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
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Simple unit testing with monoids
Suppose I testing a function echo: String => String, which is just repeating the input, with specs2.
I can write a few tests like that:
class EchoSpec extends SpecificationWithJUnit {
"echo should handle ASCII alphanumeric names" in {
…
Michael
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1 answer
Merging multiple Validated into single one
I have written this code
def valid1() : Validated[List[String], Boolean] = {...}
def valid2() : Validated[List[String], Boolean] = {...}
def valid3() : Validated[List[String], Boolean] = {...}
def valid4() : Validated[List[String], Boolean] =…
Knows Not Much
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1 answer
How to fix this compilation error with a Poly function
I am trying to map an HList of Xor to an HList of ValidatedNel and got an error:
scala> type Result[A] = Xor[String, A]
defined type alias Result
scala> type Validation[A] = ValidatedNel[String, A]
defined type alias Validation
scala> val r0 =…
Michael
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0
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1 answer
scala: Parameterize by Type Union
I needed a type Union to force restriction on types, So as per answer in here, I defined my Union as:
sealed trait Value[T]
object Value{
implicit object NumberWitness extends Value[Int]
implicit object StringWitness extends…
bistaumanga
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1 answer
Scala Unable to pimp NaturalTransformation in scalaz or cats
For some reason the following fails to work
object NtExtTest {
implicit class NaturalTransformExt[M[_], N[_]](val self: NaturalTransformation[M,N]) extends AnyVal {
def test(b:Boolean) = b
}
}
when I call the method test on a natural…
J Pullar
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2 answers
Working with Streams wrapped in Options
I am working with some nested Streams and would like to use the for comprehension syntax with them:
def handleNestedStream(as : Stream[A]) : Stream[(A, B)] = {
a <- as
b <- makeBs(a)
} yield (a, b)
However, the makeBs function returns an…
mushroom
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1 answer
Does using a library like cats make upgrading to dotty more or less difficult?
If I use cats in my scala project, would it make migrating to dotty easier or difficult?
I'm not too sure of the ramifications of using a library like this and how hard it will be to eventually migrate over to dotty.
Blankman
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1 answer
Scala cats: problem with implicits when trying to use `===` syntax for `Eq` trait
Aloha! :)
I'm not happy about running all the time to the stackoverflow forums to get some help with another piece of strangeness scala/cats has thrown at me.
Problem is: There seems to be no really useful documentation, only some worthless - at…
Alexander Schell
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votes
2 answers
Match that the result of running a computation is Invalid in a for comprehension
I am inside a for comprehension where we compose multiple operations together. When each step is completed, I need to either throw an error using MonadError.raiseError or carry on to the next step if valid.
def myFunc[F[_]: Monad](input:…
vamsiampolu
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votes
1 answer
Building a compiler for Free monad (Cats library)
I'm trying to get my head around monads and Cats. Following some examples (e.g.cats) I wrote the code like below. But can't figure out how to make compiler to do what I need and to compile, actually.
import cats.Id
import cats.free.Free
import…
kikulikov
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1 answer
Where is StateT in Cats?
I have in my sbt:
"org.typelevel" %% "cats-core" % "2.0.0-M1",
"org.typelevel" %% "cats-effect" % "1.3.1",
"org.typelevel" %% "cats-free" % "2.0.0-M3"
But can't import StateT in code.
In what module is it?
It's referred to here…
jakstack
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1 answer
Why running unsafeRunSync() twice breaks RT
I have following application that I could not figure it out, why running it twice it breaks RT:
val program = for {
_ <- IO { println("Welcome to Scala! What's your name?") }
_ <- IO { println(s"Well hello, foo") }
} yield…
softshipper
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Do tagless algebra needs laws?
I read the wonderful blog from JOHN A DE GOES regarding to tagless final. In the section 5.Fake Abstraction, he has mentioned:
Unfortunately, these operations satisfy no algebraic laws—none
whatsoever! This means when we are writing polymorphic…
softshipper
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