Sometimes it's convenient to store things in a list like '((key . value) (another-key . value)) rather than a full blown (and unordered) hash table.
It is available now in cl-irregsexp.utils but could you add the fairly standard cdr-assoc function to alexandria?
(declaim (inline cdr-assoc)) (defun cdr-assoc (alist key &key (test 'eql)) (cdr (assoc key alist :test test))) (define-setf-expander cdr-assoc (place key &key (test ''eql) &environment env) (multiple-value-bind (dummies vals newval setter getter) (get-setf-expansion place env) (with-unique-names (store key-val test-val alist found) (values (append dummies (list key-val test-val)) (append vals (list key test)) `(,store ,@newval) `(let (,@(mapcar 'list dummies vals) (,alist ,getter)) (let ((,found (assoc ,key-val ,alist :test ,test-val))) (cond (,found (setf (cdr ,found) ,store)) (t (setf ,(first newval) (acons ,key ,store ,alist)) ,setter)) ,store)) `(cdr-assoc ,getter)))))