Data.Yall

Documentation

This is a subset of Lens, exporting only the basic API. Furthermore, get, lensM, getM, setM, and modifyM are exported with more restrictive types than are found in Data.Yall.Lens, for simplicity.

You should either import this module, or Lens.

Pure lenses

type :-> = LensM Identity

a simple lens, suitable for single-constructor types

lens :: (a -> b) -> (a -> b -> a) -> a :-> b

Create a pure Lens from a getter and setter

 lens g = lensM (fmap return g) . fmap (fmap return)

get :: (a :-> b) -> a -> b

Run the getter function of a pure lens

set :: (a :-> b) -> a -> b -> a

Run the getter function of a pure lens

 set l b = runIdentity . setM l a

modify :: (a :-> b) -> (b -> b) -> a -> a

Partial lenses

type :~> = LensM Maybe

a lens that can fail in the Maybe monad on the outer type. Suitable for a normal lens on a multi-constructor type. The more general setM, getM, etc. can be used with this type.

lensM :: (a -> Maybe b) -> (a -> Maybe (b -> a)) -> a :~> b

Create a partial lens from a getter and setter

getM :: (a :~> b) -> a -> Maybe b

Try to run the getter function on a value

setM :: (a :~> b) -> a -> b -> Maybe a

try to run the setter function on an outer and new inner value

modifyM :: (a :~> b) -> (b -> b) -> a -> Maybe a

try to modify the inner type of a value