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Re: [Chicken-users] Cyclic lists and the Interpreter
From: |
Jim Ursetto |
Subject: |
Re: [Chicken-users] Cyclic lists and the Interpreter |
Date: |
Tue, 8 Apr 2008 11:56:16 -0600 |
On 4/8/08, Graham Fawcett <address@hidden> wrote:
> On Mon, Apr 7, 2008 at 3:24 PM, Alex Rozenshteyn <address@hidden>
> > 2) Is the interpreter supposed to freeze if length is passed a cyclic
> list?
> Yes, it's correct. See length and length+ in SRFI-1:
> http://srfi.schemers.org/srfi-1/srfi-1.html#Miscellaneous
> length+ will give you sane behaviour with cyclic lists.
For background, you can find some information on the design of length+ at:
http://srfi.schemers.org/srfi-1/mail-archive/msg00038.html
Of course, length+ returns #f for circular lists. If you want a
count of "distinct elements", a procedure using the tortoise and hare
algorithm is available in the same thread:
http://srfi.schemers.org/srfi-1/mail-archive/msg00096.html
The question of whether "how many elements are in a circular list" is
well-defined is also discussed.
Jim