n <= 2) Option(false) else None) res3: Option[Boolean] = Some(false) scala> F.forallM(List(1,2,3,4))(n => if (n <= 2) None else Option(false)) res4: Option[Boolean] = None
- Definition Classes
- Foldable
-
def
fproduct[A, B](fa: F[A])(f: (A) ⇒ B): F[(A, B)]
Tuple the values in fa with the result of applying a function with the value
Tuple the values in fa with the result of applying a function with the value
Example:
scala> import cats.Functor scala> import cats.implicits.catsStdInstancesForOption scala> Functor[Option].fproduct(Option(42))(_.toString) res0: Option[(Int, String)] = Some((42,42))
- Definition Classes
- Functor
-
def
get[A](fa: F[A])(idx: Long): Option[A]
Get the element at the index of the
Foldable
.Get the element at the index of the
Foldable
.- Definition Classes
- Foldable
-
final
def
getClass(): Class[_]
- Definition Classes
- AnyRef → Any
- Annotations
- @native()
-
def
hashCode(): Int
- Definition Classes
- AnyRef → Any
- Annotations
- @native()
-
def
imap[A, B](fa: F[A])(f: (A) ⇒ B)(g: (B) ⇒ A): F[B]
Transform an
F[A]
into anF[B]
by providing a transformation fromA
toB
and one fromB
toA
.Transform an
F[A]
into anF[B]
by providing a transformation fromA
toB
and one fromB
toA
.Example:
scala> import cats.implicits._ scala> import scala.concurrent.duration._ scala> val durSemigroup: Semigroup[FiniteDuration] = | Invariant[Semigroup].imap(Semigroup[Long])(Duration.fromNanos)(_.toNanos) scala> durSemigroup.combine(2.seconds, 3.seconds) res1: FiniteDuration = 5 seconds
-
def
intercalate[A](fa: F[A], a: A)(implicit A: Monoid[A]): A
Intercalate/insert an element between the existing elements while folding.
Intercalate/insert an element between the existing elements while folding.
scala> import cats.implicits._ scala> Foldable[List].intercalate(List("a","b","c"), "-") res0: String = a-b-c scala> Foldable[List].intercalate(List("a"), "-") res1: String = a scala> Foldable[List].intercalate(List.empty[String], "-") res2: String = "" scala> Foldable[Vector].intercalate(Vector(1,2,3), 1) res3: Int = 8
- Definition Classes
- Foldable
-
def
intersperseList[A](xs: List[A], x: A): List[A]
- Attributes
- protected
- Definition Classes
- Foldable
-
def
isEmpty[A](fa: F[A]): Boolean
Returns true if there are no elements.
Returns true if there are no elements. Otherwise false.
- Definition Classes
- Foldable → UnorderedFoldable
-
final
def
isInstanceOf[T0]: Boolean
- Definition Classes
- Any
-
def
lift[A, B](f: (A) ⇒ B): (F[A]) ⇒ F[B]
Lift a function f to operate on Functors
Lift a function f to operate on Functors
Example:
scala> import cats.Functor scala> import cats.implicits.catsStdInstancesForOption scala> val o = Option(42) scala> Functor[Option].lift((x: Int) => x + 10)(o) res0: Option[Int] = Some(52)
- Definition Classes
- Functor
- def map[A, B](fa: F[A])(f: (A) ⇒ B): F[B]
-
def
mapWithIndex[A, B](fa: F[A])(f: (A, Int) ⇒ B): F[B]
Akin to map, but also provides the value's index in structure F when calling the function.
-
def
maximumOption[A](fa: F[A])(implicit A: Order[A]): Option[A]
Find the maximum
A
item in this structure according to theOrder[A]
.Find the maximum
A
item in this structure according to theOrder[A]
.- returns
None
if the structure is empty, otherwise the maximum element wrapped in aSome
.
- Definition Classes
- Foldable
- See also
Reducible#maximum for a version that doesn't need to return an
Option
for structures that are guaranteed to be non-empty.minimumOption for minimum instead of maximum.
-
def
minimumOption[A](fa: F[A])(implicit A: Order[A]): Option[A]
Find the minimum
A
item in this structure according to theOrder[A]
.Find the minimum
A
item in this structure according to theOrder[A]
.- returns
None
if the structure is empty, otherwise the minimum element wrapped in aSome
.
- Definition Classes
- Foldable
- See also
Reducible#minimum for a version that doesn't need to return an
Option
for structures that are guaranteed to be non-empty.maximumOption for maximum instead of minimum.
-
final
def
ne(arg0: AnyRef): Boolean
- Definition Classes
- AnyRef
-
def
nonEmpty[A](fa: F[A]): Boolean
- Definition Classes
- Foldable → UnorderedFoldable
-
final
def
notify(): Unit
- Definition Classes
- AnyRef
- Annotations
- @native()
-
final
def
notifyAll(): Unit
- Definition Classes
- AnyRef
- Annotations
- @native()
-
def
partitionEither[A, B, C](fa: F[A])(f: (A) ⇒ Either[B, C])(implicit A: Alternative[F]): (F[B], F[C])
Separate this Foldable into a Tuple by a separating function
A => Either[B, C]
Equivalent toFunctor#map
and thenAlternative#separate
.Separate this Foldable into a Tuple by a separating function
A => Either[B, C]
Equivalent toFunctor#map
and thenAlternative#separate
.scala> import cats.implicits._ scala> val list = List(1,2,3,4) scala> Foldable[List].partitionEither(list)(a => if (a % 2 == 0) Left(a.toString) else Right(a)) res0: (List[String], List[Int]) = (List(2, 4),List(1, 3)) scala> Foldable[List].partitionEither(list)(a => Right(a * 4)) res1: (List[Nothing], List[Int]) = (List(),List(4, 8, 12, 16))
- Definition Classes
- Foldable
-
def
reduceLeftOption[A](fa: F[A])(f: (A, A) ⇒ A): Option[A]
Reduce the elements of this structure down to a single value by applying the provided aggregation function in a left-associative manner.
Reduce the elements of this structure down to a single value by applying the provided aggregation function in a left-associative manner.
- returns
None
if the structure is empty, otherwise the result of combining the cumulative left-associative result of thef
operation over all of the elements.
- Definition Classes
- Foldable
- See also
reduceRightOption for a right-associative alternative.
Reducible#reduceLeft for a version that doesn't need to return an
Option
for structures that are guaranteed to be non-empty. Example:scala> import cats.implicits._ scala> val l = List(6, 3, 2) This is equivalent to (6 - 3) - 2 scala> Foldable[List].reduceLeftOption(l)(_ - _) res0: Option[Int] = Some(1) scala> Foldable[List].reduceLeftOption(List.empty[Int])(_ - _) res1: Option[Int] = None
-
def
reduceLeftToOption[A, B](fa: F[A])(f: (A) ⇒ B)(g: (B, A) ⇒ B): Option[B]
- Definition Classes
- Foldable
-
def
reduceRightOption[A](fa: F[A])(f: (A, Eval[A]) ⇒ Eval[A]): Eval[Option[A]]
Reduce the elements of this structure down to a single value by applying the provided aggregation function in a right-associative manner.
Reduce the elements of this structure down to a single value by applying the provided aggregation function in a right-associative manner.
- returns
None
if the structure is empty, otherwise the result of combining the cumulative right-associative result of thef
operation over theA
elements.
- Definition Classes
- Foldable
- See also
reduceLeftOption for a left-associative alternative
Reducible#reduceRight for a version that doesn't need to return an
Option
for structures that are guaranteed to be non-empty. Example:scala> import cats.implicits._ scala> val l = List(6, 3, 2) This is eqivalent to 6 - (3 - 2) scala> Foldable[List].reduceRightOption(l)((current, rest) => rest.map(current - _)).value res0: Option[Int] = Some(5) scala> Foldable[List].reduceRightOption(List.empty[Int])((current, rest) => rest.map(current - _)).value res1: Option[Int] = None
-
def
reduceRightToOption[A, B](fa: F[A])(f: (A) ⇒ B)(g: (A, Eval[B]) ⇒ Eval[B]): Eval[Option[B]]
- Definition Classes
- Foldable
-
def
sequence[G[_], A](fga: F[G[A]])(implicit arg0: Applicative[G]): G[F[A]]
Thread all the G effects through the F structure to invert the structure from F[G[A]] to G[F[A]].
Thread all the G effects through the F structure to invert the structure from F[G[A]] to G[F[A]].
Example:
scala> import cats.implicits._ scala> val x: List[Option[Int]] = List(Some(1), Some(2)) scala> val y: List[Option[Int]] = List(None, Some(2)) scala> x.sequence res0: Option[List[Int]] = Some(List(1, 2)) scala> y.sequence res1: Option[List[Int]] = None
-
def
sequence_[G[_], A](fga: F[G[A]])(implicit arg0: Applicative[G]): G[Unit]
Sequence
F[G[A]]
usingApplicative[G]
.Sequence
F[G[A]]
usingApplicative[G]
.This is similar to
traverse_
except it operates onF[G[A]]
values, so no additional functions are needed.For example:
scala> import cats.implicits._ scala> val F = Foldable[List] scala> F.sequence_(List(Option(1), Option(2), Option(3))) res0: Option[Unit] = Some(()) scala> F.sequence_(List(Option(1), None, Option(3))) res1: Option[Unit] = None
- Definition Classes
- Foldable
-
def
size[A](fa: F[A]): Long
The size of this UnorderedFoldable.
The size of this UnorderedFoldable.
This is overridden in structures that have more efficient size implementations (e.g. Vector, Set, Map).
Note: will not terminate for infinite-sized collections.
- Definition Classes
- UnorderedFoldable
-
final
def
synchronized[T0](arg0: ⇒ T0): T0
- Definition Classes
- AnyRef
-
def
takeWhile_[A](fa: F[A])(p: (A) ⇒ Boolean): List[A]
Convert F[A] to a List[A], retaining only initial elements which match
p
.Convert F[A] to a List[A], retaining only initial elements which match
p
.- Definition Classes
- Foldable
-
def
toList[A](fa: F[A]): List[A]
Convert F[A] to a List[A].
Convert F[A] to a List[A].
- Definition Classes
- Foldable
-
def
toString(): String
- Definition Classes
- AnyRef → Any
-
def
traverseWithIndexM[G[_], A, B](fa: F[A])(f: (A, Int) ⇒ G[B])(implicit G: Monad[G]): G[F[B]]
Akin to traverse, but also provides the value's index in structure F when calling the function.
Akin to traverse, but also provides the value's index in structure F when calling the function.
This performs the traversal in a single pass but requires that effect G is monadic. An applicative traversal can be performed in two passes using zipWithIndex followed by traverse.
-
def
traverse_[G[_], A, B](fa: F[A])(f: (A) ⇒ G[B])(implicit G: Applicative[G]): G[Unit]
Traverse
F[A]
usingApplicative[G]
.Traverse
F[A]
usingApplicative[G]
.A
values will be mapped intoG[B]
and combined usingApplicative#map2
.For example:
scala> import cats.implicits._ scala> def parseInt(s: String): Option[Int] = Either.catchOnly[NumberFormatException](s.toInt).toOption scala> val F = Foldable[List] scala> F.traverse_(List("333", "444"))(parseInt) res0: Option[Unit] = Some(()) scala> F.traverse_(List("333", "zzz"))(parseInt) res1: Option[Unit] = None
This method is primarily useful when
G[_]
represents an action or effect, and the specificA
aspect ofG[A]
is not otherwise needed.- Definition Classes
- Foldable
-
def
tupleLeft[A, B](fa: F[A], b: B): F[(B, A)]
Tuples the
A
value inF[A]
with the suppliedB
value, with theB
value on the left.Tuples the
A
value inF[A]
with the suppliedB
value, with theB
value on the left.Example:
scala> import scala.collection.immutable.Queue scala> import cats.Functor scala> import cats.implicits.catsStdInstancesForQueue scala> Functor[Queue].tupleLeft(Queue("hello", "world"), 42) res0: scala.collection.immutable.Queue[(Int, String)] = Queue((42,hello), (42,world))
- Definition Classes
- Functor
-
def
tupleRight[A, B](fa: F[A], b: B): F[(A, B)]
Tuples the
A
value inF[A]
with the suppliedB
value, with theB
value on the right.Tuples the
A
value inF[A]
with the suppliedB
value, with theB
value on the right.Example:
scala> import scala.collection.immutable.Queue scala> import cats.Functor scala> import cats.implicits.catsStdInstancesForQueue scala> Functor[Queue].tupleRight(Queue("hello", "world"), 42) res0: scala.collection.immutable.Queue[(String, Int)] = Queue((hello,42), (world,42))
- Definition Classes
- Functor
-
def
unorderedFold[A](fa: F[A])(implicit arg0: CommutativeMonoid[A]): A
- Definition Classes
- Foldable → UnorderedFoldable
-
def
unorderedFoldMap[A, B](fa: F[A])(f: (A) ⇒ B)(implicit arg0: CommutativeMonoid[B]): B
- Definition Classes
- Foldable → UnorderedFoldable
-
def
unorderedSequence[G[_], A](fga: F[G[A]])(implicit arg0: CommutativeApplicative[G]): G[F[A]]
- Definition Classes
- Traverse → UnorderedTraverse
-
def
unorderedTraverse[G[_], A, B](sa: F[A])(f: (A) ⇒ G[B])(implicit arg0: CommutativeApplicative[G]): G[F[B]]
- Definition Classes
- Traverse → UnorderedTraverse
-
def
void[A](fa: F[A]): F[Unit]
Empty the fa of the values, preserving the structure
Empty the fa of the values, preserving the structure
Example:
scala> import cats.Functor scala> import cats.implicits.catsStdInstancesForList scala> Functor[List].void(List(1,2,3)) res0: List[Unit] = List((), (), ())
- Definition Classes
- Functor
-
final
def
wait(): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws( ... )
-
final
def
wait(arg0: Long, arg1: Int): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws( ... )
-
final
def
wait(arg0: Long): Unit
- Definition Classes
- AnyRef
- Annotations
- @native() @throws( ... )
-
def
widen[A, B >: A](fa: F[A]): F[B]
Lifts natural subtyping covariance of covariant Functors.
Lifts natural subtyping covariance of covariant Functors.
NOTE: In certain (perhaps contrived) situations that rely on universal equality this can result in a
ClassCastException
, because it is implemented as a type cast. It could be implemented asmap(identity)
, but according to the functor laws, that should be equal tofa
, and a type cast is often much more performant. See this example ofwiden
creating aClassCastException
.Example:
scala> import cats.Functor scala> import cats.implicits.catsStdInstancesForOption scala> val s = Some(42) scala> Functor[Option].widen(s) res0: Option[Int] = Some(42)
- Definition Classes
- Functor
-
def
zipWithIndex[A](fa: F[A]): F[(A, Int)]
Traverses through the structure F, pairing the values with assigned indices.
Traverses through the structure F, pairing the values with assigned indices.
The behavior is consistent with the Scala collection library's
zipWithIndex
for collections such asList
.