assoc-in

(assoc-in m keys v)

Answers the nested association down the key vector, building missing levels from empty. With no keys, associates under nil, like the oracle. A vector level steps by index, like assoc: the index equal to the count appends a new level, so (assoc-in [[0 0]] [1 0] :x) is [[0 0] {0 :x}]. As a value the key sequence walked at run time.