- Haskell-Cafe - Haskell.org

why is rpar/rpar always faster (book Simon Marlow)?
by Kees Bleijenberg 02 Feb '16

02 Feb '16

I'am reading the book Parallel and Concurrent Programming in Haskell. The book has an explanation of the Eval monad. It compares rpar/rpar (example 2-1), rpar/rseq (example 2-2), rpar/rseq/rpar (example 2-3) and rpar/rpar/rseq/rseq in rpar.hs The examples run all in the total time 0.82 s. When I run rpar/rpar (example2-1) on my computer total time is 1.34 s. All other examples have total time 2.22 s. I'am running the examples exactly as written in the book. I tried the examples in opposite order, but the rpar/rpar example remains a lot faster. I wonder why the other examples are so much slower and why is it so different from the book? I run the examples on a computer with 4 cores. I'am using ghc version 7.10.1 on Win64. The Haskell version is 32 bits. If I run the examples with +RTS -N1 all examples use the same time (2.20 sec). Kees

1 0

Question, re: failed attempt at constraining a Traversable instance.
by David Banas 02 Feb '16

02 Feb '16

Hi all, I’m trying to do this: data Tree a = Empty | Leaf a | Node (Tree a) a (Tree a) instance Functor Tree where fmap g Empty = Empty fmap g (Leaf x) = Leaf (g x) fmap g (Node t1 x t2) = Node (fmap g t1) (g x) (fmap g t2) instance Foldable Tree where foldMap f Empty = mempty foldMap f (Leaf x) = f x foldMap f (Node l k r) = foldMap f l `mappend` f k `mappend` foldMap f r instance (Monoid (f (Tree a))) => Traversable (Tree (f a)) where sequenceA Empty = pure Empty sequenceA (Leaf f) = Leaf <$> f sequenceA (Node t1 f t2) = (sequenceA t1) `mappend` (Leaf <$> f) `mappend` (sequenceA t2) And I’m being told this: The first argument of ‘Traversable’ should have kind ‘* -> *’, but ‘Tree (f a)’ has kind ‘*’ In the instance declaration for ‘Traversable (Tree (f a))’ And I don’t quite understand what I’m asking for that’s forbidden. Is it that I’m trying to declare that only a certain subset of Trees are Traversable, and that’s not okay? It’s got to be all Trees or no Trees are Traversable? Thanks, -db

2 1

Share a variable across GHCI sessions: Possible?
by Jeffrey Brown 01 Feb '16

01 Feb '16

Suppose v is a view onto some data in a graph[1]. You ask GHCI to (show $ nodes v). You would like to ask GHCI in another window to (show $ disambiguations v), referring to the same v. Is it possible? My motivation is to show disambiguations that are about the nodes. Examples of disambiguations would be "a ! character adjacent to the left of a word means it requires money", or "CAP stands for Coastal Alliance of Pharoahs", or "a(/n)b means a needs b". [1] Using the Functional Graph Library, I am writing a graph database editor, Digraphs With Text: https://github.com/JeffreyBenjaminBrown/digraphs-with-text DWT is exceptionally flexible. Relationships can be of any arity, and can involve other relationships. For instance, in DWT the relationship "_ needs _ in order to _" has a natural representation; I am unaware of any other system in which it does. I would *love* help! And I take job offers seriously! -- Jeffrey Benjamin Brown

1 0

How stable is the typerep fingerprint value?
by Anatoly Yakovenko 01 Feb '16

01 Feb '16

How stable is the typerep fingerprint value? Is it going to change between builds based on the same sources? Thanks, Anatoly

1 0

ANNOUNCE: call-haskell-from-anything 1.0
by Niklas Hambüchen 31 Jan '16

31 Jan '16

Heya, I'm happy to announce a new release of call-haskell-from-anything [1], my library for FFI-via-serialisation that allows to easily call Haskell functions from any other language that can open shared object files (`.so` via `dlopen()`) and has a MessagePack library available. This is almost all programming languages; for examples for Python and Ruby see [2]. The FFI-via-serialisation approach makes it possible to export most functions to other languages "for free": no FFI type unpacking boilerplate, everything that has a MessagePack instance (much easier to write than `Storable` instances) will do. For example if you have a function chooseMax :: [Int] -> Int all you have do to make it callable is foreign export ccall chooseMax_export :: CString -> IO CString chooseMax_export = export chooseMax Version 1.0 uses closed type families to remove the restriction that so far, pure functions has to be wrapped into the Identity monad to be exported: a -> b -> ... -> Identity r With 1.0, this is no longer necessary. You can now export any function of type a -> b -> ... -> r to be called from your favourite Haskell contender languages (of course those have no chance ...). Cheers, Niklas [1]: https://hackage.haskell.org/package/call-haskell-from-anything-1.0.0.0 [2]: https://github.com/nh2/call-haskell-from-anything

1 0

setup-Simple-Cabal-1.22.5.0-x86_64-windows-ghc-7.10.3.exe: : does not exist
by Henk-Jan van Tuyl 31 Jan '16

31 Jan '16

L.S., Why do I get the message: setup-Simple-Cabal-1.22.5.0-x86_64-windows-ghc-7.10.3.exe: : does not exist after command "cabal install", and what can I do about it ? Regards, Henk-Jan van Tuyl -- Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://folding.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

5 8

Type introduction illustrated for casual haskellers
by Takenobu Tani 30 Jan '16

30 Jan '16

Dear Haskellers, I'm enjoying Haskell. After FTP(Foldable/Traversable in Prelude proposal), newcomers encounter Foldable signatures in their early stage. So I drew a few simple illustrations about a type introduction for newcomers/casual haskellers. Type introduction illustrated for casual haskellers http://takenobu-hs.github.io/downloads/type_introduction_illustrated.pdf https://github.com/takenobu-hs/type-introduction-illustrated If I have misunderstood, please teach me. I'll correct them. Thank you =), Takenobu

1 0

[ANN] Aivika: Branching Discrete Event Simulation in Haskell
by David Sorokin 30 Jan '16

30 Jan '16

Hi Cafe, I’m glad to announce the release of three my simulation libraries [1, 2, 3]. I would like to tell more about the third library especially. The aivika-brances package [3] is new. It allows creating branches to run nested simulations within simulation so that the source simulation remains intact. It allows us to forecast the behavior looking into the future of the model. There is a similar method in the financial modeling, when estimating the option instrument. We build a tree of future possible changes to estimate the present value. The present depends on the future. My library allows building the same tree of nested simulations. At the same time, this is a general purpose discrete event simulation library with such things as random streams of orders (transacts), limited resources, queues, discontinuous processes, the global event queue, event-based activities and so on. I think that we can create very sophisticated simulation models with elements of prediction and forecasting. Probably, the library can be useful for financial modeling. Initially, a few years ago I created the aivika simulation package [1] trying to repeat what other simulation libraries and software vendors provided in the field. Then an year or two ago I generalized my simulation library and created package aivika-transformers [2] with wide use of monad transformers and type families. I actually had plans to use that second package for the distributed and parallel discrete event simulation, but the package was so general that I could use it for what I would call a «branching discrete event simulation». Today I finished my third package aivika-branches, which is a very small additional package that introduces a new computation and a couple of new functions, where the main function is as follows: futureEvent :: Double -> Event BrIO a -> Event BrIO a It creates a new independent branch of the current simulation and then returns the result of the specified event-based computation in the desired time point, leaving the current computation intact. All pending events will be processed in the derived branch as if it were the current simulation. The very important thing is that the futureEvent function is relatively cheap. It was possible thanks to wide using the functional programming approach in my libraries. We can clone the simulation world as many times as we need for running nested simulations within simulation and it works. Frankly speaking, I don’t know of other general purpose simulation libraries that would offer the same functionality. I’m looking forward to hearing of your comments. Especially, I would be interested to participate in the projects related to simulation and modeling. I think that Haskell allows doing fantastic things here! Best regards, David Sorokin [1] http://hackage.haskell.org/package/aivika [2] http://hackage.haskell.org/package/aivika-transformers [3] http://hackage.haskell.org/package/aivika-branches

1 0

Re: [Haskell-cafe] FICS client in Haskell
by Tilmann 30 Jan '16

30 Jan '16

Hi Tony, thank you for having a look! I haven't given putting it on hackage much thought yet. But I would certainly do it if it's helping someone. Macbeth probably runs on other platforms as well. It's just that I developed it with OSX in mind (I was using babaschess on windows before) and provide an OSX binary only. Am 29.01.16 um 03:35 schrieb Tony Morris: > Hi Tilmann, > I'll give it a crack, though I haven't used FICS in a while. > > Couple of questions: > * have you put it on hackage? > * is it specific to Mac OSX? (if so, why?) > > > On 29/01/16 02:37, Tilmann wrote: >> Hi, >> I've been working on a FICS (Free Internet Chess Server) Client for a >> bit over a year now and it is finally in a presentable state. It would >> be great if you would like to have a look at the source code and let me >> know what you think! >> >> When I started with this project I was just starting to learn Haskell >> and I would like to know if the code is accessible/readable/idiomatic, >> if the overall organization seems reasonable as well or if you might >> have any other suggestion about what I could improve. (ie: I haven't >> decided on what logging framework to use.) >> >> The code is on github: https://github.com/tgass/macbeth >> >> I thank you all very much in advance! >> Tilmann >> >> >> >> https://github.com/tgass/macbeth/blob/master/src/Macbeth/Fics/FicsConnectio… >> >> Opens a telnet connection to freechess.org. Using conduit and attoparsec >> messages from the server are parsed to FicsMessages and put into a Chan. >> >> https://github.com/tgass/macbeth/blob/master/src/Macbeth/Fics/FicsMessage.hs >> >> The domain model >> >> The UI is using wx widgets (wxHaskell). Each wx-frame gets a copy of >> Chan FicsMessage and updates the UI when new Messages are available, ie >> here: >> https://github.com/tgass/macbeth/blob/master/src/Macbeth/Wx/ToolBox.hs >> https://github.com/tgass/macbeth/blob/master/src/Macbeth/Wx/Game.hs >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe

1 0

Re: [Haskell-cafe] Hide the data constructor for type family instance
by David Sorokin 29 Jan '16

29 Jan '16

Hi Imants, I fogot to add that the mentioned data constructor becomes visible in the haddoc section Instances for the exported BarIO monad. I would like to see that there is such an instance but without details about data constructor. Probably, the issue is more related to that how the BarIO type is shown in the documenation. On level of the module, where the QueueStrategy instance is defined, I can regulate the export list somehow. Thanks David 29.01.2016 1:22 пользователь "Imants Cekusins" <imantc(a)gmail.com> написал: Hello David, > FCFSQueue data constructor is visible together with all its contents > I would like it would be hidden completely Did you try to export all public symbols but not the constructor? _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe

1 0