Two small questions surrounding iteration of commands

Question

Two small questions here:

• Why is Subentry3 not in \scriptsize?
• How to arrange ... Mainentry1 so that it will only appear at the end of the last Subentry (however many pairs that may be), instead of at the end of the first pair (i.e. at the end of Subentry2)?

MWE

% !TEX TS-program = lualatexmk

\documentclass{scrreprt}

%%%%%%%%%%%%%%%%%%%%%%
%
%
%
\newenvironment {mainentry} {\mainentryA}{}
\def\mainentryA#1#2#3{%
   \def\subentry##1##2{%
\scriptsize ##1 \space \Huge ##2 ... #1
   }%
#1 #2 #3
}
%
%
%
\def\subentry{\def\subentryS{\def\subentryS{\endgraf}}\futurelet\next\subentryA}
\def\subentryA{\ifx\bgroup\next\expandafter\subentryB\fi}
\def\subentryB#1#2{\subentryS\subentry{#1}{#2}\futurelet\next\subentryA}
%
%
%
%%%%%%%%%%%%%%%%%%%%%%

\begin{document}

\begin{mainentry}{
Mainentry1
}{
Mainentry2
}{
Mainentry3
}

\subentry{
Subentry1
}{
Subentry2
}{
Subentry3
}{
Subentry4
}

\end{mainentry}

\end{document}

Answer 1

\subentry{ Subentry1 }{ Subentry2 }{ Subentry3 }{ Subentry4 }

is

\scriptsize Subentry1 \space \Huge Subentry2 ... mainentry1 (Subentry3}{Subentry4}

so just the first is in \scriptsize and all the later ones are in Huge, the title asks about iteration but there is no iteration here, \subentry is only called once.

You can save mainentry1 in the begin code of the environment and use it at the end

\def\savedmain{#1}

in the begin code and use \savedmainin the end code after your subentries. Or (as in earlier questions) you could use the expl3 environment declarations that let you use #1 directly in the end code.

i think you are looking for something like this, but I would bnever use such a definition in a docuemnt. Iterating over a {] list is completely against latex syntax, where {} denotes a mandatory argument and here where you are actually using pairs it just obscures the document.

I would use simple non-iterative definitions and a syntax like

\begin{mainentry}{aa}{bb}{cc}

 \subentry{s1}{sss1}
 \subentry{s2}{sss2}
 \subentry{s3}{sss3}

\end{mainentry}

Then the code, and the document would be a lot clearer.

However:

\documentclass{scrreprt}

%%%%%%%%%%%%%%%%%%%%%%
%
%
%
\newenvironment{mainentry}[3]{#1 #2 #3\def\mainentrya{#1}\par}{\mainentrya}
%
\long\def\subentry#1#2{%
\ifx\par#1%
\endgraf\expandafter\end\else
{\scriptsize#1} {\huge#2}\expandafter\subentry
\fi}


%
%
%
%%%%%%%%%%%%%%%%%%%%%%

\begin{document}

\begin{mainentry}{
Mainentry1
}{
Mainentry2
}{
Mainentry3
}

\subentry{
Subentry1
}{
Subentry2
}{
Subentry3
}{
Subentry4
}

\end{mainentry}

\end{document}

Answer 2

One your comment of another answer here implies that you need, maybe, to add some data which is declared at the very start of LaTeX environment to the each end of \subentry usage. It means, that

\begin{mainentry}{AAA}{B}{}
\Subentry{C}{D}{E}{F}
\Subentry{U}{V}{W}{X}{Y}{Z}
\end{mainentry}

would print something like this:

AAA B
(sub C, sub D) (sub E, sub F) (end: AAA)
(sub U, sub V) (sub W, sub X) (sub Y, sub Z) (end: AAA)

But I am not sure that this is exactly your intend because you are generating many questions of this topic at this site but none of them exactly explains your intend.

You can try to experiment with this code:

\documentclass[a4paper]{scrreprt}

\newenvironment {mainentry} {\mainentryA}{}
\def\mainentryA#1#2#3{%
   \def\SubentryE{\endgraf At the end of subentry collection is again (#1).}%
   \def\SubentryC##1##2{%
      Here is external paremater (#1) and second external (#2).
      And internal parameter is (##1) and second internal (##2).
   }
}
\def\Subentry{\def\SubentryS{\def\SubentryS{\endgraf}}\futurelet\next\SubentryA}
\def\SubentryA{\ifx\bgroup\next\expandafter\SubentryB\else\SubentryE\fi}
\def\SubentryB#1#2{\SubentryS\SubentryC{#1}{#2}\futurelet\next\SubentryA}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\begin{document}
\begin{mainentry}{A}{B}{}
\Subentry{C}{D}{E}{F}
NEXT
\Subentry{U}{V}{W}{X}{Y}{Z}
\end{mainentry}
Some text.
\end{document}