A Complete RPN Expr-Eval Program Inside a Tweet? -- "YES WE CAN!", Using LISP [closed]

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The Program (115 Chars)

(defun rpn(e)(let((s()))(dolist(x e)(if(numberp x)(push x s)(push(eval(revers开发者_开发知识库e(list(pop s)(pop s)x)))s)))(car s)))

A simple test:

CL-USER> (rpn '(1 2 3 * + 4 2 / +))

And it returns 9

Anyone has some good ideas about writing an Infix-to-RPN program inside one single tweet? I failed. I can wrote that one in 235 chars.

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Here is one in Clojure (88 chars):

(defn rpn [& e](reduce #(if (fn? %2)(let [[l r & m]%](cons (%2 r l) m))(cons %2 %))[]e))

And the un-golfed version:

(defn rpn [& expr]
  (reduce (fn [stack op]
            (if (fn? op)
              (let [[l r & m] stack]
                (cons (op r l) m))
              (cons op stack)))
          []
          expr))