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04:20 PLT_Notify: racket: master Ryan Culpepper * d9f05a6 (3 files in 1 dirs): syntax/parse: better error message for unbound literals
04:20 PLT_Notify: racket: master Ryan Culpepper * abb8f63 (2 files in 1 dirs): syntax/parse: made link to pattern-directive docs more prominent, indexed ...
04:20 PLT_Notify: racket: master commits d40b43c...abb8f63 - http://bit.ly/m3yyEC
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09:31 ChibaPet: Good morning, all.
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10:40 cssteve: hello
10:40 cssteve: is anyone there
10:40 cssteve: ?
10:41 cssteve: how do I check is something is a predicate? You can check for number like number? or symbol? or list?, how do you check for predicate?????
10:43 (nick) samth_away -> samth
10:46 samth: cssteve, what would that mean?
10:46 samth: also, why do you want to do this?
10:47 cssteve: i just want to check if a statement like symbol or number is a predicate
10:48 cssteve: when given a predicate and list, return if the car of the list matches the predicate
10:48 cssteve: list this:
10:48 samth: i think that means you take the predicate as an input
10:48 yoklov: what do you mean by predicate
10:48 yoklov: racklog predicate?
10:49 samth: not that you check that the first element *is* a predicate, but that you check that the first element produces #t when provided to the predicate
10:49 cssteve: (filter number? '(a 2 4 () sb) = '(2 4)
10:49 cssteve: (filter symbol? '(a 2 4 () sb) = '(a sb)
10:50 samth: cssteve, you don't need to check if something's a predicate to implement filter
10:50 cssteve: oh ok
10:50 cssteve: so I just accept it as an input without checking?
10:52 samth: cssteve, right
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10:52 samth: are you planning to check that the second input is a list?
10:52 cssteve: here, this is what I have, but how do I make it recursive to return the output
10:52 cssteve: (define filter   (lambda (p ls)     (p (car ls))))
10:54 samth: cssteve, if (p (car ls)) produces #t, what do you want to do with it?
10:55 cssteve: input = (filter number? '(1 as 3 () 2))
10:55 cssteve: output = '(1 3 2)
10:55 samth: right, but more specifically, in your definition of filter
10:55 cssteve: i want to put it in a list and do the same thing with the cdr of the list
10:56 samth: ok, so lets think about how to deal with the rest of the list
10:56 samth: how what you want to do is go through the rest of the list and get only the elements that match p
10:57 samth: so we need something to fill in this blank: (____ p (cdr ls))
10:57 sheikra: samth: I see to have another reason to put match in the compiler ...
10:57 cssteve: if the pred returns true on car of list, I want to place car of list in a new list, and return (filter p (cdr ls)).
10:58 samth: sheikra, ?
10:58 cssteve: if pred returns false on car of list, I want to just return (filter p (cdr ls))
10:58 cssteve: I know how to do it logically, but I am having a hard time coding it
10:58 samth: ok, so how can we decide what to do based on whether (p (car ls)) produces #t?
10:58 sheikra: samth: (match `(,u ,v)  [((TVar name) (TVar name)) ...] ... )) doesn't seem to work ..
10:59 samth: sheikra, that's because you need to write (list (TVar name) (TVar name))
10:59 samth: as your pattern
10:59 samth: that or use `match*'
10:59 samth: (p1 p2) is not a list pattern
11:00 cssteve: oh wait, there is suppose to be a cons in there somewhere
11:01 samth: well, cssteve, cons is how you combine a single element with a list, so it seems like it would be useful here
11:01 sheikra: samth: oh, never mind. I should have used (match `(,u ,v)  [`(,(TVar name) ,(TVar name)) ...] ... )) doesn't seem to work ..
11:02 sheikra: samth: so there no restriction how I construct the expression being matched?
11:02 samth: sheikra, right, the first form is just an arbitrary expression
11:03 cssteve: I kind of got it, but I keep getting an error which I dont know how to fix
11:03 cssteve: (define filter   (lambda (p ls)     (p (car ls)) (cons (car ls) (filter p (cdr ls)))     (filter p (cdr ls))))
11:04 samth: cssteve, that's very close, but you need to make a decision based on whether (p (car ls)) is true or false?
11:04 samth: do you know of a construct that behaves differently conditionally depending on whether something is true or false?
11:05 sheikra: samth: cool. thanks :)
11:05 cssteve: I did know before, but with other programming languages, I forgot
11:05 samth: how about `if', cssteve?
11:05 cssteve: do you need an if statment?
11:07 cssteve: (define filter   (lambda (p ls)     (if(p (car ls)) (cons (car ls) (filter p (cdr ls))))     (filter p (cdr ls))))
11:07 samth: does that work?
11:07 cssteve: is that a correct placement of the "if"?
11:09 samth: what's the syntax of if?
11:10 cssteve: is it if then?
11:11 samth: no, it's (if test then else)
11:11 samth: cssteve, are you working with a textbook or tutorial?
11:14 cssteve: no I dont have a book or tutorial, I am just studying for finals and my professor is the worst
11:14 samth: does your class have a web page?
11:14 samth: do you have any references for the syntax of the language?
11:14 cssteve: ya, but its on blackboard
11:14 samth: does it say anything about syntax?
11:15 cssteve: yes, it says that then and else aren't identifiers
11:16 samth: right, that's true
11:16 samth: what does it say about the syntax of if?
11:17 samth: cssteve, you might also want to look at htdp.org
11:18 samth: which is an excellent introductory textbook for programming that uses similar languages
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11:27 yoklov: cssteve, your class doesn't use at textbook at all?
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14:08 gfds: dsa
14:08 gfds: anybody out there?
14:09 stamourv: yes
14:09 stamourv: just ask your question
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14:34 Blkt: good evening everyone
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14:52 pfox__: "Go cons a piece of cake onto your mouth". hee.
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15:08 askhader: I'm just gonna cadr it back...
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16:16 pfox__: hey, what's the diff between '() and quote() ?
16:17 (part) simonh
16:17 pfox__: im working through the little schemer, and i've been using the former as a shortcut for quote() in a lot of functions
16:17 pfox__: but it wouldn't work.. on a whim i swapped w/ quote() and now it works.. so im curious how i was misusing '() and why it worked
16:18 pfox__: usually was using it as the value when (null? l) was true
16:19 pfox__: but it wouldn't work on a certain question i was working through, even
16:19 pfox__: and curious why it worked on previous questions
16:23 samth: 'e is the same as (quote e), where e is an arbitrary s-expression
16:27 pfox__: https://gist.github.com/957856
16:27 pfox__: im just curious why subst works w/ '() while multirember doesn't
16:27 pfox__: so it's something with the way im writing it
16:27 pfox__: even though both the "bad" multirember and working subst seem to work basically the same
16:28 pfox__: with where they test/return the empty list at the end of the recursion chain
16:28 pfox__: i guess the difference is with how that list gets used.
16:28 bremner_: parens matter
16:28 bremner_: ('()) != '()
16:28 pfox__: yeah, i figured it was something like that
16:29 bremner_: ((quote ())) won't work either
16:32 pfox__: the "good" multirember in that gist works
16:33 bremner_: yes. count patens
16:34 bremner_: parens even
16:36 bremner_: (quote ....). is fine
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16:40 pfox__ nods. thanks.
16:46 pfox__: i can see from messing around on the repl what you're talking about
16:47 pfox__: still interesting why it i don't get an error in some applications and not others
16:47 pfox__: hm.
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17:12 PLT_Notify: racket: master Robby Findler * 507b1cd (74 files in 74 dirs): moved the docs-complete library into rackunit ... - http://bit.ly/ifqE9n
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18:31 PLT_Notify: racket: master Eli Barzilay * b4b490b (1 files in 1 dirs): Win64 build should be working now - http://bit.ly/kKwXkI
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19:05 PLT_Notify: racket: master Sam Tobin-Hochstadt * 507db7e (1 files in 1 dirs): Include extra-procs in the #:use-sources.
19:05 PLT_Notify: racket: master Sam Tobin-Hochstadt * af56616 (1 files in 1 dirs): Require numeric-predicates at the correct phase. ...
19:05 PLT_Notify: racket: master commits d7fd2b2...af56616 - http://bit.ly/jU68wY
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20:34 Counterspell: hey
20:35 Counterspell: Can Racket show me the recursive growth of a function visually?
20:35 Counterspell: For example: http://mitpress.mit.edu/sicp/full-text/book/ch1-Z-G-7.gif
20:38 mithos28: Counterspell: There is trace which might be helpful. http://docs.racket-lang.org/reference/debugging.html?q=trace#(form._((lib._racket/trace..rkt)._trace))
20:38 Counterspell: mithos28, cool, thanks
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21:33 EM03: why in old scheme implementations would define (x) 10) work?
21:33 EM03: I noticed in racket it does not
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23:56 Demosthenes: ok, so i know i can do things like (number? 1), but is there a (type-of 1) -> 'number function?