sequence powerset
integer step = 1

function pst(object key, object /*data*/, object /*user_data*/)
    integer k = 1
    while k<length(powerset) do
        k += step
        for j=1 to step do
            powerset[k] = append(powerset[k],key)
            k += 1
        end for
    end while
    step *= 2
    return 1
end function

function power_set(integer d)
    powerset = repeat({},power(2,dict_size(d)))
    step = 1
    traverse_dict(routine_id("pst"),0,d)
    return powerset
end function

integer d1234 = new_dict()
setd(1,0,d1234)
setd(2,0,d1234)
setd(3,0,d1234)
setd(4,0,d1234)
?power_set(d1234)
integer d0 = new_dict()
?power_set(d0)
setd({},0,d0)
?power_set(d0)