def partition(f, li, ys=[], zs=[])
    return ys, zs if li.empty?
    x, *xs = li 
    return partition(f, xs, [*ys, x], zs) if f.call(x)
    partition(f, xs, ys, [*zs, x])
end 

p partition(->(x){x%2==1}, [1,2,3,4,5,6])