Encode

func arabic2roman(num, roman='') {
    static lookup = [
        :M:1000, :CM:900, :D:500,
        :CD:400, :C:100,  :XC:90,
        :L:50,   :XL:40,  :X:10,
        :IX:9,   :V:5,    :IV:4,
        :I:1
    ]
    lookup.each { |pair|
        while (num >= pair.second) {
            roman += pair.first
            num -= pair.second
        }
    }
    return roman
}
say("1990 in roman is " + arabic2roman(1990))
say("2008 in roman is " + arabic2roman(2008))
say("1666 in roman is " + arabic2roman(1666))

Output:

1990 in roman is MCMXC
2008 in roman is MMVIII
1666 in roman is MDCLXVI