Navigate from a node to its previous sibling N times to reach the Nth sibling
left of the focus, or return Option.none if the focus index is less than
N.
When n is zero, the zipper is returned unchanged.
Will return Option.none if given negative indexes.
Navigate from a node to its previous sibling N times to reach the Nth sibling left of the focus, or return
Option.noneif the focus index is less than N.When
nis zero, the zipper is returned unchanged.Will return
Option.noneif given negative indexes.See previousN for an unsafe version.
Type Param: A
The underlying type of the tree.
Param: self
The zipper that will be navigated.
Param: n
Number of siblings to skip to the left.
Returns
An updated zipper pointing at a new focus or
Option.none()ifpreviouscannot be repeated N times.