Navigate from a node to its previous sibling or return Option.none if the focused node is the head node in its forest.
Option.none
See previous for an unsafe version.
The underlying type of the tree.
An updated zipper pointing at a new focus or Option.none() if there is no previous sibling.
Option.none()
Navigate from a node to its previous sibling or return
Option.noneif the focused node is the head node in its forest.See previous for an unsafe version.