time-traversals.scala

// We can re-use a simple function that goes from Time to a new Time
val adjustTime: DateTime => DateTime = ???
    
// With an appropriate traversal in scope we can apply the adjustTime function from this library to any incoming holder
def adjustTimes[T](implicit T: Traversal[T, DateTime]): T => T = 
  T.modify(adjustTime)

// Again we can keep a concrete alternative to adjustTime, we just increment it by duration:
def increaseTimeBy(duration: FiniteDuration): DateTime => DateTime = 
  _.add(duration)

// and re-use the same lense, to update the time on on transactions in a balance sheet adding to them a fixed amount.
def increaseTimesBy[T](duration: FiniteDuration)(implicit T: Traversal[T, DateTime]: T => T = 
  T.modify(increaseTimeBy(duration))