function retval = list_functions (directory)
  if (nargin == 0)
    retval = {};
    p = path ();
    idx = find (p == pathsep ());
    prev_idx = 1;
    for n = 1:length (idx)
      f = p (prev_idx:idx (n)-1);
      tmp = list_functions_in_dir (f);
      retval(end+1:end+length(tmp)) = tmp;
      prev_idx = idx (n) + 1;
    endfor
  else
    retval = list_functions_in_dir (directory);
  endif
endfunction

function retval = list_functions_in_dir (directory)
  retval = {};
  extensions = {"m", "oct", "mex"};
  for n = 1:length (extensions)
    f = fullfile (directory, ["*.", extensions{n}]);
    tmp = dir(f);
    retval(end+1:end+length(tmp)) = {tmp.name};
  endfor
  for n = 1:length (retval)
    [dir, name, ext] = fileparts (retval{n});
    retval{n} = struct ("dir", directory, "name", name, "ext", ext);
  endfor
endfunction