(1) -> u:= [9,2, 4, 7]; concat! (u, [1, 2, 42]); end := rest(u, 4); part:=rest(u, 2); setrest!(end, part);
Asking for the number of elements of u will exhibit lisp-implementation-dependend behaviour, ranging from an error to an infinite loop.
We should either fix the documentation (saying, that this is the case), or check for circularity. This could be done by calling LIST_-LENGTH instead of LENGTH in ILIST, for example.
According to the common lisp standard list-length returns nil if the list is circular.
http://www.lispworks.com/documentation/HyperSpec/Body/f_list_l.htm
In the documentation it states:"Note that using the "#" operator on a list with cycles causes Axiom to enter an infinte loop"
See: http://axiom-developer.org/axiom-website/documentation.html in Volume 0: Axiom Jenks and Sutor p41
LENGTH and LIST-LENGTH seems to be negligible. Usingclisp,
LIST-LENGTH actually seems a little faster.
w:=[random(2^31)$INT for i in 1..10^5];
)set message time on
for i in 1..10000 repeat integer(LENGTH(w)$Lisp)
Time: 0.99 (EV) = 1.00 sec
for i in 1..10000 repeat integer(LIST_-LENGTH(w)$Lisp)
Time: 0.99 (EV) = 0.99 sec
LIST-LENGTH is slower than LENGTH by a factor of roughly 1.25. (compared to gcl on my 32 bit machine, where the factor is 1.57! I'm surprised of the result above, that makes for a factor of 1.03...) I'm not sure whether this is negligible. However, for short lists, the difference really should be negligible...
Martin