On Tue, Nov 11, 2008 at 9:06 AM, Frank Mittelbach wrote:

> depends on how efficient you want to make it ...

Or how much you want it expanded.

> \def_new:Npn \tlp_reverse:N #1 {
>  \tlp_set:Nx #1
>    {\tlist_reverse:o{#1}}
> }
>
> \def_new:Npn \tlist_reverse:o { \exp_args:No \tlist_reverse:n }

\def_new:Npn \tlp_reverse:N #1 {
   \tlp_set:Nf #1
   {\tlist_reverse:o{#1\exp_stop_f:}}
}

This reverses the list, leaving \exp_stop_f: in front, which in turn
is removed by the f expansion which comes to a halt.
-- 
Morten