;;;
;;; The first attempt on macros:
;;;
;;; (getenv "asdf")
;;; => "999"
;;;
;;; (let-env (("asdf" "123"))
;;;   (getenv "asdf"))
;;; => "123"
;;;
;;; (getenv "asdf")
;;; => "999"
;;;
(define-syntax let-env
  (syntax-rules ()
    ((let-env ((var val) ...) exp exp* ...) ; pattern
     ;; Any better way?
     (let* ((env (list (cons var val) ...)) ; template
            (vars (map car env))
            (new (map cdr env))
            (old (map getenv vars)))
       (for-each setenv vars new)
       (let ((retval (begin exp exp* ...)))
         (for-each setenv vars old)
         retval)))))