I would like to define a command which creates an index with a certain name, when i pass the name, and doesn't create any index if there is no name passed.

My first idea was to write it like that:


but the compiler gets stuch when I pass an empty optional argument. How can I build an if-then structure like the following?

 if(#1 is not empty)

If you don't want to use xparse (why not?), you can use some traditional tricks, for example:


xparse's \IfValueT is safer in some cases. A safer implementation without LaTeX3 is:

  • Why the {a} in the second example? Shouldn't it be {}? – clemens Oct 20 '13 at 10:25
  • @cgnieder: Sorry, it's a typo. – Leo Liu Oct 20 '13 at 10:45

You can use the xparse package from the LaTeX3 project.

    % #1 is empty.
    % #1 has a value.

To recreate your example command:

  • 6
    More simply, \emph{#2}\IfValueT{#1}{\index{#1}}. Be careful with spurious spaces; in your example macro you have three of them. – egreg Oct 20 '13 at 9:05
  • @egreg I wasn't aware that there is a \IfValueT; it's not mentioned in the xparse documentation. – ChrisS Oct 20 '13 at 21:25
  • Yes, it is, on page 7; note that the entry in the margin is \IfValueTF with T and F in italics and underlined in red. This means that \IfValueT, \IfValueF and \IfValueTF are available. – egreg Oct 20 '13 at 21:47
  • @egreg Thanks for pointing that out; I'd seen the underlining but didn't know what it meant. – ChrisS Oct 21 '13 at 1:13
  • I upvoted your answer and edited it in order it does what's advertised; I won't do the same next time. – egreg Oct 21 '13 at 7:31

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