Luhn algorithm in Julia

luhn.jl

module Luhn

export luhn

function luhn(value::String)
    a = reverse(split(value, ""))
    s = 0
    for i = 1:length(a)
        n = parseint(a[i])
        isodd(i) || (n *= 2)
        n < 10   || (n = sum(digits(n)))
        s += n
    end
    s % 10 == 0
end

end