NOTE: If you're writing an app, you probably want
<http://hackage.haskell.org/package/microlens-platform microlens-platform> – it
has the most features. <http://hackage.haskell.org/package/microlens microlens>
is intended more for library writers who want a tiny lens library (after all,
lenses are pretty useful for everything, not just for updating records!).
This library is an extract from <http://hackage.haskell.org/package/lens lens>
(with no dependencies). It's not a toy lenses library, unsuitable for “real
world”, but merely a small one. It is compatible with lens, and should have
same performance. It also has better documentation.