One point about "Functions as variables". Ruby actually does have method objects, which you can access via the method method.

  def add(a,b)
    a+b
  end

  def process_numbers(a,b,method)
    func.call(a,b)
  end

  method(:add) => #<Method: Object#add>
  process_numbers(1,2,method(:add)) => 3

This isn't a normal programming paradigm in Ruby though.