そういえば、次の `to_s': method `to_s' overridden (TypeError) というの
はなぜ起こるんでしょうか?

% ruby -e '
a = "a"
class << a; self; end.class_eval {
define_method(:to_s, a.method(:to_s))
}
a.to_s'
-e:6:in `to_s': method `to_s' overridden (TypeError)
        from -e:6
-- 
[田中 哲][たなか あきら][Tanaka Akira]