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
2 answers
Why does scala not infer the right type when wrapping EitherT?
Here's the code:
// eventually will be an implicit class with extension methods
class EitherTWrapper [L,R] (ei: EitherT[Future,L,R])
new EitherTWrapper(??? : EitherT[Future,Nothing,Boolean])
Fails to compile with:
type mismatch;
found :…
Alvaro Carrasco
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1 answer
How do I know, which implicit that is needs?
I have a working code:
final case class Services[F[_]](c: Client[F], fooUrl: String)
(implicit cf: ConcurrentEffect[F]) {
private val dsl = Http4sDsl[F]
import dsl._
def routes: HttpRoutes[F] =…
softshipper
- 32,463
- 51
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votes
0 answers
running fs2.Stream under the method's hood?
I'm just learning FP, so maybe i'm doing this completely wrong.
Using cats, cats-effects, fs2, fs2-io.
Following code takes takes port as an argument then creates Server Socket and Client Socket connected to 127.0.0.1 on given port.
What I need this…
pool
- 11
- 1
- 1
0
votes
1 answer
Convert a list of stream values to a stream of values with fs2
I would like to define a function with the following signature using fs2 Streams, cats EitherT and cats-effect IO.
def list2Stream[A,B,F[_],S](vs: List[A],
f: A => EitherT[IO,S,Stream[IO,B]]
…
Labra
- 1,412
- 1
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0
votes
1 answer
Implementing functor map for class-tagged arguments only
I have the following data structure:
class MyDaSt[A]{
def map[B: ClassTag](f: A => B) = //...
}
I'd like to implement a Functor instance for to be able to use ad-hoc polymorphism. The obvious attempt would be as follows:
implicit val…
Some Name
- 8,555
- 5
- 27
- 77
0
votes
1 answer
Cannot convert HList to tuple after Shapeless FoldRight
I'm trying to create a parser of CSV files using Scala into a case class and I'm trying to make it generic using Shapeless.
I want my parser to allow the user to specify an extraction function extract: CsvRow => String rather than having a a 1-to-1…
ColOfAbRiX
- 1,039
- 1
- 13
- 27
0
votes
1 answer
Scala Future/Option for comprehension issues
I am trying to write a function that reads from a repository (which returns F[Option[Entry]] where F is a future) and then converts it to F[Option[Element]]. The function convert() takes a Seq[Entry] and returns ValidatedNel[LoadError,…
Chris Johnston
- 335
- 1
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- 16
0
votes
2 answers
Scala - how to make generic decoder in circe?
I have two similar functions which have different return types:
override def getUsers(uri: Uri): F[Either[CodecException, List[User]]] =
for {
response <- retrieveDataFromClient(uri)
result <- Sync[F].delay(response)
} yield…
Developus
- 1,400
- 2
- 14
- 50
0
votes
1 answer
Scala - how to refactor code in functional style
I have created two similar methods:
override def getUsers(organization: String, params: String): F[Either[CodecException, List[Users]]] = for {
resp <- getUsersFromClient(organization, params)
result <- Sync[F].delay(resp)
} yield result
…
Developus
- 1,400
- 2
- 14
- 50
0
votes
1 answer
Scala - how to get data from IO[HttpResponse] in Hammock?
I have a simple methods:
def retrieveRepositories(url: String, params: String): IO[HttpResponse] = Hammock.getWithOpts(uri"$url", createOpts).exec[IO]
Which is a http client. and json decoder:
implicit def decodeResponseEntity(response:…
Developus
- 1,400
- 2
- 14
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0
votes
1 answer
Scala - how to use foreach loop in for comprehension block?
I have a simple code:
override def createContributorsList(url: String, params: String): F[List[Contributor]] = getContributorsFromClient(url, params).fold[List[Contributor]](_ => List(), res => res)
override def createReposList(organization:…
Developus
- 1,400
- 2
- 14
- 50
0
votes
0 answers
Scala, unsafeRunSync - why it needs to be call every time?
I have a strange problem. I created two methods, which return Lists:
override def createContributorsList(url: String, params: String): F[List[Contributor]] = getContributorsFromClient(url, params).fold[List[Contributor]](_ => List(), res =>…
Developus
- 1,400
- 2
- 14
- 50
0
votes
1 answer
Scala, Hammock - retrieve http response headers and convert JSON to custom object
I have created a simple program which use Hammock(https://github.com/pepegar/hammock) and now I would like to get response from github API with reposne's headers. I created a code like this:
object GitHttpClient extends App {
implicit val decoder…
Developus
- 1,400
- 2
- 14
- 50
0
votes
1 answer
Stop long running process on a Resource
I have a resource which runs a potentially long blocking operation. In the real code, it's a ZeroMQ routine that waits for the next message (not too dissimilar to the example code here), but in this example, I've created a dummy loop that only…
Cesar Pantoja
- 173
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0
votes
1 answer
Scala Kittens: implicit Sequencer value doesn't seem to work with context bound syntax
In my understanding the following two functions and their calls should be identical:
def f1[L1 <: HList, L2](xs: L1)(implicit sequencer: Sequencer.Aux[L1, Option, L2]) {
println(xs.sequence)
}
def f2[L1 <: HList : Sequencer.Aux[*, Option, L2],…
mrArkwright
- 254
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