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00:15 <dmwit> sdrodge: (A day late, but...) looks nice!
00:15 <sdrodge> dmwit: Thanks :)
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00:36 <ertes> how do i express the empty constraint?
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00:37 <ertes> nevermind
00:37 <glguy> ()
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00:39 <ertes> yeah, i tried that, and it didn't work, but my error was elsewhere
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00:43 <fetter_oml> would someone know a nice way to build a unity vector (e.g. unityVector 5 3 would be [0,0,1,0,0]) with vector in the sense of the Numeric.LinearAlgebra.Data package?
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00:45 <fetter_oml> my current approach is building one with generate in the Data.Vector sense (which is ugly enough), then calling Data.Vector.toList on it and throwing the result into Numerical.LinearAlgebra.fromList
00:45 <fetter_oml> which is ridiculous.
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00:50 <lyxia> do you mean the hmatrix package?
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00:53 <lyxia> fetter_oml: the Vector is actually of the Storable kind if you want to go that way
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00:55 <fetter_oml> lyxia: yes, it seems it is the hmatrix package
00:55 <lyxia> fetter_oml: but Numeric.LinearAlgebra.Data.assoc seems to be a way which better respects abstraction boundaries
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00:55 <fetter_oml> it also says in the description that "1D arrays are storable vectors directly reexported from the vector package.", so I thought it should be easier
00:56 <lyxia> Yes, these are the vectors from Data.Vector.Storable
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00:59 <fetter_oml> lyxia: yes, assoc seems like it should work
01:00 <fetter_oml> i will try getting it done with that one
01:01 <jle`> fetter_oml: i've called those one hots
01:01 <jle`> i think i've done those before in hmatrix, let me see if i can pull up some code
01:01 <fetter_oml> (whilst still thinking that a unity vector creation command might not be too luxurious)
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01:02 <jle`> they're also called canonical basis vectors too in a linear algebra sense
01:02 <jle`> (if you're looking for things to google)
01:03 <jle`> fetter_oml: if you need all of them at the same time, you can just slice the identity matrix
01:03 <jle`> but Data.Vector.Storable.gen might be the best way yeah.
01:03 <jle`> s/gen/generate
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01:04 <jle`> oh, hmatrix exports generate as 'build'
01:04 <fetter_oml> slicing ident was my first attempt too, but I dont really see how I should morph a (n,1)-dim matrix to a vector
01:04 <jle`> build 5 (\i -> if i == 3 then 1 else 0)
01:05 <lyxia> nice
01:05 <jle`> build is hmatrix's re-export of generate
01:05 <lyxia> The hmatrix docs look quite daunting, I'm not sure why.
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01:07 <jle`> it's organization is kinda funky
01:07 <lyxia> the functions seem properly categorized at a glance
01:07 <jle`> maybe it's just that there are so many functions
01:08 <fetter_oml> not enough, as one can see :)
01:08 <fetter_oml> thanks lyxia and jle`, the build command should suit perfectly
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01:09 <fetter_oml> thats another (but not the last) hurdle out of the way of some neuronal-network-fun
01:09 <jle`> let me know how it goes :)
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01:09 <jle`> sounds like a fun project
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01:17 <fetter_oml> so far nothing major, just trying to fiddle with the hnn-package to learn from the mnist-database (http://yann.lecun.com/exdb/mnist/)
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01:18 <fetter_oml> but as my last line of haskell code is about 3-5 behind, the work is going rather slow :)
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01:19 <fetter_oml> 3-5 years*. also, its quite late, goodnight.
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01:22 <robertkennedy> :t diff
01:22 <lambdabot> error:
01:22 <lambdabot> • Variable not in scope: diff
01:22 <lambdabot> • Perhaps you meant ‘dff’ (imported from Data.Graph)
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01:31 <jchia> I have a module that defines a data and an instance just for its own consumption that I don't want it to export. I think there's no "export hiding". Explicitly listing everything I don't want to hide is verbose. Wrapping the module in another module that re-exports hiding the data and instance seems ugly. Any other ways?
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01:35 <jchia> I suppose I could put those things I want to hide from export in a nested 'Internal' module.
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01:38 <Koterpillar> jchia: you can just list everything else you want to export
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01:38 <Koterpillar> if I understand you right...
01:39 <Koterpillar> e.g. if you define DataType and someFunction, why not make it: module Module (someFunction) where...
01:39 <jchia> Koterpillar, yeah, and that's quite verbose. E.g. if I have a list of 20 things out of which I want to hide 2. So, I have to explicitly export 18 things.
01:39 <jchia> I think I'm going to use an 'Internal' module
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01:40 <jle`> it's not an ideal solution, but yeah, it's something i've done too
01:40 <Koterpillar> oh, sorry, I missed that part in your question. I would still do that, though, because there might be more things you don't want to export
01:40 <jle`> but usually i write explicit export lists
01:41 <jchia> I'll probably have an explicit export list when the code is more stable
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01:52 <johnw> jchia: if you use ghc -ddump-minimal-imports Foo.hs, it'll probably get you where you want to be
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01:56 <Profpatsch> edwardk: I want to hit you https://hackage.haskell.org/package/trifecta-
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01:57 <maybefbi> the GHC output is merely a STG interpreter correct? the haskell runtime included with each executable merely shuffles the STG tree around
01:57 <maybefbi> am i correct in saying this?
01:58 <benzrf> maybefbi: idk if i'd put it that way
01:58 <maybefbi> how would you put it?
01:59 <benzrf> well - my understanding is that the reduction process isn't "external" to some graph
01:59 <benzrf> rather, the nodes of the graph contain code to be jumped to
01:59 <benzrf> or something like that!
01:59 <maybefbi> woah hmm
01:59 <benzrf> it's a bit like church encoding, i think
01:59 <benzrf> (this might be way off, though)
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02:01 <benzrf> er, maybe rather a pointer to the code you wanna jump to
02:01 <benzrf> i believe the actual expressions appearing in the code get compiled to static routines
02:02 <benzrf> so if you write something like `case f x of Just n -> n + 1; Nothing -> 0' then part of the output will be a procedure doing... that
02:02 <maybefbi> i dont think modern processors allow self modifying code, so im sure we cannot have thunks written in machine code
02:02 <maybefbi> so in some sense it has to be an interpreter if it reduces thunks into normal forms
02:03 <benzrf> kind of
02:03 <benzrf> iirc, a thunk is an allocated object which has a pointer to the code for forcing it - then once forced, it gets modified to isntead be the result value
02:04 <benzrf> so we do have a graph of thunks, but the logic of reducing any thunk is directly compiled
02:04 <maybefbi> hah thats clever
02:04 <benzrf> the nice part is that any given thunk will be the result of an expression physically in the code, so you already know all of the things you'll need to compile
02:05 <maybefbi> yeah
02:05 <maybefbi> so the runtime is just the bit that converts thunks to point to either the code or the data in non-executable heap
02:05 <maybefbi> ?
02:06 <maybefbi> also im assuming the garbage collection is also done by the runtime
02:06 <benzrf> well, i don't know if i'd call that a "runtime"
02:06 <benzrf> the garbage collection, yes
02:06 <maybefbi> what is it officially called instead of the runtime
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02:06 <benzrf> well, maybe it is called the runtime... i don't know the terminology that well
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02:06 <maybefbi> copy that
02:07 <benzrf> but the logic for allocating new thunks and so on could perfectly well be inlined into the compiled expressions
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02:08 <benzrf> so even if that logic is in a fixed set of functions added to the compiled code, it doesn't precisely feel like "a runtime" to me - maybe i just don't have a good grasp of what the word means
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02:09 <maybefbi> im trying to imagine how much work went into eta, the ghc compatible haskell for the jvm. i think they just implemented a STG shuffler but i could be wrong
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02:09 <benzrf> o:
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02:09 <benzrf> i think 'STG' actually refers to the thing i was describing where you have pointers to the reduction code
02:10 <benzrf> (again - i may very well be wrong)
02:10 <maybefbi> ok
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02:12 <Profpatsch> Hm, what’s with parsers drawing in attoparsec AND parsec?
02:12 <Profpatsch> That means trifecta always pulls in everything.
02:12 <Profpatsch> Also, lenses.
02:12 <Profpatsch> That’s a lot of dependencies.
02:12 <andrei> Hi, I'd like to submit a package to Stackage but it has an external dependency. What's the way to do this?
02:12 <andrei> A non-haskell dependency, so tests will fail
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02:17 <deepfire> what tricks people use to visualise type family reduction steps?
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02:18 <maybefbi> :kind!
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02:19 <robertkennedy> Mine is `:t undefined :: T A B`
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02:23 <jle`> huh, does that really work?
02:24 <jle`> i always just use :kind! ... i don't consider that a trick, though
02:24 <jle`> it's the documented way to do it, but it doesn't show reductino steps step-by-step, admittedly
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02:31 <lyxia> andrei: it seems you just disable the tests/mark them as expected failures
02:32 <lyxia> andrei: https://github.com/fpco/stackage/issues/811 for example
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02:41 <andrei> lyxia: Thanks! I just found that I can request some debian packages to be included in the stackage environment. That should do nicely
02:43 <lyxia> oh, that's nice then
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02:50 <dosequis> hey all - I'm running a QuickCheck test in ghci and wondering if it's possible to get the test data where it failed so that I can play around with it and see what happened - is this possible?
02:52 <deepfire> thanks everyone!
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02:59 <lyxia> dosequis: doesn't it print the generated counterexample?
02:59 <dosequis> lyxia: hey thanks for answering. Yes it does. Ideally though, I would want to bind it to a variable somehow, and then manually run some tests on it in the console
02:59 <lyxia> there should also be a way to get the seed/size combination out
03:00 <dosequis> lyxia: ok yes I saw that in the Result
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03:00 <dosequis> lyxia: so if I have seen/size, then presumably I can re-generate the data that caused the failure
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03:01 <lyxia> Right.
03:01 <dosequis> ok thanks! this helps
03:01 <lyxia> I think there is an open issue about a better api
03:01 <lyxia> the problem is it's not clear how that would work
03:02 <dosequis> yeah I mean I'm not sure how to proceed
03:02 <lyxia> dosequis: https://github.com/nick8325/quickcheck/issues/117
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03:02 <dosequis> lyxia: thanks for the link!
03:03 <lyxia> oh I had forgotten there's an actual solution
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03:07 <dosequis> lyxia: yes, I found http://hackage.haskell.org/package/quickcheck-with-counterexamples. Very helpful thanks again!
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03:13 <lyxia> yw
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03:44 <johnw> I'm reading http://bentnib.org/interleaving.html, and I'm wondering, how is this not just what FreeT does? (or, rather, an equivalent FixT)
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03:48 <Cale> johnw: I don't really understand the question -- they talk about the construction of free monads in that paper.
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03:52 <monochrom> Perhaps the abstract is better rewritten as "FreeT has been in use by practical people for a while. This paper aims to introduce this concept to theorists." :)
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03:52 <monochrom> (Afterall, functional programmers regularly reading JFP?! Are you kidding me?)
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03:53 <Cale> Heh, looks like that to me, yeah
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03:54 <Cale> Also, it's from 2015 -- when did FreeT appear independently?
03:55 <Cale> Oh, I guess that would have been a few years earlier
03:55 <monochrom> free-0.1.0 was Feb 2011 on hackage.
03:56 <monochrom> "initial free"
03:56 <haskull> the state monad has 2 args, a value and a state. is it bad to use the state as a separate value, or do i somehow use 2 state monads at the same time? or am i doing something wrong and need to restructure the code?
03:57 <monochrom> I don't understand "the state monad has 2 args".
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03:57 <haskull> i dont know what they're called.. like State Int Int, for example.
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03:57 <peddie> "s" and "a"
03:57 <Cale> haskull: The first is the type of the state which is manipulated during the computation, and the second is the type of the result of the action.
03:57 <monochrom> OK, the State type.
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03:58 <Cale> So what do you mean by "use the state as a separate value"?
03:58 <Cale> Perhaps it would help if we could see what your code looks like
03:59 <monochrom> Next, I don't understand "use the state as a separate value". But the bottomline is, if your code compiles and gives the right answer, you are doing it right.
03:59 <Cale> Note that you can choose any type at all that you like to be the type of state being manipulated, so in particular, it might be a record consisting of a bunch of independent things
03:59 <monochrom> Actually maybe I only mean the converse. If your code has a type error or gives the wrong answer, then you have wrong concept.
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04:00 <monochrom> If you mean, "I will use 'get' all the time and 'put' never", OK it is legal, but then you're better off with Reader.
04:01 <haskull> I'm reading from a string, and based on the words in it I want to modify the content of 2 lists.
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04:01 <haskull> i'm having trouble clarifying as i hardly understand what i'm doing :/
04:02 <Cale> haskull: I would usually recommend trying to just write your function without any State monad first, so that you *do* understand it that way, and then if you ended up with a lot of functions of the form s -> (s,a), where you're tupling the result of the function with a new intermediate state, consider using a State monad to clean it up.
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04:03 <haskull> alright, thanks.
04:03 <Cale> From that description, it shouldn't be too hard to imagine using State, but it also might not improve things much, depending on the details
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04:03 <Cale> You could have a pair of lists as the 's' type
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04:04 <Cale> But then again, you might just be able to write a function which takes those two lists being manipulated as arguments, and which applies itself to new arguments according to how the lists are to be updated.
04:04 <Cale> (does that make sense?)
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04:05 <Cale> The main way in which variables vary is to be bound to new things when a function is applied to new arguments.
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04:06 <haskull> the part about tupling the 2 lists makes sense
04:06 <haskull> i think it'd work
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04:07 <Cale> > let f xs ys [] = (xs,ys); f xs ys (u:us) = if even u then f (u:xs) ys us else f xs (u:ys) us in f [] [] [1..10]
04:07 <lambdabot> ([10,8,6,4,2],[9,7,5,3,1])
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04:08 <Cale> ^^ have a look at how that thing manipulates the lists xs and ys, adding the next element to be processed to one or the other depending on whether it's even.
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04:09 <haskull> i see. thanks, i think i can figure it out now.
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04:16 <Ptival> DuplicateRecordFields is weird http://paste.awesom.eu/2GTa
04:17 <johnw> Cale: what I mean is, in 2015 what is it adding?
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04:17 <Ptival> the reason given in the wiki ("we do not infer the type of the argument to determine the datatype, or have any way of deferring the choice to the constraint solver") is disappointing
04:17 <johnw> Cale: or is it just clarifying the intersection between FreeT constructions and f-and-m-algebras?
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04:40 <cris_> hi, i write up some code on dates, could you check if any could be improved? https://github.com/szehk/Haskell-Carbonara-Library/tree/master/src/Data/Carbonara
04:42 <EvanR> dayToUnixTime can be done without magic numbers, using Data.Time conversion functions
04:43 <cris_> thanks EvanR, let me check
04:43 <EvanR> and unixtimeToDay
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04:44 <EvanR> posixSecondsToUTCTime :: POSIXTime -> UTCTime
04:46 <EvanR> POSIXTime is a fractional number of seconds, UTCTime is a Day paired with length of time past midnight
04:47 <cris_> thanks EvanR, i ll change it soon , I 'll go to lunch now and reply you guys later
04:47 <EvanR> Integer -> POSIXTime is fromInteger, UTCTime -> Day is utctDay
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05:06 <sssilver> Hey guys, I have this problem where I am a Haskell programmer, I know the language pretty well, have shipped production code in it, can leverage the various language features and all Haskell programs make sense to me
05:07 <Cale> Cool problem
05:07 <sssilver> however, whenever people start talking about the mathematical aspects of the type system and everything, that stuff just completely flies over my head; I get dazed and confused
05:07 <Cale> ah
05:07 <pacak> Keep getting dazed and confused, eventually you'll get used to it :)
05:08 <Cale> @remember sssilver Hey guys, I have this problem where I am a Haskell programmer, I know the language pretty well, have shipped production code in it, can leverage the various language features and all Haskell programs make sense to me
05:08 <lambdabot> I will never forget.
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05:08 <monochrom> Haha.
05:08 <Cale> sssilver: (sorry, that was too perfect, had to take it out of context)
05:09 <monochrom> But you are probably just missing some background knowledge.
05:09 <Cale> You might try Benjamin Pierce's "Types and Programming Languages" as a start
05:09 <sssilver> yes monochrom so I complained about this to a friend who's building compilers at Intel, and he advised I read this book called "Concrete Mathematics"
05:10 <subttle> sssilver: Bartosz Milewski has a great video lecture series (still in progress) if that is more your thing..
05:10 <Cale> (As a somewhat gentle intro to type theory proper)
05:10 <subttle> https://www.youtube.com/playlist?list=PLbgaMIhjbmEnaH_LTkxLI7FMa2HsnawM_
05:10 <sssilver> so I started reading it, but every paragraph makes me go "why dafuk am I doing this to myself??" in bewilderment and self loathing
05:11 <monochrom> Concrete Mathematics is going to make you an expert in determining whether a certain algorithm's running time is "n^2 + 4n arithmetic operations", and only that.
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05:12 <monochrom> It still won't tell you about types or catamorphisms.
05:13 <monochrom> "But it's a pretty thick book!" you may say. I know right?
05:13 <sssilver> the question is, do I really need to understand all of it in order to earn the moral right to feel like an accomplished programmer, when commuting from work to home?
05:13 <solrize> sssilver, concrete mathematics is kind of a streamlined and easier version of the stuff in knuth vol 1
05:14 <solrize> yes it's a very good book
05:14 <monochrom> Well, considering the fact that the typical CS student chose CS because "I flunked highschool algebra and I'm proud of it", you do need a thick book to just reteach highschool algebra (for the purpose of algebraic expressions of running times, but still.)
05:14 <solrize> very well worth reading, even if you decide that you won't get much benefit from working thru all the details
05:14 <solrize> monochrom, no it's not a rehash of hs algebra :)
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05:15 <solrize> those concrete running time calculations are usually done with generating functions
05:15 <solrize> it was an eye opener
05:16 <solrize> he analyze the running time of "find the maximum" (i.e. the obvious linear algorithm) that way
05:16 <solrize> at least in taocp vol 1, not sure if that's also in cm
05:16 <monochrom> That might be an overkill.
05:16 <solrize> well he used it to show the technique, not to find the running time of find the maximum ;)
05:18 <monochrom> P.S. Though I said "types" and "catamorphisms" together, do not think that I meant they were covered by the same book. No, they are yet two different books.
05:19 <sssilver> how did you guys come to know and understand all this stuff!
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05:19 <solrize> hmm dunno
05:19 <sssilver> you can push a LOT of JSON through TCP using Haskell and still not have to touch any of it
05:19 <subttle> sssilver: https://bartoszmilewski.com/2014/10/28/category-theory-for-programmers-the-preface/
05:19 <monochrom> "types" being covered by Types and Programming Languages as said (though I wonder if Practical Foundations for Programming Languages is shorter and cheaper). (Also you don't need to finish the whole book.)
05:20 <solrize> PFPL is online for free
05:20 <solrize> i liked it
05:20 <solrize> it was much less detailed than TAPL, but TAPL has a lot of material on subtype systems
05:20 <monochrom> "catamorphism" there are some papers and there are other books with category theory inclinations.
05:20 <conal> sssilver: I can't tell why you want to learn the math/theory stuff. Maybe it's out of reach because you don't have an intrinsic motivation.
05:20 <solrize> which i thought were unstylish around here
05:21 <monochrom> Yeah TAPL is big because subtypes.
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05:21 <sssilver> conal yes it bores me to death :(( but I consciously understand that I should be interested in it
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05:21 <solrize> i first saw catamorphism in a program derivation (i.e. bird) context i think
05:21 <monochrom> But you don't need subtypes for Haskell. And you kind of learn that subtyping is really difficult, so it might be not such a good idea to use it.
05:22 <solrize> sssilver, what kind of theory?
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05:22 <monochrom> Yeah but Bird has a category theory inclination.
05:22 <solrize> yeah
05:22 <monochrom> The most extreme being Algebra of Programming (now hard to find and expensive). But many Bird papers are not that extreme.
05:22 <solrize> for very basic intro the haskell wikibook page about categories is really nice
05:23 <solrize> does't say anything about catamorphisms though :)
05:23 <conal> sssilver: maybe it's not true that you should be interested. especially if it's for status or self-image ("the moral right to feel like an accomplished programmer"). it doesn't sound fun to learn without a genuine interest.
05:23 <monochrom> Ah yea the wikibook is good.
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05:23 <solrize> the only way to gain the moral right to feel like an accomplished programmer is to write some really good code. then you'll have accomplished something as a programmer and can feel like you've done that
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05:24 <solrize> you don't need a ton of theory to write good code
05:24 <solrize> but it helps to not be totally ignorant
05:24 <solrize> know some theory
05:24 <solrize> not necessarily a lot
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05:24 <solrize> see antirez recent blog
05:24 <solrize> http://antirez.com/news/112
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05:26 <conal> i suspect that most people who are good at math / theory got good at it because they genuinely delight in it, not for status.
05:27 <monochrom> I don't worry about people learning useless academic stuff. I do that all the time. I was learning linear algebra (specifically the kind for quantum bits). I am planning to learn Lagrangian and Hamiltonian mechanics soon. Useful for my career? No way. Rabit holes? Yes a multiverse of rabbit holes. It's a hobby, I know that.
05:27 <conal> ... and there are a lot of other things to enjoy.
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05:28 <sssilver> :(
05:29 <monochrom> Sure. I just enjoyed The Lego Batman Musical today. Nothing to do with Hermitian matrices, which I also enjoy.
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05:31 <monochrom> ObHaskell: I did code up some matrix operations (backed by Data.Vector) (naive algorithms) so I didn't always have to multiply matrices by hand.
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05:35 <spatial> http://pastebin.com/zWZxXiam After the case the varialbles go out of scope
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05:36 <monochrom> Look at the indentation shown in the paste. It completely explains why.
05:39 <haskull> execute :: Operation -> StateT ParseState IO (); cmds :: [Operation]; why can't I do execStateT (do fmap execute cmds) (..)?
05:39 <Koterpillar> haskull: you need sequence
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05:43 <fragamus> hey so what language is all that hacking code written in?
05:43 <fragamus> In my imagination it is badass haskell code
05:44 <Koterpillar> fragamus: much as you'd want it to, people's toasters aren't that fast on compiling GHC
05:45 cschneid_ joined
05:45 <fragamus> wait they can hack my toaster damn
05:46 <fragamus> what secrets lie in the crumbs at the bottom of my toaster
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05:48 <haskull> if i keep smashing my head with haskell will i eventually get it, or should i find the patience to read a book?
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05:49 <Koterpillar> haskull: both are good techniques, try combining them
05:50 <CoconutSnail> find a book and smash one's head with it?
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05:50 <c_wraith> haskull: semi-passive learning was the most effective technique I used. Hang out here for hours, and whenever a topic came up that interested me, become less passive and ask questions.
05:51 <Koterpillar> ^
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06:04 <haskull> is "Please report this as a GHC bug" a big deal or can i just ignore it?
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06:05 <Koterpillar> it'll be nice to report if you can minimize the test case
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06:05 <Koterpillar> (or maybe it's a known bug, but still)
06:06 <haskull> i'll try tomorrow, gonna sleep for now.
06:06 <haskull> bye, and thanks
06:10 <qmm> When using something like Scotty, what is a common way to setup a database connection for the entire app?
06:11 <qmm> maybe the question is, how do i pass a reference to a database around
06:12 <Koterpillar> no experience with Scotty in particular, but you usually put it inside your base monad
06:13 <Koterpillar> aha, same thing, use Web.Scotty.Trans
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06:21 <_sras_> Is there a program that can convert and HTML string into format of a Lucid template?
06:21 <_sras_> s/and/an
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06:35 <srhb> _sras_: Don't think so.
06:35 <spatial> http://pastebin.com/637shj0t Where should that return actually be placed ?
06:35 <spatial> Indented
06:36 <spatial> parse error on input `return'
06:36 <srhb> spatial: It's easier if you rewrite without re-indenting on every line
06:36 <Koterpillar> with do notation, you don't have to use 'let .. in'
06:37 <spatial> do notation - What ?
06:37 <Koterpillar> also, why is this return needed? Could probably have the same function without the Monad constraint
06:37 <Koterpillar> spatial: what is the type of this function?
06:38 <spatial> nextstate :: Player -> BoardState -> Int -> BoardState
06:38 <srhb> spatial: I don't understand what you're actually trying to do, but here the indentation is fixed at least: http://lpaste.net/1567422115374694400
06:38 <Koterpillar> spatial: what is the type of 'return'?
06:38 <Koterpillar> spatial: forget about return, you don't need it
06:38 <spatial> data BoardState = BoardState { xloc :: [Int], oloc :: [Int], index :: Int } deriving (Show)
06:39 <Koterpillar> :t return
06:39 <lambdabot> Monad m => a -> m a
06:39 <spatial> Oh what is :t return
06:40 <Koterpillar> spatial: return is a function, which you currently don't need
06:40 <Koterpillar> spatial: I think this will be a good start: http://lpaste.net/353299
06:40 <athan> Is there a way to `cancel` an `async` thread, from within the thread itself?
06:40 <athan> like an anonymous cancel?
06:41 <spatial> Right.
06:41 <Koterpillar> spatial: I suspect you are trying to write your function as, "let's assign X to Y, then let's assign some f(Y) back to Y"
06:42 <spatial> Ya OCaml syntax
06:42 <Koterpillar> spatial: it helps if you think of it instead as: "The next state of the game (?), if the previous state is this and the move is that, _is_ ..."
06:42 <spatial> Converting lisp. Right
06:43 <spatial> So return is needed in what situations ?
06:43 <spatial> Never ?
06:43 <Koterpillar> when you are using monad typeclass, and even then in modern GHC you have 'pure'
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06:47 <Rotaerk> athan, I haven't really used async in haskell so I'm not sure if my response applies, but I've used something similar in C#...
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06:48 <Rotaerk> athan, why can't the async thread just end?
06:49 <Rotaerk> if you're at a point of execution within that thread where you want to cancel, simply return
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06:50 <athan> hmm, well Control.Concurrent has myThreadId
06:50 <athan> I might just use that and killThread
06:50 <athan> (I think async just builds on top of it)
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06:50 <athan> my only issue is I also used `forever` Rotaerk
06:50 <Rotaerk> I don't understand why you would kill *this thread* though
06:51 <Rotaerk> can you replace forever with a condition that changes when ready to end?
06:51 <athan> not really :\
06:51 <Rotaerk> can you paste?
06:52 <athan> foo = async $ forever $ do { ... when bar $ killThread =<< myThreadId }
06:52 <athan> I think that should work
06:52 <athan> `async` I think intents to be more... structural or osmething
06:53 <EvanR> async provides a lot of tedious checks and exception propogation which really streamline the task
06:53 <athan> ahh hm
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06:54 <EvanR> async lets you directly cancel a task
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06:54 <EvanR> if you wait for a result and the thread crashes you get the exception
06:54 <EvanR> when the thead is spawned, weird asynchronous exception possibilities are handled
06:54 <Rotaerk> sounds like the way tasks and await work in C#... you don't get the exception until you wait for the task, even if it actually is thrown long before you await it
06:55 <Rotaerk> it just seems unnecessary to me to ... cancel a task from within itself
06:55 <Rotaerk> instead just return from it cleanly
06:55 <EvanR> killThread throws a ThreadKilled exception to a thread
06:56 <athan> :x
06:56 <EvanR> so killing yourself is the same thing (or intuitively is the same) as just thowing an exception
06:57 <EvanR> throwIO (userError "I'm dead")
06:58 <athan> but... async will ignore it unless they are `link`ed... right?
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06:59 <EvanR> what, if you throw an exception, youre not going to be continuing
06:59 <EvanR> :t throwIO
06:59 <lambdabot> Exception e => e -> IO a
06:59 <EvanR> it returns an "a"
07:00 <EvanR> its illogical to continue
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07:01 <athan> crud, thanks EvanR
07:01 <EvanR> no one may ever know you are dead, but thats another story
07:02 <EvanR> but if no one is listening, who cares
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07:17 <wizard1337> is there a name for the problem of being able to transform imperative code into functional and/or vice versa? how do i find some thoughtful articles on the topic
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07:18 <Cale> There is a name for the programs which do that sort of work, they're called compilers :)
07:18 <peddie> wizard1337: you could start with https://pdfs.semanticscholar.org/7cb9/0be27017772fa441981d3d362741056efd57.pdf
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07:23 <aces> Hi, complete beginner here, have almost no programming experience. I read that haskell is a great language to start out with and wanted to start with functional programming from scratch. Can anyone point me to a tutorial that is beginner friendly?
07:24 <wizard1337> aces: my best advice (as a newb myself) is start writing code and forget about learning more than little bits of the language
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07:24 <wizard1337> aces: then grow those bits with time
07:24 <aces> wizard1337: I don't know much about the basics as of yet. I still need to learn the concepts prior to writing code.
07:25 <peddie> @where nicta -- aces
07:25 <lambdabot> https://github.com/nicta/course
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07:25 <peddie> @where cis194 -- aces
07:25 <lambdabot> http://www.seas.upenn.edu/~cis194/spring13/
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07:27 <wizard1337> omg ghci has tab completion :D
07:27 <aces> Thank you peddie , having a look.
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07:28 <wizard1337> and use stack, not cabal
07:28 <peddie> aces: good luck and have fun
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07:51 <wizard1337> why does reid barton work on ghc
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07:58 <cocreature> why shouldn’t he?
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07:58 <wizard1337> seems like a bit of a jump from pure math
07:59 <cocreature> some people have multiple interests :)
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08:00 <wizard1337> is there any relation to his experience at rentech?
08:00 <wizard1337> and is he paid to work on ghc?
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08:01 <ezyang> "because it's fun and intellectually stimulating"
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08:03 <n1> 'pure math' is a matter of perspective!
08:04 <wizard1337> what are the major sources of funding for ghc?
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08:09 <Cale> wizard1337: Well, it's an open source project, but I suppose you could have a look at the places that the developers are working.
08:09 <wizard1337> so do people who are actually good with haskell get snapped up
08:10 <wizard1337> or is it what i have read, which is that there are tons of people who are great with haskell who are desperate to find a position anywhere
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08:10 <Cale> It's a bit of both.
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08:10 <wizard1337> *and are
08:10 <wizard1337> those are sorta mutually exclusive
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08:10 <n1> I believe SPJ works on ghc for microsoft research
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08:10 <wizard1337> right, so that would be 1 job
08:11 <Cale> wizard1337: Well, there are a fair number of us who are employed and spend our day jobs writing Haskell
08:11 <wizard1337> i guess it's appropriate to respond with an existence proof?
08:11 <wizard1337> ;-P
08:11 <Cale> I'm one of them :)
08:12 <wizard1337> right,... but it's not like there are agencies which will be absorbing pretty much anybody who is tall enough to ride the roller coaster
08:12 <wizard1337> or are there...?
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08:12 <Cale> There's Takt, they've been snapping up lots of people lately :)
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08:13 <Cale> (They're a startup, but they have quite a lot of funding from what it seems)
08:13 <wizard1337> lol ive worked at startups with about 30 times that in funding :)
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08:14 <wizard1337> 30 m is significant but not remarkable
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08:14 <Cale> Well, it's enough to hire a bunch of people and to do a bunch of business with the other Haskell development companies
08:15 <Cale> The entire community is only so large to begin with.
08:15 <wizard1337> i see
08:15 <ezyang> GHC dev is basically MSR + Well Typed + Army of PhDs
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08:15 <ezyang> with MSR and other industrial people funding the Well Typed committment
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08:16 <Cale> A couple people at Obsidian also have been getting into it a bit lately, if a bit in anger :)
08:16 <wizard1337> carmack likes haskell
08:17 <wizard1337> said that he started a project in it
08:17 <wizard1337> but other people working on it stormed his office and said "what the hell is a monad?"
08:18 <Cale> Monads are not a big deal. It's just a mathematical name for a pattern that's been showing up in functional programming for much longer than we had a name for it.
08:18 <wizard1337> yeah, i'm not saying these people had the right idea
08:20 <Cale> The harder part of learning to program in Haskell is usually going to have more to do with the change in mindset required regarding programming with immutable data structures most of the time.
08:21 <wizard1337> yaeh
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08:27 <Cale> wizard1337: Also, when it comes to IO, the fact that IO is a monad, though it seems to be what people often fixate on, is not usually going to be any kind of a problem -- it just means we have a certain API for sticking these things together. The weird part that takes some getting used to is that IO is a type at all, and that we have a type of values which represent effectful programs, and their execution is a separate process from
08:27 <Cale> evaluation of expressions.
08:28 <wizard1337> i don't fully understand monads but everything i've seen about them so far isn't troublesome
08:28 <wizard1337> containing state is a very sensible thing
08:28 <Cale> You basically learn a bunch of examples of them
08:28 <wizard1337> i did that naturally when i wrote imperative code
08:29 <wizard1337> purity, totality, state containment,...
08:29 <Cale> and gradually get a good sense that way for what kinds of things to usually expect
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08:30 <maerwald> what's a nice xml parser in haskell without lens, TH or other complexity I don't care about
08:30 <wizard1337> lol
08:30 <wizard1337> if you don't like complexity, why are you using xml
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08:31 <maerwald> because it's the input
08:31 <Cale> maerwald: What do you need it for? hexpat-pickle is old, but it might be good.
08:31 <cocreature> maerwald: I’ve used xml-conduit and found it quite nice
08:31 <maerwald> Cale: parsing the capec database
08:31 <cocreature> you don’t need to use conduit for it to be useful
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08:33 <wizard1337> use kaggle and hire someone to train a neural net to parse xml
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08:35 <rom1504> great idea
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08:41 <wizard1337> oh, it's the gghc
08:41 <wizard1337> not ghc
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08:59 <Cale> wizard1337: ??
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09:00 <Cale> oh, Glorious Glasgow Haskell Compiler? :)
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09:01 <errorondefault_> Hi everyone I'm doing a challange for a jobinterview and got stuck on level04 can I ask here for help?
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09:02 <wizard1337> will you pay us part of your salary?
09:02 <Cale> lol, "I only want 7%"
09:02 <wizard1337> and are you using gghc or ghc?
09:02 <errorondefault_> haha nice one :D its a job as working student so it probably will be barely enough to pay for rent through college :D
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09:03 <wizard1337> are you using the gghc compiler or ghc?
09:03 <Cale> What are you stuck on?
09:03 <errorondefault_> but its in infosec and thats where I want to go so I really want this job
09:03 <errorondefault_> well I probably need to start from the beginning
09:03 <Cale> wizard1337: Are you joking about the Glorious bit?
09:03 <wizard1337> because you want a pole dancer girlfriend?
09:04 <errorondefault_> so via email I get a link to this challenge cant share it because I have my personal login and Im sure they check
09:04 <errorondefault_> so lets say its www.web.com. On there it says: Intro Welcome Continue with Level00 Rules: Use your brain NO DoS, NO bruteforce. Level00 is a link to www.web.com/level00
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09:05 <wizard1337> can i use neural nets?
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09:05 <Cale> Do you have an actual Haskell question though?
09:05 <errorondefault_> no
09:06 <cocreature> if you can’t share the question then maybe the point of the challenge is that you figure out the solution yourself
09:06 <Cale> This channel is for discussion of Haskell...
09:06 <errorondefault_> right now I think its related to php and just figuering out this riddle
09:06 <wizard1337> but he has an actual potential haskell job
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09:06 <errorondefault_> and i really want this job :D
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09:07 <wizard1337> that's code for "i'm not qualified"
09:07 <wizard1337> seriously though asking other people about job interview questions is really bad,
09:07 <errorondefault_> well im not :D Im second semester but Im eager to learn ;)
09:07 <Cale> anyway, if you have questions regarding the programming language Haskell, I'm sure people here would be happy to help
09:07 <wizard1337> because if you advance to the next step,
09:07 <Cale> Otherwise, it's not really the right place
09:08 <wizard1337> you'll waste their time in that step
09:08 <wizard1337> rather than now
09:08 <errorondefault_> ok youre right sorry about that
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09:08 <wizard1337> and subsequent steps often involve actually interviewing at a whiteboard etc
09:08 <Cale> wizard1337: pls
09:08 <errorondefault_> thanks anyways guys
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09:09 <wizard1337> no etquiette allowed? even functional etiquiette?
09:09 <wizard1337> i resolved his "haskell question"
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09:11 <biglama> hi guys, I would like to use HStringTemplate with a custom datatype
09:11 tippenein joined
09:11 <biglama> but one of the field of my datatype is another datatype and I would like to have a custom show for this field
09:11 Einwq joined
09:11 <biglama> I've tried to instantiate ToSElem and Show but it still resort to the default show
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09:22 <Cale> biglama: Well, what does toSElem produce for your type?
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09:24 <lpaste_> biglama pasted “Custom formatting with HStringTemplate” at http://lpaste.net/5642642439081558016
09:24 <biglama> Cale: it returns a string
09:24 takle joined
09:24 <biglama> Cale: I've pasted the code as it may be clearer
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09:25 <lpaste_> biglama revised “Custom formatting with HStringTemplate”: “Custom formatting with HStringTemplate” at http://lpaste.net/5642642439081558016
09:26 <dxtr> Good morning, fellow youngsters
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09:27 <Cale> biglama: If you remove the Show instance for Children (you shouldn't need it after all), does it complain?
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09:28 <biglama> Cale: it does not complain but it does not change the output. Instancing show does not help either !
09:28 <Cale> Well, if it doesn't complain about the lack of an instance of Show, then writing one can't possibly help anything.
09:28 <biglama> I'm a bit confused
09:29 <Cale> oh, what's this GenericStandard business?
09:30 <Cale> Remove all the Data instances too
09:30 <Cale> Just to be sure it's not using those
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09:30 <biglama> Cale: GenericStandard avoid to define ToSElem instances actually. But then I would have to define a ToSElem instance for person too ?
09:31 <Cale> Possibly, yes
09:31 <brynedwards> The StringTemplate docs have "class Show a => StringTemplateShows a where"
09:32 <brynedwards> Which takes and optional format string, and its default is show. Have you tried instantiating that?
09:32 <Cale> ah, you'd be using the ToSElem instance for Person as it stands
09:33 <Cale> Since you're doing setAttribute with a Person value
09:33 <biglama> brynedwards: I've tried but I'm a bit confused between ToSElem and StringTemplateShows
09:33 <Cale> So if that instance is just based on the Data.Data generic representation entirely, it won't do what you want.
09:33 <biglama> I do not need the format string so I though instantiang ToSElem would be enough
09:34 <Cale> Try just writing a ToSElem instance for Person
09:34 <brynedwards> Yeah but it says the format string is optional so maybe it uses it regardless
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09:35 <Cale> You're not actually using the ToSElem instance for Children at all, iiuc
09:35 <Cale> (you should be able to comment out / delete that instance and still have the program build if I'm right)
09:37 <Cale> Personally, I avoid libraries like this. Usually it's easy enough just to concatenate strings together the way you want, and do whatever formatting is necessary in-place with whatever functions are appropriate.
09:38 systadmin joined
09:38 <Cale> (Though, I couldn't help writing one of them anyway ;) https://hackage.haskell.org/package/category-printf
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09:39 <biglama> Cale: here is a trimmed-down example with juste an instance of ToSElem, but it does not work
09:39 <biglama> Cale: http://lpaste.net/6884328818773852160
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09:40 <biglama> I'm trying with an instance of StringTemplateShows now
09:40 <Cale> What happens? You get a complaint that the name and children fields aren't present?
09:40 <biglama> Cale: well, I wanted something clean :)
09:40 <biglama> Cale: the code runs but the output is empty for the field, as in
09:40 <biglama> "Your full name is , children = ."
09:40 <Cale> nice
09:41 <Cale> I suspect that's what the SMap constructor is for
09:41 louispan joined
09:41 <Cale> Actually, I would throw this library out on the spot for producing that output rather than an error of some sort.
09:42 <biglama> :)
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09:42 <biglama> How would SMap play a role here ? I'm looking at the code but don't see where it's used
09:42 <Cale> Well, where you're currently producing a STR
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09:43 <Cale> You want the person thing to have some named subfields which you refer to in your template
09:43 <Cale> So, presumably there's some way to define what those expand to
09:43 <Cale> and if you look at the SElem type
09:44 <Cale> The only thing which looks like it could be doing that job is the SM constructor which takes an "SMap a"
09:44 <Cale> and apparently type SMap a = Map String (SElem a)
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09:44 <Cale> So I'd expect that to be a Map from the "field names" to how to format them.
09:45 defaultnick_ joined
09:46 <Cale> So try something like toSElem x = SM $ Map.fromList [("name", STR $ name x), ("children", STR $ "lol")]
09:46 <biglama> So brynedwards is right, I should instantiate StringTemplateShows instead ?
09:46 <Cale> and I think you can leave out the toSElemList
09:46 <Cale> The default instance for that should do
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09:48 <biglama> Cale: your solution works !
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09:49 <biglama> I find it a bit cumbersome though
09:49 <Cale> I do too. It's certainly much worse than just writing what you mean
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09:50 <Cale> displayPerson :: Person -> String; displayPerson x = "Your full name is " <> name x <> ", children = lol."
09:50 <biglama> yeah
09:51 <Cale> Ah I suppose you can use ++ for String
09:51 <Cale> I would usually use Text these days :)
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09:51 <biglama> I wanted a generic solution for very large datatype, where you would only have to instantiante show
09:52 <Cale> Also, generally you should try to make show x produce valid source code for constructing x
09:52 <Cale> (or something close to it)
09:53 <Unhammer> if we had no list fusion, would it be right to assume "map (a.b) l" to be more performant than "map a$map b l" ?
09:53 FreeBirdLjj joined
09:53 <Cale> Unhammer: yes
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09:53 <Unhammer> ok, cool
09:53 <Cale> Though I reserve the right to wince at "more performant than"
09:54 <biglama> Cale: can you give me an example ?
09:54 <biglama> of "producing source code"
09:54 <Cale> > show [1,2,3,4,5]
09:54 <lambdabot> "[1,2,3,4,5]"
09:55 <Unhammer> Cale, sorry, "more performanter from"
09:55 <* Unhammer> ducks
09:55 <biglama> oh right
09:55 <Cale> > M.fromList [(1,"hello"), (2,"world")] -- Data.Map tries its best as well
09:55 <osa1> sometimes I wish we had let/letrec distinction in Haskell
09:55 <lambdabot> fromList [(1,"hello"),(2,"world")]
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09:56 <biglama> Cale: thanks a bunch anyway, it was very interesting, even though not very productive :)
09:56 <Cale> biglama: What does your overall program do?
09:56 <Cale> What are you using the templates for?
09:56 <Cale> osa1: So you can get away with confusing shadowing?
09:56 <Cale> :)
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09:57 <biglama> Cale: I'm generating configuration files randomly and then call an executable
09:57 <biglama> unit testing by hand
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09:59 <biglama> my configurations files are in the INI format
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09:59 <Cale> Unhammer: hehe, I just feel that whenever someone uses the word "performant" it's because they haven't actually done enough work to justify whatever claim it is that they're about to make -- otherwise they'd talk directly about what kind of performance they meant
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10:02 <Unhammer> Cale, yeah … I haven't done any work to measure :) I just got a suggestion from hlint, and started wondering if that was a "pure style" thing, or there were some deeper reason.
10:02 <Cale> It will use less time because it does fewer allocations.
10:02 <Cale> It may use slightly less space, but not significantly less, in isolation.
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10:04 <Cale> (because the cons cells of the intermediate list will immediately become garbage the moment they're created)
10:04 <Unhammer> Even without measuring, experienced coders do kind of write more performant code "by default", pattern-matching on previous experiences or whatnot. My early emacs-lisp was full of tail-recursion because I simply didn't know that .el doesn't TCO, now I'd never think about doing that without good reason.
10:05 spatial_ joined
10:05 <SpinTensor> Hi, started learning Haskell. As exercise i wanted to rewrite the elem function. I get a compile error and I don't know why: http://pastebin.com/c6jJpQnh
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10:05 <spatial_> do val <- value a index return ( BoardState xloc oloc index) val is an IO Int. So there is an error.
10:05 <Cale> "Tail calls" are kind of a weird thing in Haskell as well. There's no need for tail call optimisation because there's nothing which really corresponds to an ordinary call stack to begin with.
10:05 <Cale> (at least in GHC)
10:06 <SpinTensor> (n==x) returns a bool, so why does the compiler want a type (Eq a) somewhere?
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10:06 <spatial_> IO Int will become Int. When ?
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10:06 <Unhammer> yeah … I pretty much don't manually recurse in haskell =P
10:06 <Cale> spatial_: I'm having trouble parsing that
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10:07 <Unhammer> spatial_, you can't really escape IO
10:07 <Cale> spatial_: What's the type of value a index?
10:07 FreeBirdLjj joined
10:07 <Cale> Is it IO (IO Int) somehow?
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10:07 <Cale> I'm assuming the triple space there is a newline
10:08 <Cale> Wait, do you use val at all?
10:08 <spatial_> http://pastebin.com/5V3uzVUq val isn't used now. It will be.
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10:09 <Cale> Well, this clearly doesn't have the type you've given it
10:09 defaultnick__ joined
10:09 <Cale> You're constructing an IO action which, when executed, is going to give a BoardState
10:09 sid_fules joined
10:09 <mniip> SpinTensor, what are the types of n and x
10:09 freusque joined
10:09 <Cale> So this has type IOArray Int Int -> BoardState -> IO BoardState
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10:10 <spatial_> Intention was to get Int from val which is IO Int and use it
10:10 <Cale> If you want to read an IOArray, you'll need to be executing an IO action, you can't do that elsewhere.
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10:10 <mniip> SpinTensor, you're saying that elem' can be applied to a value of any type and a list of values of that type
10:10 <Cale> Where's the definition of value?
10:11 <mniip> SpinTensor, and then you proceed to use == on those types, but == doesn't work on all types
10:11 <spatial_> value :: ( IOArray Int Int) -> Int -> IO Int value a index = liftIO (runReaderT (readvalue index ) a)
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10:11 <mniip> only those that are Eq, hence the type error
10:11 <SpinTensor> it should not matter what they are, right?
10:11 <Cale> mniip: thanks for answering SpinTensor's question btw :)
10:11 <mniip> SpinTensor, of course it does matter
10:11 <mniip> not all types can be =='d
10:11 <SpinTensor> mniip: oh. so I need to write elem' for specific types when using pattern matching?
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10:12 <Cale> spatial_: whaaaaa
10:12 <mniip> SpinTensor, no
10:12 <mniip> SpinTensor, you just have to specify that 'a' in your type signature should be a type that supports being =='d
10:12 <Cale> spatial_: Are you sure you don't just want value = readArray ?
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10:12 <mniip> see:
10:12 <mniip> :t (==)
10:12 <SpinTensor> mniip: how do i do that?
10:12 <lambdabot> Eq a => a -> a -> Bool
10:13 <Cale> spatial_: What's the ReaderT shenanigans about?
10:13 <mniip> that 'Eq a' is telling you that 'a' should be an instance of Eq in order to use ==
10:13 <Cale> and that liftIO is definitely unnecessary and does nothing
10:13 <Cale> liftIO :: IO a -> IO a doesn't do anything
10:13 <mniip> you should put a similar 'Eq a =>' context on your type sig
10:13 <Cale> It's only interesting when you're converting an IO action into an action of some other monad
10:14 <SpinTensor> mniip: thanks that did it. its kind of complicated to get your head around all this type stuff
10:15 <mniip> there is actually way to figure out that type signature programmatically, and that's what GHC would have done if you had omitted the type signature,
10:15 <mniip> but you should learn to see it conceptually
10:15 <Cale> SpinTensor: However, note that this advice is exactly what the compiler suggested you do (it doesn't always provide good advice, but it managed to be right in this case!)
10:16 oisdk joined
10:16 <Cale> However, it didn't actually show you the change it wanted you to make, and only described it with technical language :/
10:16 <mniip> Cale, I wouldn't expect a beginner to know what "context" means
10:16 <Cale> yeah
10:16 <mniip> yeah
10:16 <SpinTensor> cale: I saw the (Eq a) in the error, but I had no idea where to include it. I tried something like elem' :: (Eq a) -> a -> Bool but that got different errors with constraint types.
10:17 <spatial_> Cale: That is separate piece to read and write arrays. That piece works.
10:17 <Cale> yeah, needs to be =>
10:17 <spatial_> Just trying to use the value read from the array.
10:17 <* mniip> . o O ( how confusing would it be to beginners if we had Constraint ~ * )
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10:18 <SpinTensor> Thanks for your help guys. Hope i understood it.
10:18 <Cale> spatial_: So, in a do-block for an IO action, you can indeed read the array
10:18 <Cale> spatial_: But that entire do-expression will be an IO action, and will have type IO t for some type t
10:19 <Cale> spatial_: This is unavoidable -- if you want to read an IOArray, you can't do it from evaluation, you must do it from execution of an IO action.
10:19 <spatial_> Oh. How do I separate IO and non-IO ?
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10:20 <Cale> Do you need to interleave writes and reads here, or are you done with writing?
10:20 <Cale> You might want to 'freeze' the IOArray into another array type that is immutable and has operations to read it that aren't IO actions.
10:20 <mniip> SpinTensor, btw I think you defined elem pretty much how it is in Prelude
10:21 <mniip> ...unless it's something like foldr . (==)
10:21 <spatial_> Reads and writes are there here.
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10:21 <spatial_> I am going back to Java :-)
10:21 <Cale> spatial_: So, if you want to stick with using IOArray, you have no choice but to work with IO actions.
10:21 <SpinTensor> mniip: cool. the version from the book uses guards, but i refused to look at the solution.
10:22 <Cale> There are lots of other data structures you could consider using instead, if you want to avoid IO
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10:22 <Cale> I would strongly consider Map, most of the time
10:22 <Cale> (Or IntMap, given that your indices are Int values here)
10:23 <spatial_> But these are very large arrays for Machine Learning.
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10:23 <mniip> elem _ [] = False
10:23 <mniip> elem x (y:ys) = x==y || elem x ys
10:23 <mniip> --GHC.List
10:23 <Cale> and you're reading and writing them randomly?
10:23 <spatial_> Yes
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10:24 <mniip> you could use an unboxed array (I mean a library that implements arrays using one)
10:24 <Cale> Okay, then just stick with IO, and either IOArray or perhaps MVector
10:25 <Cale> Oh, and yeah, IOUArray would be more compact
10:25 <SpinTensor> mniip: i pack everything in () because I'm not at the chapter with operator priorities yet.
10:25 <spatial_> Any function that reads or writes an IOArray cannot return a non-IO state ?
10:25 <Cale> Your IOArray Int Int will be an array of pointers to code which construct Int values.
10:25 <mniip> SpinTensor, that's not an issue
10:25 <mniip> as long as it's readable
10:26 <mniip> Cale, is that a fancy way to say that it's lazy?
10:26 <Cale> spatial_: Yeah, because it might produce a different thing every time. The function itself will always produce the same IO action, but the result of that IO action will depend on when you run it.
10:26 <Cale> mniip: yeah
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10:26 <mniip> you can make it strict can't you
10:26 <Cale> mniip: and that it's boxed
10:27 <Cale> It's boxed for polymorphism's sake regardless
10:27 <mniip> right
10:27 <Cale> IOUArray sidesteps that by only working for particular types
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10:28 <spatial_> So I need to move all these smaller functions into a larger one.
10:28 <spatial_> And manage it
10:28 <Cale> spatial_: You don't necessarily have to -- IO actions can be broken up into smaller parts as well if you like
10:28 <mniip> MVector sounds cool
10:28 <mniip> looks like it works with ST
10:28 <Cale> But perhaps start with a big lump of code and decide how to carve it up later
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10:28 <mniip> which is a nice thing in this context
10:29 <Cale> Oh, and yeah, there's STArray if you want to compute something using mutable arrays and end up with a pure function in the end.
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10:29 <Cale> But stick with IOArray for the time being until you get the hang of that
10:29 <mniip> STArray is eh
10:29 <mniip> I was more hinting at STVector
10:30 <Cale> Well, it's similar
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10:32 <Cale> spatial_: Just for reference, the Vector library we're referring to is this thing: https://hackage.haskell.org/package/vector
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10:33 <Cale> It has Data.Vector.Mutable, which is not so different from IOArray or STArray, except that the single type can be used as either one.
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10:45 <kuribas> I tested this: https://www.reddit.com/r/haskell/comments/1rcc8t/performance_of_the_st_monad_over_the_state_monad/
10:45 halogenandtoast joined
10:45 <kuribas> I get the same performance, the St monad being slightly slower.
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10:47 <kuribas> I guess ghc (and base) made a lot of progress in 4 years...
10:48 <spatial_> Cale: Let me look at it. Now I have to go back to the drawing board :-)
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10:50 <Yttrill> hi, i have a question about the gc and threads: am i correct assuming the shared heap collection requires a world stop?
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10:53 <Cale> Yttrill: Yeah, GHC's GC is parallel but stops the world. I seem to recall at some point that they tried a variant which didn't stop the world, and its throughput was much worse. I could be imagining that though.
10:53 <Yttrill> do you know how they stop the threads?
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10:54 <Yttrill> it's OS dependent of course assuming native threads
10:54 <Yttrill> Linux has a signal but I still don't see how the top of stack can be found
10:55 <ongy> the RTS schedules more threads than it has OS threads either way, it can take over on every heap allocation a thread does
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10:56 <Yttrill> hang on you said two things: second, it has control on an allocation, my GC stops the world that way also
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10:56 <Cale> http://simonmar.github.io/bib/papers/parallel-gc.pdf -- I think this paper is still relevant
10:56 <Yttrill> which is not very nice if you're running something long that doesn't do any allocation ;(
10:57 <Yttrill> Yeah i read that paper, but it explains how the GC operates not how it stops the threads
10:57 defaultnick joined
10:57 <Cale> Yeah, it looks like it just describes what takes place immediately following that bit of synchronization
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10:58 <Yttrill> i have a suspicion that there is a per thread local heap that can be collected without a world stop
10:58 <Cale> yes, there is
10:58 <Yttrill> but a stop is still required, i'm curious how to organise the stop
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10:59 <Yttrill> the Boehm collector using OS hacks eg SIGSTOP on Linux
10:59 <Yttrill> but i have no idea how that helps find the stack top
10:59 <Yttrill> i know there's a way to do this on Windows
11:00 <Yttrill> so non-Linux unix and OSX remain a mystery :)
11:00 <Cale> Or at least, I think that's right... but I'm now less certain :)
11:01 <Yttrill> the paper is old so there may be improvements
11:01 <Yttrill> if the world stop is done on allocation it makes sense
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11:02 <Yttrill> it means Haskell will have to have its own mutex, condition variables etc
11:02 <Yttrill> ones that time out often enough to check for a world stop
11:03 <Cale> Well, GHC's runtime has its own n:m thread scheduler anyway
11:03 <Yttrill> but what happens if a thread is multiplying two matrices? its a long wait until the next allocation
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11:04 <Yttrill> how does the RTS do that? it would have to capture timer interrupts or make allocations reschedule points ..
11:05 <Cale> oh, right, I was thinking of this version of the GC: http://simonmar.github.io/bib/papers/local-gc.pdf
11:05 <Cale> I'm not sure the version described in that paper is what actually made it
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11:06 <_sras_> Does template haskell have a function of type [Dec] -> String ?
11:06 <Cale> _sras_: Which gives you the text of the declarations? That would be nice, but it doesn't.
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11:07 <Cale> _sras_: You can get close (sort of) using -ddump-to-file -ddump-splices
11:07 <Cale> Assuming you just want to look at the generated code
11:07 <Yttrill> that second paper is 2011 which is a bit later
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11:09 <Cale> The person to talk to about this kind of thing would be Simon Marlow, who is sometimes around as JaffaCake on IRC, but he usually hangs out in #ghc moreso than #haskell
11:09 <Yttrill> ok second paper mentions "spark pool" which i believe from docs is in there
11:10 <Yttrill> ok
11:10 <Cale> The spark pool is part of the mechanism for pure parallelism, rather than for concurrency in general.
11:10 <Yttrill> ok thanks for that info
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11:11 <Yttrill> i'm just learning Haskell but i am also a compiler writer and language designer so curious about some deeper issues
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11:11 <Cale> When you evaluate par x y, the expression x gets "sparked" which means it's added to a queue of work that can be stolen from by the various Haskell execution contexts if they have nothing better to do.
11:11 Iskarlar joined
11:12 <Yttrill> ok, sort of like a thread pool
11:12 <Cale> (and the result of the evaluation is y)
11:12 <kuribas> Cale: does it run on another core, or just another thread?
11:13 <Cale> Usually it will be another HEC, which is probably running on another core
11:13 <Yttrill> i would guess it depends on tuning parameters
11:13 <Cale> But there's no guarantee that it'll be evaluated on another core
11:14 <Cale> and if you end up needing it too soon, your thread just evaluates it as normal
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11:15 <kuribas> Why does is stop the world when it runs in parallel? Does that mean some parts run in parallel, and other stop the world?
11:15 <Cale> There is a window of a couple cycles during which the main thread and some other thread can both begin to evaluate x, and that is just allowed to happen, since they will both produce the same result anyway, and the extra mechanisms required to prevent that are more costly on average than the occasional extremely unlikely duplication
11:15 cfricke joined
11:16 <Cale> It means that it stops the world, and then all the capabilities help to collect garbage at the same time
11:16 <Yttrill> yeah, that was proposed in the 2008 paper for the GC as well
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11:17 <_sras_> Cale: Yes. Can you take a look the the fullTableText function here ( https://github.com/folsen/opaleye-gen/blob/14938df0081187539f23f8547fb1b7762e286ac3/src/Generate.hs) and see if it could work?
11:17 <Yttrill> kuribas: the usual reason to stop the world is to find all the roots, which are usually all the thread stacks
11:18 <kuribas> Does it prevent real-time code?
11:18 <Yttrill> there's some kind of new development in the GC world I believe
11:18 <kuribas> (if the stops are long)
11:19 <Yttrill> kuribas: there are collectors which are incremental
11:19 <kuribas> and ght?
11:19 <Yttrill> dunno if the Haskell one is
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11:19 <Yttrill> actually the design would appear to support the possibility
11:20 <Yttrill> a traditional copying collector copies all live stuff from one huge memory block to another so it cannot be incremental
11:21 <Yttrill> but the GHC one uses blocks and copies old to new with blocks, even the same block
11:21 <Cale> Yttrill: From what I understand, the current collector is a generational hybrid of a copy collector and mark/sweep
11:21 <Yttrill> so it can probably just give up collecting any time
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11:23 <Yttrill> mark/sweep can be incremental because you just delete garbage so you can give up any time you like
11:23 <Cale> (and most of the time, it uses the copy collector)
11:24 srbaker_ joined
11:24 <Yttrill> yeah but it uses blocks for copying
11:25 <Yttrill> it looks like it could just give up the collection part way through
11:25 <Yttrill> so you could just run the collector more often and give up after a fixed period, which would make the collector suitable for real time
11:25 <Cale> https://ghc.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage/GC -- this looks like it might be helpful
11:25 <Yttrill> the problem is more likelyt that Haskell is not suitable for real time :)
11:26 <Yttrill> yeah that looks good if its up to date thanks Cale
11:27 <Cale> In the threaded RTS, there is one nursery per Capability, as each Capability allocates independently into its own allocation area. Nurseries are therefore stored in an array nurseries[], indexed by Capability number.
11:27 <Cale> aha
11:27 <Cale> So we were right about that :)
11:27 Rainb joined
11:28 <Yttrill> well that article says "last modified 6 years ago" :)
11:28 <Cale> haha
11:28 <Yttrill> which is 2011 when the PJ/SM paper was done
11:29 <Cale> Yeah, I don't recall hearing about anything too major going on with the GC since that time though
11:29 <Cale> I could be wrong though
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11:38 <Yttrill> http://www.cs.utexas.edu/users/speedway/DaCapo/papers/immix-pldi-2008.pdf
11:39 <Yttrill> something has happened recently: Ocaml is going multicore, and that is because only now is there a suitable GC available
11:39 surelyourejoking joined
11:39 <Yttrill> but that's all i know at the moment
11:40 <Yttrill> different performance needs from Haskell though
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11:49 <Axman6> bgamari: Hey, I just have your wkt package a go and it's not liking my input, seems to not like numbers which don't have a decimal point
11:49 <Axman6> gave*
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11:56 <surelyourejoking> I'm doing the Learn You a Haskell tutorials, and I don't understand the syntax for `groupBy`
11:56 <surelyourejoking> e.g groupBy (\x y -> (x > 0) == (y > 0)) values
11:57 sh0rug0ru joined
11:57 <surelyourejoking> where values is a list of some positive and negative floats
11:57 tommd joined
11:58 <Axman6> which part do you not understand?
11:58 <surelyourejoking> I suppose the lambda
11:58 <surelyourejoking> (\x y -> (x>0) == (y>0))
11:58 <Axman6> (\x y -> (x > 0) == (y > 0)) is a lambda function which takes two argument named x and y and returns the expression (x > 0) == (y > 0)
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11:59 <surelyourejoking> what does the right hand side evaluate to
11:59 <Axman6> > (\x y -> (x > 0) == (y > 0)) 1 1
11:59 <lambdabot> mueval-core: Time limit exceeded
11:59 <int-e> > let x = 1; y = -1 in ((x > 0), (y > 0), (x > 0) == (y > 0))
11:59 <lambdabot> (True,False,False)
11:59 <Axman6> uh, come on lambdabot
11:59 <surelyourejoking> so it's true if x and y are positive
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11:59 <Ferdirand> or if x and y are not positive
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12:00 <Axman6> it's true if x and y have the same sign (roughly)
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12:00 <Axman6> (assuming 0 is negative =) )
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12:01 <surelyourejoking> ok it's an XNOR logic gate then.
12:01 <surelyourejoking> right I understand the lambda function then
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12:01 <Axman6> looks like a nice way to find groups of increasing or decreasing runs... but that's not actually what it'll do sadly, because groupBy's behaviour is a surprising
12:02 <Axman6> > groupBy (\x y -> (x > 0) == (y > 0)) [1,2,3,2,1,0,-1,-2,-3,-2,-1]
12:02 <lambdabot> mueval-core: Time limit exceeded
12:02 <Axman6> what are you doing lambdabot!
12:02 <int-e> Axman6: the given relation is symmetric, so groupBy should not produce any surprises.
12:02 <int-e> @undef
12:02 <lambdabot> Undefined.
12:02 <int-e> > groupBy (\x y -> (x > 0) == (y > 0)) [1,2,3,2,1,0,-1,-2,-3,-2,-1]
12:02 <Axman6> > groupBy (\x y -> (x > 0) == (y > 0)) [1,2,3,2,1,0,-1,-2,-3,-2,-1]
12:02 <lambdabot> [[1,2,3,2,1],[0,-1,-2,-3,-2,-1]]
12:02 <lambdabot> [[1,2,3,2,1],[0,-1,-2,-3,-2,-1]]
12:02 <surelyourejoking> so let me clarify, whenever the equality condition is met, groupBy causes a split in the list?
12:03 Snircle joined
12:03 <surelyourejoking> sorry for the appaling terminology.
12:03 <surelyourejoking> *appalling.
12:03 <fweth> is there a built-in function like f::Just a->Just a->Just a; f(x)_=Just x; f(Nothing)(Just y)=Just y; f(Nothing)(Nothing)=Nothing ?
12:03 <brynedwards> :t groupBy
12:03 <lambdabot> (a -> a -> Bool) -> [a] -> [[a]]
12:04 <brynedwards> I'd say groupBy groups a list into multiple lists ;)
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12:04 <int-e> surelyourejoking: no, it's the oppisite, a split happens when the first element of the current group is not in relation with the list element being processed
12:04 <fweth> Sorry, I mean f::Just a->Just a->Just a; f(Just x)_=Just x; f(Nothing)(Just y)=Just y; f(Nothing)(Nothing)=Nothing ?
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12:04 <jle`> fweth: looks like <|>
12:04 <Axman6> int-e: many people are surprised that the comparison isn't make on consequtive elements, so groupBy (>) would produce lists of increasing runs. I also think the current definition is useful, but both versions would have the same type and neither convey their behaviour
12:04 <jle`> fweth: or mplus
12:04 <fweth> thanks!
12:04 <jle`> no problem!
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12:05 <int-e> > groupBy (<) [3,6,4,0,6,3,-1,-2,-3]
12:05 <lambdabot> [[3,6,4],[0,6,3],[-1],[-2],[-3]]
12:05 <jle`> it's also the behavior that a lot of people want for <>/mappend for Maybe
12:05 <jle`> but we do not live in that world
12:05 <jle`> can u imagine tho
12:06 <int-e> Axman6: right, actually I should have used the term "equivalence relation" because symmetry alone is not enough to avoid such surprises.
12:06 <Axman6> > groupBy (>)[1,100,2,300,2,0,1,2]
12:06 <lambdabot> [[1],[100,2],[300,2,0,1,2]]
12:06 janos__ joined
12:06 <Axman6> uh should've been (<) (or (<=)) obviously
12:06 <Axman6> > groupBy (<)[1,100,2,300,2,0,1,2]
12:07 <Hafydd> groupBy shouldn't be used without an equivalence relation.
12:07 <lambdabot> [[1,100,2,300,2],[0,1,2]]
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12:08 <int-e> Axman6: the "surprise" really only comes up when you start thinking about how groupBy could be implemented and then see that one of the possible implementations would be useful to produce increasing runs of a sequence.
12:08 <int-e> and then you find out that the actual implementation is not the one that allows this trick.
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12:14 <surelyourejoking> ok what on earth does `groupBy (>) xs` do
12:14 <surelyourejoking> I see that it makes sublists of increasing length
12:14 <surelyourejoking> but why
12:15 <kuribas> If (m1,m2) = Data.Map.Split x is O(log n), then is Data.Map.Union m1 m2 also O(log n)?
12:15 ramzifu joined
12:15 <int-e> surelyourejoking: it doesn't.
12:15 <int-e> surelyourejoking: basically forget that you ever saw this and stick to "groupBy shouldn't be used without an equivalence relation"
12:16 <surelyourejoking> ok I'm very happy to do so.
12:16 <int-e> surelyourejoking: (the sublists that it does produce have the property that the first element is the smallest. I can't think of a case where this is useful.)
12:16 <surelyourejoking> So one more time, groupBy looks at elements of a list two at a time, and makes a split when the equality condition between those two items is not met?
12:17 <dramforever> Sounds pretty deterministic to me, actually
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12:18 <int-e> surelyourejoking: No, it always compares the next element to the first element of the current group. But if the relation is an equivalence relation then your model produces the same results.
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12:21 <surelyourejoking> and as you've said, I should stick to equivalence relations.Thank you for the help!
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12:47 <hoppfull> Hello! I would like to create a "random" function that is pure. I need it for a simulation so that I get "random" behaviour but I can easily reproduce a situation with the same starting seed. However I seem to be having trouble finding what I'm looking for. If it rings a bell do you think you could help me by pointing me in the right direction? Is there a formal term for what I am looking for?
12:49 <pacak> :t random
12:49 <lambdabot> (Random a, RandomGen g) => g -> (a, g)
12:49 <pacak> :t mkStdGen
12:49 <lambdabot> Int -> StdGen
12:50 <pacak> > fst (random (mkStdGen 10)) :: Int
12:50 <lambdabot> mueval-core: Time limit exceeded
12:50 <kuribas> hoppfull: https://xkcd.com/221/
12:50 <pacak> lambdabot: WAT?
12:51 <kuribas> > take 20 $ randomRs (0, 1) (mkStdGen 0)
12:51 <unclechu> hey guys, is registration on hackage working? it tells me that confirmation email sent but i don't see in my inbox anything, also in smap directory
12:51 <lambdabot> [1,1,1,0,0,1,1,1,1,0,1,0,0,0,0,1,0,1,1,0]
12:51 <pacak> hoppfull: Anyway, look at System.Random
12:52 <hoppfull> Thanks guys
12:53 <kuribas> > take 20 $ (randomRs (0, 1) (mkStdGen 0)) :: [Double]
12:53 <lambdabot> [0.9871468153391151,6.761085639865827e-2,5.591622274642816e-2,0.621389914632...
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12:56 <Cale> unclechu: you might want to email admin@hackage.haskell.org with that
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13:04 <kuribas> There should be an unSplit in Data.Map, the reverse of split...
13:04 <kuribas> or unSplitUnsafe.
13:05 fendor joined
13:05 <Hafydd> There should be a safePerformIO, which is the inverse of unSafePerformIO.
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13:07 <magthe> In emacs I apparently have flycheck configured to use ghc to warn me of issues in my code (my flycheck-checker is set to haskell-stack-ghc), given that I read elisp *really* badly I searched online for how this might have been down... I managed to find nothing. Anyone in here who can offer some pointers on this? (I'd like to see if I can use something similar in my git pre-commit hook)
13:07 <magthe> s/down/done
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13:08 <cocreature> Hafydd: that’s call "pure"
13:08 defaultnick joined
13:09 <cocreature> *called
13:10 <kuribas> or id?
13:10 bezirg joined
13:10 <kuribas> :t id putStrLn
13:10 <lambdabot> String -> IO ()
13:10 michael1 joined
13:10 <kuribas> magthe: try #haskell-emacs
13:11 <Hafydd> But it doesn't have the property that safePerformIO . unSafePerformIO = id. It can't recover the nondeterminism from the result of unSafePerformIO.
13:13 <hpc> safeUnPerformIO
13:13 <Hafydd> The function it produces is interesting, though... IO a -> IO a, which freezes one result in time and makes it pure.
13:14 <merijn> Hafydd: Eh, isn't this a rather indirect way of trying to reinvent ST?
13:14 <pacak> counsafePerformIO maybe...
13:14 <Tuplanolla> :t safeUnperformIO
13:14 <lambdabot> a -> IO a
13:15 <Hafydd> Ah, there we go.
13:15 <Hafydd> merijn: I don't think so. Not even ST allows you to recover an action from its result.
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13:17 <Hafydd> This is possible in the extremely powerful and esoteric Const Monad, though.
13:17 <merijn> Const isn't a monad
13:17 <merijn> Did you mean Cont?
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13:18 <spatial> http://pastebin.com/AN9S7YLW if loop standard is this ?
13:19 <Hafydd> Oh, whoops, I mean Identity.
13:19 <spatial> I mean indentation has a slight problem.
13:20 <Hafydd> It's so powerful and esoteric that I sometimes forget its name.
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13:26 <kuribas> There should be a way to delete a range from a Map in O(log n).
13:26 AndroUser joined
13:26 <merijn> kuribas: Isn't dfeuer working on that kinda thing?
13:27 <kuribas> merijn: that would be great.
13:27 AndroUser joined
13:28 <Ferdirand> assuming the number of elements covered by the range is << n ?
13:28 <maerwald> any useful xml package with xpath support?`the 'xml' package doesn't seem to have it and hxt is just useless complexity
13:28 <Ferdirand> or do you ignore the average gc cost ?
13:29 caumeslasal joined
13:29 <kuribas> Ferdirand: I don't think GC is linear in garbage collected.
13:29 <kuribas> ghc likes garbage.
13:30 <quchen_> It’s copying, so shouldn’t it be linear in the garbage *not* collected?
13:31 <spatial> http://pastebin.com/C3Fp7MAx This has the indentation problem.
13:31 <quchen_> … up to linear factors ;-)
13:32 <kuribas> quchen_: it doesn't copy the hole heap, does it?
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13:32 <quchen_> kuribas: Nope, it’s generational
13:33 ramzifu joined
13:33 <quchen_> spatial: There is no »else«
13:33 <spatial> I thought that is acceptable
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13:34 <merijn> maerwald: xml-conduit?
13:35 <quchen_> spatial: No, every »if« must have both »then« and »else« in Haskell.
13:35 <merijn> quchen_: Correct
13:35 <merijn> GHC's GC is linear in the amount of live data
13:35 ub joined
13:35 <quchen_> merijn: I know my ifs! ;-)
13:35 coot joined
13:35 <quchen_> Oh, the GC thing. Yes that too.
13:35 <merijn> quchen_: I meant the GC :p
13:35 <spatial> http://stackoverflow.com/questions/15256471/nested-control-structure-in-haskell
13:35 <kuribas> spatial: what should it return if the condition is false?
13:36 shafox joined
13:36 <spatial> No return. Only state changes.
13:36 defaultnick joined
13:36 <kuribas> :t when
13:36 <lambdabot> Applicative f => Bool -> f () -> f ()
13:36 <kuribas> spatial: perhaps you want "when"
13:36 <merijn> Basically, GHC's GC is optimised for high-throughput workloads with a, preferably, not too excessive resident set
13:37 AndroUser joined
13:37 <spatial> kuribas: haven't seen when
13:37 doodlehaus joined
13:37 <quchen_> ?src when
13:37 <lambdabot> when p s = if p then s else return ()
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13:38 <maerwald> merijn: where does it have xpath support?
13:38 <merijn> maerwald: Not direct xpath support, but the combinators are modelled after xpath
13:38 <kuribas> spatial: look at lambdabots output
13:38 <maerwald> merijn: that's pretty limited, xpath is a language
13:38 <merijn> maerwald: So most (all?) XPath queries should be fairly trivial to write
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13:39 <maerwald> not interested in that kind of oddity
13:39 <quchen_> spatial: It’s basically single-branch »if«, as long as you’re in an Applicative context.
13:39 <Aruro> is brew install ghc a trap? takes hours to compile.
13:39 <merijn> Aruro: Why are you compiling? Why aren't you installing a binary distribution?
13:40 <spatial> But this is a simple 'if'
13:40 <Aruro> i just did brew install ghc
13:40 <merijn> Aruro: In short, yes that's a trap
13:40 harfangk joined
13:40 <Aruro> wanted to be SMART.
13:40 <merijn> Aruro: I don't use brew, so I dunno wtf they do
13:40 <spatial> I have no idea what Applicative is.
13:40 cris_ joined
13:40 <Aruro> they have 8.0.2 compiling from source
13:40 <quchen_> spatial: Oh. Well, IO is an example of one. In IO, you can use »when«.
13:40 <merijn> Aruro: There's https://ghcformacosx.github.io/ but that's 7.10
13:40 <maerwald> guess this is another case of: try to find a useful library in haskell, realize there are only two options: 1. libraries that lack almost all required functionality to do a real-world project, 2. libraries that are just DSLs with a sh*tload of complexity, requiring you to invest more time than is useful
13:41 <quchen_> spatial: Hold on a second.
13:41 <Aruro> which takes more than 3 hours, im getting ready for 8 hours compiling
13:41 <kuribas> spatial: it's more general as Monad. You can substitue Monad for it.
13:41 <merijn> Aruro: There's also stack (never used it), or just manually installing the GHC bindist from the GHC website
13:41 doodlehaus joined
13:41 <merijn> Aruro: Compiling a release GHC is slow, yes. It needs to bootstrap
13:41 <Aruro> merijn: perhaps i had to install via stack, there is haskell-stack formula
13:41 <spatial> But even if loops are Monads in Haskell :-)
13:41 <Aruro> so 4 hours in i give up? :)
13:41 <cris_> hi , i write up a library an upload to git , but i am not sure if the structure is right, as i could not import all of them in ghci, see https://github.com/szehk/Haskell-Carbonara-Library/blob/master/src/Data/Carbonara.hs
13:42 <quchen_> spatial: Loops aren’t monads. (I don’t think the statement makes much sense.)
13:42 <cris_> i intended to use /src/Data/Carbonara.hs to load all the other modules, not sure if this file is correct
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13:42 <quchen_> spatial: In IO, you have a value that just does nothing: »pure ()«.
13:43 <quchen_> It’s a NOOP that does nothing but return »()«.
13:43 <quchen_> You can use that to do nothing.
13:43 <spatial> Yes
13:43 <quchen_> Sooo: if a == 0 then putStrLn "hello" else pure ()
13:43 <quchen_> This will print if a is 0, and do nothing otherwise.
13:43 <spatial> () should be in else ?
13:44 <quchen_> »when« is a convenience definition for this,
13:44 <cris_> my system is Slackware 14.2 + nixpkgs
13:44 <quchen_> when (a == 0) (putStrLn "hello")
13:44 fendor joined
13:44 <spatial> So this if loop is wrong ?
13:44 <quchen_> If loop?
13:44 cpennington joined
13:45 <spatial> http://pastebin.com/C3Fp7MAx
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13:46 <quchen_> Yes, it’s wrong. But you can fix it by adding »else« branches to all »if«.
13:46 <spatial> Let me try
13:47 <quchen_> And if you don’t want to do anything in the else branch, let it evaluate »pure ()«.
13:48 <kuribas> spatial: in C an if statement isn't an expression, it doesn't need to return anything. But in haskell it does.
13:48 <cris_> when i type ghci> :m + Data.Carbonara
13:48 <kuribas> spatial: without "else", haskell doesn't know what to return.
13:48 <cris_> this error msg appears: error: Could not find module `Data.Carbonara' It is a member of the hidden package `carbonara-0.0.1@carbonara-0.0.1-9mRaHjrFnefKzrLX1w1WSO'. Prelude>
13:49 line joined
13:49 <spatial> http://pastebin.com/bdKJ3Gr3 Like this ?
13:50 <quchen_> spatial: There’s still another else missing.
13:50 doomlord joined
13:50 <quchen_> 3 ifs, only 2 else
13:51 <Unhammer> wtf do I do with bimodal criterion graphs :-S
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13:54 <cocreature> Unhammer: run your benchmarks again and hope one mode disappears :)
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13:55 <spatial> quchen_:() is »pure ()« ?
13:56 <spatial> newnextstate :: ( IOArray Int Int) -> BoardState-> IO () That is the type
13:56 <Unhammer> cocreature, now they're trimodal! haha I should probably check top …
13:56 <dramforever> no, literal 'pure ()'
13:56 <quchen_> No, () is the (single possible) value of the () type (pronounced »unit«). »pure ()« is the »pure« function applied to it.
13:56 <dramforever> letter p, letter u, letter r, letter e, space, open paren, close paren
13:56 <quchen_> pure () :: () -> IO ()
13:57 <dramforever> you mean pure :: () -> IO ()
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13:57 <spatial> Thanks. All this for a if loop :-)
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13:58 <Logio> spatial: what should your code be doing with the IOArray it's given?
13:58 <dramforever> well, that's what you get by writing haskell programs like that :(
13:58 <Itkovian> how do I tell ghc that libgmp.a is not in the expected location?
13:59 <Logio> spatial: because right now it seems to me that the parameter a is not used at all, but instead shadowed by a <- readvalue index
13:59 <spatial> It works with all your help
13:59 <kuribas> spatial: or with multiway if http://lpaste.net/353306
13:59 <spatial> Login: Fixed that
14:00 <spatial> Logio: Fixed
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14:00 <kuribas> spatial: it looks very imperative
14:00 <Itkovian> ok nvm, -L should not have a space behind it :/
14:01 <spatial> kuribas: That is more legible.
14:01 <quchen_> spatial: There are no »if loops«. Ifs don’t loop. At best, you could argue »if« to be a loop that is run 0 to 1 times. But then you’d also have to say »statement loop« for things that run exactly once.
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14:01 <kuribas> quchen_: maybe he want multiway if, like lisp COND
14:02 <quchen_> Yes, a multi-if would be useful here.
14:02 bodisiw joined
14:02 <spatial> I got 'when' now
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14:08 <Dasio> Hello, could someoen help me how to Group list by equivalence relation, I tried something like this http://pastebin.com/JdH1J0K4
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14:10 <c_wraith> Dasio: group only groups *consecutive* elements by an equivalence relation
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14:12 <Dasio> c_wraith: I found this http://stackoverflow.com/questions/8262179/group-list-by-equivalence-relation, so i have to somehow sort it ? but idk how
14:12 <c_wraith> sort is one approach, but it's not the only one
14:13 <Dasio> is there any simpler solution ?
14:14 <c_wraith> You could repeatedly use partition
14:14 <c_wraith> well, partitionBy
14:14 <c_wraith> Err, no. partition is the one that takes a predicate
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14:29 <mathk> Hi, Anyone can show me some example of use of `Monad ((,) a)` ?
14:29 acarrico joined
14:29 <mauke> > return 42 :: (String, Integer)
14:29 <lambdabot> ("",42)
14:30 <c_wraith> mathk: It's exactly the same thing as the Writer monad, if that helps
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14:31 <mathk> I see thanks
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14:37 <mathk> c_wraith: Because of the Monoid constrain, should I understand that not only it is a Writer but it also collect the different write ?
14:38 mohsen_ joined
14:38 <c_wraith> Writer has the same Monoid constraint
14:38 <mathk> ok
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14:45 <unclechu> hi guys, does anyone know how to specify 'cabal' version for Travis-CI config?
14:45 travula joined
14:46 <cris_> hi, could you check if my "personal libraries" section are correct? thanks in advance https://hastebin.com/ijeviqoqit.rb
14:47 <cris_> this is my ~/.nixpkgs/config.nix
14:47 <Aruro> is it possible to run servant in sate monad? so the server can print its own log?
14:48 <cris_> i want to install my own library into nix ; i search over google and come up with above , but it still not working anot working
14:48 janos joined
14:48 <cris_> after i run $ nix-env -iA nixpkgs.myHaskellEnv
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14:49 <bennofs> cris_: it should look like https://hastebin.com/ilujoqaxif.m
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14:50 <bennofs> cris_: also if you want to have carbonara in the env, you should add to the list of packages in the ghcWithPackages call
14:50 <bennofs> cris_: like https://hastebin.com/hutepuxeqi.m
14:50 <bezirg> hello, I have a type erro: ambiguous type, with only one potential instance. Can I force ghc to pick that instance, even if that means that the open world assumption of type classes will be broken?
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14:52 <jan_path> bezirg: Is an explicit type signature an option?
14:54 <Aruro> does cabal have option of installing all libraries with prefix ? like : cabal install lens*
14:54 <cris_> thanks bennofs
14:54 <bezirg> jan_path: nope
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14:56 <lyxia> bezirg: can you show us the instance and the use site
14:56 <cris_> bennofs: i got this error $ nix-env -iA nixpkgs.myHaskellEnv error: value is a set while an integer was expected, at /home/hp/.nixpkgs/config.nix:4:18
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14:58 <bennofs> cris_: try https://hastebin.com/ayutuyibif.m, nix does not support ~ i believe
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14:59 <lpaste_> bezirg pasted “A subtyping ambiguity error” at http://lpaste.net/353312
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15:00 <bezirg> I lpasted it, I use an explicit subtyping function. I wish it was semi-explicit (no need to resolve the ambiguity) than explict (having to add type signatures)
15:02 <bezirg> btw, I_ is a subtype of I in that code
15:02 <bezirg> it is a contrived example
15:03 <lyxia> bezirg: will I ever be a subtype of something else
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15:03 <bezirg> lyxia: no, let's assume closed world
15:03 <lyxia> this question sound weird if taken out of context
15:03 <cris_> hi bennofs , i have changed the path to hard path , but no luck , still see the same error ... h
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15:04 <lyxia> bezirg: then you can rewrite the instance Sub I I to instance I ~ b => Sub I b
15:04 <lyxia> bezirg: it says exactly that I is only a subtype of itself, and helps type inference.
15:05 <bennofs> cris_: oh also try removing the slash at the end of the path
15:06 <bezirg> lyxia: thank you, this indeed helped
15:06 <bezirg> lyxia: however, how can I say the same for I_ ? that I_ is a subtype of itself
15:06 <tsahyt> hello! is there a type that represents floating point numbers between 0 and 1 only?
15:06 <bezirg> lyxia: if I use the same EqualityConstraints pattern, it leads to another ambiguity
15:06 <tsahyt> including both endpoints
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15:07 <lyxia> bezirg: well it's false for I_. I_ is not only a subtype of itself.
15:07 <cris_> hi bennofs, it works this time!!
15:07 <byorgey> tsahyt: no
15:07 <tsahyt> byorgey: not even in some library?
15:08 <bezirg> lyxia: indeed
15:08 <byorgey> tsahyt: I don't know, there might be one in some library somewhere, who knows
15:08 <lyxia> bezirg: you end up with an instance overlapping with Sub I_ I, so this doesn't help.
15:08 <bezirg> lyxia: OverlappingInstances will not do the job you think?
15:08 <lyxia> bezirg: you maybe it is only a super type of itself, then you could have instance a ~ I_ => Sub a I_
15:08 <byorgey> tsahyt: it depends what these numbers should represent and what kind of operations they should support.
15:09 <tsahyt> byorgey: seems easy enough to provide a wrapper around Double with smart constructors and numeric instances implementing either some form of modular or saturating arithmetic. but that seems like wasting a lot of the possible range of Double
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15:09 <tsahyt> well I want to write a function [0,1] -> a, representing the (interpolated) frequency domain of a signal
15:09 <tsahyt> so really querying it would be enough I suppose
15:10 <byorgey> tsahyt: sure, it's pretty easy, which is probably why there's no standard library for it (and because there are lots of choices one could make for the operations and no obvious "right" choice)
15:10 <tsahyt> fair enough
15:10 <cris_> hi bennofs , i believe i should have installed my carbonara library to my nix ; when i enter ghci and type this ghci> :m + Data.Carbonara , then this error msg shows: Could not find module `Data.Carbonara' It is a member of the hidden package `carbonara-0.0.1@carbonara-0.0.1-9mRaHjrFnefKzrLX1w1WSO'.
15:10 <tsahyt> I'll think about whether this is a smart idea and possibly implement my own if it makes sense
15:10 <byorgey> tsahyt: who cares about wasting the range of Double? If you really care about memory usage, then use Float instead of Double
15:10 <jan_path> bezirg: Would a functional dependency do: class Sub a b | a -> b. So any type can only be subtype of at most one supertype?
15:10 <bezirg> lyxia: I added instance (a ~ I_) => Sub a I_ where up = id , but it didn't work
15:10 <lyxia> bezirg: it won't. Let's say you had instance {-# OVERLAPPABLE #-} b ~ I_ => Sub I_ b, but also instance Sub I_ I, then the first instance will never be selected as long as b is unknown
15:11 <lyxia> because it overlaps with the second.
15:11 <tsahyt> byorgey: well I could have better precision within the same number of bits. not that it really matters in practice I guess
15:11 <byorgey> tsahyt: sure, you just have to decide what you care about.
15:11 <lyxia> bezirg: it will only be selected if you know in advance that b ~ I_, which defeats the whole point of the trick.
15:11 <tsahyt> first I need to figure out how to interpolate the spectrum in the first place
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15:12 <tsahyt> this is simultaneously an attempt at learning more about DSP, so I'm writing this code as I go and discover the concepts.
15:12 <byorgey> sounds like fun
15:12 <tsahyt> it's been quite entertaining so far. I have no idea how well my code would run in the real world yet and there are quite a few challenges to be solved still to make this actually usable
15:13 <bezirg> lyxia: y, you are right
15:14 <bezirg> jan_path: I don't think functional dependency works, because there is not a single mapping from a to b. There may be many a's mapping to different b's
15:14 <lyxia> bezirg: Oh I didn't realize instance a ~ I_ => Sub a I_ overlaps with the previous one, that's pretty bad.
15:14 <bezirg> lyxia: I also tried ClosedTypeFamilies, AllowAmbiguityTypes but it didn't work
15:15 nwf joined
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15:16 <lyxia> I can't see how these extensions would help
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15:17 <bezirg> lyxia: I thought maybe I can close somehow the Sub typeclass through ClosedTypeFamilies, but it didn't work. AllowAmbiguityTypes can be used to "delay?" ambiguity resolution to the call site. Also didn't work
15:18 <bgamari> Axman6, hi
15:18 <bgamari> Axman6, did you work it out?
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15:20 <lyxia> bezirg: you don't have definitions with ambiguous types though. The ambiguity is only at the call site.
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15:20 <bezirg> lyxia: I thought maybe "default" could help here, but that is restricted to single parameter type classes of Eq,Ord,Num,Show
15:20 ystael joined
15:20 <lyxia> bezirg: This kind of explicit subtyping relation looks like an antipattern, because of this kind of issues and hacks involved.
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15:21 <bezirg> lyxia: y definitely it is an antipattern. Standard Haskell does not support subtyping
15:21 <lyxia> But, maybe you have other good reasons. *shrugs*
15:21 <bezirg> lyxia: y indeed
15:21 <merijn> lyxia: No ambiguous definitions is only true without extensions :)
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15:22 <merijn> Higher rank types don't have a unique most general type, so there types can be ambiguous even at the definition
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15:33 <cris_> bennofs: I have resolved the issue, it was due to my old version of carbonara still lie in the system, which interfere with my current version; i just $ ghc-pkg unregister ...
15:33 janos joined
15:33 <cris_> bennofs: thanks v much for your help
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15:35 <bezirg> lyxia: what about IncoherentInstances?
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15:37 <lyxia> Don't use this.
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15:39 <merijn> IncoherentInstances secretly enables -XILikePainAndHateMyself
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15:44 <bezirg> lyxia: I understand it is bad, but do you think it will lead to false positives (programs with concrete subtyping errors compiling correctly)? I can only think that it will lead to false negatives
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15:45 <lyxia> You might end up picking instances you did not intend to.
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15:48 <nilof> If I define a typeclass that extends another, how do I declare default implementations of the second in terms of the first?
15:49 <lyxia> nilof: DefaultSignatures
15:49 <nilof> Like say fmap from return & bind, or in my case, foldl in terms of heap pop
15:49 <nilof> ah
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15:51 <lyxia> it's cleaner to define your default implementation separately and let users use it explicitly, like with Functor/Applicative/Monad in base.
15:53 <zipper> In https://github.com/tibbe/haskell-style-guide/blob/master/haskell-style.md#data-types the writer says "Additionally, unpacking simple fields often improves performance and reduces memory usage"
15:53 <zipper> What does that even mean?
15:53 <zipper> What does unpacking mean?
15:55 <zipper> LOL tibbe is in this chan, what did you mean?
15:55 <lyxia> zipper: The record "Point Double Double" is represented as a struct with two pointers to Double
15:56 <lyxia> unpacking avoids the indirection and directly puts the doubles in the fields of the struct
15:56 janos joined
15:57 <zipper> hmmm been so long since I looked at C++
15:57 <zipper> Can't remember structs clearly
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16:01 <lyxia> zipper: in memory this is the difference between two pointers and two actual values.
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16:03 <ertes> nilof: if (class (A a) => B a), then you don't need DefaultSignatures
16:03 insitu joined
16:04 <ertes> you can refer to the members of A regularly
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16:05 <unclechu> hey guys, could someone explain me why my Travis-CI tests fail on `cabal install`? https://travis-ci.org/unclechu/haskell-qm-interpolated-string/jobs/209019272
16:05 jophish_ joined
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16:05 <unclechu> I'd generated `.travis.yml` file using this tool: https://github.com/hvr/multi-ghc-travis
16:05 <unclechu> I also tried to write it by my bare hands in different ways but without any success
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16:07 <lyxia> unclechu: haskell-src-exts failed to install. You can then see that it complains about not finding happy.
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16:08 <unclechu> lyxia: I should specify `happy` dependency in my `.cabal` file?
16:08 <lyxia> I don't think so, but I don't have a solution yet.
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16:09 <osa1> unclechu: add `build-tools: happy`
16:09 smotr0n joined
16:09 <lyxia> if you're not directly depending on it you shouldn't do that
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16:10 <lyxia> apparently you need to tell travis to install it https://github.com/haskell-suite/haskell-src-exts/blob/master/.travis.yml#L18
16:10 <nilof> I'm implementing a heap typeclass, is there a way to ensure that the parameter of my heap type is always Ord?
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16:12 <lyxia> Add the constraint on all methods class Heap heap where .... insert :: Ord a => a -> heap a -> heap a ...
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16:13 <bezirg> A silly question: does an (id x) can be optimized to x? or this breaks the lazy semantics?
16:13 <lyxia> nilof: though if you can't add them I'm not sure you can
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16:13 <nilof> right, the problem is when I try to extend foldable
16:14 <mauke> bezirg: looks valid to me
16:14 pasukon joined
16:14 <nilof> I can add ord a in front of my own methods, but I'm running into issues because my foldl relies on my pop method
16:15 <nilof> and foldl as declared in Foldable doesn't require Ord
16:15 rgc joined
16:15 <nilof> so I get a type error
16:15 <lyxia> then it's not a valid implementation of Foldable
16:15 <bezirg> mauke: thanks
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16:17 <lyxia> nilof: you could technically add the Ord constraint into your heap datatype
16:17 <SpinTensor> Hi, here are two functions (http://pastebin.com/wNyMVPj3) and I thought the type def of both would mean the same, but they are not. why? First one works, second one gives compile error.
16:17 <osa1> nilof: why not add a`Ord` constraint to your instance declaration?
16:18 <lyxia> SpinTensor: Num is a type class, it's not a type.
16:18 <osa1> nilof: instance Ord a => Heap (HeapImpl a) where ...
16:18 <SpinTensor> lyxia: so i can't use a type class but i can say a is part of the type class and then use a?
16:18 <unclechu> lyxia: thanks, will try
16:19 <mauke> SpinTensor: well, an instance of the class. it's not really part of it
16:19 <osa1> nilof: similarly, instance Ord a => Foldable (HeapImpl a)
16:19 gienah_ joined
16:19 <SpinTensor> mauke: ah, ok. good to know. thanks. that actually explains a lot.
16:20 <lyxia> osa1: Foldable has kind (* -> *) -> Constraint
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16:20 <osa1> ops
16:20 <lyxia> MonoFoldable would work though
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16:22 <tsahyt> how comes that GHC can prove that (41 :: Nat) does not unify with (2 * n), but it can't infer KnownNat n from the context KnownNat (2 * n)?
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16:25 <geekosaur> seems to me that if it only knows that latter context and nothing else, it can't prove the former can't occur (which would make (KnownNat n) false)?
16:25 <geekosaur> also the machinery is not especially smart; there are plugins that improve it
16:26 <delYsid> Hmm, is there a recommended (because quite feature-complete) dbus client package?
16:26 <tsahyt> what do you mean with "the former can't occur"?
16:26 jathan joined
16:27 <geekosaur> if it doesn't know n, it can't prove n is even
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16:29 <max3> why does stack fail on a warning? http://pastebin.com/dq0abVPw
16:29 <tsahyt> hmm
16:29 <max3> is there a way to get it to soldier on?
16:29 <tsahyt> what if I introduced a constraint n ~ 2 * m
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16:29 <geekosaur> you might be interested in the ghc-typelits-* plugin packages btw
16:30 <shapr> max3: did you read /home/databrary/src/.stack-work/logs/blaze-markup- ?
16:30 <tsahyt> http://hackage.haskell.org/package/ghc-typelits-knownnat
16:30 <geekosaur> they make ghc a bit smarter about this stuff
16:30 <tsahyt> this looks interesting
16:30 <max3> shapr, it's exactly that warning
16:30 NeverDie joined
16:30 <geekosaur> ghc-typelits-natnormalize also comes highly recommended for this kind of thing
16:30 <max3> shapr, http://pastebin.com/HDkgBcUq
16:31 <tsahyt> geekosaur: since I've never used a ghc plugin before, can I handle this properly with cabal? e.g. I want to use this in a library, can I somehow put this into the cabal file and automate the process of installing and loading the plugin for the build?
16:31 rekahsoft joined
16:31 <geekosaur> that I don't know, Ive not used plugins either
16:31 <tsahyt> ok. thanks for the suggestion!
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16:32 <geekosaur> max3, can you pastebin that log file shapr mentioned?
16:32 <geekosaur> ExitFailure (-11) can in some cases mean something segfaulted
16:32 <max3> geekosaur, i did http://pastebin.com/HDkgBcUq
16:32 <geekosaur> in which case the warnings may be a red herring
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16:33 <shapr> max3: yeah, there's something else going on
16:33 <geekosaur> that's all of it? :( might make a segfault even more likely
16:33 wraithm joined
16:34 <max3> and how can i figure out what exactly is going on?
16:35 <geekosaur> painfully :/ if I suspected a segfault and couldn't find anything logged for it I'd probably haul out strace (or check syslog but linux doesn't log them as usefully as e.g. freebsd does...)
16:36 <max3> ghc[16725]: segfault at 7eff09fd6640 ip 00007eff08cfe6bb sp 00007ffe0a06f870 error 4 in libHSrts_thr-ghc7.10.3.so[7eff08ce4000+67000]
16:36 <max3> in dmesg
16:36 <shapr> max3: or you could grab the source from git and try to build that repo separately?
16:36 <max3> this is the most brittle thing ever
16:36 <shapr> no u
16:37 <shapr> I mean, I think it could be the legacy code you've inherited, rather than Haskell itself.
16:37 <max3> mime-mail had a bug and snoyberg fixed it and bumped the version number
16:37 <shapr> for example, I'm able to use stack to install blaze-builder here on my work laptop
16:37 <max3> so this has nothing to do with my code
16:38 <max3> and this segfault is on stack build --only-dependencies
16:38 <shapr> I got the same version, blaze-markup
16:38 jmcarthur joined
16:38 refold joined
16:38 <max3> and it does work for me too - if i hit stack build --only-dependencies like 3 times
16:39 jomg joined
16:39 <shapr> max3: wait what?
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16:39 <max3> shapr, if i rerun eventually it all builds
16:40 <shapr> max3: that sounds like it could be memory errors or possible disk corruption
16:40 <max3> it's in a docker
16:40 <drostie> sounds like a fun new feature, ghc --give-up-after=3
16:40 <max3> lol
16:41 <drostie> "ok fine you WANT that binary, you GOT that binary, don't say I didn't warn you!"
16:41 <MarcelineVQ> max3: the issue where you have to build multiple times to get the dependencies built was resolved for me by upgrading stack to 1.4.* stack upgrade --git --source-only
16:41 <shapr> MarcelineVQ: what was that issue?
16:42 <MarcelineVQ> I'm not sure it was reported directly, but the newer stack handles custom build options better so it seemed to have fixed it by proxy
16:42 <MarcelineVQ> most commonly when it happened was with cairo and gtk2hs
16:43 <nilof> Ah, another question: I'm trying to specialize a method using (buildheap xs) :: Ord a => ImplHeap a, but I get a type error where the compiler doesn't want to match t a1 with t a
16:43 <shapr> I sort of want to see the results of "stack dot --depth 2 --external" for databrary, but I'm afraid
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16:43 <max3> MarcelineVQ, what does the --source-only flag do?
16:44 <geekosaur> nilof, lpaste the full code and full error message?
16:44 <geekosaur> @paste
16:44 <lambdabot> Haskell pastebin: http://lpaste.net/
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16:45 <nilof> http://lpaste.net/353317
16:45 <MarcelineVQ> It's builds things locally instead of grabbing pre-built stack binaries, probably not neccesary here since --git should have a newer version number but if it didn't it may just grab binaries instead of actually fetching from git iirc
16:45 <max3> MarcelineVQ, this doesn't upgrade to nightly but the latest release right?
16:46 <MarcelineVQ> it upgrades to the current master branch of the stack git repo https://github.com/commercialhaskell/stack
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16:47 <nshepperd> nilof: you may need ScopedTypeVariables there
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16:48 <max3> MarcelineVQ, is master stable? i don't understand their workflow (i'm used to gitflow where master is always a release)
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16:49 <geekosaur> nilof, yes, you'd need ScopedTypeVariables *and* prefix the type signature of heapsort with "forall a."
16:49 <nshepperd> nilof: by default, type variables are contained to their type signature, so that the a in 'heapsort :: (Ord a, Foldable t) => t a -> [a]' is different to the a in '(buildheap xs) :: Ord a => LeftHeap a'
16:49 <geekosaur> you expliitly told it *not* to typecheck; the "a" in your type ascription has nothing to do with the one in the signature, and effectively tells ghc it doesn't know the type
16:50 <max3> haha upgrading stack failed too
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16:50 <max3> ghc: internal error: evacuate: strange closure type -129660600
16:50 <unclechu> lyxia: https://travis-ci.org/unclechu/haskell-qm-interpolated-string/jobs/209032172
16:50 <unclechu> now i added `happy` to install in `.travis.yml` https://github.com/unclechu/haskell-qm-interpolated-string/blob/feature/travis-ci-testing/.travis.yml but still have this error
16:50 <geekosaur> max3, you have a hardware issue most likely
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16:50 <geekosaur> or your docker is really broken
16:50 <max3> really? you think?
16:50 <geekosaur> and corrupting the memory image in the container
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16:51 <MarcelineVQ> max3: not sure, I don't upgrade often unless I have issues, it has been stable for me in usage. nominally there is a branch called stable that I imagine is for releases, it won't have the update that fixed the depdendency issue for me
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16:52 <lyxia> unclechu: it seems you're missing the equivalent of this line https://github.com/haskell-suite/haskell-src-exts/blob/master/.travis.yml#L35
16:52 <geekosaur> basically "strange closure type" means one of: (a) you're using a buggy ghc prerelease (b) you have FFI and some *really* wild pointers (c) you have general memory corruption
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16:54 <kadoban> max3: Can you run memtest86 or something like that without much trouble? That's usually where I start when impossible things are happening that suggest hardware failure.
16:54 <unclechu> lyxia: thanks again
16:54 <max3> kadoban, lemme see if reinstall docker helps
16:55 <nshepperd> if you suspect your machine might have faulty ram, you should reboot into memtest86+ and test it asap, because faulty ram tends to stomp all over your hard disk and destroy your data
16:55 <kadoban> That's usually where I end as well, since every time it's found a problem :-/ It always seems to be RAM failure. Though it's few data points, so that may not be representative.
16:55 <nshepperd> (also I hope you have backups)
16:56 <max3> i'll be shocked if it's corrupted memory
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17:00 <* geekosaur> hs had enough issues (and talked with enough other people who have) with docker that he'd check that first. neat idea, but the "move fast, break stuff" model tends strongly toward the latter
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17:04 <sidei> @help
17:04 <lambdabot> help <command>. Ask for help for <command>. Try 'list' for all commands
17:04 <sidei> @list
17:04 <lambdabot> What module? Try @listmodules for some ideas.
17:04 <max3> geekosaur, certainly it's not beyond the realm of possibility; after all golang is no haskell :)
17:04 <unclechu> lyxia: https://travis-ci.org/unclechu/haskell-qm-interpolated-string/jobs/209041415 kinda same story https://github.com/unclechu/haskell-qm-interpolated-string/blob/feature/travis-ci-testing/.travis.yml
17:05 <sidei> @help list
17:05 <lambdabot> list [module|command]. Show commands for [module] or the module providing [command].
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17:05 <sidei> @pl f a b = (a+b)/2
17:05 <lambdabot> f = flip flip 2 . ((/) .) . (+)
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17:06 <geekosaur> don't think the implementation langaueg matters here. too much low level stuff and types can;t save you (unless you go full Agda and I suspect *nobody* wants to write the proofs for page tables)
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17:06 <lyxia> unclechu: we made progress, haskell-src-exts was built
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17:06 <lyxia> unclechu: your version of cabal is too old
17:06 <_sras_> How can you output something like this `<div>Click <a href='#'>Here</a><div>` using lucid?
17:07 <lyxia> unclechu: "The package requires Cabal library version -any && >=1.18"
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17:09 <suppi> div_ $ a_ [ href_ "#" ] "Here" -- maybe?
17:09 <unclechu> lyxia: yep, now some another ghc versions passed
17:09 <unclechu> first good news
17:09 <suppi> i'm not in front of a computer
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17:18 <max3> geekosaur, indeed it was docker
17:19 <max3> actually i take that it back it hasn't gone all the way through yet
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17:23 <twopoint718> I’m attempting to use `runResourceT` (`resourcet` pkg) in combination with `createPool` (`resource-pool` pkg) and things are starting to feel a little funky. Am I duplicating behavior here? Should I be using one or the other? In particular, I’m planning on setting up a connection to Neo4J using `haskell-neo4j-client`‘s `newConnection` function which just returns an `IO Connection`. My idea was to get the connection with that function,
17:23 <twopoint718> then use `createPool` to manage the opening/closing for me. The issue arises when I want to close the connection. https://www.stackage.org/haddock/lts-6.11/haskell-neo4j-client- suggests that I use `runResourceT` to manually close the connection, but it would seem that I need a “primitive” close function to be able to `allocate` a ResourceT. I feel a little like I’m going in circles, any
17:23 <twopoint718> ideas?
17:24 <twopoint718> (sorry for the long question. tl;dr has anyone used ResourceT in combination with resource-pool?)
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17:26 <max3> geekosaur, yup docker
17:26 <max3> interesting
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17:27 <geekosaur> not surprising. it's doing its own page table management for the container; even tiny bugs in that lead to seriously weird behavior
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17:29 <brynedwards> twopoint718: it looks like the neo4j client uses http-conduit for connections, so it might to use http-conduit sessions instead
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17:31 <unclechu> guys, how i can write condition for ghc version for preprocessing?
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17:32 <twopoint718> brynedwards: could you elaborate a bit, I'm not sure I follow
17:32 <brynedwards> twopoint718: You can see here, a connection is just a http-conduit Manager and connection details https://hackage.haskell.org/package/haskell-neo4j-client-
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17:32 <brynedwards> Specifically, this https://hackage.haskell.org/package/http-conduit-
17:33 <unclechu> i guess i found it: http://stackoverflow.com/questions/28292476/ghc-version-check-in-code#28292585
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17:34 <brynedwards> As it says under manager, "If possible, you should share a single Manager between multiple threads and requests.
17:35 <brynedwards> I don't know if it's any different for neo4j, and the library doesn't seem to let you pass your manager
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17:35 <brynedwards> Basically, I don't know, sorry =(
17:36 <geekosaur> unclechu, https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/phases.html#standard-cpp-macros
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17:37 <twopoint718> brynedwards: well thanks for the pointer that does help, even if it tells me I have to reconsider what I was trying. Thanks!
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17:42 <EvanR> so
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17:51 <suica> how can I do something to the effect of `map 3 [(+1), (+2), ..]`? I figured it out yesterday but now I can't remember
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17:51 <osa1> > map ($ 3) [(+ 1)]
17:51 <lambdabot> [4]
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17:51 <suica> sweet, thanks
17:52 <farao> hi, I just started with haskell and am doing some exercises and I'm wondering how to split a list into two parts. I found "split" and "splitWhen" but they split the whole list. I am rather looking for an equivalent of: let part1 = takeWhile myFun xs; part2 = dropWhile myFun xs in ...
17:52 <glguy> :t span
17:52 <lambdabot> (a -> Bool) -> [a] -> ([a], [a])
17:52 <farao> cool, thanks! :-)
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17:53 <byorgey> farao: span, break, splitAt
17:53 <byorgey> also partition
17:53 <farao> :t break
17:53 <lambdabot> (a -> Bool) -> [a] -> ([a], [a])
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17:54 <byorgey> break is just the negation of span
17:54 <farao> ah ok! yeah, span is the one I'm looking for :-)
17:55 <shapr> max3: do you get consistent builds after reinstalling docker?
17:55 <max3> if 1 is enough to qualify as consistent then yes
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17:56 <suica> :t [1,2] >>= (flip map) [(+1), (+2)] . (flip $)
17:56 <lambdabot> (Num (a1 -> (a -> a) -> c), Num a) => [a1 -> c]
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17:57 <MarcelineVQ> that's quite the Num instance
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17:57 <suica> I kind of expect that to give `[2, 3, 3, 4]`
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17:59 <glguy> > [1,2] >>= (flip map) [(+1), (+2)] . (flip ($))
18:00 <glguy> so close
18:00 <lambdabot> mueval-core: Time limit exceeded
18:00 <glguy> [2,3,3,4]
18:00 <glguy> ?undefine
18:00 <lambdabot> Undefined.
18:00 <glguy> > [1,2] >>= (flip map) [(+1), (+2)] . (flip ($))
18:00 <lambdabot> [2,3,3,4]
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18:02 <Xyliton> How do I iterate over the pixels in images generated by friday and/or juicypixels?
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18:03 <MarcelineVQ> juicypixels has pixelMap iirc
18:04 <suica> glguy: thanks
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18:04 <suica> i should probably just stick with map and concat
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18:06 <MarcelineVQ> suica: you can also name your value for clarity [1,2] >>= \x -> map ($ x) [(+1), (+2)]
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18:08 <Xyliton> MarcelineVQ: I don't want to modify the image though
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18:18 <thatguy> if I need to randomly resort my list often, is it better to use arrays?
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18:23 <kadoban> thatguy: What does "randomly resort" mean? Is it always sorting by the same comparison function, or?
18:23 <_sras_> What is the best way to read some multiline content from stdin, like contents of a text file piped to the program?
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18:53 <robotrafficcop> Hey all, I'm getting this weird error on "stack build" on a VPS I just spun up. It says that it can't get a file from S3. Maybe related to the recent outage? https://gist.github.com/wyager/e18f5832e2ed29c1f9ba3b197c52432f
18:53 <thatguy> kadoban: I meant a random shuffle but I found what I needed
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18:58 <glguy> robotrafficcop: If your VPS can't resolve that hostname it's probably just misconfigured
19:01 <robotrafficcop> glguy: It resolves s3.amazonaws.com just fine. nslookup and ping both work
19:01 <robotrafficcop> Which makes me think it might be an issue with something on the Stack end
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19:07 <robotrafficcop> Well, I tried rebooting, and that seemed to fix it. Typical! No particular reason that should have done anything. Thanks for the suggestion!
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19:08 <robotrafficcop> Spoke too soon, still broken. Looks like it's doing a request in the background and it's timing out later in the build process
19:09 <marekw2143> hi, here: https://bitbucket.org/chessRepo/c7/src/a41bb7d3c99f1dfb1267ec633f898c35b585585e/main.hs?at=master&fileviewer=file-view-default#main.hs-168
19:09 <marekw2143> why there's need to be if - else in 168'th line, and not just simply let .. in ?
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19:24 <twopoint718> brynedwards: Thanks for the help. I was able to figure out a solution to my above problem. Briefly, I was able to extract the connection `Manager` inside the Neo4j `Connection` type. This has a `closeManager` function available that worked for being able to satisfy `createPool`. The slight catch is that closeManager is deprecated, but it'll work for my immediate issue.
19:25 janos joined
19:25 <Geekingfrog> I'm having a weird HandshakeFailed error using Req to query www.youtube.com: http://lpaste.net/353322 (using arch-linux, stack and req-0.2.0). Any idea ?
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19:41 <felko> how can i partially apply a parametrized type alias ?
19:42 biglama joined
19:42 <felko> for some types it is ok to type (F a) even if F a has not a * kind, but in case it doesn't work for some reason i don't know (paste incoming)
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19:42 <Tuplanolla> Can't, felko.
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19:43 <Tuplanolla> If the parameter is present in the definition, it must also be present in application.
19:43 <felko> is there a specific reason for that ?
19:44 <Tuplanolla> Yes, but I don't remember it.
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19:47 <felko> Tuplanolla: ok it doesn't matter anyway, i can do what i want without, thanks
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19:49 <Tuplanolla> I recall it's there to keep type-level lambdas out of the system.
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19:50 <Tuplanolla> Those would have troublesome computability properties.
19:52 <felko> Tuplanolla: why ?
19:52 <Tuplanolla> Lambda calculus is Turing complete.
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19:53 <felko> i agree that a type-level lambda calculus could lead to haskell black magic but is it problematic ?
19:54 <Tuplanolla> That depends on your view of problematic. It certainly is if you want to keep compilation decidable.
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19:55 <felko> ok i understand, thanks
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20:05 <unclechu> lyxia: thanks a lot for the help! now everything is green and i'm happy because i have completed everything i'd planned for today: https://hackage.haskell.org/package/qm-interpolated-string
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20:05 <lyxia> unclechu: nice! you're welcome!
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20:07 <lyxia> I'm pretty sure we already have Turing-completeness in types.
20:07 <monochrom> What does "qm" stand for there?
20:07 <lyxia> At least we have UndecidableInstances
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20:18 <byorgey> monochrom: from the readme: 'm' in 'qm' means 'multiline'.
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20:19 <byorgey> presumably the 'q' stands for 'quote' or 'quasiquote' or something like that
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20:50 <kuribas> How do I force return () to be evaluated every time in "trace errStr (return ())"?
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20:53 <monochrom> That "return()" is evaluated iff the whole "trace errStr (return())" is evaluated.
20:53 <ski> perhaps you want `errStr' outputted whenever this action is *executed* (not evaluated) ?
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20:54 <kuribas> ski: yes
20:54 <kuribas> ski: it's not IO though, it's a State monad.
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20:55 <ski> `State MyStateType' ?
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20:55 <kuribas> yes
20:55 <monochrom> My iff sentence is still true for s/evaluate/execute/
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20:56 <kuribas> :t unsafePerformIO
20:56 <lambdabot> error: Variable not in scope: unsafePerformIO
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20:57 <* ski> was thinking of something along the same lines as `evaluate'
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20:58 <ski> @type evaluate
20:58 <lambdabot> a -> IO a
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20:59 <ski> (but presumably the difference doesn't make any difference in your case, in which case what monochrom said)
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21:00 <kuribas> or maybe const (return ()) var, where var is a variable in the monad?
21:01 <ski> whatever `var' is, that is equal to just `return ()'
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21:01 <ski> (not sure what you mean by "a variable in the monad")
21:01 <monochrom> That "return()" is evaluated iff the whole "const (return()) var" is evaluated. Similarly, executed.
21:02 <kuribas> ski: A variable that is only evaluated when the monad is executed.
21:02 <monochrom> Also, the var is ignored in all 4 cases.
21:02 <ski> monads are not run-time things, that can be executed or not
21:02 <ski> monadic actions can be executed, though
21:03 <ski> `var' is not evaluated when `const (return ()) var' is evaluated
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21:04 <kuribas> ski: I don't care about var.
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21:05 <kuribas> or "trace (const msg var) (return ())"?
21:05 <ski> i'm not sure why you mentioned `const' ..
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21:06 <kuribas> I want to trick ghc into evaluating it...
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21:07 <kuribas> Doesn't work if it inlines it to msg...
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21:09 <ski> `const msg var' won't evaluate `var', regardless of inlining or not
21:09 <kuribas> ski: but it may evaluate the expression if var has changed...
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21:11 <monochrom> No, const tricks GHC into not evaluating things.
21:12 <kuribas> ski: if const where a black box, it would try to evaluate it.
21:12 <monochrom> Why are you not talking about seq which does trick GHC into evaluating things?
21:12 <kuribas> monochrom: var `seq` trace msg (return ())?
21:13 <monochrom> var does not change, and const is not a black box.
21:13 <monochrom> I'm going to be blunt and ask "what are you smoking?"
21:13 <monochrom> That will evaluate var iff the whole thing is evaluated.
21:14 <lyxia> Show some code!
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21:15 <ski> kuribas : even if `const' was in a library that was only loaded at run-time, `var' would still not be evaluated in `const (return ()) var'
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21:15 <kuribas> ski: I only want the trace...
21:16 <kuribas> ski: ghc would try evaluating it, because it doesn't know var doesn't get evaluated.
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21:17 <lyxia> kuribas: trace is already marked NOINLINE so it won't do funny things with inlining.
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21:18 <ski> kuribas : no, it would not
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21:19 <Aruro> is lense-like library should be part of haskell syntax?
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21:20 <kuribas> lyxia: this is just a part of my code: http://lpaste.net/353329
21:20 <ski> unless we're talking about speculative evaluation of some sort, the traditional way to implement non-strict semantics is to *not* have argument expressions reduced before calling the function. instead the body of the function (or perhaps even what the caller decides to do with the result of the function) will determine when and if the arguments are reduced
21:21 <dolio> Note: GHC doesn't do speculative evaluation. :)
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21:21 <monochrom> Yes, the evaluator expands the function body first. If the body doesn't mention a parameter, that parameter is ignored afterall.
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21:22 <monochrom> This is why const is not going to be a black box like you think some imported C function is.
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21:22 <monochrom> The evaluator will look inside.
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21:23 <ski> in a sense, `const' is (or could as well be) "black-box", but it would still not have the operational semantics you were thinking
21:23 <kuribas> ski: const msg var, isn't a constant expression, when var is free...
21:23 <kuribas> ski: only after inlining.
21:24 <monochrom> This is not about inlining.
21:24 <kuribas> if const were a black box function, the evalutor wouldn't know it is constant.
21:24 <kuribas> So it would have to evaluate it.
21:25 <ski> no
21:25 <ski> it passes `msg' and `var', *unevaluated*, to `const'
21:25 <monochrom> There are many experiments you can perform to refute that hypothesis.
21:25 <ski> `const' then decides which of the arguments to evaluate
21:25 <kuribas> ski: now you are admitting it will evaluate const?
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21:26 <ski> `const' itself (whose value is a function) will be evaluated, since it's the function expression in a function call
21:26 <monochrom> We have always asserted that "const" is evaluated. First.
21:26 <monochrom> Does not imply that the 2nd parameter will be evaluated. Ever.
21:27 <kuribas> monochrom: I don't care about the 2nd parameter...
21:27 <ski> `const' must be evaluated in order to determine the function body (with actual parameter expressions substituted for formal parameters) to continue evaluation at
21:27 <monochrom> You can define your own const-like function and turn off optimization and what-not. Everything we said will still hold.
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21:27 <monochrom> OK, what do you care?
21:28 <kuribas> monochrom: that the debug trace gets outputted.
21:28 <monochrom> OK, it works for me. What's the problem?
21:28 <* ski> doesn't see a `const' in the paste
21:28 <ski> (if `DEBUG' isn't defined, then `debug' is equal to `flip const', however)
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21:28 <kuribas> monochrom: well, const get inlined, so it isn't a black box...
21:29 <ski> even if it doesn't get inlined, it will still behave exactly the same
21:29 <monochrom> I don't see the relevance.
21:29 <kuribas> ok, I'll try...
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21:29 <ski> `const msg (error "boom !")' won't evaluate the `error' call, e.g.
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21:32 <monochrom> You have an experiment I can reproduce to unambiguously refute what I said?
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21:36 <kuribas> monochrom: right, I tested it. With (const msg freshVar), I see the trace, without only once.
21:37 <kuribas> monochrom: how would ghc now it cannot subsitute that with msg?
21:37 <nilof> Ah, you can't have several modules in the same file?
21:37 Sh4pe joined
21:37 <kuribas> monochrom: does it know there is an trace or unsafePerformIO function?
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21:37 <Tuplanolla> Your thought process is really difficult to follow, kuribas.
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21:38 <jle`> nilof: correct
21:38 <kuribas> Tuplanolla: well, if I have 'debugM "mesg"', I see the trace only once. If I use 'debugM (const "msg" freshvar)', I see it every time it is executed.
21:39 <kuribas> Tuplanolla: what keeps ghc from inlining const, and rewriting the second into the first?
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21:40 <Tuplanolla> Is this from `hslogger`?
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21:40 <Sh4pe> Hi folks! Quick question: I import Data.ByteString.Char8 as C. Then, the statement `newtype Foo = C.ByteString` causes this error: `Qualified name in binding position: C.ByteString`. I don't understand why and I can't find a fix myself
21:40 <lyxia> this would be so much easier if we had a minimal example.
21:40 <cocreature> Sh4pe: you need to give a name to the constructor of your newtype
21:40 <cocreature> "newtype Foo = Foo C.ByteString" will work
21:41 <Sh4pe> cocreature: Ah - I see. Thanks!
21:41 <kuribas> Tuplanolla: no...
21:42 <monochrom> kuribas, I still do not know how to reproduce your experiment. How do I reproduce your experiment?
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21:43 <monochrom> Hell, how do I do so with little effort? (Too lazy to even "stack install stuff")
21:43 janos joined
21:43 <kuribas> > traverse_ [1..4] $ \i -> trace "debug message" $ return ()
21:44 <lambdabot> error:
21:44 <lambdabot> • Couldn't match expected type ‘a0 -> f b0’
21:44 <lambdabot> with actual type ‘[Integer]’
21:44 <Itkovian> any idea why stack --compiler ghc-8.0.2 --stack-root=/usr/local/vpw/haskell/stack --extra-lib-dirs /usr/local/vpw/lib/ install split fails with a symbol from libgmp not foudn (which resides in /usr/local/vpw/lib/libgmp.a)
21:44 <Itkovian> it seems like the extra lib is not passed to ghc
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21:45 <Itkovian> however, when just running the stack ... ghc -- --make main.hs, it is found
21:45 <ezyang> Man, accelerate-llvm really is not easy to build
21:47 <nilof> So stupid question: how do I import a module in a file that is in the same directory?
21:47 <monochrom> Just do it.
21:47 <monochrom> But mind filename cases (upper or lower).
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21:49 <Athas> ezyang: if you manage to get it work with the LLVM-based GPU backend too, please let me know!
21:49 <ezyang> lol
21:49 <ezyang> I got to a GHC panic and then gave up
21:51 <nilof> ah, my ghci directory was set to the wrong directory, now everything works
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21:51 <kuribas> monochrom: try this: http://lpaste.net/2846700419663527936
21:51 <monochrom> ghci has a ":cd" command
21:51 <davean> ezyang: I feel accelerate has never been well maintained, I've never managed to actually use it
21:52 <kuribas> monochrom: behaviour is different compiled from in ghci...
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21:54 <kuribas> monochrom: the second gives 4 times "debug message", the first only once.
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21:55 <monochrom> kuribas, I am in ghci, version 8.0.2, both give me 4 messages.
21:56 <kuribas> monochrom: try compiling it
21:56 <monochrom> OK. -O0? -O1? -O2?
21:56 <kuribas> -O2
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21:56 <kuribas> ghc 8.0.1
21:57 <monochrom> OK, reproduced.
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21:58 <kuribas> I would think ghc will inline const, and make the two equivalent.
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21:59 <monochrom> But there are other moving parts. How do you know, for example, that optimizations didn't do something to traverse_ and affected this experiment too?
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21:59 <monochrom> Or even [1..4]
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22:00 <monochrom> Or the way (\i -> trace whatever) is optimzied or not optimized.
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22:01 <kuribas> @src trace
22:01 <lambdabot> trace string expr = unsafePerformIO $ do
22:01 <lambdabot> hPutStrLn stderr string
22:01 <lambdabot> return expr
22:01 <monochrom> I mean, of course, "const" is the most visible difference syntactically, but you probably need to cross this with some other things too for a real difference to be manifested.
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22:02 <monochrom> I don't think you can trust @src anymore. Look at Debug.Trace actual source code.
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22:04 <kuribas> well, at least I have my trace messages :)
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22:05 <monochrom> You will want to look at the Core code.
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22:05 <codedmart> Anyone familiar with Pool here? I use it with RethinkDB. Which in most cases it works fine, but I have one instance `Changes` where it is a blocking operation. Basically it just sits and waits for an answer https://github.com/AtnNn/haskell-rethinkdb/blob/c7df4f219f1e7251629a9e90280f1ebdfed9ec8c/Database/RethinkDB/Network.hs#L407-L413. The problem is I get
22:05 <codedmart> this error `Left thread blocked indefinitely in an MVar operation` over and over. I have a hacky way around this by using `forkFinally` to just restart it, but that is not an optimal solution. Any thoughts/ideas? I am actually not sure if this is even a Pool problem. I assumed it had something to do with reaping
22:05 <codedmart> https://github.com/bos/pool/blob/master/Data/Pool.hs#L203, but I haven't used MVar's yet so could be way off base.
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22:23 <monochrom> kuribas: "const is inlined or not" does not fully explain it, because in the Core code, there is no longer const or mention of i, it is always 'trace "debug message"'.
22:23 <kuribas> monochrom: right
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22:24 <kuribas> monochrom: so ghc is keeping track of the fresh variable i, and makes sure the expression is evaluated every time...
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22:25 <kuribas> monochrom: or something else to do with unsafePerformIO...
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22:26 <monochrom> But it is true and I don't know why that in the no-const version, a top level CAF "xxx = trace "debug message" (return ())" is introduced, then reused by the loop. Whereas in the has-const version, the trace is not a CAF, it is re-created every iteration.
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22:28 <kuribas> Does unsafePerformIO even have clear semantics?
22:28 <monochrom> Yes for GHC.
22:29 <jophish> Hi folks
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22:30 <monochrom> I consider it unlikely that unsafePerformIO caused the difference.
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22:31 <jophish> When do people find it appropriate to curry constraints to functions? i.e. `foo :: Eq a => Num a => a -> a -> a` instead of `foo = (Eq a, Num a) => a -> a -> a`
22:32 <monochrom> I consider it far more likely that the order of optimization stages caused the difference. Namely, my hypothesis: First looking for what you can factor out as CAFs, and only after perform simplication and discovering data independence.
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22:32 <jophish> I have an intuition for where this is a nice thing to do, but am having trouble formalising it
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22:33 <monochrom> So, for the no-const version: i is not mentioned anywhere syntactically, so factor out trace "dm" (return ()) as its own CAF first, call it xxx, now proceed to compile (\i -> xxx).
22:34 <monochrom> And for the has-const version: "Oh nothing to factor out as CAF". Only later to simplify const "dm" i to "dm".
22:34 <lyxia> jophish: what's an example where this is useful?
22:34 <monochrom> (And so no dependence on i after all, but the factoring ship has sailed.)
22:35 <jophish> lyxia: for example I might pass in a bunch of KnownNat constraints to a function after reifying them in a function taking a bunch of Naturals
22:36 <jophish> it's nice to highlight the similarities between these two functions by replacing the ->s with =>s
22:36 <jophish> admittedly this is a niche case, I'll try and think of a more compelling one
22:36 <kuribas> monochrom: this has the same bevaviour: http://lpaste.net/2846700419663527936
22:37 <jophish> These kind of signatures most often appear in the parts of our codebase which do a lot of type level computation and term -> type doohickery
22:38 <monochrom> Well yeah I'm just referring to the trace expression and whether it syntactically involves i or not.
22:39 <monochrom> No one will factor out "trace dm (return ()) >> return i" but the "trace dm (return ())" part can always be factored out.
22:40 <kuribas> but the inliner runs in many stages.
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22:40 <monochrom> Yes, my hypothesis still has a lot of holes.
22:41 <kuribas> anyway idk, I am not a ghc expert...
22:41 <monochrom> But a lot other hypotheses are clearly worse.
22:41 <kuribas> I guess trace, unsafePerformIO, etc... will be always unpredictable.
22:41 <kuribas> It's isn't even the same in ghci and compiled.
22:42 <kuribas> In my case it's only for debugging, so that's fine.
22:42 louispan joined
22:42 <monochrom> To some extent, trace is intended to expose compiler mutilations.
22:42 snowalpaca joined
22:43 <monochrom> It does not advertise itself as "I will show you what happens when faithfully following the vanilla naive lazy evaluation strategy".
22:44 <monochrom> It totally intends to show "what did the compiler decide to actually do"
22:44 zar joined
22:44 <monochrom> But "compiler" does vary along the axis of ghci -> O0 -> O1 -> O2.
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22:44 <bennofs> monochrom: doesn't trace inhibit at least some floating out optimization?
22:45 <monochrom> In fact, not just "compiler", also "run time system", at which point turning on or off profiling may matter, too.
22:46 <monochrom> I don't know. But it didn't inhibit this one.
22:47 <hpc> don't forget the llvm and javascript backends too
22:50 <monochrom> kuribas: Observe what happens when -fno-full-laziness
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22:58 <Axman6> bgamari: hey, no I didn't. I might have a look at how the parser can be changed, seems the use of `double` might be more strict than the WKT language allows
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22:59 <bgamari> Axman6, oh dear
23:00 <bgamari> Axman6, WKT isn't exactly the best-specified format I've written a parser for
23:00 <bgamari> so please do submit PRs
23:00 <bgamari> ideally I would start collecting some examples for a testsuite
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23:22 <lpaste_> robkennedy revised “Classes on Functions - Why won't this typecheck?”: “Classes on Functions - Why won't this typecheck?” at http://lpaste.net/699260116473479168
23:23 <robkennedy> If anyone could look at that it'd help a lot
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23:27 <robkennedy> In particular it's seeming to not unify `forall a. a -> o` where o is free
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23:33 <lpaste_> robkennedy revised “Classes on Functions - Why won't this typecheck?”: “Classes on Functions - Why won't this typecheck?” at http://lpaste.net/699260116473479168
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23:36 <rick_rustled> i can't for the life of me see how "seperating syntactic analysis from execution" makes any difference in terms of SICP's metaevaluator
23:36 <rick_rustled> https://mitpress.mit.edu/sicp/full-text/book/book-Z-H-26.html#%_sec_4.1.7
23:36 ramzifu joined
23:36 <rick_rustled> i see no gain in efficiency whatsoever
23:36 <rick_rustled> it seems like the same thing is happening either way; seperating analysis from execution seems inconsequential to me (i'm obviously missing something here)
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23:42 <EvanR> syntactic analysis doesnt seem to have anything to do with execution to me
23:43 <EvanR> especially in the haskell channel, where even evaluation has nothing to do with execution
23:43 <hpc> the lexical syntax of comments, though?
23:43 <hpc> definitely execution
23:45 <lpaste_> glguy annotated “Classes on Functions - Why won't this typecheck?” with “Classes on Functions - Why won't this typecheck? (annotation)” at http://lpaste.net/699260116473479168#a7876565830081708032
23:46 <glguy> robkennedy: When you're making this much of a mess, mixing rank-n types in is easiest to manage under a newtype
23:46 botolhejo joined
23:46 <glguy> (that version loads)
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23:50 <sphinxo> So i'd like to make a version of State, where get and put take an additional param
23:50 <sphinxo> so example usage would be {put True 10; put False 20} and then doing get 15 yields True, but get 25 would yield Fals
23:50 Rainb joined
23:50 <Koterpillar> sphinxo: why not use a State over Map Int Bool?
23:51 defaultnick joined
23:51 <sphinxo> or (Ord a) Map a b ?
23:52 <Koterpillar> whatever suits you
23:52 <Koterpillar> then you can have convenience functions putKey :: k -> v -> State (Map k v) (), getKey :: k -> State (Map k v) (Maybe v)
23:53 <sphinxo> I'm not sure that's what I want
23:53 <Koterpillar> then what do you want?
23:53 <sphinxo> I want like a time traveling k/v store
23:54 <sphinxo> so for example put <k> <v> timestamp
23:54 <sphinxo> so for example put <k> <v> timestamp + 5
23:54 <sphinxo> and then get <k> timestamp + 3 would give me the first v
23:55 <Koterpillar> all of this is still a State over some structure
23:55 <sphinxo> actually yeah
23:55 <Koterpillar> not necessarily a Map, but you get to reuse the State instance
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23:57 <sphinxo> but say it's not a Map, say I want to set the state to be x and <timestamp> and then set it to y at <timestamp + 5> and then get it at timestamp + 3, which should give me x
23:57 <sphinxo> to be x *at <timestamp>
23:57 <Koterpillar> right, so that's a data structure you can have
23:57 <Koterpillar> ...actually, still map
23:57 <Koterpillar> it has a "get the first key that's lower than X"
23:58 <sphinxo> ahh ok
23:58 <robkennedy> glguy: thanks. Don't understand how that fixed it
23:58 <sphinxo> Koterpillar: what's the name of that function?
23:59 <Koterpillar> sphinxo: lookupLT
23:59 <Koterpillar> (LE/GE/etc.)
23:59 <sphinxo> ahh wonderful