gethash

(gethash key table &optional default)

Looks up key in table and returns the associated value, or default (nil when omitted) if the key is absent. Keys are compared structurally as if by equal, so an equal list, string, or number key matches. To store a value, use gethash as a setf place: (setf (gethash key table) value), which also cooperates with incf/decf/push. Under multiple-value-bind (and the other multiple-value consumers) a gethash call also supplies a second present-p value distinguishing a stored nil from a missing key.