lens-2.1: Lenses, Folds and Traversals
Lenses for working with products.
Due to their ubiquity, _1 and _2 are defined in Control.Lens.
both :: Traversal (a, a) (b, b) a bSource
Traverse both parts of a tuple with matching types.
value :: (k -> Bool) -> SimpleIndexedTraversal k (k, v) vSource
This provides a Traversal that checks a predicate on a key before
allowing you to traverse into a value.
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