Lenses with a southern twang.
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
andw
), and look likea -> 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 complementsLens
powerfullya rich set of category-level class instances (for now from "categories") for
Lens
andIso
. 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
TODOs:
a module providing template haskell deriving of Lenses
pre-define lenses for prelude types, State
CHANGES:
depend on categories >= 1