Different calls to hygienic macros should create unique hygiene values

[jcubic]

This code from SRFI-210 doesn't work correctly:

(define-syntax call/mv
  (syntax-rules ()
    ((call/mv consumer producer1 ...)
     (letrec-syntax
         ((aux (syntax-rules ::: ()
                 ((aux %consumer () ((%producer1 args1) :::))
                  (let-values (((proc) %consumer)
                               (args1 %producer1) :::)
                    (apply proc (append args1 :::))))
                 ((aux %consumer (%producer1 producer2 :::) (temp :::))
                  (aux %consumer (producer2 :::) (temp ::: (%producer1 args1)))))))
       (aux consumer (producer1 ...) ())))))


(print (call/mv string (values #\a #\b) (values #\c #\d)))
;; ==> cdcd

It should print abcd the same as Gauche, all different implementations fail to run this code.

The problem is that this is a recursive deep first expansion and each expansion should create new unique value of args1 that is a free variable in this pattern. But because syntax-rules just collect the name and use them inside the macro they are the same. And last value is used.

It's because this also works:

(let-values ((x (values 1 2 3))
             (x (values 4 5 6)))
  (display x)
  (newline))
;; ==> (4 5 6)

the same value in let-values works and x shadow previous x.