Your example helped.
I can reason with (conc equences) now =)
> AFAIK there is only one empty `list' in PL, and that is `NIL'. So
> after `conc'atenating to it's end it would no longer be empty.
> [de ex2 
> [let [R [list]]
> [do 10
> [conc R [list 'A]] ]
> # Will have to find the end of `R' each time!!
> # Even worse if `R' is `circ'ular, which will result in
> infinite recursion and out of stack memory.
> # In Your second implementation `'[A]' was `conc'ed to itself,
> which resulted in `circ'ular list `[A .]'.
> # : [setq L1 '[A]] [conc  L1 L1]
> # -> [A .]
> # To avoid that it was corrected to `[list 'A]'.
> (cdr R) ] ]