- Haskell-Cafe - Haskell.org

ANNOUNCE: Haddock 2.6.0
by David Waern 22 Dec '09

22 Dec '09

-------------------------------------------- -- Haddock 2.6.0 -------------------------------------------- A new version of Haddock, the Haskell documentation tool, is out! This is the version that comes with GHC 6.12.1. It contains the main results of Isaac Dupree's Summer of Code project, which are: * Cross-package documentation (exporting something that comes from another package is handled correctly. The full documentation of that thing shows up in your documentation) * Lexing and parsing of Haddock comment markup is moved from GHC back into Haddock. This will make it easier to make changes to the markup format We have decided to drop compatibility with older GHC versions in order to speed up development. -------------------------------------------- -- Full list of changes in version 2.6.0 -------------------------------------------- * Drop support for GHC 6.10.* * Add support for GHC 6.12.1 * Cross-package documentation * Move lexing and parsing of the Haddock comment markup back to Haddock * Slightly prettier printing of instance heads * Support platforms for which GHC has no native code generator * Add a flag --print-ghc-libdir * Minor bug fixes -------------------------------------------- -- Links -------------------------------------------- Homepage: http://www.haskell.org/haddock Hackage page: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haddock-2.6.0 Bugtracker and wiki: http://trac.haskell.org/haddock Mailing list: haddock(a)projects.haskell.org Code repository: http://code.haskell.org/haddock -------------------------------------------- -- Contributors -------------------------------------------- The following people contributed patches to this release: Isaac Dupree Ian Lynagh Simon Peyton-Jones David Waern -------------------------------------------- -- Get Involved -------------------------------------------- We would be very happy to get more contributors. To get involved, start by grabbing the code: http://code.haskell.org/haddock Then take a look at the bug and feature tracker for things to work on: http://trac.haskell.org/haddock

1 0

How can i set the seed random number generator ?
by zaxis 22 Dec '09

22 Dec '09

In erlang, first i use the following function to set the seed: new_seed() -> {_,_,X} = erlang:now(), {H,M,S} = time(), H1 = H * X rem 32767, M1 = M * X rem 32767, S1 = S * X rem 32767, put(random_seed, {H1,M1,S1}). then use random:uniform/1 to get the random number. In haskell, i just use the following function to get the random number. It seems i donot need to set the seed of random number generator manually? rollDice :: Int -> IO Int rollDice n = randomRIO(1,n) Sincerely! ----- fac n = foldr (*) 1 [1..n] -- View this message in context: http://old.nabble.com/How-can-i-set-the-seed-random-number-generator---tp26… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

3 2

Parse do block problem
by joeltt 22 Dec '09

22 Dec '09

I'm trying to write my first Haskell program. The below is the first real logic block I've tried to write, unfortunately I get a "The last statement in a 'do' construct must be an expression" error when loading the method. However, the location of this problem isn't very clear. Is there a way to get more detailed parse message from Haskell, or can someone tell me where the problem is (and better "why"?). I don't think I actually need to use a "do" IO/Monad theme here, but its not clear to me either way. This isn't homework, its just for fun... do_solve_iter guess tried = do let actual = count_occurences guess if guess == actual then putStrLn "ANSWER!!" else if (find (==actual) tried) == Just actual then do putStrLn "NO ANSWER!" putStrLn tried else do putStrLn "ITER" do_solve_iter actual (actual : tried) -- View this message in context: http://old.nabble.com/Parse-do-block-problem-tp26883702p26883702.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

3 3

Pattern matching, and bugs
by András Mocsáry 21 Dec '09

21 Dec '09

Hello, I was advised respectfully to post my query here. Please, read the whole letter before you do anything, because I tried to construct the problem step by step. Also keep in mind, that the problem I query here is more general, and similar cases occur elsewhere, not just in this particular example I present below. *Intro story* ( Skip if you are in a hurry ) I'm participating in several open-source server development projects, most of them are written in C, and some of them have C++ code hidden here and there. These programs, are developed by many, and by many ways, and so, more often than not it is very hard to determine the 'real cause of bugs'. This almost always leads to 'bugfixes' which 'treat the crash'. Sometimes they are a few lines of extra checks, like IFs. Sometimes they are complex, and even surprisingly clever hacks. Thus understanding the 'code' of them is challenging, but the end result is a pile of ... hacks fixing bugs fixing hacks fixing bug, which also were put there to fix yet another bugs. + When I started to learn functional programming, I was told, that the correctness of a functional program can be proved a lot more easily, in fact in a straight mathematical way. + *My concern* is about predictable failure of sw written in Haskell. To illustrate it let's see a Haskell pattern matching example: Let's say I have defined some states my object could be in, and I did in a switch in some C-like language: > switch ( x ) { Case 0: "Unchecked" Case 1: "Checked" Case 2: "Unknown" } And in Haskell pattern matching: switch 1 = "Unchecked" switch 2 = "Checked" switch 3 = "Unknown" Let's say, these are clearly defined states of some objects. Then let's say something unexpected happens: x gets something else than 0 1 2. Now we have a problem, which is most generally fixed in these ways: C-like: > switch ( x ) { Case 0: "Unchecked" Case 1: "Checked" Case 2: "Unknown" Default: "Nothing" } Haskell like: switch 1 = "Unchecked" switch 2 = "Checked" switch 3 = "Unknown" switch x = "Nothing" These general ways really avoid this particular crash, but does something real bad to the code in my opinion. Below are some cases x can go wrong: *1. The bad data we got as 'x', could have came from an another part of our very program, which is the REAL CAUSE of the crash, but we successfully hide it.* * Which makes it harder to fix later, and thus eventually means the death of the software product. Eventually someone has to rewrite it. Which is economically bad for the company, since rewriting implies increased costs. 2. The bad data we got as 'x', could also could have come form a real word object, we have underestimated, or which changed in the meantime. 3. This 'x' could have been corrupted over a network, or by 'mingling' or by other faulty software or something. Point 1: If we allow ourself such general bugfixes, we eventually kill the ability of the project to 'evolve'. Point 2: Programmers eventually take up such 'arguably bad' habits, thus making harder to find such bugs. Thus it would be wiser to tell my people to never write Default cases, and such general pattern matching cases. * Which leads to the very reason I wrote to you: I want to propose this for Haskell prime: I would like to have a way for Haskell, not to crash, when my coders write pattern matching without the above mentioned general case. Like having the compiler auto-include those general cases for us, but when those cases got hit, then* instead of crashing*, it *should **report some error* on *stdout *or *stderr*. (It would be even nicer if it cold have been traced.) This is very much like warning suppression, just that it's crash suppression, with the need of a report message of course. *I would like to hear your opinion on this.* I also think, that there are many similar cases in haskell, where not crashing, just error reporting would be way more beneficial. In my case for server software, where network corrupted data, ( and data which has been 'tampered with' by some 'good guy' who think he's robin hood if he can 'hack' the server ) is an every day reality. Thanks for your time reading my 'storm'. Greets, Andrew

7 6

Infix instance headers
by Bas van Dijk 21 Dec '09

21 Dec '09

Hello, What's the reason that infix class declarations and infix constraints are supported but infix instance heads aren't? For example the following code from my regions package is allowed but writing the instance header infix results in a "Malformed instance header" error: class (Monad pr, Monad cr) => pr `ParentOf` cr instance Monad r => ParentOf r r instance ( Monad cr , cr `TypeCast2` RegionT resource s pcr , pr `ParentOf` pcr ) => ParentOf pr cr regards, Bas

1 0

Haskell Web News: Looking back on 2009
by Don Stewart 21 Dec '09

21 Dec '09

The Haskell Web News is a monthly summary of the hottest news about the Haskell programming language, as found in our online communities. If you want to catch up with what’s been happening in Haskell, this might be the journal for you. In this edition, we look back on the major events of 2009. http://haskellwebnews.wordpress.com/2009/12/20/the-year-in-haskell/ -- Don

2 1

no sparks?
by Jamie Morgenstern 21 Dec '09

21 Dec '09

Hello; I am writing a parallel theorem prover using Haskell, and I am trying to do several things. As a first cut, I want to try using the par construct to attempt right and left rules simultaneously, and to evaluate both branches of an and clause in parallel. My code (attached) does not seem to generate sparks, however. When I run ./proposition +RTS -N2 -sstderr I get that no sparks are created. What am I doing wrong? Also, I was wondering if something akin to a "parallel or" exists. By this, I mean I am looking for a function which, given x : a , y : a, returns either, whichever computation returns first. Can I use strategies to code up something like this? I suppose this doesn't play nicely with the idea of determinism, but thought it might be worth asking anyway. Thanks, -Jamie

8 13

Largest types in SYB
by Paul Keir 21 Dec '09

21 Dec '09

I was looking for a simple generic technique targeting and transforming the "largest" terms of a particular type. For example, with Expr and Val declared as: data Expr = Val Val | Add Expr Expr | Sub Expr Expr deriving (Show, Eq, Typeable, Data) data Val = Var String | Struct [Expr] deriving (Show, Eq, Typeable, Data) and a test Expr "e", e = Sub (Val $ Var "A") (Add (Val $ Var "X1") (Val $ Struct [Add (Val $ Var "Y1") (Val $ Var "Y2")])) I wanted to replace only the inner "Add" expression Add (Val $ Var "Y1") (Val $ Var "Y2") because its "parent" is not of the same type as itself (it's a list), using a function such as chopAdd: chopAdd (Add _ _) = Val $ Var "AddChop" chopAdd e = e But using "everywhere" from Scrap Your BoilerPlate (SYB): everywhere (mkT repAdd) e I'd get: Sub (Val (Var "A")) (Val (Var "AddChop")) while I was hoping for: Sub (Val (Var "A")) (Add (Val (Var "X1")) (Val (Struct [Val (Var "AddChop")]))) The Haskell.org SYB wiki presents "listifyWholeLists". This is relevant, though it applies queries rather than transformations. It uses a function called synthesize, which I was ultimately unable to properly reference, or apply to the problem at hand. So here is my solution: everywhereBar :: GenericQ Bool -> GenericT -> GenericT everywhereBar q f x | q x = (gmapT (everywhereBar (typeEq x) f) x) | otherwise = f (gmapT (everywhereBar (typeEq x) f) x) where typeEq p c = typeOf p == typeOf c It's like SYB's "everywhereBut", except 1. The consequence of q x being True is only to remove the application of f to the "parent"; not to stop traversal. 2. q is not constant. Instead it is the partial application of a local function, "typeEq". An application looks like: everywhereBar (const False) (mkT repAdd) e with (const False) the user is choosing the outcome of the very first "q x" in "everywhereBar". I'm enjoying using SYB, and had hoped to use only functions from the package, but couldn't find a way; and this does the job for now. I've also seen that there are many other approaches to generic programming than SYB (even for AST transformations in particular) but I wanted to understand SYB first. I'm interested to know if anyone has a more elegant SYB solution. And here's the monadic version: everywhereBarM :: Monad m => GenericQ Bool -> GenericM m -> GenericM m everywhereBarM q f x | q x = gmapM (everywhereBarM (typeEq x) f) x | otherwise = do x' <- gmapM (everywhereBarM (typeEq x) f) x f x' where typeEq p c = typeOf p == typeOf c Cheers, Paul The University of Glasgow, charity number SC004401

2 1

HList and SQL ... looking for working examples
by Günther Schmidt 21 Dec '09

21 Dec '09

Hi, I'm trying express relational algebra terms by using Oleg's HList. Table definitions and such. Are there any working examples for this? Günther

2 2

Dead links for Web frameworks.
by Jason Dusek 20 Dec '09

20 Dec '09

I recently removed dead links on the web frameworks page, for "EdComb" and "Generative Implementation Strategies for Data-Centric Web Applications". http://www.haskell.org/haskellwiki/?title=Applications_and_libraries/Web_pr… I'm curious what happened to these two projects and if any docs remain for them. -- Jason Dusek

1 0

Search a directory for files
by Eitan Goldshtrom 20 Dec '09

20 Dec '09

Hi, I'm trying to make a program to make it easy to rename files in bulk. What I'm wondering is how to get a list of all files in a particular directory. I found System.Posix.Files and I'm planning on using the rename function in it for actually renaming, but I can't find an easy way to get all filenames in a particular directory. Does anyone know how to do it? -Eitan

3 3

sizeOf on a type
by Gregory Crosswhite 20 Dec '09

20 Dec '09

Hey everyone, I would like to write a routine like nextPtr :: Storable a => Ptr a -> Ptr a nextPtr = (`plusPtr` sizeOf (undefined :: a)) which increments a pointer by the correct amount, but GHC complains that the type variable "a" is ambiguous. I can see what's going on: it can't tell that the "a" I am writing there is the same "a" that's in the type specification, but is there any way that I can make it identify "a" with the "a" in the specification for nextPtr? Cheers, Greg

4 3

How to use Control.Failure?
by ntupel 19 Dec '09

19 Dec '09

I have looked at the recently released Control.Failure library but I admit, I couldn't understand it completely. So given the example below, how would Control.Failure help me here? Thanks, nt -- Theirs (other library code stubs) data TheirError = TheirErrorCase deriving Show data TheirData = TheirData deriving Show theirFunc :: [String] -> Either TheirError TheirData theirFunc = undefined -- Mine (my own code stubs) data MyError = MyErrorCase deriving Show data MyData = MyData deriving Show myFuncA :: TheirData -> Either MyError MyData myFuncA = undefined -- Ugly. How to apply Control.Failure here? myFuncB :: IO (Either MyError MyData) myFuncB = do let x = theirFunc [] case x of Right x' -> return $ myFuncA x' Left _ -> return . Left $ MyErrorCase

2 2

Haskell Weekly News: Issue 144 - December 19, 2009
by jfredett＠gmail.com 19 Dec '09

19 Dec '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20091219 Issue 144 - December 19, 2009 --------------------------------------------------------------------------- Welcome to issue 144 of HWN, a newsletter covering developments in the [1]Haskell community. The big news this week is the release of the Glorious Glasgow Haskell compiler version 6.12.1, lots of exciting new improvements, congratulations from the whole community go out to the devs, good work GHC Team! Otherwise, this week has been quiet, with some interesting discussions about associated types and the new GHC, and some excellent new packages announced. Finally, due to the incoming holidays, there won't be an HWN for the next two weeks, I'll see you Haskellers in 2010, until then, your Haskell Weekly News! Announcements GHC version 6.12.1. Ian Lynagh [2]announced the (Interactive) Glasgow Haskell Compiler, version 6.12.1. Including improved support for parallel execution, Dynamic linking support on Linux, and many other improvments. atom-0.1.4. Tom Hawkins [3]announced a bug fix release of the atom package, affecting floating point variable initialization. text 0.7, fast Unicode text. Bryan O'Sullivan [4]announced a new release of the text package adds support for Unicode I/O explicit-iomodes-0.1. Bas van Dijk [5]announced explicit-iomodes version 0.1, a wrapper around System.IO that provides a Handle type which is parametrized with the IOMode it is in. Hemkay, the 100% Haskell MOD player. Patai Gergely [6]announced a Hemkay, an old-school MOD player in pure Haskell. GT-VMT 2010: deadlines extended. Emilio Tuosto [7]announced a deadline extension to the GT-VMT call for papers. Discussion Restrictions on associated types for classes. Stephen Lavelle [8]asked if there was a way to wrap a associated type in a class constraint. Yay 6.12.1! Evan Laforge [9]talked about some of the changes in the new version of GHC. Blog noise [10]Haskell news from the [11]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Michael Snoyman: [12]data-object family. * Bryan O'Sullivan: [13]Making GHC's I/O manager more scalable. * Conor McBride: [14]Epilogue for Epigram: 2+2=4. * Sebastian Fischer: [15]Thesis submitted. * Bryan O'Sullivan: [16]Data.Text 0.7 gains I/O support. * Ketil Malde: [17]Searching for poly(A) tails. * Mark Jason Dominus: [18]Monads are like burritos. * Sean Leather: [19]"Upwards and downwards accumulations on trees" translated into Haskell. Quotes of the Week * yrlnry: <byorgey> yrlnry: just some lady who had a lot of money and decided she wanted poor grad students to have some of it after she died... pretty nice of her, actually <yrlnry> senile dementia, more likely. * Philonous: A 'newbie', in Haskell, is someone who hasn't yet implemented a compiler. They've only written a monad tutorial. * kmc: Right, for example Either (pun not intended) * kmc: One thing I've learned from open-source software is that if you invent enough wheels, one of them will turn out to be round and capable of rolling. * PhilipWadler: To see that "in" and "out" are inverses, stare at the following diagram * kmc: Data.Map is like a C++ STL map<k,v>, without the suck * edwardkmett: Most monad tutorials are written by people who barely understand monads, if at all, but unfortunately nothing can stop someone from writing a monad tutorial. We've tried, there was blood everywhere. * Cale: A small category is a monad in the 2-category of spans of sets. About the Haskell Weekly News New editions are posted to [20]the Haskell mailing list as well as to [21]the Haskell Sequence and [22]Planet Haskell. [23]RSS is also available, and headlines appear on [24]haskell.org. To help create new editions of this newsletter, please see the information on [25]how to contribute. Send stories to jfredett . at . gmail . dot . com. The darcs repository is available at darcs get [26]http://patch-tag.com/r/jfredett/HWN2/pullrepo HWN2 . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.general/17678 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/68009 4. http://article.gmane.org/gmane.comp.lang.haskell.cafe/67946 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/67931 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/67923 7. http://article.gmane.org/gmane.comp.lang.haskell.general/17676 8. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/68084 9. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/67950 10. http://planet.haskell.org/ 11. http://haskell.org/haskellwiki/Blog_articles 12. http://snoyberg.wordpress.com/2009/12/17/data-object-family/ 13. http://www.serpentine.com/blog/2009/12/17/making-ghcs-io-manager-more-scala… 14. http://www.e-pig.org/epilogue/?p=266 15. http://www-ps.informatik.uni-kiel.de/~sebf/haskell/thesis.html 16. http://www.serpentine.com/blog/2009/12/15/data-text-0-7-gains-io-support/ 17. http://blog.malde.org/index.php/2009/12/14/searching-for-polya-tails/ 18. http://blog.plover.com/prog/burritos.html 19. http://feedproxy.google.com/~r/splonderzoek/~3/4E8TZPDZ-aM/upwards-and-down… 20. http://www.haskell.org/mailman/listinfo/haskell 21. http://sequence.complete.org/ 22. http://planet.haskell.org/ 23. http://sequence.complete.org/node/feed 24. http://haskell.org/ 25. http://haskell.org/haskellwiki/HWN 26. http://patch-tag.com/r/jfredett/HWN2/pullrepo%20HWN2

1 0

Re: Pattern matching, and bugs
by John Lato 19 Dec '09

19 Dec '09

> From: Felipe Lessa <felipe.lessa(a)gmail.com> > > On Fri, Dec 18, 2009 at 02:13:02PM +0000, John Lato wrote: >> So now the program needs a result of some type (String in your >> example) and gets an undefined, and then immediately crashes >> with an "Exception - undefined" error. > > I think this is the second time this is said in this thread, but > please don't as it may confuse the OP. "undefined"s, including > those generated by missing cases, do *not* crash the program. > They also do not *immediately* close the program. They are > propagated as exceptions are, however most of the time we write > programs without explicitly catching them. Of course you're correct. I was careful to note that undefined's generate exceptions, but left out the rest on the assumption that the OP would be familiar with exception handling and propagation. But it is best to be perfectly explicit. > > So the proper wording would be that the "undefined"s propagate > through the functions and whenever they reach the top function > (i.e. main), they are caught by the runtime system, which prints > the String associated with the "undefined" and exits the proccess > with an error code. > > I should note also that *pure* code *can't* catch those > "undefined"s. If they could, then Nasty Things Would Happen(TM) > and we don't want that. However IO code may catch them without > any problem using Control.Exception's functions. I agree this is an important point, particularly as it's different from declarative/OOP exception mechanisms. John

1 0

Re: [Haskell-cafe] Double free-ing (was: Reading from a process)
by Mitar 18 Dec '09

18 Dec '09

Hi! On Thu, Dec 17, 2009 at 5:28 AM, Jason Dusek <jason.dusek(a)gmail.com> wrote: > It seems like the message delimiter to me because you keep > buffering till you receive it. Hm, true. I have changed code to this: getLastMyData :: MySate (Maybe MyData) getLastMyData = do p <- gets process case p of Nothing -> fail "No process" Just (MyProcess processOut processPid processBuffer) -> do processRunning <- io $ getProcessExitCode processPid case processRunning of Just _ -> processExited _ -> do ret <- io $ tryJust (guard . isEOFError) $ slurpMyData processOut processBuffer case ret of Left _ -> processExited -- EOF Right (datalist, currentBuffer) -> do modify (\s -> s { process = Just (MyProcess processOut processPid currentBuffer) }) if null datalist then return Nothing else return $ Just $ head datalist -- MyData is stored in the reverse order so head is the last MyData from the process slurpMyData :: Handle -> DataBuffer -> IO ([MyData], DataBuffer) slurpMyData = slurpMyData' [] where slurpMyData' datalist h buffer@(DataBuffer capacity array bytecount) = do ready <- hReady h if not ready then return (datalist, buffer) else do let array' = advancePtr array bytecount count <- hGetBufNonBlocking h array' (capacity - bytecount) let bytecount' = bytecount + count chars <- peekArray bytecount' array let (d, rest) = readData . dataToString $ chars rest' = stringToData rest if null d then if length rest' == capacity then error "Invalid data from the process" else return (datalist, buffer) else do assert (length rest' <= capacity) $ pokeArray array rest' let buffer' = DataBuffer capacity array (length rest') slurpMyData' (d ++ datalist) h buffer' readData :: String -> ([MyData], String) readData = readData' [] where readData' datalist "" = (datalist, "") readData' datalist string = case reads string of [(x, rest)] -> readData' ((head x):datalist) rest -- x is a list and currently it has only one element [] -> (datalist, string) -- we probably do not have enough data to read MyData properly _ -> error "Ambiguous parse from the process" And now it works. I just do not like using malloc and free. And talking about free, I have now a problem of double freeing this buffer. I am getting it after I send ctrl-c to the main process (with underlying process I am communicating with). I am freeing it in processExited: processExited :: MyState a processExited = do terminateDataProcess fail "Process exited" terminateDataProcess :: MyState () terminateDataProcess = do p <- gets process case p of Just (MyProcess _ processPid (DataBuffer _ array _)) -> do modify (\s -> s { process = Nothing }) io $ free array io $ terminateProcess processPid _ -> return () So I run processExited if there is EOF from underlying process. But I also run terminateDataProcess in a bracket I am calling getLastMyData. Code is like this: bracket initDataProcess terminateDataProcess (... read getLastMyData repeatedly and process it ...) Why I am getting this double free-ing errors? Should I introduce some locks on terminateDataProcess? I am using Linux 2.6.30 amd64 and 6.10.4. Mitar

3 7

getPtrSize works, but is annoying
by Gregory Crosswhite 18 Dec '09

18 Dec '09

Ugh, I figured out how to write code to do what I wanted, but it seems like an ugly solution: getPtrSize :: Ptr a -> Int getPtrSize = getFrom dummy where getFrom :: a -> Ptr a -> Int getFrom dummy _ = sizeOf dummy Any thoughts on a less ugly solution, or is this really the best that I can do? Cheers, Greg

2 1

Cabal
by Philippos Apolinarius 18 Dec '09

18 Dec '09

I made small improvements in the Small Japi Binding, and asked how to make it available. I received a few private messages advising me to build and package the library using a tool called cabal. Since I have used installation tools for PLT, R and LaTeX libraries, I thought cabal was something similar. However, I noticed that there are a lot of complaints against cabal. Therefore, I decided to install cabal, and try it. It seems that it is easier to install packages by hand than using cabal. Here is a typical cabal session: D:\ghc\ghcapi>cabal update Downloading the latest package list from hackage.haskell.org D:\ghc\ghcapi>cabal install mkcabal Resolving dependencies... Downloading pcre-light-0.3.1... Configuring pcre-light-0.3.1... Downloading readline-1.0.1.0... Configuring readline-1.0.1.0... cabal: Error: some packages failed to install: mkcabal-0.4.2 depends on readline-1.0.1.0 which failed to install. pcre-light-0.3.1 failed during the configure step. The exception was: exit: ExitFailure 1 readline-1.0.1.0 failed during the configure step. The exception was: exit: ExitFailure 1 As one can see, it is much more difficult to use than R installation tools, or MikTeX installation tools. If cabal is so difficult, why use it? I am sure that I have done something very stupid mistake, but believe me, a lot of people is trying to use cabal and failing. I am not sure that it is a good idea to distribute libraries using cabal. However, this is irrelevant, because I am sure that creating a package with cabal is well beyond my powers. It is much easier to write a complete JAPI library, than packaging it in cabal. __________________________________________________________________ Looking for the perfect gift? Give the gift of Flickr! http://www.flickr.com/gift/

5 11

Allowing hyphens in identifiers
by Deniz Dogan 18 Dec '09

18 Dec '09

Has there been any serious suggestion or attempt to change the syntax of Haskell to allow hyphens in identifiers, much like in Lisp languages? E.g. hello-world would be a valid function name. -- Deniz Dogan

24 59

Re: Pattern matching, and bugs
by John Lato 18 Dec '09

18 Dec '09

Hello, > Date: Fri, 18 Dec 2009 13:04:47 +0100 > From: Andr?s Mocs?ry <amocsy(a)gmail.com> > > > switch 1 = "Unchecked" > > switch 2 = "Checked" > > switch 3 = "Unknown" > > switch x = "Nothing" > > These general ways really avoid this particular crash, but does something > real bad to the code in my opinion. ...snip... > Which leads to the very reason I wrote to you: > > I want to propose this for Haskell prime: > > I would like to have a way for Haskell, not to crash, when my coders write > pattern matching without the above mentioned general case. I will first make a recommendation, then some comments on your proposal. My recommendation is this: if you know that a function should only be called with certain values, you should create a data type that has *only* those values, like: data ForSwitch = One | Two | Three then your switch function is switch :: ForSwitch -> String and now it can be guaranteed *at compile-time* that switch will never be called with an incorrect argument, because only arguments are available in the ForSwitch type and they're all valid. It's now impossible for another part of the program to generate invalid data. It either generates a ForSwitch, which is guaranteed to be valid, or it doesn't, in which case the code won't typecheck. Note that if you really just want to wrap Int's, you can use a newtype and a smart constructor, which if written correctly gives you the same guarantees but is in my mind less convenient. Now, as for a general response to your proposal, I'm not sure that what you're requesting is possible, and I'm quite certain it would be more trouble than it's worth. > Like having the compiler auto-include those general cases for us, > but when those cases got hit, then* instead of crashing*, it *should **report > some error* on *stdout *or *stderr*. > (It would be even nicer if it cold have been traced.) What should the program do after reporting an error? Because of Haskell's non-strict evaluation, a function is only evaluated when your program *needs the result*. The compiler can't infer a meaningful value for an arbitrary type, and the only value that can be in every type is undefined. So now the program needs a result of some type (String in your example) and gets an undefined, and then immediately crashes with an "Exception - undefined" error. As for network-corrupted data, the solution is the same. Make a type that reflects *only* the values you want. Then it's the responsibility of the serializer/deserializer to ensure that you have a correct value, using explicit error handling (Maybe or Either come to mind). Then you know that all data in your system is valid, and you only need to worry about invalid data at borders, where the problem is much easier to address. John

2 1

lhs2tex, Haskell Platform and cygwin
by Jacques Carette 18 Dec '09

18 Dec '09

I just downloaded a fresh copy of Haskell Platform, and successfully got cabal to update itself. I installed smallcheck-0.4 successfully too. But then I tried to install lhs2tex, which 'worked' until the point of saying: Linking dist\build\lhs2TeX\lhs2TeX.exe ... Installing executable(s) in C:\Program Files (x86)\Haskell\bin setup.exe: The program mktexlsr is required but it could not be found And I do have 'mktexlsr' in my cygwin PATH (where I was running 'cabal install lhs2tex'). It's true that mktexlsr isn't in my Windows PATH. I would have thought someone else would have encountered this already, but my google searchers found other (long fixed) problems with lhs2tex under cygwin, but not this one. Jacques

3 5

[Fwd: Termination Competition 2009 live on the web!]
by Janis Voigtländer 18 Dec '09

18 Dec '09

Hi all, This contest should be of interest to Haskellers. There is an "FP Category" in which termination of Haskell programs is automatically checked. The current state can be observed by following the corresponding "View Results" link from the page http://termcomp.uibk.ac.at/termcomp/competition/categoryList.seam?competiti… Ciao, Janis. -- Jun.-Prof. Dr. Janis Voigtländer http://www.iai.uni-bonn.de/~jv/ mailto:jv@iai.uni-bonn.de

1 0

openFd under -threaded gets interrupted
by Mitar 18 Dec '09

18 Dec '09

Hi! I am using such code: fd <- openFd device ReadWrite Nothing OpenFileFlags { append = False, noctty = True, exclusive = False, nonBlock = True, trunc = False } And if I compile my program with -threaded option I always get such error: interrupted (Interrupted system call) But without -threaded it works flawlessly. I am using Linux 2.6.30 amd64, GHC 6.10.4. It was the same with 6.8. Why is this? Is there any workaround? Does it work in 6.12? Mitar

1 1

Restrictions on associated types for classes
by Stephen Lavelle 17 Dec '09

17 Dec '09

Given class MyClass k where type AssociatedType k :: * Is there a way of requiring AssociatedType be of class Eq, say?

9 13

Haskell Platform mailing list?
by Gregory Collins 17 Dec '09

17 Dec '09

Hi all, I'm getting the following error trying to post to the haskell-platform list: haskell-platform(a)projects.haskell.org Delay reason: SMTP error from remote mail server after end of data: host community.haskell.org [72.249.126.23]: 451 Temporary local problem - please try later G -- Gregory Collins <greg(a)gregorycollins.net>

1 0

REMINDER: Next BostonHaskell meeting TONIGHT at MIT
by Ravi Nanavati 17 Dec '09

17 Dec '09

The full details of the event are here: http://groups.google.com/group/bostonhaskell/t/792df9787155b5cc I'm just sending out this reminder to make sure more people hear about the event. If you're planning to come please respond to our attendance poll at: http://doodle.com/p2zcnca6k39iptb4 This will help us get a better count of attendees for refreshments (since my wife has volunteered to make more goodies). Please also respond to the poll if you're interested in BostonHaskell, but couldn't come this month because of scheduling or location constraints. That will help us improve planning for future meetings. I look forward to seeing many Boston-area Haskellers tonight! Thanks, - Ravi Nanavati

1 0

Re: [Haskell-cafe] ANN: Hemkay, the 100% Haskell MOD player
by Patai Gergely 17 Dec '09

17 Dec '09

> Patai, I asked a similar question about a week ago, inquiring about > efficient buffers for audio. I got a good response: > > http://thread.gmane.org/gmane.comp.lang.haskell.cafe/67258/focus=67293 Well, the general lesson seems to be that using stream fusion or something analogous is the way to go. In this particular case I don't need any fancy processing, and I have no feedback loops. All I do in my mixing routine is to calculate a weighted (volume+panning) sum of samples and stretch them in time as dictated by their frequency. The song is flattened into a series of play states first, so all the information required for mixing is readily available. I could try rewriting the mixer to return an iterative generator function instead, which could be passed to an appropriate sound interface. The latter would have to be written once and for all. Gergely -- http://www.fastmail.fm - Does exactly what it says on the tin

2 3

Haskell and "memoization"
by michael rice 17 Dec '09

17 Dec '09

I'm looking here at the Fibonacci stuff: http://www.haskell.org/haskellwiki/Memoization Since (I've read) Haskell never computes the value of a function more than once, I don't understand the need for memoization. Enlighten me. Michael

6 14

Haskell arrays
by michael rice 17 Dec '09

17 Dec '09

Based upon docs I've looked at, Haskell seems to store both an array element value AND its index/indices, whereas most languages just store the value and find its location in memory through mapping calculations. Is it true? Michael

5 5

Reading from a process
by Mitar 17 Dec '09

17 Dec '09

Hi! I would like to make an one-directional inter-process communication in a way that one process is printing out read-compatible Haskell data types and Haskell program is reading them from a pipe. I would like to make a function which would return Nothing if there is no data type in a pipe or Just last data type there was in a pipe (discarding all before). So it should behave in a non-blocking way. In an attempt I made this: getLastMyData :: MyState (Maybe MyData) getLastMyData = do p <- gets process case p of Nothing -> fail "No process" Just (MyProcess processOut processPid processBuffer) -> do processRunning <- io $ getProcessExitCode processPid case processRunning of Just _ -> processExited _ -> do ret <- io $ tryJust (guard . isEOFError) $ slurpInput processOut processBuffer case ret of Left _ -> processExited -- EOF Right currentBuffer -> do let (datalist, currentBuffer') = readData currentBuffer modify (\s -> s { process = Just (MyProcess processOut processPid currentBuffer') }) if null datalist then return Nothing else return $ Just $ head datalist -- MyData is stored in the reverse order so head is the last MyData from the process slurpInput :: Handle -> String -> IO String slurpInput h buffer = do ready <- hReady h if not ready then return buffer else do char <- hGetChar h slurpInput h (buffer ++ [char]) readData :: String -> ([MyData], String) readData buffer = readData' [] buffer where readData' datalist [] = (datalist, []) readData' datalist buf = case reads buf of [(x, rest)] -> readData' ((head x):datalist) rest -- x is a list and currently it has only one element [] -> if length buf > 5 * maxMyDataDescLength then error "Invalid data from process" else (datalist, buf) -- we probably do not have enough data to read MyData properly _ -> error "Ambiguous parse from process" (I have cleaned a code somewhat, I hope I have not introduced any errors. MyData is encapsulated in a list when printed from a process, this is why is there "head".) The problem is that I do not like this approach. And it does not look nice. For example I am reading byte per byte and appending it to the end. Then the problem is that if process is sending garbage faster then Haskell can consume it Haskell stays in slurpInput function and never gets to readData where it would found out that there is garbage coming in. I could use hGetBufNonBlocking? But it would still not solve garbage problem. So is there some better way to do it? Mitar

2 3

Boxed Mutable Arrays
by Brad Larsen 16 Dec '09

16 Dec '09

Is anyone working on fixing ticket #650 <http://hackage.haskell.org/trac/ghc/ticket/650>? In short, STArray and the garbage collector don't play well together, resulting in array updates being non-constant time operations. This bug makes it very difficult/impossible to write efficient array algorithms that depend upon mutation in Haskell. On another note, does this (or perhaps better phrased, will this) bug also affect Data Parallel Haskell? I would really like to see highly efficient, mutable, boxed arrays in Haskell! Unfortunately, I don't have the know-how to fix Ticket 650. Sincerely, Brad

12 30

Broken GHC doc links
by Edward Z. Yang 16 Dec '09

16 Dec '09

Hello, I think the recent GHC 6.12 release broke all of the old links to Haddock documentation; as of writing Hoogle still points to the wrong Haddock docs and stuff like: http://www.haskell.org/ghc/staging/docs/latest/html/libraries/mtl/Control-M… is now 404ing despite being the number one Google result. As the W3C would say, "Cool URLs don't Change". Can we at least setup redirects to the new pages? Thanks, Edward

2 1

Optimizing Parsec 3 -- was: Wiki software?
by Paulo Tanimoto 16 Dec '09

16 Dec '09

Hello! On Mon, Nov 23, 2009 at 12:29 PM, Antoine Latter <aslatter(a)gmail.com> wrote: > On Sun, Nov 22, 2009 at 11:56 AM, Antoine Latter <aslatter(a)gmail.com> wrote: >> >> Running 'pandoc --strict' over the Markdown readme.text takes: >> >> ~0.09s with pandoc built against parsec-2 >> ~0.19s with pandoc built against parsec-3 >> >> on my machine. >> >> I have a branch of parsec-3 which seems to brings us back to parsec-2 >> numbers, but also fails the rst-reader test-case in the pandoc testing >> suite: >> >> http://community.haskell.org/~aslatter/code/parsec/cps > > In reply to my own post, the branch of parsec posted now passes all of > the pandoc test cases. > > If there are any other consumers of the parsec library that have tests > I can run let me know. > > The 'many' combinator is one of those things that can look right, be > wrong, yet work for almost everything. > I finally had some time to test it. After running it multiple times (of course, it would be nice to use criterion here), I'm getting numbers in this neighborhood: $ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.12.0.20091121 $ time pandoc --strict README > /dev/null parsec 2: --- real 0m0.140s user 0m0.130s sys 0m0.010s parsec 3 - antoine's: --- real 0m0.151s user 0m0.150s sys 0m0.010s parsec 3 - hackage: --- real 0m0.243s user 0m0.240s sys 0m0.010s Nice work, Antoine! Paulo

9 14

Design question
by Jeff Wheeler 16 Dec '09

16 Dec '09

On Wed, Dec 16, 2009 at 10:40 AM, haskell(a)kudling.de <haskell(a)kudling.de> wrote: > 1) Is the way i define and use "SubSet", the only/valid way to define > subsets? > > 2) What's the best way to make "doSomethingElse" polymorphic? I'm not very familiar with them, so I'm not sure if it's totally applicable, but generalized algebraic datatypes (GADTs) might be what you're looking for. -- Jeff Wheeler (Sorry, sent this to the author originally.)

1 0

changelogs for packages on Hackage
by Valery V. Vorotyntsev 16 Dec '09

16 Dec '09

It would be nice if Hackage displayed ``recent changes'' of a package. [severity: wishlist] You see, I am subscribed to the ``hackage - recent additions'' feed [http://hackage.haskell.org/packages/archive/recent.rss] and receive entries that look like this: Cabal 1.8.0.2 Added by DuncanCoutts, Wed Dec 16 04:19:24 UTC 2009. A framework for packaging Haskell software This is sweet. But how can I tell what's new in Cabal since 1.6.0.3? (`Cabal' is just an example here.) * * * -- these are snowflakes Dear Santa, This year, I have been a very good boy (in his thirties). I have not pillaged, and I have often helped my children with their homework. And I always say `thank you', which makes me polite and so I deserve lots of presents this year! Please bring this stuff for me and the people in Haskell community. -- vvv

5 5

Difference in Runtime but no explanation
by Johann Höchtl 16 Dec '09

16 Dec '09

Hello, I'm still to Haskell, and after I read through http://users.aber.ac.uk/afc/stricthaskell.html#seq I thought, that these tow fragments after term rewriting are really the same: myLength :: [a] -> Integer myLength xs = len xs 0 where len [] l = l len (x:xs) l = l `seq` len xs (l+1) main = print $ myLength [1..10000000] -- vs. myLength :: [a] -> Integer myLength xs = len xs 0 where len [] l = l len (x:xs) l = len xs $! (l+1) main = print $ myLength [1..10000000] main = print $ myLength [1..10000000] But the first expression evaluates more then twice as fast as the second one. Tested on GHC 6.10.4 and Windows XP, dual core (for what it's worth) It's on http://moonpatio.com/fastcgi/hpaste.fcgi/view?id=5321#a5321 btw. I can't see the difference, especially as $! is expressed in terms of seq

4 9

[ANN] text 0.7, fast Unicode text
by Bryan O'Sullivan 16 Dec '09

16 Dec '09

The new 0.7 release of the text package<http://hackage.haskell.org/package/text>adds support for Unicode I/O, using either the new locale-aware Handle code in 6.12 or a fallback on older releases. Details: http://www.serpentine.com/blog/2009/12/15/data-text-0-7-gains-io-support/

5 10

consulting and contracting
by Tim Newsham 16 Dec '09

16 Dec '09

I was wondering how many haskell consultants and contractors (ie. freelance programmers) there are and how much demand there is for their work. Also what kind of work do most haskell consultants and contractors get? Is it primarily focused around developing and maintaining haskell compilers and tools? Mostly related to academia? Spread out around several areas? Tim Newsham | www.thenewsh.com/~newsham | thenewsh.blogspot.com

6 8

ANN: atom-0.1.4
by Tom Hawkins 16 Dec '09

16 Dec '09

A bug fix affecting floating point variable initialization. http://hackage.haskell.org/package/atom

1 0

Status of Haskell Platform for Snow Leopard
by R J 16 Dec '09

16 Dec '09

Could someone provide the status and expected release date of the Haskell Platform for Snow Leopard (Mac OS X 10.6.2)? Thanks. _________________________________________________________________ Your E-mail and More On-the-Go. Get Windows Live Hotmail Free. http://clk.atdmt.com/GBL/go/171222985/direct/01/

2 1

Token parsers in parsec consume trailing whitespace
by Edward Z. Yang 15 Dec '09

15 Dec '09

I recently ran into a nasty little bug where token parsers in parsec consume trailing whitespace, which were consuming newlines and thus bamboozling a higher-level "sepBy" combinator. I replaced my instances of 'natural' with 'read <$> many1 digit', but this gave rise to the following questions: 1. Is there a more elegant way of doing number parsing? In particular, are there token parsers that don't consume trailing whitespace, or is there a better way to do this with the primitives. 2. It seems that the "token" approach of parsing lends itself to a different style of parsing than the one I'm doing, namely, instead of assuming all of your parsers consume exactly what they need, and no more, you assume that they consume what they need and spaces. Thus, code that looks like: do foo <- fooParser spaces bar <- barParser spaces baz <- bazParser return $ FooBarBaz foo bar baz becomes: FooBarBaz <$> fooParser <*> barParser <*> bazParser And instead of using sepBy you just use many. One of the problems I see with this approach is if I was using sepBy newline, the new token oriented parser has no way of distinguishing "foo bar baz\nfoo bar baz" from "foo bar baz foo bar baz", which is something I might want to care about. Which method do you prefer? 3. Not so much a question as a comment: when parsing entire files, be sure to add the eof combinator at the end! Cheers, Edward

2 2

(semi OT) Fwd: Old math reveals new thinking in children's cognitive development
by Brandon S. Allbery KF8NH 15 Dec '09

15 Dec '09

Begin forwarded message: > Date: December 11, 2009 8:00:00 PM EST > Subject: Old math reveals new thinking in children's cognitive > development > Source: ScienceDaily: Latest Science News > > Five-year-olds can reason about the world from multiple perspectives > simultaneously, according to a new theory by researchers in Japan > and Australia. Using an established branch of mathematics called > Category Theory, the researchers explain why specific reasoning > skills develop in children at certain ages, particularly at age > five. The new theory shows that these reasoning skills have similar > profiles of development because they involve related sorts of > processes. > Read more… > Unexpected applications of category theory for $500, Alex.... -- 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

3 2

Re: [Haskell-cafe] Re: Re: Allowing hyphens in identifiers
by Colin Paul Adams 15 Dec '09

15 Dec '09

>>>>> "Richard" == Richard O'Keefe <ok(a)cs.otago.ac.nz> writes: Richard> The real point is that the revised version, with command Richard> line arguments and all, is still just 52 SLOC. (41 if Richard> you don't count type specifications the compiler could Richard> have inferred or the two import directives.) This looks really good. When I first started writing Haskell seriously, just over a year ago, I wrote with underscores, but the mix of style caused by the standard library names was so disconcerting that IReluctantlySwitchedToHumpyIlliterateStyle (though not for comments, where I stuck to standard English punctuation). So I welcome this chance to switch to natural English style (hyphens). The main that puzzles me at the moment is how to write a cabal file. That is, I can specify the ghc options to invoke the preprocessor in the cabal file, but this supposes the compiled program is available on the system concerned. This won't necessarily be the case if I distribute code written in this style on hackage. So the answer seems to be to release this preprocessor on hackage, and then make it a dependcy. But can a library depend upon an executable program? looking at the Cabal users guide, I can't see anywhere that says it can't. -- Colin Adams Preston Lancashire

1 0

Fwd: [Haskell-cafe] Boxed Mutable Arrays
by Alberto G. Corona 15 Dec '09

15 Dec '09

---------- Forwarded message ---------- From: Alberto G. Corona <agocorona(a)gmail.com> Date: 2009/12/15 Subject: Re: [Haskell-cafe] Boxed Mutable Arrays To: Daniel Peebles <pumpkingod(a)gmail.com> Ok, so the state content is not accessible. Nice. 2009/12/15 Daniel Peebles <pumpkingod(a)gmail.com> No, they are actually being mutated. ST is basically IO with a > universal state thread (IO uses RealWorld) to prevent you from letting > any of the mutable structures out (or any in) of the block. The whole > point of ST is to have real mutable references/arrays that have a > referentially transparent if you look at them from outside. > > Dan > > On Tue, Dec 15, 2009 at 9:23 AM, Alberto G. Corona <agocorona(a)gmail.com> > wrote: > > AFAIK, ST Arrays are pure data structures. They are not really mutable. > They > > are destroyed and recreated on every update. The mutation is just > simulated > > thanks to the hidden state in the state monad. Sure, the garbage > collector > > must have a hard work in recycling all the "backbones" of the discarded > > arrays (not the elements). > > > > 2009/12/14 Brad Larsen <brad.larsen(a)gmail.com> > >> > >> Is anyone working on fixing ticket #650 > >> <http://hackage.haskell.org/trac/ghc/ticket/650>? In short, STArray > >> and the garbage collector don't play well together, resulting in array > >> updates being non-constant time operations. This bug makes it very > >> difficult/impossible to write efficient array algorithms that depend > >> upon mutation in Haskell. > >> > >> On another note, does this (or perhaps better phrased, will this) bug > >> also affect Data Parallel Haskell? > >> > >> I would really like to see highly efficient, mutable, boxed arrays in > >> Haskell! Unfortunately, I don't have the know-how to fix Ticket 650. > >> > >> Sincerely, > >> Brad > >> _______________________________________________ > >> 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

writing graphs with do-notation
by Soenke Hahn 15 Dec '09

15 Dec '09

Hi! Some time ago, i needed to write down graphs in Haskell. I wanted to be able to write them down without to much noise, to make them easily maintainable. I came up with a way to define graphs using monads and the do notation. I thought this might be interesting to someone, so i wrote a small script to illustrate the idea. Here's an example: example :: Graph String example = buildGraph $ do a <- mkNode "A" [] b <- mkNode "B" [a] mkNode "C" [a, b] In this graph there are three nodes identified by ["A", "B", "C"] and three edges ([("A", "B"), ("A", "C"), ("B", "C")]). Think of the variables a and b as outputs of the nodes "A" and "B". Note that each node identifier needs to be mentioned only once. Also the definition of edges (references to other nodes via the outputs) can be checked at compile time. The attachment is a little script that defines a Graph-type (nothing elaborate), the "buildGraph" function and an example graph that is a little more complex than the above. The main function of the script prints the example graph to stdout to be read by dot (or similar). By the way, it is possible to define cyclic graphs using mdo (RecursiveDo). I haven't come across something similar, so i thought, i'd share it. What do you think? Sönke

5 5

ForSyDe (parameterized-data) fails to build
by Dominic Steinitz 15 Dec '09

15 Dec '09

I'm not sure how actively this is maintained or used but I couldn't get it to build. Downloading parameterized-data-0.1.3... Configuring parameterized-data-0.1.3... Preprocessing library parameterized-data-0.1.3... Building parameterized-data-0.1.3... src\Data\Param\FSVec.hs:1:46: Warning: -XPatternSignatures is deprecated: use -XScopedTypeVariables or pragma {-# LANGUAGE Sco pedTypeVariables#-} instead src\Data\Param\FSVec.hs:462:0: warning: no newline at end of file [1 of 2] Compiling Data.Param.FSVec ( src\Data\Param\FSVec.hs, dist\build\Data\Param\FSVec.o ) src\Data\Param\FSVec.hs:103:22: Couldn't match expected type `t -> ExpQ' against inferred type `FSVec s a1' In the expression: (readFSVec str) (lift :: (Nat s, Lift a) => FSVec s a -> ExpQ) In the expression: ((readFSVec str) (lift :: (Nat s, Lift a) => FSVec s a -> ExpQ), undefined) In the definition of `parseFSVecExp': parseFSVecExp str = ((readFSVec str) (lift :: (Nat s, Lift a) => FSVec s a -> ExpQ), undefined) cabal.exe: Error: some packages failed to install: ForSyDe-3.0 depends on parameterized-data-0.1.3 which failed to install. parameterized-data-0.1.3 failed during the building phase. The exception was: exit: ExitFailure 1

1 0

ANNOUNCE: explicit-iomodes-0.1
by Bas van Dijk 15 Dec '09

15 Dec '09

Hello, I just released the small package explicit-iomodes-0.1: http://hackage.haskell.org/package/explicit-iomodes-0.1 It's a wrapper around System.IO that provides a Handle type which is parametrized with the IOMode it is in. All operations on handles specify the needed IOMode which makes it a type error if you read from a write-only handle or if you write to a read-only handle for example. Thanks to Lee Houghton, Brandon S. Allbery and Jason Dagit for providing initial feedback! regards, Bas

1 1

Yay 6.12.1!
by Evan Laforge 15 Dec '09

15 Dec '09

So far, this new release has let me remove: - The new "Import of xyz is redundant" warning pointed out tons of cruft in my imports: 117 of them! Apparently it's better than the 6.10 algorithm. It's amazing how much cruft builds up in import lists over time even with -Wall. One issue is that I can still get a spurious warning from it: if I have 'import qualified Text.Read as Read' and then have some Read instances, it will think the import is redundant even though it won't compile without it (`readPrec' is not a (visible) method of class `Read'). The interesting thing is that even though I'm importing it qualified, I write the readPrec in the instance without qualification since 'instance Read X where Read.readPrec = ...' is not allowed. So maybe ghc is confused by that since it doesn't see a Read. anywhere. Importing unqualified doesn't make the warning. - I removed {-# OPTIONS_GHC -fno-warn-unused-imports #-} from a lot of files, now that the bugs that make spurious import warns are fixed. And the bogus warnings with view patterns are gone. - I removed a local version of Data.Map, now that toDescList is in. - Passing -I/path/to/ghc/include to hsc2hs to get it to include HsFFI.h seems to no longer be necessary. - The warnings "-#include is deprecated: No longer has any effect" are not quite right, because they are reuired by hsc2hs, and in fact hsc2hs is inserting {-# INCLUDE "c_interface.h" #-}. Maybe it should be updated to not do that? I know these are small improvements and not as cool as faster parallelism, but I want so say that these little fixes are noticed and much appreciated, and give a big thank you to the Simons and Ian and anyone else involved with this release. It's so satisfying to finally see a warning free compile!

1 0

Parallel foldl doesn't work correctly
by Philip Beadling 15 Dec '09

15 Dec '09

Hi, Can anyone put me right here. I am trying to use a setup similar to parMap to spark each valuation in a list in parallel, where the resulting (evaluated) list is folded to produce a final single result. Having done the obligatory google, I modified a few common examples to give: pfoldl f acc xs = foldl' f acc (xs `using` parList rwhnf) This compiles and if I monitor my CPUs it starts to use both cores, but after approx 10 seconds, one core drops to low rate (I'm using a 2 core machine). The end result is that -N2 is actually a bit slower than -N1! I'm guessing I haven't grasped the concept properly - although as map is just 'foldl (+) 0' I'm at a loss to see why this approach wouldn't work given it is pretty similar to parMap - could anyone point out what I'm missing? If it's any use the context of the code is below. Many thanks! Phil. mc :: MonteCarloUserData -> [[Double]] -> Double mc userData rndss = existentialResult (pfoldl f existenAvg rndss) $ numOfSims userData where f = flip $ existentialCombine . payOff' . expiryValue payOff' = existentialPayOff userData expiryValue = foldl' (existentialEvolve userData) (stock userData) existenAvg = averager userData

5 8

Re: How Can Haskell Be Saved?
by Richard O'Keefe 15 Dec '09

15 Dec '09

On Dec 14, 2009, at 6:16 AM, John D. Earle wrote: > I am already familiar with SUA and it doesn't make Windows POSIX > complaint in a way that I would call genuine. I grant you that certain aspects of Windows POSIX support have earned it the "DeathStation 9000" label, but it's genuine enough to have earned this claim in the Wikipedia entry for POSIX: "Microsoft Windows Services for UNIX 3.5 – enables >>> full POSIX compliance for certain Microsoft Windows products." I also grant you that the Microsoft POSIX subsystem only supported the 1990 version of POSIX and has been described as "close to useless". But of SUA it has been said "As of 2004, server versions of Windows have a POSIX subsystem that supports threads, signals, sockets, and shared memory, less than twenty years after the standard was finalized, and only a little over a decade after Microsoft began advertising POSIX compliance." > It was something I evaluated. There was no point in your mentioning > that it exists unless you had ulterior motives. "ulterior: being intentionally concealed so as to deceive". Nope. You said that Apple and Microsoft hadn't gone down the POSIX line. I pointed out that current MacOS _is_ a Unix; until today I've relied on Single Unix Specification version 3 documents to guide my Mac programming which makes it close enough for me. Today I downloaded the SUSv4 spec (POSIX 2008). I also pointed out that Windows NT had a fully compliant POSIX subsystem, by design, and that Microsoft cared at least enough about POSIX support to buy the company that made what is now SUA. For that matter, no version of Linux, no version of BSD, and no version of OpenSolaris is certified POSIX-compliant (open source projects change too fast for certification to be cheap). Microsoft can't "go the POSIX route" exclusively without killing their cash cow. VMS was the first POSIX-certified system, but that didn't mean DEC or VMS users abandoning VMS. zOS is POSIX-compliant, but I expect most sites running zOS have no intention of switching, and IBM have no intention of making them. > > It isn't what they are telling you that matters; it is what they are > not telling you. It is called a half truth. If Haskell wants to be > saved, it has got to give up the lying. What on earth is Haskell lying about? What does Haskell need to be saved from? (Its growing popularity and mushrooming library?)

6 11