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When I change the cabal file to say preference: base >= 4
by caseyh＠istar.ca 30 Sep '10

30 Sep '10

When I change the cabal file to say preference: base >= 4 I still get, "you are using base 3.0 which is deprecated." When I change the overall cabal profile, the error message still comes up. It seems like some other part of the install process is controlling the base version, besides the *.cabal and cabal profile file.

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ICFP2010 contest results?
by Ryan Ingram 30 Sep '10

30 Sep '10

I saw the winner was announced. Is there a highscore table? We were in the top 5, I want to see how well we did. -- ryan

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Re: [Haskell-cafe] Retargeting Haskell compiler to embedded/hardware
by Atze Dijkstra 30 Sep '10

30 Sep '10

Hi Tom, The Utrecht Haskell Compiler (UHC) is internally organized as a set of compilers, for which you can configure the aspects you want. It is relatively easy to extract such a particular combination and use it as a starting point. Or you might install UHC itself and use the installed libraries, which include abstract syntax, parser, etc. There is some variation depending on what you need, so check out http://www.cs.uu.nl/wiki/UHC for initial reading, and let me know whether you need more info. regards, On 29 Sep, 2010, at 16:49 , S. Doaitse Swierstra wrote: > > > Begin forwarded message: > >> From: Tom Hawkins <tomahawkins(a)gmail.com> >> Date: 29 september 2010 03:58:11 GMT+02:00 >> To: haskell-cafe <haskell-cafe(a)haskell.org> >> Subject: [Haskell-cafe] Retargeting Haskell compiler to embedded/hardware >> >> A few years ago I attempted to build a Haskell hardware compiler >> (Haskell -> Verilog) based on the Yhc frontent. At the time I was >> trying to overcome several problems [1] with implementing a hardware >> description language as a light eDSL, which convinced me a proper >> compiler may be a better approach. Yhc was recommended as a good >> starting point since it had a simpler IR compared with GHC -- at least >> at the time. >> >> I am considering restarting this effort, but this time to target hard >> realtime embedded code. What is the recommended compiler to start >> from? I need an IR that is post type checking with as much desugaring >> as possible, and a code base that is relatively easy to splice and >> build. >> >> My other requirement is not to be bound to IO () for 'main'. The top >> level will be a monad, but with different semantics than IO. I would >> also like to reuse the standard library, with exception to the values >> related to IO. >> >> What are my options? >> >> Thanks. >> >> -Tom >> >> [1] Lack of observable sharing; function definitions, case >> expressions, ADTs disappear at compile time; etc. >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe > - Atze - Atze Dijkstra, Department of Information and Computing Sciences. /|\ Utrecht University, PO Box 80089, 3508 TB Utrecht, Netherlands. / | \ Tel.: +31-30-2534118/1454 | WWW : http://www.cs.uu.nl/~atze . /--| \ Fax : +31-30-2513971 .... | Email: atze(a)cs.uu.nl ............ / |___\

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Re: [Haskell-cafe] Help to create a function to calculate a n element moving average ??
by S. Doaitse Swierstra 30 Sep '10

30 Sep '10

On 29 sep 2010, at 00:58, ok(a)cs.otago.ac.nz wrote: >> Avoiding repeated additions: >> >> movingAverage :: Int -> [Float] -> [Float] >> movingAverage n l = runSums (sum . take n $l) l (drop n l) >> where n' = fromIntegral n >> runSums sum (h:hs) (t:ts) = sum / n' : runSums (sum-h+t) hs ts >> runSums _ _ [] = [] >> >> Doaitse > > I very very carefully avoided doing any such thing in my example code. > For each output result, my code does two additions and one division. > Yours does one addition, one subtraction, and one division, for the > required case n = 3. The way I formulated it, each calculation is > independent. The way you've formulated it, the error in one > calculation accumulates into the next. NOT a good idea. If this an issue then: module MovingAverage where movingAverage :: [Float] -> [Float] movingAverage (x:y:l) = movingAverage' x y l where movingAverage' x y (z:zs) = (x+y+z)/3:movingAverage' y z zs movingAverage' _ _ _ = [] movingAverage _ = [] has far fewer pattern matches, Doaitse > >

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Help to create a function to calculate a n element moving average ??
by rgowka1 30 Sep '10

30 Sep '10

Type signature would be Int -> [Double] -> [(Double,Double)] Any thoughts or ideas on how to calculate a n-element moving average of a list of Doubles? Let's say [1..10]::[Double] what is the function to calculate the average of the 3 elements? [(1,0),(2,0),(3,2),(4,3)....] :: [(Double,Double)] (1,0) the average is zero as the length is less than 3 (2,0) the average is zero as the length is less than 3 (3,2) the average is (1+2+3)/3 = 2 (4,3) the average is (2+3+4)/3 = 9 ......

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can't find in hayoo
by Roderick Ford 29 Sep '10

29 Sep '10

I need the trick to get from ByteString -> [GHC.Word.Word8] and Hayoo is not helping. Super simple I expected. I haven't even tried to compile it yet. I am just trying to read in the bytes and encode with base64: import Codec.Binary.Base64 import Data.ByteString import System.Directory import System.Environment main :: do args <- getArgs bFileExist <- System.Directory.doesFileExist (args !! 0) let bytedata = --ByteString -> [GHC.Word.Word8] if bFileExist then putStrLn $ Codec.Binary.Base64.encode bytedata else putStrlLn ("File does not exist: " ++ (args !! 0)) return ()

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Candlestick charts
by rgowka1 29 Sep '10

29 Sep '10

Hi - What are the libraries to use in Haskell to generate a stock candlestick chart like http://stockcharts.com/h-sc/ui?s=SPY&p=D&b=5&g=5&id=p05007254056 I will use Finance-Quote-Yahoo to get the quote data from Yahoo. thanks for all your help.

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ANN: collada-output-0.1
by Tillmann Vogt 29 Sep '10

29 Sep '10

A new graphics library: http://hackage.haskell.org/package/collada-output Most of the graphics libraries on hackage use OpenGL to visualize 3d objects. With this library you now have the choice to use an external tool for visualization and enjoy the flexibility of a standard format for 3d data exchange. I.e. one could generate a raytraced animation or load the objects in a game engine. I think that the generation of 3d objects can be much more powerful and elegant than in other languages. Since this library can be an output for some other libraries on hackage, I would agree to various changes to achieve composability of libraries. Cheers, Tillmann

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Announce: lhae-0.0.3
by Alexander Bau 29 Sep '10

29 Sep '10

lhae[1] is a spreadsheet program. It features a simple formula language and some basic statistical methods, like descriptive statistics and pivot tables. 0.0.2 -> 0.0.3: --------------- Improvements: - Right click menu at columns/row headers and cells - Insert rows/columns between exisiting rows/columns - Boolean values - New functions: ==,/=,<,<=,>,>=,not - If-then-else expressions - New constants: true,false,pi - Filtering of columns/rows - Relative references - Copy formulas into multiple cells Fixed bugs: - Import from csv files - Table updates when deleting/inserting rows/columns - When closing tables: no more "Want to save?" queries on already saved tables [1] http://hackage.haskell.org/package/lhae

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Web application framework comparison?
by Dave Hinton 29 Sep '10

29 Sep '10

There are 179 packages in the Web category on Hackage. It am finding it difficult, as someone who is not familiar with any of the Haskell web application frameworks on Hackage (and there seem to be at least 9), to determine which are good quality, which do things I would like a web framework to do for me, and which insist on doing things I would rather do myself. Is there a page comparing the major frameworks somewhere? I've been unable to find one via Google.

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Retargeting Haskell compiler to embedded/hardware
by Tom Hawkins 29 Sep '10

29 Sep '10

A few years ago I attempted to build a Haskell hardware compiler (Haskell -> Verilog) based on the Yhc frontent. At the time I was trying to overcome several problems [1] with implementing a hardware description language as a light eDSL, which convinced me a proper compiler may be a better approach. Yhc was recommended as a good starting point since it had a simpler IR compared with GHC -- at least at the time. I am considering restarting this effort, but this time to target hard realtime embedded code. What is the recommended compiler to start from? I need an IR that is post type checking with as much desugaring as possible, and a code base that is relatively easy to splice and build. My other requirement is not to be bound to IO () for 'main'. The top level will be a monad, but with different semantics than IO. I would also like to reuse the standard library, with exception to the values related to IO. What are my options? Thanks. -Tom [1] Lack of observable sharing; function definitions, case expressions, ADTs disappear at compile time; etc.

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Re: [Haskell-cafe] Relaxing atomicity of STM transactions
by Arie Middelkoop 29 Sep '10

29 Sep '10

Hi Tom, You wrote that you are interested in the programming experience with relaxed atomicity. What you are asking for are the ideas behind Twilight STM, written in these papers: > http://proglang.informatik.uni-freiburg.de/projects/syncstm/techreport2010t… (brief summary of the underlying ideas + rationale. Newer version available upon request) > http://www.cs.uu.nl/research/techreps/repo/CS-2010/2010-020.pdf (about a nicer API for Twilight using Haskell + formalization. Search in the document for "twilight") For experimental purposes, we have implementations in C, Java and Haskell. Annette already replied to this thread with a link to our Haskell implementation. The main idea is to change (only) the commit protocol of a transaction. The transaction (speculatively/lockless) executes as always: depending on its semantics, it may restart when it reads a value that has been modified since the start of a transaction, or if you use a multi-versioning STM, perhaps read data from older memory snapshots. What semantics you choose here is of no real concern as long as the transaction reaches its commit-point while having read data from a consistent memory snapshot. At the commit-point, however, we do something special: the programmer can provide code to manually validate the transaction using a special API. At the commit point, we first put the transaction in an irrevocable state. This ensures that at any point the programmer's validation code gives an OK, we can publish the outcome of the transaction. We then validate the transaction (without restarting) to discover inconsistencies. Finally, the validation code is executed to inspect these inconsistencies. To easily inspect these inconsistencies, you can tag all reads in the transactional body with region identifiers. In the validation code, you can then query if this region has become inconsistent, and what the new values are. These new values are again taken from a consistent memory snapshot - important! In the example that you provided, this would mean that the reference that you want to loosely read from, you tag with a special region. In the validation code, you can then easily ignore its inconsistency. Or, more likely: inspect the new value to see if the difference with the actual read value is not too big. Additionally, in the validation code, since the transaction is irrevocable, it is possible to safely do I/O, and you can change the outcome of the transaction slightly based on the new values inspected, i.e. repair the inconsistencies. These ideas provide a more fundamental way to deal with relaxed atomicity, whereas just reading "loosely" from a variable is not. In the latter case, you have no clue how out-dated the values are that you read, for example. Hope this is useful to you, Arie > Thanks for the responses, but I think I should explain a bit more. > I'm not interested in being able to read the live value of a TVar at > any arbitrary time (via. unsafeIOToSTM). But rather I would like > looslyReadTVar to have exactly the same semantics as readTVar, except > that the STM runtime would not reject the transaction if the TVar is > modified by another transaction before the atomic commit takes place. > > Also, as I would be implementing something similar in Atom, I'm not > necessarily interested in a Haskell implementation, but rather if the > programming experience is elevated by these alternative semantics. > > For example: > > incr :: TVar -> STM () > incr a = looslyReadTVar a >>= writeTVar a . (+ 1) > > decr a :: TVar -> STM () > decr a = readTVar a >>= writeTVar a . (- 1) > > If incr and decr where atomically started at the same time with the > same TVar, decr would be rejected if incr completed first, but not the > other way around. The initial reaction may be that this seriously > breaks the atomicity of STM, but there may be cases where this could > be useful. For instance, it allow a computationally expensive > transactions to complete, even if their inputs are constantly being > modified. In the embedded domain, this could be a fault monitor that > reads a bunch of constantly changing sensors.

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Relaxing atomicity of STM transactions
by Tom Hawkins 29 Sep '10

29 Sep '10

Has anyone in the STM community considered the ability to read a TVar, such that it would allow the transaction to complete even if the TVar was modified by another transaction? (I am assuming this is not how STM works by default.) For example: looselyReadTVar :: TVar a -> STM a Atom [1] has similar semantics to STM. If Atom were to relax it's rule atomicity in this fashion, it could open the door to improved task scheduling and higher levels of program description. Has STM research already gone down this path? -Tom [1] http://hackage.haskell.org/package/atom

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A model theory question
by Patrick Browne 29 Sep '10

29 Sep '10

Hi, Below is an assumption (which could be wrong) and two questions. ASSUMPTION 1 Only smaller models can be specified using the sub-class mechanism. For example if we directly make a subclass A => B then every instance of B must also be an instance of A (B implies A or B is a subset of A). Hence, type classes cannot be combined using sub-classing to provide specifications of bigger models. QUESTIONS 1) If assumption 1 is correct, is there a mechanism whereby the module system can be used to construct bigger models? 2) If there is such a mechanism does it involve type classes or is it a module only solution? Regards, Pat This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. http://www.dit.ie

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Re: [Haskell-cafe] Relaxing atomicity of STM transactions
by Brandon Moore 29 Sep '10

29 Sep '10

On Sep 28, 2010, at 6:36 PM, Tom Hawkins <tomahawkins(a)gmail.com> wrote: Thanks for the responses, but I think I should explain a bit more. I'm not interested in being able to read the live value of a TVar at any arbitrary time (via. unsafeIOToSTM). But rather I would like looslyReadTVar to have exactly the same semantics as readTVar, except that the STM runtime would not reject the transaction if the TVar is modified by another transaction before the atomic commit takes place. Given the current implementation, I think the easiest way to get those semantics is to lift the untracked readTVarIO into STM with unsafeIOToSTM.

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Non-strict evaluation and concurrency (STM) : conflict?
by Romain Demeyer 29 Sep '10

29 Sep '10

Hi, I'm working on Concurrent Haskell, especially with the monad STM. I don't fully understand the way my program is executed. I think the lazy evaluation leads to a loss of performance, if we don't pay attention to this problem. A short example will be more explicit : Imagine this scenario : we have a set of threads (the workers) that have (each) a result to compute (purely). When finished, they try to save the result in an shared inbox, using STM. If the inbox is full, the thread waits until the inbox is empty. A specific thread is looking at the inbox: when it finds a value in the inbox, it prints the value on the screen (for example, it could be any processing based on the value) and then empty the inbox and wait that a remaining thread add a new value). Let's a function "do_job", the function to execute by the threads (the workers) : do_job :: (b -> a) -> b -> Inbox a -> IO () do_job f input inbox = do { value <- return (f input) ; atomically ( writeMsg inbox value ) } The idea is : (f input) is the function to compute. Once compute, we want to save the result atomically. The problem is, because of the lazy evaluation, the "value" is computed in the atomic section, and not before, resulting in a loss of efficiency. Indeed, to be fast, a concurrent program has to keep the atomic sections as "small" as possible, because it limits the parallelism. To illustrate this, let's see this source code : module Main where import Control.Concurrent import Control.Concurrent.STM import Data.Maybe import System.Random import System.IO {-- Inbox --} type Inbox a = TVar (Maybe a) createInbox :: STM (Inbox a) createInbox = newTVar Nothing readMsg :: Inbox a -> STM a readMsg inbox = do { inboxContent <- readTVar inbox ; if (isNothing inboxContent) then retry else do { writeTVar inbox Nothing ; return (fromJust inboxContent) } } writeMsg :: Inbox a -> a -> STM () writeMsg inbox value = do { inboxContent <- readTVar inbox ; if (isNothing inboxContent) then writeTVar inbox (Just value) else retry } {-- Workers --} * do_job :: (b -> a) -> b -> Inbox a -> IO ()* *do_job f input inbox = do { value <- return (f input) * * ; atomically ( writeMsg inbox value ) }* do_jobs_in_threads :: [((b->a),b)] -> Inbox a -> TVar Int -> IO () do_jobs_in_threads [] _ _ = return () do_jobs_in_threads ((f,input):xs) inbox flag = do { forkIO_and_notify flag (do_job f input inbox) ; do_jobs_in_threads xs inbox flag } {-- Caller --} * * *caller :: Inbox a -> (a -> IO ()) -> Int -> IO ()* *caller _ _ 0 = return ()* *caller inbox process n = do { msg <- atomically (readMsg inbox)* * ; process msg * * ; caller inbox process (n-1) }* caller_in_thread flag inbox process n = forkIO_and_notify flag (caller inbox process n) {-- forkIO with notification --} create_flag = atomically ( newTVar 0 ) forkIO_and_notify :: TVar Int -> IO () -> IO () forkIO_and_notify tvar action = do { atomically ( do { oldValue <- readTVar tvar ; writeTVar tvar (oldValue + 1) } ) ; forkIO (do { action ; atomically ( do { oldValue <- readTVar tvar ; writeTVar tvar (oldValue - 1) } ) } ) --; putStrLn "Tread lancé" } ; return () } waitFlag flag = atomically ( do { valueflag <- readTVar flag ; if valueflag > 0 then retry else return () } ) {-- main --} main :: IO () main = do { flag <- create_flag ; inbox <- atomically (createInbox) ; *caller_in_thread flag inbox (\x -> putStrLn ("Caller : "++ (show (x)))) 3* * ; do_jobs_in_threads [(perm,[1..11]),(perm,[1..8]),(perm,[1..3])] inbox flag* ; waitFlag flag ; return () } where perm (l:ls) = injectett l (perm ls) injectett x (l:ls) = injecte x l ++ injectett x ls injecte x (l:ls) = [x:l:ls]++map (l:) (injecte x ls) inputs = zip (replicate 3 f) [[1..11],[1..8],[1..3]] As you can see, we ask for 3 threads to compute permutations for [1..11], [1..8] and [1..3]. The "Caller" write a message when a thread finished. What we expect is that the second and third thread finish their work before the first one. But the output of this program is : *Caller : 39916800* *Caller : 40320* *Caller : 6* ... which means that threads 2 and 3 have to wait the first thread before being able to save (and probably compute) their own result. If I force to evaluate "value" before the atomic section, by defining : do_job :: (b -> a) -> b -> Inbox a -> IO () do_job f input inbox = do { value <- return (f input) ; value `seq` atomically ( writeMsg inbox value ) } Then I obtain a more efficient program, as the output confirms : *Caller : 6* *Caller : 40320* *Caller : 39916800* That's what we want, but what is the explanation of this behavior? STM is designed to be optimistic, not blocking. So, does it means that the "value" is evaluated at "commit-time"? Do you know some problems that are related or do you know some works that can be useful at this subject? Thanks for your help, rde

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HackageDB: Haddock parse failure
by Jonas Almström Duregård 28 Sep '10

28 Sep '10

HackageDB reports a build failure for happy-meta-0.1.1 (http://hackage.haskell.org/package/happy-meta-0.1.1) but from the log it seems that the failure occurs when building the documentation. The error is src/LALR.lhs:230:2: parse error on input `numberSets' I'm guessing there is no syntax error in this file (it is taken from Happy), but rather an error in Haddock? Also, perhaps HackageDB should ignore errors in building the documentation? Currently the reported build failure propagates to the dependencies of the library... /J

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Question on monad transformers stack
by Arnaud Bailly 28 Sep '10

28 Sep '10

Hello Cafe, I have the following type which represents some action using Git > newtype (Monad m) => Git m a = Git { runGit :: ErrorT String (StateT Environment m) a } > deriving (Monad, MonadState Environment, MonadError String) and the following typeclass whose purpose is to abstract away the details of executing commands in the OS, with an obvious IO instance, and to ease testing of commands effects: > -- | A monad for simple execution of a process within the > class (MonadError e m) => MonadExec e m where > debug :: String -> m () > exec :: String -> [String] -> m String > -- ^Do not really execute commande but output the command string and arguments passed > exec' :: String -> [String] -> m String > exec' proc args = return $ program proc args The type environment is : > data Environment = Env { debugMode :: Bool, > baseDirectory :: FilePath, > maven :: FilePath, > git :: FilePath, > p4 :: FilePath, > javaHome :: FilePath} > deriving (Eq, Show, Read) This follows the monad stack pattern presented in RWH and in Don Stewart's presentation on scripting with haskell. Actually, what I am trying to achieve is to be able to write my own scripts in Haskell. What I would like to do is to be able to wrap each Git action occuring in a MonadExec instance into a call to debug according to the status of the debugMode flag in environment, in order to prevent the need of explicit calls to debug. Something like the -v flag in bash... I can imagine being able to do this using 2 different ways: - add a constraint on Git monad and write explicitly return and >>= to use debug - push the environment or part of it inside the MonadExec, for example as a Reader. What is the "best" (i.e. most economical) way of doing this? Thanks for your advices. Arnaud Bailly

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Can't make a derived instance of `Typeable (A B)': `A' has arguments of kind other than `*'
by Christopher Done 28 Sep '10

28 Sep '10

Suppose I have a data type: data A f = A { a :: f Integer } why can't I derive a Typeable instance like so? deriving instance Typeable (A Maybe) I get: Can't make a derived instance of `Typeable (A Maybe)': `A' has arguments of kind other than `*' In the stand-alone deriving instance for `Typeable (A Maybe)' I would have expected that the arguments are instantiated by the Maybe type constructor and thus the type of A would be: Maybe Integer -> A What am I missing?

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Why can't libraries/frameworks like wxHaskell/gtk2hs/... be used with newer versions of ghc/wxWidgets/GTK+/... ?
by caseyh＠istar.ca 28 Sep '10

28 Sep '10

Why can't libraries/frameworks like wxHaskell/gtk2hs/... be used with newer versions of ghc/wxWidgets/GTK+/... ?

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parsec manyTill documentation question
by Peter Schmitz 28 Sep '10

28 Sep '10

I am new to parsec and having difficulty understanding the explanation of manyTill in http://legacy.cs.uu.nl/daan/download/parsec/parsec.html. (I really appreciate having this doc by the way; great reference.) I.e.: > manyTill :: GenParser tok st a -> GenParser tok st end -> GenParser tok st [a] > > (manyTill p end) applies parser p zero or more times until parser > end succeeds. Returns the list of values returned by p . This parser > can be used to scan comments: > > simpleComment = do{ string "")) > } > > Note the overlapping parsers anyChar and string "", ... since anyChar begins reading input beginning with the char *after* string ""). Second, manyTill, by definition, keeps applying p (anyChar) until end (string "-->") is satisfied, so I would expect one could just write: manyTill anyChar (string "-->") Assuming the documentation is correct on both counts, I would really appreciate any explanation someone could offer. Thanks very much, (really like Haskell & parsec) -- Peter (If anyone knows of a collection of parsec demos or good examples, I would appreciate a link; thanks)

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Re: [Haskell-cafe] parsec manyTill documentation question
by Peter Schmitz 28 Sep '10

28 Sep '10

On Fri, Sep 24, 2010 at 9:28 PM, Evan Laforge <qdunkan(a)gmail.com> wrote: >>> simpleComment = do{ string "")) >>> } >>> >>> Note the overlapping parsers anyChar and string "", ... > > Yes, I think the doc just made a mistake there. In fact, it looks > like the same mistake is in the current doc at > http://hackage.haskell.org/packages/archive/parsec/3.1.0/doc/html/Text-Pars… Evan, Thanks very much for the typo confirmation, the explanation about backtracking below, and the tip about the source distribution for the examples. I need to remember that multiple char strings imply backtracking, and that backtracking is not the default, hence "try". Thanks. -- Peter > >> Second, manyTill, by definition, keeps applying p (anyChar) until >> end (string "-->") is satisfied, so I would expect one could just >> write: >> >> manyTill anyChar (string "-->") > > The problem is that "-->" has multiple characters. So if you have > "-not end comment", it will match the '-' against the (string "-->"). > Since it doesn't backtrack by default, it's committed now and will > fail when it hits the 'n'. The 'try' will make it backtrack to > 'anyChar' when the second '-' fails to match. > >> (If anyone knows of a collection of parsec demos or good examples, I >> would appreciate a link; thanks) > > I thought the parsec source included some example parsers for simple > languages? In any case, there is lots of material floating around, > though I found parsec so intuitive and the docs so good that I just > started hacking. I think the 'build scheme in haskell' tutorial uses > parsec for the parsing. >

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Help us test gtk2hs darcs!
by Andy Stewart 27 Sep '10

27 Sep '10

Hi all, We have add many APIs in gtk2hs darcs, and ready to release gtk2hs-0.12.0 Please help us test gtk2hs darcs, we can fix it before release gtk2hs-0.12.0 You can get gtk2hs darcs with below command: darcs get code.haskell.org/gtk2hs Please send any bug report to gtk2hs-users(a)lists.sourceforge.net Thanks! -- Gtk2hs Team

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BelHac: A Hackaton in Belgium, 5-7 November
by Jasper Van der Jeugt 27 Sep '10

27 Sep '10

Hello all, We are very pleased to officially announce an international Hackaton/Get-together in Ghent, Belgium, on 5, 6 and 7 November 2010. If you are interested in attending, we have put some information on the wiki [1]. We will soon put up more details about transportation, accommodation and food. (And Belgian beer, of course!) You can register here [2]. WHEN Friday November 5: 2pm - 7pm Saturday November 6: 10am - 6pm Sunday November 7: 10am - 6pm WHERE In “The Therminal”, in Ghent, Belgium. Please see the wiki [1] for more details. We hope to see you in Belgium! [1]: http://www.haskell.org/haskellwiki/Ghent_Functional_Programming_Group/BelHac [2]: http://www.haskell.org/haskellwiki/Ghent_Functional_Programming_Group/BelHa… On behalf of the GhentFPG organizing committee, Kind regards, Jasper Van der Jeugt

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WANTED: Haskell web developer for two Yesod projects
by Michael Snoyman 27 Sep '10

27 Sep '10

Hi all, I have been working on two projects for a client, but will not be able to continue on them. I am currently looking for someone interested in some freelance work maintaining and adding features to two Yesod web applications. Please contact me if interested. Michael

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ANN: Atom 1.0.7
by Lee Pike 27 Sep '10

27 Sep '10

Announcing Atom 1.0.7 http://hackage.haskell.org/package/atom/ Recent changes include: atom 1.0.6: Support for math.h expressions (contributed by Sebastian Niller) atom 1.0.7: Support for using a HW clock to control the duration of phases. The patch to atom 1.0.7 adds the ability to use your HW to control precisely the duration of phases. Previously, this would have to be done using "ad-hoc" C code. For example, on an AVR microprocessor[1], I might call compile[2] with compile name defaults { cCode = prePostCode , hardwareClock = Just defaultClock { clockName = "millis" , clockType = Word32 , delta = 50 , delay = "delay" , err = Just "error" } } atomFn to have phases of 50 milliseconds each, calling the user-defined error() C function if that bound is violated. See Code.hs[2] for documentation. It'll generate code that looks something like the following: void main_atom_loop() { __global_clock = millis(); ... Scheduled Atom functions ... // In the following we sample the hardware clock, waiting for the next phase. uint32_t const __phase_len = 30; uint32_t const __max = 255; uint32_t __curr_time = millis(); // An error check for when the phase has already expired. // The first disjunct is for when the current time has not overflowed, // and the second for when it has. if ( ( (__curr_time >= __global_clock) && (__curr_time - __global_clock > __phase_len)) || ( (__curr_time < __global_clock) && ((__max - __global_clock) + __curr_time > __phase_len))) { error(); } __curr_time = millis(); // Update the current time. // Wait until the phase has expired. If the current time hasn't // overflowed, execute the first branch; otherwise, the second. if (__curr_time >= __global_clock) { delay(__phase_len - (__curr_time - __global_clock)); } else { delay(__phase_len - (__curr_time + (__max - __global_clock))); } } Suggestions, bug reports, improvements welcomed. Regards, Lee [1] http://www.nongnu.org/avr-libc/ [2] http://hackage.haskell.org/packages/archive/atom/1.0.7/doc/html/Language-At… [3] http://hackage.haskell.org/packages/archive/atom/1.0.7/doc/html/Language-At… -- <http://www.galois.com> <http://www.cs.indiana.edu/~lepike/> Phone: +1 503.808.7185 Fax: +1 503.350.0833

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ANNOUNCE: Utrecht Haskell Compiler (UHC), version 1.1.0
by Atze Dijkstra 27 Sep '10

27 Sep '10

Utrecht Haskell Compiler -- second release 1.1.0 ================================================ The UHC team is happy to announce the second public release of the Utrecht Haskell Compiler (UHC). UHC supports almost allmost all Haskell98 and Haskell2010 features plus some experimental extensions. The compiler runs on MacOSX, Windows (cygwin), and various Unix flavors. This second release has the following highlights relative to the previous first release: * Supports most of the Haskell2010 features. * Generic deriving [1]. * UHC knows about packages, and Cabal version 1.9.3 and later have basic support for UHC, so that Cabal can be used to build UHC packages. * For the default backend libraries are provided until including package haskell98. * The runtime system is no longer dependent on Boehm garbage collector, but uses UHCs own, a swap space collector allowing parameterization with backend specifics. * More programs from the nofib test suite compile and run. * Many smaller and larger problems fixed. For more info see http://www.cs.uu.nl/wiki/UHC Getting started & Download -------------------------- UHC is available for download as source distribution via the UHC home page: http://www.cs.uu.nl/wiki/UHC Here you will also find instructions to get started and the specifics of what UHC can and cannot do. Status of the implementation ---------------------------- Over the past year much effort by many people has been put into improving UHC, in particular to make it compile and run more library modules and test programs. Although the UHC project is very much work in progress overall reliability has improved, bugs have been fixed, and some Hackage packages compile. Warning ------- Although we think that the compiler is stable enough to compile substantial Haskell programs, we do not recommend yet to use it for any serious development work in Haskell. We ourselves use the GHC as a development platform! We think however that it provides a great platform for experimenting with language implementations, language extensions, etc. Mailing lists ------------- For UHC users and developers respectively: http://mail.cs.uu.nl/mailman/listinfo/uhc-users http://mail.cs.uu.nl/mailman/listinfo/uhc-developers Bug reporting ------------- Please report bugs at: http://code.google.com/p/uhc/issues/list The UHC Team [1] Jose Pedro Magalhaes, Atze Dijkstra, Johan Jeuring, and Andres Loeh. A generic deriving mechanism for Haskell. http://dreixel.net/research/pdf/gdmh_draft.pdf (see Section 7.1 for the discussion on constrained datatypes) - Atze - Atze Dijkstra, Department of Information and Computing Sciences. /|\ Utrecht University, PO Box 80089, 3508 TB Utrecht, Netherlands. / | \ Tel.: +31-30-2534118/1454 | WWW : http://www.cs.uu.nl/~atze . /--| \ Fax : +31-30-2513971 .... | Email: atze(a)cs.uu.nl ............ / |___\

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capture of idioms and patterns
by Luc TAESCH 26 Sep '10

26 Sep '10

in real life I am doing architecture (appication and system) and I tend to see things differently with my haskell background. when reading what system XYZ does, I see folds, maps, lazy sort, memoisation , monads, etc...ie my mind apply idioms learned at code design level to architecture level So the following questions raised in me : - are there any prior art in documenting idioms and patterns in FP, and especially haskell. - have any work been done refering to architecture level , using these idioms, or "FP specific architecture"... (the idea germinated to extend the FP contiunum from code, design to architecture (and requirement) thank you, folks luc

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ANN: ieee version 0.7
by Patrick Perry 26 Sep '10

26 Sep '10

ieee is a Haskell library for dealing with IEEE floating numbers. It was originally written to make testing with floating point values less painful. The library provides an "approximate equality" type class, AEq, with approximate equality operator "~==". One property of "~==" is that nearby floating point numbers are deemed equivalent, so that, for example, "1 ~== 1.00000001" evaluates to True. Documentation is on hackage: http://hackage.haskell.org/package/ieee Changes since the last release: * Add IEEE type class with instances for Double, Float, CDouble, and CFloat * Add functions for getting/setting NaN payloads * Add succIEEE/predIEEE for advancing up and down the IEEE number line (ported from Tango's nextUp and nextDown) * Add bisectIEEE for midpoints of two numbers on the IEEE number line (ported from Tango's ieeeMean) * Add identicalIEEE for exact (bitwise) equality of IEEE numbers * Add copySign for setting the sign bit of an IEEE number * Add sameSignificandBits for seeing how many significand bits of two IEEE numbers agree, ported from Tango's feqrel * Add nan, infinity, maxFinite, minNormal constants for IEEE numbers * Add maxNum and minNum * Rename maxF and minF to maxNaN and minNaN * Switch to a simpler "~==" comparison for complex numbers * Make "~==" comparison use sameSignificandBits for IEEE types * Make "===" comparison use bitwise equality for IEEE types * Remove old "eqRel" comparisons. * Remove old epsilon' and delta constants * Remove (RealFloat a) => AEq (Complex a) instance in favor of explicit instances for Complex {Double,Float,CDouble,CFloat}

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Polymorphic record field?
by Kevin Jardine 26 Sep '10

26 Sep '10

I have an almost finished Haskell program and I discovered that I needed to change the type of one record field. The problem is that the new type is polymorphic. Being new to Haskell, I simply changed: data MyStruct = MyStruct {myField :: myType} to data MyStruct = MyStruct {myField :: MyTypeClass a => a} and then ended up in a maze of compiler messages about Rank N types and "Inferred type is less polymorphic than expected". Upon Googling for this issue, I have discovered that Haskell records do not support polymorphic types and that there is a large literature about options to fix this. Although the literature is interesting, what I am looking for right now is a simple fix. I really don't want to have to rewrite all the many type and value references to MyStruct in my code. Is there a way to redefine the definition of MyStruct without changing any of my other code? If I have to change the way myField is accessed, I can handle that. What I don't really want to do is change the type signature of functions that take MyStruct parameters (of which there are many). Is this possible? What is the simplest way to do this? Kevin

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Applicative instances for Monads
by Gregory Crosswhite 26 Sep '10

26 Sep '10

Hey everyone, There is something that has been bugging me recently about the Applicative class and the Monad class. Any type constructor F that is a Monad has a natural Applicative instance, (<$>) :: F (a -> b) -> F a -> F b mf <$> ma = do f <- mf a <- ma return (f a) So it seems that defining something to be a Monad should automatically make it an instance of Applicative with this definition for (<$>). So far so good, but there are times when this implementation is too "sequential". The nature of Applicative is that later actions are not allowed to depend on earlier actions, which means that it is natural to run them in parallel when possible. So for example, considering the following alternative of Applicative for a newtype AIO that wraps an IO computation: ====================================================================== import Control.Applicative import Control.Concurrent import Control.Concurrent.MVar newtype AIO a = AIO {unAIO :: IO a} instance Monad AIO where return = AIO . return (AIO x) >>= f = AIO (x >>= unAIO . f) instance Functor AIO where fmap f (AIO x) = AIO (fmap f x) instance Applicative AIO where pure = return (AIO mf) <*> (AIO ma) = AIO $ do f_box <- newEmptyMVar forkIO (mf >>= putMVar f_box) a_box <- newEmptyMVar forkIO (ma >>= putMVar a_box) f <- takeMVar f_box a <- takeMVar a_box return (f a) ====================================================================== This seems to me to be an arguably better way to implement Applicative because it uses the fact that we know that the second action is independent from the first to gain parallelism by sparking them in separate threads. So for example if one has six actions m1 ... m6 that could run in parallel then one could write something like the following: ====================================================================== main = do ... (x1,x2,x3,x4,x5,x6) <- (,,,,,) <$> a1 <*> a2 <*> a3 <*> a4 <*> a5 <*> a6 ... ====================================================================== Here is another example: Consider the following instance of Applicative for the Either type: ====================================================================== import Control.Applicative import Data.Monoid instance Monoid error => Applicative (Either error) where pure = Right Right f <*> Right x = Right (f x) Left error <*> Right _ = Left error Right _ <*> Left error = Left error Left error1 <*> Left error2 = Left (error1 `mappend` error2) display :: Either String Int -> IO () display = putStrLn . show main = mapM_ (putStrLn . show) [Right (+1) <*> Right 1 ,Right (+1) <*> Left "[bad value]" ,Left "[bad function]" <*> Right 1 ,Left "[bad function]" <*> Left "[bad value]" ] ====================================================================== This is much like the instance used by the Error monad, but it has the advantage that rather than terminating at the first sign of error it instead gathers together the errors produced by each subcomputation. Again, we can do this because we know that we do not need the result of the first computation in order to evaluate the second computation. To summarize: on the one hand every Monad has a generic instance for Applicative, and yet on the other hand this instance is often arguably not the "correct" one because it ignores the fact that the second computation is independent of the first, which is a fact that can be exploited given additional knowledge about the structure of the Monad. I bring this up because there has been talk here of automatically having instances of Monad also be instances of Applicative, and what bugs me is that on the one hand this makes perfect since as every Monad can also be viewed as an Applicative, and yet on the other hand not only is there often more than one natural way to define an Applicative instance for selected Monads but furthermore the "generic" instance is often an inferior definition because it ignores the structure of the Monad. Thoughts? Cheers, Greg

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Re: [Haskell-cafe] Inverse of HaskellDB
by Jonathan Geddes 26 Sep '10

26 Sep '10

>Have you given any thought as to how you want to approach versioning? After giving this some more thought, I realized: 1) One of the "best practices" (even though I despise the term) of versioning schema is to include a script with the code which checks for each change to the tables, and makes the change if it is needed [1]. Each time you check out new code, you run the script to ensure that the code you are working with matches the tables you are working with. 2) A system that generates tables from Haskell types could also be made to check if a given table faithfully represents a given Haskell record type. It could then make any changes to the table so that it _does_ faithfully represent the record type. 3) In this way, your Haskell records ARE your table update script, just (like most Haskell code) incredibly terse. Your usual code repository will track when and by whom changes are made to the record. Of course, there are some issues with this, but I think it could be made to work well. >Hibernate does this, more or less, for Java classes. That might be a >good place to look for ideas. Good point. I'll start there. [1] http://www.codeproject.com/KB/database/DatabaseSchemaVersioning.aspx --Jonathan On Sat, Sep 25, 2010 at 3:45 PM, Rogan Creswick <creswick(a)gmail.com> wrote: > On Sat, Sep 25, 2010 at 12:31 PM, Jonathan Geddes > <geddes.jonathan(a)gmail.com> wrote: >> >> Does such a thing exist? If not, would you find it useful? I may take >> this up as a side project if it does not already exist and others >> would find it useful. >> > > I've been looking for something along these lines too. > > Hibernate does this, more or less, for Java classes. That might be a > good place to look for ideas. > > --Rogan > >> Thanks, >> >> --Jonathan >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >

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Shared thunk optimization. Looking to solidify my understanding
by David Sankel 26 Sep '10

26 Sep '10

The following code (full code available here[1], example taken from comments here[2]), const' = \a _ -> a test1 c = let a = const' (nthPrime 100000) in (a c, a c) test2 c = let a = \_ -> (nthPrime 100000) in (a c, a c) in a ghci session (with :set +s): *Primes> test1 1 (9592,9592) (0.89 secs, 106657468 bytes) *Primes> test2 1 (9592,9592) (1.80 secs, 213077068 bytes) test1, although denotationally equivalent to test2 runs about twice as fast. My questions are: - What is the optimization that test1 is taking advantage of called? - Is said optimization required to conform to the Haskell98 standard? If so, where is it stated? - Could someone explain or point to a precise explanation of this optimization? If I'm doing an operational reduction by hand on paper, how would I take account for this optimization? Thanks, David [1] http://hpaste.org/40033/operational_semantics [2] http://conal.net/blog/posts/lazier-functional-programming-part-2/ -- David Sankel Sankel Software www.sankelsoftware.com

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Re: [Haskell-cafe] Simple question about the function composition operator
by wren ng thornton 26 Sep '10

26 Sep '10

On 9/24/10 5:35 AM, Axel Benz wrote: > Can anybody explain why this happens and how I can compose f and g? > > Hint: It works fine if f is defined as an unary function. As already mentioned: (g . f) x y = (\z-> g (f z)) x y = g (f x) y In order to get it to work you need to say that you want to pass two arguments to f. The immediate answer is ((g .) . f) but that doesn't really give you a general pattern to use. The general pattern is, -- | Binary composition. (...) :: (c -> d) -> (a -> b -> c) -> (a -> b -> d) (...) = (.) . (.) {-# INLINE (...) #-} infixl 8 ... and then (g ... f) x y = g (f x y). Note that the fixity is set up so that (...) plays nicely with (.). You may also be interested in, -- | Compose on second arg. (.^) :: (a -> c -> d) -> (b -> c) -> (a -> b -> d) (.^) = flip ... (.) . flip {-# INLINE (.^) #-} infix 9 .^ -- | Function composition which calls the right-hand -- function eagerly. (.!) :: (b -> c) -> (a -> b) -> a -> c (.!) = (.) . ($!) {-# INLINE (.!) #-} infixr 9 .! -- Live well, ~wren

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ANN: JMacro 0.3.2, A library/dsl for generating Javascript
by Gershom B 25 Sep '10

25 Sep '10

JMacro on hackage: http://hackage.haskell.org/package/jmacro This is the first official release announcement for JMacro, which has been on hackage in some form for over a year, and in the current version since July. JMacro is a library for the programmatic generation of Javascript code. It is designed to be multipurpose -- it is useful whether you are writing nearly vanilla Javascript or you are programmatically generating Javascript either in an ad-hoc fashion or as the backend to a compiler or EDSL. It provides support for hygienic names, as well as sharing of names between the generated Javascript and embedded Haskell antiquotation. In this release it also includes a module which allows the generation of RPC request/response pairs, allowing a lightweight implementation of AJAX-heavy applications. JMacro provides a simple, lightweight quasiquoted syntax that is mainly compatible with standard Javascript. Most Javascript code in the wild can be used as JMacro code with no or minimal modification. However, JMacro extends Javascript syntax in a number of Haskell-friendly ways, including whitespace function application and single character lambdas. Syntax is statically checked at compile time. JMacro expressions may contain antiquoted Haskell code. This code may generate further JMacro code, or it may generate any of a range of standard Haskell types, which are able to be marshalled into JMacro through typeclass methods. JMacro also provides an executable, which allows the standalone processing of JMacro code into Javascript. For more information, see both Hackage and the JMacro documentation on the HaskellWiki: http://www.haskell.org/haskellwiki/Jmacro Some examples or idiomatic JMacro code are available in the source of its provided Javascript Prelude: http://hackage.haskell.org/packages/archive/jmacro/0.3.2/doc/html/src/Langu… Future work on JMacro, when time is available, is geared towards providing an optional layer of static typing with type inference. Patches, bug reports, and feature requests are all very welcome.

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Tree Construction
by Tom Hawkins 25 Sep '10

25 Sep '10

Hi, Often I need to assemble a tree from things with unstructured hierarchical paths. I built a function [1] to do this for ImProve. But does a library already exist that does this? If not I may create one, as I need it for a few different libraries. data Tree a b = Branch a [Tree a b] | Leaf a b tree :: (Eq a, Ord a) => (b -> [a]) -> [b] -> [Tree a b] Note, type 'a' is some sort of label, most often a string, and type 'b' form the leaves of the tree. The function passed into 'tree' returns the hierarchical path of a leaf object. -Tom [1] http://hackage.haskell.org/packages/archive/improve/0.0.12/doc/html/Languag…

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Throwing and catching exceptions in STM
by Bas van Dijk 25 Sep '10

25 Sep '10

Hello, The IO monad has the following function for throwing an exception: throwIO :: Exception e => e -> IO a Is there an analogous way of throwing an exception in the STM monad? I can try using: throw :: Exception e => e -> a. But does this guarantee ordering with respect to other STM actions? The IO monad has the following function for catching exceptions: catch :: Exception e => IO a -> (e -> IO a) -> IO a Why is catchSTM defined as: catchSTM :: STM a -> (SomeException -> STM a) -> STM a And not as the more general and more consistent: catchSTM :: Exception e => STM a -> (e -> STM a) -> STM a Thanks, Bas

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Re: [Haskell-cafe] Simple question about the function composition operator
by Miguel Mitrofanov 24 Sep '10

24 Sep '10

(g . f) x y = (\z -> g (f z)) x y = g (f x) y, and you need g (f x y), which is definitely not the same thing. 24.09.2010 13:35, Axel Benz пишет: > > Hello, > > this is maybe a simple question: > > cbinary :: a -> b -> (a -> b -> b) -> (b -> c) -> c > > -- Version 1 works: > > cbinary x y f g = g (f x y) > > -- Version 2 should be exactly the same according > > -- to my understanding of the "." operator definition, > > -- but fails with: > > -- Occurs check: cannot construct the infinite type: b = b -> b > > -- When generalising the type(s) for `cbinary' > > -- cbinary x y f g = (g . f) x y > > Can anybody explain why this happens and how I can compose f and g? > > Hint: It works fine if f is defined as an unary function. > > Thank you very much! > > Axel > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

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Simple question about the function composition operator
by Axel Benz 24 Sep '10

24 Sep '10

Hello, this is maybe a simple question: cbinary :: a -> b -> (a -> b -> b) -> (b -> c) -> c -- Version 1 works: cbinary x y f g = g (f x y) -- Version 2 should be exactly the same according -- to my understanding of the "." operator definition, -- but fails with: -- Occurs check: cannot construct the infinite type: b = b -> b -- When generalising the type(s) for `cbinary' -- cbinary x y f g = (g . f) x y Can anybody explain why this happens and how I can compose f and g? Hint: It works fine if f is defined as an unary function. Thank you very much! Axel

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ANNOUNCE: tableaux-0.1
by Pedro Baltazar Vasconcelos 24 Sep '10

24 Sep '10

Hi everyone, I'd just like to announce the first release of Tableaux, a web-based interactive theorem prover for first-order logic based on the method of semantic tableaux (cf. "First-Order Logic", Raymond Smullyan, Dover). This prover was intended as a teaching aid for undergraduate students and enforces a step-by-step construction of proofs. It could also be used as a basis for provers for other logics. Tableaux runs on any web server supporting the CGI interface; uou can check it out at http://www.ncc.up.pt/~pbv/cgi/tableaux.cgi. The source package is available from Hackage: http://hackage.haskell.org/package/tableaux. Best regards, Pedro Vasconcelos

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problems using macports?
by S. Doaitse Swierstra 24 Sep '10

24 Sep '10

I am in my yearly fightto get a working combination of operating system (Snow Leopard), compiler version (6.12) , wxWidgets and wxHaskell on my Mac . After deleting most of my stuff, starting afresh, hours of building using macports etc. I finally get the message: loeki:Opgave doaitse$ ghc --make Turtle.hs [1 of 1] Compiling Main ( Turtle.hs, Turtle.o ) Linking Turtle ... Undefined symbols: "_iconv_open", referenced from: _hs_iconv_open in libHSbase-4.2.0.2.a(iconv.o) (maybe you meant: _hs_iconv_open) "_iconv", referenced from: _hs_iconv in libHSbase-4.2.0.2.a(iconv.o) (maybe you meant: _hs_iconv_open, _hs_iconv , _hs_iconv_close ) "_iconv_close", referenced from: _hs_iconv_close in libHSbase-4.2.0.2.a(iconv.o) (maybe you meant: _hs_iconv_close) ld: symbol(s) not found collect2: ld returned 1 exit status loeki:Opgave doaitse$ Some Googling showed me that the same problem has shown up with Yi, The solution however is not there. Can someone enlighten me. Doaitse

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ANNOUNCE: http-enumerator 0.0.1
by Michael Snoyman 23 Sep '10

23 Sep '10

Hi all, After I made the 0.0.0 release of http-enumerator, Vincent Hanquez informed me of his wonderful tls package[1]. I've just release version 0.0.1 of the http-enumerator package which will use the tls package by default for establishing SSL connections. If you still want to use the OpenSSL package, just give cabal the build flag openssl, ie: cabal install -fopenssl http-enumerator The only other change to happen in this release is a modification to the chunked encoding parser to allow whitespace after the size of chunks. I think the HTTP spec does not mention that whitespace, but yahoo.com uses it. As before, consider this experimental, please try it and give me feedback. Cheers, Michael [1] http://hackage.haskell.org/package/tls

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packaging a cgi binary using cabal
by Pedro Baltazar Vasconcelos 23 Sep '10

23 Sep '10

I wrote a simple interactive tableaux theorem prover as a cgi in Haskell (http://www.ncc.up.pt/~pbv/cgi/tableaux.cgi) and would like to submit to hackage but need some advice on how to package it using cabal. In particular, the binary, CSS and bitmap files need to be installed under the web server directory (public_html or alike) rather than system or user directories. Any thoughts on how to do this? Regards, Pedro Vasconcelos

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Re: [Haskell-beginners] Current status of GUM
by Antoine Latter 23 Sep '10

23 Sep '10

On Thu, Sep 23, 2010 at 9:09 AM, Luca Ciciriello <luca_ciciriello(a)hotmail.com> wrote: > Hi Monica. > This one is a good question. > I'm based on this site: > > http://www.macs.hw.ac.uk/~dsg/gph/papers/abstracts/gum.html > > but it is a quite old site. > > Of the same year is the article "Accidents always come in threes: A case > Study of data-intensive programs in parallel Haskell". Here GUM is used. > Now I'm using GHC 6.12.3 on a multicore system using +RTS -N4 command for my > parallel programs. The performance aren't too bad. Have I to still use GUM? > > Bye. > > Luca. > > > ________________________________ > Date: Thu, 23 Sep 2010 10:02:17 -0300 > From: monicaspais(a)gmail.com > To: beginners(a)haskell.org > Subject: [Haskell-beginners] Current status of GUM > > Hello, > > I would like to know about the current status of GUM: > > - What is the latest version available? > - Does it run on distributed memory multiprocessors - clusters? What type of > architectures? > > thanks. > > Monica > The question may be better answered on the haskell-cafe mailing list, where more folks might know about specific Haskell implementations/extensions/libraries. Antoine

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Re: [Haskell-cafe] packaging a cgi binary using cabal
by Joachim Breitner 23 Sep '10

23 Sep '10

Hi, Am Donnerstag, den 23.09.2010, 11:19 +0100 schrieb Pedro Baltazar Vasconcelos: > On Thu, 23 Sep 2010 10:44:17 +0200 > Joachim Breitner <mail(a)joachim-breitner.de> wrote: > > > > In case of such research programs, where ease of installability is > > usually more important than performance, I just include the data files > > into the program. For example, in > > http://darcs.nomeata.de/sem_syn/ > > the JQuery library and the file BUtils.hs are turned into Haskell > > string literals using http://github.com/jgm/hsb2hs > > > > This way, the resulting binary is really stand-alone and can be just > > moved to the appropriate place on the web server. > > > > OK, thanks for the suggestion. For my needs I think this will be very > straightforward to do manually --- the CSS and image files a pretty > short anyway. for CSS, this is what I’m doing as well... but for binary image data? Greetings, Joachim -- 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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ANN: network-2.2.1.8 (GHC 7.0 compatibility release)
by Johan Tibell 23 Sep '10

23 Sep '10

Hi all, network-2.2.1.8 is now out. This release makes network compatible with GHC 7.0. There are no API changes. Cheers, Johan

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ANN: alex-meta-0.1.1 and happy-meta-0.1.1
by Jonas Almström Duregård 23 Sep '10

23 Sep '10

I'm pleased to announce alex-meta and happy-meta! These libraries provide quasi-quoter frontends and Template Haskell backends to the Alex lexer generator and the Happy parser generator respectively. Usage is something like this: {-# Language QuasiQuotes #-} module LexParse where import Text.Alex.Quote import Text.Happy.Quote compileAlex [$alex| <ALEX CODE HERE> |] compileHappy [$happy| <HAPPY CODE HERE> |] With a bit of luck, the module will contain everything that alex and happy would generate from these scripts. I say with a bit of luck because these libraries haven't really been tested except on a few auto-generated alex/happy scripts (specifically those produced by the BNF Converter). Issues: * The libraries depend on haskell-src-meta to parse the output of alex/happy and translate it to TH. This means that the libraries are only compatible with lexers and parsers that don't generate code outside the scope of this library. * Currently the libraries contain copies of most of the alex/happy source code, hopefully in the future the alex/happy packages can expose a few modules as libraries or the core of alex/happy can be factored out into a third library (used by both these libraries and the programs). Best regards Jonas Duregård

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ANNOUNCE: plugins 1.5.1. a framework for dynamic extension of Haskell programs
by Don Stewart 23 Sep '10

23 Sep '10

I'm pleased to announce the release 1.5.1 of the Haskell "plugins" library, $ cabal install plugins The "plugins" library provides a comprehensive API for: * dynamic loading and linking native Haskell modules * runtime compilation and meta-programming in Haskell * runtime hotswapping of Haskell code In short, it provides a framework for dynamic extension of Haskell programs [1]. This release is due to great work by Manuel Chakravarty, who cleaned up much of the code and helped migrate it from GHC 6.8 to 6.12. -- Don 1. The approach to dynamic extension developed in the library is described in: * Plugging Haskell In. André Pang, Don Stewart, Sean Seefried, and Manuel M. T. Chakravarty. In Proceedings of the ACM SIGPLAN Workshop on Haskell, pages 10-21. ACM Press, 2004 * Dynamic Applications From the Ground Up. Don Stewart and Manuel M. T. Chakravarty. In Proceedings of the ACM SIGPLAN Workshop on Haskell, pages 27-38. ACM Press, 2005 * Dynamic Extension of Typed Functional Languages, Don Stewart. University of New South Wales, Sydney, Australia. 2010

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Fwd: Haskell at bettercodes.org
by Malcolm Wallace 23 Sep '10

23 Sep '10

Forwarded, for the interest of the community: > From: Sandra Jüssen <sandra.juessen(a)googlemail.com> > Subject: Haskell at bettercodes.org > > > Dear Haskell Community, > > we are an open source project called bettercodes.org and our goal is > to build up the leading developer community and collaboration with a > broad range of useful developer tools and feature, including a free > code hosting with a full project management. > > bettercodes.org should be no binded to any technology, programming > language, philosophy. A true place for all developers from around the > world. > > We are online since nearly five month, but we have a lack of Haskell > enthusiats. We want to invite the Haskell community to join > bettercodes.org and establish a strong presence their. Not instead of > the pure Haskell communty server, but as an extention to force the > exchange with other developers. > > For any question, please contact me... > > Kind Regards, > Sandra >

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haskell.org committee: Call for nominations
by Ian Lynagh 22 Sep '10

22 Sep '10

Dear Haskellers, The recent discussion indicates there is consensus for forming a haskell.org committee. We are therefore calling for nominations for members of the initial committee. To nominate yourself, please send an e-mail to committee(a)haskell.org by 29 September 2010. Please feel free to include any information about yourself that you think will help us to make a decision. We do not expect that being a member of the committee will require a significant amount of time, but committee members should aim to be responsive during discussions when the committee is called upon to make a decision. More details about the committee's roles and responsibilities are on http://www.haskell.org/haskellwiki/Haskell.org_committee If you have any questions about the process, please feel free to e-mail us at committee(a)haskell.org or to contact one of us individually. Thanks Ian

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