(defstruct ro (value nil :read-only t))

(defmacro immutable-let ((&rest bindings) &body body)
  (let* ((values (mapcar (lambda (binding)       (list (gensym) `(make-ro :value ,(second binding)))) bindings))
         (immuts (mapcar (lambda (binding value) (list (first binding) `(ro-value ,(first value)))) bindings values)))
    `(let ,values
       (symbol-macrolet ,immuts ,@body))))

(pprint (macroexpand-1 '(immutable-let ((x 42)
                                        (y (+ 2 3)))
                         (setf x 33)
                         (list x y))))

(let ((#1=#:g42316 (make-ro :value 42))
      (#2=#:g42317 (make-ro :value (+ 2 3))))
  (symbol-macrolet ((x (ro-value #1#))
                    (y (ro-value #2#)))
    (setf x 33)
    (list x y)))


(immutable-let ((x 42)
                (y (+ 2 3)))
  (setf x 33)
  (list x y))

(42 5)