A robust delete has to do nothing gracefully - removing a key that is absent, or deleting from an empty list, must leave everything untouched and report that nothing happened. Today you pin those no-op cases and have Delete report whether it removed anything.
Make Delete a no-op that returns false when the key is absent or the list is empty.
Every mutating operation needs a graceful “nothing to do” path, and delete is the clearest case. After the descent, the node just ahead on level 0 is the only candidate; if it does not exist (empty list, or you walked off the end) or its key is not an exact match, there is simply nothing to remove. Delete should touch no pointers, change no length, and return false so the caller knows the key was absent - versus true when it really unlinked a node.
This makes Delete total: it is safe to call with any key at any time, including on
an empty list, and its boolean result doubles as a membership answer. Pinning the
no-op cases now, before they can hide bugs, follows the same instinct as testing the
boundaries of every other operation: the interesting behavior is often at the edges,
where the list is empty or the key falls between existing ones. With insert and
delete both complete and total, the rest of the chapter adds the ordered queries a
sorted collection is expected to answer.
// The descent already lands on the successor of `key`. If it is not an// exact match, remove nothing and report false; otherwise unlink, trim,// and report true.x = x.forward[0]if x == nil || x.key != key {return false}// ... unlink, lower level, s.length--, return true