Witherable.Lens

Documentation

withered :: (Applicative f, Witherable t) => (a -> Withering f b) -> t a -> f (t b)

A variant on traverse that allows the targets to be filtered out of the Witherable structure. Note that this introduces a change in types down the lens composition chain, which means that it is not a a valid optic at all. The use of Withering in the changed type also means that standard lens combinators don't fit

To address these issues, you can use unwithered to strip the Withering type back out. This allows the composed optic to be used with standard combinators from lens. In addition, the sequence withered . unwithered will act like a type-restricted version of traverse for all lawful instances of Witherable.

In some sense, this is a catch-like combinator. This marks the point where removing elements stops propagating and actually modifies the structure being focused.

unwithered :: Functor f => (a -> f b) -> a -> Withering f b

Restore types in a lens composition chain that has had Withering introduced. Makes no changes to what elements are focused on.

rewithered :: (Applicative f, Witherable t) => (a -> Withering f b) -> t a -> Withering f (t b)

A variant of withered for when you're already working in a Withering chain and want to change what structure elements are being removed from.

rewithered = unwithered . withered

decayed :: Applicative f => pafb -> s -> Withering f t

The trivial optic in a Withering chain that removes everything.

The arguments are unused.

guarded :: Applicative f => (a -> Bool) -> (a -> Withering f b) -> a -> Withering f b

Remove elements from the current Withering context if they don't match the predicate. This is similar in concept to filtered from lens. The major that instead of merely removing non-matching targets from the traversal, it removes those targets (and their parents up to the next withered combinator) from the data structure entirely.

filterOf :: ((a -> Withering Identity a) -> s -> Identity s) -> (a -> Bool) -> s -> s infix 2

Remove elements matched by a specific Withering context if they don't match a predicate.

mapMaybeOf :: ((a -> Withering Identity b) -> s -> Identity t) -> (a -> Maybe b) -> s -> t infix 2

Transform and filter elements matched by a specific Withering context, a la mapMaybe.

witherOf :: ((a -> Withering f b) -> s -> f t) -> (a -> f (Maybe b)) -> s -> f t infix 2

Transform and effectfully filter elements matched by a specific Withering context, a la wither.