Partial function example in Ruby

partial_function.rb

def divide(dividend, divisor)
  dividend / divisor
rescue ZeroDivisionError
  p $!.message
end

def average(*values)
  raise ArgumentError.new('No values given')            if     values.empty?
  raise ArgumentError.new('Not all values are numbers') unless values.all? { |value| value.is_a? Numeric }
  values.reduce(:+) / values.length
end