PROGRAM find_all_lower_case_characters;

CONST string_size = 30;

TYPE low_set = SET OF 'a'..'z';

VAR data_set    : low_set;
    storage     : STRING[string_size];
    index       : 1..string_size;
    print_group : STRING[26];

BEGIN  (* main program *)
data_set := [];
print_group := '';
storage := 'This is a SET test.';

  FOR index := 1 TO length(storage) DO
  BEGIN
    IF storage[index] IN ['a'..'z'] THEN
    BEGIN
      IF storage[index] IN data_set THEN
        WRITELN(index:4,'   ',storage[index],
                     ' is already in the set')
      ELSE
      BEGIN
        data_set := data_set + [storage[index]];
        print_group := print_group + storage[index];
        WRITELN(index:4,'   ',storage[index],
                     ' added to group, complete group = ',
                     print_group);
      END;
    END
    ELSE
      WRITELN(index:4,'   ',storage[index],
                    ' is not a lower case letter');
  END;
END.  (* of main program *)