function r = isnum(a)
  if ( isnumeric(a) )
    r = 1;
  else
    r = ~isnan(str2double(a));
  endif
endfunction

% tests
disp(isnum(123))      % 1
disp(isnum("123"))    % 1
disp(isnum("foo123")) % 0
disp(isnum("123bar")) % 0
disp(isnum("3.1415")) % 1