- Haskell-Cafe - Haskell.org

hmatrix's fitModel function crashes ghc(i)
by Roel van Dijk 07 Nov '10

07 Nov '10

Hello, I would like to use hmatrix to do some function fitting with the Levenberg Marquardt algorithm. As an example I would like to fit the very simple function "f x = a*x + b" on some data points. The problem is that executing the 'fitModel' function crashes GHC(i) with a segmentation fault. This makes debugging difficult. Can anyone spot what I am doing wrong? Given all the lists of Double's it seems very easy to make an error regarding the number of arguments with the model function or the derivative. Try to evaluate the 'test' function in the small program listed below. I would expect an output of [1, 0] (y = 1*x + 0) instead of a segmentation fault. Relevant versions: - hmatrix-0.10.0.0 - gsl-1.14 - ghc-6.12.3 (64 bit) Small program: module Test where -- from base: import Control.Arrow ( second ) import Control.Applicative ( pure ) -- from hmatrix: import Data.Packed.Matrix ( Matrix ) import Numeric.GSL.Fitting ( FittingMethod(LevenbergMarquardt), fitModel ) -- input list of (x, y) pairs, output coefficients of "f x = a x * b" fitLinear :: [(Double, Double)] -> ([Double], Matrix Double) fitLinear samples = fitModel 1 1 10 (linearModel, linearDer) (map (second pure) samples) [0, 0] linearModel :: [Double] -> Double -> [Double] linearModel [a, b] x = [a*x + b, 0] linearModel _ x = error "wrong arguments" linearDer :: [Double] -> Double -> [[Double]] linearDer [_, _] x = [[x, 0]] linearDer _ _ = error "wrong arguments" test = fitLinear [(0,0), (1,1), (2,2)]

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Fwd: [Haskell-cafe] DSL libraries
by Dupont Corentin 07 Nov '10

07 Nov '10

Nobody had the compilation messages I had? ---------- Forwarded message ---------- From: Dupont Corentin <corentin.dupont(a)gmail.com> Date: Tue, Nov 2, 2010 at 2:30 PM Subject: [Haskell-cafe] DSL libraries (Was: Map constructor in a DSL) To: steffen <steffen.siering(a)googlemail.com>, haskell-cafe(a)haskell.org Hello Steffen, can you compile AwesomePrelude? I've got error messages (see below). By the way, I've looked at some DSLs made in Haskell, if I don't mistake there are lots of similarities between them. There similarities could be put in a library to help the implementors of a DSL, more or less like AwesomePrelude. Is there already packages on Hackage dealing with that? Cheers, Corentin AwesomePrelude compilation error: I'm using GHC 6.12.1. > cd tomlokhorst-AwesomePrelude-9819315 > cabal install (...) Warning: Lang.Haskell: Instances of type and data families are not yet supported. Instances of the following families will be filtered out: H Then, when trying with a very simple GATD in GHCI, I've got: <interactive>: HSAwesomePrelude-0.1.0.o: unknown symbol `AwesomePreludezm0zi1zi0_ CompilerziLiftDefinitions_inline_closure' ghc: unable to load package `AwesomePrelude-0.1.0' On Thu, Oct 28, 2010 at 2:02 PM, steffen <steffen.siering(a)googlemail.com>wrote: > I think you would love to have a look at AwesomePrelude[1] or a fork > of AwesomePrelude using associated types[2] > Some more background information by Tom Lokhorst [3][4]. > > [1] http://github.com/tomlokhorst/AwesomePrelude > [2] http://github.com/urso/AwesomePrelude > [3] http://tom.lokhorst.eu/2009/09/deeply-embedded-dsls > [4] http://tom.lokhorst.eu/2010/02/awesomeprelude-presentation-video > > On 28 Okt., 12:09, Dupont Corentin <corentin.dup...@gmail.com> wrote: > > Thank you for your rich responses. > > > > Indeed I think I miss some thinks in my DSL, that would make things > easier > > to deal with lists and first class functions. > > I don't really know what for now. > > Perhaps a List Constructor? Or a constructor on functions like yours > Ryan? > > EAp :: Exp ref (a -> b) -> Exp ref a -> Exp ref b > > It's from which DSL? It is accessible on the net? > > > > Chris suggested me that I can only define the Foldr constructor and > deduce > > Map from it. > > But maybe I have to add a List constructor for that. > > > > But in the suggestions from Ryan and Brandon I don't understand why I > should > > add an extra type parameter and what it is! > > > > Steffen: Wow nice. I'll integrate that ;) > > > > I'm also looking at the Atom's DSL to get inspiration. > > Something I don't understand in it is that it has two languages, on > typed: > > > > data E a where > > VRef :: V a -> E a > > Const :: a -> E a > > Cast :: (NumE a, NumE b) => E a -> E b > > Add :: NumE a => E a -> E a -> E a > > etc. > > > > And, along with it, an untyped counterpart: > > > > -- | An untyped term. > > data UE > > = UVRef UV > > | UConst Const > > | UCast Type UE > > | UAdd UE UE > > etc. > > > > What that for? What's the use of having beautiful GADT if you have to > > maintain an untyped ADT aside?? > > > > Corentin > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-C...@haskell.orghttp:// > 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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ANNOUNCE: language-cil
by Tom Lokhorst 07 Nov '10

07 Nov '10

Hi all, I've just uploaded language-cil [1], a library for manipulating a Common Intermediate Language (CIL) [2]. CIL is the lowest level language used by Microsoft .NET and Mono on Mac an Linux. With language-cil, you can construct an AST and pretty print it to concrete syntax. The assembler `ilasm`, can create a .exe file which can be run by Mono or .NET. The package is not finished, it only supports a subset of the full language, but it's already usable. For more information, as well as an example to quickly get started, see the github page [3]. Cheers, Tom Lokhorst [1]: http://hackage.haskell.org/package/language-cil [2]: http://en.wikipedia.org/wiki/Common_Intermediate_Language [3]: https://github.com/tomlokhorst/language-cil#readme

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Review request for my baby steps towards a "platform independent interactive graphics" using VNC
by C K Kashyap 07 Nov '10

07 Nov '10

Hi, I started with the implementation of a VNC server library intended to be used as a library for rendering graphics and interacting with the user(mouse/keyboard). I'd appreciate it very much if I could get some feedback on my approach to binary parsing and Haskellism. Also, any reference/suggestion on how I could go about using a state machine to deal with the RFB protocol. http://hpaste.org/41131/vnc_server It's really early - but just wanted to get some advice on the approach. -- Regards, Kashyap

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internship opportunities in France
by Lorenzo Fundaró 06 Nov '10

06 Nov '10

Hello folks ! I am a Computer Science student looking for an internship of 6 months here in France. Does anybody know of any company working with Haskell ? Thanks in advance :D, Lorenzo Fundaró García

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Most popular haskell applications
by Bulat Ziganshin 06 Nov '10

06 Nov '10

Hello haskell, people, are you know haskell apps that has more than 50k downloads per month (or more than 25k users) ? -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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What do you call Applicative Functor Morphism?
by roconnor＠theorem.ca 06 Nov '10

06 Nov '10

An applicative functor morphism is a polymorphic function, eta : forall a. A1 a -> A2 a between two applicative functors A1 and A2 that preserve pure and <*>: eta (pure c) = pure c eta (f <*> x) = eta f <*> eta x What do you guys call such a thing? My leading candidate is "idomatic transformation". -- Russell O'Connor <http://r6.ca/> ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.''

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Flagstone problem
by michael rice 06 Nov '10

06 Nov '10

Hi, I've been looking at a "flagstone problem," where no two adjacent n-tuples can be identical. I solved the problem with Icon using an array of stacks and was going to explore how to do it in Haskell when I saw another way to do it explained in the same text. Just count the ones between the zeros in a(n) to get b(i), a non-repeating sequence of zeros, ones, and twos. An a(n) is 0 if the number of one bits in the binary representation of n is even, otherwise odd, and the initial a(n) must be even. n a(n) b(i) 20 = 010100 0 21 = 010101 1 2 22 = 010110 1 23 = 010111 0 0 24 = 011000 0 25 = 011001 1 2 26 = 011010 1 27 = 011011 0 1 28 = 011100 1 29 = 011101 0 0 30 = 011110 0 31 = 011111 1 2 32 = 100000 1 33 = 100001 0 0 34 = 100010 0 1 35 = 100011 1 36 = 100100 0 ========= Here's my Haskell code ======== import Data.Bits import Data.List flagstone n = foldl (++) "" (take n (map show (f $ group [if even y then 0 else 1 | y <- [bitcount x | x <- [20..]]]))) bitcount :: (Integral t) => t -> t bitcount 0 = 0 bitcount n = let (q,r) = quotRem n 2 in bitcount q + r f [] = [] f ([0]:xs) = f xs f ([0,0]:xs) = 0 : f xs f ([1]:xs) = 1 : f xs f ([1,1]:xs) = 2 : f xs ========= My question ======== A further exercise in the text: "Exercise 5.-(a) Define a(n) as the sum of the binary digits in the binary representation of n. Define b(i) as the number of a's between successive zeros as before. Then T = b(1) b(2) b(3) b(4) ... gives an infinite sequence of *seven* symbols with no repeats. (b) Write a routine to generate a sequence for seven colors of beads on a string with no repeats." I may be misreading, but does this make any sense? There's a reference to The American Mathematical Monthly, June-July 1963, p. 675, by C. H. Braunholtz. Michael

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http://functionalley.eu
by Alistair Ward 06 Nov '10

06 Nov '10

I've just written a few packages which I think may be useful, and have made them available as free opensource on a personal website http://functionalley.eu. I opted to host them there rather than uploading them to Hackage, because they're part of a wider project. The main offerings are; a regex-engine which is polymorphic in terms of the type of the input-data, a traditional character-based regex-engine derived from it, and an application to determine the most efficient order in which to pack files into a given storage-space. I understand this isn't the ideal venue in which announce new packages, but having looked briefly at the "haskell(a)haskell.org" mail-group and the cerebral offerings there, I'm rather concerned that my meagre offerings may resemble germs in a Dettol factory. Is there a more appropriate forum ? If anyone has the time, I'd also greatly appreciate any feedback on this s/w. Regards, Alistair Ward P.S. This is my first posting.

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How to put a string into Data.Binary.Put
by C K Kashyap 06 Nov '10

06 Nov '10

Hi, I was trying to put a String in a ByteString import qualified Data.ByteString.Lazy as BS message :: BS.ByteString message = runPut $ do let string="SOME STRING" map (putWord8.fromIntegral.ord) string -- this ofcourse generates [Put] How can I convert the list of Put's such that it could be used in the Put monad? For now I used the workaround of first converting the string to ByteString like this - stringToByteString :: String -> BS.ByteString stringToByteString str = BS.pack (map (fromIntegral.ord) str) and then using putLazyByteString inside the Put monad. -- Regards, Kashyap

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