|Maintainer||Neil Sculthorpe <firstname.lastname@example.org>|
This module defines the KURE
Lens type, along with some useful operations.
- data Lens c m a b
- lens :: Translate c m a ((c, b), b -> m a) -> Lens c m a b
- lensT :: Lens c m a b -> Translate c m a ((c, b), b -> m a)
- focusR :: Monad m => Lens c m a b -> Rewrite c m b -> Rewrite c m a
- focusT :: Monad m => Lens c m a b -> Translate c m b d -> Translate c m a d
- pureL :: Monad m => (a -> b) -> (b -> a) -> Lens c m a b
- failL :: Monad m => String -> Lens c m a b
- catchL :: MonadCatch m => Lens c m a b -> (String -> Lens c m a b) -> Lens c m a b
- testLensT :: MonadCatch m => Lens c m a b -> Translate c m a Bool
- bidirectionalL :: Monad m => BiTranslate c m a b -> Lens c m a b
- injectL :: (Monad m, Injection a g) => Lens c m a g
- projectL :: (Monad m, Injection a g) => Lens c m g a
Lens is a way to focus on a sub-structure of type
b from a structure of type
The primitive way of building a
If the unfocussing function is applied to the value focussed on then it should succeed,
and produce the same value as the original argument (of type
Lens from two pure functions.
Lens is deemed to have failed (and thus can be caught) if either it fails on the way down, or,
crucially, if it would fail on the way up for an unmodified value. However, actual failure on the way up is not caught
(as by then it is too late to use an alternative
Lens). This means that, in theory, a use of
catch could cause a succeeding
Lens application to fail.
lens is used correctly, this should never happen.
Check if the focusing succeeds, and additionally whether unfocussing from an unchanged value would succeed.