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00:00 <Lazersmoke> cause what you are really doing is *deconstructing* the data and inspecting the individual parts
00:01 <Lazersmoke> so instead of `(MessageTree leaf)`, just match on `Leaf`
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00:32 <amIaName> So now I am facing another issue: I am getting a parsing issue when I type in the line "insert message tree@(left (Unknown _) right) = tree"
00:32 <amIaName> The compiler does not like my use of "left". Why is this happening?
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00:33 <kadoban> You probably mean Left
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00:34 <amIaName> There is no "Left" type
00:34 <amIaName> Why should this be capitalized?
00:34 <kadoban> There is an Either type though, which has the constructors Left and Right
00:35 <amIaName> Sorry, this is part of a conversation from 30 minutes ago. Here is the relevant paste: http://lpaste.net/6474668988335915008
00:35 <amIaName> I am in the second week of the cis194 course
00:38 <Lazersmoke> amIaName: you need to include Node in there
00:38 <Lazersmoke> tree@(Node left (Unknown _) right)
00:38 <amIaName> But what if it is a leaf?
00:38 <Lazersmoke> then have another pattern that is just Leaf
00:38 <Lazersmoke> like "insert message Leaf = ..."
00:39 <Lazersmoke> or if it doesn't matter if its a leaf or not a leaf, then just do "insert message tree = ..."
00:39 <Lazersmoke> follow?
00:40 <amIaName> It doesn't matter if on the second layer is a leaf or a node
00:41 <amIaName> That's what I'm hoping for at least
00:41 <Lazersmoke> when you use an @-pattern, you still need to specify the data constructor
00:42 <Lazersmoke> when you write "tree@(left (LogMessage _ timeStampTree _) right)", it doesn't know you are talking about a Node
00:42 <Lazersmoke> tree@(Node left (LogMessage _ timeStampTree _) right)
00:42 <Lazersmoke> ^ this is the correct way to write what you intend
00:43 <amIaName> Oh! I completely misunderstood what you were saying. I though you meant applying node on the left, which would mean putting it on the right too
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00:47 <amIaName> Thank you for your help. This now works correctly
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02:13 <mounty> What's the correct import to obtain nominalDay :: NominalTimeDiff ? https://hackage.haskell.org/package/time-1.8.0.1/docs/Data-Time-Clock.html says it exports it but it lies.
02:14 <mounty> ScorePost.hs:28:50: error:
02:14 <mounty> Module ‘Data.Time.Clock’ does not export ‘nominalDay’
02:14 <mounty> It appears to be in an 'Internal' package but that's presumably not the official/portable way to get it.
02:15 <mounty> And yes, I know 86400 but I want it to be portable.
02:15 <geekosaur> make sure youy have that actual version of the time package
02:17 <MarcelineVQ> if you're using stack the latest time on an lts is only 1.6.0.1 note however https://hackage.haskell.org/package/time-1.8.0.1/docs/src/Data-Time-Clock-Internal-NominalDiffTime.html#nominalDay
02:18 <mounty> geekosaur: I'm relying on cabal to pull in the package. Obviously I don't so I suppose the question is: where is nominalDay officially declared now? I know about that Internal package but surely that's not for general use?
02:18 <mounty> If I try to import the internal package:
02:18 <mounty> ScorePost.hs:29:1: error:
02:18 <mounty> Failed to load interface for ‘Data.Time.Clock.NominalDiffTime’
02:18 <mounty> Use -v to see a list of the files searched for.
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02:19 <MarcelineVQ> it's declared in that internal package and exported from the package named in the docs you linked, it's quite new though so be sure to check you have the same version as geekosaur mentioned
02:19 <geekosaur> I don't know where the version you are usin g defines it, because I don't know what version you are using
02:20 <geekosaur> if you are not using 1.8.0.1 then the documentation does not reflect what you have available, and in whatever version you have the Internal module might well be the only place it exists
02:20 <mounty> I'm using a cabal sandbox. I'm trying to find out now what version it has pulled-in.
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02:24 <* mounty> bangs head on wall.
02:24 <mounty> The version information must be somewhere.
02:25 <mounty> find .cabal-sandbox/* -type f ! -name '*.dyn_hi' ! -name '*.hi' | xargs grep -w Data.Time.Clock
02:25 <mounty> returns only binary files.
02:25 <geekosaur> I think there's a .cabal-sandbox/lib with separate directories for each package it installed, named by the package name+version?
02:26 <geekosaur> you can reconstruct it from the binaries the way you tried *but* you need to be able to read z-encoding :)
02:26 <MarcelineVQ> cabal sandbox --help says you can write cabal sandbox hc-pkg list dunno what that'll display though
02:28 <MarcelineVQ> looks like it'll have two sections, the libs your ghc has and the libs in the sandbox
02:29 <MarcelineVQ> iow cabal sandbox hc-pkg list | grep 'time' should let you know what time you have, and if it lists two I'd expect it's the latter
02:30 <mounty> Thanks geekosaur and MarcelineVQ: time-1.6.0.1
02:30 <mounty> I don't really know cabal that well but getting everything up to date is a pain right? I don't mind blowing it away and restarting, as it's a sandbox.
02:31 <geekosaur> you might just need to `cabal update`, then blow away .cabal-sandbox and try again
02:32 <geekosaur> but if something you use depends on the older time, that won't work and you may have to use the internal symbol
02:32 <MarcelineVQ> it might just use the one that comes with his ghc, start by specifying the version of time you want in your .cabal file at lesat
02:32 <MarcelineVQ> *at least
02:32 <geekosaur> ^
02:32 <MarcelineVQ> really though if you just want nominalDay this is not necesary :> my link earlier was to point out that the definition for it is just: nominalDay = 86400
02:33 <MarcelineVQ> it's good to work with cabal though so I'm not trying to dissuade you if you're wanting to
02:33 <mounty> I'm happy to blow it away and restart. I can get on with other things while it does it, such as doing a stack build on another VM.
02:35 <mounty> I build with cabal on Gentoo Linux and stack on CentOS.
02:35 <mounty> That of course has its challenges. Stack reports:
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02:36 <mounty> Not in scope: type constructor or class ‘Yesod.PersistQueryRead’
02:36 <mounty> Perhaps you meant ‘Yesod.PersistQuery’
02:36 <MarcelineVQ> is this the same project? you don't use a cabal sandbox with stack :>
02:36 <mounty> That code was fine on Gentoo+cabal.
02:37 <mounty> MarcelineVQ: it is the same project. I use the sandbox on Gentoo but .stack-work on CentOS.
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02:37 <mounty> I use symlinks to keep the built stuff separate on the separate machines.
02:37 <MarcelineVQ> hmm sounds complicated, but if your versions are fully specified in your .cabal file I guess it would work out
02:38 <mounty> It seems to work alright. For example: .stack-work -> /var/tmp/mounty/JackRose/stack-work
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02:38 <mounty> .cabal-sandbox -> /var/tmp/mounty/JackRose/sandbox
02:38 <MarcelineVQ> complete side-note curiosity, what are you wanting to use nominalDiff to do?
02:38 <MarcelineVQ> *nominalDay
02:38 <mounty> Well it's a bit involved. Do you know anything about flashcards and spaced repetition software?
02:39 <MarcelineVQ> Not a bit but now I'm interested
02:39 <MarcelineVQ> actually maybe I do, you mean like learning flashcards?
02:39 <mounty> Yes, I do.
02:39 <MarcelineVQ> I've used Anki some
02:39 <mounty> I use Anki myself.
02:40 <mounty> So the first time a card is presented, the software has no prior knowledge of how you've scored so it doesn't have enough information to re-schedule the card.
02:40 <mounty> So I just schedule one day * (your score / 4)
02:40 <mounty> (based on a score of 0 .. 5)
02:41 <mounty> https://github.com/mounty1/JackRose for more.
02:41 <mounty> The scoring/rescheduling is that last little piece that makes the software basically usable.
02:42 <MarcelineVQ> utc tracks the day but you'd like to use something like nominalDay so that it's straightforward to decrement to the next interval?
02:42 <mounty> It's nothing like as sophisticated as Anki yet though.
02:42 <mounty> MarcelineVQ: sorry; I don't really understand what you mean.
02:43 <mounty> I should explain that JackRose uses a 'continuous time' spacing algorithm; it calculates spacing in terms of seconds; not days.
02:44 <mounty> So if you give yourself 4/5 on the first scoring of an item, it sets the next review to 86400 seconds.
02:47 <MarcelineVQ> :>
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02:49 <mounty> Rats; did a stack update but I still have that Yesod.PersistQueryRead problem.
02:49 <MarcelineVQ> have you specified the specific version of persistent to use?
02:50 <mounty> IIRC newer versions of Persistent distinguish between read and write access for greater safety and it looks like the newer version hasn't made it to stack's suppository yet.
02:50 <MarcelineVQ> this is quite important when working accross multiple tools, especially since stack relies on resolvers to pick versions if you don't tell it otherwise
02:50 <mounty> No; I just rely on stack to use the latest.
02:51 <MarcelineVQ> 2.5 is the earliest version with PersistQueryRead
02:53 <mounty> OK, so stack.yaml says "resolver: lts-6.27"
02:53 <mounty> Presumably I should try something a bit more bleeding-edge to get Persistent 2.5 ?
02:54 <MarcelineVQ> 7.0 and newer
02:54 <mounty> resolver: lts-7.0 ?
02:55 <mounty> "Downloading lts-7.0 build plan"
02:55 <MarcelineVQ> yeah https://www.stackage.org/diff/lts-6.30/lts-7.0
02:55 <mounty> here we go ...
02:56 <mounty> Meanwhile back on Gentoo/cabal: Module ‘Data.Time.Clock’ does not export ‘nominalDay’
02:56 <MarcelineVQ> Did you specify the version that has nominalDay in your .cabal file?
02:56 <mounty> I think I stuffed up. I deleted my cabal.sandbox.config
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02:57 <mounty> cabal sandbox init again ?
02:57 <MarcelineVQ> cabal sandbox init should make one of those
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02:57 <Guest9155> is there an HTTP lib that's built in to Haskell or do i need to go download something?
02:59 <MarcelineVQ> Guest9155: there's a lot of options for http libs, I'd try asking in #haskell where they may have good opinions on what's easy to start with
02:59 <geekosaur> there is little "built in"
02:59 <geekosaur> the compiler ships with the minimum it needs to provide full compile functionality including TH etc. it is *not* batteries-included, and the community decided it hated batteries-included.
02:59 <geekosaur> so yes you must download something
03:03 <Guest9155> okay so i found this and it looks good https://github.com/haskell/HTTP and i have an app created by stack
03:03 <Guest9155> what do i put where in i assume my .cabal file? to get it
03:04 <Guest9155> wait
03:04 <Guest9155> i think i got it
03:04 <Guest9155> just HTTP in the build-depends section?
03:04 <Guest9155> look at that, Haskell isn't that hard
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03:06 <MarcelineVQ> good job, note that isn't the github version you have but will be one of the versions from http://hackage.haskell.org/package/HTTP that's linked at the top of that page you linked
03:07 <Guest9155> yeah I was confused by it being imported in examples as Network.HTTP but having to add just "HTTP" to the cabal file
03:08 <Guest9155> does using a function that has an IO return type mean everything that calls it has to be "IO"?
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03:10 <geekosaur> Guest36413, it can have a MonadIO constraint but then you use liftIO to evaluate it
03:10 <geekosaur> otherwise yes
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03:23 <mounty> Coming back to building with cabal on Gentoo, I rmed .cabal-sandbox and cabal sandbox init
03:24 <mounty> after cabal install, cabal sandbox hc-pkg list | grep time
03:24 <mounty> gives time-1.6.0.1
03:24 <mounty> How can I get it up to 1.8?
03:25 <mounty> I don't see any reference to a resolver or similar concept in cabal.sandbox.config
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03:34 <geekosaur> that would imply you have a dependency that wants that version
03:34 <geekosaur> there is no resolver; that's a stack thing
03:35 <geekosaur> what's your cabal file look like?
03:35 <mounty> So some other package is requiring time <= 1.6 ?
03:35 <geekosaur> @paste
03:35 <lambdabot> Haskell pastebin: http://lpaste.net/
03:35 <mounty> I'll use pastebin if you don't mind because I have an account.
03:35 <mounty> Do you mean cabal.sandbox.config ?
03:36 <geekosaur> no, I mean the cabal file
03:36 <monochrom> *.cabal
03:36 <geekosaur> foo.cabal that specifies your dependencies and potentially versions thereof
03:36 <monochrom> pastebin wastes vertical space. It almost double-spaces your code.
03:37 <geekosaur> (for "foo" being whatever you used, which might be named after your project or not)
03:37 <monochrom> I would use pastebin for submitting my PhD thesis because the school requires it to be double-spaced. That's how helpful pastebin is.
03:37 <mounty> http://pastebin.com/pk3zhLr8
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03:38 <mounty> OK monochrom but my life is already too complicated and as you can see, I paste stuff other than Haskell source.
03:39 <mounty> (at least, I assume you can see that)
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03:39 <mounty> No explicit version numbers specified there.
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03:40 <monochrom> It may still choose 1.6 because you already have it from GHC.
03:41 <mounty> You mean the constraint is wired into GHC ??? I'm on 8.0.2 on Gentoo.
03:41 <geekosaur> if it has a package and there's no other reason to download one, yes
03:41 <monochrom> I don't mean wired. I mean no reason to do extra work. I mean laziness.
03:41 <geekosaur> otherwise you can try specifying time == 1.8.0.1 in your dependencies
03:42 <monochrom> To be fair I am not completely sure, there was a time cabal would aggressively bring in newest versions.
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03:45 <mounty> So it's just down to a policy setting? Like conservative/LTS/bleedingEdge/reckless ?
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03:46 <monochrom> But there is no policy setting.
03:47 <geekosaur> no policy setting, it used to default to latest but now defaults to installed so it's less likely to trash your package db in non-sandboxed ode
03:47 <geekosaur> *mode
03:48 <geekosaur> (ghc has ... odd notions of how dependencies work. or rather, they make perfect sense for what ghc is doing under the covers, but everyone conditioned by C libraries expects something different)
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03:50 <mounty> trying: HDBC-2.4.0.1/installed-Cvh... (user goal)
03:50 <mounty> next goal: JackRose (user goal)
03:50 <mounty> rejecting: JackRose-0.8 (conflict: HDBC => time==1.6.0.1/installed-1.6..., JackRose => time>=1.8.0.1)
03:51 <mounty> Backjump limit reached (currently 2000, change with --max-backjumps or try to run with --reorder-goals).
03:51 <mounty> So it looks like HDBC is keeping the version of time down.
03:51 <mounty> I don't really understand why, when I only just rmed .cabal-sandbox and cabal sandbox init again, it's not pulling the latest stable versions of all packages.
03:53 <mounty> Trying cabal update outside the sandbox, in response to geekosaur's comment "it used to default to latest but now defaults to installed so it's less likely to trash your package db in non-sandboxed code".
03:53 <monochrom> When you rmed .cabal-sandbox and cabal sandbox init again, did that get rid of HDBC? How do you know?
03:54 <mounty> If you rm .cabal-sandbox, you get rid of all built packages, n'est-ce pas?
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03:54 <mounty> Surely?
03:54 <geekosaur> that was my suggestion, and no I am not completely certain --- but I don't recall where the ghc package db goes in a sandbox and I don't currently have any (populated) sandboxes
03:54 <monochrom> If you are asking me, you don't know.
03:54 <geekosaur> you still likely have the package db entries
03:55 <geekosaur> ghc's package db and cabal's package libraries are two different things
03:55 <geekosaur> one should point to the other, but they're distinct and managed separately. (but i would have expected the package db to be in .cabal-sandbox...)
03:55 <mounty> Surely if you're using a sandbox, the global cabal stuff (in my case, at $HOME/.cabal) is ignored?
03:56 <geekosaur> yes
03:56 <monochrom> To be fair, I don't know either, but I don't use sandboxing, and I am not running into problems.
03:56 <geekosaur> but that is user, not global
03:56 <mounty> True.
03:56 <mounty> Hmm.
03:56 <geekosaur> the truly global stuff is likely to be in /usr/lib/ghc-<version> ad you can;t and indeed must not ignore that, because you need base from it
03:56 <* mounty> scratches head.
03:57 <monochrom> The two high-probability scenerios I know are:
03:57 <monochrom> 1. You have HDBC in global. You got it from Gentoo?
03:58 <monochrom> 2. Your HDBC is just in the sandbox but it was built before you said "time 1.8"
03:59 <monochrom> There may be other scenerios I don't know of, of course.
03:59 <mounty> Just finding out. Some packages do come from Gentoo because it pulls them in to build cabal-install.
03:59 <mounty> find /usr -iname '*HDBC*'
03:59 <geekosaur> you might be better off using stack if you've got distro package manager libraries installed in ghc's global db --- they WILL mess with your builds
03:59 <monochrom> But HDBC would not be one of them. HTTP sure.
03:59 <mounty> Can't use stack on Gentoo.
03:59 <geekosaur> (don;t do that. but if you have already done it, you need stack's idea of sandboxing --- which involves beating ghc over the head)
04:00 <monochrom> I thought it didn't beat GHC. (No one could.) I thought it simply downloaded one more GHC.
04:00 <mounty> If I could use stack on Gentoo I would. Better to have one build system on all platforms, obviously.
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04:01 <monochrom> Err OK I guess they could use a GHC feature to say "ignore global, use mine instead".
04:02 <mounty> So now that I've constrained time >= 1.8.0.1 can I tell cabal sandbox to pull HDBC etc. to be consistent with that?
04:05 <geekosaur> recent enough ghc has something like that. earlier versions it has to do evil things to make ghc use stack's global db instead of its own
04:06 <mounty> Just flicking back to my stack build for a moment. https://www.stackage.org/diff/lts-6.30/lts-8.5 which is the newest version still constrains time to 1.6.0.1
04:07 <geekosaur> then I think you're stuck with what it has
04:07 <geekosaur> meaning the internal module or use hardcoded (or locally defined) day constant
04:08 <mounty> I think so too. Thanks geekosaur, monochrom and MarcelineVQ for your help again.
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05:29 <zipper> Hello, so last night I had an issue with writing pure for `newtype Compose f g a = Compose {getCompose :: f (g a)} deriving (Eq, Show)` and you guys said the solution was in f and g having applicative instances
05:29 <zipper> I still haven't figured it out.
05:31 <Cale> Should just be using pure twice, once for f and once for g
05:31 <Cale> (and then wrapping up the result)
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05:32 <zipper> Cale: I thought of that but f and g won't be in scope
05:33 <zipper> and if I pass them it stops being `pure :: a -> Compose f g a`
05:33 <kadoban> zipper: 'pure' is definitely in scope
05:33 <zipper> f and g won't be in scope
05:34 <zipper> `pure a = Compose $ pure f ((pure g) a) `
05:34 <zipper> `pure a = Compose $ \f g -> pure f ((pure g) a) `
05:34 <kadoban> Yes, there are no values named f and g. They are types
05:34 <zipper> breaks the type sig
05:34 <zipper> They are functions
05:34 <zipper> hmmmm
05:35 <zipper> pure and pure are also functions
05:35 <zipper> I get you
05:35 <zipper> `pure a = Compose $ pure $ pure a`
05:35 <kadoban> Very nice :)
05:35 <zipper> so pure will be f and g
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05:35 <zipper> kadoban: Thanks
05:36 <obh15> can someone enlighten me what is resolver in stack?
05:36 <zipper> I have been off the book for like 5 weeks, picking up where I left off.
05:36 <kadoban> Yeah, 'pure' is polymorphic, so it'll be the one for f's intstance of Applicative and the one from g's instance of Applicative
05:36 <zipper> obh15: What do you mean? It helps stack figure out your depends.
05:36 <kadoban> obh15: A resolver is a set of packages and their exact versions.
05:36 <zipper> *dependencies
05:36 <zipper> WOW I didn't know that
05:37 <kadoban> https://www.stackage.org/lts-8.5 is an example
05:38 <obh15> so in lts haskell 8.5 there's a package named abstract-deque with version 0.3 ?
05:38 <obh15> to resolve something like that
05:38 <obh15> what about if I want to use another version that isn't included in the resolver
05:38 <kadoban> In lts-8.5, yeah that package has that version
05:38 <kadoban> Then you add an "extra-dep" which specifies a package and a version
05:39 <kadoban> It can either be a new package that's not in the resolver, or you can override the version of one that was already in there.
05:39 <obh15> Sorry for asking for that, I was a bit confused, about it
05:39 <kadoban> But once you start adding extra-deps, you end up a little on your own, in that it's not guaranteed to all work together. The "lts" and "nightly" resolvers are useful starting places because they're curated and tested to actually at least compile together in one set
05:40 <kadoban> Adding extra-deps is normal though
05:40 <obh15> kk
05:40 <kadoban> No need to apologize, it can be more than a little confusing.
05:40 <zipper> obh15: No need to be sorry for asking :)
05:40 <obh15> I was confused since i've never heard about something like resolver in another package manager of a language
05:41 <obh15> since you can just drop a package and its version and expect it to work
05:41 <obh15> thanks!
05:42 <zaquest> do they release lts every week? i just switched to 8.3 and to 8.4 in couple days after that and it turns out there's already 8.5 for 3 days
05:45 <kadoban> I'm not sure what the actual schedule is, it seems fairly hard to predict to me
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05:49 <zipper> If I have a type f g (a->b) and f g a with fmap I would need to compose fmap twice to apply a -> b to a
05:49 <zipper> How would the same be done with Applicative?
05:52 <zipper> Oh wait fmap and pure kinda serve the same purpose
05:52 <zipper> Well no
05:52 <MarcelineVQ> <*> is more like fmap than pure is
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06:00 <zipper> f -> g -> (a -> b) and f -> g -> a, one <*> will only achieve g -> (a -> b) -> g a.
06:00 <zipper> Which makes no sense
06:06 <zipper> Which is just asking for another <*>
06:06 <MarcelineVQ> give it a try
06:09 <zipper> MarcelineVQ: I can see the types in my head but I can't get the syntax right. idk if that makes sense.
06:09 <zipper> I can see I need to apply <*> to the first result but
06:10 <zaquest> you have `cf :: f (g (a -> b))` and `ca :: f (g a)` since you only have Functor and Applicative instances for `f` and `g`, the best you can do to apply a wrapped function to a wrapped value is to use `<*>`. so you do `_ <*> ca`, now what is `_`, it should have type `f (g a -> g b)`, but you have only `cf :: f (g (a -> b))`, so you need to transform `g (a -> b)` into `g a -> g b` inside `f`, looks like a job for `fmap`, now you have `(_ <$>
06:10 <zaquest> cf) <*> ca` where `_` should have type `g (a -> b) -> (g a -> g b)` but this is a type signature of `<*>` for `g`, so: `((<*>) <$> cf) <*> ca`.
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06:16 <MarcelineVQ> you seem to be on the right track, note that `(_ <$> cf) <*> ca` is the same as `_ <$> cf <*> ca` it gets messy pretty quick with <*> and <$> I'd use liftA2 as a helper to write this which is liftA2 x y z = x <$> y <*> z
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06:17 <MarcelineVQ> it's a good mnemonic you're lifting over f and lifting over g to apply (a -> b) to a
06:17 <zipper> Ok I like your thought process
06:17 <zipper> Which is working behind from the solution you want
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06:23 <MarcelineVQ> the question you end up with on the way is _what_ are you lifting, all we want to do is apply a function we already have to a value we already have, do you know of an function/operator for that?
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06:32 <MarcelineVQ> gotta go, keep plugging at it you've got the pieces :>
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06:36 <zipper> MarcelineVQ: fmap
06:36 <MarcelineVQ> simpler than that
06:37 <MarcelineVQ> if <*> is f (a -> b) -> f a -> f b and fmap is (a -> b) -> f a -> f b what
06:38 <MarcelineVQ> 's the next simpler thing after that
06:40 <lpaste_> MarcelineVQ pasted “zipper” at http://lpaste.net/353519
06:42 <zipper> The next simpler thing? that's just function application
06:42 <zipper> MarcelineVQ: `___ :: (a -> b) -> a -> b`
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06:44 <MarcelineVQ> exactly right but we can't pass that around because it's syntactic, so we make a function to apply a function so it has a name :>
06:44 <MarcelineVQ> :t ($)
06:44 <lambdabot> (a -> b) -> a -> b
06:46 <MarcelineVQ> this is where the dollar you may see often is really useful, people tend to use it to avoid ( ) but it's usefulness is also in that it's a name and passable value for function application
06:47 <MarcelineVQ> so in the sense that for this problem you want to lift over f and lift over g to apply (a -> b) to a that fits ($) nicely
06:48 <MarcelineVQ> Hopefully that's more helpful than confusing :X those are all the pieces you need for the problem so good luck
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07:31 <zipper> MarcelineVQ: Yes it really is. Just trying to juggle code at work with what you are saying :)
07:32 <zipper> I really appreciate you taking the time to break it down for me.
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10:36 <Geekingfrog> How can I transform ExceptT String (Reader.ReaderT Int IO) Int Into something less specific using constraints like MonadIO m, MonadReader and the like ?
10:37 <Geekingfrog> Currently I have (MonadReader Int m, MonadIO m) => ExceptT String m Int but the compilers isn't happy
10:37 <Akii> The compiler suggests to use a certain language extension
10:38 <Akii> FlexibleContexts I think
10:39 <Akii> if not, just paste some minimal code on lpaste
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10:40 <Geekingfrog> I have this extension already. Let me setup a paste with a minimal example
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10:43 <Geekingfrog> Oh wait, I'm stupid. The type signature is fine.
10:44 <Geekingfrog> I have an issue with the implementation -_-
10:44 <Akii> :D
10:46 <Geekingfrog> Ah ok, if I use Control.Monad.Trans.Reader.ask that doesn't work. But Control.Monad.Reader.Class.ask does work.
10:46 <Akii> kinda makes sense
10:46 <Akii> idk I just use ClassyPrelude and most of the time the correct function is already imported xD
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10:57 <Geekingfrog> I should really start trying using classy prelude
10:57 <Geekingfrog> I'm getting a bit tired to always import some basic stuff
10:58 <Akii> absolutely
10:59 <Akii> can only highly recommend it
10:59 <Geekingfrog> yet another thing to learn though.
10:59 <Akii> doesn't take much time
10:59 <Geekingfrog> And I really like qualified import
11:00 <Geekingfrog> Well, I was planning to refactor a few things today, might as well get the classy prelude
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13:00 <tapirus> If I want to enter a multi-line command in ghci, I can surround it with :{ :}
13:03 <tapirus> however, when I do that, the prompt changes, to show all imported modules
13:03 <tapirus> e.g.
13:03 <tapirus> ghci> :{
13:03 <tapirus> Prelude Data.Maybe Data.List Control.Applicative Data.Function Control.Monad Data.Char Data.List.Split| do
13:04 <tapirus> The reason I'm using :{ :} is because I want to enter commands in a way that's more readable than separating them by semicolons, but with that prompt it sort of defeats the purpose....is there any way around this?
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13:22 <jmg> is there a vim plugin or ghci option that can watch a .hs file for changes and then reload it and run the last command?
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13:34 <jmg> oh I found this http://unix.stackexchange.com/questions/72086/ctrl-s-hang-terminal-emulator which is basically what I want to do
13:35 <jmg> whoops I meant this http://stackoverflow.com/questions/2782752/how-can-i-open-a-shell-inside-a-vim-window
13:36 <jmg> or actually this http://stackoverflow.com/questions/7705717/automatically-reloading-ghci-running-hlint-on-file-updates
13:36 <jmg> lol
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13:36 <Cale> you might find ghcid useful
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13:39 <Cale> the --test flag lets you specify an expression to run as GHCi would every time that a file in your project changes
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13:40 <jmg> yah this looks exactly like what I want
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13:49 <jmg> thanks Cale, this is working great
13:49 <Cale> Great :)
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13:51 <Cale> We use it pretty extensively where I work
13:51 <Cale> I often have two of them running, for the frontend and backend of one of our web applications
13:52 <Cale> and it's also good for regenerating CSS while working on the Haskell code that generates it :)
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16:48 <jmg> so If I have a type defined as newtype (Eq a, Fractional a) => PowSe a = PowSe [a]
16:49 <jmg> that basically beans I can have a PowSe of anything as long as it derives Eq and Fractional?
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17:06 <lpaste_> saylu pasted “applicative for Reader” at http://lpaste.net/353536
17:09 <Geekingfrog> I'm getting a Text from a network with the string "\163" (which correspond to "£"). Is there a way to display the £ symbol and not the escaped version ?
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17:13 <geekosaur> Geekingfrog, don't use Show
17:13 <geekosaur> (depending on what is happening between reception and display, this may not be under your control though)
17:13 <Geekingfrog> Ah, you're right, that may just come from me displaying things in ghci
17:14 <geekosaur> use putStrLn in ghci instead of letting ghci do it (which will use show)
17:15 <saylu> Hey mates! I'm a bit confused about writing an applicative instance for Reader
17:16 <Geekingfrog> geekosaur: yes, you're right. I don't have the issue with putStrLn. Thanks.
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17:24 <lpaste_> saylu revised “applicative for Reader”: “applicative for Reader” at http://lpaste.net/353536
17:24 <saylu> Ah! Got it working, though it's super ugly!
17:25 <saylu> I ended up writing this:
17:25 <saylu> Oops nevermind -- I'm going to look this up in docs to see the right way
17:26 <saylu> Well, I wrote:
17:26 <saylu> (Reader rab) <*> (Reader ra) = Reader $ \r -> (rab r) . ra $ r
17:26 <saylu> which would have been prettier as
17:26 <saylu> ` (Reader rab) <*> (Reader ra) = Reader (rab <*> ra)`
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18:16 <nil_> Is it at least informally true that if 'a' is an ArbitraryTypeclass then (e -> a) is also an ArbitraryTypeclass?
18:17 <glguy> no
18:17 <nil_> Counterexample?
18:17 <glguy> class Length a where length :: a -> Int
18:18 <nil_> Umm, instance Length a => Length (e -> a) where length = fmap length ?
18:18 <glguy> Eq, Ord
18:18 <glguy> no
18:20 <nil_> ...elaborate please?
18:20 <glguy> Your code doesn't typecheck, so it's not a valid instance
18:20 <glguy> and Eq and Ord and further examples
18:20 <nil_> Oh :)
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20:12 <kori> hey! this isn't 100% a haskell question, it's more like 50%. I'm implementing something similar to Maybe in scheme and I need help translating (Maybe:>>= (Just 10) (lambda (x) (Maybe:>>= (Just 5) (lambda (y) (/ x y))))) to Haskell to see if the behavior of that function is correct
20:12 <kori> it returns (Just (Just 2)) and that makes sense considering how bind was implemented but I'm not sure if that's analogue to how it works in Haskell
20:13 <kori> https://github.com/kori/monad-mandala/blob/master/maybe.scm the code is here
20:13 <kori> I tried (Just 10) >>= \x -> (Just 5) >>= \y -> x / y but that returns type errors I'm not sure how to solve
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20:15 <glguy> > (Just 10) >>= \x -> (Just 5) >>= \y -> Just (x / y)
20:15 <lambdabot> Just 2.0
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20:16 <lpaste_> saylu pasted “Reader Monad” at http://lpaste.net/353541
20:16 <saylu> Hey folks! I'm having some trouble with writing this. I'm trying to write an instance of monad for Reader
20:16 <geekosaur> at a guess the type errors had more to do with Fractional than Maybe
20:17 <kori> I see hmmmm
20:17 <kori> https://github.com/kori/monad-mandala/blob/master/maybe.scm#L21
20:18 <kori> so, should it be (f (Unwrap a)) here?
20:18 <kori> I thought about making Just "flattening" so (Just (Just (Just... a))) would return (Just a) but I saw that Just doesn't behave like that in haskell
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20:19 <glguy> kori: http://hackage.haskell.org/package/base-4.9.1.0/docs/src/GHC.Base.html#line-665
20:19 <geekosaur> are you missing the join part of bind, perhaps?
20:19 <glguy> This isn't the place to get help with Scheme, but if you need help understanding the Haskell, we can do that
20:20 <kori> glguy: yeah I'm aware this is kind of a mixed question
20:20 <kori> geekosaur: probably! I'm kinda constrained but i'm trying to work within those constraints
20:20 <glguy> Since you don't seem to understand how >>= works on Maybe in Haskell, that's a good place to start
20:21 <kori> glguy: I looked at the definitions
20:21 <kori> but that probably wasn't enough
20:22 <glguy> Yeah, if you don't understand what the definition means you might have some questions about what it does
20:24 <kori> glguy: I got confused because I thought >>= was supposed to return a monadic value every time, considering the type signature
20:24 <kori> so I decided to return (Just (f (Unwrap a))) instead of just (f (Unwrap a))
20:24 <kori> (this is going to get confusing fast)
20:28 <kori> well I think I know what to return now considering the example glguy gave above
20:28 <kori> thanks
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20:30 <kori> Prelude> (Just 10) >>= \x -> (Just 5) >>= \y -> return (x * y)
20:30 <kori> Just 50
20:30 <kori> yeah
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20:42 <lpaste_> saylu revised “Reader Monad”: “Reader Monad” at http://lpaste.net/353541
20:42 <saylu> Got it!
20:43 <saylu> But I'm curious -- is this the "right" way to write this instance?
20:43 <saylu> Is there a cleaner way?
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21:11 <Gurkenglas> I think you don't need the first pair of brackets in line 6, and Data.Coerce could do the wrappery for you, leaving something like (>>=) = coerce $ \x f -> f x x
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