julia> f()=(); f(i::Real, I...)=f(I...); f(i,I...)=tuple(length(i),f(I...)...);

julia> f(1:5)
(5,)

julia> function g(); @show "A<", (); x=(); @show x, ">A"; x; end;

julia> function g(i::Real, I...); @show "B<", i, I; x=g(I...); @show x, ">B"; x; end;

julia> function g(i, I...); @show "C<", i, I; x=tuple(length(i), g(I...)...); @show x, ">C"; x; end;

julia> g(1:5)
("C<",i,I) => ("C<",1:5,())
("A<",()) => ("A<",())
(x,">A") => ((),">A")
ERROR: no method start(Nothing)
 in g at none:1