Coding system to encode arguments to groff?

[Tim Landscheidt <tim@tim-landscheidt.de>]

Hi,

I pass text arguments from Emacs Lisp to a groff command
with the "-d" option.  For ASCII strings, this is trivial;
for strings with umlauts, I need to use:

| (encode-coding-string variable-to-pass 'iso-latin-1)

For strings with other Unicode characters like "–" (#x2013),
I need to call groff's preconv like:

| (shell-command-to-string (concat "preconv -r <(echo " (shell-quote-argument variable-to-pass) ")"))

which for "ä–ö" returns something like:

| \[u00E4]\[u2013]\[u00F6]

Now in Emacs, this looks very much like what a coding system
would do.  The info documentation for elisp just laconically
says:

|    How to define a coding system is an arcane matter, and is not
| documented here.

Has someone implemented such a coding system for groff so
that something like:

| (encode-coding-string variable-to-pass 'x-groff)

would do what is needed?

TIA,
Tim