lang/m2/test/queens.mod

   1 MODULE queen;
   2 FROM InOut IMPORT WriteString, WriteLn;
   3         TYPE row = ARRAY[1..8] OF INTEGER;
   4         VAR  maxpos: INTEGER;
   5              d: row;
   6         PROCEDURE free(i,j: INTEGER): BOOLEAN;
   7                 VAR k: INTEGER;
   8         BEGIN
   9                 FOR k := 1 TO i-1 DO
  10                         IF (d[k]=j) OR (j-d[k]=i-k) OR (d[k]-j=i-k) THEN
  11                                 RETURN FALSE;
  12                         END;
  13                 END;
  14                 RETURN TRUE;
  15         END free;
  16
  17         PROCEDURE print;
  18                 VAR i,j: INTEGER;
  19         BEGIN
  20                 FOR j := maxpos TO 1 BY -1 DO
  21                         FOR i := 1 TO maxpos DO
  22                                 IF d[i] = j THEN
  23                                         WriteString("D ");
  24                                 ELSE
  25                                         WriteString(". ");
  26                                 END;
  27                         END;
  28                         WriteLn;
  29                 END;
  30                 WriteLn;
  31         END print;
  32
  33         PROCEDURE queen(k: INTEGER);
  34                 VAR i: INTEGER;
  35         BEGIN
  36                 IF k = maxpos THEN
  37                         FOR i := 1 TO maxpos DO
  38                                 IF free(k,i) THEN
  39                                         d[k] := i;
  40                                         print();
  41                                 END;
  42                         END;
  43                 ELSE
  44                         FOR i := 1 TO maxpos DO
  45                                 IF free(k,i) THEN
  46                                         d[k] := i;
  47                                         queen(k+1);
  48                                 END;
  49                         END;
  50                 END;
  51         END queen;
  52 BEGIN
  53         maxpos := 8;
  54         queen(1);
  55 END queen.