scala-cats

问题 In Scala community I see often, that classes end with Ops are very common. For example: ApplicativeErrorIdOps What does Ops stand for? 回答1: Ops = Operations. This is quite commonly used shortcut not only in Scala but in general. In Cats it's used as a suffix of an extension methods class because it enriches the value with operations related to some type class. 来源： https://stackoverflow.com/questions/62553798/what-does-ops-stand-for

问题 I was learning Cats library and found * as a generic type, like that: implicit def catsDataSemigroupKForValidated[A](implicit A: Semigroup[A]): SemigroupK[Validated[A, *]] = new SemigroupK[Validated[A, *]] { def combineK[B](x: Validated[A, B], y: Validated[A, B]): Validated[A, B] = x match { case v @ Valid(_) => v case Invalid(ix) => y match { case Invalid(iy) => Invalid(A.combine(ix, iy)) case v @ Valid(_) => v } } } My guess is that the * is used, because the combineK method return

问题 Just for the sake of quick clarity for someone who wants to start working with Scala FP library, on a journey to become better at pure FP. Would someone clarify the difference/relation between Cats and Cats-Effect, Cats-Effects IO? On top of that, where does Zio, and Monix stand with respect to it? Finally, what would be the relation to ScalaZ 7/8? So far based on what I have read, a good combination of the library to work with based on the documentation available and what they do would be

问题 I am trying to use Cats datatype Ior to accumulate both errors and successes of using a service (which can return an error). def find(key: String): F[Ior[NonEmptyList[Error], A]] = { (for { b <- service.findByKey(key) } yield b.rightIor[NonEmptyList[Error]]) .recover { case e: Error => Ior.leftNel(AnotherError) } } def findMultiple(keys: List[String]): F[Ior[NonEmptyList[Error], List[A]]] = { keys map find reduce (_ |+| _) } My confusion lies in how to combine the errors/successes. I am

问题 cats does not provide ListT monad transformer so how could we rewrite the following snippet which uses scalaz ListT in a for-comprehension to a semantically equivalent snippet in cats import scalaz._ import ListT._ import scalaz.std.option._ val seeds: Option[List[String]] = Some(List("apple", "orange", "tomato")) def grow(seed: String): Option[List[String]] = Some(List(seed.toUpperCase)) def family(seed: String, plant: String): Option[List[(String, String)]] = Some(List(seed -> plant)) (for

问题 I have a program which consumes an infinite stream of data. Along the way I'd like to record some metrics, which form a monoid since they're just simple sums and averages. Periodically, I want to write out these metrics somewhere, clear them, and return to accumulating them. I have essentially: object Foo { type MetricsIO[A] = StateT[IO, MetricData, A] def recordMetric(m: MetricData): MetricsIO[Unit] = { StateT.modify(_.combine(m)) } def sendMetrics: MetricsIO[Unit] = { StateT.modifyF { s =>

问题 I would like to know how to convert a List[Try[T]] to Try[List[T]] in Scala? I have tried using an accumulator and folding right but it doesn't seem ideal. 回答1: Using cats it's as easy as: import cats._ import cats.data._ import cats.implicits._ import scala.util.{Try, Success, Failure} val tries: List[Try[Int]] = List(Success(1), Success(2), Success(3)) tries.sequence More information in the Traverse docs. 回答2: Try(list.map(_.get)) This will return only the first failure, so you need

问题 I know that I can compose Apply to work with nested structures, like in def mapAll[A, B, C, D](o1: List[Option[A]], o2: List[Option[B]], o3: List[Option[C]]) (f: (A, B, C) => D) : List[Option[D]] = { import cats._ import cats.implicits._ Apply[List].compose[Option].map3(o1, o2, o3)(f) } However, is there a way to convince the compiler to accept (o1, o2, o3).mapN(f) instead of Apply[List].compose[Option].map3(o1, o2, o3)(f) , so that mapN gets applied using the composed Apply ? 回答1: This is

问题 There is a typeclass called Parallel in Cats . The purpose of this class is to provide parallel computations for some monads that don't support parallel computations out of the box like Either for example. I know that Monad is used for dependent computations and thus requires sequential execution. Applicative is used for independent computations, so such computations can be parallelized. It's also known that each Monad is Applicative (monad is applicative functor). So now I can't put together

问题 There is a typeclass called Parallel in Cats . The purpose of this class is to provide parallel computations for some monads that don't support parallel computations out of the box like Either for example. I know that Monad is used for dependent computations and thus requires sequential execution. Applicative is used for independent computations, so such computations can be parallelized. It's also known that each Monad is Applicative (monad is applicative functor). So now I can't put together