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
4
votes
2 answers
Scala: no-name parameters in function with List and Option
2 different examples, the first one works:
import cats.syntax.either._
val e = 10.asRight[String]
def i2s(i:Int):String = i.toString
e.map(i => List(i2s(i))) //using explicit parameter
e.map(List(i2s(_))) //using no-name _ parameter
Now…
Alexandr
- 9,213
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4
votes
1 answer
How to work with timer in cats effect without ExecutionContext.global and IOApp?
I have a simple sequence of IO operaion with 5 second pause.
implicit val timer = IO.timer(ExecutionContext.global)
def doSth(str: String): IO[Unit] = IO(println(str))
def greeting(): IO[Unit] =
doSth("Before timer.") *>
…
Vadim
- 753
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- 22
4
votes
2 answers
Tail recursive algorithm for generating all topological orderings in a graph
Given a graph i need to generate all topological orderings.
For instance, given the following graph:
i want to generate all topological orderings, which are:
2 4 7 5
2 7 4 5
2 4 5 7
Because many topological orderings may exist, I need to generate…
Kevin
- 2,813
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4
votes
1 answer
MonoidK and Monad relation
I'm trying to understand well known phrase A monad is just a monoid in the category of endofunctors and map some category theory concepts to cats library.
There is a MonoidK typeclass in cats and it's polymorphic on combineK method. So one instance…
Bogdan Vakulenko
- 3,380
- 1
- 10
- 25
4
votes
1 answer
Composition of Readers for Dependency Injection in Scala
Here is a simple service example, whose methods return reader:
trait Service1_1{
def s1f1:Reader[Map[String,Int],Int] =
Reader(_("name"))
def s1f2:Reader[Map[String,Int],Int] =
Reader(_("age"))
}
Here is a service-consumer, that…
Alexandr
- 9,213
- 12
- 62
- 102
4
votes
1 answer
How to pass implicit vals defined through package objects from Scala in Java
I am using the Cats library. In Scala the code looks like:
import cats.Semigroupal
import cats.instances.option._
val r = Semigroupal.tuple2(Option(1), Option(2))
The tuple2 defined as:
def tuple2[F[_], A0, A1](f0:F[A0], f1:F[A1])(implicit…
Alexandr
- 9,213
- 12
- 62
- 102
4
votes
1 answer
Model multiple function calls with a stream (in a safe, FP way)
Given a function A => IO[B] (aka Kleisli[IO, A, B]) that is meant to be called multiple times, and has side effects, like updating a DB, how to delegate such multiple calls of it into a stream (I guess Pipe[IO, A, B]) (fs2, monix…
V-Lamp
- 1,630
- 10
- 18
4
votes
1 answer
Getting around invariant result type in State
I would like to define a State that builds a concrete subtype of a trait, as per decodeFoo:
sealed trait Foo
case class Bar(s: String) extends Foo
case class Baz(i: Int) extends Foo
val int: State[Seq[Byte], Int] = State[Seq[Byte], Int] {
case bs…
Synesso
- 37,610
- 35
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- 207
4
votes
1 answer
Chaining a number of transitions with the state Monad
I am starting to use the state monad to clean up my code. I have got it working for my problem where I process a transaction called CDR and modify the state accordingly.
It is working perfectly fine for individual transactions, using this function…
Luis Sisamon
- 101
- 7
4
votes
1 answer
Cats Effect IO: Compose IO with Scala collections
This is a toy Scala program, that reads 10 numbers from the console and adds 1 to each prints them out:
import cats._
import cats.effect._
import cats.implicits._
object Main extends IOApp {
def printLine[A](x: A)(implicit show: Show[A]):…
pathikrit
- 32,469
- 37
- 142
- 221
4
votes
1 answer
How to go from a List[F[String]] to F[List[String]] using Scala and Cats?
I'm new to Cats and I don't know how to overcome this situation. In the code bellow:
class Example[F[_]] {
import cats._
import cats.data._
import cats.syntax.all._
def saveAll(list: List[String])(implicit M: Monad[F]): F[List[String]] = {
…
user10503105
4
votes
1 answer
Recursions with the State-Monad
I am using the State-Monad from the cats library to take care of the state of a card game I am implementing in Scala.
I have a function simulateGame which should end as soon as the status of a the current state is Over. The function looks like…
Lando-L
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- 19
4
votes
1 answer
How do I explain the difference between fold and foldK?
In the context of a programmer newly learning functional programming and completing the online Scala Exercises for Cats here, the following result seems puzzling:
import cats._
import cats.implicits._
object Foo {
def main(args: Array[String]):…
David Rawson
- 20,912
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- 124
4
votes
1 answer
Twitter Future & Cats Arrow
I'm trying to combine Twitter Future with Cats Kleisli and Arrow and I have a compilation error that I don't know how to solve it.
The code is the following:
package com.example
import scala.language.higherKinds
import cats.arrow.Arrow
import…
Octavian R.
- 1,231
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- 12
4
votes
1 answer
Replacing all JSON String values recursively with Circe
Using the CIRCE library & Cats, it would be incredibly useful to be able to transform all the string values of an arbitrary Json object such as
{
"topLevelStr" : "topLevelVal",
"topLevelInt" : 123,
"nested" : { "nestedStr" : "nestedVal" },
…
Tobias Roland
- 1,182
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