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00:22 Phil: Hi - I have a question on how to write an integer division function in scheme. Can anyone look at my function and help me out?
00:22 jonrafkind: sure
00:22 jonrafkind: you know one exists though, right?
00:22 Phil: Yeah
00:23 Phil: It's a homework assignment and I just have a question about it.
00:23 Phil: http://www.heypasteit.com/clip/PFT
00:23 jonrafkind: ok
00:23 Phil: We are supposed to return a list with the remainder in it
00:23 Phil: (quotient_of_x/y remainder_of_x/y)
00:23 Phil: And I don't understand how to increment the quotient as I go down while keeping the remainder as I recurse up
00:23 Phil: Does that make sense?
00:24 jonrafkind: hm
00:25 Phil: Right now, its just returning the remainder
00:25 Phil: obviously
00:25 Phil: I've also got it to return only the quotient
00:25 Phil: But I can't get it to do both....
00:25 jonrafkind: you could use a third argument for the quotient
00:26 jonrafkind: right now you just have x and y
00:26 Phil: We aren't allowed to for the assignment. Otherwise that would work...
00:27 Phil: Here are the specs...
00:27 Phil: http://www.heypasteit.com/clip/PFU
00:28 askhader: `
00:29 jonrafkind: '
00:30 Phil: So its stumped you too jonrafkind?
00:31 askhader: (define (div) (lambda (x y) `((/ x y) (modulo x y))))
00:31 askhader: I think that, or something like that should do the trick.
00:31 Phil: I have to use the minus function otherwise I'd just use / and remainder
00:31 askhader: Oh\
00:31 askhader: Of course
00:32 Phil: Its cool though. Thanks for giving it a look!
00:32 askhader: What language level do you have?
00:32 askhader: I can whip it up for you if you like.
00:32 Phil: Whip what up for me?
00:32 askhader: I really shouldn't since it's an assignment, but I'll take any opportunity to write a scheme function.
00:32 askhader: div according to the specification..
00:32 Phil: It's Advanced Student
00:33 askhader: Okay, momento
00:33 Phil: I'd be immensely greatful - I've done the rest of the assignment GCD, trees, etc.
00:33 askhader: CS studnet?
00:33 askhader: student, even
00:34 askhader: hush now
00:34 askhader fires up drracket
00:36 Phil: Yup. It's Discrete Structures. The whole class seems to be focused on Sets, Grammars, and data structures like that. But none of it actually describes implementation. It's all very theoretical and it makes it a real challenge when the programming assignments come up.
00:37 askhader: (div x y) is x >= y ?
00:37 askhader: Phil: ^
00:37 Phil: yes
00:37 askhader: Goodie gumdrops.
00:37 Phil: Let me send the specs
00:38 Phil: http://www.heypasteit.com/clip/PFV
00:41 Phil: The other solution would be to recurse twice which works... But it crashed when I started using bigger numbers.
00:41 Phil: Plus its obviously ineffecient
00:49 askhader: Phil: ping
00:49 Phil: What's up?
00:50 askhader: (define div
00:50 askhader: (lambda (x y)
00:50 askhader: (letrec ((recDiv (lambda (a b count)
00:50 askhader: (cond ((< a b) (list count a))
00:50 askhader: ((= a b) (list (add1 count) 0))
00:50 askhader: (true (recDiv (- a b) b (add1 count)))))))
00:50 askhader: (recDiv x y 0))))
00:50 askhader: gah
00:50 askhader: Terribly sorry!
00:51 askhader: http://paste.lisp.org/display/116755
00:51 askhader: Stupid cygwin
00:51 Phil: Thanks a lot!
00:51 askhader: My pleasure
00:51 askhader: Do you understand how it works?
00:52 Phil: Kinda... You've got two functions.
00:52 Phil: One that recieves the x and y
00:52 Phil: That calls the second function which takes x y and count
00:52 askhader: You are familiar with lambda?
00:53 Phil: Just in the sense that I'm supposed to put it in all my functions. What is its actual purpose?
00:53 askhader: Let me demonstrate it in code
00:53 askhader: One moment.
00:53 Phil: I'll pull up the docs too haha
00:54 askhader: lambda is an anonymous function for which you can define an arbitrary number of paramaters.
00:55 askhader: (define (addOne x) (+ x 1))    (define addOne (lambda (x) (+ x 1))
00:55 askhader: lambda becomes convenient when you want to define a function that exists purely within the scope of another function. As in recDiv
00:58 Phil: I'm reading up on it now! Thanks a lot!
00:58 askhader: My pleasure. Happy racketeering and scheming!
00:58 Phil: Racketeering :). I forgot about that.
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13:54 thewolf: hi
13:55 thewolf: how can i combine 2 lists and save them in another?
13:55 thewolf: (append list1 list2) only does it "temporarily"
13:55 thewolf: i want something like list1 = (append list1 list2)
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14:32 Kirill: hi! does Racket support parallel execution of map & co?
14:32 Kirill: is there some special version of map, filter, and so on, that would run the computation in parallel?
14:39 jonrafkind: you could probably use futures with map
14:39 jonrafkind: i dont know how expensive it is to create a future though
14:39 carleastlund: Kirill, Racket's support for parallelism is currently experimental, and not built in to any of our primitives yet.
14:39 jonrafkind: and it would only be parallel if you happen not to call back into the racket vm
14:40 carleastlund: We have two mechanisms: "futures" and "places"; for the fine-grained parallelism you're talking about, you'd want futures.  And like jonrafkind says, they may not get you what you're looking for, as they don't behave quite like parallelism in other langauges.
14:50 Kirill: I guess I could write it myself using a thread pool or something..
14:50 Kirill: does racket have thread pools? =)
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14:56 jonrafkind: it has green threads, places are native threads
14:56 jonrafkind: try using futures, if it doenst work then you can try something else
14:56 Kirill: sure
14:56 Kirill: So I'll have to write my own "map" function that will use future/touch?
14:58 jonrafkind: yea
14:59 clklein: Kirill: Be sure to read this section of the docs: http://docs.racket-lang.org/guide/performance.html?q=futures#%28part._effective-futures%29
14:59 rudybot: http://tinyurl.com/23fczbw
14:59 Kirill: reading it now =)
15:00 Kirill: so for example, if each operation requires spawning a subprocess, then it's "not safe for parallelism"?
15:01 jonrafkind: yea
15:01 jonrafkind: you can use communicating processes through pipes, if you don;t have to share any data
15:02 Kirill: Yeah there's no data sharing between the subprocesses
15:02 Kirill: so spawning a subprocess in a thunk that's given to "future" is a bad idea, correct?
15:02 Kirill: I think the best approach in this case is to use "thread" and manage a thread pool somehow
15:03 jonrafkind: yea but they will only execute on one processor
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15:03 jonrafkind: so you will get concurrency but not parallelism
15:03 jonrafkind: futures potentially give you parallelism
15:03 Kirill: jonrafkind: why? racket threads are "green threads"?
15:03 jonrafkind: meaning they execute in one process
15:04 Kirill: hold on. does racket use native threads?
15:04 jonrafkind: for futures it does
15:04 jonrafkind: green threads are fake threads basically
15:04 jonrafkind: the vm will schedule and manage green threads itself
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15:06 jonrafkind: and places are native threads too
15:08 Kirill: how can I find out what's "safe" parallelism and what isn't? can I spawn a subprocess from a future?
15:11 jonrafkind: well thats a good question, and looking through the docs i dont see a list of operations that are unsafe
15:11 jonrafkind: would you like to send an email to the list requesting a specific list?
15:11 jonrafkind: if not i can do so on your behalf
15:14 Kirill: please, if it's not too much trouble =)
15:15 jonrafkind: ok
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15:20 Kirill: thanks
15:21 Kirill: where can I track the mailing list thread?
15:22 samth: Kirill, the mailing lists are listed here: http://racket-lang.org/community.html
15:22 jonrafkind: http://www.mail-archive.com/users@racket-lang.org/
15:22 jonrafkind: it should show up here very soon
15:22 Kirill: great, bookmarked
15:22 clklein: Kirill: I think you're expected to try (future (lambda () potentially-unsafe-thing)) and run "racket -W" to see the debug info
15:23 clklein: If it's not safe, the debug info will say "future blocked on ..."
15:23 samth: clklein, that's not really a great story, though
15:23 jonrafkind: yea it should be listed in the docs
15:23 clklein: samth: I never claimed it is.
15:23 samth: right
15:24 jonrafkind: tangentially related.. i still hate mailing lists and wish we would move or at least add a forum option too
15:24 jonrafkind: i think someone tried that at one point but it failed for some reason..?
15:24 samth: jonrafkind, get off my lawn!
15:25 clklein: jonrafkind: because they're not convenient for casual users?
15:25 samth: or for heavy users
15:25 clklein: How would a forum be more convenient for heavy users?
15:25 jonrafkind: maling lists? yea there are multiple problems. 1. causal users 2. i have to skip a lot of crap 3. correlated with 2, i am prevented from sending "silly" messages because it would bother other users
15:25 carleastlund: Yeah, I'm not a fan of forums in general.
15:26 clklein: I'd just end up using whatever RSS, email notification, etc. the forum provided to find out about new discussions
15:26 jonrafkind: once I tried subscribing to the linux mailing lists just to see what was going on, but having received something like 400 emails per day I quickly got off
15:26 carleastlund: jonrafkind, if forum usage would prompt you or others to start spamming racket or racket-dev with "silly" messages, then I'm all for mailing lists.  Work mail does not need to be intermingled with joke time, no matter the method of transmission
15:27 jonrafkind: im not saying i would post lolcat pictures, but there are some less serious emails that don't get sent because they have a slightly higher noise to signal ratio than other emails
15:27 jonrafkind: maybe its for the best, but sometimes i find it annoying
15:27 carleastlund: You're complaining about the volume of messages already, but then paradoxically you want to increase it in another medium.
15:28 jonrafkind: another medium where you can ignore the volume
15:28 carleastlund: I guess I don't understand what you're hoping for in a forum.
15:28 carleastlund: Ignoring the volume means ignoring messages.
15:28 jonrafkind: yes but in my email client i have to do some action to ignore messages (yes get a better email client.. not gonna happen)
15:28 jonrafkind: forums streamline the process of ignoring stuff you dont care about
15:29 carleastlund: jonrafkind, if you're not willing to get a new client but you're asking us to entirely switch technologies... pot, kettle, black
15:29 samth: see earlier discussion of your trespass on the property adjacent to my house
15:29 jonrafkind: there are no email clients that work allow the same functionality as forum software, afaik
15:30 samth: jonrafkind, i recommend gmane and a news reader
15:30 clklein: The mailing list needs a "don't send me p% of the traffic" option
15:30 carleastlund: What forum functionality do you want?
15:30 carleastlund: Every time I've used a forum, I wished it wasn't missing features I could use in my email reader.  But perhaps you have used better forums.
15:31 jonrafkind: i like being able to selectively read threads when I feel like instead of messages being pushed to me
15:32 carleastlund: That works for casual things, but racket and racket-dev are places where we PLT folks provide technical assistance with our research products.  Our users don't want us putting off their threads until we feel like it.
15:32 samth: also, racket-dev is a place for the developers to get work done, not just a forum for random people to blather
15:33 jonrafkind: yes because thats what i was saying the entire time. great job
15:33 samth: so which traffic should go into this forum?
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16:03 clklein: tewk: ping
16:04 clklein: Is this record ever enough to track down a crash?
16:05 clklein: http://pastebin.com/35EWrTVy
16:06 clklein: Unfortunately, I have no more information at all. I eval'd a random program involving delimited continuations, continuation marks, and dynamic-wind.
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16:36 eli: jonrafkind: gmail has an option to "mute" a thread, which makes it silently archive it as it comes in, unless someone directs a message to you.  Sounds close to what you're describing.
16:36 jonrafkind: yea, i wish i had something like that
16:36 eli: Otherwise, i don't see the big conceptual difference between scanning subject lines in your mailbox from and scanning them on a forum page.
16:36 eli: Gmail is free, you know?
16:37 jonrafkind: ive been debating moving to gmail for a while now, but basically its impractical for me
16:37 eli: Two more options:
16:37 jonrafkind: well not entirely impractical, just inconvenient
16:37 eli: You can just use gmail for the plt lists,
16:37 eli: or you can use it via gmane, which will give you a newsgroup interface.
16:37 eli: (Where newsgroup readers are very tuned to being able to ignore threads.)
16:38 jonrafkind: ill keep it in mind
16:38 eli: You're using FF right?
16:39 jonrafkind: chrome
16:39 jonrafkind: i use thunderbird for email
16:39 eli: OK, and thunderbird does newsgroups too, right?
16:40 eli: If so, just point it at nntp://news.gmane.org/gmane.comp.lang.racket.user
16:40 eli: And if/when that works, you can flip a mailman switch to avoid mail delivery to your mailbox, so you can still post, but you don't get the emails pushed to you.
16:47 jonrafkind: hm, seems like thunderbird forces me to click on newsgroup posts to read them, just like normal email
16:49 eli: And forums are somehow clickless?
16:49 jonrafkind: yes, you dont need to click on a topic if you dont want
16:49 jonrafkind: each time a new message appears
16:49 eli: I'm not getting it.
16:50 jonrafkind: i mean, if a message appears in the newsgroup and I hit 'n' to goto the next message thunderbird will direct me to the newsgroup message
16:50 eli: If you don't want to read a topic in a forum, you say that you don't click on it.
16:50 jonrafkind: i can't skip over the message
16:50 eli: What's the difference from the newsreader?
16:50 jonrafkind: what i just said
16:50 jonrafkind: i mean ok, essentially nothing, but the fact that I use 'n' to move between messages is the only difference
16:51 jonrafkind: but moving between messages without using 'n' would make life impossible
16:51 eli: So, things boil down to your use of some specific key in thunderbird?
16:51 jonrafkind: its the only possible way to navigate email
16:51 eli: That doesn't sound like a good reason to switch everyone to a completely different medium.
16:52 eli: My laptop's keyboard has problems with `x'.
16:52 eli: I need to use `x' to read my mail in Emacs.
16:52 eli: Conclusion: I'll suggest disassembling the list and move to phone calls.
16:52 jonrafkind: good job
16:52 jonrafkind: if thats your logic im not gonna even try
16:53 eli: You *did* say that it's due to whatever thunderbird is doing with `n'.
16:53 eli: Another interface you can try is http://blog.gmane.org/gmane.comp.lang.racket.user
16:53 jonrafkind: yes but its about navigating email, not about the 'n' key itself (i dont know if thats what you're trying to imply)
16:54 eli: Or: http://news.gmane.org/gmane.comp.lang.racket.user
16:54 eli: Or one of the four RSS feeds it gives you, with some RSS reader.
16:54 eli: I don't see any conceptual difference between navigating email and navigating a forum.
16:55 eli: It sounds like whatever your complaint is, it's between you and your mailer.
16:55 eli: You can switch that.
16:55 jonrafkind: there are no reasonable alternatives
16:55 eli: Or with the NNTP interface you can use a newsreader.
16:55 jonrafkind: ive been through basically all of them and thunderbird is the best
16:55 eli: Or with the RSS feed you can use an RSS reader.
16:56 eli: Clearly, thunerbird is not the best if it fails on some feature that is so important for you.
16:56 jonrafkind: thats true, but it wins on every other feature thats important
16:56 eli: Make up your own reader then.
16:57 jonrafkind: yea.. ill just write my own os first.. see you in 40 years
16:57 eli: Having all of these alternative forms of the mailing list should make it easy.
16:57 eli: Whatever it is, it's far from being a good reason to switch *everyone*.
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20:17 seeingstars115: Can anyone help me on a homework question
20:17 seeingstars115: ??
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20:20 seeingstars115: Can someone help me on a homework question??
20:21 (part) seeingstars115
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20:24 seeingstars115: HELLO?!?!?!?
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20:28 jonrafkind: seeingstars115, try sitting in the channel for more than 2 seconds
20:28 seeingstars115: ok sorry
20:29 seeingstars115: So my question is: In a small school, the students are divided into homerooms by last name. Students with last names that begin with A-E are in homeroom 1, F-L are in homeroom 2, M-R are in homeroom 3, and S-Z are in homeroom 4. Write the function find-homeroom-number. It takes in a student's last name (as a string) and gives back the student's correct homeroom number.
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21:03 carleastlund: seeingstars115, what is your question about that assignment?
21:06 seeingstars115: It's fine I just figured it out. But thanks anyway
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21:34 maelstorm: is this room for assistance with racket?
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21:52 Quetzalcoatl_: Yes. That's one of the purposes of this room.
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