1   with TEXT_IO ; use TEXT_IO ;
    2   procedure MAIN is  --       A SMALL SAMPLE TO INTRODUCE  ACCESS  TYPES
    3
    4     type NODE ; -- just introduce type name
    5     type NODE_PTR is access NODE ; -- define an access type
    6                                    -- ie the type of a pointer
    7     type NODE is  -- now, really define the type NODE
    8       record
    9         BF    : INTEGER      ; -- balance factor for later use
   10         LEFT  : NODE_PTR     ; -- this records predecessor
   11         RIGHT : NODE_PTR     ; -- this records sucessor
   12         NAME  : STRING(1..2) ; -- data, the "sort" key
   13         PHONE : STRING(1..2) ; -- more tag along data
   14       end record ;
   15
   16     ROOT_PTR   : NODE_PTR := new NODE'(0, null, null, "D ", "4 ") ;
   17                  -- build a dummy root node using qualified aggregate
   18     LEFT_PTR   : NODE_PTR ;  -- just some scratch objects
   19     RIGHT_PTR  : NODE_PTR ;
   20
   22     procedure OUTPUT(T : NODE_PTR ) is -- recursive procedure to walk tree
   23     begin
   24       if T /= null then
   25         OUTPUT(T.LEFT) ;                    -- recursive, down left
   26         PUT(T.NAME) ; PUT_LINE(T.PHONE) ;
   27         OUTPUT(T.RIGHT) ;                   -- recursive, down right
   28       end if ;
   29     end OUTPUT ;
   30
   31   begin
   32     PUT_LINE(" basic access types ") ;
   33     -- build a tree manually for testing
   34     --
   35     --                         D 4
   36     --                        /   \
   37     --                    B 2        F 6          first tier
   38     --                   /   \      /   \
   39     --                 A 1   C 3   E 5  G 7       second tier
   40     --
   41       -- first tier
   42       LEFT_PTR        := new NODE'(0, null, null, "B ", "2 ") ;
   43       ROOT_PTR.LEFT   := LEFT_PTR ;
   44       RIGHT_PTR       := new NODE'(0, null, null, "F ", "6 ") ;
   45       ROOT_PTR.RIGHT  := RIGHT_PTR ;
   46         -- second tier
   47         LEFT_PTR.LEFT   := new NODE'(0, null, null, "A ", "1 ") ;
   48         LEFT_PTR.RIGHT  := new NODE'(0, null, null, "C ", "3 ") ;
   49         RIGHT_PTR.LEFT  := new NODE'(0, null, null, "E ", "5 ") ;
   50         RIGHT_PTR.RIGHT := new NODE'(0, null, null, "G ", "7 ") ;
   52     OUTPUT(ROOT_PTR) ; -- print the tree
   54   end MAIN ;
 basic access types 
 A 1   B 2   C 3   D 4   E 5   F 6   G 7 <-- printed down page