Looking to complete my self-obsessive list of cdr, car functions

[Anonymous]

I am trying with all my might to gain understanding of car, cdr, etc. for some specific projects.

I've made a list of functions and have been typing them in the ACAD command line to see what works and what doesn't.  Yes, OK, I'm a monkey trying to type Shakespeare....

My list is (1 2 3)(4 5 6)(7 8 9).

I can't find a way to extract 6, 8 or 9.  Also, can't get (8 9)

I've attached a text file that shows my accumulated list.  Could someone fill in these blanks for me?  Thanks very much in advance!! 

[Ranjit_Singh · Accepted solution]

Command: (cddadr '((1 2 3) (4 5 6) (7 8 9)))
(6)
Command: (cdaddr '((1 2 3) (4 5 6) (7 8 9)))
(8 9)

car cdr can only be nested upto 4 levels

, so to extract 6 and 8 and 9 as car's and not lists ...

Command: (car (cddadr '((1 2 3) (4 5 6) (7 8 9))))
6
Command: (car (cdaddr '((1 2 3) (4 5 6) (7 8 9))))
8
Command: (cadr (cdaddr '((1 2 3) (4 5 6) (7 8 9))))
9

[Anonymous]

Great!  Thanks!  I learned a lot from your answer 

[martti.halminen]

A style hint: while understanding the CxxxR functions is useful, they should be hidden inside higher-level tools or your programs will be pretty hard to read.

For example picking out 6 from that list would be more readable as 

(z (second '((1 2 3)(4 5 6)(7 8 9))), assuming your application is using x,y,z coordinates.

- Defining Z and SECOND should be easy for you at this stage.

-- 

[Anonymous]

Hahaha, it can be done THAT easily? Thanks for the extra tip, the example code I'm learning from is definitely NOT that straightforward 

[pbejse]

I downloaded a .txt file sometime ago specifically for car / cadr   combinations [ cant remember where though ] 

These concatenations are the equivalent of nested calls to car and cdr. Each a represents a call to car, and each d represents a call to cdr

Read through it, either you will have a better understanding on how the nesting works or give you a massive headache 🙂

pBe

[Anonymous]

Thanks for the list!