set-cdr! does not work

[Tang Chenglong]

When I modify cdr of a list, set-cdr! does not work for me, and throw an exception.

I tried on both Windows 7 and Freebsd 10, 0.6.10 and 0.6.6 respectively.

Attached please find.

[Takashi Kato]

Thank you for the report!

The behaviour is intentional. Your definition of a is literal list ('(a)) and modifying such expressions is an error both R6RS and R7RS. Sagittarius follows the 'Should' behaviour described in R6RS which is raising &assertion. So this won't be fixed.

The easiest way to avoid this error is the following:

(import (rnrs) (rnrs mutable-pairs))
(define a `(a)) ;; using quasiquote creates non literal list
(set-cdr! a 'b)

[Tang Chenglong]

Yes, you are right. I bypass it by

(define a (list 'a))
(set-cdr! a 'b)

Thanks for your work！