detokenize only active character

Question

Few year ago, I asked a question about the best way to make active character inactive, in order to solve an issue with reledmac.

inputenc, active catcode and \csnsame

The answer was to use \detokenize macro of etex.

But this macro also make controlsequence character catcode to 12. It direct use create some bug in some specific case in reledmac (too complex here to explaine why).

What I would like is to transform the already read character with catcode 13 to character with catcode 12, but be able to read \ and so one, because I need them in a \edef definition.

Here a MWE

\documentclass{article}
\usepackage[polutonikogreek]{babel}
\usepackage[utf8]{inputenc}

\begin{document}
\def\emph#1{#1}

\expandafter\def\csname a\endcsname{toto}

%\edef\one{a \emph{ω a}}%That can't work

\edef\two{\detokenize{a \emph{ᾧ a}}}

\show\two%->a \emph {ᾧ a}
% What I would like is to set definition of two to
% a ᾧ a
% While ᾧ inactive character
\end{document}

Answer 1

With a current latex you could use \protected@edef:

\documentclass{article}
\usepackage[polutonikogreek]{babel}
\usepackage[utf8]{inputenc}

\begin{document}
\def\emph#1{#1}

\makeatletter
\protected@edef\two{a \emph{ᾧ a} \textbf{a}}
\show\two%

\end{document}

This gives:

> \two=macro:
->a ᾧ a \protect \textbf  {a}.

Answer 2

First things first, \detokenize is an e-TeX primitive, not a macro. :-)

What about this?

\documentclass{article}
\usepackage[polutonikogreek]{babel}
\usepackage[utf8]{inputenc}
\usepackage{xparse}

\ExplSyntaxOn

\tl_new:N \g__maieul_tmp_tl
\cs_generate_variant:Nn \tl_to_str:n { e }

\NewDocumentCommand \myConversionFunc { m m }
  {
    \group_begin:
      \clist_map_inline:nn { \emph, \textbf } % you can add more, of course
        { \cs_set_eq:NN ##1 \use:n }

      \tl_gset:Nx \g__maieul_tmp_tl { \tl_to_str:e { \text_expand:n {#2} } }
    \group_end:
    \tl_set_eq:NN #1 \g__maieul_tmp_tl
  }

\ExplSyntaxOff

\begin{document}

\myConversionFunc{\result}{a \emph{ᾧ a}}
\show\result

\myConversionFunc{\result}{a ᾧ \textbf{éêè }\emph{ᾧ a} Û}
\show\result

\end{document}

Terminal output:

> \result=macro:
->a ᾧ a.
l.27 \show\result

> \result=macro:
->a ᾧ éêè ᾧ a Û.
l.30 \show\result

If this is not what you want, please explain what you meant with “but be able to read \ and so on, because I need them in a \edef definition.”

Note: \text_expand:n is a recent addition to expl3, as far as I know.