anchor.diff:  	 list_head/1, list_length/1, list_prefix/1,
   	 list_suffix/1, list_tail/1, macro/1, macro/2,
   	 macro_arguments/1, macro_name/1, make_tree/2,
  -	 match_expr/2, match_expr_body/1, match_expr_pattern/1,
  +         map_expr/1,
  +         map_expr/2,
  +         map_expr_argument/1,
  +         map_expr_fields/1,
  +         map_field_assoc/2,
  +         map_field_assoc_name/1,
  +         map_field_assoc_value/1,
  +         map_field_exact/2,
  +         map_field_exact_name/1,
  +         map_field_exact_value/1,
  +         match_expr/2, match_expr_body/1, match_expr_pattern/1,
   	 meta/1, module_qualifier/2, module_qualifier_argument/1,
   	 module_qualifier_body/1,
            named_fun_expr/2,
   	 named_fun_expr_arity/1,
   	 named_fun_expr_clauses/1,
   	 named_fun_expr_name/1,
  -         map_elements/1,
  -         map_field_elements/1,
            nil/0, normalize_list/1,
   	 operator/1, operator_literal/1, operator_name/1,
   	 parentheses/1, parentheses_body/1,
  
positive.code:     io_lib:write_atom(atom_value(Node)).
  
  %% =====================================================================
  map_elements(Node) ->
      case unwrap(Node) of
  	{map, _, List} ->
  	    List;
  	Node1 ->
              data(Node1)
      end.
  
  map_field_elements(Node) ->
      case unwrap(Node) of 
          {map_field_assoc, _, K, V} ->
              [K,V];
          {map_field_exact, _, K, V} ->
              [K, V];
          Node1 ->
              data(Node1)
      end.
  
  map(List) ->
      tree(map, List).
  
  map_field_assoc(List) ->
      tree(map_field_assoc, List).
  
  map_field_exact(List) ->
      tree(map_field_exact, List).
  
  %% =====================================================================
  %% @spec tuple(Elements::[syntaxTree()]) -> syntaxTree()
  
negative.code:       {match, _, _, _} -> match_expr;
        {op, _, _, _, _} -> infix_expr;
        {op, _, _, _} -> prefix_expr;
        {map,_,_} -> map_expr;
        {map, _, _, _} -> map_expr;
        {map_field_assoc,_,_,_} -> map_field_assoc;
        {map_field_exact,_,_,_} -> map_field_exact;
        {'query', _, _} -> query_expr;
  