(shadow '(let* let))

(defmacro let ((&rest bindings) &body body)
  `((lambda ,(mapcar (lambda (binding)
                       (if (listp binding)
                           (first binding)
                           binding))
              bindings)
      ,@body)
    ,@(mapcar (lambda (binding)
                (if (listp binding)
                    (second binding)
                    'nil))
              bindings)))

(defmacro let* ((&rest bindings) &body body)
  (if (endp bindings)
      `((lambda () ,@body))
      `((lambda (,(if (listp (first (last bindings)))
                      (first (first (last bindings)))
                      (first (last bindings))))
          (let* ,(butlast bindings) ,@body))
        ,(if (listp (first (last bindings)))
             (second (first (last bindings)))
             'nil))))

(macroexpand-1 '(let ((x 6) (y (* x x))) (+ x y)))
--> ((lambda (x y) (+ x y)) 6 (* x x))
    t

(macroexpand-1 '(let* ((x 6) (y (* x x))) (+ x y)))
--> ((lambda (y) (let* ((x 6)) (+ x y))) (* x x))
    t