triple-ref-trick.a68
1 COMMENT
2
3 @section Synopsis
4
5 The "Algol 68 triple-REF trick" implementation of quicksort.
6
7 Identifier "place" in procedure "insert" has mode REF REF REF NODE.
8 This is one of the few practical examples of using a pointer to a
9 pointer to a pointer.
10
11 COMMENT
12
13 MODE NODE = STRUCT (REAL v, REF NODE less, more);
14 REF NODE end = NIL;
15 REF NODE root := end;
16
17 PROC insert = (REAL v) VOID:
18 BEGIN REF REF NODE place := root;
19 WHILE place ISNT end
20 DO place := (v < v OF place | less OF place | more OF place)
21 OD;
22 REF REF NODE (place) := HEAP NODE := (v, end, end)
23 END;
24
25 PROC print tree = (REF NODE n) VOID:
26 IF n ISNT NIL
27 THEN print tree (less OF n);
28 print ((new line, fixed (v OF n, 10, 4)));
29 print tree (more OF n)
30 FI;
31
32 TO 10
33 DO insert (next random)
34 OD;
35
36 print tree (root)
