Scheme generator macro

generator.scm

(define-macro generator
  (lambda (params . body)
    (let ((cont (gensym "gen-cont"))
          (yieldc (gensym "gen-yield")))
      `(lambda ,params
         (let ((,cont #f))
           ;; cont will point to the last yield call.
           (lambda ()
             (let/cc ,yieldc
                     ;; yieldc returns from the generator.
                     (if ,cont (,cont ,yieldc))
                     (let-syntax
                         ((yield (syntax-rules ()
                                   ((yield val)
                                    ;; Yield syntax: Update cont and return a value.
                                    ;; yieldc is set to the cc when the gen is re-entered.
                                    (set! ,yieldc (let/cc x (set! ,cont x) (,yieldc val)))))))
                       ,@body))))))))