Hi, The arguments (x,y) to dqAppend are "double ended queue", implemented as "head-tail linked list", note that the car and cdr of x/y have shared cons cell, for example:
(setq l1 '(a b c d e)) (setq x (cons l1 (last l1))) (setq l2 '(k l m n o)) (setq y (cons l2 (last l2))) (rplacd (cdr x) (car y)) ;; connects l2 to the end of l1 (rplacd x (cdr y)) ;; replace the end node of l1 by the end node of l2 ;; now x is ((A B C D E K L M N O) O) - Qian On 9/26/21 23:12, Hill Strong wrote: > > When looking at the function dqAppend found in the btscan2.boot file > (given below) > > dqAppend(x,y)== > if null x > then y > else if null y > then x > else > RPLACD (CDR x,CAR y) > RPLACD (x, CDR y) > x > what is the purpose of the line > > RPLACD(CDR x,CAR y) > > This appears to be entirely superfluous to the function. Is this > correct? I have tried these two lines in the interface on > https://rextester.com/l/common_lisp_online_compiler with the following code > > (setq l1 (list 'a 'b 'c 'd 'e)) > (print l1) > (setq l2 (list 'k 'l 'm 'n 'o)) > (print l2) > (rplacd (cdr l2) (car l1)) > (print l2) > (rplacd l2 (cdr l1)) > (print l2) > > and I get the results > > (A B C D E) > (K L M N O) > (K L . A) > (K B C D E) > > Is this the expected results or is something else actually expected? > > greetings > > Hill Strong > > -- > You received this message because you are subscribed to the Google > Groups "FriCAS - computer algebra system" group. > To unsubscribe from this group and stop receiving emails from it, send > an email to fricas-devel+unsubscr...@googlegroups.com > <mailto:fricas-devel+unsubscr...@googlegroups.com>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/fricas-devel/ea73f865-45d0-4ad7-b600-859f9f7db9b7n%40googlegroups.com > <https://groups.google.com/d/msgid/fricas-devel/ea73f865-45d0-4ad7-b600-859f9f7db9b7n%40googlegroups.com?utm_medium=email&utm_source=footer>. -- You received this message because you are subscribed to the Google Groups "FriCAS - computer algebra system" group. To unsubscribe from this group and stop receiving emails from it, send an email to fricas-devel+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/fricas-devel/2ac654f9-3111-072c-e599-b86bd4a7e01b%40gmail.com.
