Demo of how Reader works

ReaderDemo.scala

import cats._
import cats.instances.all._
import cats.syntax.all._

final case class Configuration()
final case class Database()
final case class HttpServer()

object Test extends App {

  def initLog(): Configuration ⇒ Unit = ???
  def initDatabase(): Configuration ⇒ Database = ???
  def initHttp(db: Database): Configuration ⇒ HttpServer = ???

  val initAll: Configuration ⇒ HttpServer = for {
    _    ← initLog()
    db   ← initDatabase()
    http ← initHttp(db)
  } yield http
}

To complete this we'd need the following no? Or you are using something I missed and Cats picks up Reader implicits automatically?

import cats.data.Reader

final case class Configuration()
final case class Database()
final case class HttpServer()

object Test extends App {

def initLog(): Configuration ⇒ Unit = c => ()
def initDatabase(): Configuration ⇒ Database = c => Database()
def initHttp(db: Database): Configuration ⇒ HttpServer = c => HttpServer()

val initAll: Reader[Configuration, HttpServer] = for {
_ ← Reader(initLog())
db ← Reader(initDatabase())
http ← Reader(initHttp(db))
} yield http

val http = initAll.run(Configuration())
// do something with http
}