Repeated differentiation is not type stable

[harris-mit]

The function

function differentiate(p, x, deg::Val{N}) where N
...
end

is not type stable because sometimes it throws an error. Should this be changed to the following?

function differentiate(p, x, deg::Val{N}) where N
    for i = 1:deg
        p = differentiate(p, x)
    end
    return p
end