sample code for Cats MTL ApplicativeAsk

applicativeAsk.sc

import cats.FlatMap
import cats.data.Kleisli
import cats.syntax.flatMap._
import cats.syntax.functor._
import cats.effect.Sync
import cats.mtl.ApplicativeAsk
import monix.eval.Task

type Config = Map[String, String]

def askFunc[F[_]: FlatMap: Sync](key: String)(implicit F: ApplicativeAsk[F, Config]): F[String] =
  for {
    config <- F.ask
    result =  config.getOrElse(key, "none")
    _      <- Sync[F].delay { println(s"$key -> $result") }
  } yield result

import cats.mtl.instances.local._
import monix.execution.Scheduler.Implicits.global

import cats.syntax.traverse._
import cats.instances.list._

val program: Task[List[String]] =
  List("21", "42", "63")
    .traverse(askFunc[Kleisli[Task, Config, ?]])
    .run(Map("42" -> "foo"))

program.runSyncUnsafe()
// 21 -> none
// 42 -> foo
// 63 -> none
// res0: List[String] = List(none, foo, none)