TO-DOs:

These are features that have been requested, and have been considered,
but are not yet implemented, because I'm undecided about how they
should be implemented, and/or because they are difficult to implement.


* Add a += operator, so that additional elements can be appended to a list or
  array. The issue with this is defining a consistent syntax. For example:

  x = ( 1, 2, 3 );
  x += ( 4, 5 );

  Should this result in ( 1, 2, 3, 4, 5 ), or ( 1, 2, 3, ( 4, 5 ))? I believe
  it should be the latter. However, only the former makes sense for arrays.


* Add limited support for preserving comments?


* Add support for unicode strings? A bit problematic, since flex doesn't
  support unicode input, AFAICT. But maybe supply convenience functions to
  convert between parsed UTF-8 strings and std::wstring.
