* Can be used as unordered function parameters.  This is useful
  when you are trying to unify duplicated code.  Unordered parameter
  lists are very beneficial when you are unifying code that has
  common parameters but they are in different order.
* Instead of adding or removing a function parameter, using an
  implicit parameter gives less confusing error messages.  Once
  the code works with the implicit parameter converting it to a real
  function parameter is easier.
* Constraint can be bundled into a type alias.