It's probably more idiomatic to implement something similar to the with-slots macro by using symbol-macrolet:
(defmacro with-keys (keys table &body body)
(let ((gtable (gensym)))
`(let ((,gtable ,table))
(symbol-macrolet ,(loop for k in keys
collect `(,k (gethash ',k ,gtable)))
,@body))))
This way you can both access and set the keys:
CL-USER> (defparameter *table* (make-hash-table))
*TABLE*
CL-USER> (setf (gethash 'a *table*) 10
(gethash 'b *table*) 20)
20
CL-USER> (with-keys (a b) *table*
(list a b))
(10 20)
CL-USER> (with-keys (a b) *table*
(setf a 100
b 200))
200
CL-USER> (list (gethash 'a *table*)
(gethash 'b *table*))
(100 200)
If you really want to destructure a hash-table when its an argument, it is not much harder to write a new version of defun on top of with-keys or zeroyzeroa's solution (his/hers only takes a single argument).
(defk login (user pass) (and (string= user "Bob") (string= pass "secret")))
(login (list-to-hash '(user "Bob" pass "secret")) (list-to-hash '(user "Bob" pass "secret"))
Given the following definitions:
(defmacro defk(name h-list &rest body) `(defun ,name (h) (let ,h-list ,@(loop for k in h-list collect `(setq ,k (gethash (quote ,k) h))) ,@body)))
(defun list-to-hash(list) (let ((h (make-hash-table))) (loop for (k v) on list by #'cddr do (setf (gethash k h) v)) h))