how to figure out the number of elements inside \defineconversion?

["Mojca Miklavec" <mojca.miklavec.lists@gmail.com>]

Hello,

I would like to \defineconversion and the use that set of symbols
inside a metapost graphic. But I need to know the number of symbols,
so that I can define enough "metapost images with symbols" in advance.
I realise that there might be a problem since conversion can sometimes
take an arbitrary number (using a command defined elsewhere), but if I
could have a reasonable guess for conversions defined explicitely,
that would already help a lot. (As a workaround and/or if there is no
easy method to figure that out I can still hardcode "25" and wait
until someone complains that that is not enough to satisfy his/her
needs.)

Thanks a lot,
    Mojca


\startMPextensions
  numeric variant; variant = 1;
  vardef gp_the_symbol(expr n) =
    picture pict;
    % using metapost
    if variant=1:
      pict := image( fill fullcircle scaled 4pt; ); % TODO
    % using TeX, variant = 2
    else: % TODO: limit the number first
      pict := sometxt(n);
    fi;
    pict shifted -center pict
  enddef ;

  def gp_point(expr x, y, n) =
    draw (gp_the_symbol(n) scaled 1 shifted (x,y));
  enddef ;
\stopMPextensions

\starttext

\defineconversion[abc][$\star$,$\bullet$,$\ast$]

\startTeXtexts
% TODO: 6 is only a guess: I need a better guess (3 in this case)
\dostepwiserecurse{1}{6}{1}{\TeXtext{\recurselevel}{{\convertnumber{abc}{\recurselevel}}}}
\stopTeXtexts

\startMPcode
  variant := 1;
  gp_point(1cm,0cm,1);
  gp_point(2cm,0cm,2);
  variant := 2;
  gp_point(1cm,1cm,1);
  gp_point(2cm,1cm,2);
  gp_point(3cm,1cm,3);
  gp_point(4cm,1cm,4);
  gp_point(5cm,1cm,8);
\stopMPcode

\stoptext