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00:06 waltermai: I'm calling my own predicate procedure with a symbol pointing to a list as the only argument. inside the predicate procedure, the length of the symbol/list evaluates to 1, but the list has 10 elements. anyone know what's going on?
00:27 waltermai: figured it out. thanks for entertaining me.
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01:28 shkk: Hi All, I am writing a program that takes the radius of circle as argument and returns its area and circumference, as a list
01:28 shkk: Here is my code: (define (area-and-circum radius)   ((cons '(* 3.14 (* radius radius))) ((cons '(* 2 3.14 radius)) '())))
01:28 shkk: Its obviously not working .. But I am not able to understand why
01:32 jonrafkind: type in '(+ 1 2) in the repl
01:32 jonrafkind: what do you get?
01:33 shkk: Oopss .. So how should I pass the value as a list element?
01:33 jonrafkind: now type in (+ 1 2)
01:34 jonrafkind: what do you get
01:34 shkk: its 3 . but its a value ..
01:34 jonrafkind: do you see the difference between '(+ 1 2) and (+ 1 2) ?
01:35 shkk: Yes.. the former creates a string and sends it back .. the latter actually computes the value
01:35 jonrafkind: more or less
01:35 jonrafkind: now do you see where you went wrong?
01:35 jonrafkind: well one part of where you went wrong
01:35 shkk: But actually, I had removed the quotes .. And I still got the error
01:36 shkk: I had initially this as the code: (define (area-and-circum radius)   ((cons (* 3.14 (* radius radius))) ((cons (* 2 3.14 radius)) '())))
01:36 jonrafkind: ok i dont know how to lead you to discovering the problem so ill just tell you: you have too many parenthesis. ((cons ..)) will try to invoke the result of (cons ) as a function
01:37 jonrafkind: you want (cons ...)
01:42 shkk: Got it : (define (area-and-circum radius)   (cons (* 3.14 (* radius radius)) (cons (* 2 2.14 radius) '())))
01:43 shkk: Thank you. Just another query: How do we know for sure when a error is related to parenthesis ?
01:44 jonrafkind: usually it will say something like "expected procedure given blah and blah"
01:45 jonrafkind: one way to reduce parenthesis nesting is to bind results to intermediate variables
01:45 jonrafkind: (let ([area (* 3.14 ...)] [circumference (* 3.14 ...)]) (cons area (cons circumference '())))
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01:46 shkk: Aahhhh yes that should simplify things
01:47 shkk: Thank you jonrafkind
01:47 jonrafkind: np
01:47 shkk: There should be some kind of reward system in this community chat !!
01:48 jonrafkind: you can send me money
01:48 shkk: I would for sure .. Once I start earning :)
01:48 jonrafkind: ok well ill be here
01:49 shkk: Me too ..
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12:47 jonrafkind: isn't there some way to get a field out of a struct instance given just an instance of the struct and a name of a field (like 'a') ?
12:50 Lajla: jonrafkind, name.a
12:50 Lajla: But that's a huge hack.
12:50 Lajla: Ehh instance.a
12:50 jonrafkind: that doesnt mean anything in racket
12:50 Lajla: Is probably a better way of naming it.
12:50 Lajla: That is correct
12:50 Lajla: that is wh y it's a hack.
12:50 jonrafkind: ok how would you implement that?
12:50 Lajla: Basically the interface makes available a variable 'instance.a'
12:51 Lajla: When you make a struct and give it its values, it makes variables like 'instance-name.password'
12:51 Lajla: I'm just saying something.
12:51 Lajla: Which are just variables like anything else.
12:51 Lajla: (struct-ref instance a) would be much eleganterer
12:51 jonrafkind: well ok but even in that case it wouldn't work, you'd have to override all bindings forms that ever existed.
12:51 Lajla: But also much verboserer
12:51 jonrafkind: (define foo (make-foo 1 2 3)), now you want to bind foo.a
12:51 jonrafkind: ok bad example because i used the smae name
12:51 jonrafkind: (define x (make-foo 1 2 3)); x.a
12:52 jonrafkind: x is not in scope when `foo' was defined
12:52 Lajla: jonrafkind, well, the interface does that.
12:52 Lajla: And I stress that it's a huge hack.
12:52 Lajla: I would really rather have structs be functions that take symbols as arguments really.
12:52 jonrafkind: ok well I need a non-hack (or at least less of a hack way)
12:52 Lajla: Like (name 'field)
12:52 Lajla: jonrafkind, make your own macro I guess.
12:52 jonrafkind: yea, but thats pretty slow
12:53 jonrafkind: I can use classes with get-field I guess
12:53 Lajla: jonrafkind, that's also okay.
12:53 Lajla: I should note that I never used structs though, I think I read this at some point
12:53 Lajla: Let's see if I can get the manual.
12:58 Lajla: jonrafkind, the manual is unresponsive to google chrome I fear.
12:58 Lajla: But let's dance to Mathäus Passion in the mean while.
12:58 jonrafkind: worksf or me in chrome
12:58 Lajla does the robot to Mathäus Passion
12:58 Lajla: Damnit, your chrome outchromes my chrome.
13:03 stamourv: jonrafkind: do you know the # of the field, or just the name?
13:04 Lajla: samth, we must continue our immortal debate by the wy.
13:04 Lajla: way*
13:06 jonrafkind: just the name
13:07 stamourv: ok, so unsafe-struct-ref is no help
13:11 Lajla: jonrafkind: http://www.ccs.neu.edu/home/dorai/t-y-scheme/t-y-scheme-Z-H-11.html#node_idx_402
13:11 Lajla: I found it here.
13:11 Lajla: But I'm not a fan of TYS, even though it was my first resource on Scheme.
13:12 jonrafkind: that assumes you know the struct name, thats what im missing
13:12 jonrafkind: all they've done is replace - with .
13:13 Lajla: Ohhh, I read 'and the name and a field ..'
13:13 Lajla: Instead of 'and the name of ..'
13:13 Lajla: Pardon.
13:13 jonrafkind: heh
13:15 Lajla: jonrafkind, maybe you could dive in the macro and see if instances store the name of their struct at some point.
13:23 Lajla: If they don't store it you're basically out of luck I guess, because they store it inside in an array.
13:23 Lajla: The refs themselves just translate a symbol to an array index.
13:23 Lajla: vector*
13:24 jonrafkind: i thought they translated a number to a value stored in the vector
13:26 Lajla: That's what the instances do.
13:26 Lajla: The refs translate the symbol to a number.
13:27 Lajla: You could just use hash tables though.
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13:43 Lajla: emma, maybe you know the answer.
13:43 Lajla: After all, being British means you are omniscient.
13:45 emma: I am not British.
13:45 Lajla: emma, why didn't you tell me?
13:46 Lajla: Were you afraid I'd like you less? Because I'm okay with it.
13:46 Lajla: I accept people for what they are.
13:46 emma: Lajla: Are you mindful that this channel is logged so that all manner of silliness will be recorded and archived for as long as you live?
13:47 Lajla: No God, I must stop at once.
13:47 Lajla: emma, it's not that silly is it?
13:47 Lajla: I'm sure there exists at least one prime time animated comedy show on Fox that uses similar humour as a vihicle to let Americans buy things they don't need thereby ensuring the continued existence of Fox.
13:48 (quit) tov: Quit: tov
13:48 emma: Logging channels just makes me very self conscious.
13:48 Lajla: Hmm, afraid you'll say things you'll regret?
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13:55 samth: jonrafkind, there's no way to do that
13:56 samth: tov, ping
13:56 samth: Lajla, i'm now bored of our debate
13:56 tov: samth: ping
13:56 samth: tov, when will you be around the office?
13:56 tov: i am around the office
13:57 samth: you don't appear to be around the office :)
13:57 samth: more seriously, i hope to have comments for you fairly soon
13:58 tov: thanks.
13:58 Lajla: samth, =(
13:58 Lajla: Let's find another thing to debate then. =(
13:58 Lajla: Like if continatuions are lambda abstractions or if they aren't.
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14:59 hepek: hello
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15:20 Lajla greets hepek by offering her a dead bird.
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15:55 shkk: Hi All, my code for reversing a list is : (define (rev lis)   (cond      ((null? lis) '())     ((null? (cdr lis)) lis)     (else (list (rev (cdr lis)) (car lis)))))
15:55 shkk: For input '(1 2 3) the output comes as : (((3) 2) 1)
15:57 shkk: I dont understand which parenthesis is causing this problem
16:01 shkk: Got it .. used append instead of list..
16:05 Lajla: shkk, hold on.
16:05 Lajla: I will show you a cool trick
16:09 shkk: lajla: What ?
16:09 Lajla: http://codepad.org/ARNiFJLg
16:09 Lajla: shkk, that
16:09 Lajla: It is what we call, proper tail recursion, and it's awesome.
16:09 Lajla: shkk, also, do you know the 'named let'
16:10 shkk: @Lajla: No, I am a beginner ..
16:10 Lajla: shkk, well, it's really handy, like when you have syntax like (let random-name ((variable expressoin) ...) body ...)
16:10 Lajla: It's like a normal let.
16:11 Lajla: ऴहूBut in body, there's available a function now which has body ... as it's body.
16:11 Lajla: So you can easily recurse.
16:11 Lajla: It just basically means it starts the let over again when you call the function
16:11 Lajla: Look how I call inner again at the end of the let.
16:12 Lajla: It just means it starts the let over again basically but with the arguments as the new values for the variables.
16:12 bremner: Lajla: don't you want (display (rev ...) ) on the last line?
16:13 Lajla: bremner, ny function is called reverse, not rev.
16:13 Lajla: shkk: http://codepad.org/baglwqcE
16:13 Lajla: This should simply illustrate how a named-let works
16:13 Lajla: bremner, ehh
16:13 Lajla: yeah, you're right.
16:13 bremner: Lajla: not in your paste it isn't
16:13 Lajla: Pardon
16:13 bremner: a'ok
16:14 Lajla: shkk, have you seen the words 'tail call' or 'tail recursion' come by at some points?
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16:16 Lajla: shkk_, have you seen the words 'tail call' or 'tail recursion' come by at some pints?
16:16 (quit) shkk: Ping timeout: 252 seconds
16:17 shkk_: Why am I getting disconnected
16:17 shkk_: Anyways, Lajla: You have called reverse but the actual function name is rev. I did not understand that.
16:19 Lajla: shkk_, yeah, my mistake.
16:19 Lajla: It still works if youy call rev.
16:19 Lajla: णद्ाCodepad'sscheme has rev built in.
16:21 Lajla: shkk_, but have you ever heard the names 'tail call' and 'tail recursion', because the main essense of my modication is not that it uses a named let, but that it's 'tail recursive'
16:22 shkk_: Yaa I have heard tail recursion
16:22 shkk_: But ur not even calling rev .. ur calling reserve .. What is that ?
16:22 bremner: a typo
16:23 shkk_: But reverse is anyways a built in function right
16:23 bremner: oh, not that.  reserve is not a typo, sorry.
16:23 bremner: yes, reverse is built in
16:24 shkk_: so where is the tail recursion .. the function definition is rev .. and its calling reserve
16:25 Lajla: shkk_, no, reserve is asomething different then reverse.
16:25 Lajla: I'm not calling it
16:25 Lajla: It's a value, not a function
16:25 Lajla: It's in the let.
16:25 Lajla: You could have renamed it to 'x' that's not the point, it's a bound variable.
16:26 Lajla: shkk_, but what my implementation basically does is, it creates two stacks, it initizializes one (acc) as empty and the other (reserve) as the original list you want to reverse.
16:26 shkk_: okie
16:27 Lajla: And then, each time, it checks if reserve is empty, if so, it outputs acc, if not, then it basically takes the front element of reserve, and prepends it to the front of acc, and repeats the cycle.
16:27 Lajla: So if they start like () and (1 2 3), then after the first go you have (1) and (2 3), and then (2 1) and (3) and ten (3 2 1) and (), and now reserve is empty, so it outputs (3 2 1)
16:28 Lajla: The point is that this version is tail recursive, so it's going to run _a lot_ faster.
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16:33 shkk_: Okie got it .. thanks a lot lajla
16:37 Lajla: shkk_, http://codepad.org/FPQZez3f
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17:26 Mathew: is anyone there?
17:27 Mathew: anyone?
17:28 jonrafkind: yea
17:29 (quit) Mathew: Client Quit
17:29 jonrafkind: oh wel
17:30 chandler: not enough patience for an asynchronous communications method
17:49 Lajla: Maybe we should call him back with the current continuation and try again.
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