Modifying constructor for fgl-env structures.
(change-fgl-env x [:obj-alist <obj-alist>] [:bfr-vals <bfr-vals>])
This is an often useful alternative to make-fgl-env.
We construct a new fgl-env structure that is a copy of
This is an ordinary
(defmacro change-fgl-env (x &rest args) (std::change-aggregate 'fgl-env x args '((:obj-alist . fgl-env->obj-alist) (:bfr-vals . fgl-env->bfr-vals)) 'change-fgl-env 'remake-fgl-env))