Cats is a library that provides abstractions for functional programming in Scala.
Cats is a library that provides abstractions for functional programming in Scala.
The name is a playful shortening of the word category.
Questions tagged [scala-cats]
929 questions
0
votes
1 answer
Type resolution with flatMap
why do i need to add the type annotation at the first line?
c.get[List[String]]("primary-group") is Decoder.Result[List[String]] after flatMap it should keep the top type and be Decoder.Result[String] but it changes to Either[DecodingFailure,…
user1698641
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1 answer
OptionalT fromOptional and liftF in ScalaZ
I´ve been watching some examples of monads transformers with Cats, and I was trying to reproduce those in Scalaz
Here I have a for comprehension where I first receive an optional which I flatMap with OptionalT, and the second function return a…
paul
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Monad of Nothing doesn't work in cats
I am having issues with cats/monads/understanding.
Please consider following snippet:
import cats._
import cats.implicits._
final case class My[T]()
implicit val monadMy: Monad[My] = new Monad[My] { ... }
// this compiles
def test11[A, B](m:…
Dmytro Starosud
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0
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1 answer
Applicative style using cats library
This is a follow-up to my previous question:
Suppose I want to use Applicative to apply function A => B => C to List[A] and List[B].
I believe it looks like that in Haskell:
pure f <*> as <*> bs // apply f to List[A] and List[B]
or
f <$> as <*> bs…
Michael
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3 answers
Merging 2 Eithers with Cats Cartesian
I wrote this code
import cats.Cartesian
import cats.instances.option._
val x = Some(1)
val y = Some(2)
Cartesian[Option].product(x, y)
This gave me Some((1, 2)). Good!
So I tried again
import cats.Cartesian
import cats.instances.either._
val x :…
Knows Not Much
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1 answer
Hide for comprehension
I´m working in a DSL using monads and for comprenhension. Since my client has no idea of Scala I´m trying to hide so much syntax as I can. So far I have this DSL
(for {
* <- Given("A message", message(path = "esb", version = TWO))
* <-…
paul
- 12,873
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0
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2 answers
How can I define an instance of a typeclass in scala that can be used for all subclasses of a particular type?
I am trying to define an instance of Show (from cats 0.9) that can be used for all members of an ADT as follows:
import $ivy.`org.typelevel::cats:0.9.0`, cats.Show
sealed abstract class Colour(val name: String)
implicit val ColourShow = new…
Rich Ashworth
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2 answers
Scala: How to use Functors for multi type parameter trait
I have and ADT which is basically a wrapper over Function1:
case class Abstract[M[_], A, B](f:M[A] => M[B]) {
def fn: M[A] => M[B] = { case x: M[A] => f(x) }
}
I want to map over these, so I defined a Functor like so:
trait AbstractAPI[E] {
…
ixaxaar
- 6,411
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0
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2 answers
Check lists of numbers and accumulate errors
Suppose I need to check if a given list of numbers starts with of one or more 1, one or more 2 and one or more 3. If the check fails I would like to get all errors accumulated, e.g.
val check: List[Int] => Either[String, Unit] = ???
check(Nil) …
Michael
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0
votes
1 answer
Scala type inference does not work with type bounds, unless the type is specified explicitly
I'm trying to create a documentation wrapper around functions in scala like, so that the wrapper can be queried for its containing function's documentation, like so:
trait WrappedFunction1[A, B] {
def f : Function1[A, B]
def doc: String
def…
ixaxaar
- 6,411
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0
votes
1 answer
Chaining Cats Validated with andThen
I am reading this article
http://typelevel.org/cats/datatypes/validated.html
It says that Validated can be used to do Sequential validations using "andThen" method. This means we stop at the first error and not collect all the errors.
I tried the…
Knows Not Much
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0
votes
1 answer
How to provide an execution context to a future functor?
Using Cats, I have my functor declarations in a package object. This works fine, except for the futureFunctor, as it requires an implicit ExecutionContext:
package object util {
implicit val futureFunctor: Functor[Future] = new Functor[Future] {
…
Lasf
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0
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2 answers
Validating list of strings
This is a follow up to my previous question.
Suppose I need to write a function validate in order to make sure that a given list of strings consists of "a", "b", and one or more "c".
def validate(ss: List[String]): Either[NonEmptyList[MyError],…
Michael
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0
votes
1 answer
value pure is not a member of
I have written this code
import scala.concurrent._
import scala.concurrent.ExecutionContext.Implicits.global
import cats.Applicative
import cats.data.OptionT
import cats.instances.future._
import cats.syntax.applicative._
object PureTest extends…
Knows Not Much
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0
votes
1 answer
Cannot upgrade Cats from 0.7.8 to 0.9.0
My project is using Cats 0.7.8 and Scala 2.11.8. If I update by build.sbt file and change my cats dependency from
"org.typelevel" % "cats-core_2.11" % "0.7.8"
to
"org.typelevel" % "cats-core_2.11" % "0.9.0"
and then try to do a sbt clean compile I…
Knows Not Much
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