2009 Nov 09 00:38:58  <inimino> hm
2009 Nov 09 00:39:28  <inimino> aamar: should we meet in 20 minutes or 40 minutes ago? :)
2009 Nov 09 00:39:48  <aamar> ha, I was thinking 20 minutes from now
2009 Nov 09 00:39:52  <inimino> ok, good
2009 Nov 09 00:40:07  <inimino> maybe I can get a little further then
2009 Nov 09 01:02:56  <aamar> got through 4.22
2009 Nov 09 01:04:41  <inimino> ah, I only got up to 4.17
2009 Nov 09 01:05:15  -*- inimino was short on time the last two weeks
2009 Nov 09 01:07:21  <aamar> same here
2009 Nov 09 01:07:40  <inimino> alright, shall we start?
2009 Nov 09 01:07:48  <aamar> yes
2009 Nov 09 01:07:50  <aamar> 4.11
2009 Nov 09 01:07:55  <inimino> ok
2009 Nov 09 01:08:17  <aamar> http://github.com/aalearn/aalearn-sicp/blob/master/ch4-outline.scm#L254-261
2009 Nov 09 01:08:45  <inimino> http://inimino.org/~inimino/projects/2009/SICP/chap_4/4.11
2009 Nov 09 01:12:11  <inimino> the thing about (set-cdr! frame frame) is that you will get an infinite structure, even after you set-car!
2009 Nov 09 01:14:29  <inimino> I think you could copy the entire contents of frame, however, then (set-cdr! frame copy), and that would work
2009 Nov 09 01:14:40  <inimino> I don't know how to create a copy of a list in Scheme though
2009 Nov 09 01:14:41  <aamar> hm.
2009 Nov 09 01:15:47  <inimino> if you think of it in terms of pointers, after (set-cdr! frame frame), frame is a pair, the cdr of which contains a pointer to itself
2009 Nov 09 01:16:28  <aamar> got ir
2009 Nov 09 01:16:30  <aamar> got it
2009 Nov 09 01:16:31  <aamar> ok
2009 Nov 09 01:16:34  <aamar> right
2009 Nov 09 01:16:41  <inimino> ok
2009 Nov 09 01:16:56  <aamar> copying doesn't seem to be the right solution...
2009 Nov 09 01:17:40  <inimino> I'm not sure how well that would work either
2009 Nov 09 01:19:17  <aamar>   (set-cdr! frame (cons (car frame) (cdr frame)))
2009 Nov 09 01:19:53  <inimino> ah, that looks plausible
2009 Nov 09 01:20:03  <aamar> I will try it out later
2009 Nov 09 01:20:07  <inimino> create a new pair... that seems like it should work
2009 Nov 09 01:20:10  <inimino> ok
2009 Nov 09 01:20:32  <inimino> would be more elegant than my (list 'frame ...) stuff I think
2009 Nov 09 01:20:38  <inimino> alright, next one?
2009 Nov 09 01:20:44  <aamar> yeah
2009 Nov 09 01:20:51  <inimino> ok
2009 Nov 09 01:21:04  <inimino> http://inimino.org/~inimino/projects/2009/SICP/chap_4/4.12
2009 Nov 09 01:21:34  <aamar> http://github.com/aalearn/aalearn-sicp/blob/master/ch4-outline.scm#L265-282
2009 Nov 09 01:21:58  <aamar> http://github.com/aalearn/aalearn-sicp/blob/master/ch4-outline.scm#L265-296 actually
2009 Nov 09 01:25:28  <inimino> I agree with your ';non-intuitive' comment, but I did it the same way
2009 Nov 09 01:27:44  <aamar> yes, interesting
2009 Nov 09 01:27:50  <inimino> I wondered about the inner env-loop too
2009 Nov 09 01:29:16  <inimino> possibly it was to make lookup-variable-value and set-variable-value! look more similar, so that this very exercise would make more sense
2009 Nov 09 01:30:53  <aamar> So our answers are pretty similar -- except I couldn't figure out a way to make passing #f back look clean, which is why I added the if-not-found proc
2009 Nov 09 01:31:29  <inimino> ah
2009 Nov 09 01:32:02  <inimino> that's probably a better idea, I had to add a comment about a possible bug returning #f could have caused
2009 Nov 09 01:32:19  <aamar> Well, both answers seem correct to me.
2009 Nov 09 01:32:29  <inimino> yeah, agreed
2009 Nov 09 01:32:48  <aamar> Let's go to 4.13
2009 Nov 09 01:33:07  <inimino> ok
2009 Nov 09 01:33:12  <inimino> http://inimino.org/~inimino/projects/2009/SICP/chap_4/4.13
2009 Nov 09 01:33:38  <aamar> http://github.com/aalearn/aalearn-sicp/blob/master/ch4-outline.scm#L297-318
2009 Nov 09 01:36:09  <inimino> hm, my implementation of deleting the head of a list was completely incorrect
2009 Nov 09 01:37:02  <inimino> your delete-head! looks correct, though
2009 Nov 09 01:37:40  <aamar> yes, was just testing them out to make sure
2009 Nov 09 01:38:14  <aamar> mine seems to work -- you have to set-car! and set-cdr!
2009 Nov 09 01:38:32  <inimino> yeah, (set-car! x (cdr x)) should be a type error
2009 Nov 09 01:38:43  <inimino> putting a list in the place of an element
2009 Nov 09 01:39:12  <aamar> type error!
2009 Nov 09 01:39:28  <aamar> Are there type-safe lisps?
2009 Nov 09 01:39:40  <inimino> I don't know, I guess there must be
2009 Nov 09 01:39:46  <inimino> they have everything else ;)
2009 Nov 09 01:40:11  <aamar> likely true
2009 Nov 09 01:40:37  <aamar> ok otherwise our answers are exactly the same, modulo differences in the previous answer
2009 Nov 09 01:41:02  <aamar> should we go to 4.14 ?
2009 Nov 09 01:41:25  <inimino> ok, sure
2009 Nov 09 01:41:34  <inimino> http://inimino.org/~inimino/projects/2009/SICP/chap_4/4.14
2009 Nov 09 01:41:54  <aamar> http://github.com/aalearn/aalearn-sicp/blob/master/ch4-outline.scm#L319-323
2009 Nov 09 01:42:18  <inimino> looks the same
2009 Nov 09 01:42:28  <inimino> except that I spelled "created" as "creating"...
2009 Nov 09 01:42:31  <aamar> similar, I think
2009 Nov 09 01:42:49  <inimino> ever since I switched to Dvorak I can't seem to keep my suffixes straight :/
2009 Nov 09 01:43:15  <aamar> when did you switch?
2009 Nov 09 01:43:29  <inimino> about a year ago, I think
2009 Nov 09 01:44:06  <inimino> took a few weeks to get used to it
2009 Nov 09 01:44:24  <aamar> I tried once a while back, didn't stick with it though.
2009 Nov 09 01:44:24  <inimino> it is fast and a lot more comfortable
2009 Nov 09 01:44:39  <inimino> yeah, it didn't do anything for my accuracy
2009 Nov 09 01:44:57  <inimino> I end up spelling things phonetically a lot more frequently now
2009 Nov 09 01:45:22  <inimino> I'm not sure how that worked
2009 Nov 09 01:45:50  <aamar> that's surprising; hadn't heard that happening before
2009 Nov 09 01:46:04  <inimino> yeah, I wasn't expecting it
2009 Nov 09 01:46:18  <aamar> My main problem was switching back to qwerty mid-sentence
2009 Nov 09 01:46:55  <inimino> heh, I don't think I had that, except for a few things like passwords
2009 Nov 09 01:47:28  <inimino> I can still type on qwerty but I have to look at the keys now
2009 Nov 09 01:47:37  <inimino> strange how the brain works
2009 Nov 09 01:49:05  <inimino> but it just seems like there's some sort of thought -> sound -> typing loop that happens now so I end up mixing up homophones quite frequently
2009 Nov 09 01:49:19  <inimino> anyway... shall we look at the next one?
2009 Nov 09 01:50:04  <aamar> yes
2009 Nov 09 01:50:23  <inimino> ah, this one :)
2009 Nov 09 01:50:26  <inimino> http://inimino.org/~inimino/projects/2009/SICP/chap_4/4.15
2009 Nov 09 01:50:32  <aamar> http://github.com/aalearn/aalearn-sicp/blob/master/ch4-outline.scm#L325-332
2009 Nov 09 01:52:15  <aamar> ok, we both have seen this before, I think.
2009 Nov 09 01:52:23  <inimino> yeah, similar answers, though we started from opposite ends of the proof
2009 Nov 09 01:52:26  <inimino> yeah, looks like it ;-)
2009 Nov 09 01:53:09  <inimino> alright, 4.16?
2009 Nov 09 01:53:36  <aamar> interesting, long post about busy beaver numbers which makes use of this result on aaronson's blog
2009 Nov 09 01:53:41  <aamar> http://www.scottaaronson.com/writings/bignumbers.html
2009 Nov 09 01:53:44  <aamar> yes,
2009 Nov 09 01:53:45  <inimino> oh?
2009 Nov 09 01:54:07  <inimino> heh
2009 Nov 09 01:54:28  <aamar> Yeah, I had not previously heard about this busy beaver sequence, and found it very interesting.
2009 Nov 09 01:54:35  <aamar> But let's go to 4.165
2009 Nov 09 01:54:37  <aamar> 4.16
2009 Nov 09 01:54:38  <aamar> http://github.com/aalearn/aalearn-sicp/blob/master/ch4-outline.scm#L335-373
2009 Nov 09 01:55:26  <inimino> ah, yeah, ok
2009 Nov 09 01:55:32  -*- inimino snaps back to attention ;)
2009 Nov 09 01:55:48  <inimino> http://inimino.org/~inimino/projects/2009/SICP/chap_4/4.16
2009 Nov 09 01:56:33  <aamar> hm, very different answers
2009 Nov 09 01:56:56  <inimino> ah, yeah, yours is correct
2009 Nov 09 01:57:22  <inimino> I will do this one again for next time (and finish b and c properly)
2009 Nov 09 01:57:40  <aamar> ok
2009 Nov 09 01:57:49  <aamar> should we do 4.17?
2009 Nov 09 01:57:59  <aamar> I skimped some on this one
2009 Nov 09 01:58:33  <inimino> yeah, I ended this one in mid-sentence I'm afraid
2009 Nov 09 01:59:12  <inimino> http://inimino.org/~inimino/projects/2009/SICP/chap_4/4.17
2009 Nov 09 01:59:31  <inimino> and I'm still not quite sure that where I was going with that sentence even made a lot of sense
2009 Nov 09 02:01:04  <aamar> It might have ended up where I ended up.  Mine ends with a period, but I'm not sure it's complete thought.
2009 Nov 09 02:01:21  <inimino> but yeah, I think we were heading to the same place there
2009 Nov 09 02:01:52  <aamar> 4.17 to 4.20 all took a lot of hard thinking and were not very satisfying.
2009 Nov 09 02:01:56  <inimino> I didn't feel that I quite had a solid grasp of what the consequences of all of this are
2009 Nov 09 02:02:34  <inimino> heh, I was actually hoping the coming exercises would clear things up but perhaps not
2009 Nov 09 02:02:52  <aamar> 4.21 was a good one, and helpful
2009 Nov 09 02:03:04  <aamar> 4.22 was difficult and I'm not sure I got it right.
2009 Nov 09 02:03:26  <aamar> In order to 4.24, which is a performance test, it actually wants us to get all of the code from the book evaluated.
2009 Nov 09 02:03:29  <aamar> Which I didn't do.
2009 Nov 09 02:03:41  <inimino> ah
2009 Nov 09 02:03:55  <inimino> by the way: http://mitpress.mit.edu/sicp/code/index.html
2009 Nov 09 02:04:06  <aamar> handy!
2009 Nov 09 02:04:08  <inimino> complete code from the book, I found that last week
2009 Nov 09 02:04:11  <inimino> yeah
2009 Nov 09 02:04:37  <inimino> haven't tested any of it, but it may help
2009 Nov 09 02:04:52  <inimino> I suspect some of the stuff coming up I may be more likely to want to actually try and run
2009 Nov 09 02:06:04  <inimino> 4.21 looks quite cool
2009 Nov 09 02:07:08  <aamar> where should we pick up for next time?
2009 Nov 09 02:07:17  <inimino> good question
2009 Nov 09 02:08:36  <inimino> 4.18 through something in the middle of 4.2?
2009 Nov 09 02:08:45  <aamar> sounds good
2009 Nov 09 02:09:03  <aamar> 4.26 is the end of 4.2.1
2009 Nov 09 02:09:23  <aamar> 4.2.2 gets us to 4.31
2009 Nov 09 02:09:27  <aamar> 4.3.1 I mean
2009 Nov 09 02:09:43  <aamar> n/m got it right the first time
2009 Nov 09 02:09:59  <aamar> 4.34 is the last exercise in 4.2
2009 Nov 09 02:10:14  <aamar> I think getting all the way through 4.34 might be challenging.
2009 Nov 09 02:10:21  <inimino> hm, maybe 4.31 or 4.34?
2009 Nov 09 02:10:33  <inimino> hm, it does look like a lot of text
2009 Nov 09 02:10:42  <aamar> much shorter than 4.1 though
2009 Nov 09 02:10:58  <aamar> I think we can make it to 4.34, actually
2009 Nov 09 02:11:15  <inimino> or rather a lot of code
2009 Nov 09 02:11:27  <inimino> yeah, I think we can do taht
2009 Nov 09 02:11:40  <aamar> ok
2009 Nov 09 02:11:41  -*- inimino will make an effort to make more time this time around
2009 Nov 09 02:13:06  <inimino> alright, see you in two weeks, then, and should we meet at 0100 UTC again next time?
2009 Nov 09 02:14:48  <aamar> yes, sounds great
2009 Nov 09 02:14:58  <inimino> ok, see you then