Given string 'a.bc.' -- each dot(.) is to be replaced with 0 or 1

How can i write this function simply?   (in Scheme (Gauche))
-- Given a string  'a.bc.' -- each dot(.) is to be replaced with 0 or 1.
        -- So the value is a list of 4 strings:
                                ['a0bc0',  'a0bc1',  'a1bc0',  'a1bc1']
-- The order is not important.
             If the string has 3 dots, the value is a list of length 8.
If the program is going to be simpler,
                        pls use, say,   (a $ b c $)  rather than  'a.bc.'