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14:53 RacketCommitBot: [racket] plt pushed 1 new commit to master: http://git.io/DQdRMA
14:53 RacketCommitBot: [racket/master] Fixing PR 12690 - Jay McCarthy
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15:22 RacketCommitBot: [racket] plt pushed 5 new commits to master: http://git.io/y50kMg
15:22 RacketCommitBot: [racket/master] [Distributed Places] Merge place and connection - Kevin Tew
15:22 RacketCommitBot: [racket/master] [Distributed Places] fully connected network patch - Kevin Tew
15:22 RacketCommitBot: [racket/master] [Distributed Places] add solo connections and tcp-connection-died handler - Kevin Tew
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15:42 maahes: doing htdp, what's a better way to write the area of an open pipe other than (define (area_of_pipe inner outer length) (+ (+ (+ (* 2 (* pi (* inner length) etc.?
15:43 maahes: oh, define a function for the inner and outer surface area
15:43 maahes: nvm
15:43 chrissbx: Hi. What are the changes between srfi-42 and what racket uses? Is there a comparison somewhere, or can the diffs be found in the Git repo?
15:44 chrissbx: (For the iterations and comprehensions.)
15:45 maahes: the htdp program specifies a rather terrible way of writing that problem (consuming only inner, outer, and length)
15:47 jonrafkind: chrissbx, do you need to use srfi-42? otherwise you can use the for stuff
15:47 chrissbx: Yes, I've got code that uses for, and I want to port it to a Scheme system with srfi-42
15:48 chrissbx: so I need to know what macros to write for the adaption.
15:49 chrissbx: maahes: What are your (+ (+ (+ are doing there? I'm not sure what your question is.
15:50 chrissbx: Well, porting racket's implementation of for etc. would work, too.
15:50 jonrafkind: racket's for uses a lot of macro stuff that might be hard to port
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15:59 maahes: chris: the problem in the book says: define a function for producing the area of a pipe (open cylinder) it consumes 3 variables: Its inner radius, length, and thickness of it's wall. that would be (+ (+ (+ (* 2 ( * pi (* inner_radius length))) (* 2 (* pi (* outer_radius length))) (* 2 (- (* pi (* outer_radius outer_radius)) (* pi (* inner_radius inner_radius)))))))
16:00 maahes: which is a terrible way of writing that program.
16:01 bremner: can't + and * take multiple arguments? or is that restricted in student languages?
16:02 bremner: but yeah, it looks like 'let' could help
16:03 maahes: let hasn't been introduced yet, I'm just defining separate functions which feeds to a final area_of_pipe function
16:03 bremner: ok
16:12 maahes: hrrm, is there a way to make it infer for the function, that if I do: (inner_radius 5) (outer_radius 5) (length 5) (area_of_pipe) -> output for area of pipe?
16:13 Haffe: That would be constraint propagation.
16:13 Haffe: And message passing.
16:13 Haffe: But I don't think you have covered that yet.
16:13 maahes: ah, not there yet then.
16:14 Haffe: I guess you could curry it.
16:15 Haffe: Three nested lambdas.
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16:37 maahes: is normal lisp like this? (define (somevar arg1 arg2 arg3) (/ (arg1 + arg2) arg3))) such that you get different outputs if you do (define (somevar arg3 arg1 arg2) (/ (arg1+arg2) arg3))) ?
16:38 jonrafkind: what is arg1+arg2
16:38 maahes: variable names.
16:38 jonrafkind: arg1+arg2 is not bound to anything
16:38 jonrafkind: so you should get an error
16:39 maahes: i.e., it doesn't matter what the are, the body of the statement remains the same.
16:39 maahes: the only thing that has changed is the order of the variables in the definition.
16:39 jonrafkind: ah right, well yes then thats a different function
16:39 jonrafkind: since order of arguments matter
16:40 jonrafkind: of course you meant (+ arg1 arg2) but thats probably just a typo
16:40 jonrafkind: if you want your function to be independant of argument ordering you can use keywords, (define (somevar #:arg1 arg1 #:arg2 arg2 #:arg3 arg3) ...)
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16:42 maahes: ah! indeed, that's what I *would* want, but can you help me understand why the order matters? I don't know what the lisp is inferring from the order. (I.e., I think about the statements, not the order of my function variables in their definition)
16:42 jonrafkind: order matters because there needs to be some protocol between a function definition and its use
16:43 jonrafkind: the most traditional protocol is just a sequence of values
16:43 jonrafkind: an insane protocol could be alphabetical
16:43 jonrafkind: but the two protocols that exist today are order and keyword based
16:44 jonrafkind: in terms of your function it doesn't actually matter what order you choose, but if you choose one ordering then changing the ordering will mean clients of the function must also change
16:44 jonrafkind: so (lambda (x y) ...) is not the same as (lambda (y x) ...) even if their bodies are the same
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16:47 gciolli: maahes: you might read about alpha-equivalence in lambda calculus
16:49 maahes: thanks :)
16:52 gciolli: :)
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17:00 maahes: okay, wait, I have a followup question then what would be the correct values? or rather how would you be able to determine if (define (somevar foo bar baz) (/ (+ foo bar) baz)) produces the correct value, and (define (somevar baz bar foo) (/ (+ foo bar) baz)) does not?
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17:06 maahes: ah! I understand now
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17:08 maahes: it's the values of the function (somevar foo bar baz) -> (somevar 3 2 1) being different from (somevar baz bar foo) (somevar 3 2 1)
17:08 maahes: I forgot that portion from the last time I opened the book, heh
17:11 maahes: hrrm, okay, why would lisp *prefer* doing things that way vs using keywords?
17:12 jonrafkind: because its simpler
17:12 jonrafkind: and pretty much every language ever uses that way
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17:38 asumu: maahes: C, Java, etc. all have arguments whose order is significant.
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18:01 maahes: yeah, I see what my confusion was, I was holding the values in my head.
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18:25 jonrafkind: how do you get a < to show up in scribble
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18:28 samth: jonrafkind: you write a literal <
18:28 samth: it's not a special character
18:28 jonrafkind: somehow its not showing up
18:28 jonrafkind: inside a verbatim
18:29 samth: jonrafkind: are you generating html?
18:29 samth: or latex?
18:29 jonrafkind: latex
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18:38 samth: weird
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18:51 bobajett: howdy folks, Im trying to work my way through htdp, but Im using racket in emacs - how can I use the DrRacket teachpacks from within my racket shell in emacs?
18:52 bobajett: Im on chapter 6 and trying to figure out how to get the "make-posn" function available to me
18:53 samth: bobajett: you need to use the beginning student language
18:54 samth: which is not fully supported in emacs
18:54 samth: i encourage you to (a) use drracket
18:54 samth: and (b) take a look at htdp 2nd edition
18:55 samth: which is here: http://www.ccs.neu.edu/home/matthias/HtDP2e/
18:55 bobajett: oh ok, thanks samth - oh wow I didn't know about the 2nd ed
18:55 samth: bobajett: the 2nd ed uses a lot of graphics, which will work much better in drracket
18:55 samth: note that 2e isn't complete yet
18:56 samth: so you'll want to start with that
18:56 bobajett: Awesome! Thanks so much!
18:56 samth: and then transition back to the 1st ed when it runs out
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19:00 bobajett: I just ordered the hardcover dead tree version today of the 1st version :(
19:01 samth: it's a great book
19:01 samth: you won't regret it
19:02 bobajett: :-) I read a great review of it by some PhD student who said it enlightened him even after having programmed for so many years, and that its a book to re-read every 5 years.
19:04 samth: bobajett: i've gotten a phd (from the author of htdp), and taught htdp to undergrads many times, and it's still worth re-reading for me
19:05 bobajett: :) that's awesome to hear. I guess it will be a valuable addition to my bookshelf then.
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19:57 kvda: Hi, I'm a graphic designer learning Scheme/Racket, I'm looking to contributing to the visual part of Racket, (site/docs).. are you looking for help in these areas?
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20:06 rapacity: kvda: try asking on the mailing list
20:07 kvda: Ok, thanks rapacity
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20:47 asumu: kvda: I think that would be great.
20:48 asumu: kvda: Just don't be discouraged if it becomes a bikeshedding argument. It would be great if a we had a designer around to just make decisions. :)
20:50 asumu: bobajett: another anecdote. Today I wrote part of a solution set for students. I followed the design recipe, wrote a bunch of tests, and it passed them all first try.
20:50 asumu: (it is a good feeling)
20:50 kvda: asumu: Do you know who's taking care of the design at the moment?
20:51 asumu: kvda: depends on which aspect of design you mean. I believe eli is mostly responsible for the website.
20:51 asumu: Neil Toronto has been working on some icons and logo stuff, I think.
20:52 asumu: I'm not sure about other things.
20:52 kvda: That's a good start, thanks asumu
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20:59 bobajett: asumu: nice!
20:59 bobajett: 
21:03 maahes: what's the proper way to do something like this (define (interest-paid amount) (- (* amount pay-back-rate) payback-rate))? Since it complains about payback-rate expecting a function call.
21:03 maahes: or rather (- (amount pay-back-rate) pay-back-rate)
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21:04 maahes: (also why does it error for (* amount pay-back-rate) but not (amount pay-back-rate)?
21:06 bobajett: is amount a function?
21:08 maahes: no, amount is a value
21:08 maahes: well, er, its a function argument
21:09 maahes: i.e., I'd do (interest-paid 100) or whatnot
21:09 bobajett: that function compiles and runs for me? But I had to define pay-back-rate first
21:09 bobajett: (define pay-back-rate 0.5)
21:09 bobajett: (define (interest-paid amount)
21:09 bobajett: (- (* amount pay-back-rate) pay-back-rate))
21:09 bobajett: > (interest-paid 100)
21:09 bobajett: 49.5
21:13 maahes: I think it's a beginning student language issue
21:14 bobajett: :)
21:14 asumu: maahes: how are you defining pay-back-rate?
21:16 maahes: asumu: I'm not done writing that function actually, so I'll use the previous one as an example (which is built up in the same fashion) http://pastie.org/3759142
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21:20 bobajett: maahes: when you write (* grosspay hours), "*" is expecting two numbers as arguments, but grosspay is not a number, its a function.
21:20 maahes: ah, gotcha
21:22 bobajett: if you did want to multiply the result from grosspay hours with another number, you would write (* (grosspay hours) 123), this way (grosspay hours) would get evaluated as a function, return some number (Im assuming the grosspay function returns some number) and multiply it with 123.
21:22 maahes: makes sense, thanks :)
21:22 bobajett: you're welcome
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22:21 bobajett: wow htdp2 is a whole lot of fun, even better than "The Land of Lisp"!
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