rsc.scm

(define-syntax swap! 
  (rsc-macro-transformer
   (lambda (form env)
     (let ((a (cadr form))
           (b (caddr form))
           (value (make-syntactic-closure env '() 'value))
           (let-r (make-syntactic-closure env '() 'let))
           (set!-r (make-syntactic-closure env '() 'set!)))
       `(,let-r ((,value ,a))
          (,set!-r ,a ,b)
          (,set!-r ,b ,value))))))