There is no example in official Arc. If we're talking hypothetically, here's one way to make sense of it:
arc> (= x '(2))
(2)
arc> (= (~car x) t)
t
arc> (~car x)
t
arc> x
(nil)
arc> (= (~x 0) nil)
nil
arc> (~x 0)
nil
arc> x
(t)
Since (~foo ...) only ever returns nil or t, this kind of place can't faithfully store other values:
arc> (= (~x 0) "something unique and special")
Error: Can't assign "something unique and special" as boolean
-- or --
arc> (= (~x 0) "something unique and special")
"something unique and special"
arc> (~x 0)
t
I don't see much purpose to implementing this feature, since every time someone would type (= (~foo bar) baz), they could just type (= foo.bar no.baz) instead.
