How to control expansion order to define variables from a prefix and a command?

Question

The following is a command that does basic arithmetic with nine variables.

\documentclass{article}
\usepackage{xfp}
\newcommand\functesta[9]{
    \edef\myvara{#1}
    \edef\myvarb{#2}
    \edef\myvarc{#3}
    \edef\myvard{#4}
    \edef\myvare{#5}
    \edef\myvarf{#6}
    \edef\myvarg{#7}
    \edef\myvarh{#8}
    \edef\myvari{#9}
    $\inteval{\myvara + \myvarb - \myvarc + \myvard - \myvare + \myvarf - \myvarg + \myvarh - \myvari}$
}
\begin{document}
\functesta{1}{2}{3}{4}{5}{6}{7}{8}{100}
\end{document}

-94

I tried shrinking the nine lines of definition into one for loop but it didn't work. My intention was that as a loop iterates through 1 to 9, it would expand \alphalph{\iteration} first, which would be combined with \myvarx to become \myvarxa, \myvarxb, ..., \myvarxi. In the same way #\iteration would expand to #1 to #9. However I probably got the syntax wrong.

\documentclass{article}
\usepackage{xfp}
\usepackage{pgffor}
\usepackage{alphalph}
\newcommand\functestb[9]{
    \foreach \iteration in {1,...,9} {
        \edef\expandafter\myvarx\alphalph{\iteration}{#\iteration}
    }
    $\inteval{\myvarxa + \myvarxb - \myvarxc + \myvarxd - \myvarxe + \myvarxf - \myvarxg + \myvarxh - \myvarxi}$
}
\begin{document}
\functestb{1}{2}{3}{4}{5}{6}{7}{8}{100}
\end{document}

! Illegal parameter number in definition of \functestb.

Then I replaced #\iteration with a constant to see if I got the rest of the code right. Nope. What is the right way to achieve what I want? The reason I am not directly accessing #1 to #9 is because I will write a more complex command in which the nine numbers given need to be saved and changed multiple times. I am open to alternatives such as passing a list as a parameter or generating a list inside the command if it is possible to do so in LaTeX.

\documentclass{article}
\usepackage{xfp}
\usepackage{pgffor}
\usepackage{alphalph}
\newcommand\functestb[9]{
    \foreach \iteration in {1,...,9} {
        \edef\expandafter\myvarx\alphalph{\iteration}{17}
    }
    $\inteval{\myvarxa + \myvarxb - \myvarxc + \myvarxd - \myvarxe + \myvarxf - \myvarxg + \myvarxh - \myvarxi}$
}
\begin{document}
\functestb{1}{2}{3}{4}{5}{6}{7}{8}{100}
\end{document}

! Undefined control sequence.

use \csname primitive to concat strings to form a control token. See https://tex.stackexchange.com/questions/39380/what-exactly-do-csname-and-endcsname-do — LdBeth, Jul 30 '23 at 17:11

score 1 · Answer 1 · answered Jul 30 '23 at 18:51

This probably isn't how I would do this, but you could use \pgffor's facility to expand the list of arguments and just count them.

\documentclass{article}
\usepackage{xfp}
\usepackage{pgffor}
\usepackage{alphalph}
\newcommand\functesta[9]{%
  \edef\myvara{#1}%
  \edef\myvarb{#2}%
  \edef\myvarc{#3}%
  \edef\myvard{#4}%
  \edef\myvare{#5}%
  \edef\myvarf{#6}%
  \edef\myvarg{#7}%
  \edef\myvarh{#8}%
  \edef\myvari{#9}%
  $\inteval{\myvara + \myvarb - \myvarc + \myvard - \myvare + \myvarf - \myvarg + \myvarh - \myvari}$%
}
\newcommand\functestb[9]{%
  \foreach [count=\ino,expand list=true] \iteration in {#1,#2,#3,#4,#5,#6,#7,#8,#9} {% \xdef is needed as we want to use the definitions outside the loop
    \expandafter\xdef\csname myvarx\alphalph{\ino}\endcsname{\iteration}%
  }%
  $\inteval{\myvarxa + \myvarxb - \myvarxc + \myvarxd - \myvarxe + \myvarxf - \myvarxg + \myvarxh - \myvarxi}$%
}
\begin{document}
\functestb{1}{2}{3}{4}{5}{6}{7}{8}{100}
\functesta{1}{2}{3}{4}{5}{6}{7}{8}{100}
\end{document}

score 0 · Answer 2 · answered Jul 30 '23 at 19:46

I'm not sure you need to name variables.

\documentclass{article}
%\usepackage{xfp} % no longer needed
\usepackage{alphalph}
\ExplSyntaxOn
\NewDocumentCommand\functesta{mm}
 {
  \tl_set:Nn \l_tmpa_tl { #1 }
  \regex_replace_all:nnN
   { \cP#([0-9]+) } % find #<digits>
   { \c{seq_item:Nn} \c{l_tmpa_seq} \cB{\1\cE} } % replace with the seq item
   \l_tmpa_tl
  % make the sequence from the input
  \seq_set_from_clist:Nn \l_tmpa_seq { #2 }
  % evaluate
  $\int_eval:n { \tl_use:N \l_tmpa_tl }$
 }
\ExplSyntaxOff
\begin{document}
\functesta{#1+#2-#3+#4-#5+#6-#7+#8-#9}{1,2,3,4,5,6,7,8,100}
\functesta{(#1#2+#3#4)*#5}{1,2,3,4,5}
\functesta{#1+#2+#3+#4+#5+#6+#7+#8+#9+#10+#11}{1,2,3,4,5,6,7,8,9,10,11}
\end{document}

As you see, the function gets any definition you like and the values are given as a list.

The trick is to replace #<digits> with \seq_item:N \l_tmpa_tl { <digits> }, so we have a syntax similar, but not restricted to nine parameters, to a macro definition.

How to control expansion order to define variables from a prefix and a command?

2 Answers2