Add meaningful instances to ZipList

[Roman Cheplyaka]

* wren ng thornton <wren at freegeek.org> [2011-12-19 16:45:50-0500]
> While we're on the topic, is there any reason why ZipList is a data
> type instead of a newtype? Is the extra bottom actually necessary for
> the Applicative semantics? If not, then I'd suggest changing it to a
> newtype in order to remove the extra indirection.

It is actually a newtype, and has been at least since base-3.0.3.1 (the
oldest 'base' available on hackage).

-- 
Roman I. Cheplyaka :: http://ro-che.info/