\def\lst{{\multiply \cals@borderwidthL by 3\relax}{}{}}
\llt@desnoc{\lst}
\show\lst
\show\llt@car
\def\lst{{item1}{item2}{item3}}
\llt@desnoc{\lst}
\show\lst
\show\llt@car

\def\aaa{aaa}
\def\bbb{bbb}
\def\ccc{ccc}
\def\lst{}         % empty list
\show\lst
\llt@cons\bbb\lst  % \lst -> "{bbb}"
\show\lst
\llt@snoc\lst\ccc  % \lst -> "{bbb}{ccc}"
\show\lst
\llt@cons\aaa\lst  % \lst -> "{aaa}{bbb}{ccc}"
\show\lst
\llt@decons\lst    % \llt@car -> "aaa", \lst -> "{bbb}{ccc}"
\show\llt@car
\show\lst
\llt@rot\lst       % \llt@car -> "bbb", \lst -> "{ccc}{bbb}"
\show\llt@car
\show\lst