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import cats.{MonadError, StackSafeMonad}

import scala.concurrent.{ExecutionContext, Future}
import scala.util.{Failure, Success, Try}

package object effects {
  type F[E, A] = ExecutionContext => Future[Either[E, A]]
  
  object F {

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package effects

import cats.{MonadError, StackSafeMonad}

import scala.concurrent.{ExecutionContext, Future}
import scala.util.{Failure, Success, Try}

final case class F[+E, +A](value: Future[Either[E, A]]) extends AnyVal {

  def fold[B](fe: E => B, fa: A => B)(implicit ec: ExecutionContext): Future[B] = value.map {

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import cats.{Id, Monad, Traverse, ~>}

import scala.concurrent.{Await, Future}
import scala.concurrent.duration.Duration

object TagLess extends App {

  case class PurchaseOrderId(value: String)
  case class ProductId(value: String)
  case class LocationId(value: String)

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import shapeless.{ ::, Generic, HList, HNil, Lazy }

object ShapelessDSL extends App {

  trait Amount[A] {
    def zero: A
    def plus(a: A, b: A): A
    def times(a: A, b: BigDecimal): A
  }

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object FinanceDSL extends App {

  trait PrettyPrint[A] {
    def prettify(a: A): String
    class Ops(a: A) {
      def pretty: String = prettify(a)
    }
  }
  object PrettyPrint {

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object FreeMonadExplained {

  import scala.language.higherKinds
  import scala.language.implicitConversions

  sealed trait Interact[A]
  case class Ask(prompt: String)   extends Interact[String]
  case class Tell(message: String) extends Interact[Unit]

  // No access to the username captured by the Ask