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
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Unable to recover exception in Future in Scala
The following Scala code uses cats EitherT to wrap results in a Future[Either[ServiceError, T]]:
package com.example
import com.example.AsyncResult.AsyncResult
import cats.implicits._
import…
Robo
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2 answers
Scala - Is there a function to map Seq[A] => Seq[Either[Throwable, B]]?
I am looking for a function that will map over a collection coll: Seq[A] while applying a function f: A => B and returning a Seq[Either[Throwable, B]] so that errors can be handled downstream.
Is there a function similar to this that is pre-baked…
D Cohen
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1 answer
Scala Cats Validated with Parameterized Validation Result
I am following the example in https://typelevel.org/cats/datatypes/validated.html but with a twist: the type of the elements in the NEL is not a DomainValidation but a DomainValidation[A] and I'm not sure how to do this. Below is my attempt but am…
luddy2018
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- 3
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1 answer
Lifting functions to monad transformers in Scala cats
Suppose there's a trait with abstract methods having different signatures (see below). To enable for-comprehension, I could define the same signature Result[A] for every abstract method.
However, to simplify trait's subclasses, I'd like to keep…
schrödingcöder
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2 answers
Scala-Cats :- Is it possible to combine errors from different NonEmptyLists?
Is there any possibility to combine different errors from multiple variables using NonEmptyList
type ValidationResult[A] = ValidatedNel[String, A]
def throwErrorsWhenNumberIsLessThan6(x:Int):ValidationResult[Int] = if(x<6) s"$x !> 6".invalidNel…
Puneeth Reddy V
- 1,538
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2 answers
Traversing Either in Scala
I wrote the following simple code:
import cats.effect.IO
import cats.instances.either._
import cats.syntax.TraverseSyntax
object Test extends App with TraverseSyntax{
val e: Either[String, IO[Int]] = Right(IO(2))
e.sequence //error…
St.Antario
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2 answers
How to explicitly summon and use Functor for function
import scala.language.higherKinds
import cats.Functor
import cats.instances.list._
import cats.instances.function._
val list1 = List(1, 2)
val list2 = Functor[List].map(list1)(i => i + 1)
But things don't work so smoothly for functions,
val f1 =…
sarveshseri
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1 answer
What is the purpose of using [T : Type] in cats?
I'm learning to use Scala cats library. Quite often I see this type of definition like
implicit def validatedApplicative[E : Semigroup]: Applicative[Validated[E, ?]] = ???
def parallelValidate[E : Semigroup, A, B, C](v1: Validated[E, A], v2:…
Puneeth Reddy V
- 1,538
- 13
- 28
0
votes
1 answer
Scala - Flatten Sequence of EitherT
Suppose I have the following:
val ints: Seq[Int] = ???
def foo(i: Int): EitherT[Future, Error, Seq[String]] = ???
I want to invoke the foo with the ints and accumulate Seq[String] result to eventually return EitherT[Future, Error,…
gyoho
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1 answer
logback.xml appender not used with cats IOApp
I have a scala app which uses the AWS Kinesis Client Library.
I am using logback with the logstash encoder to format the logs from my app and the KCL as JSON.
My App is also written using cats.effects.IO.
import cats.effects._
object Main extends…
tmortiboy
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2 answers
cats.data.EitherT with traverse
I have a question about using Traverse together with EitherT. Let's say we have a code like this:
def validate(s: String): EitherT[Future, NumberFormatException, Int] = {
EitherT(Future.successful(try { Right(s.toInt) } catch { case e:
…
tomas.tunkl
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How to combine type parameter bounds and functors using Cats?
I am encountering a number of use cases where I am end of attempting to write Functor, Applicative, Monad, etc instances in contexts where I am also using type parameter bounds.
For example...
import cats._
trait Preference[A] extends…
davidrpugh
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1 answer
Apply, Applicative, Monad, etc for contravariant functors in cats?
I have the following trait...
import cats._
import cats.implicits._
trait Preference[-A] {
self =>
def compare(a1: A, a2: A): Int
final def ordering[A1 <: A]: Ordering[A1] = {
new Ordering[A1] {
def compare(a1: A1, a2: A1): Int =…
davidrpugh
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0
votes
1 answer
How to abstract over a second type parameter when defining functors?
Learning idiomatic FP with Scala and Cats. I have the following code...
package org.economicsl.mechanisms
import cats._
import cats.implicits._
trait Preference[-A] {
self =>
def compare(a1: A, a2: A): Int
final def ordering[A1 <: A]:…
davidrpugh
- 4,363
- 5
- 32
- 46
0
votes
1 answer
cats-effect: How to transform `List[IO[A]]` to `IO[List[A]]`
I have an List[IO[A]] and I want to convert it to an IO[List[A]]
In scalaz I would use sequenceU but I don't find the equivalent in cats
nam
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