June 2014 - Haskell-Cafe

Simple but slow, and complex but fast Forth emulation [Was: Bang, a drum DSL for Haskell]
by oleg＠okmij.org 12 Jun '14

12 Jun '14

Emulation of a simple subset of Forth in Haskell seems easy. The trick, continuation-passing style, has been known for a long time. The trick underlies `functional unparsing' by Olivier Danvy. http://www.brics.dk/RS/98/12/BRICS-RS-98-12.pdf (published in JFP in 1998). Chris Okasaki later extended the technique http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.121.1890 http://dl.acm.org/citation.cfm?id=581699 He also noted huge types and slow compilation times. But there is another way. It is far more complex, and far fast. It is used in HSXML, which handles polyvariadic functions with literally thousands of arguments (some of my web pages are long). The following complete code illustrates the idea. {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE FlexibleInstances, FlexibleContexts #-} {-# LANGUAGE TypeFamilies #-} -- Simple Forth module SimpleForth where -- The simple way: Danvy's Functional unparsing begin k = k () n st x k = k ((x::Int),st) add (n1,(n2,st)) k = k (n1+n2,st) end (top,st) = top t1 = begin n 1 n 2 add end -- Uncomment the following to get a hint why t2 is too slow -- t1 = begin _h n 1 n 2 add end -- Uncomment the following only if you are prepared to wait {- t2 = begin n 1 n 2 n 3 n 4 n 5 n 6 n 7 n 8 n 9 add add add add add add add add end -} -- A more complex but faster way -- Start with a stack 'stack' and then continue class Forth stack r where build :: stack -> r data End = End instance (a ~ stack) => Forth stack (End -> a) where build stack _ = stack data Add = Add -- Start with (Int, (Int, stack)), see Add and continue with (Int,stack) instance Forth (Int,stack) r => Forth (Int,(Int,stack)) (Add -> r) where build (n1,(n2,stack)) _ = build (n1+n2,stack) data N = N instance (a ~ Int, Forth (Int,stack) r) => Forth stack (N -> a -> r) where build stack _ n = build (n,stack) -- All of the following typecheck instantaneously, even on my slow -- laptop tt1 = build () N 1 N 2 Add End tt2 = build () N 1 N 2 N 3 N 4 N 5 N 6 N 7 N 8 N 9 Add Add Add Add Add Add Add Add End tt3 = build () N 1 N 2 Add N 3 Add N 4 Add N 5 Add N 6 Add N 7 Add N 8 Add N 9 Add End

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Deleting mailing list
by Jürgen Nicklisch-Franken 12 Jun '14

12 Jun '14

I want to delete the mailman mailing list for leksah (leksah(a)projects.haskell.org.) since it is not used anymore and only collects spam. It looks as I can't do this on my own, so I need help. My mails to support(a)community.haskell.org didn't produce any response. So I try this for years now. Please! Is someone out there that can help me? Kind regards Jürgen Nicklisch-Franken

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Unable to make a HList-like to deal with Kleisli Arrows and State
by Gautier DI FOLCO 12 Jun '14

12 Jun '14

Hi all, My goal is to compose Kleisli arrows with (State s) as parameteric Monadic type. So, I end up with the following code: data REnv :: [*] -> * -> * -> (* -> * -> *) -> ((* -> *) -> * -> * -> *) -> * where Last :: k (s t) i o -> REnv (t ': '[]) i o s k RCons :: k (s t) i o' -> REnv ts o' o s k -> REnv (t ': ts) i o s k Which, of course, gives me the following error when I try to play with it: *H> :t Last genRanking <interactive>:1:6: Kind incompatibility when matching types: s :: * -> * -> * StateT Ranking :: (* -> *) -> * -> * Expected type: Kleisli (s t) Ticket Ranking Actual type: Kleisli (State Ranking) Ticket Ranking In the first argument of ‘Last’, namely ‘genRanking’ In the expression: Last genRanking <interactive>:1:6: Kind incompatibility when matching types: t :: * Data.Functor.Identity.Identity :: * -> * Expected type: Kleisli (s t) Ticket Ranking Actual type: Kleisli (State Ranking) Ticket Ranking In the first argument of ‘Last’, namely ‘genRanking’ In the expression: Last genRanking*H> :t LastLast :: k (s t) i o -> REnv '[t] i o s k*H> :t genRanking genRanking :: Kleisli (State Ranking) Ticket Ranking I understand why it fails (State is * -> * -> *, while s is * -> *), but I can't figure out how to write this, I tried (s t o), but it isn't correct because k waits for a (* -> *). If you have any ideas, I'm curious to read them. Thanks in advance for your help.

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Re: [Haskell-cafe] 自动回复： HP's "The Machine"
by Vasili I. Galchin 12 Jun '14

12 Jun '14

2014-06-11 23:26 GMT-05:00 <zhangliu529(a)sina.com>: > 您发的邮件我已收到，我将尽快给您答复。 I too speak/read Chinese .. we can share info :-)

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HP's "The Machine"
by Vasili I. Galchin 12 Jun '14

12 Jun '14

a google of "The Machine" ... https://www.google.com/search?q=HP+%22The+Machine%22&ie=utf-8&oe=utf-8&aq=t… Let's assume this paradigm actually will work, what are the implications for FPLs in general and Haskell in particular?? Regards, Vasili

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Haskell Weekly News: Issue 296
by Daniel Santa Cruz 11 Jun '14

11 Jun '14

Welcome to issue 296 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers from May 25 to June 7, 2014 Quotes of the Week * mbrock: then you get into a whole thing about the epistemology of abstract algebra, and someone brings up Wittgenstein, somebody brings out a bottle of wine, and it's yet another one of those nights Top Reddit Stories * An alternative Haskell home page Domain: chrisdone.com, Score: 160, Comments: 57 Original: [1] http://goo.gl/Yw2G3a On Reddit: [2] http://goo.gl/m19Ujx * Third generation of the attoparsec parsing library Domain: serpentine.com, Score: 82, Comments: 22 Original: [3] http://goo.gl/kk8i50 On Reddit: [4] http://goo.gl/LZzevb * Music-Suite Domain: music-suite.github.io, Score: 81, Comments: 44 Original: [5] http://goo.gl/u69ybm On Reddit: [6] http://goo.gl/EYKMwI * Erik Meijer: Introduction to Functional Programming Domain: edx.org, Score: 79, Comments: 11 Original: [7] http://goo.gl/YrfbA3 On Reddit: [8] http://goo.gl/oLRm6k * The abject failure of weak typing Domain: techblog.realestate.com.au, Score: 72, Comments: 28 Original: [9] http://goo.gl/h5XDVZ On Reddit: [10] http://goo.gl/nfnLNN * Lazy Dynamic Programming Domain: jelv.is, Score: 64, Comments: 12 Original: [11] http://goo.gl/kdSbkh On Reddit: [12] http://goo.gl/I6XVa8 * First Person 3D Navigation, written in Elm Domain: github.com, Score: 62, Comments: 0 Original: [13] http://goo.gl/qLM3FD On Reddit: [14] http://goo.gl/CRNW6M * Haskell Platform Redesign Domain: self.haskell, Score: 57, Comments: 39 Original: [15] http://goo.gl/A2OqV4 On Reddit: [16] http://goo.gl/A2OqV4 * Benjamin Pierce on clean-slate security architectures Domain: intelligence.org, Score: 54, Comments: 2 Original: [17] http://goo.gl/dCWGlr On Reddit: [18] http://goo.gl/ns7SF6 * Idris 0.9.13 released, featuring a new erasure implementation, Haddock- and Hoogle-inspired tools, and improved IDE support Domain: idris-lang.org, Score: 53, Comments: 6 Original: [19] http://goo.gl/rf9i2U On Reddit: [20] http://goo.gl/tByoYR * Brilliant explanation of Free Monad + Interpreter pattern. Domain: programmers.stackexchange.com, Score: 52, Comments: 16 Original: [21] http://goo.gl/5wVfG1 On Reddit: [22] http://goo.gl/bCb0tD * I got lenses in my Functor Domain: izbicki.me, Score: 52, Comments: 35 Original: [23] http://goo.gl/9xAo4g On Reddit: [24] http://goo.gl/kZBcK8 * The GHC Runtime System [pdf] Domain: scs.stanford.edu, Score: 50, Comments: 15 Original: [25] http://goo.gl/J2iH4W On Reddit: [26] http://goo.gl/B2AiSo * The typeparams library provides a lens-like interface for type level parameters; it allows unboxing unboxed vectors (with benchmarks indicating a 25% performance gain) and supercompilation-like optimizations (with benchmarks showing 40x performance gain in some cases) Domain: github.com, Score: 49, Comments: 14 Original: [27] http://goo.gl/jzIn2E On Reddit: [28] http://goo.gl/fdiRHU * LiquidHaskell: Pointers Gone Wild Domain: goto.ucsd.edu, Score: 48, Comments: 16 Original: [29] http://goo.gl/aKyRnQ On Reddit: [30] http://goo.gl/pexvtf * Sed implementation in Haskell - Episode 6 [youtube] Domain: youtube.com, Score: 45, Comments: 5 Original: [31] http://goo.gl/JQ2ONf On Reddit: [32] http://goo.gl/vLQWVJ * Call Arity [pdf]: A new analysis implemented in GHC Domain: joachim-breitner.de, Score: 44, Comments: 6 Original: [33] http://goo.gl/BdEFfs On Reddit: [34] http://goo.gl/OSv5Rb Top StackOverflow Questions * Understanding Haskell's Bool Deriving an Ord votes: 17, answers: 2 Read on SO: [35] http://goo.gl/7W9WRb * Precise flow control in Haskell votes: 14, answers: 0 Read on SO: [36] http://goo.gl/uoA9i1 * Why aren't there existentially quantified type variables in GHC Haskell votes: 14, answers: 2 Read on SO: [37] http://goo.gl/ZeBJTK * Is the concept of an “interleaved homomorphism” a real thing? votes: 14, answers: 3 Read on SO: [38] http://goo.gl/gpIH6b * Is it possible to get `-=` working with literals? votes: 12, answers: 1 Read on SO: [39] http://goo.gl/R40i7q * How much overhead does sparking incur? votes: 11, answers: 1 Read on SO: [40] http://goo.gl/ixWkKL Until next time, [41]+Daniel Santa Cruz References 1. http://chrisdone.com/posts/haskell-lang 2. http://www.reddit.com/r/haskell/comments/26rilp/an_alternative_haskell_home… 3. http://www.serpentine.com/blog/2014/05/31/attoparsec/ 4. http://www.reddit.com/r/haskell/comments/26xyah/third_generation_of_the_att… 5. http://music-suite.github.io/docs/ref/ 6. http://www.reddit.com/r/haskell/comments/27djwy/musicsuite/ 7. https://www.edx.org/course/delftx/delftx-fp101x-introduction-functional-2126 8. http://www.reddit.com/r/haskell/comments/27bnt7/erik_meijer_introduction_to… 9. http://techblog.realestate.com.au/the-abject-failure-of-weak-typing/ 10. http://www.reddit.com/r/haskell/comments/26pi5b/the_abject_failure_of_weak_… 11. http://jelv.is/blog/Lazy-Dynamic-Programming 12. http://www.reddit.com/r/haskell/comments/26jh2w/lazy_dynamic_programming/ 13. https://github.com/evancz/first-person-elm#first-person-3d-navigation-in-elm 14. http://www.reddit.com/r/haskell/comments/26mjak/first_person_3d_navigation_… 15. http://www.reddit.com/r/haskell/comments/26g9y8/haskell_platform_redesign/ 16. http://www.reddit.com/r/haskell/comments/26g9y8/haskell_platform_redesign/ 17. http://intelligence.org/2014/05/11/benjamin-pierce/ 18. http://www.reddit.com/r/haskell/comments/274k69/benjamin_pierce_on_cleansla… 19. http://www.idris-lang.org/idris-0-9-13-released/ 20. http://www.reddit.com/r/haskell/comments/279wl7/idris_0913_released_featuri… 21. http://programmers.stackexchange.com/questions/242795/what-is-the-free-mona… 22. http://www.reddit.com/r/haskell/comments/2788cw/brilliant_explanation_of_fr… 23. http://izbicki.me/blog/i-got-lenses-in-my-functors 24. http://www.reddit.com/r/haskell/comments/27h0wk/i_got_lenses_in_my_functor/ 25. http://www.scs.stanford.edu/14sp-cs240h/slides/ghc-rts.pdf 26. http://www.reddit.com/r/haskell/comments/26qshw/the_ghc_runtime_system_pdf/ 27. https://github.com/mikeizbicki/typeparams#the-typeparams-library 28. http://www.reddit.com/r/haskell/comments/27avw8/the_typeparams_library_prov… 29. http://goto.ucsd.edu/~rjhala/liquid/haskell/blog/blog/2014/05/28/pointers-g… 30. http://www.reddit.com/r/haskell/comments/26redl/liquidhaskell_pointers_gone… 31. https://www.youtube.com/watch?v=GKRjVITL_oA 32. http://www.reddit.com/r/haskell/comments/26th92/sed_implementation_in_haske… 33. http://www.joachim-breitner.de/publications/CallArity-TFP.pdf 34. http://www.reddit.com/r/haskell/comments/26fdxq/call_arity_pdf_a_new_analys… 35. http://stackoverflow.com/questions/23880626/understanding-haskells-bool-der… 36. http://stackoverflow.com/questions/23869547/precise-flow-control-in-haskell 37. http://stackoverflow.com/questions/23940487/why-arent-there-existentially-q… 38. http://stackoverflow.com/questions/24090758/is-the-concept-of-an-interleave… 39. http://stackoverflow.com/questions/23875471/is-it-possible-to-get-working-w… 40. http://stackoverflow.com/questions/23877737/how-much-overhead-does-sparking… 41. https://plus.google.com/105107667630152149014/about

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Announcement: Bang, a drum DSL for Haskell
by Benjamin J Kovach 11 Jun '14

11 Jun '14

Hi haskell-cafe, I've been working on "Bang" on and off for about a month or two now, and finally thought it was "good enough" to open-source and show to the public! I've been having fun with it, and hopefully some of you will, too. It currently supports basically all of the primitive transformations that I could think of doing on a drum sequence, such as reversing, mirroring, changing duration and tempo. There are a bunch of operators built in that make it easy to write things like polyrhythms, and infinite sequences of notes are possible as well. The source code and basic tutorial are up on Github: https://github.com/5outh/Bang And the package + more detailed documentation is up on Hackage: http://hackage.haskell.org/package/Bang Let me know if you have any questions, comments, and/or suggestions. I'd love to hear them. Thanks! 5outh?

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Re: [Haskell-cafe] Deploy Haskell application
by Corentin Dupont 11 Jun '14

11 Jun '14

Hi, it seems that 'cabal configure' fails if some dependencies are missing. Then cabal copy complains that I should run 'cabal configure' first... On Wed, Jun 11, 2014 at 4:23 PM, Tom Feron <tho.feron(a)gmail.com> wrote: > Hi Corentin, > > I think you're searching for `cabal configure && cabal copy`. It will > still have an exit code of 1 if you don't compile anything but it will copy > the files from data-files (and alike). > > On my machine, it copies share/index.html into > .cabal-sandbox/share/x86_64-openbsd-ghc-7.6.3/dummy-0.1.0.0/share/index.html. > > Tom > > > On 11 June 2014 16:00, Corentin Dupont <corentin.dupont(a)gmail.com> wrote: > >> In the .cabal file you can put a directive "data-files" and they will be >> deployed in ~/.cabal/share... >> I want to trigger only this. >> >> >> On Wed, Jun 11, 2014 at 3:40 PM, Tom Nielsen <tanielsen(a)gmail.com> wrote: >> >>> Not sure what you mean - cabal doesn't do any deployment, or at least I >>> have not found a useful way of making it do so. In our case the deployment >>> is done by running apt-get update && apt-get install on the server. >>> >>> Tom >>> >>> >>> >>> >>> On Wed, Jun 11, 2014 at 3:18 PM, Corentin Dupont < >>> corentin.dupont(a)gmail.com> wrote: >>> >>>> Thanks for your response! >>>> Is there a way to ask Cabal to just deploy the resources and not >>>> compile everything? >>>> >>>> >>>> >>>> On Wed, Jun 11, 2014 at 11:47 AM, Tom Nielsen <tanielsen(a)gmail.com> >>>> wrote: >>>> >>>>> We package up the executables and other files into a Debain .deb >>>>> package using fpm after running cabal. Here is an example Makefile which >>>>> runs cabal, creates the debian package and adds it to our apt server: >>>>> >>>>> https://github.com/openbrainsrc/debcd/blob/master/Makefile >>>>> >>>>> This is run by our CI server after every commit to GitHub. >>>>> >>>>> Tom >>>>> >>>>> >>>>> On Wed, Jun 11, 2014 at 11:33 AM, Vo Minh Thu <noteed(a)gmail.com> >>>>> wrote: >>>>> >>>>>> Hi, >>>>>> >>>>>> These days, an increasingly popular solution to package an application >>>>>> with its dependencies is to use Docker. You can build the Docker image >>>>>> locally and push it to a Docker registry and retrieve it on your >>>>>> remote machine, or you can dump it as a tarball and load it on your >>>>>> remote machine. >>>>>> >>>>>> You have different ways to create the Docker image, one of which would >>>>>> be similar to pushing your Haskell binary to your remote machine. That >>>>>> way is simply to compile your exectuable locally, and copy it to the >>>>>> remote machine with is assets if any (you might even move it to a >>>>>> .cabal directory as if it was installed through `cabal install`). By >>>>>> default your executable will be statically linked, except for libgmp >>>>>> that you have to install on the remote machine. >>>>>> >>>>>> I recommand you look into Docker. You will be able to e-use its >>>>>> knowledge to package increasingly complex applications (that might >>>>>> have more numerous dependencies that you wouldn't have to manage on >>>>>> the host). >>>>>> >>>>>> HTH, >>>>>> Thu >>>>>> >>>>>> 2014-06-11 12:24 GMT+02:00 Corentin Dupont <corentin.dupont(a)gmail.com >>>>>> >: >>>>>> > Hi guys! >>>>>> > Is there a procedure to deploy a Haskell application? >>>>>> > I have an Amazon EC2 micro instance to run my application, but it's >>>>>> way too >>>>>> > small to compile it using cabal (compilation takes half a day >>>>>> rouhgly), so I >>>>>> > compile it on my computer. >>>>>> > Is there a convenient way to bundle the executable with the >>>>>> resources and >>>>>> > ship it to the server? >>>>>> > >>>>>> > Thanks! >>>>>> > Corentin >>>>>> > >>>>>> > _______________________________________________ >>>>>> > Haskell-Cafe mailing list >>>>>> > Haskell-Cafe(a)haskell.org >>>>>> > http://www.haskell.org/mailman/listinfo/haskell-cafe >>>>>> > >>>>>> _______________________________________________ >>>>>> Haskell-Cafe mailing list >>>>>> Haskell-Cafe(a)haskell.org >>>>>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>>>>> >>>>> >>>>> >>>> >>> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> >

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Deploy Haskell application
by Corentin Dupont 11 Jun '14

11 Jun '14

Hi guys! Is there a procedure to deploy a Haskell application? I have an Amazon EC2 micro instance to run my application, but it's way too small to compile it using cabal (compilation takes half a day rouhgly), so I compile it on my computer. Is there a convenient way to bundle the executable with the resources and ship it to the server? Thanks! Corentin

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non-exhaustive pattern match(es)?
by Semen Trygubenko / Семен Тригубен ко 11 Jun '14

11 Jun '14

Dear Haskell Cafe, In the following program f :: Int -> [(Int,Int)] -> [(Int,Int)] -> [(Int,Int)] f _ cs [] = cs f _ [] _ = [] f i (c:cs) ((i',t):os) | i < i' = [] | i == i' = [] | i > i' = [] -- | otherwise = [] main :: IO () main = do print $ f 0 [] [] without the "otherwise" clause (commented) I get the warning example.hs:2:1: Warning: Pattern match(es) are non-exhaustive In an equation for `f': Patterns not matched: _ (_ : _) ((_, _) : _) Could someone help me uncover which cases that are not… erm… covered by the above patterns? Many thanks, Semen PS This definition, on the other hand, f _ cs [] = cs f _ [] _ = [] f i (c:cs) ((i',t):os) = [] is exhaustive… -- Семен Тригубенко http://trygub.com

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