LaTeX list processing example

mxmtest.tex

\documentclass{standalone}
\usepackage{xparse}
\usepackage{ifthen}

\newcommand\SepCount{0}
\newcommand\s{\renewcommand\SepCount{0}}
\NewDocumentCommand\ApplySep{m}{\ifthenelse{\SepCount=1}{&}{}#1\renewcommand\SepCount{1}}
\NewDocumentCommand\x
{
    s
    >{\SplitList{,}}o
    >{\SplitList{,}}o
    >{\SplitList{,}}o
    >{\SplitList{,}}o
    >{\SplitList{,}}o
    >{\SplitList{,}}o
    >{\SplitList{,}}o
    >{\SplitList{,}}o
}{
    \expandafter\begin{\IfBooleanTF{#1}{pmatrix}{bmatrix}}
         \IfValueT{#2}{\s\ProcessList{#2}{\ApplySep}}
         \IfValueT{#3}{\\\s\ProcessList{#3}{\ApplySep}}
         \IfValueT{#4}{\\\s\ProcessList{#4}{\ApplySep}}
         \IfValueT{#5}{\\\s\ProcessList{#5}{\ApplySep}}
         \IfValueT{#6}{\\\s\ProcessList{#6}{\ApplySep}}
         \IfValueT{#7}{\\\s\ProcessList{#7}{\ApplySep}}
         \IfValueT{#8}{\\\s\ProcessList{#8}{\ApplySep}}
         \IfValueT{#9}{\\\s\ProcessList{#9}{\ApplySep}}
    \expandafter\end{\IfBooleanTF{#1}{pmatrix}{bmatrix}}
}


% This is how far I had gotten working on it myself. It does not work for even the first element of the list.
%\newcommand\MCount{0}
%\NewDocumentCommand\ProcessSingle{m}{\ifthenelse{\MCount=0}{#1}{}\renewcommand\MCount{1}}
%\NewDocumentCommand\mxm
%{
%    s
%    >{\SplitList{*}}o
%    >{\SplitList{*}}o
%    >{\SplitList{*}}o
%    >{\SplitList{*}}o
%    >{\SplitList{*}}o
%    >{\SplitList{*}}o
%    >{\SplitList{*}}o
%    >{\SplitList{*}}o
%}{
%    %\message{Two: #2}
%    %\message{Res: \ProcessList{#2}{\ProcessSingle}\renewcommand\MCount{0}}
%    \expandafter\csname\IfBooleanTF{#1}{x}{x*}\endcsname
%        \IfValueT{#2}{\ProcessList{#2}{\ProcessSingle}\renewcommand\MCount{0}}
%        \IfValueT{#3}{\ProcessList{#3}{\ProcessSingle}\renewcommand\MCount{0}}
%        \IfValueT{#4}{\ProcessList{#4}{\ProcessSingle}\renewcommand\MCount{0}}
%        \IfValueT{#5}{\ProcessList{#5}{\ProcessSingle}\renewcommand\MCount{0}}
%        \IfValueT{#6}{\ProcessList{#6}{\ProcessSingle}\renewcommand\MCount{0}}
%        \IfValueT{#7}{\ProcessList{#7}{\ProcessSingle}\renewcommand\MCount{0}}
%        \IfValueT{#8}{\ProcessList{#8}{\ProcessSingle}\renewcommand\MCount{0}}
%        \IfValueT{#9}{\ProcessList{#9}{\ProcessSingle}\renewcommand\MCount{0}}
%}

\begin{document}
$$\x[3,2]
    [1,1]
  \x[-3, 0]
    [ 0,-2]
  \x[ 1,-2]
    [-1, 3]$$
$$\mxm[ [3,2]*[-3, 0]*[ 1,-2] ]
      [ [1,1]*[ 0,-2]*[-1, 3] ]$$