PotOptionCats
Value members
Concrete methods
Pairs elements of two structures along the union of their shapes, using Ior
to hold the results.
Pairs elements of two structures along the union of their shapes, using Ior
to hold the results.
Example:
scala> import cats.implicits._
scala> import cats.data.Ior
scala> Align[List].align(List(1, 2), List(10, 11, 12))
res0: List[Ior[Int, Int]] = List(Both(1,10), Both(2,11), Right(12))
- Definition Classes
- Align
Combines elements similarly to align
, using the provided function to compute the results.
Combines elements similarly to align
, using the provided function to compute the results.
Example:
scala> import cats.implicits._
scala> Align[List].alignWith(List(1, 2), List(10, 11, 12))(_.mergeLeft)
res0: List[Int] = List(1, 2, 12)
- Definition Classes
- Align
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
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
Handle any error, potentially recovering from it, by mapping it to an
F[A]
value.
Handle any error, potentially recovering from it, by mapping it to an
F[A]
value.
- See also:
handleError to handle any error by simply mapping it to an
A
value instead of anF[A]
.recoverWith to recover from only certain errors.
- Definition Classes
- ApplicativeError
pure
lifts any value into the Applicative Functor.
pure
lifts any value into the Applicative Functor.
Example:
scala> import cats.implicits._
scala> Applicative[Option].pure(10)
res0: Option[Int] = Some(10)
- Definition Classes
- Applicative
Lift an error into the F
context.
Lift an error into the F
context.
Example:
scala> import cats.implicits._
// integer-rounded division
scala> def divide[F[_]](dividend: Int, divisor: Int)(implicit F: ApplicativeError[F, String]): F[Int] =
| if (divisor === 0) F.raiseError("division by zero")
| else F.pure(dividend / divisor)
scala> type ErrorOr[A] = Either[String, A]
scala> divide[ErrorOr](6, 3)
res0: ErrorOr[Int] = Right(2)
scala> divide[ErrorOr](6, 0)
res1: ErrorOr[Int] = Left(division by zero)
- Definition Classes
- ApplicativeError
Keeps calling f
until a scala.util.Right[B]
is returned.
Keeps calling f
until a scala.util.Right[B]
is returned.
Based on Phil Freeman's Stack Safety for Free.
Implementations of this method should use constant stack space relative to f
.
- Definition Classes
- FlatMap
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
- Definition Classes
- Traverse
Inherited methods
Transform certain errors using pf
and rethrow them.
Non matching errors and successful values are not affected by this function.
Transform certain errors using pf
and rethrow them.
Non matching errors and successful values are not affected by this function.
Example:
scala> import cats._, implicits._
scala> def pf: PartialFunction[String, String] = { case "error" => "ERROR" }
scala> ApplicativeError[Either[String, *], String].adaptError("error".asLeft[Int])(pf)
res0: Either[String,Int] = Left(ERROR)
scala> ApplicativeError[Either[String, *], String].adaptError("err".asLeft[Int])(pf)
res1: Either[String,Int] = Left(err)
scala> ApplicativeError[Either[String, *], String].adaptError(1.asRight[String])(pf)
res2: Either[String,Int] = Right(1)
The same function is available in ApplicativeErrorOps
as adaptErr
- it cannot have the same
name because this would result in ambiguous implicits due to adaptError
having originally been included in the MonadError
API and syntax.
- Definition Classes
- MonadError -> ApplicativeError
- Inherited from:
- MonadError
Align two structures with the same element, combining results according to their semigroup instances.
Align two structures with the same element, combining results according to their semigroup instances.
Example:
scala> import cats.implicits._
scala> Align[List].alignCombine(List(1, 2), List(10, 11, 12))
res0: List[Int] = List(11, 13, 12)
- Inherited from:
- Align
Align two structures with the same element, combining results according to the given function.
Align two structures with the same element, combining results according to the given function.
Example:
scala> import cats.implicits._
scala> Align[List].alignMergeWith(List(1, 2), List(10, 11, 12))(_ + _)
res0: List[Int] = List(11, 13, 12)
- Inherited from:
- Align
Given a value and a function in the Apply context, applies the function to the value.
Given a value and a function in the Apply context, applies the function to the value.
Example:
scala> import cats.implicits._
scala> val someF: Option[Int => Long] = Some(_.toLong + 1L)
scala> val noneF: Option[Int => Long] = None
scala> val someInt: Option[Int] = Some(3)
scala> val noneInt: Option[Int] = None
scala> Apply[Option].ap(someF)(someInt)
res0: Option[Long] = Some(4)
scala> Apply[Option].ap(noneF)(someInt)
res1: Option[Long] = None
scala> Apply[Option].ap(someF)(noneInt)
res2: Option[Long] = None
scala> Apply[Option].ap(noneF)(noneInt)
res3: Option[Long] = None
- Definition Classes
- FlatMap -> Apply
- Inherited from:
- FlatMap
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
ap2 is a binary version of ap, defined in terms of ap.
ap2 is a binary version of ap, defined in terms of ap.
- Definition Classes
- FlatMap -> Apply
- Inherited from:
- FlatMap
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
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
Handle errors by turning them into scala.util.Either values.
Handle errors by turning them into scala.util.Either values.
If there is no error, then an scala.util.Right
value will be returned instead.
All non-fatal errors should be handled by this method.
- Inherited from:
- ApplicativeError
Similar to attempt, but it only handles errors of type EE
.
Similar to attempt, but it only handles errors of type EE
.
- Inherited from:
- ApplicativeError
Similar to attempt, but wraps the result in a cats.data.EitherT for convenience.
Similar to attempt, but wraps the result in a cats.data.EitherT for convenience.
- Inherited from:
- ApplicativeError
Reifies the value or error of the source and performs an effect on the result,
then recovers the original value or error back into F
.
Reifies the value or error of the source and performs an effect on the result,
then recovers the original value or error back into F
.
Note that if the effect returned by f
fails, the resulting effect will fail too.
Alias for fa.attempt.flatTap(f).rethrow
for convenience.
Example:
scala> import cats.implicits._
scala> import scala.util.{Try, Success, Failure}
scala> def checkError(result: Either[Throwable, Int]): Try[String] = result.fold(_ => Failure(new java.lang.Exception), _ => Success("success"))
scala> val a: Try[Int] = Failure(new Throwable("failed"))
scala> a.attemptTap(checkError)
res0: scala.util.Try[Int] = Failure(java.lang.Exception)
scala> val b: Try[Int] = Success(1)
scala> b.attemptTap(checkError)
res1: scala.util.Try[Int] = Success(1)
- Inherited from:
- MonadError
Often E is Throwable. Here we try to call pure or catch and raise.
Often E is Throwable. Here we try to call pure or catch and raise.
- Inherited from:
- ApplicativeError
Often E is Throwable. Here we try to call pure or catch and raise
Often E is Throwable. Here we try to call pure or catch and raise
- Inherited from:
- ApplicativeError
Evaluates the specified block, catching exceptions of the specified type. Uncaught exceptions are propagated.
Evaluates the specified block, catching exceptions of the specified type. Uncaught exceptions are propagated.
- Inherited from:
- ApplicativeError
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
Compose an Applicative[F]
and an Applicative[G]
into an
Applicative[λ[α => F[G[α]]]]
.
Compose an Applicative[F]
and an Applicative[G]
into an
Applicative[λ[α => F[G[α]]]]
.
Example:
scala> import cats.implicits._
scala> val alo = Applicative[List].compose[Option]
scala> alo.pure(3)
res0: List[Option[Int]] = List(Some(3))
scala> alo.product(List(None, Some(true), Some(false)), List(Some(2), None))
res1: List[Option[(Boolean, Int)]] = List(None, None, Some((true,2)), None, Some((false,2)), None)
- Inherited from:
- Applicative
Compose an Apply[F]
and an Apply[G]
into an Apply[λ[α => F[G[α]]]]
.
Compose an Apply[F]
and an Apply[G]
into an Apply[λ[α => F[G[α]]]]
.
Example:
scala> import cats.implicits._
scala> val alo = Apply[List].compose[Option]
scala> alo.product(List(None, Some(true), Some(false)), List(Some(2), None))
res1: List[Option[(Boolean, Int)]] = List(None, None, Some((true,2)), None, Some((false,2)), None)
- Inherited from:
- Apply
Compose Invariant F[_]
and Contravariant G[_]
then produce Invariant[F[G[_]]]
using F's imap
and G's contramap
.
Compose Invariant F[_]
and Contravariant G[_]
then produce Invariant[F[G[_]]]
using F's imap
and G's contramap
.
Example:
scala> import cats.implicits._
scala> import scala.concurrent.duration._
scala> type ToInt[T] = T => Int
scala> val durSemigroupToInt: Semigroup[ToInt[FiniteDuration]] =
| Invariant[Semigroup]
| .composeContravariant[ToInt]
| .imap(Semigroup[ToInt[Long]])(Duration.fromNanos)(_.toNanos)
// semantically equal to (2.seconds.toSeconds.toInt + 1) + (2.seconds.toSeconds.toInt * 2) = 7
scala> durSemigroupToInt.combine(_.toSeconds.toInt + 1, _.toSeconds.toInt * 2)(2.seconds)
res1: Int = 7
- Definition Classes
- Functor -> Invariant
- Inherited from:
- Functor
Compose an Applicative[F]
and a ContravariantMonoidal[G]
into a
ContravariantMonoidal[λ[α => F[G[α]]]]
.
Compose an Applicative[F]
and a ContravariantMonoidal[G]
into a
ContravariantMonoidal[λ[α => F[G[α]]]]
.
Example:
scala> import cats.kernel.Comparison
scala> import cats.implicits._
// compares strings by alphabetical order
scala> val alpha: Order[String] = Order[String]
// compares strings by their length
scala> val strLength: Order[String] = Order.by[String, Int](_.length)
scala> val stringOrders: List[Order[String]] = List(alpha, strLength)
// first comparison is with alpha order, second is with string length
scala> stringOrders.map(o => o.comparison("abc", "de"))
res0: List[Comparison] = List(LessThan, GreaterThan)
scala> val le = Applicative[List].composeContravariantMonoidal[Order]
// create Int orders that convert ints to strings and then use the string orders
scala> val intOrders: List[Order[Int]] = le.contramap(stringOrders)(_.toString)
// first comparison is with alpha order, second is with string length
scala> intOrders.map(o => o.comparison(12, 3))
res1: List[Comparison] = List(LessThan, GreaterThan)
// create the `product` of the string order list and the int order list
// `p` contains a list of the following orders:
// 1. (alpha comparison on strings followed by alpha comparison on ints)
// 2. (alpha comparison on strings followed by length comparison on ints)
// 3. (length comparison on strings followed by alpha comparison on ints)
// 4. (length comparison on strings followed by length comparison on ints)
scala> val p: List[Order[(String, Int)]] = le.product(stringOrders, intOrders)
scala> p.map(o => o.comparison(("abc", 12), ("def", 3)))
res2: List[Comparison] = List(LessThan, LessThan, LessThan, GreaterThan)
- Inherited from:
- Applicative
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
Tests if fa
contains v
using the Eq
instance for A
Tests if fa
contains v
using the Eq
instance for A
- Inherited from:
- UnorderedFoldable
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
Turns a successful value into an error if it does not satisfy a given predicate.
Turns a successful value into an error if it does not satisfy a given predicate.
- Inherited from:
- MonadError
Turns a successful value into an error specified by the error
function if it does not satisfy a given predicate.
Turns a successful value into an error specified by the error
function if it does not satisfy a given predicate.
- Inherited from:
- MonadError
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
- Inherited from:
- FlatMapArityFunctions
- Inherited from:
- FlatMapArityFunctions
- Inherited from:
- FlatMapArityFunctions
- Inherited from:
- FlatMapArityFunctions
- Inherited from:
- FlatMapArityFunctions
- Inherited from:
- FlatMapArityFunctions
- Inherited from:
- FlatMapArityFunctions
- Inherited from:
- FlatMapArityFunctions
- Inherited from:
- FlatMapArityFunctions
- Inherited from:
- FlatMapArityFunctions
- Inherited from:
- FlatMapArityFunctions
- Inherited from:
- FlatMapArityFunctions
- Inherited from:
- FlatMapArityFunctions
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
Apply a monadic function and discard the result while keeping the effect.
Apply a monadic function and discard the result while keeping the effect.
scala> import cats._, implicits._
scala> Option(1).flatTap(_ => None)
res0: Option[Int] = None
scala> Option(1).flatTap(_ => Some("123"))
res1: Option[Int] = Some(1)
scala> def nCats(n: Int) = List.fill(n)("cat")
nCats: (n: Int)List[String]
scala> List[Int](0).flatTap(nCats)
res2: List[Int] = List()
scala> List[Int](4).flatTap(nCats)
res3: List[Int] = List(4, 4, 4, 4)
- Inherited from:
- FlatMap
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
"flatten" a nested F
of F
structure into a single-layer F
structure.
"flatten" a nested F
of F
structure into a single-layer F
structure.
This is also commonly called join
.
Example:
scala> import cats.Eval
scala> import cats.implicits._
scala> val nested: Eval[Eval[Int]] = Eval.now(Eval.now(3))
scala> val flattened: Eval[Int] = nested.flatten
scala> flattened.value
res0: Int = 3
- Inherited from:
- FlatMap
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)
- 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 implemented by mapping A
values into B
and then
combining them using the given Monoid[B]
instance.
Fold implemented by mapping A
values into B
and then
combining them using the given Monoid[B]
instance.
- 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
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
Like an infinite loop of >> calls. This is most useful effect loops that you want to run forever in for instance a server.
Like an infinite loop of >> calls. This is most useful effect loops that you want to run forever in for instance a server.
This will be an infinite loop, or it will return an F[Nothing].
Be careful using this. For instance, a List of length k will produce a list of length k^n at iteration n. This means if k = 0, we return an empty list, if k = 1, we loop forever allocating single element lists, but if we have a k > 1, we will allocate exponentially increasing memory and very quickly OOM.
- Inherited from:
- FlatMap
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
Convert from scala.Either
Convert from scala.Either
Example:
scala> import cats.ApplicativeError
scala> import cats.instances.option._
scala> ApplicativeError[Option, Unit].fromEither(Right(1))
res0: scala.Option[Int] = Some(1)
scala> ApplicativeError[Option, Unit].fromEither(Left(()))
res1: scala.Option[Nothing] = None
- Inherited from:
- ApplicativeError
Convert from scala.Option
Convert from scala.Option
Example:
scala> import cats.implicits._
scala> import cats.ApplicativeError
scala> val F = ApplicativeError[Either[String, *], String]
scala> F.fromOption(Some(1), "Empty")
res0: scala.Either[String, Int] = Right(1)
scala> F.fromOption(Option.empty[Int], "Empty")
res1: scala.Either[String, Int] = Left(Empty)
- Inherited from:
- ApplicativeError
If the error type is Throwable, we can convert from a scala.util.Try
If the error type is Throwable, we can convert from a scala.util.Try
- Inherited from:
- ApplicativeError
Convert from cats.data.Validated
Convert from cats.data.Validated
Example:
scala> import cats.implicits._
scala> import cats.ApplicativeError
scala> ApplicativeError[Option, Unit].fromValidated(1.valid[Unit])
res0: scala.Option[Int] = Some(1)
scala> ApplicativeError[Option, Unit].fromValidated(().invalid[Int])
res1: scala.Option[Int] = None
- Inherited from:
- ApplicativeError
Get the element at the index of the Foldable
.
Get the element at the index of the Foldable
.
- Inherited from:
- Foldable
Handle any error, by mapping it to an A
value.
Handle any error, by mapping it to an A
value.
- See also:
handleErrorWith to map to an
F[A]
value instead of simply anA
value.recover to only recover from certain errors.
- Inherited from:
- ApplicativeError
Simulates an if/else-if/else in the context of an F. It evaluates conditions until one evaluates to true, and returns the associated F[A]. If no condition is true, returns els.
Simulates an if/else-if/else in the context of an F. It evaluates conditions until one evaluates to true, and returns the associated F[A]. If no condition is true, returns els.
scala> import cats._
scala> Monad[Eval].ifElseM(Eval.later(false) -> Eval.later(1), Eval.later(true) -> Eval.later(2))(Eval.later(5)).value
res0: Int = 2
Based on a gist by Daniel Spiewak with a stack-safe implementation due to P. Oscar Boykin
- See also:
See https://gitter.im/typelevel/cats-effect?at=5f297e4314c413356f56d230 for the discussion.
- Inherited from:
- Monad
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
Transform an F[A]
into an F[B]
by providing a transformation from A
to B
and one from B
to A
.
Transform an F[A]
into an F[B]
by providing a transformation from A
to B
and one from B
to A
.
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
- Definition Classes
- Functor -> Invariant
- 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
iterateForeverM is almost exclusively useful for effect types. For instance, A may be some state, we may take the current state, run some effect to get a new state and repeat.
iterateForeverM is almost exclusively useful for effect types. For instance, A may be some state, we may take the current state, run some effect to get a new state and repeat.
- Inherited from:
- FlatMap
Execute an action repeatedly until its result satisfies the given predicate and return that result, discarding all others.
Execute an action repeatedly until its result satisfies the given predicate and return that result, discarding all others.
- Inherited from:
- Monad
Apply a monadic function iteratively until its result satisfies the given predicate and return that result.
Apply a monadic function iteratively until its result satisfies the given predicate and return that result.
- Inherited from:
- Monad
Execute an action repeatedly until its result fails to satisfy the given predicate and return that result, discarding all others.
Execute an action repeatedly until its result fails to satisfy the given predicate and return that result, discarding all others.
- Inherited from:
- Monad
Apply a monadic function iteratively until its result fails to satisfy the given predicate and return that result.
Apply a monadic function iteratively until its result fails to satisfy the given predicate and return that result.
- Inherited from:
- Monad
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
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
Applies the pure (binary) function f to the effectful values fa and fb.
Applies the pure (binary) function f to the effectful values fa and fb.
map2 can be seen as a binary version of cats.Functor#map.
Example:
scala> import cats.implicits._
scala> val someInt: Option[Int] = Some(3)
scala> val noneInt: Option[Int] = None
scala> val someLong: Option[Long] = Some(4L)
scala> val noneLong: Option[Long] = None
scala> Apply[Option].map2(someInt, someLong)((i, l) => i.toString + l.toString)
res0: Option[String] = Some(34)
scala> Apply[Option].map2(someInt, noneLong)((i, l) => i.toString + l.toString)
res0: Option[String] = None
scala> Apply[Option].map2(noneInt, noneLong)((i, l) => i.toString + l.toString)
res0: Option[String] = None
scala> Apply[Option].map2(noneInt, someLong)((i, l) => i.toString + l.toString)
res0: Option[String] = None
- Definition Classes
- FlatMap -> Apply
- Inherited from:
- FlatMap
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
Similar to map2 but uses Eval to allow for laziness in the F[B]
argument. This can allow for "short-circuiting" of computations.
Similar to map2 but uses Eval to allow for laziness in the F[B]
argument. This can allow for "short-circuiting" of computations.
NOTE: the default implementation of map2Eval
does not short-circuit
computations. For data structures that can benefit from laziness, Apply
instances should override this method.
In the following example, x.map2(bomb)(_ + _)
would result in an error,
but map2Eval
"short-circuits" the computation. x
is None
and thus the
result of bomb
doesn't even need to be evaluated in order to determine
that the result of map2Eval
should be None
.
scala> import cats.{Eval, Later}
scala> import cats.implicits._
scala> val bomb: Eval[Option[Int]] = Later(sys.error("boom"))
scala> val x: Option[Int] = None
scala> x.map2Eval(bomb)(_ + _).value
res0: Option[Int] = None
- Definition Classes
- FlatMap -> Apply
- Inherited from:
- FlatMap
Akin to map, but allows to keep track of a state value when calling the function.
Akin to map, but allows to keep track of a state value when calling the function.
- Inherited from:
- Traverse
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
Pair A
with the result of function application.
Pair A
with the result of function application.
Example:
scala> import cats.implicits._
scala> List("12", "34", "56").mproduct(_.toList)
res0: List[(String, Char)] = List((12,1), (12,2), (34,3), (34,4), (56,5), (56,6))
- Inherited from:
- FlatMap
Execute a callback on certain errors, then rethrow them. Any non matching error is rethrown as well.
Execute a callback on certain errors, then rethrow them. Any non matching error is rethrown as well.
In the following example, only one of the errors is logged, but they are both rethrown, to be possibly handled by another layer of the program:
scala> import cats._, data._, implicits._
scala> case class Err(msg: String)
scala> type F[A] = EitherT[State[String, *], Err, A]
scala> val action: PartialFunction[Err, F[Unit]] = {
| case Err("one") => EitherT.liftF(State.set("one"))
| }
scala> val prog1: F[Int] = (Err("one")).raiseError[F, Int]
scala> val prog2: F[Int] = (Err("two")).raiseError[F, Int]
scala> prog1.onError(action).value.run("").value
res0: (String, Either[Err,Int]) = (one,Left(Err(one)))
scala> prog2.onError(action).value.run("").value
res1: (String, Either[Err,Int]) = ("",Left(Err(two)))
- Inherited from:
- ApplicativeError
Same as align
, but forgets from the type that one of the two elements must be present.
Same as align
, but forgets from the type that one of the two elements must be present.
Example:
scala> import cats.implicits._
scala> Align[List].padZip(List(1, 2), List(10))
res0: List[(Option[Int], Option[Int])] = List((Some(1),Some(10)), (Some(2),None))
- Inherited from:
- Align
Same as alignWith
, but forgets from the type that one of the two elements must be present.
Same as alignWith
, but forgets from the type that one of the two elements must be present.
Example:
scala> import cats.implicits._
scala> Align[List].padZipWith(List(1, 2), List(10, 11, 12))(_ |+| _)
res0: List[Option[Int]] = List(Some(11), Some(13), Some(12))
- Inherited from:
- Align
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
point
lifts any value into a Monoidal Functor.
point
lifts any value into a Monoidal Functor.
Example:
scala> import cats.implicits._
scala> InvariantMonoidal[Option].point(10)
res0: Option[Int] = Some(10)
- Inherited from:
- InvariantMonoidal
Combine an F[A]
and an F[B]
into an F[(A, B)]
that maintains the effects of both fa
and fb
.
Combine an F[A]
and an F[B]
into an F[(A, B)]
that maintains the effects of both fa
and fb
.
Example:
scala> import cats.implicits._
scala> val noneInt: Option[Int] = None
scala> val some3: Option[Int] = Some(3)
scala> val noneString: Option[String] = None
scala> val someFoo: Option[String] = Some("foo")
scala> Semigroupal[Option].product(noneInt, noneString)
res0: Option[(Int, String)] = None
scala> Semigroupal[Option].product(noneInt, someFoo)
res1: Option[(Int, String)] = None
scala> Semigroupal[Option].product(some3, noneString)
res2: Option[(Int, String)] = None
scala> Semigroupal[Option].product(some3, someFoo)
res3: Option[(Int, String)] = Some((3,foo))
- Definition Classes
- FlatMap -> Apply -> Semigroupal
- Inherited from:
- FlatMap
Compose two actions, discarding any value produced by the second.
Compose two actions, discarding any value produced by the second.
- See also:
productR to discard the value of the first instead. Example:
scala> import cats.implicits._ scala> import cats.data.Validated scala> import Validated.{Valid, Invalid} scala> type ErrOr[A] = Validated[String, A] scala> val validInt: ErrOr[Int] = Valid(3) scala> val validBool: ErrOr[Boolean] = Valid(true) scala> val invalidInt: ErrOr[Int] = Invalid("Invalid int.") scala> val invalidBool: ErrOr[Boolean] = Invalid("Invalid boolean.") scala> Apply[ErrOr].productL(validInt)(validBool) res0: ErrOr[Int] = Valid(3) scala> Apply[ErrOr].productL(invalidInt)(validBool) res1: ErrOr[Int] = Invalid(Invalid int.) scala> Apply[ErrOr].productL(validInt)(invalidBool) res2: ErrOr[Int] = Invalid(Invalid boolean.) scala> Apply[ErrOr].productL(invalidInt)(invalidBool) res3: ErrOr[Int] = Invalid(Invalid int.Invalid boolean.)
- Definition Classes
- FlatMap -> Apply
- Inherited from:
- FlatMap
Sequentially compose two actions, discarding any value produced by the second. This variant of productL also lets you define the evaluation strategy of the second action. For instance you can evaluate it only ''after'' the first action has finished:
Sequentially compose two actions, discarding any value produced by the second. This variant of productL also lets you define the evaluation strategy of the second action. For instance you can evaluate it only ''after'' the first action has finished:
scala> import cats.Eval
scala> import cats.implicits._
scala> var count = 0
scala> val fa: Option[Int] = Some(3)
scala> def fb: Option[Unit] = Some(count += 1)
scala> fa.productLEval(Eval.later(fb))
res0: Option[Int] = Some(3)
scala> assert(count == 1)
scala> none[Int].productLEval(Eval.later(fb))
res1: Option[Int] = None
scala> assert(count == 1)
- Inherited from:
- FlatMap
Compose two actions, discarding any value produced by the first.
Compose two actions, discarding any value produced by the first.
- See also:
productL to discard the value of the second instead. Example:
scala> import cats.implicits._ scala> import cats.data.Validated scala> import Validated.{Valid, Invalid} scala> type ErrOr[A] = Validated[String, A] scala> val validInt: ErrOr[Int] = Valid(3) scala> val validBool: ErrOr[Boolean] = Valid(true) scala> val invalidInt: ErrOr[Int] = Invalid("Invalid int.") scala> val invalidBool: ErrOr[Boolean] = Invalid("Invalid boolean.") scala> Apply[ErrOr].productR(validInt)(validBool) res0: ErrOr[Boolean] = Valid(true) scala> Apply[ErrOr].productR(invalidInt)(validBool) res1: ErrOr[Boolean] = Invalid(Invalid int.) scala> Apply[ErrOr].productR(validInt)(invalidBool) res2: ErrOr[Boolean] = Invalid(Invalid boolean.) scala> Apply[ErrOr].productR(invalidInt)(invalidBool) res3: ErrOr[Boolean] = Invalid(Invalid int.Invalid boolean.)
- Definition Classes
- FlatMap -> Apply
- Inherited from:
- FlatMap
Sequentially compose two actions, discarding any value produced by the first. This variant of productR also lets you define the evaluation strategy of the second action. For instance you can evaluate it only ''after'' the first action has finished:
Sequentially compose two actions, discarding any value produced by the first. This variant of productR also lets you define the evaluation strategy of the second action. For instance you can evaluate it only ''after'' the first action has finished:
scala> import cats.Eval
scala> import cats.implicits._
scala> val fa: Option[Int] = Some(3)
scala> def fb: Option[String] = Some("foo")
scala> fa.productREval(Eval.later(fb))
res0: Option[String] = Some(foo)
- Inherited from:
- FlatMap
Returns raiseError
when cond
is false, otherwise F.unit
Returns raiseError
when cond
is false, otherwise F.unit
- Example:
val tooMany = 5 val x: Int = ??? F.raiseUnless(x < tooMany)(new IllegalArgumentException("Too many"))
- Inherited from:
- ApplicativeError
Returns raiseError
when the cond
is true, otherwise F.unit
Returns raiseError
when the cond
is true, otherwise F.unit
- Example:
val tooMany = 5 val x: Int = ??? F.raiseWhen(x >= tooMany)(new IllegalArgumentException("Too many"))
- Inherited from:
- ApplicativeError
Recover from certain errors by mapping them to an A
value.
Recover from certain errors by mapping them to an A
value.
- See also:
handleError to handle any/all errors.
recoverWith to recover from certain errors by mapping them to
F[A]
values.- Inherited from:
- ApplicativeError
Recover from certain errors by mapping them to an F[A]
value.
Recover from certain errors by mapping them to an F[A]
value.
- See also:
handleErrorWith to handle any/all errors.
recover to recover from certain errors by mapping them to
A
values.- Inherited from:
- ApplicativeError
Returns a new value that transforms the result of the source,
given the recover
or map
functions, which get executed depending
on whether the result is successful or if it ends in error.
Returns a new value that transforms the result of the source,
given the recover
or map
functions, which get executed depending
on whether the result is successful or if it ends in error.
This is an optimization on usage of attempt and map, this equivalence being available:
fa.redeem(fe, fs) <-> fa.attempt.map(_.fold(fe, fs))
Usage of redeem
subsumes handleError because:
fa.redeem(fe, id) <-> fa.handleError(fe)
Implementations are free to override it in order to optimize error recovery.
- Value parameters:
- fa
is the source whose result is going to get transformed
- recover
is the function that gets called to recover the source in case of error
- See also:
MonadError.redeemWith, attempt and handleError
- Inherited from:
- ApplicativeError
Returns a new value that transforms the result of the source,
given the recover
or bind
functions, which get executed depending
on whether the result is successful or if it ends in error.
Returns a new value that transforms the result of the source,
given the recover
or bind
functions, which get executed depending
on whether the result is successful or if it ends in error.
This is an optimization on usage of attempt and flatMap, this equivalence being available:
fa.redeemWith(fe, fs) <-> fa.attempt.flatMap(_.fold(fe, fs))
Usage of redeemWith
subsumes handleErrorWith because:
fa.redeemWith(fe, F.pure) <-> fa.handleErrorWith(fe)
Usage of redeemWith
also subsumes flatMap because:
fa.redeemWith(F.raiseError, fs) <-> fa.flatMap(fs)
Implementations are free to override it in order to optimize error recovery.
- Value parameters:
- bind
is the function that gets to transform the source in case of success
- fa
is the source whose result is going to get transformed
- recover
is the function that gets called to recover the source in case of error
- See also:
redeem, attempt and handleErrorWith
- Inherited from:
- MonadError
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
- Inherited from:
- Foldable
Given fa
and n
, apply fa
n
times to construct an F[List[A]]
value.
Given fa
and n
, apply fa
n
times to construct an F[List[A]]
value.
Example:
scala> import cats.data.State
scala> type Counter[A] = State[Int, A]
scala> val getAndIncrement: Counter[Int] = State { i => (i + 1, i) }
scala> val getAndIncrement5: Counter[List[Int]] =
| Applicative[Counter].replicateA(5, getAndIncrement)
scala> getAndIncrement5.run(0).value
res0: (Int, List[Int]) = (5,List(0, 1, 2, 3, 4))
- Inherited from:
- Applicative
Given fa
and n
, apply fa
n
times discarding results to return F[Unit].
Given fa
and n
, apply fa
n
times discarding results to return F[Unit].
Example:
scala> import cats.data.State
scala> type Counter[A] = State[Int, A]
scala> val getAndIncrement: Counter[Int] = State { i => (i + 1, i) }
scala> val getAndIncrement5: Counter[Unit] =
| Applicative[Counter].replicateA_(5, getAndIncrement)
scala> getAndIncrement5.run(0).value
res0: (Int, Unit) = (5,())
- Inherited from:
- Applicative
Inverse of attempt
Inverse of attempt
Example:
scala> import cats.implicits._
scala> import scala.util.{Try, Success}
scala> val a: Try[Either[Throwable, Int]] = Success(Left(new java.lang.Exception))
scala> a.rethrow
res0: scala.util.Try[Int] = Failure(java.lang.Exception)
scala> val b: Try[Either[Throwable, Int]] = Success(Right(1))
scala> b.rethrow
res1: scala.util.Try[Int] = Success(1)
- Inherited from:
- MonadError
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[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
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
- Inherited from:
- ApplyArityFunctions
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
Returns an F[Unit]
value, equivalent with pure(())
.
Returns an F[Unit]
value, equivalent with pure(())
.
A useful shorthand, also allowing implementations to optimize the
returned reference (e.g. it can be a val
).
Example:
scala> import cats.implicits._
scala> Applicative[Option].unit
res0: Option[Unit] = Some(())
- Inherited from:
- Applicative
Returns the given argument (mapped to Unit) if cond
is false
,
otherwise, unit lifted into F.
Returns the given argument (mapped to Unit) if cond
is false
,
otherwise, unit lifted into F.
Example:
scala> import cats.implicits._
scala> Applicative[List].unlessA(true)(List(1, 2, 3))
res0: List[Unit] = List(())
scala> Applicative[List].unlessA(false)(List(1, 2, 3))
res1: List[Unit] = List((), (), ())
scala> Applicative[List].unlessA(true)(List.empty[Int])
res2: List[Unit] = List(())
scala> Applicative[List].unlessA(false)(List.empty[Int])
res3: List[Unit] = List()
- Inherited from:
- Applicative
- Definition Classes
- Traverse -> UnorderedTraverse
- Inherited from:
- Traverse
This repeats an F until we get defined values. This can be useful for polling type operations on State (or RNG) Monads, or in effect monads.
This repeats an F until we get defined values. This can be useful for polling type operations on State (or RNG) Monads, or in effect monads.
- Inherited from:
- FlatMap
Execute an action repeatedly until the Boolean
condition returns true
.
The condition is evaluated after the loop body. Collects results into an
arbitrary Alternative
value, such as a Vector
.
This implementation uses append on each evaluation result,
so avoid data structures with non-constant append performance, e.g. List
.
Execute an action repeatedly until the Boolean
condition returns true
.
The condition is evaluated after the loop body. Collects results into an
arbitrary Alternative
value, such as a Vector
.
This implementation uses append on each evaluation result,
so avoid data structures with non-constant append performance, e.g. List
.
- Inherited from:
- Monad
Execute an action repeatedly until the Boolean
condition returns true
.
The condition is evaluated after the loop body. Discards results.
Execute an action repeatedly until the Boolean
condition returns true
.
The condition is evaluated after the loop body. Discards results.
- Inherited from:
- Monad
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
Returns the given argument (mapped to Unit) if cond
is true
, otherwise,
unit lifted into F.
Returns the given argument (mapped to Unit) if cond
is true
, otherwise,
unit lifted into F.
Example:
scala> import cats.implicits._
scala> Applicative[List].whenA(true)(List(1, 2, 3))
res0: List[Unit] = List((), (), ())
scala> Applicative[List].whenA(false)(List(1, 2, 3))
res1: List[Unit] = List(())
scala> Applicative[List].whenA(true)(List.empty[Int])
res2: List[Unit] = List()
scala> Applicative[List].whenA(false)(List.empty[Int])
res3: List[Unit] = List(())
- Inherited from:
- Applicative
Execute an action repeatedly as long as the given Boolean
expression
returns true
. The condition is evaluated before the loop body.
Collects the results into an arbitrary Alternative
value, such as a Vector
.
This implementation uses append on each evaluation result,
so avoid data structures with non-constant append performance, e.g. List
.
Execute an action repeatedly as long as the given Boolean
expression
returns true
. The condition is evaluated before the loop body.
Collects the results into an arbitrary Alternative
value, such as a Vector
.
This implementation uses append on each evaluation result,
so avoid data structures with non-constant append performance, e.g. List
.
- Inherited from:
- Monad
Execute an action repeatedly as long as the given Boolean
expression
returns true
. The condition is evaluated before the loop body.
Discards results.
Execute an action repeatedly as long as the given Boolean
expression
returns true
. The condition is evaluated before the loop body.
Discards results.
- Inherited from:
- Monad
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
Pairs elements of two structures along the union of their shapes, using placeholders for missing values.
Pairs elements of two structures along the union of their shapes, using placeholders for missing values.
Example:
scala> import cats.implicits._
scala> Align[List].zipAll(List(1, 2), List(10, 11, 12), 20, 21)
res0: List[(Int, Int)] = List((1,10), (2,11), (20,12))
- Inherited from:
- Align