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Re: Where can I find a non-fee-based version of Hudak's paper, "Conception, evolution, and application of functional programming languages"?
by jean legrand 18 Sep '09

18 Sep '09

> Does anybody know where I can find a non-fee-based version of Paul > Hudak's paper, "Conception, evolution, and application of functional > programming languages" [1]? There used to be a version that did not seems you can get a djvu copy here http://lib.org.by/info/Cs_Computer science/CsPl_Programming languages/Hudak P. Conception, evolution, and application of functional programming languages (ACM comp.surveys 21, 1989)(T)(53s).djvu the site is in Russian and you wait 30s before a link to the file appears.

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About the parse error (possibly incorrect indentation)
by xu zhang 18 Sep '09

18 Sep '09

Hi, I am trying to get the function showMinProp to return String, but I always get an error of parse error (possibly incorrect indentation) Who can help with this? any idea? Thank u in advance! data Prop = Var String | Negation Prop | BinOp Op Prop Prop data Op = And | Or | Implies | Equiv derived Eq showOp :: Op -> String showOp And = "&" showOp Or = "|" showOp Implies = "=>" showOp Equiv = "<=>" instance Show Op where show = showOp precList = [(And,4),(Or,3),(Implies,2),(Equiv,1)] showProp :: Prop -> String showProp (Var s) = s showProp (Negation p) = "~" ++ showProp p showProp (BinOp op p q) = paren (showProp a p ++ space (showOp op) ++ showProp a q) showMinProp :: Int -> Prop -> String showMinProp preNo (BinOp op p q) = case op of And -> let a = 4 Or -> let a = 3 Implies -> let a = 2 Equiv -> let a = 1 if (a > preNo) then (showMinProp a p ++ space (showOp op) ++ showMinProp a q) else paren (showMinProp a p ++ space (showOp op) ++ showMinProp a q)) space s = " " ++ s ++ " " paren s = "(" ++ s ++ ")" instance Show Prop where show = showProp

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Where can I find a non-fee-based version of Hudak's paper, "Conception, evolution, and application of functional programming languages"?
by Benjamin L.Russell 18 Sep '09

18 Sep '09

Does anybody know where I can find a non-fee-based version of Paul Hudak's paper, "Conception, evolution, and application of functional programming languages" [1]? There used to be a version that did not require an ACM account available at http://www.cs.berkeley.edu/~jcondit/pl-prelim/hudak89functional.pdf , but when I try to download that file, the following error message appears: >The server has encountered a problem because access is restricted. > >Your request was : > http://www.cs.berkeley.edu/~jcondit/pl-prelim/hudak89functional.pdf -- Benjamin L. Russell [1] Hudak, Paul. "Conception, Evolution and Application of Functional Programming Languages." New York, NY: _ACM Computing Surveys (CSUR)_ 21(3) (September 1989): 359-411. <http://portal.acm.org/citation.cfm?id=72551.72554&coll=ACM&dl=ACM&idx=J204&…>. Also available at <http://www.cs.berkeley.edu/~jcondit/pl-prelim/hudak89functional.pdf>. -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^

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How to understand the 'forall' ?
by zaxis 18 Sep '09

18 Sep '09

data Branch tok st a = forall b. Branch (PermParser tok st (b -> a)) (GenParser tok st b) please shed a light on me, thanks! -- View this message in context: http://www.nabble.com/How-to-understand-the-%27forall%27---tp25250783p25250… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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help with FFI
by José Prous 17 Sep '09

17 Sep '09

Hello Lets say I have a library in C with a header like this: #include <stdio.h> /*really big structure*/ typedef struct { int *a; int *b; /*lots of stuff ... */ int *z; } foo; /*this function allocate memory and fill the structure, reading from a file*/ int create_foo(foo *f,FILE *file,int x,int y); /*some functions that use the structure*/ int use_foo(foo *f,int w); /*a funtion that releases the memory*/ int destroy_foo(foo *f); And I want to use it in haskell using FFI. I can create a .hsc file like this: {-# LANGUAGE CPP, ForeignFunctionInterface #-} import Foreign import Foreign.C.Types #include "foo.h" newtype Foo = Foo () foreign import ccall "static foo.h create_foo" c_create_foo :: Ptr (Foo) -> Ptr (CFile) -> CInt -> CInt -> IO CInt foreign import ccall "static foo.h use_foo" c_use_foo :: Ptr (Foo) -> CInt -> IO CInt foreign import ccall "static foo.h destroy_foo" c_destroy_foo :: Ptr (Foo) -> IO CInt It compiles but I have no idea how to call c_create_foo and get back Foo Any suggestions? thanks

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ANN: Unification in a Commutative Monoid (cmu 1.1) and a new release of Abelian group unification and matching (agum 2.2)
by John D. Ramsdell 17 Sep '09

17 Sep '09

Package cmu 1.1 provides unification in a commutative monoid, also know as ACU-unification. The core computation finds the minimal non-zero solutions to homogeneous linear Diaphantine equations. The linear equation solver has been place in a separate module so it can be used for other applications Package agum 2.2 provides unification and matching in an Abelian group, also know as AG-unification and matching. The core computation finds the integer solutions to inhomogeneous linear equations. The linear equation solver has been place in a separate module so it can be used for other applications John

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matching types in Haskell
by pat browne 17 Sep '09

17 Sep '09

Hi, I wish to align or match some Haskell types in order to represent a set of ontologies and their embedded concpts [1]. I am not sure wheather modules or classes could be used. I have done this task in a language called Maude[2]. The code is below. I appreciate that Maude is not very popular so there is a brief description below. This diagram below represents the semantics of what I am trying to achive. I want to construct MERGEDONTOLOGY from ONTOLOGY1 and ONTOLOGY2 both of which are based on COMMON. MERGEDONTOLOGY { Woman, RiverBank, FinancialBank, HumanBeing} /\ /\ / \ / \ / \ / \ / \ / \ ONTOLOGY1 ONTOLOGY2 {Woman, Bank, Person} {Woman, Bank, Human} /\ /\ \ / \ / \ / \ / \ / \ / \ / {Woman , Person} COMMMON Each Maude module represents (below) a distinct ontology, each sort (or type in Haskell) represents a concept. This example includes both synonyms and homonyms. I want to align ONTOLOGY1 and ONTOLOGY2 w.r.t COMMON to produce MERGEDONTOLOGY. The details of the concepts are as follows. The Woman concept should be the same in all ontologies, there is only one Woman concept and it is named as such in each ontology. Hence there should be only one Woman.MERGEDONTOLOGY There is only one concept HumanBeing.MERGEDONTOLOGY, but there are 3 synonyms Human.ONTOLOGY2, Person.ONTOLOGY1, and Person.COMMON It would seem that Person.COMMON should be mapped (or renamed?) to Human.ONTOLOGY2 which in turn is renamed (or mapped) to HumanBeing.MERGEDONTOLOGY. The homonyms are Bank.ONTOLOGY1 and Bank.ONTOLOGY2 which should become distinct entities in RiverBank.MERGEDONTOLOGY and FinancialBank.MERGEDONTOLOGY My question is how should this be done in Haskell. Is there a classes only solution? Is ther a module only solution? Or do I need both? Regards, Pat ============================================= Brief description of Maude code In the Maude Language the module is the basic conceptual unit. Sorts are declared in modules Every line ends with a space dot. In this case each module is bracketed by fth .. endfth There are various types of mappings between modules. In this case I used renamings where the syntax is *( name_in_source_module to name_in_target_module....) The keyword protecting is a type of inport. The + symbol between the modules forms a new module that includes all the information in each of its arguments ============================== fth COMMON is sorts Woman Person . endfth fth ONTOLOGY1 is protecting COMMON . sorts Bank . endfth fth ONTOLOGY2 is protecting COMMON *( sort Person to Human) . sorts Bank . endfth fth MERGEDONTOLOGY is including (ONTOLOGY1 * (sort Bank to RiverBank,sort Person to HumanBeing)) + (ONTOLOGY2 * (sort Human to HumanBeing, sort Bank to FinancialBank)) . endfth with the command show all MERGEDONTOLOGY the system will produce the following module fth MERGEDONTOLOGY0 is sorts Woman HumanBeing FinancialBank RiverBank . endfth ================================ Reference [1]Shapes of Alignments Construction, Combination, and Computation by Oliver Kutz, Till Mossakowsk, and Mihai Codescu http://www.informatik.uni-bremen.de/~okutz/shapes.pdf [2] Informa tiom on Maude at: http://maude.cs.uiuc.edu/

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algebra/grammar/language for expressing time intervals
by Jeremy Shaw 17 Sep '09

17 Sep '09

Hello, I need some cron-like functionality for long running daemon written in Haskell. I want to be able to schedule an event to be run: 1. once, at a specific time 2. some regularly scheduled time I don't see an existing library to do this, so I am starting work on my own. The first issue I am looking at is how to specify time intervals. The primary example I have looked at is cron. Cron is pretty good, but I don't see a way to do something like, run a job every other Wednesday. I also want to be able to display the interval schedule to the user, allow them to modify it, and also save the schedule to disk and reload it. So this essentially means that the type for describing the intervals can not contain any functions. Does anyone know of a good language for describing intervals? I want to be able to express things like: - run every other wednesday - run at 15 minutes past the hour - run at 15 minutes past the hour every wednesday - run at 15 and 25 minutes past the hour between the hours of 2 and 6 AM. - run every weekday at 8AM unless it is a holiday (the list of holidays would be supplied). Basically, everything you can express with cron, and a bit more. Is there any existing languages/grammars/algebras for this that I should look at? thanks! - jeremy

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Composition, delegation and interfaces -- a 20K ft critique of Noop
by Greg Meredith 17 Sep '09

17 Sep '09

Dear Programmers, Someone just asked me to give my opinion on Noop's composition proposal<http://code.google.com/p/noop/wiki/ProposalForComposition>. It reminds me a little bit of Self<http://en.wikipedia.org/wiki/Self_%28programming_language%29>which found its way into JavaScript. It also reminds me a little of Haskell's type classes <http://en.wikipedia.org/wiki/Type_class>. In general, movement away from inheritance is good. The proposal, however, feels a bit like looking for the lost quarter where the light is good, rather than where you lost it. Before considering delegation machinery, let's consider the *value*of an interface. How many interfaces are there? One way to see that is just to consider all the sub interfaces of a single interface with n methods on it. Hmmm... that's 2^n interfaces. That's a lot. Does that give us any confidence that any one way of carving up functionality via interfaces is going to be sane? Further, in practice, do we see random distribution through this very large space? What we see over and over again in practice is that the answer to these questions is 'no!'. That means that there is *something* that binds a collection of methods together. What might that something be? One place to look is mathematics. Which maths should we look at? The maths of category has been very fruitful both in explaining existing functional programming techniques and -- perhaps more importantly -- suggesting ways to improve them as well as wholly new techniques. What we find in category theory is that it is natural to collect maps (read functions) together. A good example of such a beast is a monad. A monad -- viewed categorically -- is - a map, T, taking types to new types and functions on those types to new functions. Let's call the universe of types and functions expressible in our model of computation (as proscribed by our programming language), C. Then T : C -> C. - a higher order map, unit. Just like T takes C to C, we can understand a "noop" like map that takes C to C, call it Id. Then unit : Id -> T. We intuitively think about it as putting basic types inside the container T, but it's really a higher order map. - another higher order map, mult : T^2 -> T. We talk about it as a kind of flattening (and in Scala it's called flatMap), but it's a higher order map. Now, one is not finished spelling out a monad when giving this collection of maps. One must also show that they satisfy certain constraints. - T is functorial, meaning T g f = T(g) T(f) - unit and mult are natural transformations, look up the meaning because unpacking it here would take to long - mult( mult T ) = mult( T mult ) - mult( unit T ) = mult( T unit ) This set of constraints must go with the monad. This example provides a little more detail in terms of what binds a group of maps together, and hence of what *might* replace the notion of interface and *explain* what we see in practice. Good programmers invariably pick out just a few factorizations of possible interfaces -- from the giant sea of factorizations (read different ways to carve up the functionality). The reason -- i submit -- is because in their minds there are some constraints they know or at least intuit must hold -- but they have no good way at the language level to express those constraints. A really practical language should help the programmer by providing a way express and check the constraints that hold amongst the maps in an interface. i submit that this idea is not the same as "design by contract". i am not proposing an Eiffel-like mechanism. Again, taking a functional approach to computation via category theory leads one towards modeling interfaces as categorical "situations" like monads, comonads, distribution laws, etc. This means that a large number of the constraints come down to - functoriality - naturality - coherence Language support for this approach might include *keywords for these kinds of assertions*. It is a gnarly beast to offer automatic and/or compiler support for checking general constraints. Even this limited family of constraints that i'm proposing can generate some very difficult computations, with very bad complexity. However, for those situations where a general purpose solution to check assertions of functoriality, naturality and coherence are infeasible, one can use these hints to generate tests to probe for possible failures. This idea follows the in the same spirit of replacing proof with proof-checking. Of course, this is not the only way to go. i've yet to be convinced that category theory offers a good account of concurrency. Specifically, categorical composition does not line up well with concurrent composition. So, interfaces organized around types for concurrency is also something to consider. In this case, one might find a natural beginning in interfaces in which -- roughly speaking -- the methods constitute the tokens of a formal language the constructors of which are given by the types for concurrency paradigm. Best wishes, --greg On Thu, Sep 17, 2009 at 11:14 AM, Charles F. Munat <charles(a)munat.com>wrote: > http://code.google.com/p/noop/wiki/ProposalForComposition > -- L.G. Meredith Managing Partner Biosimilarity LLC 1219 NW 83rd St Seattle, WA 98117 +1 206.650.3740 http://biosimilarity.blogspot.com

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Trouble installing leksah
by Gregory Propf 17 Sep '09

17 Sep '09

I now have the Haskell platform install problem solved but I'm now trying to get the leksah IDE installed and I'm getting this. runhaskell Setup configure Configuring leksah-0.6.1... Setup: At least the following dependencies are missing: glib >=0.10, gtk >=0.10, gtksourceview2 >=0.10.0 I am aware that these are actually C development libraries, not Haskell modules. The thing is that they are all installed, using the Ubuntu synaptic tool. This is Ubuntu 9.04. Is there something I need to tell cabal about where these libraries are?

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ANNOUNCE: graphviz-2999.5.1.0
by Ivan Lazar Miljenovic 17 Sep '09

17 Sep '09

I'm pleased to announce version 2999.5.1.0 [1] of the graphviz library, which provides bindings to the GraphViz [2] suite of tools for drawing graphs. [1] http://hackage.haskell.org/package/graphviz-2999.5.1.0 [2] http://www.graphviz.org/ This is mainly a bug-fix release; as such, there is no API change (though if you use the graphvizWithHandle function in Data.GraphViz.Commands, you should ensure that your Handle -> IO a function closes the Handle when done). Changes in this release are: * Potentially fixed the graphvizWithHandle bug where warnings would be emitted about Handles not being closed correctly or too early; correct approach spotted by Nikolas Mayr. * Fixed up Parsing of various Attribute sub-values, especially Point and Spline (and hence Pos, which uses them). * Pre-process out comments and join together multi-line strings before parsing. * Properly parse Doubles like ".2". -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

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Re: Question about haskell.cs.yale.edu/
by Magnus Therning 17 Sep '09

17 Sep '09

Today I received the request below. At first the URL confused me, but apparently www.haskell.org is known under two names :-) The request should probably be handled by someone involved in ICFP. /M On Wed, Sep 16, 2009 at 11:53 PM, Peter Green <peter.green(a)frixo.com> wrote: > Hi, > > I was wondering whether you would be interested in linking to my website http://www.frixo.com from your page? > > http://haskell.cs.yale.edu/haskellwiki/icfp_2009_local_arrangements > > Frixo is a road traffic reporting site and think it may be a useful resource for your readers. It provides users with live traffic information and gets updated every 3 minutes using various road sensors. > > Thank you for your consideration. > > Kind Regards, > Peter > http://www.frixo.com > > -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe

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GHC threaded runtimes and pure functions
by Gregory Propf 17 Sep '09

17 Sep '09

One of the things I liked about Haskell was the notion of pure functions and the fact that they can be, in theory, automatically parallelized on multicore hardware. I think this will become a huge deal in a few years as cores multiply. My question is simply this: under GHC is this what really happens with, say a mapping over a pure function. Yes, I compiled with --threaded and am using the +RTS -N2 options on my dual core machine. Here's the code I wrote as a speed test. It just doesn't seem any faster with -N2. Using the ps command I found that multiple threads are indeed launched (this is Linux) but all but one show as being in a state of waiting for some event to finish (the ps output flags them all 'Sl'. main = do rg <- getStdGen let rs = take 10000000 $ randomRs (1::Int,100000::Int) rg rs'= map (\n -> n*n) rs print rs'

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Can't install Haskell Platform (Ubuntu 9.02)
by Gregory Propf 17 Sep '09

17 Sep '09

I'm trying to install the Haskell Platform. I'm using Ubuntu 9.02 and GHC 6.10.4 on a 64 bit AMD and keep getting this crap when I do 'make install'. The stuff builds OK and the script in question does indeed exist. Anybody know what this is. I've looked online and none of the other people with this issue seem to know the fix. Error: The mtl-1.1.0.2/Setup script does not exist or cannot be run

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Parallel lazy zip
by Henning Thielemann 16 Sep '09

16 Sep '09

When reading http://www.macs.hw.ac.uk/~dsg/gph/papers/html/Strategies/strategies.html I got the impression, that when I want to compute in parallel I have to suppress laziness at all costs, otherwise only a neglible portion of the code is run in parallel. How can I parallelize the computation of two lazily generated lists, where the list generation is expensive, but the combination of the lists is cheap? For example: module Main where expensiveList :: Int -> [Int] expensiveList n = map (\m -> sum [n..m]) [10000000..] sequentialZip :: [Int] sequentialZip = zipWith (+) (expensiveList 1) (expensiveList 2) main :: IO () main = mapM_ print $ take 10 sequentialZip It seems to me that this program must run almost twice as fast when using two cores, because the expensive lists can be computed perfectly in parallel. It requires however, that the zipWith can fetch data lazily across threads. However applying a Parallel strategy to the expensive list, will certainly try to evaluate it completely.

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Using tiny (atomic) mutables between multiple threads
by Belka 16 Sep '09

16 Sep '09

Hello, Haskell Cafe! I used an MVar to signalize to many threads, when it's time to finish their business (I called it a LoopBreaker). Recently I realized, that it might be too expensive (to use MVar) for cases when threads are many and all of them read my LoopBreaker intensively. This assumption appeared in a case, where I widely (in many threads) used my stopableThreadDelay, which checks LoopBreaker every d = 100 milliseconds. So I decided that I don't really need all the great features, that MVar provides, and that a simpler memory usage concept might be applied here. In a most (machinely) reduced view, all I need is a mutable byte. It would be thread safe, since reading and writing are atomic operations. I then wrote a simple experimental module (my first experience with Ptr in Haskell): ----------------- import Control.Monad import Foreign.Marshal.Utils import Foreign.Ptr import Foreign.Storable newtype MyVar a = MyVar { mvPtr :: Ptr a } newMyVar :: Storable a => a -> IO (MyVar a) newMyVar val = MyVar `liftM` new val readMyVar :: Storable a => (MyVar a) -> IO a readMyVar val = peek $ mvPtr val writeMyVar :: Storable a => (MyVar a) -> a -> IO () writeMyVar var val = poke (mvPtr var) val ----------------- Now, please, help me to answer few questions about all it: 1. Might readMVar really be computationally expensive under heavy load, (with all it's wonderful blocking features)? How much (approximately) more expensive, comparing to a assembler's "mov"? 2. Are the above readMyVar and writeMyVar really atomic? Or are they atomic only if I apply them to <MyVar Word8> type? 3. Are the above readMyVar and writeMyVar safe against asynchronous exceptions? Or again, only if I use <MyVar Word8> type? Belka -- View this message in context: http://www.nabble.com/Using-tiny-%28atomic%29-mutables-between-multiple-thr… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Some question about c2hs.
by Andy Stewart 16 Sep '09

16 Sep '09

Hi all, I try to binding Haskell to VTE library. Below are Vte.chs file i wrote. I use c2hs with below command LANG=C c2hs -d trace -l $(pkg-config --cflags vte | sed 's/-I/-C-I/g') vte/vte.h Vte.chs generate Vte.hs file. When i compile Vte.hs file, i got below error: Vte.chs:67:89: Couldn't match expected type `Widget' against inferred type `()' Expected type: IO (Ptr Widget) Inferred type: IO (Ptr ()) In the second argument of `($)', namely `vte_terminal_new' In the second argument of `($)', namely `liftM (castPtr :: Ptr Widget -> Ptr Terminal) $ vte_terminal_new' for binding code: terminalNew :: IO Terminal terminalNew = makeNewObject mkTerminal $ liftM (castPtr :: Ptr Widget -> Ptr Terminal) $ {#call unsafe terminal_new#} In C code, fucntion `GtkWidget *vte_terminal_new(void);' return `IO (Ptr Widget), then i use castPtr transform (Ptr Widget) to (Ptr Terminal), right? Why GHC report function `vte_terminal_new` return `IO (Ptr ())', I do something wrong? Any help? Thanks! -- Andy

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Haskell -> .NET
by Peter Verswyvelen 16 Sep '09

16 Sep '09

I heard that compiling Haskell to Java is not obvious since tail calls are not supported. .NET's intermediate language (IL) does support tail calls, however it is currently slower than regular calls, and is not always supported by all JITs. But given that F# will soon be officially released, I hope that eventually tail calls will work as expected, and fast See e.g. http://blogs.msdn.com/clrcodegeneration/archive/2009/05/11/tail-call-improv… So, might it be worth considering a .NET backend for a Haskell compiler? Peter Verswyvelen

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Building a monoid, continuation-passing style
by Martijn van Steenbergen 16 Sep '09

16 Sep '09

Hello cafe, Inspired by Sean Leather's xformat package [1] I built a datatype with which you can build a monoid with holes, yielding a function type to fill in these holes, continuation-passing style. Here are some primitives and their types: > now :: m -> ContSt m r r > later :: (a -> m) -> ContSt m r (a -> r) > run :: ContSt m m r -> r > instance Monoid m => Category (ContSt m) Here's an example of how to use it: > run (now "hello" . now "world") "helloworld" > run (later id . now "world") "hello" "helloworld" > run (later id . later show) "hello" 567 "hello567" The source code is available at [2]. I have a couple of questions: * ContSt is a Category. Is it also an Arrow? Why (not)? * Did I miss any other obvious classes this type is an instance of? * What is its relation with the Cont and Reader monads? * Are there any other useful applications other than printf-like functionality? * ContSt is a horrible name. What is a better one? For those who have a bit more time: I appreciate any comments and suggestions on the code. :-) Many thanks in advance, Martijn. [1] http://hackage.haskell.org/package/xformat [2] http://code.google.com/p/monoid-cont/source/browse/trunk/ContSt.hs

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Hopefully simple monad question
by Gregory Propf 16 Sep '09

16 Sep '09

I'm playing around with a little program that implements a simple virtual machine. I want to use a monad to represent machine state. I created a data type for the machine (VM) and a monadic type for the monadic computations using it. I declared this an instance of MonadState and Monad and created the usual operators. That stuff works. My issue is that I want to run some functions in the machine monad, call it VMS - "virtual machine w/state" and then pull the underlying VM data structure out and print it. I've read about monad transformers, lift, liftM, liftIO and all these instances in the libraries like MonadIO and am rather confused. The most sensible conclusion I can reach is that I probably need to create my own Transformer monad and define liftIO. Is this where I need to go? Also, my VMS monad doesn't really do anything different from the State monad except explicitly specify that state is a VM and not a generic type. Am I doing too much work creating my own instances here? Would a simple "type" statement work?

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ANNOUNCE: levmar-0.2
by Bas van Dijk 16 Sep '09

16 Sep '09

Hello, We like to announce a new release of the high-level Levenberg-Marquardt library levmar: http://hackage.haskell.org/package/levmar-0.2 Changes: * There's one new major feature: automatic calculation of the Jacobian using automatic differentiation with Conal Elliott's vector-space library. (Conal: would you like to take a quick look at the implementation and see if I'm using vector-space the way it supposed to be used, thanks) * Furthermore we made the type Model from LevMar more type-safe by replacing: type Model m r = NFunction m r [r] with: type Model m n r = NFunction m r (SizedList n r) * Finally we did lot's of internal refactorings and updated the documentation. regards, Bas and Roel van Dijk

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ANNOUNCE: bindings-levmar-0.1.1
by Roel van Dijk 16 Sep '09

16 Sep '09

I am pleased to announce the release of bindings-levmar-0.1.1: http://hackage.haskell.org/package/bindings-levmar The most important change compared to the previous version is a custom configure script (copied from hmatrix) that detects which libraries are needed. The cabal file also has some flags which allow you to choose for instance intel's mkl library instead of the normal lapack (also copied from hmatrix). Happy hacking, Roel and Bas van Dijk

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Re: retrieving arguments for functions from a heterogenous list
by oleg＠okmij.org 16 Sep '09

16 Sep '09

Andrew U. Frank wrote: > I have a number of functions which have some arguments and produce a single > result. all the arguments are in a heterogenous list and the results should > update the list. If I understand the problem correctly, you have a typed-indexed collection TIP and you would like to apply a transformation function to it, whose argument types and the result type are in the TIP. The function should locate its arguments based on their types, and update the TIP with the result. The function may have any number of arguments, including zero; the order of arguments should not matter. Then the following code seems to solve the problem. It starts with the examples. {-# LANGUAGE MultiParamTypeClasses, FlexibleInstances #-} {-# LANGUAGE ScopedTypeVariables, UndecidableInstances #-} -- Transforming a TIP: applying to a TIP a (polyvariadic) function -- that takes arguments from a TIP and updates the TIP with the result module TIPTransform where import Data.HList import Data.HList.TIP import Data.HList.TypeEqGeneric1 import Data.HList.TypeCastGeneric1 import Data.HList.Label5 newtype MyVal = MyVal Int deriving Show -- A sample TIP tip1 = MyVal 20 .*. (1::Int) .*. True .*. emptyTIP -- TIP (HCons (MyVal 20) (HCons 1 (HCons True HNil))) -- Update the Int component of tip1 to 2. The Int component must -- exist. Otherwise, it is a type error tip2 = ttip (2::Int) tip1 -- TIP (HCons (MyVal 20) (HCons 2 (HCons True HNil))) -- Negate the boolean component of tip1 tip3 = ttip not tip1 -- TIP (HCons (MyVal 20) (HCons 1 (HCons False HNil))) -- Update the Int component from the values of two other components tip4 = ttip (\(MyVal x) y -> x+y) tip1 -- TIP (HCons (MyVal 20) (HCons 21 (HCons True HNil))) -- Update the MyVal component from the values of three other components tip5 = ttip (\b (MyVal x) y -> MyVal $ if b then x+y else 0) tip1 -- TIP (HCons (MyVal 21) (HCons 1 (HCons True HNil))) -- The same but with the permuted argument order. -- The order of arguments is immaterial: the values will be looked up using -- their types tip5' = ttip (\b y (MyVal x)-> MyVal $ if b then x+y else 0) tip1 -- TIP (HCons (MyVal 21) (HCons 1 (HCons True HNil))) -- The implementation class TransTIP op db where ttip :: op -> db -> db instance (HMember op db b, TransTIP' b op (TIP db)) => TransTIP op (TIP db) where ttip = ttip' (undefined::b) class TransTIP' b op db where ttip' :: b -> op -> db -> db -- If op is found in a TIP, update the TIP with op instance (HTypeIndexed db, HUpdateAtHNat n op db db, HType2HNat op db n) => TransTIP' HTrue op (TIP db) where ttip' _ = tipyUpdate -- If op is not found in a TIP, it must be a function. Look up -- its argument in a TIP and recur. instance (HOccurs arg db, TransTIP op db) => TransTIP' HFalse (arg -> op) db where ttip' _ f db = ttip (f (hOccurs db)) db

1 0

(weird stuff) Kernel Modules in Haskell ;-)
by Matthias Kilian 16 Sep '09

16 Sep '09

A fellow openbsd developer told me the URL below... I hope this hasn't been posted on this list already (at least I didn't find it in my local archives): http://tommd.wordpress.com/2009/09/13/kernel-modules-in-haskell/ Ciao, Kili -- Logging should be in debug mode only. If every network driver did a dmesg printf everytime they came up, would that be a better world? -- Theo de Raadt

2 1

adding state in GUIs (qtHaskell)
by Michael P Mossey 16 Sep '09

16 Sep '09

I'm trying to learn qtHaskell. I realize few people on this list know anything about qtHaskell, but I have a question that probably relates to all GUIs as implemented in Haskell. I just need a hint that could help me figure out the next step, which I might be able to infer from the qtHaskell API. I don't think is any tutorial-type or step-by-step type documentation for qtHaskell. I have sent some questions to the author of qtHaskell, David Harley, but he hasn't responded yet, and anyway I don't want to trouble him every time I have a question, so I'm trying to infer as much as I can. The problem relates to state. In Qt, one adds state to a widget by subclassing it and adding new member variables. For example, I want to create a widget that responds to keypresses and remembers what keypresses have taken place. I'm totally stuck on this part, because Haskell doesn't have state. There must be some kind of Haskell call that adds state to a widget, but it is hard to figure out from the qtHaskell examples David provides. Thanks, Mike

8 9

loading object code with ghci
by Ryan Wisnesky 15 Sep '09

15 Sep '09

Hello, I'm having some trouble correctly linking to externally generated object code when using ghci. I'm loading a Cabal package Foo, that has already been successfully installed: >ghci -package Foo ghc-6.8.3: unknown symbol `_iceExePath' Loading package Foo-0.1 ... linking ... ghc-6.8.3: unable to load package `Foo-0.1' I have a file Bar.o which contains the definition of _iceExePath: >nm ./Bar.o ... U _ProcessInformationCopyDictionary 000000a0 b _exepath 00000000 T _iceExePath U _kCFBundleExecutableKey ... The documentation at http://www.haskell.org/ghc/docs/6.8.3/html/users_guide/ghci-invocation.html… says that: "GHCi can also load plain object files (.o or .obj depending on your platform) from the command-line. Just add the name the object file to the command line." So, I've tried both of these command lines: > ghci ./Bar.o -package Foo > ghci -package Foo ./Bar.o but ghci still can't find _iceExePath, and the same error occurs. I'm using GHC 6.8.3. I'm not sure how to proceed and would appreciate any advice. Thanks for your help, Ryan Wisnesky

1 0

What does it mean that objects are fixpoints? (OO'Haskell)
by Manuel Simoni 15 Sep '09

15 Sep '09

Hello! I'm trying to wrap my head around OO'Haskell's notion of objects as fixpoints. Is OO'Haskell's use of mfix simply a use of something like a monadic Y-combinator to give the object access to its own "identity"? Thanks, Manuel

3 2

Announce: EnumMap-0.0.1
by John Van Enk 15 Sep '09

15 Sep '09

Hi List, I've uploaded a first version of EnumMap to hackage. EnumMap is a generalization of IntMap that constrains the key to Enum rather than forcing it to be Int. I have no idea what impact this has on performance, but it still passes all the tests that ship with IntMap. (My guess is that performance will be similar/identical unless I've missed something.) If this package competes in speed (especially with an Int key) with IntMap, I'd expect this could be merged into the containers package as an IntMap replacement. The source comments/copyright/license hasn't been changed since this is a derivative work of the original IntMap package. http://hackage.haskell.org/package/EnumMap Comments/benchmarks/criticism is appreciated. Merging this in with containers eventually would be more appreciated. :) John Van Enk

7 29

Typeclasses vs simple functions?
by Olex P 15 Sep '09

15 Sep '09

Hey guys, It's a dumb question but I'd like to know a right answer... Let's say we have some geometry data that can be Sphere, Cylinder, Circle and so on. We can implement it as new data type plus a bunch of functions that work on this data: data Geometry = Sphere Position Radius | Cylinder Position Radius Height | Circle Position Radius deriving (Show) perimeter (Sphere _ r) = 0.0 perimeter (Cylinder _ r h) = 0.0 perimeter (Circle _ r) = 2.0 * pi * r Perimeter doesn't make sense for Sphere or Cylinder. So we could define a type class for objects that have perimeter and make an instance of it only for Circle (data Circle = Circle Position Radius). Make sense. But these three functions above have desired behaviour. If user has a list of objects like [Sphere, Circle, Circle, Cylinder] he would like to calculate perimeters of each object using map perimerer list (in this case we also have to modify Geometry data type). So we could make instances of "perimeter" type class for all objects and return zero in case if perimeter doesn't make sense. Same as previous version but with typeclasses and with additional constructors (constructors for each type of object + constructors in Geometry data). Looks a bit overcomplicated. Any reasons to use type classes in this case? Maybe there is something I'm missing? Cheers, -O

3 6

Re: [Haskell-cafe] Typeclasses vs simple functions?
by Olex P 15 Sep '09

15 Sep '09

Sure! I completely forgot about Maybe. The only one question is is it good from the point of view of ordinary user who doesn't know about such things like functional programming, monads etc. Imagine average user who is looking into a spreadsheet and sees values 0.1, 1.4, Nothing... From other side it seems to be logical. Why not. Thanks for the idea :) On Tue, Sep 15, 2009 at 12:05 PM, Lyndon Maydwell <maydwell(a)gmail.com>wrote: > I think the problem is that you want to compose a list with no > indication of weather one member can have a perimeter or not. I'm not > sure if this is a good solution or not, but I immediately think to > make all Geometry objects instances of a class that return a Maybe > value for the perimeter: > > e.g. > > --- > > import Data.Maybe > > data Geometry = Sphere Position Radius | Circle Position Radius deriving > (Show) > > type Position = (Double, Double) > type Radius = Double > type Height = Double > > class Encircled x where > perimeter :: x -> Maybe Double > > instance Encircled Geometry where > perimeter (Sphere _ r) = Nothing > perimeter (Circle _ r) = Just $ 2.0 * pi * r > > list = [Sphere (1,1) 1, Circle (2,2) 2] > > main = (print . catMaybes . map perimeter) list > > --- [12.566370614359172] > > On Tue, Sep 15, 2009 at 6:29 PM, Olex P <hoknamahn(a)gmail.com> wrote: > > Hey guys, > > > > It's a dumb question but I'd like to know a right answer... > > Let's say we have some geometry data that can be Sphere, Cylinder, Circle > > and so on. We can implement it as new data type plus a bunch of functions > > that work on this data: > > > > data Geometry = Sphere Position Radius > > | Cylinder Position Radius Height > > | Circle Position Radius > > deriving (Show) > > > > perimeter (Sphere _ r) = 0.0 > > perimeter (Cylinder _ r h) = 0.0 > > perimeter (Circle _ r) = 2.0 * pi * r > > > > Perimeter doesn't make sense for Sphere or Cylinder. So we could define a > > type class for objects that have perimeter and make an instance of it > only > > for Circle (data Circle = Circle Position Radius). Make sense. But these > > three functions above have desired behaviour. If user has a list of > objects > > like [Sphere, Circle, Circle, Cylinder] he would like to calculate > > perimeters of each object using map perimerer list (in this case we also > > have to modify Geometry data type). > > So we could make instances of "perimeter" type class for all objects and > > return zero in case if perimeter doesn't make sense. > > Same as previous version but with typeclasses and with additional > > constructors (constructors for each type of object + constructors in > > Geometry data). Looks a bit overcomplicated. > > Any reasons to use type classes in this case? Maybe there is something > I'm > > missing? > > > > Cheers, > > -O > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > >

2 2

Typeclasses vs simple functions?
by Lyndon Maydwell 15 Sep '09

15 Sep '09

---------- Forwarded message ---------- From: Lyndon Maydwell <maydwell(a)gmail.com> Date: Tue, Sep 15, 2009 at 10:03 PM Subject: Re: [Haskell-cafe] Typeclasses vs simple functions? To: Olex P <hoknamahn(a)gmail.com> I think it depends on what is going to be using the functions, data. As far as I can tell, type classes seem to be used in code designed for reuse. So if it is just for a small part of a project that is hidden behind an interface or something, then it's probably fine to just use data/functions without type classes. Keep in mind that these are the musings of someone who only recently began using Haskell. If someone else has a better explanation, then I'd be interested as well :) On Tue, Sep 15, 2009 at 9:57 PM, Olex P <hoknamahn(a)gmail.com> wrote: > Well... How this: > > instance Encircled Geometry where > perimeter (Sphere _ r) = Nothing > perimeter (Circle _ r) = Just $ 2.0 * pi * r > > differs from this: > > perimeter :: Geometry -> Maybe Double > perimeter (Sphere _ r) = Nothing > perimeter (Circle _ r) = Just $ 2.0 * pi * r > > and from this: > > perimeter :: Geometry -> Double > perimeter (Sphere _ r) = 0.0 > perimeter (Circle _ r) = 2.0 * pi * r > > The latter is even simpler because there is no need in extraction of Double > value from Maybe. > So the question is still there: do I need a type class? > > On Tue, Sep 15, 2009 at 12:21 PM, Olex P <hoknamahn(a)gmail.com> wrote: >> >> Sure! I completely forgot about Maybe. The only one question is is it good >> from the point of view of ordinary user who doesn't know about such things >> like functional programming, monads etc. Imagine average user who is looking >> into a spreadsheet and sees values 0.1, 1.4, Nothing... From other side it >> seems to be logical. Why not. >> Thanks for the idea :) >> >> On Tue, Sep 15, 2009 at 12:05 PM, Lyndon Maydwell <maydwell(a)gmail.com> >> wrote: >>> >>> I think the problem is that you want to compose a list with no >>> indication of weather one member can have a perimeter or not. I'm not >>> sure if this is a good solution or not, but I immediately think to >>> make all Geometry objects instances of a class that return a Maybe >>> value for the perimeter: >>> >>> e.g. >>> >>> --- >>> >>> import Data.Maybe >>> >>> data Geometry = Sphere Position Radius | Circle Position Radius deriving >>> (Show) >>> >>> type Position = (Double, Double) >>> type Radius = Double >>> type Height = Double >>> >>> class Encircled x where >>> perimeter :: x -> Maybe Double >>> >>> instance Encircled Geometry where >>> perimeter (Sphere _ r) = Nothing >>> perimeter (Circle _ r) = Just $ 2.0 * pi * r >>> >>> list = [Sphere (1,1) 1, Circle (2,2) 2] >>> >>> main = (print . catMaybes . map perimeter) list >>> >>> --- [12.566370614359172] >>> >>> On Tue, Sep 15, 2009 at 6:29 PM, Olex P <hoknamahn(a)gmail.com> wrote: >>> > Hey guys, >>> > >>> > It's a dumb question but I'd like to know a right answer... >>> > Let's say we have some geometry data that can be Sphere, Cylinder, >>> > Circle >>> > and so on. We can implement it as new data type plus a bunch of >>> > functions >>> > that work on this data: >>> > >>> > data Geometry = Sphere Position Radius >>> > | Cylinder Position Radius Height >>> > | Circle Position Radius >>> > deriving (Show) >>> > >>> > perimeter (Sphere _ r) = 0.0 >>> > perimeter (Cylinder _ r h) = 0.0 >>> > perimeter (Circle _ r) = 2.0 * pi * r >>> > >>> > Perimeter doesn't make sense for Sphere or Cylinder. So we could define >>> > a >>> > type class for objects that have perimeter and make an instance of it >>> > only >>> > for Circle (data Circle = Circle Position Radius). Make sense. But >>> > these >>> > three functions above have desired behaviour. If user has a list of >>> > objects >>> > like [Sphere, Circle, Circle, Cylinder] he would like to calculate >>> > perimeters of each object using map perimerer list (in this case we >>> > also >>> > have to modify Geometry data type). >>> > So we could make instances of "perimeter" type class for all objects >>> > and >>> > return zero in case if perimeter doesn't make sense. >>> > Same as previous version but with typeclasses and with additional >>> > constructors (constructors for each type of object + constructors in >>> > Geometry data). Looks a bit overcomplicated. >>> > Any reasons to use type classes in this case? Maybe there is something >>> > I'm >>> > missing? >>> > >>> > Cheers, >>> > -O >>> > >>> > _______________________________________________ >>> > 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 > >

1 0

ANNOUNCE: LambdaINet-0.1.0, Graphical Interaction Net Evaluator for Optimal Evaluation
by Paul L 15 Sep '09

15 Sep '09

It's available on Hackage DB at http://hackage.haskell.org/package/LambdaINet Thanks to Kim-Ee Yeoh for pushing me into releasing this piece of code I wrote two years ago. I'll just quote the README from the source tarball below. LambdaINet ========== LambdaINet implements an interaction net based optimal evaluator following Lambdascope [1], with an interactive graphical interface allowing user to view and directly manipulate interaction net. [1] Vincent van Oostrom, Kees-Jan van de Looij, Marijn Zwitserlood, Lambdascope, Workshop on Algebra and Logic on Programming Systems (ALPS), Kyoto, April 10th 2004 USAGE ===== After "cabal install", just type "LambdaINet" to start the application. Once it starts, press H for help, and ESC to quit. To understand all the operations in detail, you'll have to read the above mentioned paper by Oostrom et. al. Currently there is no way to load input programs except modifying the source, Try src/Main.lhs if you want to change the start-up program, or any of the 1..9 preset programs. At this moment, the object language supports lambda expression with recursion, tuples, and primitives such as numbers, strings and functions. SIDE NOTE ========= The bulk of code was put together in two weeks when I was working on the leak problem for FRP in 2007. So it was really a rushed job with no guarantee of correctness, although I tried to stay faithful to the original paper as much as I could. I only did some moderate clean-ups before releasing this application to public, and the code itself was sparingly documented when it was originally written. Some parts are probably still buggy, like the translation from net to term; other parts could use more improvements, like the node positioning and line layout algorithm. But I decide to release it anyway -- maybe some people some where will find it useful. DEVELOPMENT =========== Please forward bug reports or feedbacks to me (Paul Liu at paul at thev dot net), but don't hold your hope high on timely bug fixes. Help is also needed to develop LambdaINet further, for example, it really needs a way to read lambda expressions from a separate file or standard input, which should be a simple feature to add, but alas! I don't have the time in the nearest future to do this kind of things myself. -- Regards, Paul Liu Yale Haskell Group http://www.haskell.org/yale

2 3

HDBC Oracle bindings(?/!)
by Thiago Arrais 15 Sep '09

15 Sep '09

Are there Oracle bindings for HDBC anywhere? The HDBC project page talks about Oracle backends but there isn't an Oracle-specific driver listed (I assume one can reach an Oracle backend through the ODBC interface?). I started writing Oracle bindings for HDBC based on the Takusen code. It was done mostly for playing than for anything else and certainly isn't production ready, but it is available in a darcs repo at http://thiagoarrais.com/repos/hdbc-oracle in case anyone is interested. This code isn't ready for prime time yet and I'm looking for some that *is*. Is there such a thing already? Cheers, Thiago Arrais -- Enjoy Chaos - http://blog.thiagoarrais.com Thoughts, ideas and useless ranting about software development and technology

4 6

Cabal install on Windows 7
by Peter Verswyvelen 15 Sep '09

15 Sep '09

I tried the "cabal install" command on Windows 7, and I had to run it with administrative privileges, otherwise I got access denied (it failed to create the Haskell folder in C:\Program Files) Not sure if this is also the case on Vista. Is this the intended behavior?

10 27

Can't install chp (confused by cabal yet again)
by Colin Paul Adams 14 Sep '09

14 Sep '09

I tried a cabal install chp: It complained that base was hidden. So I unpacked the archive, and tried installing using runhaskell Setup configure/build/install. Now I get (from install): Setup: You need to re-run the 'configure' command. The version of Cabal being used has changed (was Cabal-1.6.0.3, now Cabal-1.6.0.2). So I repeated the process and get the same message again. ghc version is 6.10.3 Also: cabal --version cabal-install version 0.6.2 using version 1.6.0.2 of the Cabal library Where does this 1-6.0.3 come from (Ghc HEAD perhaps?)? What can I do about it? -- Colin Adams Preston Lancashire

3 2

trouble compiling Crypto-4.2.0 / trouble with cabal
by mf-hcafe-15c311f0c＠etc-network.de 14 Sep '09

14 Sep '09

Hi, Cabal is still fighting me all the time. Its latest move is to be oblivious of some of the installed packages: $ cabal unpack crypto Unpacking Crypto-4.2.0... $ cd Crypto-4.2.0/ $ runghc ./Setup.hs configure --prefix=/tmp2/ Configuring Crypto-4.2.0... Setup.hs: At least the following dependencies are missing: HUnit -any, QuickCheck -any $ ghc-pkg list | grep -i -e '$cabal\|hunit$' Cabal-1.6.0.3, array-0.2.0.0, base-3.0.3.1, base-4.1.0.0, HTTP-4000.0.8, HUnit-1.2.2.0, ObjectName-1.0.0.0, OpenGL-2.3.0.0, My ghc version is 6.10.4.20090719. (Perhaps I should go get myself a more stable version?) How does Cabal find its packages other than by ghc-pkg? I read the documentation, and did a quick search, but came up empty-handed. thanks, matthias

3 3

ANNOUNCE: hssqlppp, sql parser and type checker, pre-alpha
by Jake Wheat 14 Sep '09

14 Sep '09

Hello all, I've started on a SQL parser and type checker, which I'm currently planning on evolving into a lint-type program for PL/pgSQL, called HsSqlPpp. It currently parses a subset of PostGreSQL SQL and PL/pgSQL, can type check some select, insert, update, delete and create statements, and is pretty rough all round at the moment. It uses Parsec and UUAGC, comes with a small HUnit test suite, and has a Cabal file. The code is on Launchpad here: https://launchpad.net/hssqlppp You can get a snapshot here: http://launchpad.net/hssqlppp/prealpha/secondtypechecking/+download/hssqlpp… More information in the readme: http://bazaar.launchpad.net/~jakewheat/hssqlppp/trunk/annotate/head%3A/READ… and brief the usage guide gives you an idea of what you can do with it right now: http://bazaar.launchpad.net/~jakewheat/hssqlppp/trunk/annotate/head%3A/usage I'm pretty new to Haskell, parsing, attribute grammars and type checking - any comments, advice, criticism welcome. Thanks, Jake Wheat

3 3

Coercion from a Word32/64 to a Float/Double
by minh thu 14 Sep '09

14 Sep '09

Hi, I'd like to know if this should work: -- GHC coercion getFloat :: BHeader -> Get Float getFloat h = case endianness h of LittleEndian -> fmap (coerce . fromIntegral) getWord32le BigEndian -> fmap (coerce . fromIntegral) getWord32be where coerce (I32# x) = F# (unsafeCoerce# x) -- GHC coercion getDouble :: BHeader -> Get Double getDouble h = case endianness h of LittleEndian -> fmap (coerce . fromIntegral) getWord64le BigEndian -> fmap (coerce . fromIntegral) getWord64be where coerce (I64# x) = D# (unsafeCoerce# x) Loading this into ghci compiles fine (but I haven't try to parse data), but compiling with ghc (6.10.1 or 6.10.4) reports: /tmp/ghc1967_0/ghc1967_0.s: Assembler messages: /tmp/ghc1967_0/ghc1967_0.s:287:0: Error: bad register name `%fake0' /tmp/ghc1967_0/ghc1967_0.s:349:0: Error: bad register name `%fake0' Thanks for any help, Thu

3 4

Fwd: [Haskell-cafe] Native windowing for glut applications on OS X.
by Lyndon Maydwell 14 Sep '09

14 Sep '09

I just realized that I only replied to Brandon. Sorry about that :) ---------- Forwarded message ---------- From: Lyndon Maydwell <maydwell(a)gmail.com> Date: Sat, Sep 5, 2009 at 4:22 PM Subject: Re: [Haskell-cafe] Native windowing for glut applications on OS X. To: "Brandon S. Allbery KF8NH" <allbery(a)ece.cmu.edu> I installed opengl via macports. Can I adjust my path somehow so that it prefers the native libraries? On Sat, Sep 5, 2009 at 8:57 AM, Brandon S. Allbery KF8NH<allbery(a)ece.cmu.edu> wrote: > On Sep 4, 2009, at 03:13 , Lyndon Maydwell wrote: >> >> I recently updated glut through cabal to version GLUT-2.2.1.0, and >> where once I had native windowing, now I can only seem to use X11. >> >> Does anyone know how to use native windowing? > > > Do you use Fink or MacPorts? Check for OpenGL libraries installed via > those; they're probably shadowing the native libraries. > > -- > brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery(a)kf8nh.com > system administrator [openafs,heimdal,too many hats] allbery(a)ece.cmu.edu > electrical and computer engineering, carnegie mellon university KF8NH > > >

1 1

ANNOUNCE: A Levenberg-Marquardt implementation
by Bas van Dijk 14 Sep '09

14 Sep '09

Dear all, We like to announce the release of a Haskell binding to Manolis Lourakis's C levmar library at: http://www.ics.forth.gr/~lourakis/levmar/ This library implements the Levenberg-Marquardt algorithm which is an iterative technique that finds a local minimum of a function that is expressed as the sum of squares of nonlinear functions. It has become a standard technique for nonlinear least-squares problems and can be thought of as a combination of steepest descent and the Gauss-Newton method. When the current solution is far from the correct one, the algorithm behaves like a steepest descent method: slow, but guaranteed to converge. When the current solution is close to the correct solution, it becomes a Gauss-Newton method. Our binding consists of three packages: * http://hackage.haskell.org/package/bindings-levmar-0.1 A low-level wrapper around the C library. Note that the C library is lightly patched so that the functions can be safely called inside unsafePerformIO. The patched C library is bundled with this package. * http://hackage.haskell.org/package/levmar-0.1 A high-level wrapper around bindings-levmar. It provides a more familiar Haskell interface. For example, instead of passing a 'Ptr r' to the levmar function you can pass a [r]. levmar also provides some higher-level modules that use some type-level programming to add more type safety. * http://hackage.haskell.org/package/levmar-chart-0.1 Finally levmar-chart is a small package for quickly viewing the output of levmar in a chart. Unfortunately the documentation of these libraries is not available from hackage because bindings-levmar won't configure because of a missing dependency (lapack) on the hackage server. Instead I put the documentation at the following places: http://code.haskell.org/bindings-levmar/bindings-levmar-0.1/doc/html/bindin… http://code.haskell.org/levmar/levmar-0.1/doc/html/levmar/index.html Here follows a quick example: Suppose we have the following model functions: constant :: Num r => Model N1 r r linear :: Num r => Model N2 r r quadratic :: Num r => Model N3 r r cubic :: Num r => Model N4 r r constant a _ = a linear b a x = b * x + constant a x quadratic c b a x = c * x*x + linear b a x cubic d c b a x = d * x*x*x + quadratic c b a x And the jacobians: constantJacob :: Num r => Jacobian N1 r r linearJacob :: Num r => Jacobian N2 r r quadraticJacob :: Num r => Jacobian N3 r r cubicJacob :: Num r => Jacobian N4 r r constantJacob _ _ = 1 ::: Nil linearJacob _ a x = x ::: constantJacob a x quadraticJacob _ b a x = x*x ::: linearJacob b a x cubicJacob _ c b a x = x*x*x ::: quadraticJacob c b a x Now assume we have some sample data. If you call levmar like this: levmar cubic (Just cubicJacob) (-0.05 ::: 0.5 ::: -12 ::: 10 ::: Nil) samples 1000 defaultOpts Nothing Nothing noLinearConstraints Nothing You get the following fit (using levmar-chart): http://code.haskell.org/~roelvandijk/code/levmar-chart/cubicFit.png Note that levmar contains a demo with a lot more examples: http://code.haskell.org/levmar/Demo.hs Happy fitting, Roel and Bas van Dijk

5 16

Program with ByteStrings leads to memory exhaust.
by Grigory Sarnitskiy 14 Sep '09

14 Sep '09

I have a simple program that first generates a large (~ 500 mb) file of random numbers and then reads the numbers back to find their sum. It uses Data.Binary and Data.ByteString.Lazy. The problem is when the program tries to read the data back it quickly (really quickly) consumes all memory. The source: http://moonpatio.com/fastcgi/hpaste.fcgi/view?id=3607#a3607 or: module Main where import Data.Binary import Data.Int import System.Random import qualified Data.ByteString.Lazy as BL encodeFileAp f = BL.appendFile f . encode path = "Results.data" n = 20*1024*1024 :: Int getBlockSize :: BL.ByteString -> Int64 getBlockSize bs = round $ (fromIntegral $ BL.length bs) / (fromIntegral n) fillFile :: StdGen -> Int -> IO () fillFile _ 0 =return () fillFile gen i = do let (x, gen') = random gen :: (Double, StdGen) encodeFileAp path x fillFile gen' (i-1) processFile :: BL.ByteString -> Int64 -> Int -> Double -> Double processFile bs blockSize 0 sum = sum processFile bs blockSize i sum = let tmpTuple = BL.splitAt blockSize bs x = decode $ fst $! tmpTuple in processFile (snd tmpTuple) blockSize (i-1) $! sum + x main = do fillFile (mkStdGen 42) n results <- BL.readFile path putStrLn $ show $ processFile results (getBlockSize results) n 0

3 3

why these two are not equivalent?
by Diego Souza 14 Sep '09

14 Sep '09

Hi, I was trying to solve a simple problem in SPOJ, however, after two weeks trying almost everything I could think of, I was still getting WrongAnswer. Then I decided to do the same thing in C++ and I really got puzzled when I got ACcepted. I tried to understand what was different without success. I hope someone can tell me why spoj says the Haskell version is wrong: http://moonpatio.com/fastcgi/hpaste.fcgi/view?id=3583 [Haskell,WA] http://moonpatio.com/fastcgi/hpaste.fcgi/view?id=3582 [C++,AC] The problem I'm talking about is this one: https://www.spoj.pl/problems/SBANK/ Thanks, -- ~dsouza yahoo!im: paravinicius gpg key fingerprint: 71B8 CE21 3A6E F894 5B1B 9ECE F88E 067F E891 651E

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Plotting parametric functions in Haskell
by Rafael Cunha de Almeida 14 Sep '09

14 Sep '09

Hello, I think it would be interesting to plot and visualize parametric (and other kind of functions) using the haskell language to define them [functions]. Does anyone know about some software or API that does just that? I started writing a plotter to do that using hopengl. But my computer graphics skills are rather bad and I couldn't produce anything really useful. []'s Rafael

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Community.haskell.org is down
by Neil Mitchell 14 Sep '09

14 Sep '09

Hi, http://community.haskell.org/ seems to be down for me. In general, who should this be reported to? Thanks Neil

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HECC License (was: [Haskell-cafe] Haskell Weekly News: Issue 130 - September 12, 2009)
by Thomas DuBuisson 14 Sep '09

14 Sep '09

> hecc-0.1. Marcel Fourn√© [5]announced the first release of hecc, the > Elliptic Curve Cryptography Library for Haskell. Implemented are > affine, projective, jacobian and modified jacobian point formats with > the basic operations. Included as an Example is a basic ECDH as well as > a basic speed test. This is great news - I hope it finds its way into the crypto library. One question - is this license a derivative of something I would have heard about? IANAL, but have just read the license it sounds fairly permissive in that it doesn't mandate distribution of source code (BSDish). Was this the intent? Did I miss something? Thomas

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RE: Darcs and NFS Resolution
by Lewis-Sandy, Darrell 13 Sep '09

13 Sep '09

Thanks to everyone who pointed me in the right direction on this problem, I have been able to find a work around that allows me to push to an archive on a network file share. After some digging, I discovered the root of the problem. Briefly, Darcs uses the standard library System.Directory to perform file manipulations. This library make use of compiler pragmas to conditionally compile either the Windows or Linux specific functions based on the host operating system. This approach assumes that when your operating system is a Linux variant, all your mounted volumes will natively support POSIX. When you have mounted CIFS volumes, this will result in errors when calling those library functions to create, rename, copy and delete files or folders! Given the flexibility of the Linux operating system, A more versatile implementation for System.Directory might be able to detect the file system of each volume at runtime and choose the appropriate functions to call. But I digress... To workaround the inability to push to a CIFS volume in darcs, I modified the workaround.hs module to shell out to the OS's rename function rather than using the Haskell library's rename function. Specifically: I added the following code after the #else near line 80: renameFile :: FilePath -> FilePath -> IO () renameFile old new = do ecode <- System.Cmd.rawSystem "mv" [old,new] case ecode of ExitSuccess -> return () ExitFailure n -> putStrLn ("renameFile failed with exit code" ++ show n) which ensures that when the operating system is not WIN32, that renaming of files will be performed by the OS shell. I then added the System.Cmd module to the list of imports by inserting the following code near line 21 import qualified System.Cmd(rawSystem) after a recompile I could push to a CIFS volume, for example: sudo darcs push /mnt/cifsvol this is an obvious hack, and does not address the inability to put to a CIFS share (put depends upon copyFile and would need to be hacked to shell-out as well). Archives on the CIFS share have to be created by navigating to that folder and initializing. Shelling out is clearly a poor long term solution; a longer term solution would ideally introduce into the Haskell System.Directory library the ability to apply the correct functions transparently in accordance with the file system of the volume. Cheers -Darrell Lewis-Sandy

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ANNOUNCE: arbtt-0.1
by Joachim Breitner 13 Sep '09

13 Sep '09

Hi, I just uploaded the Automatic Rule-Based Time Tracking tool on hackage. It is written in Haskell (duh :-)) and might be interesting for some of you to either use or hack on (or both). I have put an introduction on https://www.joachim-breitner.de/blog/archives/336-The-Automatic-Rule-Based-… As always, comments are very welcome. Enjoy, Joachim PS: If you don’t like to use the DSL I created for the rule, but rather want to use Haskell, it might also be possible to do the xmonad approach (maybe using dyre). If so, I’m curious to hear about it :-) -- Joachim "nomeata" Breitner mail: mail(a)joachim-breitner.de | ICQ# 74513189 | GPG-Key: 4743206C JID: nomeata(a)joachim-breitner.de | http://www.joachim-breitner.de/ Debian Developer: nomeata(a)debian.org

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yhc compiled hbc
by Fernan Bolando 13 Sep '09

13 Sep '09

Hi all Are there any yhc users here? Can anybody send me a precompiled yhc cross-platform hbc file? regards fernan -- http://www.fernski.com

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[ANNOUNCE] A statistics library
by Bryan O'Sullivan 13 Sep '09

13 Sep '09

I'm pleased to announce a new Haskell statistics library, imaginatively named statistics <http://hackage.haskell.org/package/statistics>: http://hackage.haskell.org/package/statistics - Support for common discrete and continuous probability distributions (binomial, gamma, exponential, geometric, hypergeometric, normal, and Poisson) - Kernel density estimation - Autocorrelation analysis - Functions over sample data - Quantile estimation - Resampling techniques: jackknife and bootstrap estimation The statistics library certainly isn't yet comprehensive, but it has some features that I think make it very attractive as a base for further work: - It's very fast, building on some of the fantastic software that's available on Hackage these days. I make heavy use of Don Stewart's uvector library <http://hackage.haskell.org/package/uvector> (itself a port of Roman Leshchinskiy's vector library), which means that many functions allocate no memory and execute tight loops using only machine registers. I use Dan Doel's uvector-algorithms library<http://hackage.haskell.org/package/uvector-algorithms>to perform fast partial sorts. I also use Don's mersenne-random library <http://hackage.haskell.org/package/mersenne-random> for fast random number generation when doing bootstrap analysis. - I've put a fair amount of effort into finding and using algorithms that are numerically stable (trying to avoid problems like catastrophic cancellation). Whenever possible, I indicate which methods are used in the documentation. (For more information on numerical stability, see What Every Scientist Should Know About Floating-Point Arithmetic<http://docs.sun.com/app/docs/doc/800-7895> ). If you want to contribute, please get the source code and hack away: darcs get http://darcs.serpentine.com/statistics For more details, see http://bit.ly/ykOeK

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flexible contexts problem
by Sean McLaughlin 13 Sep '09

13 Sep '09

I'm having trouble understanding the following behavior. The following program compiles: {-# OPTIONS_GHC -XMultiParamTypeClasses -XFlexibleContexts #-} import Control.Monad.State class Has α s where has :: s -> (α, s) project :: (MonadState s m, Has α s) => m α project = do (α, s) <- gets has put s return α f :: (MonadState s m, Has Int s) => m Int f = do x <- project return x However, if you replace the function f with f :: (MonadState s m, Has Int s) => m Int f = do x <- project y <- project return x then it fails with the error Could not deduce (Has α s) from the context (MonadState s m, Has Int s) arising from a use of `project' at /Users/sean/uploads/Weird.hs:16:12-18 Possible fix: add (Has α s) to the context of the type signature for `f' In a stmt of a 'do' expression: y <- project In the expression: do x <- project y <- project return x In the definition of `f': f = do x <- project y <- project return x I don't see how the second call to project could possibly make a difference. Could someone please tell me what I'm doing wrong? Thanks in advance. Sean

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