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last edited 9 years ago by test1 |
Edit detail for #432 List doesn't check for circularity in length revision 6 of 6
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Editor: test1
Time: 2015/10/27 14:23:42 GMT+0 |
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From test1 Tue Oct 27 14:23:42 +0000 2015
From: test1
Date: Tue, 27 Oct 2015 14:23:42 +0000
Subject:
Message-ID: <20151027142342+0000@axiom-wiki.newsynthesis.org>
Status: open => rejected
axiom
u:= [9,2, 4, 7]; concat! (u, [1, 2, 42]); end := rest(u, 4); part:=rest(u, 2); setrest!(end, part);
Type: List(PositiveInteger?)
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
re: documentation --Bill Page, Mon, 01 Sep 2008 12:23:09 -0700 reply
On Mon, Sep 1, 2008 at 4:27 PM, Tim Daly wrote
In the documentation it states:Using FriCAS built with GCL-2.6.8pre the difference between"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.
axiom
w:=[random(2^31)$INT for i in 1..10^5];
Type: List(Integer)
axiom
)set message time on
axiom
for i in 1..10000 repeat integer(LENGTH(w)$Lisp)
Type: Void
axiom
Time: 0.01 (IN) + 3.09 (EV) + 0.03 (OT) = 3.13 sec
axiom
for i in 1..10000 repeat integer(LIST_-LENGTH(w)$Lisp)
Type: Void
axiom
Time: 4.13 (EV) = 4.13 secOn sbcl 32bit,
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
Status: open => rejected