                       `(prog1 ,id (setq ,id (1- ,id))))))
     (assign    . ,(lambda (token assign)
                     (destructuring-bind (lhs eq expr) assign
-                      `(setf ,lhs ,expr))))
+                      (if (symbolp lhs)
+                          `(setq ,lhs ,expr)
+                        (destructuring-bind (obj field) lhs
+                          (let ((obj-sym (gensym)))
+                            `(let ((,obj-sym (copy-alist ,obj)))
+                               (setcdr (assq ,field ,obj-sym) ,expr)
+                               ,obj-sym)))))))
     (+         . ,(lambda (token op) (psl--apply 'psl-+ (nth 1 op))))
     (-         . ,(lambda (token op) (psl--apply 'psl-- (nth 1 op))))
     (<         . ,(lambda (token op) (psl--apply '< (nth 1 op))))

;;; Known bugs:

;; * Assignment is an issue right now
;;   * Objects are mutable (object assignment semantics are wrong)
;;   * Operators += and -= not yet implemented
;; * Equality tests are incomplete
;; * The empty object is currently (), so it evaluates to false

    (inc-post  id "++")
    (dec-pre   "--" id)
    (dec-post  id "--")
    (assign    [index= id] "=" expr)

    ;; Objects
    (pairs     pair [("," pairs) ""])
    (pair      id ":" expr)
    (object    "{" [pairs ""] "}")
    (index     [pexpr id] [by-id index-str])
    (index=    [pexpr id] [by-id index-str])
    (message   [pexpr id] "@" [index-str field] args)
    (by-id     "\\." field)
    (field   . id)
