class Numeric
  @@currencies = {'dollar' => 1.0, 'yen' => 0.0093, 'euro' => 1.204, 'rupee' => 0.019, 'baht' => 0.03}
  def method_missing(method_id, *args, &block)
    if method_id == :in
      convert_to = args[0].to_s.gsub( /s$/, '')
      if @@currencies.has_key?(convert_to)
        self / @@currencies[convert_to]
      else
        super
      end
    else
      singular_currency = method_id.to_s.gsub( /s$/, '')
      if @@currencies.has_key?(singular_currency)
        self * @@currencies[singular_currency]
      else
        super
      end
    end
  end
end

val = (3.dollars).in(:baht)
puts val