repeating

Hello again,

I'm hoping again that someone can help me. I'd like to repeat
indefinately until the user types in 'stop' in the following way:

start :- repeat,
         write('w00t: '),
         read_line(Input),
         (Input=[stop,'.'],stop;
          write('I\'m terribly sorry. I don\'t understand the meaning
of that sentence'),nl).

unfortunately it won't work correctly for some reason. am I using
repeat incorrectly? i got the read_line/1 from
http://www.csupomona.edu/~jrfisher/www/prolog_tutorial/read_linepl.txt

I appreciate the help!

CB