The yall package
Why yet another lens library? First, none of the existing libraries for Lenses were adequate for my needs (specifically for my use of lenses in pez). And anyway, why not try to create something novel and better?
Lenses are parameterized over two Monads (by convention m and w), and look like a -> m (b -> w a, b). this lets us define lenses for sum types, that perform validation, that do IO (e.g. persist data to disk), etc., etc.
a module Data.Yall.Iso that complements Lens powerfully
a rich set of category-level class instances (for now from categories) for Lens and Iso. These along with the pre-defined primitive lenses and combinators give an interface comparable to Arrow
You should import either Data.Yall or Data.Yall.Lens, and optionally Data.Yall.Iso. Data.Yall is a simplified, but mostly-compatible, version of a subset of Data.Yall.Lens.
UPDATE: I have stopped developing this package. Instead you should take a look at and contribute to http://hackage.haskell.org/package/lens
a module providing template haskell deriving of Lenses
pre-define lenses for prelude types, State
depend on categories >= 1
|Versions||0.1, 0.2, 0.2.0.1, 0.2.1|
|Dependencies||base (4.*), categories (≥1.0), transformers|
|Source repository||git clone https://github.com/jberryman/yall.git|
|Upload date||Fri Sep 21 16:34:49 UTC 2012|
|Build failure||ghc-7.6 (log)|