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
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)
Alias for productR.
Alias for productL.
Alias for ap.
ap2 is a binary version of ap, defined in terms of ap.
ap2 is a binary version of ap, defined in terms of ap.
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)
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)
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)
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)
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!)
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))
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
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)
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
Similar to map2 but uses Eval to allow for laziness in the F[B]
argument.
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
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)
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))
Compose two actions, discarding any value produced by the second.
Compose two actions, discarding any value produced by the second.
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.)
Compose two actions, discarding any value produced by the first.
Compose two actions, discarding any value produced by the first.
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.)
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))
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))
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))
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(())
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()
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((), (), ())
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(())
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)
Higher-arity ap methods
Higher-arity map methods
Higher-arity tuple methods
Applicative functor.
Allows application of a function in an Applicative context to a value in an Applicative context
See: The Essence of the Iterator Pattern Also: Applicative programming with effects
Must obey the laws defined in cats.laws.ApplicativeLaws.