Define command that contains a command that cannot be executed in the preamble

Question

I have a command like this:

\def\command#1{%
    \calc{#1}%
    \doStuff%
}

\calc sets certain lengths based on the current size. As such it cannot be executed in the preamble. This works as expected.

However, I want to define a new command

\def\command2{%
    \command{default}%
}

How can I do that? I can’t put the above in the preamble since the compiler is trying to evaluate \calc and the expected errors occur.

Sorry, but it's impossible to answer without knowing what you're trying to achieve. What's \calc doing, precisely? — egreg, Apr 27 '22 at 21:24
please make your example a real test document that shows the problem, and state your expected outcome. You can not have a command \command2 but the replacement text is not evaluated at all so you can make the definition anywhere — David Carlisle, Apr 27 '22 at 21:24
If you want to defer something to not executed in the preable you can use \AtBeginDocument{} or \AtEndPreamble{}. — Peter Grill, Apr 27 '22 at 21:30
I’m voting to close this question because it was solved in the comments. — José Carlos Santos, Apr 28 '22 at 07:08

score 1 · Accepted Answer · answered Apr 27 '22 at 22:16

1

If you want to defer something to not executed in the preable you can use \AtBeginDocument{} or \AtEndPreamble{}.

References:

How to automatically add text immediately after \begin{document}.

answered Apr 27 '22 at 22:16

Peter Grill

223,288

Ulrich Diez · Answer 2 · 2022-04-28T10:01:09.860

\def\command#1{%
    \calc{#1}%
    \doStuff%
}
% ...
\def\command2{%
    \command{default}%
}

I suppose you are misinterpreting error-messages:

\def does not trigger but does prevent evaluation.

But when reading/tokenizing the .tex-input file TeX does tokenize the sequence \command2 as control-word-token \command trailed by the explicit character token 2 of category 12(other).

Thus with \def\command2{\command{default}} the control-word-token \command is redefined to be something that is delimited by 2 and that as replacement-text delivers the control-word-token \command for calling itself (which implies unwanted recursion), trailed by character-tokens {, d, e, f, a, u, l, t and }.

Any attempt at expanding the macro \command without a trailing 2 yields a message about usage of \command not matching its definition.

Even if the first instance of \command is trailed by 2 you get this message because in this case expansion of \command 2 yields \command {default} where you have an instance of the control-word-token \command which is not trailed by 2.

Between \makeatletter..\makeatother you can probably do something like

\def\command#1{%
    \calc{#1}%
    \doStuff%
}%
% ... 
% defining the command:
\@namedef{command2}{%
    \command{default}%
}%
% ...
% calling/using the command:
\@nameuse{command2}%

(\@namedef / \@nameuse internally use \csname..\endcsname for constructing control-word-tokens whose names may also contain digits like 2.)

Define command that contains a command that cannot be executed in the preamble

2 Answers2