The call \myTable{\variable} passes a list of length one. You need to access at the value of \variable before \myTable does its job.
So, as the other answer suggests is right, although there's no need to add an \expandafter in front of \addtablerow.
I suggest a different method, with expl3 that avoids polluting the code with \def, using the analog of a namespace.
The \printlist macro takes a * if you want to use a list defined previously.
If all lists you need are like this, you can avoid the * variant, changing the code should be easy.
The working is much like that of \docsvlist, but with some advantages: spaces around the comma delimiters are ignored, for instance. Here \clist_map_inline:nN has a role similar to \docsvlist and instead of redefining \do you define a set of two macros, the first of which is the analog of \addtablerow, but has to be split into an external and an internal part.
The table preamble has been fixed to avoid overfull: your table is longer than the text width, because you aren't taking into account the intercolumn spaces.
\documentclass[a4paper,11pt]{article}
\ExplSyntaxOn
\NewDocumentCommand{\definelist}{mm}
{
\clist_clear_new:c { l_fauszt_list_#1_clist }
\clist_set:cn { l_fauszt_list_#1_clist } { #2 }
}
\NewDocumentCommand{\printlist}{sm}
{% the star variant uses a list name
% otherwise a full list is passed
\IfBooleanTF{#1}
{
\fauszt_list_print:v { l_fauszt_list_#2_clist }
}
{
\fauszt_list_print:n { #2 }
}
}
\cs_new_protected:Nn \fauszt_list_print:n
{
\begin{tabular}{
|p{\dimexpr0.4\textwidth-2\tabcolsep}
|p{\dimexpr0.2\textwidth-2\tabcolsep}
|p{\dimexpr0.2\textwidth-2\tabcolsep}
|p{\dimexpr0.2\textwidth-2\tabcolsep}|
}
\hline
Name & Role & Presence & Present \
\hline
\clist_map_function:nN { #1 } __fauszst_list_print_row:n
\end{tabular}
}
\cs_generate_variant:Nn \fauszt_list_print:n { v }
\cs_new_protected:Nn __fauszst_list_print_row:n
{
__fauszt_list_print_row:w #1 \q_stop
}
\cs_new_protected:Npn __fauszt_list_print_row:w #1 / #2 / #3 / #4 \q_stop
{
\textbf{#1} & #2 & #3 & #4 \ \hline
}
\ExplSyntaxOff
\definelist{variable}{
Person 1/Active/Online/X,
Person 2/Active/-/-,
Person 3/Intern/Office/X
}
\begin{document}
\noindent
\printlist{Person 1/Developer/Online/X,Person 2/Developer/-/-,Person 3/Intern/Office/X}
\bigskip
\noindent
\printlist*{variable}
\end{document}
Further generalizations are possible.
For completeness, I'll prove my statement that, in the solution proposed by user237299, the token \expandafter in \expandafter\addtablerow##1 can be removed as it does nothing useful (and it can even do evil in corner cases).
Let's just follow the expansions. When \variable is defined as in the question and the call is
\noindent\expandafter\myTable\expandafter{\variable}
(first proposed solution), this is just the same as calling
\noindent\myTable{Person 1/Developer/Online/X,Person 2/Developer/-/-,Person 3/Intern/Office/X}
Then \docsvlist will determine the first item and pass it as a braced argument to \do, so the first cycle in the loop will perform
\do{Person 1/Developer/Online/X}
which would become
\expandafter\addtablerow Person 1/Developer/Online/X!
and the \expandafter is clearly useless.
In the second solution, the call is \myTable{\variable} and then the main bit is
\expandafter\docsvlist\expandafter{\variable}
but it's just a variation on the first one and the working is exactly the same.
Then user237299 purports that the \expandafter I'm referring to will be useful in case the call is \myTable{\variableTwo}, where there has been
\def\variableTwo{\variable}
Unfortunately, this is not true. Indeed, using the first solution (but using the second would be exactly the same), one has
\expandafter\myTable\expandafter{\variableTwo}
that becomes
\myTable{\variable}
which calls \docsvlist{\variable}. The argument has no comma, so a single cycle is performed and the call becomes
\expandafter\addtablerow\variable
Nothing useful, because we'd get
\addtablerow Person 1/Developer/Online/X,Person 2/Developer/-/-,Person 3/Intern/Office/X!
Of course, doing \def\variableTwo{\variable} is quite meaningless in this context. If one wants to alias \variable, maybe for augmenting it while having the previous list still available, one should do \let\variableTwo=\variable.
\expandaftercould make sense, which is when one stores a complete person inside a macro, something like\printlist{\personA,\personB,\personC}(but I'd use a\tl_count:nto only expand the first token when the input contains just a single token). – Skillmon Mar 16 '21 at 07:58