(define (execute expr)
  (lambda (x)
    (let recur ((expr expr))
      (case expr
        ((x) x)
        ((+) +)
        ((-) -)
        ((*) *)
        ((/) /)
        (else
         (if (list? expr)
             (apply (recur (car expr)) (map recur (cdr expr)))
             expr))))))

> (define foo (execute '(* (+ 1 x) (- x (* 2 3)))))
> (foo 42)
=> 1548