DefaultTraverse
Document{}
- Inherited from
- FoldableNFunctions
Value members
Inherited methods
Replaces the A
value in F[A]
with the supplied value.
Replaces the A
value in F[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)
- Inherited from
- Functor
Like collectFirst
from scala.collection.Traversable
but takes A => Option[B]
instead of PartialFunction
s.
Like collectFirst
from scala.collection.Traversable
but takes A => Option[B]
instead of PartialFunction
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
- Inherited from
- Foldable
Monadic version of collectFirstSome
.
Monadic version of collectFirstSome
.
If there are no elements, the result is None
. collectFirstSomeM
short-circuits,
i.e. once a Some element is found, no further effects are produced.
For example:
scala> import cats.implicits._
scala> def parseInt(s: String): Either[String, Int] = Either.catchOnly[NumberFormatException](s.toInt).leftMap(_.getMessage)
scala> val keys1 = List("1", "2", "4", "5")
scala> val map1 = Map(4 -> "Four", 5 -> "Five")
scala> Foldable[List].collectFirstSomeM(keys1)(parseInt(_) map map1.get)
res0: scala.util.Either[String,Option[String]] = Right(Some(Four))
scala> val map2 = Map(6 -> "Six", 7 -> "Seven")
scala> Foldable[List].collectFirstSomeM(keys1)(parseInt(_) map map2.get)
res1: scala.util.Either[String,Option[String]] = Right(None)
scala> val keys2 = List("1", "x", "4", "5")
scala> Foldable[List].collectFirstSomeM(keys2)(parseInt(_) map map1.get)
res2: scala.util.Either[String,Option[String]] = Left(For input string: "x")
scala> val keys3 = List("1", "2", "4", "x")
scala> Foldable[List].collectFirstSomeM(keys3)(parseInt(_) map map1.get)
res3: scala.util.Either[String,Option[String]] = Right(Some(Four))
- Inherited from
- Foldable
Tear down a subset of this structure using a PartialFunction
.
Tear down a subset of this structure using a PartialFunction
.
scala> import cats.implicits._
scala> val xs = List(1, 2, 3, 4)
scala> Foldable[List].collectFold(xs) { case n if n % 2 == 0 => n }
res0: Int = 6
- Inherited from
- Foldable
Tear down a subset of this structure using a A => Option[M]
.
Tear down a subset of this structure using a A => Option[M]
.
scala> import cats.implicits._
scala> val xs = List(1, 2, 3, 4)
scala> def f(n: Int): Option[Int] = if (n % 2 == 0) Some(n) else None
scala> Foldable[List].collectFoldSome(xs)(f)
res0: Int = 6
- Inherited from
- Foldable
Compose Invariant F[_]
and G[_]
then produce Invariant[F[G[_]]]
using their imap
.
Compose Invariant F[_]
and G[_]
then produce Invariant[F[G[_]]]
using their imap
.
Example:
scala> import cats.implicits._
scala> import scala.concurrent.duration._
scala> val durSemigroupList: Semigroup[List[FiniteDuration]] =
| Invariant[Semigroup].compose[List].imap(Semigroup[List[Long]])(Duration.fromNanos)(_.toNanos)
scala> durSemigroupList.combine(List(2.seconds, 3.seconds), List(4.seconds))
res1: List[FiniteDuration] = List(2 seconds, 3 seconds, 4 seconds)
- Inherited from
- Invariant
- Definition Classes
- Functor -> Invariant
- Inherited from
- Functor
Compose Invariant F[_]
and Functor G[_]
then produce Invariant[F[G[_]]]
using F's imap
and G's map
.
Compose Invariant F[_]
and Functor G[_]
then produce Invariant[F[G[_]]]
using F's imap
and G's map
.
Example:
scala> import cats.implicits._
scala> import scala.concurrent.duration._
scala> val durSemigroupList: Semigroup[List[FiniteDuration]] =
| Invariant[Semigroup]
| .composeFunctor[List]
| .imap(Semigroup[List[Long]])(Duration.fromNanos)(_.toNanos)
scala> durSemigroupList.combine(List(2.seconds, 3.seconds), List(4.seconds))
res1: List[FiniteDuration] = List(2 seconds, 3 seconds, 4 seconds)
- Inherited from
- Invariant
Count the number of elements in the structure that satisfy the given predicate.
Count the number of elements in the structure that satisfy the given predicate.
For example:
scala> import cats.implicits._
scala> val map1 = Map[Int, String]()
scala> val p1: String => Boolean = _.length > 0
scala> UnorderedFoldable[Map[Int, *]].count(map1)(p1)
res0: Long = 0
scala> val map2 = Map(1 -> "hello", 2 -> "world", 3 -> "!")
scala> val p2: String => Boolean = _.length > 1
scala> UnorderedFoldable[Map[Int, *]].count(map2)(p2)
res1: Long = 2
- Inherited from
- UnorderedFoldable
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
.
- Inherited from
- Foldable
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
- Inherited from
- Foldable
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 a true
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
- Inherited from
- Foldable
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
.
- Inherited from
- Foldable
Find the first element matching the predicate, if one exists.
Find the first element matching the predicate, if one exists.
- Inherited from
- Foldable
Find the first element matching the effectful predicate, if one exists.
Find the first element matching the effectful predicate, if one exists.
If there are no elements, the result is None
. findM
short-circuits,
i.e. once an element is found, no further effects are produced.
For example:
scala> import cats.implicits._
scala> val list = List(1,2,3,4)
scala> Foldable[List].findM(list)(n => (n >= 2).asRight[String])
res0: Either[String,Option[Int]] = Right(Some(2))
scala> Foldable[List].findM(list)(n => (n > 4).asRight[String])
res1: Either[String,Option[Int]] = Right(None)
scala> Foldable[List].findM(list)(n => Either.cond(n < 3, n >= 2, "error"))
res2: Either[String,Option[Int]] = Right(Some(2))
scala> Foldable[List].findM(list)(n => Either.cond(n < 3, false, "error"))
res3: Either[String,Option[Int]] = Left(error)
- Inherited from
- Foldable
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
- Inherited from
- Traverse
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))
- Inherited from
- Traverse
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!)
- Inherited from
- Functor
Fold implemented using the given Monoid[A]
instance.
Fold implemented using the given Monoid[A]
instance.
- Inherited from
- Foldable
Fold implemented using the given Applicative[G]
and Monoid[A]
instance.
Fold implemented using the given Applicative[G]
and Monoid[A]
instance.
This method is similar to fold, but may short-circuit.
For example:
scala> import cats.implicits._
scala> val F = Foldable[List]
scala> F.foldA(List(Either.right[String, Int](1), Either.right[String, Int](2)))
res0: Either[String, Int] = Right(3)
See this issue for an explanation of @noop
usage.
- Inherited from
- Foldable
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 a Monoid[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)
- Inherited from
- Foldable
Perform a stack-safe monadic left fold from the source context F
into the target monad G
.
Perform a stack-safe monadic left fold from the source context F
into the target monad G
.
This method can express short-circuiting semantics. Even when
fa
is an infinite structure, this method can potentially
terminate if the foldRight
implementation for F
and the
tailRecM
implementation for G
are sufficiently lazy.
Instances for concrete structures (e.g. List
) will often
have a more efficient implementation than the default one
in terms of foldRight
.
- Inherited from
- Foldable
Fold in an Applicative context by mapping the A
values to G[B]
. combining
the B
values using the given Monoid[B]
instance.
Fold in an Applicative context by mapping the A
values to G[B]
. combining
the B
values using the given Monoid[B]
instance.
Similar to foldMapM, but will typically be less efficient.
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].foldMapA(evenNumbers)(evenOpt)
res0: Option[Int] = Some(30)
scala> Foldable[List].foldMapA(evenNumbers :+ 11)(evenOpt)
res1: Option[Int] = None
- Inherited from
- Foldable
Fold implemented by mapping A
values into B
in a context G
and then
combining them using the MonoidK[G]
instance.
Fold implemented by mapping A
values into B
in a context G
and then
combining them using the MonoidK[G]
instance.
scala> import cats._, cats.implicits._
scala> val f: Int => Endo[String] = i => (s => s + i)
scala> val x: Endo[String] = Foldable[List].foldMapK(List(1, 2, 3))(f)
scala> val a = x("foo")
a: String = "foo321"
- Inherited from
- Foldable
Monadic folding on F
by mapping A
values to G[B]
, combining the B
values using the given Monoid[B]
instance.
Monadic folding on F
by mapping A
values to G[B]
, combining the B
values using the given Monoid[B]
instance.
Similar to foldM, but using a Monoid[B]
. Will typically be more efficient than foldMapA.
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
- Inherited from
- Foldable
- Inherited from
- Foldable
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
- Inherited from
- Foldable
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 a false
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
- Inherited from
- Foldable
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))
- Inherited from
- Functor
Pair the result of function application with A
.
Pair the result of function application with A
.
Example:
scala> import cats.Functor
scala> import cats.implicits.catsStdInstancesForOption
scala> Functor[Option].fproductLeft(Option(42))(_.toString)
res0: Option[(String, Int)] = Some((42,42))
- Inherited from
- Functor
Get the element at the index of the Foldable
.
Get the element at the index of the Foldable
.
- Inherited from
- Foldable
Lifts if
to Functor
Lifts if
to Functor
Example:
scala> import cats.Functor
scala> import cats.implicits.catsStdInstancesForList
scala> Functor[List].ifF(List(true, false, false))(1, 0)
res0: List[Int] = List(1, 0, 0)
- Inherited from
- Functor
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
- Inherited from
- Foldable
Returns true if there are no elements. Otherwise false.
Returns true if there are no elements. Otherwise false.
- Definition Classes
- Foldable -> UnorderedFoldable
- Inherited from
- Foldable
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)
- Inherited from
- Functor
Akin to map, but also provides the value's index in structure F when calling the function.
Akin to map, but also provides the value's index in structure F when calling the function.
- Inherited from
- Traverse
Find all the maximum A
items in this structure according to an Order.by(f)
.
For all elements in the result Order.eqv(x, y) is true. Preserves order.
Find all the maximum A
items in this structure according to an Order.by(f)
.
For all elements in the result Order.eqv(x, y) is true. Preserves order.
- See also
Reducible#maximumByNel for a version that doesn't need to return an
Option
for structures that are guaranteed to be non-empty.minimumByList for minimum instead of maximum.
- Inherited from
- Foldable
Find the maximum A
item in this structure according to an Order.by(f)
.
Find the maximum A
item in this structure according to an Order.by(f)
.
- Returns
None
if the structure is empty, otherwise the maximum element wrapped in aSome
.- See also
Reducible#maximumBy for a version that doesn't need to return an
Option
for structures that are guaranteed to be non-empty.minimumByOption for minimum instead of maximum.
- Inherited from
- Foldable
Find all the maximum A
items in this structure.
For all elements in the result Order.eqv(x, y) is true. Preserves order.
Find all the maximum A
items in this structure.
For all elements in the result Order.eqv(x, y) is true. Preserves order.
- See also
Reducible#maximumNel for a version that doesn't need to return an
Option
for structures that are guaranteed to be non-empty.minimumList for minimum instead of maximum.
- Inherited from
- Foldable
Find the maximum A
item in this structure according to the Order[A]
.
Find the maximum A
item in this structure according to the Order[A]
.
- Returns
None
if the structure is empty, otherwise the maximum element wrapped in aSome
.- 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.
- Inherited from
- Foldable
Find all the minimum A
items in this structure according to an Order.by(f)
.
For all elements in the result Order.eqv(x, y) is true. Preserves order.
Find all the minimum A
items in this structure according to an Order.by(f)
.
For all elements in the result Order.eqv(x, y) is true. Preserves order.
- See also
Reducible#minimumByNel for a version that doesn't need to return an
Option
for structures that are guaranteed to be non-empty.maximumByList for maximum instead of minimum.
- Inherited from
- Foldable
Find the minimum A
item in this structure according to an Order.by(f)
.
Find the minimum A
item in this structure according to an Order.by(f)
.
- Returns
None
if the structure is empty, otherwise the minimum element wrapped in aSome
.- See also
Reducible#minimumBy for a version that doesn't need to return an
Option
for structures that are guaranteed to be non-empty.maximumByOption for maximum instead of minimum.
- Inherited from
- Foldable
Find all the minimum A
items in this structure.
For all elements in the result Order.eqv(x, y) is true. Preserves order.
Find all the minimum A
items in this structure.
For all elements in the result Order.eqv(x, y) is true. Preserves order.
- See also
Reducible#minimumNel for a version that doesn't need to return an
Option
for structures that are guaranteed to be non-empty.maximumList for maximum instead of minimum.
- Inherited from
- Foldable
Find the minimum A
item in this structure according to the Order[A]
.
Find the minimum A
item in this structure according to the Order[A]
.
- Returns
None
if the structure is empty, otherwise the minimum element wrapped in aSome
.- 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.
- Inherited from
- Foldable
Separate this Foldable into a Tuple by a separating function A => H[B, C]
for some Bifoldable[H]
Equivalent to Functor#map
and then Alternative#separate
.
Separate this Foldable into a Tuple by a separating function A => H[B, C]
for some Bifoldable[H]
Equivalent to Functor#map
and then Alternative#separate
.
scala> import cats.implicits._, cats.Foldable, cats.data.Const
scala> val list = List(1,2,3,4)
scala> Foldable[List].partitionBifold(list)(a => ("value " + a.toString(), if (a % 2 == 0) -a else a))
res0: (List[String], List[Int]) = (List(value 1, value 2, value 3, value 4),List(1, -2, 3, -4))
scala> Foldable[List].partitionBifold(list)(a => Const[Int, Nothing with Any](a))
res1: (List[Int], List[Nothing with Any]) = (List(1, 2, 3, 4),List())
- Inherited from
- Foldable
Separate this Foldable into a Tuple by an effectful separating function A => G[H[B, C]]
for some Bifoldable[H]
Equivalent to Traverse#traverse
over Alternative#separate
Separate this Foldable into a Tuple by an effectful separating function A => G[H[B, C]]
for some Bifoldable[H]
Equivalent to Traverse#traverse
over Alternative#separate
scala> import cats.implicits._, cats.Foldable, cats.data.Const
scala> val list = List(1,2,3,4)
`Const`'s second parameter is never instantiated, so we can use an impossible type:
scala> Foldable[List].partitionBifoldM(list)(a => Option(Const[Int, Nothing with Any](a)))
res0: Option[(List[Int], List[Nothing with Any])] = Some((List(1, 2, 3, 4),List()))
- Inherited from
- Foldable
Separate this Foldable into a Tuple by a separating function A => Either[B, C]
Equivalent to Functor#map
and then Alternative#separate
.
Separate this Foldable into a Tuple by a separating function A => Either[B, C]
Equivalent to Functor#map
and then Alternative#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))
- Inherited from
- Foldable
Separate this Foldable into a Tuple by an effectful separating function A => G[Either[B, C]]
Equivalent to Traverse#traverse
over Alternative#separate
Separate this Foldable into a Tuple by an effectful separating function A => G[Either[B, C]]
Equivalent to Traverse#traverse
over Alternative#separate
scala> import cats.implicits._, cats.Foldable, cats.Eval
scala> val list = List(1,2,3,4)
scala> val partitioned1 = Foldable[List].partitionEitherM(list)(a => if (a % 2 == 0) Eval.now(Either.left[String, Int](a.toString)) else Eval.now(Either.right[String, Int](a)))
Since `Eval.now` yields a lazy computation, we need to force it to inspect the result:
scala> partitioned1.value
res0: (List[String], List[Int]) = (List(2, 4),List(1, 3))
scala> val partitioned2 = Foldable[List].partitionEitherM(list)(a => Eval.later(Either.right(a * 4)))
scala> partitioned2.value
res1: (List[Nothing], List[Int]) = (List(),List(4, 8, 12, 16))
- Inherited from
- Foldable
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.- 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
- Inherited from
- Foldable
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.- 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 equivalent 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
- Inherited from
- Foldable
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
- Inherited from
- Traverse
Sequence F[G[A]]
using Applicative[G]
.
Sequence F[G[A]]
using Applicative[G]
.
This is similar to traverse_
except it operates on F[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
- Inherited from
- Foldable
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.
- Inherited from
- UnorderedFoldable
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
.
- Inherited from
- Foldable
Convert F[A] to an Iterable[A].
Convert F[A] to an Iterable[A].
This method may be overridden for the sake of performance, but implementers should take care not to force a full materialization of the collection.
- Inherited from
- Foldable
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
- Inherited from
- Traverse
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[A] in a G context, ignoring the values returned by provided function.
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[A] in a G context, ignoring the values returned by provided function.
Example:
scala> import cats.implicits._
scala> import java.io.IOException
scala> type IO[A] = Either[IOException, A]
scala> def debug(msg: String): IO[Unit] = Right(())
scala> List("1", "2", "3").traverseTap(debug)
res1: IO[List[String]] = Right(List(1, 2, 3))
- Inherited from
- Traverse
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.
- Inherited from
- Traverse
Traverse F[A]
using Applicative[G]
.
Traverse F[A]
using Applicative[G]
.
A
values will be mapped into G[B]
and combined using
Applicative#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 specific A
aspect of G[A]
is not otherwise
needed.
- Inherited from
- Foldable
Tuples the A
value in F[A]
with the supplied B
value, with the B
value on the left.
Tuples the A
value in F[A]
with the supplied B
value, with the B
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))
- Inherited from
- Functor
Tuples the A
value in F[A]
with the supplied B
value, with the B
value on the right.
Tuples the A
value in F[A]
with the supplied B
value, with the B
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))
- Inherited from
- Functor
- Definition Classes
- Traverse -> UnorderedTraverse
- Inherited from
- Traverse
- Definition Classes
- Traverse -> UnorderedTraverse
- Inherited from
- Traverse
Un-zips an F[(A, B)]
consisting of element pairs or Tuple2 into two separate F's tupled.
Un-zips an F[(A, B)]
consisting of element pairs or Tuple2 into two separate F's tupled.
NOTE: Check for effect duplication, possibly memoize before
scala> import cats.Functor
scala> import cats.implicits.catsStdInstancesForList
scala> Functor[List].unzip(List((1,2), (3, 4)))
res0: (List[Int], List[Int]) = (List(1, 3),List(2, 4))
- Inherited from
- Functor
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((), (), ())
- Inherited from
- Functor
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 as map(identity)
, but
according to the functor laws, that should be equal to fa
, and a type
cast is often much more performant.
See this example
of widen
creating a ClassCastException
.
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)
- Inherited from
- Functor