with javascript_semantics
function s_of_n(integer i, sequence samples, integer item)
    samples = deep_copy(samples)
    integer n = length(samples)
    i += 1
    if i<=n then
        samples[i] = item
    elsif n/i>rnd() then
        samples[rand(n)] = item
    end if
    return {{i,samples},samples}
end function

function s_of_n_creator(integer n)
    return define_lambda(s_of_n,{0,repeat(0,n)},true)
end function

function test(integer n, sequence items)
    lambda l = s_of_n_creator(n)
    sequence samples
    for item in items do
        samples = call_lambda(l,item)
    end for
    return samples
end function

procedure main()
    sequence items_set = tagset(9,0),
           frequencies = repeat(0,length(items_set))
    for i=1 to 100000 do
        sequence res = test(3, items_set)
        for fdx in res do
            frequencies[fdx+1] += 1
        end for
    end for
    ?frequencies
end procedure
main()