2009 Sep 28 00:03:12  <inimino> hey aamar, you around?
2009 Sep 28 00:04:30  <aamar> hey inimino
2009 Sep 28 00:04:37  <inimino> hey
2009 Sep 28 00:05:13  <aamar> how's it going?
2009 Sep 28 00:05:23  <inimino> good
2009 Sep 28 00:06:28  <inimino> had a busy couple weeks and didn't get very far in SICP though
2009 Sep 28 00:06:47  <aamar> how did SICP go since last time?
2009 Sep 28 00:07:12  <aamar> busy with work?
2009 Sep 28 00:07:19  <aamar> do you have a startup?
2009 Sep 28 00:07:33  <inimino> work, yeah
2009 Sep 28 00:07:50  <inimino> just freelance stuff, not a startup
2009 Sep 28 00:09:30  <inimino> I am up to 3.77, did you finish the whole chapter?
2009 Sep 28 00:10:11  <aamar> I got to the last one
2009 Sep 28 00:10:16  <aamar> Didn't finish that one.
2009 Sep 28 00:10:22  <inimino> ok
2009 Sep 28 00:10:26  <aamar> 3.81 was unexpectedly hard
2009 Sep 28 00:11:12  <inimino> ah
2009 Sep 28 00:12:32  <aamar> should we start?
2009 Sep 28 00:12:40  <inimino> sure
2009 Sep 28 00:12:41  <aamar> 3.71 ?
2009 Sep 28 00:12:54  <inimino> ok
2009 Sep 28 00:13:14  <aamar> http://github.com/aalearn/aalearn-sicp/blob/master/ch3-outline.scm#L1355-1379
2009 Sep 28 00:13:25  <inimino> http://inimino.org/~inimino/projects/2009/SICP/chap_3/3.71
2009 Sep 28 00:16:37  <aamar> hadn't seen "let*" before -- handy
2009 Sep 28 00:17:09  <inimino> I've been trying to use only things given in the text
2009 Sep 28 00:17:16  <inimino> but I was lazy in that case :)
2009 Sep 28 00:18:03  <inimino> it could be rewritten as nested lets
2009 Sep 28 00:18:18  <inimino> so, different approaches
2009 Sep 28 00:18:40  <inimino> I think using dupes is a more abstract, composable approach
2009 Sep 28 00:19:22  <aamar> roughly corresponds to weight-equal
2009 Sep 28 00:19:26  <inimino> I wanted to have the pairs in the output though
2009 Sep 28 00:19:36  <inimino> yeah, similar
2009 Sep 28 00:19:48  <aamar> I think dupes is handy if we just want to return the weights, rather than the pairs
2009 Sep 28 00:19:52  <aamar> right
2009 Sep 28 00:20:21  <inimino> yeah
2009 Sep 28 00:20:36  <inimino> weight-equal came out a bit ungainly and I wasn't really satisfied with it
2009 Sep 28 00:20:54  <inimino> but we did get the same numbers :)
2009 Sep 28 00:21:05  <aamar> ok, I find them conceptually similar as well
2009 Sep 28 00:21:08  <aamar> okay, next one?
2009 Sep 28 00:21:11  <inimino> sure
2009 Sep 28 00:21:22  <inimino> http://inimino.org/~inimino/projects/2009/SICP/chap_3/3.72
2009 Sep 28 00:21:38  <aamar> http://github.com/aalearn/aalearn-sicp/blob/master/ch3-outline.scm#L1381-1400
2009 Sep 28 00:22:58  <aamar> you solved, numbers which can be written as the sum of two cubes in 3 different ways
2009 Sep 28 00:23:07  <aamar> instead of numbers that are the sum of two squares
2009 Sep 28 00:23:49  -*- inimino re-reads the problem
2009 Sep 28 00:24:02  <inimino> oh
2009 Sep 28 00:24:05  <inimino> heh
2009 Sep 28 00:24:31  <inimino> you're right
2009 Sep 28 00:24:39  <inimino> that explains why the numbers are different
2009 Sep 28 00:24:56  <inimino> (and why this took some time to run)
2009 Sep 28 00:26:11  <inimino> alright, your solution looks correct
2009 Sep 28 00:26:15  <aamar> I was about to ask why you only compute third-pair / third-weight after doing the first test...
2009 Sep 28 00:26:24  <aamar> But I imagine that is for performance reasons
2009 Sep 28 00:26:29  <inimino> yes
2009 Sep 28 00:26:56  <aamar> ok
2009 Sep 28 00:27:10  <aamar> changing the cube-sums to cube-squares, I think yours will work too
2009 Sep 28 00:27:21  <inimino> I think the exercise I solved turned out to be much more interesting, but it's not what the book asked for ;)
2009 Sep 28 00:27:22  <aamar> I mean square-sum !
2009 Sep 28 00:27:38  <inimino> yeah, agreed
2009 Sep 28 00:27:42  <inimino> ok, next one?
2009 Sep 28 00:28:09  <inimino> erm, I actually skipped 3.73
2009 Sep 28 00:28:09  <aamar> ok
2009 Sep 28 00:28:10  <aamar> http://github.com/aalearn/aalearn-sicp/blob/master/ch3-outline.scm#L1401-1411
2009 Sep 28 00:28:14  <aamar> ok
2009 Sep 28 00:28:24  <inimino> it looked kind of straightforward
2009 Sep 28 00:28:35  <aamar> this one took a lot of time too
2009 Sep 28 00:28:54  <inimino> I was confused by the diagram
2009 Sep 28 00:29:07  <inimino> I may come back and fill it in
2009 Sep 28 00:29:16  <aamar> let's go to 3.74
2009 Sep 28 00:29:21  <inimino> ok
2009 Sep 28 00:29:28  <aamar> http://github.com/aalearn/aalearn-sicp/blob/master/ch3-outline.scm#L1413-1439
2009 Sep 28 00:29:36  <inimino> http://inimino.org/~inimino/projects/2009/SICP/chap_3/3.74
2009 Sep 28 00:30:24  <aamar> slightly different answers
2009 Sep 28 00:30:47  <inimino> yeah, I had yours originally and changed it
2009 Sep 28 00:30:57  <aamar> same, I had yours and changed it
2009 Sep 28 00:31:01  <aamar> :)
2009 Sep 28 00:31:02  <inimino> hehe
2009 Sep 28 00:31:03  <aamar> as best as I can tell -- sign-change-detector expects arguments in the nonintuitive order
2009 Sep 28 00:31:09  <aamar> (sign-change-detector new old)
2009 Sep 28 00:31:33  <inimino> ok
2009 Sep 28 00:31:56  <aamar> hm...
2009 Sep 28 00:32:12  <inimino> I guess there are four ways you could write this
2009 Sep 28 00:32:26  <aamar> really?
2009 Sep 28 00:32:54  <inimino> based on the permutations of argument order in sign-change-detector, and of whether you start the output stream 'one ahead' or 'one behind'
2009 Sep 28 00:33:06  <aamar> right
2009 Sep 28 00:33:23  <inimino> probably doesn't matter much in practice
2009 Sep 28 00:33:28  <aamar> well, only 2 combinations will give you the same result as "Alyssa"'s version
2009 Sep 28 00:33:46  <aamar> the other two will give you the wrong zero crossing values
2009 Sep 28 00:34:09  <inimino> ah, true
2009 Sep 28 00:34:42  <aamar> since sign-change-detector (in the book) appears to accept arguments in the new old order,
2009 Sep 28 00:35:01  <aamar> you want to pass it into stream-map as follows:
2009 Sep 28 00:35:18  <aamar> (stream-map detector (item-n+1) (item-n))
2009 Sep 28 00:35:35  <inimino> yes I think you are right
2009 Sep 28 00:35:38  <aamar> that means that the first of the two streams should be one further ahead of the second
2009 Sep 28 00:35:46  <aamar> which means that the second stream should start later.
2009 Sep 28 00:36:12  <aamar> ok
2009 Sep 28 00:36:26  <lmr> are any of the people doing this group learning session learning scheme as a first language
2009 Sep 28 00:36:27  <inimino> yeah, I think yours is correct
2009 Sep 28 00:36:52  <inimino> lmr: I don't think so, in this group
2009 Sep 28 00:36:59  <aamar> lmr: no, not my first language
2009 Sep 28 00:37:08  <aamar> not even my first programming language
2009 Sep 28 00:37:14  <inimino> haha
2009 Sep 28 00:37:32  <lmr> hmm.
2009 Sep 28 00:37:36  <lmr> ok.
2009 Sep 28 00:37:41  <aamar> 3.75 ?
2009 Sep 28 00:37:44  <inimino> sure
2009 Sep 28 00:37:51  <aamar> http://github.com/aalearn/aalearn-sicp/blob/master/ch3-outline.scm#L1442-1452
2009 Sep 28 00:37:56  <inimino> http://inimino.org/~inimino/projects/2009/SICP/chap_3/3.75
2009 Sep 28 00:38:11  <lmr> rofl.
2009 Sep 28 00:38:23  <lmr> brb food.
2009 Sep 28 00:38:50  <inimino> I think that's just about character-for-character the same
2009 Sep 28 00:39:02  <aamar> yep, except for the argument order on sign-change-detector
2009 Sep 28 00:39:06  <aamar> otherwise exact match
2009 Sep 28 00:39:12  <aamar> cool
2009 Sep 28 00:39:38  <inimino> oh, right
2009 Sep 28 00:39:45  <inimino> ok, 3.76?
2009 Sep 28 00:40:13  <aamar> yes
2009 Sep 28 00:40:21  <aamar> http://github.com/aalearn/aalearn-sicp/blob/master/ch3-outline.scm#L1453-1461
2009 Sep 28 00:40:55  <inimino> http://inimino.org/~inimino/projects/2009/SICP/chap_3/3.76
2009 Sep 28 00:41:45  <inimino> hm, typo in mine
2009 Sep 28 00:42:05  <inimino> should be s/smooth/smoothed in two places
2009 Sep 28 00:42:39  <inimino> also argument order, again :)
2009 Sep 28 00:43:03  <aamar> ah, I missed that part of the question
2009 Sep 28 00:43:34  <aamar> yours looks right, with that change
2009 Sep 28 00:43:52  <inimino> ok
2009 Sep 28 00:44:02  <inimino> yours looks right also
2009 Sep 28 00:44:05  <inimino> next one?
2009 Sep 28 00:44:26  <aamar> http://github.com/aalearn/aalearn-sicp/blob/master/ch3-outline.scm#L1463-1490
2009 Sep 28 00:44:29  <inimino> http://inimino.org/~inimino/projects/2009/SICP/chap_3/3.77
2009 Sep 28 00:44:40  <inimino> ah, this one seemed quite obvious, unless I missed some subtlety
2009 Sep 28 00:45:43  <aamar> there is a subtlety, though it's not a very interesting one
2009 Sep 28 00:46:01  <aamar> I think you have to delay the first argument to the recursive call to integral
2009 Sep 28 00:46:07  <inimino> oh, delay
2009 Sep 28 00:46:35  <inimino> I guess you could just use cdr instead of stream-cdr there
2009 Sep 28 00:46:52  <inimino> since the cdr of a stream is already a promise
2009 Sep 28 00:47:01  <aamar> yes, without that it gives ;Aborting!: maximum recursion depth exceeded
2009 Sep 28 00:47:20  <aamar> oh, interesting
2009 Sep 28 00:49:11  <inimino> well, that's as far as I got
2009 Sep 28 00:49:23  <aamar> ok
2009 Sep 28 00:49:42  <aamar> I only did a few more... pick up here next time?
2009 Sep 28 00:50:03  <inimino> yeah, I kind of want to review the rest of these
2009 Sep 28 00:50:43  <inimino> this was a long chapter :)
2009 Sep 28 00:50:51  <aamar> ok -- through 4.1 ?
2009 Sep 28 00:51:02  <aamar> yep
2009 Sep 28 00:51:09  <inimino> yeah, have you looked ahead?
2009 Sep 28 00:51:12  <aamar> lots of reading in the first part of Ch. 4
2009 Sep 28 00:51:21  <aamar> just looked ahead for a minute
2009 Sep 28 00:51:37  <aamar> 4.1.1 only has one exercise
2009 Sep 28 00:51:45  <aamar> but a lot of reading
2009 Sep 28 00:51:51  <aamar> 4.1.2 goes through 4.10
2009 Sep 28 00:52:11  <aamar> (exercise 4.10, that is)
2009 Sep 28 00:52:28  <aamar> And those look substantial, basically re-implementing lots of scheme in scheme
2009 Sep 28 00:52:30  <inimino> I see
2009 Sep 28 00:52:32  <inimino> yeah
2009 Sep 28 00:52:45  <inimino> maybe just through 4.1.1?
2009 Sep 28 00:53:12  <aamar> agreed
2009 Sep 28 00:53:16  <inimino> ok, cool
2009 Sep 28 00:53:25  <inimino> see you in a couple weeks then :)
2009 Sep 28 00:53:57  <aamar> cool, see you then
2009 Sep 28 01:07:14  <lmr> so there's only the two of you?
2009 Sep 28 01:08:08  <inimino> lmr: by now, yes, unless mariorz catches back up
2009 Sep 28 01:08:36  <inimino> haven't seen him since three or four meetings ago though
2009 Sep 28 01:09:16  <inimino> all the others dropped off even earlier :)
2009 Sep 28 01:10:57  <lmr> hmm.
2009 Sep 28 01:11:20  <lmr> hehe.
2009 Sep 28 01:11:47  <inimino> yeah, it's a pity
2009 Sep 28 01:12:25  <inimino> I would say, do /lots/ of recruitment before you start, because you won't be picking up new people on the way and there will be a lot of attrition
2009 Sep 28 01:14:51  <lmr> yeah, only problem I have is the math in chapters 3/4.
2009 Sep 28 01:15:21  <lmr> But, well I'm in chapter one still so I have a while.
2009 Sep 28 01:15:31  <inimino> there's very little math
2009 Sep 28 01:15:52  <inimino> algebra will get you through, I'd say, pretty much all the exercises
2009 Sep 28 01:16:36  <inimino> some of them touch on calculus but only in passing, so far anyway
2009 Sep 28 01:17:05  <lmr> oh ok
2009 Sep 28 01:17:53  <inimino> there's actually a lot of math, what I meant to say is that there is no advanced math
2009 Sep 28 01:20:22  <lmr> hehe
2009 Sep 28 01:20:32  <lmr> ;\