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HGamer3D - version 0.4
by Peter Althainz 12 Aug '14

12 Aug '14

You will find version 0.4 of HGamer3D on github and hackage now. It also comes with some updated introductions on http://www.hgamer3d.org . best regards Peter (uotbw)

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Any tips on "doing it right" for a small program?
by Bram Neijt 12 Aug '14

12 Aug '14

Dear reader, I'm still new to haskell, and decided to convert a simple bash script to a full-on-bells-and-whistles Haskell program (as a learning experience). As you might guess I could use some help. The program is very simple, in Bash it reads: CMDPATTERN="$@" while [[ "`pgrep --count --full "$CMDPATTERN"`" -gt 1 ]]; do sleep 5 done AKA: while there is a command running with the given string, loop. I called this script "after" and use it on the commandline to chain commands from different terminals. The Haskell version is available at https://github.com/bneijt/after What I have done: - Add Travis CI - Add a first test case using test-framework - Add commandline option parsing using "options" - Implement a fork-join behavior using parallel-io What I would like help with: - How to add a --version that reflects the after.cabal version? - Is there a library for what I'm doing in Process.hs (listing running processes, etc.)? - How to add "-p <pid>" support, so I can do "after -p 129 -p 402" (after both pids) - Should I move from exitcode-stdio-1.0 to detailed-1.0? - Any and all other hints you might have Also if you have projects you want to point to for inspiration, I'd be happy to take a look. Greetings, Bram

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New Functional Programming Job Opportunities
by Functional Jobs 11 Aug '14

11 Aug '14

Here are some functional programming job opportunities that were posted recently: Big Data Engineer / Data Scientist at Recruit IT http://functionaljobs.com/jobs/8731-big-data-engineer-data-scientist-at-rec… Cheers, Sean Murphy FunctionalJobs.com

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Irritating Referential Transparency behavior?
by martin 10 Aug '14

10 Aug '14

Hello all, I came across something strange: This code compiles: ------------------------------------------------------------ data LProcess a = LP {lstep :: Writer [String] (Event a -> ([Event a], LProcess a))} ------------------------------------------------------------ exProcess2 :: ProcState -> Location -> LProcess EvtData exProcess2 pState loc = LP {lstep = xxx} where xxx = myStep pState myStep _ = return $ \(E t l _) -> ([E (t+1) l Wakeup], (proc' pState)) proc' state = exProcess2 (trc state) loc but when I replace xxx by myStep pState as in exProcess2 pState loc = LP {lstep = myStep pState} where xxx = myStep pState myStep _ = return $ \(E t l _) -> ([E (t+1) l Wakeup], (proc' pState)) proc' state = exProcess2 (trc state) loc I get No instance for (Monad m0) arising from a use of `myStep' The type variable `m0' is ambiguous Possible fix: add a type signature that fixes these type variable(s) It compiles again when I remove the xxx = line. Why is that so?

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Get out structured data from a C/C++ library in Haskell
by Nicola Gigante 10 Aug '14

10 Aug '14

Hello everybody. I'm new to the list so I'd like to say hello to you. I'm a student of computer science and early practitioner of Haskell. I've decided to implement the next project in Haskell but I need to interface a C++ library. I've read all the wikis material about the matter and I have an understanding of how FFI to C works in general. The library in question is a SAT solver for LTL formulas, and all I need to do is to be able to create the AST of the formula (Haskell will do the parsing) and pass it to the library, and then get back the reply. From the C++ point of view, the AST of the formulas consists simply of objects linked together with raw pointers. Nodes are of the same type, with an internal enum that specifies the type of node, so it's not an inheritance hierarchy or fancy things... What I would like to do is to be able to declare an algebraic data type that represents the AST and somehow mangle it to a form that can be passed to the C++ function of the library (that I can wrap into an extern "C" function to be able to use it through FFI if needed). How can I do that? In general, I've only seen example of how to exchange primitive types with C functions through the FFI, but not for example structures or pointers to structures. Note that I have control over the source code of the C++ library too, so the question includes suggestions about how to structure the C++ data as well, to ease the integration. Thank you for your help, Nicola

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ANN: immortal-0.1
by Roman Cheplyaka 10 Aug '14

10 Aug '14

I am pleased to announce the first release of the "immortal" package. Immortal allows you to create threads that never die. If the action executed by such a thread finishes or is killed by an exception, it is automatically restarted. Such a behavior is often desired when writing servers, so I decided to release a package that does exactly that. http://hackage.haskell.org/package/immortal https://github.com/feuerbach/immortal Roman

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Haskell Platform 2014.2.0.0 is Released!
by Mark Lentczner 09 Aug '14

09 Aug '14

On behalf of the Haskell Platform team, I'm happy to announce the release of *Haskell Platform 2014.2.0.0* featuring: GHC 7.8.3 53 packages 860+ public modules 4 tools This release features a major upgrade to OpenGL and GLUT. In addition, "behind the scenes", this release of the platform is produced with a new build system, and many improvements to the installations on all three OS families. Get it now: Download Haskell Platform <http://www.haskell.org/platform/> — for Windows <http://www.haskell.org/platform/windows.html> — for Mac OS X <http://www.haskell.org/platform/mac.html> — for Linux <http://www.haskell.org/platform/linux.html> (and similar systems) N.B.: You may need to explicitly re-fresh those links when visiting in your browser - those pages tend to get cached for very long periods of time. — Mark "platform wrangler" Lentczner P.S.: I realize this one was a long time a'comin'. I take the responsibility for the decisions that lead up to being this late, including deciding it was worth it to wait for GHC 7.8, and that this was the right time to re-write the platform build system. I hope the speed that we can now turn the platform will be evident in future releases. Haskell Platform is created by a team of many hands. Special call out to Randy Polen for the new Windows build, and Yitzchak Gale and Neil Mitchell for help with the new build system. Thanks also to all the intrepid folks that tried out the early alphas and release candidates. Additional help is always welcome!

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Free monad based EDSL for writing LLVM programs.
by arrowdodger 09 Aug '14

09 Aug '14

Hello. I'm new with Haskell and FP, so i wanted someone to give comments on the package i've made [1]. It's, actually, my first attempt to create something more or less real, so any feedback would be welcome. I've used Free monad to create EDSL that allows writing LLVM IR code. Afterwards it could be converted into pure AST structure provided by llvm-general-pure[2] package. Currently, it supports almost every instruction, but i haven't yet come up with sensible defaults for them. Another thing that bugs me is the ability to transform the code in syb way. I want take a user-supplied function that would pattern-match instruction and produce another code block and apply this function everywhere in the code, but still can't get my head around it. I've come up with extF function, that unlike extM, would resort to wrap instead of return, but that's all i've managed to do. Thanks in advance. [1] https://bitbucket.org/arrowdodger/llvm-general-edsl [2] http://hackage.haskell.org/package/llvm-general-pure

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Re: [Haskell-cafe] Free monad based EDSL for writing LLVM programs.
by Matt Giles 08 Aug '14

08 Aug '14

For transforming the code, have you checked out the uniplate package? It seems like it could fit your problem pretty well. On 8 August, 2014 at 5:00:19 AM, haskell-cafe-request(a)haskell.org (haskell-cafe-request(a)haskell.org) wrote: Send Haskell-Cafe mailing list submissions to haskell-cafe(a)haskell.org To subscribe or unsubscribe via the World Wide Web, visit http://www.haskell.org/mailman/listinfo/haskell-cafe or, via email, send a message with subject or body 'help' to haskell-cafe-request(a)haskell.org You can reach the person managing the list at haskell-cafe-owner(a)haskell.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Haskell-Cafe digest..." Today's Topics: 1. Re: Side-by-side pretty printing (J. Waldmann) 2. Free monad based EDSL for writing LLVM programs. (arrowdodger) 3. parsec: problem combining lookAhead with many1 (bug?) (silly8888) 4. Re: parsec: problem combining lookAhead with many1 (bug?) (Andreas Reuleaux) 5. Performance of StateT and best practices for debugging (Kyle Hanson) 6. [ANN] rtorrent-state 0.1.0.0 (Mateusz Kowalczyk) 7. Re: Performance of StateT and best practices for debugging (John Lato) 8. How to improve the zipwith's performance (jun zhang) 9. Re: Performance of StateT and best practices for debugging (Bardur Arantsson) 10. Visualising Haskell function execution (Jan Paul Posma) 11. Re: Performance of StateT and best practices for debugging (John Lato) ---------------------------------------------------------------------- Message: 1 Date: Thu, 7 Aug 2014 12:33:43 +0000 (UTC) From: J. Waldmann <waldmann(a)imn.htwk-leipzig.de> To: haskell-cafe(a)haskell.org Subject: Re: [Haskell-cafe] Side-by-side pretty printing Message-ID: <loom.20140807T142947-462(a)post.gmane.org> Content-Type: text/plain; charset=us-ascii This is what I use http://autolat.imn.htwk-leipzig.de/gitweb/?p=autolib;a=blob;f=todoc/Autolib… it's of the works-but-looks-ugly-and-is-terribly-inefficient variety but since it's applied to small Docs only (like, columns of matrices), I don't really care. - J.W. ------------------------------ Message: 2 Date: Thu, 7 Aug 2014 18:16:57 +0400 From: arrowdodger <6yearold(a)gmail.com> To: haskell-cafe(a)haskell.org Subject: [Haskell-cafe] Free monad based EDSL for writing LLVM programs. Message-ID: <CALH631%3DEbZ8aTZi%3DoPdfsP97J2XrRCTf%3DDpX%2BuaZ5m9%3D0mxXhw(a)mail.gmail.com> Content-Type: text/plain; charset="utf-8" Hello. I'm new with Haskell and FP, so i wanted someone to give comments on the package i've made [1]. It's, actually, my first attempt to create something more or less real, so any feedback would be welcome. I've used Free monad to create EDSL that allows writing LLVM IR code. Afterwards it could be converted into pure AST structure provided by llvm-general-pure[2] package. Currently, it supports almost every instruction, but i haven't yet come up with sensible defaults for them. Another thing that bugs me is the ability to transform the code in syb way. I want take a user-supplied function that would pattern-match instruction and produce another code block and apply this function everywhere in the code, but still can't get my head around it. I've come up with extF function, that unlike extM, would resort to wrap instead of return, but that's all i've managed to do. Thanks in advance. [1] https://bitbucket.org/arrowdodger/llvm-general-edsl [2] http://hackage.haskell.org/package/llvm-general-pure -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20140807/6d973f16…> ------------------------------ Message: 3 Date: Thu, 7 Aug 2014 15:25:23 +0100 From: silly8888 <silly8888(a)gmail.com> To: haskell-cafe(a)haskell.org Subject: [Haskell-cafe] parsec: problem combining lookAhead with many1 (bug?) Message-ID: <CAMmzbfWA9S3YGjJ1iQaa72rKZyuV4psvEP3LsQuDGC3QED-YVw(a)mail.gmail.com> Content-Type: text/plain; charset=UTF-8 Suppose that we have the following parser: p = lookAhead (char 'a') >> char 'b' If we use it like so parse p "" "a" we get the following error: Left (line 1, column 1): unexpected "a" expecting "b" What happened is that char 'a' succeeded by consuming the 'a' from the input and then lookAhead rewinded the input stream (as it does on success). Then, char 'b' tries to parse (again) the first character of the input and fails. Everything works as expected. Now let's slightly modify our parser: p' = lookAhead (many1 $ char 'a') >> char 'b' I've only added a many1. I was expecting this parser to give the same error as the previous one: many1 $ char 'a' will succeed consuming one 'a' and then lookAhead will rewind the input (as it does on success). Thus when we call char 'b' we are going to be in the beginning of the input again. Well, that doesn't happen: Left (line 1, column 2): unexpected end of input expecting "b" As you can see, lookAhead did not rewind the input as it was supposed to. ------------------------------ Message: 4 Date: Thu, 07 Aug 2014 17:32:11 +0100 From: Andreas Reuleaux <reuleaux(a)web.de> To: silly8888 <silly8888(a)gmail.com> Cc: haskell-cafe(a)haskell.org Subject: Re: [Haskell-cafe] parsec: problem combining lookAhead with many1 (bug?) Message-ID: <87y4v0z2es.fsf(a)web.de> Content-Type: text/plain While I haven't tried out your example in parsec, I can at least confirm that in trifecta it does work that way you expect it, ie. there is no difference between the error messages in both of your cases: (parsec's many1 = trifecta's some) Prelude > :m +Text.Trifecta Prelude Text.Trifecta > :m +Text.Parser.LookAhead Prelude Text.Trifecta Text.Parser.LookAhead > ... Prelude Text.Trifecta Text.Parser.LookAhead > parseTest (lookAhead (char 'a') >> char 'b') "a" ... Loading package reducers-3.10.2.1 ... linking ... done. Loading package trifecta-1.5.1 ... linking ... done. (interactive):1:1: error: expected: "b" a<EOF> ^ Prelude Text.Trifecta Text.Parser.LookAhead > parseTest (lookAhead (some $ char 'a') >> char 'b') "a" (interactive):1:1: error: expected: "b" a<EOF> ^ Prelude Text.Trifecta Text.Parser.LookAhead > Hope this helps. -Andreas silly8888 <silly8888(a)gmail.com> writes: > Suppose that we have the following parser: > > p = lookAhead (char 'a') >> char 'b' > > If we use it like so > > parse p "" "a" > > we get the following error: > > Left (line 1, column 1): > unexpected "a" > expecting "b" > > What happened is that char 'a' succeeded by consuming the 'a' from the > input and then lookAhead rewinded the input stream (as it does on > success). Then, char 'b' tries to parse (again) the first character of > the input and fails. Everything works as expected. > > Now let's slightly modify our parser: > > p' = lookAhead (many1 $ char 'a') >> char 'b' > > I've only added a many1. I was expecting this parser to give the same > error as the previous one: many1 $ char 'a' will succeed consuming one > 'a' and then lookAhead will rewind the input (as it does on success). > Thus when we call char 'b' we are going to be in the beginning of the > input again. Well, that doesn't happen: > > Left (line 1, column 2): > unexpected end of input > expecting "b" > > As you can see, lookAhead did not rewind the input as it was supposed to. > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe ------------------------------ Message: 5 Date: Thu, 7 Aug 2014 10:57:47 -0700 From: Kyle Hanson <me(a)khanson.io> To: haskell-cafe(a)haskell.org Subject: [Haskell-cafe] Performance of StateT and best practices for debugging Message-ID: <CAMJUouBqFbSi%2BifFsbYdXpba7pPVoP8BkyZxZaUoqLNuHc7VzQ(a)mail.gmail.com> Content-Type: text/plain; charset="utf-8" Hello, I was looking at cleaning up my refactoring a core loop of template rendering to go from a loop with many parameters loop :: RenderConfig -> BlockMap -> InputBucket m -> Builder -> [Pieces] -> ExceptT StrapError m Builder to a looped state monad transformer loop :: [Pieces] -> RenderT m Builder newtype RenderT m a = RenderT { runRenderT :: ExceptT StrapError (StateT (RenderState m) m) a } deriving ( Functor, Applicative, Monad, MonadIO ) data RenderState m = RenderState { position :: SourcePos , renderConfig :: RenderConfig , blocks :: BlockMap , bucket :: InputBucket m } however, there is a big slow down (about 6-10x) using a StateT. I think it might have something to do with laziness but I am not exactly sure of where to begin in tracking it down. Swapping out the Lazy State to a Strict State helps a little (only a 5x slow down) You can find some of the processing code here: https://github.com/hansonkd/StrappedTemplates/blob/321a88168d54943fc217553c… With my old loop commented out. Its messy right now since I am just trying a number of different approaches. I did some more work factoring out the lifts, trying different iterations of foldlM and stuff but that didn't have that much of an effect on performance. After profiling I see in the StateT, the report has a lot more CAFs and garbage collecting. Here is the profiling report from my original version w/o StateT http://lpaste.net/108995 Slow version with StateT http://lpaste.net/108997 Here is the "makeBucket" function that is referenced (it is the same in both state and nonstate): https://github.com/hansonkd/StrappedTemplates/blob/321a88168d54943fc217553c… Looking at stacked overflow and the official docs I have gotten an idea of what is going on. The heaps generated between them tells me that a lot more memory is being allocated to lists. These heaps were generated running my render function against a template with nested loops and a list of elements. http://imgur.com/a/2jOIf I am hoping that maybe someone could give me a hint at what to look at next. I've played around with Strictness and refactoring loops to no avail and now am kind of stuck. Any help would be appreciated. -- Kyle Hanson -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20140807/a82b99f5…> ------------------------------ Message: 6 Date: Thu, 07 Aug 2014 21:07:02 +0200 From: Mateusz Kowalczyk <fuuzetsu(a)fuuzetsu.co.uk> To: haskell-cafe(a)haskell.org Subject: [Haskell-cafe] [ANN] rtorrent-state 0.1.0.0 Message-ID: <53E3CE56.6090500(a)fuuzetsu.co.uk> Content-Type: text/plain; charset=windows-1252 Hi, rtorrent-state is a library that allows working with rtorrent state files (SOMEHASH.torrent.rtorrent) placed in your session directory. If you're an rtorrent user and ever had to manually muck around with those files, you should be able to use this library to make your life easier. For example, you can stop all torrents in your session directory with just: ?overFilesIn "rtorrent/session/dir" stopTorrent? The way it works is by parsing the session files, modifying the resulting data type and serialising it back into the file. I did not do optimisation but I had no problem with test sample of 100,000 files. I need to add IOException handling and maybe extra utility functions but otherwise I consider the library finished. Thanks -- Mateusz K. ------------------------------ Message: 7 Date: Thu, 7 Aug 2014 15:39:53 -0700 From: John Lato <jwlato(a)gmail.com> To: Kyle Hanson <me(a)khanson.io> Cc: haskell-cafe <haskell-cafe(a)haskell.org> Subject: Re: [Haskell-cafe] Performance of StateT and best practices for debugging Message-ID: <CAJ727GjPpMn3xMDs%3D4EmJGG0FpndsBwvq5Zkc97X6yQ-H21KEA(a)mail.gmail.com> Content-Type: text/plain; charset="utf-8" I haven't looked very closely, but I'm suspicious of this code from "instance Block Piece" ListLike l -> forM l (\obj -> ...) >>= (return . mconcat) The "forM" means that "l" will be traversed once and create an output list, which will then be mconcat'd together. The list has to be created because of the monadic structure imposed by forM, but if the result of the mconcat isn't demanded right away it will be retained as a thunk that references the newly-created list. I'd suggest that you replace it with something like ListLike l -> foldM (\(!acc) obj -> ... >>= return . mappend acc) mempty l Here I've justed added a bang pattern to the accumulator. If whatever is being returned has some lazy fields, you may want to change that to use deepseq instead of a bang pattern. Also, "foo >>= return . bar" is often regarded as a bit of a code smell, it can be replaced with "bar <$> foo" or "bar `liftM` foo", or sometimes something even simpler depending on circumstances (but IMHO sometimes it's more clear to just leave it alone). The heap profile does look like a space leak. The line <StrappedTemplates-0.1.1.0:Text.Strapped.Render.sat_sc1z> is a thunk (you can tell because it's in '<>' brackets), so whatever is referencing that is not strict enough. Sometimes another heap profile report, e.g. "-hc" or maybe "-hy" will give more useful information that lets you identify what exactly "sat_sc1z" is. You could also try compiling with -ddump-stg, which will dump the intermediate STG output which usually shows those names. But then you'll probably also need to re-run the profile, since the names change between compilations. Also IIRC some of values aren't named until the cmm phase, but that's harder to map back to Haskell so if you can identify the code from stg it's simpler. If you haven't seen http://blog.ezyang.com/2011/06/pinpointing-space-leaks-in-big-programs/, I'd highly recommend it if you need to track down a space leak. John L. On Thu, Aug 7, 2014 at 10:57 AM, Kyle Hanson <me(a)khanson.io> wrote: > Hello, > > I was looking at cleaning up my refactoring a core loop of template > rendering to go from a loop with many parameters > > loop :: RenderConfig -> BlockMap -> InputBucket m -> Builder -> [Pieces] > -> ExceptT StrapError m Builder > > to a looped state monad transformer > > loop :: [Pieces] -> RenderT m Builder > > newtype RenderT m a = RenderT > { runRenderT :: ExceptT StrapError (StateT (RenderState m) m) a > } deriving ( Functor, Applicative, Monad, MonadIO ) > > data RenderState m = RenderState > { position :: SourcePos > , renderConfig :: RenderConfig > , blocks :: BlockMap > , bucket :: InputBucket m > } > > however, there is a big slow down (about 6-10x) using a StateT. I think it > might have something to do with laziness but I am not exactly sure of where > to begin in tracking it down. Swapping out the Lazy State to a Strict State > helps a little (only a 5x slow down) > > You can find some of the processing code here: > > > https://github.com/hansonkd/StrappedTemplates/blob/321a88168d54943fc217553c… > > With my old loop commented out. > > Its messy right now since I am just trying a number of different > approaches. I did some more work factoring out the lifts, trying different > iterations of foldlM and stuff but that didn't have that much of an effect > on performance. > > After profiling I see in the StateT, the report has a lot more CAFs and > garbage collecting. > > Here is the profiling report from my original version w/o StateT > http://lpaste.net/108995 > > Slow version with StateT > http://lpaste.net/108997 > > Here is the "makeBucket" function that is referenced (it is the same in > both state and nonstate): > > > https://github.com/hansonkd/StrappedTemplates/blob/321a88168d54943fc217553c… > > Looking at stacked overflow and the official docs I have gotten an idea of > what is going on. The heaps generated between them tells me that a lot more > memory is being allocated to lists. These heaps were generated running my > render function against a template with nested loops and a list of elements. > > http://imgur.com/a/2jOIf > > I am hoping that maybe someone could give me a hint at what to look at > next. I've played around with Strictness and refactoring loops to no avail > and now am kind of stuck. Any help would be appreciated. > > -- > Kyle Hanson > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20140807/b4c26366…> ------------------------------ Message: 8 Date: Fri, 8 Aug 2014 11:24:29 +0800 From: jun zhang <zhangjun.julian(a)gmail.com> To: haskell-cafe(a)haskell.org Subject: [Haskell-cafe] How to improve the zipwith's performance Message-ID: <CAGjcJLcT0FAmNxFLbdaZZfMFg5aEL1rZDPEWOpRxvsKJsau3ew(a)mail.gmail.com> Content-Type: text/plain; charset="utf-8" Dear All I write a code for Clustering with Data.Clustering.Hierarchical, but it's slow. I use the profiling and change some code, but I don't know why zipwith take so many time? (even I change list to vector) My code is as blow, Any one kindly give me some advices. ====================== main = do .... let cluster = dendrogram SingleLinkage vectorList getVectorDistance .... getExp2 v1 v2 = d*d where d = v1 - v2 getExp v1 v2 | v1 == v2 = 0 | otherwise = getExp2 v1 v2 tfoldl d = DV.foldl1' (+) d changeDataType:: Int -> Double changeDataType d = fromIntegral d getVectorDistance::(a,DV.Vector Int)->(a, DV.Vector Int )->Double getVectorDistance v1 v2 = fromIntegral $ tfoldl dat where l1 = snd v1 l2 = snd v2 dat = DV.zipWith getExp l1 l2 ======================================= build with ghc -prof -fprof-auto -rtsopts -O2 log_cluster.hs run with log_cluster.exe +RTS -p profiling result is log_cluster.exe +RTS -p -RTS total time = 8.43 secs (8433 ticks @ 1000 us, 1 processor) total alloc = 1,614,252,224 bytes (excludes profiling overheads) COST CENTRE MODULE %time %alloc getVectorDistance.dat Main 49.4 37.8 tfoldl Main 5.7 0.0 getExp Main 4.5 0.0 getExp2 Main 0.5 1.5 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20140808/d29aa298…> ------------------------------ Message: 9 Date: Fri, 08 Aug 2014 06:31:49 +0200 From: Bardur Arantsson <spam(a)scientician.net> To: haskell-cafe(a)haskell.org Subject: Re: [Haskell-cafe] Performance of StateT and best practices for debugging Message-ID: <ls1jrl%247gp%241(a)ger.gmane.org> Content-Type: text/plain; charset=utf-8 On 2014-08-07 19:57, Kyle Hanson wrote: > Hello, > > Here is the "makeBucket" function that is referenced (it is the same in > both state and nonstate): > > https://github.com/hansonkd/StrappedTemplates/blob/321a88168d54943fc217553c… > Just a shot in the dark, but I notice that you're using "modify" and not "modify'" which was added in a recent version of transformers. Strict.StateT is not always "strict enough" and you may need to use modify'. At any rate, it's worth a shot, I think. Regards, ------------------------------ Message: 10 Date: Thu, 7 Aug 2014 22:30:25 -0700 From: Jan Paul Posma <me(a)janpaulposma.nl> To: haskell-cafe(a)haskell.org Subject: [Haskell-cafe] Visualising Haskell function execution Message-ID: <CAPtY9n%2B6onYBYb%3DpWP4NRmLq43zY6MGXQMuhmp2HfnUzhuOiyA(a)mail.gmail.com> Content-Type: text/plain; charset="utf-8" Hey all, Last weekend my friend Steve and I did a small project for visualising Haskell function execution in the browser. It's meant to be used in education, and uses a tiny custom parser. I figured it could be of interest for anyone here learning or teaching Haskell: https://stevekrouse.github.io/hs.js/ To see it in action, scroll a bit down to the red bordered box, and click on "map", and then keep clicking on each new line. I hope it can be useful to someone. Cheers, JP -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20140807/3c4dabe9…> ------------------------------ Message: 11 Date: Thu, 7 Aug 2014 23:56:43 -0700 From: John Lato <jwlato(a)gmail.com> To: Bardur Arantsson <spam(a)scientician.net> Cc: haskell-cafe <haskell-cafe(a)haskell.org> Subject: Re: [Haskell-cafe] Performance of StateT and best practices for debugging Message-ID: <CAJ727GipLL12TXfrMBeLJBX2_GdoD0W-CKJd4U1cu48CvnkrBg(a)mail.gmail.com> Content-Type: text/plain; charset="utf-8" On Thu, Aug 7, 2014 at 9:31 PM, Bardur Arantsson <spam(a)scientician.net> wrote: > On 2014-08-07 19:57, Kyle Hanson wrote: > > Hello, > > > > Here is the "makeBucket" function that is referenced (it is the same in > > both state and nonstate): > > > > > https://github.com/hansonkd/StrappedTemplates/blob/321a88168d54943fc217553c… > > > > Just a shot in the dark, but I notice that you're using "modify" and not > "modify'" which was added in a recent version of transformers. > > Strict.StateT is not always "strict enough" and you may need to use > modify'. > > At any rate, it's worth a shot, I think. > Good point. I think that even modify' will not be strict enough without adding strictness to RenderState as well. John L. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20140807/ce617687…> ------------------------------ Subject: Digest Footer _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ------------------------------ End of Haskell-Cafe Digest, Vol 132, Issue 11 *********************************************

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Performance of StateT and best practices for debugging
by Kyle Hanson 08 Aug '14

08 Aug '14

Hello, I was looking at cleaning up my refactoring a core loop of template rendering to go from a loop with many parameters loop :: RenderConfig -> BlockMap -> InputBucket m -> Builder -> [Pieces] -> ExceptT StrapError m Builder to a looped state monad transformer loop :: [Pieces] -> RenderT m Builder newtype RenderT m a = RenderT { runRenderT :: ExceptT StrapError (StateT (RenderState m) m) a } deriving ( Functor, Applicative, Monad, MonadIO ) data RenderState m = RenderState { position :: SourcePos , renderConfig :: RenderConfig , blocks :: BlockMap , bucket :: InputBucket m } however, there is a big slow down (about 6-10x) using a StateT. I think it might have something to do with laziness but I am not exactly sure of where to begin in tracking it down. Swapping out the Lazy State to a Strict State helps a little (only a 5x slow down) You can find some of the processing code here: https://github.com/hansonkd/StrappedTemplates/blob/321a88168d54943fc217553c… With my old loop commented out. Its messy right now since I am just trying a number of different approaches. I did some more work factoring out the lifts, trying different iterations of foldlM and stuff but that didn't have that much of an effect on performance. After profiling I see in the StateT, the report has a lot more CAFs and garbage collecting. Here is the profiling report from my original version w/o StateT http://lpaste.net/108995 Slow version with StateT http://lpaste.net/108997 Here is the "makeBucket" function that is referenced (it is the same in both state and nonstate): https://github.com/hansonkd/StrappedTemplates/blob/321a88168d54943fc217553c… Looking at stacked overflow and the official docs I have gotten an idea of what is going on. The heaps generated between them tells me that a lot more memory is being allocated to lists. These heaps were generated running my render function against a template with nested loops and a list of elements. http://imgur.com/a/2jOIf I am hoping that maybe someone could give me a hint at what to look at next. I've played around with Strictness and refactoring loops to no avail and now am kind of stuck. Any help would be appreciated. -- Kyle Hanson

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