jdegoes

final case class ZIO[-R, +E, +A](run: R => Either[E, A]) {
  final def map[B](f: A => B): ZIO[R, E, B] = 
    ZIO(r => run(r).map(f))

  final def flatMap[R1 <: R, E1 >: E, B](f: A => ZIO[R1, E1, B]): ZIO[R1, E1, B] = 
    ZIO(r => run(r).flatMap(a => f(a).run(r)))

  final def provide(r: R): ZIO[Any, E, A] = 
    ZIO(_ => run(r))