Macro with local variables expanding over several tab-points

Question

I finally developed from egreg's answer in my previous question ( Defining a macro with three optional arguments in the form \newmacro{a}{b}[c]{d}[e][f] and \newmacro{a}{b}[c]{d}*[f] ) While my original answer was about making a shorter code, I ended up with a ~190 lines package. For the curious you can check it here in github, and it is also documented here.

The macro works fine, except for a display mode I would like to achieve: I want the macro to work inside tabular environments such as array or align: that would allow to typeset several function definitions preserving some alignment.

However I found a problem.

Let's took a look of the following code:

\documentclass{article}
\def\tempi{0}
\def\tempii{1}
\newcommand\mymacro[1]{
  \let\tempiii\tempi
  \def\tempi{#1\tempiii}
  \def\tempii{#1}
  \mymacroi
}
\newcommand\mymacroi{\tempi & \tempii}
\begin{document}
\[
  \begin{array}{cccc}
    a & \mymacro{1} & b \\
    \mymacro{2} & \mymacro{3}
  \end{array}
\]
\end{document}

It gets this result:

Changing the definition of \mymacroi

\newcommand\mymacroi{\tempi , \tempii}

The new result is:

In the first code, the changes in \tempii are not preserved after the tab character &. The second one shows the modification of \tempii (but does not align).

Using \begingroup in \mymacro:

\newcommand\mymacro[1]{
  \begingroup
  \let\tempiii\tempi
  \def\tempi{#1\tempiii}
  \def\tempii{#1}
  \mymacroi
  \endgroup
}

And, with the original \mymacroi (the one with &) I get an error.

So the problem is indeed trying to use & from the macro, while preserving changes local to my macro, while expanding these changes over several cells.

---

(In this MWE there is a circular reference which does not exist in my original macro.)

---

Update:
My original example was too simple to show some desired result, and given that my macro should work both inside tabular environment and non-tabular environments, I will mimic that in this MWE by redefining \mymacroi. I copy only the document environment.

\begin{document}
\[
  \begin{array}{cccccc}
    a & \mymacro{7} & b & \tempi & \tempii \\
    \mymacro{2} & \mymacro{3} & \tempi & \tempii 
  \end{array}
\]
\renewcommand\mymacroi{%
  \edef\tmp{\tempi,\tempii}%
  \tmp
}
\par Test 1 \(\mymacro{5};\tempi,\tempii\)
\par Test 2 \(\mymacro{4};\tempi,\tempii\)
\end{document}

The expected result is:

and

Answer 1

Each of the cells within the table forms a group. So, your use of

\mymacro{2}

expands to

\let\tempiii\tempi
\def\tempi{2\tempiii}
\def\tempii{2}
\mymacroi

which defines \tempi as 2\tempiii (which is equivalent to 2\tempi) and \tempii as 2. Then you call \mymacroi which expands to

\tempi & \tempii

Both \tempi and \tempii are defined, but the updated definition was done inside the (first) group/cell. As such, the second cell containing \tempii would revert back to the original definition (as done in the preamble as \def\tempii{1}). This happens with every use of \mymacro, and it seems like you wish to have your local re-definitions to span across these cells. To do that, use a global re-definition (or possibly an expanded global re-definition):

\documentclass{article}
\newcommand\tempi{0}
\newcommand\tempii{1}
\makeatletter
\newcommand{\storetemps}{%
  \global\let\store@tempi\tempi%
  \global\let\store@tempii\tempii}
\newcommand{\restoretemps}{%
  \global\let\tempi\store@tempi%
  \global\let\tempii\store@tempii}
\newcommand\mymacro[1]{
  \storetemps%
  \xdef\tempi{#1\tempi}%
  \xdef\tempii{#1}%
  \mymacroi%
}
\newcommand\mymacroi{%
  \ifnum\pdfstrcmp{\@currenvir}{array}=0
    \let\select@type\@firstoftwo%
  \else
    \let\select@type\@secondoftwo%
  \fi
  \select@type{\tempi & \tempii}{\tempi, \tempii}%
  \restoretemps%
}
\makeatother

\begin{document}
$
  \begin{array}{cccccc}
    a & \mymacro{7} & b & \tempi & \tempii \\
    \mymacro{2} & \mymacro{3} & \tempi & \tempii 
  \end{array}
$

Test 1 \(\mymacro{5};\tempi,\tempii\) \par
Test 2 \(\mymacro{4};\tempi,\tempii\)
\end{document}

The above version of \mymacroi conditions on whether you're in an array environment or not, allowing you to use it as-is inside one or not.

Answer 2

You appear to want to expand the macros in the current group but evaluate them in a different group, so separate expansion and typesetting with \edef (or if there are any user supplied LaTeX input, \protected@edef). Also you had several % missing from ends of lines.

\documentclass{article}
\def\tempi{0}
\def\tempii{1}
\newcommand\mymacro[1]{%
  \let\tempiii\tempi
  \def\tempi{#1\tempiii}%
  \def\tempii{#1}%
  \mymacroi
}
\newcommand\mymacroi{%
\edef\tmp{\tempi&\tempii}%
\tmp}

\begin{document}
\[
  \begin{array}{cccc}
    a & \mymacro{1} & b \\
    \mymacro{2} & \mymacro{3}
  \end{array}
\]
\end{document}