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
Why does the code with extension method compile?
I have two functions:
override def build_url(dbType: DbDriverType, dbAddr: String, dbName: String): F[DbAddr] = dbType match {
case PostgresSql =>
Applicative[F].pure(DbAddr("jdbc:postgresql://" |+| dbAddr |+| "/" |+| dbName))
case _…
softshipper
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0
votes
1 answer
What does private[routes] mean?
I have the following code snippet:
final class UserRoutes[F[_]: Defer: JsonDecoder: MonadThrow](
auth: Auth[F]
) extends Http4sDsl[F] {
private[routes] val prefixPath = "/auth"
private val httpRoutes: HttpRoutes[F] =
HttpRoutes.of[F] {
…
softshipper
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0
votes
1 answer
Write laws or unit test for tagless algebras
I have written two tagless algebras and I would like to write the laws for one of them.
The algebras are as follows:
@newtype case class Variable(v: String)
@newtype case class Value(v: String)
trait Environment[F[_]] {
def get(v: Variable):…
softshipper
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0
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0 answers
value pure is not a member of io.databaker.db.DbParameter
I have the following code, that does not compile:
import cats._
import cats.implicits._
import cats.data._
import cats.syntax.applicative._ // for pure
import cats.syntax.applicativeError._ // for raiseError etc
final class…
softshipper
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0
votes
1 answer
The first final tagless approach
I am trying to use the first time tagless final pattern in Scala and struggling a bit.
I have the following algebras definition:
trait DbSetting[F[_]] {
def read(url: String, user: String, pw: String): F[DbParameter]
}
trait Environment[F[_]] {
…
softshipper
- 32,463
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0
votes
1 answer
fs2 Stream scala No implicit of type : Stream.Compiler[Eval,G_]
I'm trying to create a Stream[Eval, String] as follows :
import cats.Eval
import cats.effect.{ExitCode, IO, IOApp}
import fs2._
object StringEval extends IOApp {
def evalString: Eval[String] = Eval.always{
val r = new…
Her sincerly
- 373
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0
votes
1 answer
Use mapN to apply values
I have the following code snippet:
final case class Configuration(env: Env, user: String, password: String, address: String)
trait DbSetup[F[_]] {
type EnvT[A] = OptionT[F, A]
def system: EnvT[Env]
def user: EnvT[String]
def password:…
softshipper
- 32,463
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0
votes
1 answer
Generate apply methods creating a class
Scala 2.13
I have tons of similar traits of the form
trait SomeTrait[F[_]]{
def someOp(): F[Unit]
//...
}
and their implementations
class SomeTraitImpl[F[_]: Sync] extends SomeTrait[F]{
//...
}
object SomeTrait{
def apply[F[_]:…
Some Name
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0
votes
1 answer
Testing Higher order functions scala + Cats Resource
I have one question. I'm using the following function together with the Scala cats Library.
def process(
client: Resource[IO, HttpClient] = HttpClientFactory.createClient()
): IO[Long] =
client.use(httpClient => {
for {
…
Jorge Machado
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0
votes
1 answer
Missing Implicit for Log Cats.Effect.IO
I am trying to get this simple example running using the redis4cats library:
import cats.effect._
import cats.implicits._
import dev.profunktor.redis4cats.Redis
import dev.profunktor.redis4cats.effect.Log.noop
object QuickStart extends IOApp {
…
Mojo
- 1,152
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0
votes
2 answers
Combining two EitherT, return first if it succeeds else return second
Consider the following snippet:
def foo(x:String): EitherT[F, Throwable, String] = ???
def bar(x:String): EitherT[F, Throwable, String] = ???
I want the following:
On some input s, first call foo(s) and if it "fails" return the output of bar(s)…
Jus12
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- 157
0
votes
1 answer
Scala how to call a future function on hashmap items
I have a hashmap map: Map[A, Seq[B]] and I want to call a future function (that returns Future[Either[Error, Unit]]) for each B in my map.
For example, given the following function def fooFunc(hashMap: Map[A, Seq[B]]): Future[Either[Error, Unit]]…
khan7
- 75
- 2
- 8
0
votes
1 answer
Require semigroup to be associative in scala
A semigroup is required to be associative, but I could define a Semigroup like:
trait Semigroup[T] {
def op(t1:T, t2:T) : T
}
def plus = new Semigroup[Int] { def op(t1:Int, t2:Int) = t1 - t2 }
I am able to implement plus which is not…
Rob
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0
votes
1 answer
Lifting A Future using EitherT.liftF When Value Is Already a Future
I have a value like this:
val ss: Option[Future[List[Either[Error, File]]]]
And what I want to do is to lift this to an EitherT.liftF[Future, Error, List[Either[Error, File]]] so what I did was this:
ss match {
case Some(value) =>…
Mojo
- 1,152
- 1
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- 16
0
votes
2 answers
Mixing Future and F[] inside a for comprehension
I have hit a problem withe my for comprehension as follows:
def doSomething(): F[String] = {
for {
_ <- Future.traverse(items)(item => doSomeWork(item)) // Future[]
_ <- doSomeOtherWork(42) //F[]
} yield (())
}
The…
Mojo
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- 16