Class
class
type
empty
= object ...
end
class
type
mutually
= object ...
end
class
type
recursive
= object ...
end
class
recursive'
: recursive
class
type virtual
empty_virtual
= object ...
end
class
virtual
empty_virtual'
: empty
class
type 'a
polymorphic
= object ...
end
class 'a
polymorphic'
:
'a
polymorphic