currency converter with symbols, singular, plural

gistfile1.txt

class Numeric
    @@currencies = {'yen' => 0.013, 'euro' => 1.292, 'rupee' => 0.019}
    @@currencies['dollar']=1
    def method_missing(method_id)
        singular_currency = method_id.to_s.gsub( /s$/, '')
        if @@currencies.has_key?(singular_currency)
            self * @@currencies[singular_currency]
        else
            super
        end
    end

    def in(currency)
        if @@currencies.has_key?(currency)
            self / @@currencies[currency] 
        elsif @@currencies.has_key?(currency.to_s.gsub( /^:|s$/, ''))
            self / @@currencies[currency.to_s.gsub( /^:|s$/, '')] 
        end
    end
end