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2020-11-19 05:05:15 × tumdedum quits (~tumdedum@unaffiliated/espiral) (Ping timeout: 265 seconds)
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2020-11-19 05:32:55 n00b is now known as n0042
2020-11-19 05:33:34 <n0042> Hello folks. May I ask what is probably a pretty common newbie question? I have done a lot of research on it and am starting to feel a little stumped at having not found the proper answer
2020-11-19 05:33:48 × xerox_ quits (~xerox@unaffiliated/xerox) (Ping timeout: 272 seconds)
2020-11-19 05:34:52 → zyklotomic joins (~ethan@unaffiliated/chocopuff)
2020-11-19 05:35:29 <n0042> I have a situation where I need to take an unknown # of lines from stdin (no more, no less, finite but unknown until runtime). I have tried a hundred different ways of trying to use getLine programmatically so that it collects exactly n-amount of lines, after n is known. Is there a good article I can read on this?
2020-11-19 05:36:11 <zyklotomic> what have you tried so far
2020-11-19 05:37:33 <n0042> So far my most promising approach has been to get the initial number of lines with getLine (because that input is known) parse it and extract the number, and then try to run getLine that amount of times.
2020-11-19 05:37:59 <glguy> that sounds right
2020-11-19 05:37:59 <zyklotomic> i'm just a beginner, but maybe replicateM might help
2020-11-19 05:38:04 <dsal> It'd be easier to show code and describe the confusion than to describe the problem.
2020-11-19 05:38:06 × hidedagger quits (~nate@unaffiliated/hidedagger) (Quit: WeeChat 2.9)
2020-11-19 05:38:18 <glguy> ?paste
2020-11-19 05:38:18 <lambdabot> A pastebin: https://paste.debian.net/
2020-11-19 05:38:20 <zyklotomic> replicateM n getLine
2020-11-19 05:38:39 <n0042> I have not tried replicateM. I'll try that.
2020-11-19 05:38:41 <glguy> zyklotomic, maybe, but n0042 ought to be able to do this without any library functions first
2020-11-19 05:39:13 <glguy> n0042, Do you have any attempts yet? What have you tried?
2020-11-19 05:39:32 <n0042> I did try: "take n (repeat getLine)" and wound up with a list of getLine functions that I then wasn't sure how to turn into values
2020-11-19 05:39:54 <n0042> I also tried recursive-do as described in the ghc docs, but that didn't want to compile the way I was trying to do it.
2020-11-19 05:40:29 <glguy> recursive-do is something you don't need
2020-11-19 05:40:29 <dsal> Showing code (and errors/confusion) is more informative than describing code.
2020-11-19 05:40:42 × cosimone quits (~cosimone@5.170.241.44) (Quit: cosimone)
2020-11-19 05:40:45 <glguy> You can paste your code on a pastebin so that people can see what you've got
2020-11-19 05:40:56 <n0042> I'll use pastebin real quick to show you what I've got so far. uno momento
2020-11-19 05:41:04 <glguy> showing code will help us see what you do know how to do
2020-11-19 05:41:52 → agrajag` joins (~agrajag`@84.39.117.57)
2020-11-19 05:43:24 <dsal> Some confusion seems to be between functions and actions. replicating `getLine` will make a bunch of `getLine` actions, but it won't get lines. There's a path from there, but it's probably not what you want.
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2020-11-19 05:44:49 <zyklotomic> on a seperate thread, i have a question about folds vs monads
2020-11-19 05:44:59 <zyklotomic> hope you guys don't mind juggling the convo a bit
2020-11-19 05:45:11 <glguy> go for it
2020-11-19 05:45:29 <zyklotomic> is there any deeper relationship b/w them? I was reading https://mail.haskell.org/pipermail/beginners/2014-August/013993.html
2020-11-19 05:45:43 <zyklotomic> as a result of a google search, after noticing that foldl was kinda like State
2020-11-19 05:46:20 <zyklotomic> then I was writing another function that folded with a monoid (list appending)
2020-11-19 05:46:30 <glguy> There's not much relating folds to monads
2020-11-19 05:46:31 <zyklotomic> and it basically was Writer (i think)
2020-11-19 05:46:38 <zyklotomic> are these just coincidences?
2020-11-19 05:46:56 <zyklotomic> I should generally prefer using folds right
2020-11-19 05:47:11 <zyklotomic> I can show an example
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2020-11-19 05:47:37 <n0042> https://pastebin.com/zwuqHsSY
2020-11-19 05:47:37 × chkno quits (~chkno@75-7-2-127.lightspeed.sntcca.sbcglobal.net) (Read error: Connection reset by peer)
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2020-11-19 05:48:02 <glguy> zyklotomic, foldl is similar to traverse used with State
2020-11-19 05:48:04 <n0042> Here's sort of what I got so far. It's for an assignment but there's no need to get into the assignment itself. I already have that part figured out. It's just the I/O that's confusing me
2020-11-19 05:48:08 <glguy> but that's not much about being a monad
2020-11-19 05:48:17 <zyklotomic> https://paste.debian.net/1173146/
2020-11-19 05:48:32 <zyklotomic> wait yeah, you're right, I probably shouldn't have jumped to monad
2020-11-19 05:48:35 <glguy> that's more about foldl being related to State specifically in the context of foldable types
2020-11-19 05:49:44 → hidedagger joins (~nate@unaffiliated/hidedagger)
2020-11-19 05:49:56 <glguy> :t \f t -> runState(traverse (state . f) t)
2020-11-19 05:49:57 <lambdabot> Traversable t => (a -> s -> (b, s)) -> t a -> s -> (t b, s)
2020-11-19 05:50:08 → aoei joins (~aoei@li2174-104.members.linode.com)
2020-11-19 05:50:12 <glguy> :t foldl
2020-11-19 05:50:13 <lambdabot> Foldable t => (b -> a -> b) -> b -> t a -> b
2020-11-19 05:50:36 <glguy> :t scanl
2020-11-19 05:50:38 <lambdabot> (b -> a -> b) -> b -> [a] -> [b]
2020-11-19 05:50:46 <glguy> :t mapAccumL
2020-11-19 05:50:47 <lambdabot> Traversable t => (a -> b -> (a, c)) -> a -> t b -> (a, t c)
2020-11-19 05:51:01 <zyklotomic> or actually, I mean, what about Writer and State
2020-11-19 05:51:17 <zyklotomic> would you like classify them as some kind, or am I looking into this too much
2020-11-19 05:51:27 <zyklotomic> and it is just a nice coincidenec
2020-11-19 05:51:51 <zyklotomic> where the behavior is "traversing"
2020-11-19 05:51:52 <glguy> there's no deep connection that I can think of
2020-11-19 05:52:21 <zyklotomic> ah fair enough, thanks for entertaining my q
2020-11-19 05:52:43 <dsal> n0042: what do you want `results` to be?
2020-11-19 05:53:14 <dsal> From the application, it looks like you want it to be a single string.
2020-11-19 05:54:18 <n0042> So, results is going to print a line for each "packet" showing the time it was processed or if it was processed. That's all going to be handled by the program logic which i've got covered, and it'll just print off a list of strings. But to get there I need to collect the strings which contain the arrival time and time-to-process for each packet,
2020-11-19 05:54:18 <n0042> which is the programmatic input part.
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