\forcsvlist and expansion

Question

I've got an expansion issue with the following code:

\def\sizes{huge, LARGE, Large, large, normalsize, small, footnotesize, scriptsize, tiny}
\forcsvlist\sampletext{\sizes}

My problem is that \sizes should be expanded before being passed to \forcsvlist, otherwise \sampletext will simply receive the list and not know how to parse it.

How can I make it so that \sizes is expanded?

Note: Putting the list hardcoded in the \sampletext call works, but I don't want to do that because I might override \sizes with other values.

Answer 1

This is the standard way:

\expandafter\forcsvlist\expandafter\sampletext\expandafter{\sizes}

The first \expandafter expands the second one, which in turn expands the third and this last does the job, expanding \sizes. The primitive \expandafter expands to nothing, after having caused the expansion of the second token after it; just jump over one token, when checking the action of \expandafter. It's a bit more complicated when there are arguments, but \expandafter and \sizes don't take them. The expansion performed by \expandafter is only one step: after

\def\y{\z} \def\z{a}

saying

\expandafter\x\y

is like saying

\x\z

In your case the three \expandafter commands vanish, but TeX now has

\forcsvlist\sampletext{huge,LARGE,...}

and continues expanding from here.

Another trick is

\begingroup\edef\x{\endgroup\noexpand\forcsvlist\noexpand{\sizes}}\x

which works because the expansion of \sizes consists of characters; it wouldn't if \sizes had been defined as

\def\sizes{\huge,\LARGE,...}