anchor.diff:          , to_list/1
           , to_term/1
           , to_binterm/1
  +        , to_timestamp/1
  +        , to_datetime/1
           , to_name/1
           , to_text/1
           ]).
  
positive.code:             , add_dt, add_ts, diff_dt, diff_ts
              , to_atom, to_string, to_binstr, to_integer, to_float, to_number
              , to_tuple, to_list, to_term, to_binterm, from_binterm
              , to_decimal, from_decimal
              , byte_size, bit_size, nth, sort, usort, reverse, last
              , remap
              ]).
  
negative.code:     unary_fun({Op, A});
  expr_fun({Op, A}) when Op=='to_atom';Op=='to_tuple';Op=='to_list';Op=='to_term';Op=='to_name';Op=='to_text';Op=='is_nav' ->
      unary_fun({Op, A});
  expr_fun({Op, A}) when Op=='to_datetime';Op=='to_timestamp' ->
      unary_fun({Op, A});
  expr_fun({Op, A}) ->
      ?UnimplementedException({"Unsupported expression operator", {Op, A}});
  %% Binary custom filters
  