21:14 (topic) -: Racket -- http://racket-lang.org/ (logs at http://racket-lang.org/irc-logs/ )
21:14 (names) -: gabot mithos28 lewis1711 Blkt tony_ _danb_ lucian shachaf shofetim askhader evhan coyo abbe rapacity em mattmight Tasser fmu Gwyth clklein _p4bl0 martinhex danking MK_FG drhodes alexsuraci` samth jasond lisppaste tewk stamourv` Lajla cpach eli Fill zakwilson jeapostrophe bremner hyko cky rudybot mario-goulart @ChanServ
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21:51 eli: danking: Sounds good -- I'd love to see some examples of how it's used (drracket tools like syntax check, macros, etc).  Probably worth a blog post too.
21:52 eli: danking: As for your question, see my interactive hack at http://barzilay.org/misc/interactive.rkt -- gives you exactly this kind of commands.
21:53 eli: (And more.)
22:00 em: look at the second example in section 4.9 here -- http://docs.racket-lang.org/guide/set_.html?q=random
22:00 em: why doesn't that just make n = 0 each time it's called?
22:06 rapacity: it does ?
22:06 em: well obviously it doesn't but im asking why not
22:06 rapacity: no the make-runnint-total function does
22:06 rapacity: but that function returns another function
22:06 rapacity: and the function it returns has its own n
22:08 rapacity: (define x (let ([a 0]) (lambda () (set! a (add1 a)) a)))
22:08 rapacity: rudybot: (define x (let ([a 0]) (lambda () (set! a (add1 a)) a)))
22:08 rudybot: rapacity: Done.
22:08 rapacity: (x)
22:08 rapacity: rudybot: (x)
22:08 rudybot: rapacity: ; Value: 1
22:08 rapacity: rudybot: (x)
22:08 rudybot: rapacity: ; Value: 2
22:10 rapacity: the function that's getting caled is (lambda () (set! n (+ n 1)) n)
22:10 em: yeah i dont get what's going on there becaues i thought let was setting a to be zero through out its scope
22:10 rapacity: as long as you don't mutate it
22:10 rapacity: (set! n
22:10 rapacity: changes its value
22:11 rapacity: rudybot: (let ([n 0]) (set! n 100) n)
22:11 rudybot: rapacity: ; Value: 100
22:15 em: i guess somehow the key to it is that x is returning a function itself.
22:16 em: where is the value of a being stored?
22:16 em: this doesn't seem like functional programming?
22:16 rapacity: it isn't
22:17 rapacity: it isn't functional programming
22:18 em: i dont get why the let is not called each time that your 'x' is called, and so it just puts n back to 0 again.
22:18 rapacity: the let is not wrapped in a function
22:18 em: it's wrapped in the definition of 'x'
22:19 rapacity: the function that x gets was inside the body of the let, that's why it has access to "a"
22:20 rapacity: but let isn't being called inside a function
22:20 rapacity: rudybot: (define y (let ([u 0]) u)) (display y)
22:20 rudybot: rapacity: ; stdout: "0"
22:21 rapacity: "y" isn't a function here
22:21 rapacity: the let is not wrapped in a function
22:22 rapacity: rudybot: (define y (let ([u 0])  (lambda () (set! u (+ 1 u)) u ))
22:22 rudybot: rapacity: error: eval:1:0: read: expected a `)' to close `('
22:22 rapacity: rudybot: (define y (let ([u 0])  (lambda () (set! u (+ 1 u)) u )))
22:22 rudybot: rapacity: Done.
22:22 rapacity: the let is wrapping around a function and returning it
22:24 em: so when you call y doesn't it expand to (let ([u 0]) (lambda () (Set! u (+ 1 u)) u)) ?
22:25 rapacity: y is just the procedure  (lambda () (set! u (+ 1 u)) u)
22:26 em: why isn't it also the (let .. ) part since that's part of the definition of y ?
22:26 rapacity: the let gets evaluated
22:26 rapacity: returning its body
22:27 rapacity: whose value gets binded to y
22:27 rapacity: is (define x 2) a function ?
22:28 em: well the let is evaluated to (lambda
22:29 rapacity: yeah, it's already evaluated
22:29 rapacity: why would it get evaluated again ?
22:29 rapacity: rudybot: (define x (let ([n 0]) n))
22:29 rudybot: rapacity: Done.
22:29 rapacity: rudybot: x
22:29 rudybot: rapacity: ; Value: 0
22:29 rapacity: rudybot: x
22:29 rudybot: rapacity: ; Value: 0
22:29 rapacity: rudybot: (x)
22:29 rudybot: rapacity: error: procedure application: expected procedure, given: 0 (no arguments)
22:30 rapacity: rudybot: (define x (let ([n 0]) (set! n (+ n 1)) n))
22:30 rudybot: rapacity: Done.
22:30 rapacity: rudybot: x
22:30 rudybot: rapacity: ; Value: 1
22:30 rapacity: rudybot: x
22:30 rudybot: rapacity: ; Value: 1
22:30 rapacity: sorry, I'm not good at explaining things
22:31 em: you see it's not just y it's (y) if you get me.
22:33 lewis1711: is there anyway to get racket to print the line number of your errors, instead of just bad syntax? maybe it does it in dr racket but that's not working for me
22:34 rapacity: (define x (let ([n 0]) (lambda () (set! n (add1 n)) n)))  => (define x (lambda () (set! n (add1 n)) n))
22:34 rapacity: that's how it evaluates
22:35 rapacity: now the n is a hidden variable only accessible within that lambda
22:40 em: is there a way to do something like this..
22:41 em: (define six (lambda () (display "SIX")))   (define SIX (lambda () (display "6")))
22:41 em: so that you could go ((six)) to return 6 ?
22:42 rapacity: yeah
22:42 rapacity: rudybot: (define six (lambda () (lambda () (display "6"))))
22:42 rudybot: rapacity: Done.
22:42 em: it didn't work when i tried it but maybe it needs something other than display?
22:42 rapacity: rudybot: ((six))
22:42 rudybot: rapacity: ; stdout: "6"
22:43 rapacity: are you perhaps confused about (define (x) vs (define x ?
22:43 rapacity: rudybot: (define six (lambda () (lambda () 6)))
22:43 rudybot: rapacity: Done.
22:43 rapacity: rudybot: ((six))
22:43 rudybot: rapacity: ; Value: 6
22:45 em: i dont think that's doig what i have in mind anyway
22:45 em: (six) returns SIX so i thought ((six)) should expand to (SIX) which should then return 6
22:46 rapacity: o_O
22:47 rapacity: it doesn't work like that
22:47 em: isnt that applicative order evaluation?
22:48 rapacity: ah
22:48 rapacity: SIX is another variable?
22:48 rapacity: which is a function?
22:48 rapacity: or is it "SIX" ?
22:48 em: yeah
22:48 rapacity: well if SIX is a function
22:48 rapacity: then it would work
22:49 em: i was saying: (define six (lambda () (display "SIX")))
22:49 rapacity: rudybot: (define (SIX) 6) (define (six) SIX)
22:49 rudybot: rapacity: Done.
22:49 rapacity: rudybot: (six)
22:49 rudybot: rapacity: ; Value: #<procedure:SIX>
22:49 em: (define SIX (lambda () (display "6")))
22:49 rapacity: rudybot: ((six))
22:49 rudybot: rapacity: ; Value: 6
22:49 rapacity: ok
22:49 rapacity: rudybot: (define SIX (lambda () (display "6")))
22:49 rudybot: rapacity: Done.
22:50 rapacity: rudybot: (define six (lambda () SIX))
22:50 rudybot: rapacity: Done.
22:50 rapacity: rudybot: (six)
22:50 rudybot: rapacity: ; Value: #<procedure:SIX>
22:50 rapacity: rudybot: ((six))
22:50 rudybot: rapacity: ; stdout: "6"
23:04 (quit) mithos28: Quit: mithos28
23:58 (part) lewis1711