How can I find out how many arguments (i.e. {} pairs) are used when 'calling' a macro? (my favorite error, that I extend a macro, i.e. it needs one more argument, then I use it to compile a text prepared for a macro having one less argument. I receive a variety of errors, depending of the environment of the macro call in the text.)
In other words: can I find out within the macro, whether it was called with the right number of {} arguments?
Depending on how you define "number of macro arguments" the answer may or may not be obtainable from tex and you may need to rely on the package documentation.
If you do
\newcommand\fooa[2]{abc}
\show\fooa
you see
> \fooa=\long macro:
#1#2->abc.
So you could take this #1#2-> as one definition of the command taking two {} arguments
but if you do
\newcommand\foob[2][]{abc}
\show\foob
Then you may document that as being one optional [] argument and one {} argument but \show shows the primitive definition:
> \foob=macro:
->\@protected@testopt \foob \\foob {}.
\foob technically takes no arguments at all.
Similarly after
\newcommand\fooc{\fooa}
Then \fooc operates in almost all contexts just like \fooa and acts as if it takes two arguments but
\show\fooc
shows
> \fooc=\long macro:
->\fooa .
confirming that it has no arguments at all as a primitive control sequence definition.
<balanced text> arguments or given an error. You might of course find that what TeX thinks are the arguments are not what was intended!
– Joseph Wright♦
Jul 16 '16 at 17:56
{} are optional if you omit them you just get the next tokens so if you forget a section title \section Once upon a time then you can not (easily) give an error that the {} argument is missing as the input is identical to \section{O}nce upon a time so the section argument is provided, and is O.
– David Carlisle
Jul 16 '16 at 18:48
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\usepackage{xparse} \NewDocumentCommand\macro{gggg}{\IfValueTF{#4}{<your definition with #1, #2, #3, and #4>}{<what you want to output in case of error>}. You just have to write the lettergthe numer of times of the argument (ggggin case of four arguments), and also\IfValueTF{#4}should have also the last argument. For instance, if you want seven arguments, you cangggggggand\IfValueTF{#7}. But it's not perfect, and you better do whatever other approach to get to where you want. – Manuel Jul 16 '16 at 18:11