Lens.Micro.Extras

Documentation

view :: Getting a s a -> s -> a

view is a synonym for (^.):

>>> view _1 (1, 2)
1

The reason it's not in Lens.Micro is that view in lens has a more general signature:

view :: MonadReader s m => Getting a s a -> m a

So, you would be able to use this view with functions, but not in various reader monads. For most people this shouldn't be an issue; if it is for you, use view from microlens-mtl.

preview :: Getting (First a) s a -> s -> Maybe a

preview is a synonym for (^?):

>>> preview _head [1,2,3]
Just 1

The reason it's not in Lens.Micro is that preview in lens has a more general signature:

preview :: MonadReader s m => Getting (First a) s a -> m (Maybe a)

Just like with view, you would be able to use this preview with functions, but not in reader monads; if this is an issue for you, use preview from microlens-mtl.