anchor.diff:          end
       catch
           _:R -> {error, {R, erlang:get_stacktrace()}}
  -    end.
  +    end;
  +boxed_from_pt(ParseTree) ->
  +    {error, {not_implemented_for, ParseTree}}.
  +
   
   %% Operator Binding Power -------------------------------
   
  
positive.code: 
  indent(Ind) -> lists:duplicate(Ind*2,32).
  
  boxed_from_pt(ParseTree) ->
      try
          case foldb(ParseTree) of
              {error, _} = Error -> Error;
  
negative.code:     end.
  
  -spec pretty_from_pt(term()) -> binary() | {error, binary()}.
  pretty_from_pt(#box{name=N} = ParseTree) when N=='select';N=='union';N=='union all' ->
      case foldb(ParseTree) of
          {error, Reason} -> {error, Reason};
          SqlBox -> pretty_from_box(SqlBox)
      end;
  pretty_from_pt(ParseTree) ->
      {error, {not_implemented_for, ParseTree}}.
  
  -spec pretty_from_box([#box{}] | #box{}) -> binary().
  pretty_from_box([]) -> [];
  