Coloring letters, or patterns, automatically

Question

I'm dealing with some data that I would like to apply a automatic formatter. I'm trying to use the listings package in order to define a "language" that fits in my model, but I'm not having success.

For example, I would like to format this:

3 HHHHHHHHHHHHHHLLLHH  21
        |||  |   |   
3 LLHHHHHHHHHHHHLLLLL  21

To something like this:

I.e., the letter H with a specific color, letter L with another color and so on. It would be pretty simple if there is spaces between the letters, since

\lstdefinelanguage{MyKindOfLanguage}
    {morekeywords={H,L,E},
    sensitive=true,
}

Would recognize H, L and E as keywords, but in my case there is not spaces between those characters. Maybe I'm using the wrong package to do this, so I'm asking if there is a way to do this. If I would use regex to specify the patters it would be better. I could write a program to translate this code to a formated one using \textcolor, but I would like to let the compiler do this for me.

Answer 1

\documentclass{article}
\usepackage{color}

{
\catcode`H\active
\catcode`L\active
\catcode`\ \active
\gdef\foo{%
\catcode`H\active
\catcode`L\active
\catcode`\ \active
\ttfamily\obeylines\obeyspaces
\def {\ }%
\defH{\textcolor{magenta}{\stringH}}%
\defL{\textcolor{yellow}{\stringL}}%
}%
}%
\def\endfoo{\par}
\begin{document}

\begin{foo}
3 HHHHHHHHHHHHHHLLLHH  21
        |||  |   |   
3 LLHHHHHHHHHHHHLLLLL  21
\end{foo}

\end{document}

Answer 2

Use listings's literate option to specify a search-and-replace for each of the letters you want to colour:

\documentclass{article}

\usepackage{listings,xcolor}
\lstnewenvironment{foo}[1][]
  {\lstset{
   basicstyle=\ttfamily,
   literate={H}{{{\color{red!20!blue}H}}}1
            {L}{{{\color{yellow!20!green}L}}}1,
   #1
   }}
  {}

\begin{document}

\begin{foo}
3 HHHHHHHHHHHHHHLLLHH  21
        |||  |   |   
3 LLHHHHHHHHHHHHLLLLL  21
\end{foo}

\end{document}

Answer 3

A bit complex, but with a much friendlier interface for defining the colors:

\documentclass{article}
\usepackage{xparse,l3regex,xcolor}
\usepackage{lipsum}

\ExplSyntaxOn
\NewDocumentCommand{\foo}{}
 {
  \begin{flushleft}\ttfamily
  % we need to make spaces active, so we let them to a skip
  % the change is local to the flushleft environment
  \char_set_active_eq:nN { `\  } \buzatto_foo_space:
  \char_set_catcode_active:n { `\  }
  \buzatto_foo_process:n
 }
\NewDocumentCommand{\definefoocolor}{mm}
 {
  % store in a property list: <letter> -> <color>
  \prop_gput:Nnn \g_buzatto_foo_prop { #1 } { #2 }
 }

\tl_new:N \l_buzatto_foo_arg_tl
\prop_new:N \g_buzatto_foo_prop

\cs_new_protected:Nn \buzatto_foo_space:
 {
  \hspace*{.5em}
 }
\cs_new_protected:Nn \buzatto_foo_process:n
 {
  \tl_set:Nn \l_buzatto_foo_arg_tl { #1 }
  % process all the keys in the property list
  \prop_map_inline:Nn \g_buzatto_foo_prop
   {
    % any run of the current letter is changed into
    % \textcolor{<color>}{<run of letters>}
    \regex_replace_all:nnN
     { (##1+) }
     { \c{textcolor}\cB\{##2\cE\}\cB\{\1\cE\} }
     \l_buzatto_foo_arg_tl
   }
  % use the returned token list
  \tl_use:N \l_buzatto_foo_arg_tl
  \end{flushleft}
 }
\ExplSyntaxOff

\definefoocolor{H}{red!20!blue}
\definefoocolor{L}{yellow!20!green}

\begin{document}

\lipsum[2]

\foo{
3 HHHHHHHHHHHHHHLLLHH  21 \\
        |||  |   |        \\
3 LLHHHHHHHHHHHHLLLLL  21
}

\lipsum[3]

\end{document}