Syntax sugar to effortlessly interoperate between Reader monads

ScalaReaderSugar.scala

case class has[Owner, A](get: Owner => A)

implicit def ownerHasPairs[Owner, A, B](implicit a: Owner has A, b: Owner has B): Owner has (A,B) = 
  has(owner => (a.get(owner), b.get(owner)))

implicit def pairHas1st[A,B]: (A,B) has A = has(_._1)
implicit def pairHas2nd[A,B]: (A,B) has B = has(_._2)  

implicit def widenReaderToOwner[Owner, O, A](reader: Reader[O, A])(implicit ev: Owner has O): Reader[Owner, A] = 
  reader.local[Owner](implicitly[Owner has O].get)
  
// For custom classes:
case class Config(db: DB, cred: Cred, lang: Lang)
implicit val configHasDB: Config has DB = has(_.db)
implicit val configHasCred: Config has Cred = has(_.cred)
implicit val configHasLang: Config has Lang = has(_.lang)

// Each function can have minimal dependencies
// without an interoperability penalty or manually argument-passing

val dependsOnDB: Reader[DB, String] = ???
val dependsOnLang: Reader[Lang, String] = ???
val dependsOnCred: Reader[Cred, String] = ???
val dependsOnDBAndCred: Reader[(DB, Cred), String] = ???

def doConfigStuff: Reader[Config, String] = for {
  a <- dependsOnDB
  b <- dependsOnLang
  c <- dependsOnDBAndCred
} yield List(a,b,c)

def doPairStuff: Reader[(Lang, Cred), String] = for {
  a <- dependsOnLang
  b <- dependsOnCred
} yield List(a,b)