@hackage yall0.2

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?

Distinguishing features:

• 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.

TODOs:

• a module providing template haskell deriving of Lenses

CHANGES:

• remove setEmpty variants only useful on lenses better expressed in Iso

• create a class for lens operations, supporting...

• use newtype wrappers for different monadic lifting schemes

• better ordering for set, allowing let-floating for partial application