On Fri, Mar 07, 2014 at 11:03:57PM -0500, Carl Eastlund wrote:
> The first/rest operations do not use a memoization table. They test using
> the list? primitive, which is built in and actually has a couple of tag
> bits reserved on every cons object for memoizing its results. So the
> operation really is quite fast.
I take this to mean there is a bit in the cons object for storing
whether it is a list, and that this bit is set via `list?'.
Why wouldn't the bit be set via `cons'?
Also, when I do:
$ racket
Welcome to Racket v6.0.0.2.
> (let ((ls (make-list 50000000 0)))
(time (list? ls))
(time (list? ls))
(time (list? ls))
(time (list? ls))
(time (list? ls)))
cpu time: 220 real time: 220 gc time: 0
cpu time: 112 real time: 112 gc time: 0
cpu time: 60 real time: 58 gc time: 0
cpu time: 28 real time: 29 gc time: 0
cpu time: 16 real time: 15 gc time: 0
#t
Why does the time decrease gradually, rather than the 2nd and subsequent
times being roughly equivalent?
Thanks.
David
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