Latex \newcommand restrict the value of an argument

Question

When defining a macro, is it possible to restrict the value of an argument, so that if the thing followed it is a number, then it takes it as an argument, but if it is not, then it is just empty.

To be concrete, I defined

\newcommand{\R}[1]{\ensuremath{\mathbb{R}^{#1}}}

for a real vector space, so the \R2 and \R3 give the 2-dim and 3-dim real spaces respectively. But what do I do if I want to input \R only?

Answer 1

Insert `$\R{}$`