How to detect a tab character when processing a literate in lstlistings?

Question

In the solution to Making more easy the itemized of item with tabulation system, I am counting up the number of spaces in order to determine the type of leading character to insert. However, if the I replace the leading spaces with a tab character, the solution does not work.

If I could detect the tab character in the literate, then I could have \ProcessSpace increment the counter NumOfContigousSpaces appropriately, but I don't know how to test for it?

I thought adding tabsize=4, keepspaces=true would do the job but this is not quite enough. So I attempted to use lstag@tabulator from How to automatically skip leading white spaces in listings, but was not able to get that to work.

The code below has a 4 leading spaces before the W in the first line and a tab as the leading character before the W in the second line. This produces no bullet for the line with a tab:

The correct output can be seen by using 4 spaces before the W in both lines:

Note:

• It appears the posting a code snippet here replaces a tab with 4 spaces. So to use the MWE below you will need to replace the four leading spaces before the Wxxx with a tab character.

Code:

\documentclass{article}
\usepackage{pgf}
\usepackage{xstring}
\usepackage{listings}
\newcounter{NumOfContigousSpaces}%
\setcounter{NumOfContigousSpaces}{0}%
\newcommand{\Width}{1}%
\newcommand{\AddApproriateBulletIfFirstChar}[1]{%
    \pgfmathtruncatemacro{\BulletType}{\arabic{NumOfContigousSpaces}/4}%
    \IfEqCase{\BulletType}{%
        {0}{\gdef\Width{1}}
        {1}{\gdef\Width{3}$\bullet$ }
        {2}{\gdef\Width{3}$\circ$ }
        {3}{\gdef\Width{3}$\times$ }
        {4}{\gdef\Width{3}$\star$ }
        {5}{\gdef\Width{3}$-$ }
    }[\gdef\Width{3}$\bullet$ ]%
    #1%
    \setcounter{NumOfContigousSpaces}{0}%
}%
\newcommand{\ProcessSpace}{%
    \addtocounter{NumOfContigousSpaces}{1}%
    \space%
}%
\newcommand*{\ProcessTab}{%
    \addtocounter{NumOfContigousSpaces}{4}%
    \space\space\space\space%
}%
\makeatletter
\lstdefinestyle{MyItemize}{%
    basicstyle=\ttfamily,
    columns=flexible,
    tabsize=4, keepspaces=true,
     literate=%
        {\ }{{{\ProcessSpace}}}1% Count contigous spaces
        {lstag@tabulator}{{{\ProcessTab}}}4% ??? how detect a tab?
        %
        %--- much code removed here (See https://tex.stackexchange.com/questions/57939/making-more-easy-the-itemized-of-item-with-tabulation-system for full code)
        {W}{{{\AddApproriateBulletIfFirstChar{W}}}}\Width
        {x}{{{\AddApproriateBulletIfFirstChar{x}}}}\Width
}%
\makeatother
\begin{document}
\begin{lstlisting}[style=MyItemize]
    Wxxx xxx
    Wxxx xx xx
\end{lstlisting}
\end{document}

Answer 1

Using \^^I is the 'safe' way to type in a tab, and will let listings do the conversion.

Replacing the line using lstag@tabulator with the following:

    {\^^I}{{{\ProcessTab}}}4%

produces:

(There seems to be something up with the width of characters used when columns = flexible is set, as the space used for the 'tab' bullet is different from that for the 'four space' bullet.)

Answer 2

you can try something like:

\lstset{
  ...
  tab=$\bullet$\space,
    
  showtabs=true,
    
  ...
}