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Translating perl -> haskell, string "fill ins" with an error on invalid input seems awfully complex. Is there a way to simplify?
by Thomas Hartman 14 Apr '07

14 Apr '07

I was translating some perl code to haskell as a learning exercise and wound up with the following. (below) Simple code that accepts some string arguments, and prints a string -- so, of type String -> String -> String -> String -> IO (). I like to be concise, but I get the feeling something went awry. What seems to be costing me the most is checking whether the various arguments are legitimate, and printing a helpful error message if not. I was able to achieve this by using Maybe and error on failed pattern match, but as said, seems kind of overly complicated. Is there a simpler way to do the following, eg for function gen_gnuplot_financial_script :: String -> String -> String -> String -> IO () ? By the way this is being used in http://code.google.com/p/gnuplotwebinterface/ ************** module Common where gnuplot_png_settings = "set terminal png transparent nocrop enhanced size 600,400\n" ++ "set pm3d implicit at s" gnuplot_math_settings = gnuplot_png_settings ++ "\n" ++ "set border 4095 \n\ \ set xlabel \"x\" \n\ \ set ylabel \"y\"" gnuplot_timeseries_settings = gnuplot_png_settings ++ "\n" ++ "set xdata time # The x axis data is time \n" ++ "set timefmt \"%d-%b-%y\" # The dates in the file look like 10-Jun-04 \n" ++ "set format x \"%b %d\" #On the x-axis, we want tics like Jun 10" gen_gnuplot_math_script :: String -> String -> IO () gen_gnuplot_math_script style function = let maybePlotCmd = lookup style style_to_plotcmd style_to_plotcmd = [("math-2d","plot"),("math-3d","splot")] in case maybePlotCmd of Just plotcmd -> putStrLn $ gnuplot_math_settings ++ "\n" ++ plotcmd ++ " " ++ function _ -> error $ "bad style: " ++ style gen_gnuplot_financial_script :: String -> String -> String -> String -> IO () gen_gnuplot_financial_script company displaymode startDate endDate = let maybeCompanyFile = lookup company company_to_companyfile maybeModeString = lookup displaymode displaymode_to_modestring maybeTitleEnd = lookup displaymode displaymode_to_titleend company_to_companyfile = [("ibm","data/ibm.dat"),("cisco","data/cisco.dat")] displaymode_to_modestring = [("points", "using 1:2 with linespoints"), ("candles","using 1:($2+$3+$4+$5)/4:4:3 with yerrorbars")] displaymode_to_titleend = [("points","daily prices"),("candles","opening prices")] in case ( maybeCompanyFile, maybeModeString, maybeTitleEnd ) of ( Just companyfile, Just modestring, Just titleEnd) -> putStrLn $ gnuplot_timeseries_settings ++ "\n" ++ "plot [\"" ++ startDate ++ "\":\"" ++ endDate ++ "\"]" ++ " '" ++ companyfile ++ "'" ++ modestring ++ " title \"" ++ company ++ " " ++ titleEnd ++ "\"" _ -> error $ "bad lookup. " ++ company ++ " -> company file: " ++ ( show maybeCompanyFile ) ++ "\n" ++ " " ++ displaymode ++ " -> displaymode: " ++ ( show maybeModeString ) ++ "\n" ++ " " ++ displaymode ++ " -> titleEnd: " ++ ( show maybeTitleEnd)

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replacement
by hossein rohani 14 Apr '07

14 Apr '07

Write a function with three parameters, two atoms and a list, (say p1, p2 and L) that returns the list, L, with all occurrences of the first given atom, p1, replaced by the second one, p2. If P2 be nil, the given atom should be deleted and the returned list cannot contain anything in place of it, no matter how deep it occurred in the list. Note: Remember it says that "no matter how deep it occurred in the list.".It means thatwe may have nested list example: replace 1 2 [1 2 3 4] => [2 2 3 4] replace 1 2 [[1 2 3][3 4 5 1]] => [[2 2 3][3 4 5 1]] --------------------------------- Ahhh...imagining that irresistible "new car" smell? Check outnew cars at Yahoo! Autos.

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Type checking with Haskell
by Joel Reymont 14 Apr '07

14 Apr '07

Folks, The ghc/compiler/typecheck directory holds a rather large body of code and quick browsing through did not produce any insight. How do you implement type checking in haskell? Assume I have an Expr type with a constructor per type and functions can take lists of expressions. Do I create a function taking an Expr, pattern-matching on appropriate constructor and returning True on a match and False otherwise? Thanks, Joel -- http://wagerlabs.com/

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generate Haskell code from model
by Steffen Mazanek 14 Apr '07

14 Apr '07

Hello everybody, I would like to start a discussion on how to generate best-practice Haskell code from a model, e.g. from EMF. It seems to be very difficult and unconvenient to simulate OOP with Haskell (as described in the paper "Object-oriented style overloading for Haskell"). However, I think it might be possible to generate "something useful" out of a model to not start from scratch an implementation. For example, I could imagine to generate for every class a module, import and export lists and a type class (with some restrictions) at the very least. In the EMF book there is an example, PurchaseOrder, look at http://www.awprofessional.com/content/images/0131425420/samplechapter/budin… at page 11. How would you like generated code from this model to look like? The most obvious way would be something like this: data PurchaseOrder = PurchaseOrder {shipTo::String, billTo:: String, items::[Item]} data Item = Item {productName::String, quantity::Int, price::Float} This does not work well if function names are reused or inheritance comes into play, however, even this might be a useful starting point (better than nothing). The benefits of the model+generate approach are well known. Best practices in programming are propagated, for Haskell e.g. use different modules for different things, use the tedious import/export lists, Haddock your code... What are your ideas? Best regards, Steffen -- Dipl.-Inform. Steffen Mazanek Institut für Softwaretechnologie Fakultät Informatik Universität der Bundeswehr München 85577 Neubiberg Tel: +49 (0)89 6004-2505 Fax: +49 (0)89 6004-4447 E-Mail: steffen.mazanek(a)unibw.de

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A monad using IO, Reader, Writer, State and Error
by Martin Huschenbett 14 Apr '07

14 Apr '07

Hi all, for my current project I need a monad that is an instance of MonadIO, MonadReader, MonadWriter, MonadState, and MonadError. I see two ways for defining such a monad using the mtl. 1) type MyMonad = ErrorT E (RWST R W S IO) and 2) type MyMonad = RWST R W S (ErrorT E IO) I can't figure out what is the difference between these two definitions and therefore which one is more suitable for my problem. Or are the equivalent and it is unimportant which one I use? Or is it even better define a new type like newtype MyMonad a = MyMonad { runMyMonad :: R -> S -> IO (Either E a,S,W) } and declare instances for all 5 type classes? Thanks for your help in advance, Martin.

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implementing try for RWST ?
by Jeremy Shaw 14 Apr '07

14 Apr '07

Hello, I defined a newtype like this (the ()s will be replace with something more useful in the future): > newtype DryRunIO a = DryRunIO { runDryRunIO :: RWST Bool () () IO a } > deriving (Monad, MonadIO, MonadError IOError, MonadFix, Functor, MonadReader Bool, MonadWriter (), MonadState ()) > > run :: Bool -> DryRunIO a -> IO a > run dryRun action = (runRWST (runDryRunIO action)) dryRun () >>= \ (a, _, _) -> return a and I want to define a function similar to |try| like this: > tryDR :: DryRunIO a -> DryRunIO (Either IOError a) > tryDR m = catchError (m >>= return . Right) (return . Left) unfortunately, when I use it, it does not work the way I want: *Main> run False (tryDR (error "cheese")) *** Exception: cheese This is because 'error' raises an |Exception|, not a |IOError|. I would like to instead define tryDR to deal with exceptions: > newtype DryRunIO a = DryRunIO { runDryRunIO :: RWST Bool () () IO a } > deriving (Monad, MonadIO, MonadError Exception, MonadFix, Functor, MonadReader Bool, MonadWriter (), MonadState ()) > > tryDR :: DryRunIO a -> DryRunIO (Either Exception a) > tryDR m = catchError (m >>= return . Right) (return . Left) But to do this, I need an different instance of MonadError for IO, namely: > instance MonadError Exception IO where > throwError = throwIO > catchError = catch -- (from Control.Exception) However, if I add that to my module I get this error: Functional dependencies conflict between instance declarations: instance MonadError Exception IO -- Defined at /tmp/DR.hs:17:0 instance MonadError IOError IO -- Defined in Control.Monad.Error Where do I go from here? Also, what is the justificiation for the current default of IOError instead of the more general Exception? thanks! j. ps. As a hack I have implemented tryDR as: > tryDR' :: DryRunIO a -> DryRunIO (Either Exception a) > tryDR' (DryRunIO m) = DryRunIO $ RWST $ \r s -> > catch (runRWST m r s >>= \(a, s, w) -> return (Right a, s, w)) -- uses catch from Control.Exception > (\e -> runRWST (return $ Left e) r s) However, I think this is buggy, because changes to 's' and 'w' will be lost if 'm' raises an exception. For example in: > tryDR' (io $ putStr "hello" >> updatePosition (length "hello") >> error "goodbye") The updatedPosition would reflect the position before the tryDR, but the cursor on the screen would be somewhere else. It is my hope that the earlier definition does not have this bug.

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Parsing indentation-based languages with Parsec
by George Pollard 13 Apr '07

13 Apr '07

Hi, first time list poster :) I've searched around a bit but haven't been able to find any examples of this. I want to be able to parse a language (such as Haskell, Python) which has only EOL as the 'statement' separator and has indentation levels to indicate block structure. Whilst doing this I want to use Parsec's nice library. The first thing I noticed was that Parsec's whiteSpace parser will ignore EOL as just whiteSpace, so I need to redefine that. Is this the correct way to do it? I've only been using Haskell for a week or so so I'm not too sure on the record structures and updating them... lexer :: P.TokenParser () lexer = ( P.makeTokenParser emptyDef { commentLine = "#", nestedComments = True, identStart = letter, identLetter = letter, opStart = oneOf "+*/-=", opLetter = oneOf "+*/-=", reservedNames = [], reservedOpNames = [], caseSensitive = False } ) { --update lexer fields P.whiteSpace = do --just gobble spaces many (char ' ') return () } (I got the basic code from the tutorial contained within the Parsec docs.) For handling the indented blocks I thought I would use something to hold current indentation state, as Parsec has support for threading state through all the parsers. Is this the right way to go about this? Has anyone done the 'groundwork' with parsing such languages so I don't need to reinvent this? Thanks in advance, - porges.

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Re: [Haskell-cafe] Compiling GHC
by Chris Witte 13 Apr '07

13 Apr '07

On 4/11/07, Andrew Appleyard <aja(a)cse.unsw.edu.au> wrote: > The source paths for these copies are derived from the path of the > gcc binary ($GccDir). Did you call configure with '--with-gcc=C:/ > Mingw/bin/gcc.exe'? I received those errors when I forgot to do that. Yep that fixed that. Thanks. > I think that 'gettimeofday' is statically linked into the ghc > executable, so it's just that GHCi doesn't know about it. Adding a: > > Sym(gettimeofday) \ > > line to the RTS_MINGW_ONLY_SYMBOLS #define in rts/Linker.c (from line > 265) seemed to fix the problem for me. > > I'm not sure if this is a GHCi bug or something else being awry. > 'gettimeofday' was added to the mingwex library in mingw- > runtime-3.10, which was released in July last year, so I would have > expected this problem to have come up before now... I made this change but I still get the error unknown symbol `_gettimeofday' I'm using mingw 5.1.3 which as far as i can tell should use the 3.11 runtime.

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xmonad window manager mailing list
by dons＠cse.unsw.edu.au 13 Apr '07

13 Apr '07

I'm pleased to announce that the xmonad window manager now has a mailing list set up: http://www.haskell.org/mailman/listinfo/xmonad For those who don't know, xmonad is a tiling window manager written in Haskell. You can find more about it at: http://xmonad.org and Lennart Kolmodin's recent blog post http://lennartkolmodin.blogspot.com/2007/04/xmonad.html Additionally, the lead xmonad developer, Spencer Janssen, has been accepted by PSU to work on XCB bindings to Haskell, for the Google Summer of Code. XCB is a simpler, smaller, threadsafe replacement for Xlib, which should simplify further the window manager code base. We hope to have the 0.1 release of xmonad out shortly, until then, hope to see you on the mailing list! -- Don

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more problems with c2hs
by Ruben Zilibowitz 13 Apr '07

13 Apr '07

Hi, I've built and installed c2hs on my Mac OS X system now. I read through the research paper on c2hs available on the website for c2hs and decided I would need to try it out to learn it. But it gives me errors which I am having trouble trying to understand. Here are the error messages: c2hs file.chs powerpc-apple-darwin8-gcc-4.0.1: c: No such file or directory powerpc-apple-darwin8-gcc-4.0.1: c: No such file or directory powerpc-apple-darwin8-gcc-4.0.1: warning: '-x -x' after last input file has no effect powerpc-apple-darwin8-gcc-4.0.1: no input files c2hs: Error during preprocessing custom header file Can anyone figure out what is going on here? Is it my chs file or is it to do with c2hs? Regards, Ruben

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Re: Why Perl is more learnable than Haskell
by Ryan Dickie 13 Apr '07

13 Apr '07

I thought I could resist this thread but I'll bite =:-() The first language i learned was basic. No real functions, simple step by step instructions. I then learned hypercard, c, c++, python, assembly, vhdl, and too many others! Now i've decided to learn haskell. I view it as a mathematicians language. I do research in the field of medical imaging.. particularly processing large cardiac data sets to figure out characteristics, diseases, etc. Why workflow generally starts out as 1) mathematical idea 2) turn that pure equation into a numerical recipe 3) implement, debug 5) analyze 6) goto step 1. I find doing my thinking in the continous domain makes things a lot easier. But here's where i differ from everyone else. I already have the mathematical relationships all nice and tidy (hopefully!) in my head before i start. I literally just implement it. I don't want to care about threading, IO, message passing, or numerical stability. I have to care about performance but only so far as it hampers my productivity. Preferably the language will do it implicitly. Your average programmer wants a language to do tasks. Having to think about the math and relationships behind it all is rather sickening to them (and me too!). I am a new haskell programmer (basically a week into it!). It is by far the hardest language i've had to pick up. A lot of my code could be structured in a functional way.. but almost all reply on looping techniques (would take a lot of work to rethink my gradient descent method and make it fast!). Regardless of actually using haskell.. i like to transfer these techniques to c++. Before i even knew of haskell i knew some FP methods and i found that using these shrunk my code, shrunk the bugs, and did nice things for performance + concurrency. In fact, I just read a google paper on their batch system. They use to functions: map and reduce. They can easily split it up over their cluster etc... these are the ideas of FP that i like! That and the set-builder notation. I also hate matlab to death. Is there any possibility of using haskell as a replacement using ghci? Mostly i care about linalg when it comes to using matlab. ps: sorry if gmail butchered this reply. I had subscribed to the digest and turns out that was a mistake :D

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c2hs on mac
by Ruben Zilibowitz 12 Apr '07

12 Apr '07

Hi, I am having trouble building c2hs on Mac OS X. I noticed that Darwinports has a port for this, but I'd like to install it without using Darwinports because I already have ghc compiled and installed on my system. Does anyone know how to get c2hs to work on the mac (or why it doesn't work in the first place)? Regards, Ruben

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hackage.haskell.org
by David Waern 12 Apr '07

12 Apr '07

Hi, I'd like to set up a Trac for Haddock on hackage.haskell.org. Who should I contact? /David

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Re: [Haskell-cafe] k-minima in Haskell
by Nicolas Frisby 12 Apr '07

12 Apr '07

[sorry for the double, ajb] Since there seemed to be a disconnect between the expectation and the previous answers, I thought an alternative suggestion might help out. This sort of thing (haha) usually isn't my cup o' tea, so please point out any blunders. RM, is this more like what you had in mind? It leans more towards an iterative approach. If so, I encourage you to compare this to the other solutions and try understand how those solutions rely upon laziness. Stefan and Andrew, feel free to point out the drawbacks to this approach that I'm probably overlooking. kminima n l = map fst (foldr insert' (List.sort pre) suf) where (pre, suf) = (splitAt n . zip [0..]) l -- I think this insertion sort could be -- O(log k) with a better data structure. insert' x [] = [] insert' x (y : ys) | snd x < snd y = x : y : dropLast ys' | otherwise = y : insert' x ys where dropLast ys = take (length ys - 1) ys We grab the first k elements and sort them, this list is our first approximation to the k-minima. We then process the rest of the list, checking if the current element is smaller than any of the minima of the current approximation. If the current element is smaller, we improve the current approximation by inserting the new element and dropping the biggest (i.e. last) minimum from the minima accumulator. The worst behavior is: sort(k) + (n-k) * k comparisons. This could be improved (to: sort(k) + (n-k) * log k comparisons, I think) with a better data structure for the minima approximation. On 4/12/07, ajb(a)spamcop.net <ajb(a)spamcop.net> wrote: > G'day all. > > Quoting raghu vardhan <mrvr84(a)yahoo.co.in>: > > > So, any algorithm that sorts is no good (think of n as huge, and k small). > > The essence of all the answers that you've received is that it doesn't > matter if k is small, sorting is still the most elegant answer in Haskell. > > The reason is that in Haskell, a function which sort function will produce the > sorted > list lazily. If you don't demand the while list, you don't perform > the whole sort. > > Some algorithms are better than others for minimising the amount of > work if not all of the list is demanded, but ideally, producing the > first k elements will take O(n log k + k) time. > > Cheers, > Andrew Bromage > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Re: [Haskell-cafe] Why Perl is more learnable than Haskell
by Dave Feustel 12 Apr '07

12 Apr '07

-----Original Message----- >From: "Mark T.B. Carroll" <mark(a)ixod.org> >Sent: Apr 11, 2007 10:18 AM >To: kynn <kynnjo(a)gmail.com> >Cc: haskell-cafe(a)haskell.org >Subject: Re: [Haskell-cafe] Why Perl is more learnable than Haskell > >Sorry to hear of your struggles. There has been a lot of work lately on >writing Haskell tutorials but there's still a long way to go, >unfortunately, as I discovered when I tried recently to find the >collection of sample code fragments on the wiki that I'm sure are around >somewhere. A serious omission in Haskell tutorials is a collection of examples of how to write Haskell solutions for problems that would use arrays in any imperative language. I see that arrays can be defined in Haskell, but I don't see their use as computationally efficient in Haskell. http://RepublicBroadcasting.org - Because You CAN Handle The Truth! http://iceagenow.com - Because Global Warming Is A Scam!

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Re: [Haskell-cafe] k-minima in Haskell
by raghu vardhan 12 Apr '07

12 Apr '07

And just to remind people, the question is to find the indices and not the numbers themselves. For example on input '3, [10,9,8,..., 3,2,1]' the output must be '[9,8,7]'. ----- Original Message ---- From: Stefan O'Rear <stefanor(a)cox.net> To: raghu vardhan <mrvr84(a)yahoo.co.in> Sent: Wednesday, 11 April, 2007 11:17:15 PM Subject: Re: [Haskell-cafe] k-minima in Haskell On Thu, Apr 12, 2007 at 09:30:22AM +0530, raghu vardhan wrote: > Hmmm. That's not something I was looking for. I'm not sure the > running time is good enough (think of k as being 2 - then you should > not make more than 2n comparisons) - even with lazy evaluation, > quick sort won't have a bound of O(k*n). Muahahahaha! Muahahahahahahahahahaha! Muahaha! Actually it DOES. (this list courtesy of a ghci one-liner) find the 3 minima of [71,71,17,14,16,91,18,71,58,75,65,79,76,18,4,45,87,51,93,36] ============ take 3 (sort [71,71,17,14,16,91,18,71,58,75,65,79,76,18,4,45,87,51,93,36]) vvvvvvvvvvvv take 3 (sort (filter (<71) [71,71,17,14,16,91,18,71,58,75,65,79,76,18,4,45,87,51,93,36]) ++ a bunch of stuff I won't track because it won't be evaluated) vvvvvvvvvvvv (comparisons so far: 20) take 3 (sort [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36]) take 3 (sort (filter (<17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36]) ++ filter (==17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36] ++ sort (filter (>17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36])) vvvvvvvvvvvv (31) take 3 (sort [14, 16, 18, 4] ++ filter (==17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36] ++ sort (filter (>17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36])) take 3 (sort (filter (<14) [14, 16, 18, 4]) ++ sort (filter (==14) [14, 16, 18, 4]) ++ sort (filter (>14) [14, 16, 18, 4]) ++ filter (==17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36] ++ sort (filter (>17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36])) vvvvvvvvvvvv (39) take 3 (sort [4] ++ sort [14] ++ sort (filter (>14) [14, 16, 18, 4]) ++ filter (==17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36] ++ sort (filter (>17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36])) take 3 (4 : 14 : sort (filter (>14) [14, 16, 18, 4]) ++ filter (==17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36] ++ sort (filter (>17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36])) 4 : 14 : take 1 (sort (filter (>14) [14, 16, 18, 4]) ++ filter (==17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36] ++ sort (filter (>17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36])) vvvvvvvvvvvv (43) 4 : 14 : take 1 (sort [16, 18] ++ filter (==17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36] ++ sort (filter (>17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36])) vvvvvvvvvvvv (47) [4, 14, 16] 47 close enough to O(n*k) for you? (remember this is quicksort we are dealing with, O(n^2) worst case) Stefan Send a FREE SMS to your friend's mobile from Yahoo! Messenger. Get it now at http://in.messenger.yahoo.com/

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Haskell Weekly News: April 12, 2007
by dons＠cse.unsw.edu.au 12 Apr '07

12 Apr '07

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20070412 Issue 60 - April 12, 2007 --------------------------------------------------------------------------- Welcome to issue 60 of HWN, a weekly newsletter covering developments in the [1]Haskell community. With the ICFP deadline passed, your Haskell Weekly News returns to its regularly scheduled programming. This week: a truckload of new libraries! 1. http://haskell.org/ Announcements ndp-0.1: nested data parallelism in Haskell. Roman Leshchinskiy [2]announced the first release of [3]the NDP package, a library for writing nested data-parallel programs in Haskell, on shared-memory multiprocessors. The NDP library is part of the Data Parallel Haskell project. The paper [4]Data Parallel Haskell: a status report describes the underlying design and go through an example program. 2. http://article.gmane.org/gmane.comp.lang.haskell.general/15006 3. http://haskell.org/haskellwiki/GHC/Data_Parallel_Haskell 4. http://www.cse.unsw.edu.au/~chak/papers/CLPKM07.html binary 0.3: bigger, better, faster. Lennart Kolmodin [5]announced binary 0.3. The 'binary' package provides efficient serialization of Haskell values to and from lazy ByteStrings. ByteStrings constructed this way may then be written to disk, written to the network, or further processed (e.g. stored in memory directly, or compressed in memory with zlib or bzlib). It's available [6]through Hackage, or via its [7]homepage. 5. http://article.gmane.org/gmane.comp.lang.haskell.general/15044 6. http://hackage.haskell.org/packages/archive/binary/binary-0.3.tar.gz 7. http://www.cse.unsw.edu.au/~dons/binary.html Text.HTML.Chunks. Matthew Sackman [8]announced the [9]Text.HTML.Chunks library, a clone with improvements of the Perl HTML::Chunks module. The main achievement is the use of template-haskell to combine the template into the code at compile time. This then allows for static checking that the variables/fields that the templates are expecting are indeed being provided and that the templates the code is trying to use do indeed exist. The template is then incorporated within the code, removing the dependency on the template. 8. http://article.gmane.org/gmane.comp.lang.haskell.general/15028 9. http://www.wellquite.org/chunks Phooey 1.0 and GuiTV 0.3. Conal Elliott [10]announced a new version of Phooey, a library for functional user interfaces. Highlights in this release: uses new TypeCompose package, which includes a simple implementation of data-driven computation; new Applicative functor interface; eliminated the catch-all Phooey.hs module. Now import any one of Graphics.UI.Phooey.{Monad ,Applicative,Arrow}; Phooey.Monad has two different styles of output widgets, made by owidget and owidget' and more. Phooey is also used in GuiTV, a library for composable interfaces and 'tangible values'. 10. http://article.gmane.org/gmane.comp.lang.haskell.general/15047 The real Monad Transformer. Henning Thielemann [11]announced the real monad transformer! It has been argued that people avoid Haskell because of terms from Category theory like 'Monad'. This problem can now be solved by a wrapper which presents all the internet entirely without monads! Start [12]the parallel Haskell wiki. Of course the tool is written in Haskell, that is, Haskell helps solving problems which only exist because of Haskell. Bug reports and feature requests can be tracked at [13]here. 11. http://article.gmane.org/gmane.comp.lang.haskell.general/15059 12. http://tinyurl.com/2e32r4 13. https://sourceforge.net/projects/parallelweb GHC 6.6.1 Release Candidate. Ian Lynagh [14]announced the Release Candidate phase for GHC 6.6.1. Snapshots beginning with 6.6.20070409 are release candidates for 6.6.1. You can download snapshots from [15]here. 14. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/11964 15. http://www.haskell.org/ghc/dist/stable/dist/ Haskell Cryptographic Library 4.0.3. Dominic Steinitz [16]announced the release of a new version of the Haskell Cryptographic Library based on the [17]crypto proposal. See [18]the crypto home for more details. There is now no dependency on NewBinary. The downside is the library contains no support for ASN.1 which will be released in separate package. 16. http://article.gmane.org/gmane.comp.lang.haskell.libraries/6761 17. http://www.haskell.org/haskellwiki/Crypto_Library_Proposal 18. http://www.haskell.org/crypto/ TagSoup library 0.1. Neil Mitchell [19]announced TagSoup, a library for extracting information out of unstructured HTML code, sometimes known as [20]tag-soup. The HTML does not have to be well formed, or render properly within any particular framework. This library is for situations where the author of the HTML is not cooperating with the person trying to extract the information, but is also not trying to hide the information. The library provides a basic data type for a list of unstructured tags, a parser to convert HTML into this tag type, and useful functions and combinators for finding and extracting information. 19. http://article.gmane.org/gmane.comp.lang.haskell.general/15100 20. http://www-users.cs.york.ac.uk/~ndm/tagsoup/ ParseP library 0.1. Twan van Laarhoven [21]announced a generalized/improved variant of the ReadP parser library. Unlike ReadP ParseP can handle any type of token, and actually generates error messages in case something goes wrong. It is also possible to use things other then a list as an input stream, for example ByteStrings. 21. http://article.gmane.org/gmane.comp.lang.haskell.general/15101 Debian library for Haskell. Jeremy Shaw [22]announced the availability of a library for interacting with the Debian system from Haskell. This library does not (currently) depend on dpkg or apt for any functionality. Contributions are welcome, and the library is available from [23]Hackage. Well-Support Modules: parsing/Printing Debian control files, parsing/printing sources.list files, comparing Debian version numbers, a data type for encoding Debian relations and more. 22. http://article.gmane.org/gmane.comp.lang.haskell.general/15064 23. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/debian-1.2 Call for Contributions: HC and A Report. Andres Loeh [24]mentioned that it is nearly time for the twelfth edition of the [25]Haskell Communities and Activities Report. If you are working on any project that is in some way related to Haskell, write a short entry and submit it. Even if the project is very small or unfinished or you think it is not important enough -- please reconsider and submit an entry anyway! 24. http://article.gmane.org/gmane.comp.lang.haskell.general/15096 25. http://www.haskell.org/communities/ System.FilePath 1.0. Neil Mitchell [26]announced the [27]System.FilePath 1.0 release! The FilePath library is a library for manipulating FilePaths in a cross platform way on both Windows and Unix. [28]Documentation. 26. http://article.gmane.org/gmane.comp.lang.haskell.general/15097 27. http://www-users.cs.york.ac.uk/~ndm/filepath/ 28. http://www.cs.york.ac.uk/fp/haddock/filepath/ FGL - A Functional Graph Library. Martin Erwig [29]announced a new release of [30]the Functional Graph Library for Haskell. This release fixes some bugs in the implementation of several basic inspection functions. 29. http://article.gmane.org/gmane.comp.lang.haskell.general/15052 30. http://eecs.oregonstate.edu/~erwig/fgl/haskell/ TypeCompose 0.0. Conal Elliott [31]announced TypeCompose, which provides some classes and instances for forms of type composition. It also includes a very simple implementation of data-driven computation. 31. http://article.gmane.org/gmane.comp.lang.haskell.general/15046 Haskell SWF generation library. Jeremy Shaw [32]announced the availability of an Adobe Shockwave Flash (SWF) [33]library for Haskell. It is primarily useful for compiling ActionScript assembly into a .swf file. 32. http://article.gmane.org/gmane.comp.lang.haskell.general/15095 33. http://www.n-heptane.com/nhlab/repos/haskell-swf/ New web-devel mailinglist for Haskell. Marc Weber [34]announced a new web-devel mailinglist on haskell.org has been set up. You can subscribe [35]here. 34. http://article.gmane.org/gmane.comp.lang.haskell.general/15045 35. http://www.haskell.org/mailman/listinfo/web-devel strict-0.1: strict versions of Haskell types. Roman Leshchinskiy [36]announced the first release of [37]package 'strict' which provides strict versions of standard Haskell types. At the moment, pairs, Maybe and Either are defined. The library is available [38]from hackage. 36. http://article.gmane.org/gmane.comp.lang.haskell.general/15017 37. http://www.cse.unsw.edu.au/~rl/code/strict.html 38. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/strict-0.1 Chess in Haskell. Steffen Mazanek [39]announced a straightforward implementation of [40]a chess engine in Haskell, available as a tutorial exercise. 39. http://article.gmane.org/gmane.comp.lang.haskell.general/15002 40. http://www.steffen-mazanek.de/blog/2007/02/haskell-chess.html storylen: story word count and categorization. Dino Morelli [41]announced storylen, a [42]command-line utility that counts the words in files and classifies them into story types (short story, novella, novel...). Its operation and output are very similar to the *nix program wc. This is useful for books in plain ascii text. 41. http://article.gmane.org/gmane.comp.lang.haskell.general/15083 42. http://ui3.info/d/proj/storylen.html Haskell' This section covers the [43]Haskell' standardisation process. * [44]Type aliases and Id * [45]Strict bits of datatypes * [46]Literate Haskell specification 43. http://hackage.haskell.org/trac/haskell-prime 44. http://thread.gmane.org/gmane.comp.lang.haskell.prime/2152 45. http://thread.gmane.org/gmane.comp.lang.haskell.prime/2139 46. http://thread.gmane.org/gmane.comp.lang.haskell.prime/2177 Libraries This week's proposals and extensions to the [47]standard libraries. * [48]Reduce base from the top * [49]Make Data.Graph.Inductive.NodeMap handle slightly messy input * [50]ByteString based datagram communication 47. http://haskell.org/haskellwiki/Library_submissions 48. http://article.gmane.org/gmane.comp.lang.haskell.libraries/6716 49. http://article.gmane.org/gmane.comp.lang.haskell.libraries/6727 50. http://article.gmane.org/gmane.comp.lang.haskell.libraries/6559 Discussion Haskell in the real world: building a commercial website in Haskell with WASH. Adam Peacock [51]described how he implemented a commercial website in Haskell, using WASH 51. http://article.gmane.org/gmane.comp.lang.haskell.cafe/21159 Haskell communities worthy of academic study?. Claus Reinke [52]wondered about the software archeology of Haskell. 52. http://article.gmane.org/gmane.comp.lang.haskell.general/15048 Type level programming to eliminate array bound checking in the real world. Vivian McPhail [53]mentioned an attempt to write code that will receive an array from C land and convert it to a type safe representation. 53. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/21314 Conference roundup Commercial Users of Functional Programming. Simon Peyton-Jones [54]announced the call for speakers for this year's [55]CUFP. If you use functional programming as a means, rather than as an end, this message is an invitation for you to offer to give a talk at the workshop. 54. http://article.gmane.org/gmane.comp.lang.haskell.general/14989 55. http://cufp.galois.com/ Jobs One-year INRIA post-doctoral position. Frederic Blanqui [56]announced a one-year INRIA post-doctoral position is available investigating 'Generation of construction functions guaranteeing algebraic invariants on concrete data types' 56. http://article.gmane.org/gmane.comp.lang.haskell.general/15018 Blog noise [57]Haskell news from the blogosphere. * [58]What Programming Languages Should You Know? * [59]Monads in 15 minutes: Backtracking and Maybe * [60]Time to learn a little Haskell... * [61]Say what you mean, mean what you say * [62]Fundamental Ideas of Computing * [63]On Code Generation * [64]Monads in the unix shell * [65]Haskell Eye for the Ruby Guy * [66]2D Mouse Picking with OpenGL and GLUT * [67]Implementing chess in Haskell * [68]Port Scanner in Haskell * [69]Command line arguments in Haskell * [70]IFS In Haskell * [71]Spider Solitaire, Intro * [72]Learning Haskell... * [73]Quick and Dirty Theorem Prover. * [74]Software Transactional Memory for concurrency * [75]Haskell thoughts. * [76]What Haskell teaches us about writing Enterprise-scale software * [77]Unit testing in Haskell * [78]The imaginary concurrency debate: Erlang versus Haskell * [79]On Haskell: Writing a black-list filter using the Writer Monad * [80]A simple file filter * [81]Haskell: an Imperative Language with Mutable State * [82]Pattern matching in Haskell and Ruby * [83]Haskell for C# Programmers 57. http://planet.haskell.org/ 58. http://tinyurl.com/2aczfr 59. http://www.randomhacks.net/articles/2007/03/12/monads-in-15-minutes 60. http://edge-loop.spaces.live.com/Blog/cns!8F028CC27525BEA1!1175.entry 61. http://notes-on-haskell.blogspot.com/2007/03/say-what-you-mean-mean-what-yo… 62. http://notes-on-haskell.blogspot.com/2007/03/fundamental-ideas-of-computing… 63. http://blog.twifkak.com/articles/2007/03/12/on-code-generation 64. http://freeshells.ch/~revence/monads.html 65. http://antoniocangiano.com/articles/2007/03/13/haskell-eye-for-the-ruby-guy 66. http://mad-computer-scientist.com/blog/?p=14 67. http://www.steffen-mazanek.de/blog/2007/02/haskell-chess.html 68. http://tinyurl.com/2fs39r 69. http://leiffrenzel.de/papers/commandline-options-in-haskell.html 70. http://www.alpheccar.org/en/posts/show/69 71. http://partiallyappliedlife.blogspot.com/2007/03/spider-solitaire-intro.html 72. http://a-w-j.blogspot.com/2007/03/learning-haskell.html 73. http://vandreev.wordpress.com/2006/12/24/quick-and-dirty-theorem-prover/ 74. http://mikeburrell.wordpress.com/2007/03/20/software-transactional-memory-f… 75. http://saladwithsteve.com/2007/04/haskell-thoughts.html 76. http://weblog.raganwald.com/2007/04/haskell-not-just-for-language-weenies.h… 77. http://cohatoe.blogspot.com/2007/04/unit-testing-in-haskell.html 78. http://toomuchcode.blogspot.com/2007/04/imaginary-concurrency-debate.html 79. http://austin.youareinferior.net/?q=node/22 80. http://praisecurseandrecurse.blogspot.com/2007/04/haskell-for-short-attenti… 81. http://neilbartlett.name/blog/2007/04/11/haskell-an-imperative-language-wit… 82. http://etorreborre.blogspot.com/2007/04/pattern-matching-with-ruby.html 83. http://themechanicalbride.blogspot.com/2007/04/haskell-for-c-3-programmers.… Quotes of the Week * AdamPeacock: Once I looked at the source code, 25000 lines of ASP, I reckoned it would be easier to rewrite it in a real language. * JesseVincent: Perl's idea of a type system is: 'La-La-La, I don't hear you' * LPhas: [In reference to HAppS.SimpleHTTP] When I first saw the type of 'h' my reaction was to hide under my bed * SvenPanne: Taking away the prelude is a little bit like taking away 'int', 'double', 'for' and 'while' from a C programmer * sjanssen: Threads are fine, its your language that sucks. * thorat: C should only be used to implement something better About the Haskell Weekly News Each week, new editions are posted to [84]the Haskell mailing list as well as to [85]the Haskell Sequence and [86]Planet Haskell. [87]RSS is also available, and headlines appear on [88]haskell.org. Headlines are available as [89]PDF. To help create new editions of this newsletter, please see the [90]contributing information. Send stories to dons at cse.unsw.edu.au. The darcs repository is available at darcs get [91]http://www.cse.unsw.edu.au/~dons/code/hwn 84. http://www.haskell.org/mailman/listinfo/haskell 85. http://sequence.complete.org/ 86. http://planet.haskell.org/ 87. http://sequence.complete.org/node/feed 88. http://haskell.org/ 89. http://www.cse.unsw.edu.au/~dons/code/hwn/archives/20070412.pdf 90. http://haskell.org/haskellwiki/HWN 91. http://www.cse.unsw.edu.au/~dons/code/hwn

1 0

Matlab in Haskell
by oleg＠pobox.com 12 Apr '07

12 Apr '07

Ryan Dickie wrote: > I also hate matlab to death. Is there any possibility of using haskell as a > replacement using ghci? Yes. The strongly typed linear algebra project (Vectro) does exactly that. With an added guarantee that attempting to add or multiply matrices of inappropriate sizes is a type error. Thus typical errors like forgetting to transpose a matrix/vector are reported before the computation starts. The paper shows a few examples, including a larger example of a learning algorithm. http://ofb.net/~frederik/stla/

1 0

Google SoC - student allocations
by Malcolm Wallace 12 Apr '07

12 Apr '07

Although there is still about one hour before Google officially publish the final tally of accepted Summer of Code projects, I think I now can safely reveal the 9 projects chosen for haskell.org, since we have no outstanding conflicts with other mentoring orgs. We received 64 proposals in total. Some students made several proposals. Of those proposals, we wanted to mentor about 22 individual students, but Google only gave us funding for 9, so if you weren't accepted, that doesn't mean your proposal was bad, just that the competition was stiff. Also, the mentors group tended to place language- and community-infrastructure projects at a higher priority than just plain application-oriented libraries. (By the way, several students who applied to haskell.org also applied to other organisations, and may well have been accepted by them instead of us.) So here they are! The list states * project title, * the student who will be funded, * the primary mentor from haskell.org, * and a set of backup mentors who have expressed interest in looking after things too. (These sets may continue to grow.) ----------------------- Darcs Conlict Handling Jason Dagit, David Roundy { Igloo, Patrik Janssen } Hackage Web Interface, Doc-Browser Sascha B?hme, Ross Paterson { Simon Marlow, BryanOS, Bjorn Bringert } Rewrite the typechecker for YHC and nhc98 Mathieu Boespflug, Malcolm Wallace { Neil Mitchell } Cabal Configurations Thomas Schilling, Michael Isaac Jones { Bjorn Bringert, BryanOS, PatrikJ, Simon Marlow, Ross } Update the Hat tracer Kenn Knowles, Malcolm Wallace { PatrikJ, BryanOS } Generalizing Parsec to ParsecT and arbitrary input (ByteStrings) Paolo Martini, Philippa Jane Cowderoy { Don Stewart, Dmitry Astapov, BryanOS, Bjorn Bringert } Shared Libraries for GHC Clemens Fruhwirth, Simon Marlow { BryanOS } HTTP Library Replacement Mieczys?aw B?k, Bryan O'Sullivan { Shae Erisson, Dmitry Astapov, Don Stewart, Bulat Ziganshin, Bjorn Bringert } Extending GuiHaskell: An IDE for Haskell Hackers Asumu Takikawa, Neil David Mitchell { Duncan Coutts, Bulat Ziganshin } ----------------------- Congratulations if you got accepted. Commiserations if you didn't. The official start date of the SoC (when students begin to receive their initial payments) is 28th May. Until then, the students have courses and exams (no doubt), but also (we hope) some time to familiarise themselves with the existing codebase and background of their project. Regards, Malcolm

1 0

Re: [Haskell-cafe] Why Perl is more learnable than Haskell
by David Tolpin 12 Apr '07

12 Apr '07

Hi, I'm guessing you're not doing it the right way. cvs -d :pserver:anoncvs@cvs.davidashen.net:/srv/CVSROOT co SYRENE/src > By using types, you implementation becomes a lot more readable. Being readable is not enough for being readable aloud. And I think a lot of people here will disagree with you... That's good news. I would not bother to express my option if I thought that there would not be a lot of people who would disagree. David

1 0

Weaving fun
by Dominic Steinitz 12 Apr '07

12 Apr '07

I've been dying to do this all day but work and then family intervened. Dominic. import Data.List weave = unfoldr f where f ([],_,_) = Nothing f (x:xs,[],zs) = Just (x,([],[],[])) f (x:xs,ys,zs) = Just (x,(ys,zs,xs))

1 0

Skipping keywords with Parsec
by Joel Reymont 12 Apr '07

12 Apr '07

Is there a way to have any Parsec combinator skip a certain set of keywords? I tried lexeme = P.lexeme lexer . (skip >>) but I don't think lexeme is called for every keyword. Thanks, Joel -- http://wagerlabs.com/

1 1

Re: [Haskell-cafe] Why Perl is more learnable than Haskell
by David Tolpin 12 Apr '07

12 Apr '07

> > If you first language is LISP probably you find easy Haskell and difficult > pearl. Hi, my first programming language is lisp (that is, the language I am most fluent in -- recently Common Lisp, earlier Scheme) and I find Haskell a problematic programming language (this is a fresh experience -- I am writing a syndrome-networks based DSS in Haskell now) because it is not a language. Lisp is a language and Haskell is not, in the sense that lisp allows to write programs that can be read aloud and understood from reading the code. Haskell is a notation that is not a literature by itself, and for Haskell, literate programming, that is, writing more comments than code, is a must; while for lisp it is a rather exotic practice. David

1 0

GHC 6.6 hangs
by Gleb Alexeyev 11 Apr '07

11 Apr '07

Dmitry Antonyuk (lomeo) came up with a piece of code that hung GHC 6.6: newtype Foo a = Foo (Foo a -> a) bar x@(Foo f) = f x baz = bar (Foo bar) See the original discussion (in Russian) at: http://lomeo.livejournal.com/35674.html

2 2

A convenient way to deal with conditional function composition?
by Maxime Henrion 11 Apr '07

11 Apr '07

Hello all, I have found myself writing instances of Show for some types of mine, and I did so by defining the showsPrec function, for performance reasons. I ended up with code that I find quite inelegant. Here's an example: data Move = Move { movePiece :: PieceType, moveFile :: Maybe File, moveTarget :: Square, moveIsCapture :: Bool --movePromotion :: Maybe PieceType } deriving (Eq) instance Show Move where showsPrec _ Move { movePiece = p, moveFile = f, moveTarget = s, moveIsCapture = c } = (if p /= Pawn then shows p else id) . (maybe id shows f) . (if c then ('x':) else id) . shows s I considered writing a conditional composiion combinator to avoid all the 'if foo then f else id' code. Something looking like this: f .? True g = f . g f .? False g = f I'm not sure this is the best approach though, and I would be happy to hear about your suggestions for improving the style of this code, or any other comment that you think is appropriate. Thanks, Maxime

4 5

Profiling makes memory leak go away? Is Haskell a practical language?
by Oren Ben-Kiki 11 Apr '07

11 Apr '07

On Tue, 2007-04-10 at 12:14 +0200, apfelmus wrote: > Oren Ben-Kiki wrote: > > The code is in http://hpaste.org/1314#a1 if anyone at all is willing > > to take pity on me and explain what I'm doing wrong. > > There is an important point to note about streaming, namely that it > conflicts with knowing whether the input is syntactically correct or > not. True, this is the core issue. Think of a turing machine processing an infinite tape. It is writing output and producing a final result; it is possible to examine the output tape before knowing the final result. Haskell parsers insist on having the "output tape" live in memory until the final result is known, and then give it to you as one huge object when done (or discard it and just give you the error message). NOT a good idea if your input tape is a 200 MB file! > You've probably noticed this already and introduced rToken for that > reason but I'm not sure. The idea is that the parser generates a stream of tokens. If/when it hits an error, you get an error token at the end and parsing stops. > > Chasing down my memory leak I got into a weird situation where adding > > a magic manual SCC section and compiling with -prof makes the leak > > disappear. > > That sounds fishy. Note that manual SCC annotations + optimization > currently is a bit buggy in GHC, in the sense that optimization disturbs > correct cost attribution. Er... I just added '-prof'. No '-O' flag at all so no optimizations, right? > Does the program eat the output of yes 'a' without memory explosion > showed by "top"? If so, it could perhaps be a problem of the > optimization phase which maybe expands > > D.append parsed (case result of ...) > > to > > case result of { > Nothing -> D.append parsed D.empty > Just .. -> D.append parsed (D.singleton...) } > > The latter won't stream because of the reason noted above. Ah, but it *does* stream! This is the beauty of lazy evaluation. The "free" code is basically: reply = parse ... -- Lazily evaluated tokens = rTokens reply -- Has some values "immediately" list = D.toList tokens -- Has some values "immediately" mapM_ list print -- Start printing "immediately"! Where what "parse" does is: reply = Reply { rTokens = D.append concreteToken lazyTokens, -- "Immediate" rResult = lazyResult -- Only available at end of parsing } So every time the parser calls "D.append" into the tokens, the printing "D.toList" is able to extract, print and GC the token immediately. And this works perfectly, with constant memory consumption. The problem occurs when I peek at the final "rResult" field. The "leak" code says: reply = parse ... -- Lazily evaluated result = rResult reply -- Lazy; has value when parsing is done extra = case result ... -- Lazy; has value when parsing is done parsed = rTokens reply -- Has some values "immediately" tokens = D.append parsed extra -- Has some values "immediately" list = D.toList tokens -- Has some values "immediately" mapM_ list print -- Starts printing "immediately"! This *still* starts printing tokens immediately. However, while in the previous case the GC is smart enough to keep the program in constant memory size, in the second case it for some reasons starts missing more and more PAP objects so memory usage goes through the roof. > But it's > highly unlikely that GHC performs a transformation that changes > semantics this radically. You'd think... but the fact of the matter is that while the first version works fine, the second doesn't, UNLESS I add the magic SCC section: extra = {-# SCC "magic" #-} case result ... And compile with '-prof' (no '-O' flags). Then it somehow, finally, "get the idea" and the program runs perfectly well with constant memory consumption. Which, as you aptly put it, is very "fishy" indeed... > > I can achieve the results I want in very short elegant code... > > In my opinion, your streaming parser is not as elegant as it could be > which makes it hard to read the code. Well... one point is the above basically establishes two "threads", one printing tokens and one producing them. communicating through a sort of message queue (rTokens). I think that's pretty elegant compared to the hoops you need to jump through to do this in any other language :-) Another point is that this is a dumbed-down toy example. In the real program the parser does much more which justifies the awkwardness you point out. Specifically there are nifty ways to handle decision points (parsing isn't much good unless there are alternatives to be tested at each point :-). > With monad transformers, we almost > have > > Parser a ~= StateT State (WriterT (D.DList Token) Maybe) a > ~= State -> (D.DList Token, Maybe (a,State)) Monad transformers are a bit beyond my grasp at this point, but from the little I know about them I don't see how they would help me with the GC/memory problem. They definitely might make the code even more elegant... > Also, I'm really missing type signatures, especially for many. When > reading the code, I expected > > many :: Parser a -> Parser [a] > > but had to conclude > > many :: Parser a -> Parser () > > by inspecting its code. Sorry about that. Yes, all the "syntax" functions have this signature. I added these as www.hpaste.org/1314#a2. Is it possible I have hit on a bug in GHC's implementation, and adding '-prof' somehow caused it to work around it? Thanks, Oren Ben-Kiki

4 3

What I learned from my first serious attempt low-level Haskell programming
by Stefan O'Rear 11 Apr '07

11 Apr '07

As a learning excersize, I re-wrote and re-optimized Data.Binary.Builder yesterday. 1. Intuition is NOT your friend. Most obvious pessimizations I made were actually wins, and vice versa. 2. Parameters are very expensive. Our type of functions that build (ignoring CPS for the time being) was MBA# -> Int# -> [ByteString], where the Int# is the current write pointer. Adding an extra Int# to cache the size of the array (rather than calling sMBA# each time) slowed the code down ~2x. Conversely, moving the write pointer into the byte array (storing it in bytes 0#, 1#, 2#, and 3#) sped the code by 4x. 3. MBA# is just as fast as Addr#, and garbage collected to boot. 4. You can't keep track of which version of the code is which, what is a regression, and what is an enhancement. Don't even try. Next time I try something like this I will make as much use of darcs as possible. 5. State# threads clog the optimizer quite effectively. Replacing st(n-1)# with realWorld# everywhere I could count on data dependencies to do the same job doubled performance. 6. The inliner is a bit too greedy. Removing the slow-path code from singleton doesn't help because popSingleton is only used once; but if I explicitly {-# NOINLINE popSingleton #-}, the code for singleton itself becomes much smaller, and inlinable (15% perf gain). Plus the new singleton doesn't allocate memory, so I can use even MORE realWorld#s. And probably a few more I forgot about because of #4. The code is online at http://members.cox.net/stefanor/hackedbuilder if anyone cares (but see #4). Some parting numbers: (Builder7 is my current version, Builder1 is the unmodified rossp/kolmodin builder) stefan@stefans:~/hackedbuilder$ ghc -v0 --make -O2 -fforce-recomp -DBUILDER=Builder7 Bench.hs ; time ./Bench 2 10000000 330000000 real 0m5.580s user 0m5.540s sys 0m0.032s stefan@stefans:~/hackedbuilder$ ghc -v0 --make -O2 -fforce-recomp -DBUILDER=Builder7 -DUNROLL Bench.hs ; time ./Bench 2 10000000 330000000 real 0m2.948s user 0m2.908s sys 0m0.036s stefan@stefans:~/hackedbuilder$ ghc -v0 --make -O2 -fforce-recomp -DBUILDER=Builder1 Bench.hs ; time ./Bench 2 10000000 330000000 real 0m55.708s user 0m54.695s sys 0m0.208s stefan@stefans:~/hackedbuilder$ ghc -v0 --make -O2 -fforce-recomp -DBUILDER=Builder1 -DUNROLL Bench.hs ; time ./Bench 2 10000000 330000000 real 0m25.888s user 0m25.546s sys 0m0.156s stefan@stefans:~/hackedbuilder$ gcc -O2 -march=pentium4 CBuilder.c -o CBuilder ; time ./CBuilder 10000000 real 0m0.861s user 0m0.860s sys 0m0.000s Stefam

7 12

Compiling GHC
by Chris Witte 11 Apr '07

11 Apr '07

I'm tying to compile GHC under mingw (winxp with mingw no cygwin), everything appears to go OK but when I run make install it fails to copy some files cp -rp ./../include/* /usr/local/include/mingw cp: cannot stat `./../include/*': No such file or directory make: [install] Error 1 (ignored) cp -rp ./../lib/gcc-lib/mingw32/3.4.2/* /usr/local/gcc-lib cp: cannot stat `./../lib/gcc-lib/mingw32/3.4.2/*': No such file or directory make: [install] Error 1 (ignored) cp -rp ./../lib/gcc/mingw32/3.4.2/* /usr/local/gcc-lib cp: cannot stat `./../lib/gcc/mingw32/3.4.2/*': No such file or directory make: [install] Error 1 (ignored) cp -rp ./../libexec/gcc/mingw32/3.4.2/* /usr/local/gcc-lib cp: cannot stat `./../libexec/gcc/mingw32/3.4.2/*': No such file or directory make: [install] Error 1 (ignored) cp ./../lib/*.* /usr/local/gcc-lib cp: cannot stat `./../lib/*.*': No such file or directory make: [install] Error 1 (ignored) cp ./gcc.exe /usr/local cp: cannot stat `./gcc.exe': No such file or directory make: [install] Error 1 (ignored) cp ./as.exe /usr/local/gcc-lib cp: cannot stat `./as.exe': No such file or directory make: [install] Error 1 (ignored) cp ./ld.exe /usr/local/gcc-lib cp: cannot stat `./ld.exe': No such file or directory make: [install] Error 1 (ignored) cp ./dllwrap.exe /usr/local/gcc-lib cp: cannot stat `./dllwrap.exe': No such file or directory make: [install] Error 1 (ignored) cp ./dlltool.exe /usr/local/gcc-lib cp: cannot stat `./dlltool.exe': No such file or directory make: [install] Error 1 (ignored) cp /c/ghc/ghc-6.6/bin/../perl.exe /usr/local cp /c/ghc/ghc-6.6/bin/../perl56.dll /usr/local for i in ANNOUNCE LICENSE README; do \ /bin/install -c -m 644 $i /usr/local; \ done and then when I try and run, say, GHCi I get $ ghcii.sh ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 6.7.20070323, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Loading package base ... linking ... ghc.exe: unable to load package `base' ghc.exe: C:/msys/1.0/local/HSbase.o: unknown symbol `_gettimeofday' any ideas on what could be causing this. Cheers Chris Witte

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Type error
by Alfonso Acosta 11 Apr '07

11 Apr '07

Hi all, I have a type problem in my code which I dont know how to solve (and I'm not really sure why is caused). I have made a simplified example, can anyone have a look at it? Thanks in advance, The error is: Example.hs:24:47: Ambiguous type variable `a' in the constraint: `HDPrimType a' arising from use of `supplySig' at Example.hs:24:47-55 Probable fix: add a type signature that fixes these type variable(s) Here is the code --- module Example where data HDSignal a = HDSignal class HDPrimType a where class PortIndex a where class SourcePort s where -- Plug an external signal to the port plugSig :: (HDPrimType a, PortIndex ix) => ix -> s -> (HDSignal a -> b) -> b class DestPort d where -- Supply a signal to the port supplySig :: (PortIndex ix, HDPrimType a) => HDSignal a -> ix -> d -> d -- Connect providing indexes connectIx :: (SourcePort s, PortIndex six, DestPort d, PortIndex dix) => six -> s -> dix -> d -> d -- This can seem ugly, -- it would be easier for us having different types for plugSig and supplySig -- but the final user would find it much more difficult to deal with -- supplysig connectIx six s dix d = plugSig six s $ (push2 supplySig) dix d push2 :: (a -> b -> c -> d) -> b -> c -> a -> d push2 f = (\b c a -> f a b c)

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Re: [Haskell-cafe] Weaving fun
by Dave Feustel 11 Apr '07

11 Apr '07

Talk about synchronicity! I was just wondering whether 'weaving' of infinite lists is possible. eg weave the infinite lists [2,4..], [3,6..], [5,10..] to get [2,3,4,5,6,8,9,10,..] Is this kind of lazy evaluation possible? Thanks, Dave Feustel -----Original Message----- >From: Bas van Dijk <v.dijk.bas(a)gmail.com> >Sent: Apr 10, 2007 6:13 PM >To: haskell-cafe(a)haskell.org >Subject: [Haskell-cafe] Weaving fun > >Hello, > >For my own exercise I'm writing a function 'weave' that "weaves" a >list of lists together. For example: > > weave [[1,1,1], [2,2,2], [3,3]] ==> [1,2,3,1,2,3,1,2] > weave [[1,1,1], [2,2], [3,3,3]] ==> [1,2,3,1,2,3,1] > >Note that 'weave' stops when a list is empty. Right now I have: > > weave :: [[a]] -> [a] > weave ll = work ll [] [] > where > work ll = foldr f (\rst acc -> work (reverse rst) [] acc) ll > f [] g = \_ acc -> reverse acc > f (x:xs) g = \rst acc -> g (xs:rst) (x:acc) > >However I find this definition hard to read and I'm questioning its >efficiency especially due to the 'reverse' parts (how do they impact >performance and can they be removed?) > >So I'm wondering if 'weave' can be defined more "elegantly" (better >readable, shorter, more efficient, etc.)? > >happy hacking, > >Bas van Dijk >_______________________________________________ >Haskell-Cafe mailing list >Haskell-Cafe(a)haskell.org >http://www.haskell.org/mailman/listinfo/haskell-cafe http://RepublicBroadcasting.org - Because You CAN Handle The Truth! http://iceagenow.com - Because Global Warming Is A Scam!

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Prettyprinting infix expressions with HughesPJ
by Alfonso Acosta 11 Apr '07

11 Apr '07

Hi all, I have to prettyprint infix expressions writing the least possible parenthesis (taking in account precedence and associativity). A simplified expression type could be: data Expr = Val String | -- Binary operators (using infix constructors) Expr :+: Expr | Expr :-: Expr | Expr :*: Expr | Expr :/: Expr | Expr :^: Expr | -- Unary operators Negate Expr I'm using HughesPJ for the rest of my AST (not just expressions) but the library doesn't provide any mechanism to help coding this kind of prettyprinter so I decided to simply use the standard showsPrec and then feed HughesPJ with the obtained text . showsPrec helps to take advantage of the precedence information. However, I don't find a way to remove parenthesis according to associativity. I'm sure this kind of prettyprinting has been already done zillions of times in Haskell. Any suggestions? Thanks in advance, Alfonso Acosta

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Type checking and locating token with Parsec
by Joel Reymont 11 Apr '07

11 Apr '07

Folks, Imagine a language where Num + Num yields a Num and Str + Num yields a Str but Num + Str should not be allowed. I implemented parsing for such a language in OCaml with a yacc-based parser without an additional type-checking pass, entirely within the yacc grammar. I tried to take such an approach with Parsec but hit the roadblock with buildExpressionParser since it returns the same type as the token parser given to it. Rather than have numerical expressions, string expressions, etc., as separate types, I simplified things down to a single expression type that holds my booleans, strings and numbers. I now need to implement type checking of my parsed AST. The main issue is error reporting. I'm not sure where to get token location with Parsec and how to elegantly embed it in my AST. Has anyone implemented type checking on top of a Parsec-based parser? How did you locate your tokens? Thanks, Joel -- http://wagerlabs.com/

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Re: [Haskell-cafe] Weaving fun
by Dave Feustel 11 Apr '07

11 Apr '07

I ask this question because I want to program a recently published algorithm for directly enumerating all prime numbers. The algorithm description uses infinite sets. The algorithm could possibly be programmed using lazy evaluation. -----Original Message----- >From: Ricardo Herrmann <rherrmann(a)gmail.com> >Sent: Apr 10, 2007 7:24 PM >To: Haskell-Cafe(a)haskell.org >Subject: Re: [Haskell-cafe] Weaving fun > >This reminded me of "interleaving" as in: > >Backtracking, Interleaving, and Terminating Monad Transformers >http://www.cs.rutgers.edu/~ccshan/logicprog/LogicT-icfp2005.pdf > >On 4/10/07, Dave Feustel <dfeustel(a)mindspring.com> wrote: >> >> Talk about synchronicity! I was just wondering whether 'weaving' of >> infinite lists is possible. >> >> eg weave the infinite lists [2,4..], [3,6..], [5,10..] >> to get [2,3,4,5,6,8,9,10,..] >> >> Is this kind of lazy evaluation possible? >> >> Thanks, >> Dave Feustel http://RepublicBroadcasting.org - Because You CAN Handle The Truth! http://iceagenow.com - Because Global Warming Is A Scam!

1 0

operating on a hundred files at once
by Jefferson Heard 10 Apr '07

10 Apr '07

I have a series of NxM numeric tables I'm doing a quick mean/variance/t-test etcetera on. The cell t1 [i,j] corresponds exactly to the cells t2..N [i,j], and so it's perfectly possible to read one item at a time from each of the 100 files and compute the mean/variance etcetera on all cells that way. So what I propose to do is something along the lines of: openAndProcess filename = f <- readFile filename return (map (L.split ',') . lines $ f) main = do fs <- getArgs let items = map (map read) . map openAndProcess fs in do print . map (map $ mean) items print . map (map $ variance) items How close am I to doing the right thing here? As I understand it, this will result in one hundred IO [String] instances being returned by the call to (map openAndProcess $ filenames). Do I need to do something special to lift (read), (mean), and (variance), or even (map) into the IO monad so they can process the input as needed? Thanks in advance, -- Jeff

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Checking for correct invocation of a command line / shell haskell program
by Thomas Hartman 10 Apr '07

10 Apr '07

New wiki page: Checking for correct invocation of a command line haskell program at http://haskell.org/haskellwiki/Checking_for_correct_invocation_of_a_command… This is a simple cookbook / boilerplate example I thought should go in a haskell wiki somewhere. I linked it from http://haskell.org/haskellwiki/Simple_unix_tools Perhaps it could be linked from other places as well. Hope this helps!

1 1

Type level programming to eliminate array bound checking, a real world use
by Vivian McPhail 10 Apr '07

10 Apr '07

Hi All,Inspired by Oleg's "Eliminating Array Bound Checking through Non-dependent types" http://okmij.org/ftp/Haskell/types.html#branding,I am attempting to write code that will receive an array from C land and convert it to a type safe representation. The array could have n dimensions where n > 2. I receive the number of dimensions as a list of Ints [Int]. To do type-safe programming I need to convert this to a type level representation. Using CPS (thanks to ski on #haskell) I can convert an Int to the type level. But I have found it impossible to insert this type-level Digits representation into an HList. In Oleg's examples with vectors he types in by hand the data whose type represents the size of the vector: sample_v = listVec (D2 Sz) [True,False] where (D2 Sz) is the size of the vector and the type is: ArbPrecDecT> :t sample_v Vec (D2 Sz) Bool In a real program we can't expect the programmer to type in the size of the data, it needs to be done programmatically, and this is where I am stuck. Could someone please point me in the right direction, or explain why what I'm trying to do won't work? Basically I'm looking for a function int2typelevel :: (HList l) :: [Int] -> l I thought that this would work because HLists can have elements of different types and I can already (modulo CPS) convert an Int to it's Digits type level representation. One approach which won't work is existentially wrapping the result of num2digits in a GADT, because this hides the type from the type-checker and then can't be used for bounds checking. Here is an example of what I want to be able to do: add :: Equal size1 size2 => Array size1 idx -> Array size2 idx -> Array size1 idx for example: data Array size idx = Array size (MArray idx Double) add (Array (DCons (D1 (D2 Sz)) (DCons (D3 Sz) DNil)) (12,3)) (Array (DCons (D1 (D2 Sz)) (DCons (D3 Sz) DNil)) (12,3)) the sizes are statically checked and I don't have to do runtime checking on the idx. This message is a literate source file. The commented out function at the end illustrates the problem. Thanks, Vivian >{-# OPTIONS -fglasgow-exts #-} > >-- copied from http://okmij.org/ftp/Haskell/number-parameterized-types.html > >module Digits where > >data D0 a = D0 a deriving(Eq,Read,Show) >data D1 a = D1 a deriving(Eq,Read,Show) >data D2 a = D2 a deriving(Eq,Read,Show) >data D3 a = D3 a deriving(Eq,Read,Show) >data D4 a = D4 a deriving(Eq,Read,Show) >data D5 a = D5 a deriving(Eq,Read,Show) >data D6 a = D6 a deriving(Eq,Read,Show) >data D7 a = D7 a deriving(Eq,Read,Show) >data D8 a = D8 a deriving(Eq,Read,Show) >data D9 a = D9 a deriving(Eq,Read,Show) > >class Digits ds where -- class of digit sequences > ds2num:: (Num a) => ds -> a -> a -- CPS style > >data Sz = Sz -- zero size (or the Nil of the sequence) > deriving(Eq,Read,Show) > >instance Digits Sz where > ds2num _ acc = acc > >instance (Digits ds) => Digits (D0 ds) where > ds2num dds acc = ds2num (t22 dds) (10*acc) >instance (Digits ds) => Digits (D1 ds) where > ds2num dds acc = ds2num (t22 dds) (10*acc + 1) >instance (Digits ds) => Digits (D2 ds) where > ds2num dds acc = ds2num (t22 dds) (10*acc + 2) >instance (Digits ds) => Digits (D3 ds) where > ds2num dds acc = ds2num (t22 dds) (10*acc + 3) >instance (Digits ds) => Digits (D4 ds) where > ds2num dds acc = ds2num (t22 dds) (10*acc + 4) >instance (Digits ds) => Digits (D5 ds) where > ds2num dds acc = ds2num (t22 dds) (10*acc + 5) >instance (Digits ds) => Digits (D6 ds) where > ds2num dds acc = ds2num (t22 dds) (10*acc + 6) >instance (Digits ds) => Digits (D7 ds) where > ds2num dds acc = ds2num (t22 dds) (10*acc + 7) >instance (Digits ds) => Digits (D8 ds) where > ds2num dds acc = ds2num (t22 dds) (10*acc + 8) >instance (Digits ds) => Digits (D9 ds) where > ds2num dds acc = ds2num (t22 dds) (10*acc + 9) > >t22::(f x) -> x; t22 = undefined > >-- Class of non-negative numbers >-- This is a restriction on Digits. It is not possible to make >-- such a restriction in SML. >class {- (Digits c) => -} Card c where > c2num:: (Num a) => c -> a > >instance Card Sz where c2num c = ds2num c 0 >--instance (NonZeroDigit d,Digits (d ds)) => Card (Sz (d ds)) where >instance (Digits ds) => Card (D1 ds) where c2num c = ds2num c 0 >instance (Digits ds) => Card (D2 ds) where c2num c = ds2num c 0 >instance (Digits ds) => Card (D3 ds) where c2num c = ds2num c 0 >instance (Digits ds) => Card (D4 ds) where c2num c = ds2num c 0 >instance (Digits ds) => Card (D5 ds) where c2num c = ds2num c 0 >instance (Digits ds) => Card (D6 ds) where c2num c = ds2num c 0 >instance (Digits ds) => Card (D7 ds) where c2num c = ds2num c 0 >instance (Digits ds) => Card (D8 ds) where c2num c = ds2num c 0 >instance (Digits ds) => Card (D9 ds) where c2num c = ds2num c 0 > >-- Support for "generic" cards >-- We introduce a data constructor CardC_unused merely for the sake of >-- Haskell98. With the GHC extension, we can simply omit the data >-- constructor and keep the type CardC purely abstract and phantom. >data CardC c1 c2 = CardC_unused > >cardc:: (Card c1, Card c2) => c1 -> c2 -> CardC c1 c2 >cardc = undefined >cardc1::CardC c1 c2 -> c1; cardc1 = undefined >cardc2::CardC c1 c2 -> c2; cardc2 = undefined > >instance (Card c1, Card c2) => Card (CardC c1 c2) where > c2num c12 = c2num (cardc1 c12) + c2num (cardc2 c12) > >----------------------------------------------------------------------------- >-- make lists > >-- copied from HList: http://okmij.org/ftp/Haskell/types.html#HList > >data DNil = DNil deriving (Eq,Show,Read) >data DCons e l = DCons e l deriving (Eq,Show,Read) > >class DList l >instance DList DNil >instance (Digits e, DList l) => DList (DCons e l) > >dNil :: DNil >dNil = DNil > >dCons :: forall e. Digits e => (DList l => e -> l -> DCons e l) >dCons e l = DCons e l > >-- ^ Oleg >----------------------------------------------------------------------------- >-- v Vivian > >-- CPS >num2digits :: (Integral a, Show a) => a -> (forall ds. (Digits ds) => ds -> o) -> o >num2digits n = str2digits (show n) > >str2digits :: String -> (forall ds. (Digits ds) => ds -> o) -> o >str2digits [] k = k Sz >str2digits ('0' : ss) k = str2digits ss (\ds -> k (D0 ds)) >str2digits ('1' : ss) k = str2digits ss (\ds -> k (D1 ds)) >str2digits ('2' : ss) k = str2digits ss (\ds -> k (D2 ds)) >str2digits ('3' : ss) k = str2digits ss (\ds -> k (D3 ds)) >str2digits ('4' : ss) k = str2digits ss (\ds -> k (D4 ds)) >str2digits ('5' : ss) k = str2digits ss (\ds -> k (D5 ds)) >str2digits ('6' : ss) k = str2digits ss (\ds -> k (D6 ds)) >str2digits ('7' : ss) k = str2digits ss (\ds -> k (D7 ds)) >str2digits ('8' : ss) k = str2digits ss (\ds -> k (D8 ds)) >str2digits ('9' : ss) k = str2digits ss (\ds -> k (D9 ds)) > >----------------------------------------------------------------------------- > >--test = num2str 10 (\x -> dCons x dNil)

1 0

Profiling makes memory leak go away? Is Haskell a practical language?
by Oren Ben-Kiki 10 Apr '07

10 Apr '07

Chasing down my memory leak I got into a weird situation where adding a magic manual SCC section and compiling with -prof makes the leak disappear. Now, I'll take any solution I can find - but this black voodoo only works for the short program I created for investigating the leak. It fails on the real program. Probably not enough fingernails in the voodoo doll or something :-( The code is in http://hpaste.org/1314#a1 if anyone at all is willing to take pity on me and explain what I'm doing wrong. This is the second system I tried writing in Haskell, and in both cases I hit a brick wall due to uncontrollable memory consumption. I'm just about ready to give up on Haskell as a practical language for non-trivial tasks. I can achieve the results I want in very short, elegant code... and as such it will have a place in my toolbox for various small tasks... but I lack the deep lore required to make it behave well for "large" inputs. At this point I have to take it on faith that it is even possible to do so in the first place :-(

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Parsec: Help needed with simple parser
by Joel Reymont 10 Apr '07

10 Apr '07

Folks, I wrote a parser for what should be a simple expression but it's not working. Any help is appreciated! My expression is x + 1 where x can be either "Close", or "Close[N]" or "Close[N] of DataM where N and M are positive integers. What happens in my case is that 1 + x parses fine but x + 1 doesn't. In fact, I would be fine with parsing Close + such that it ignores the plus and returns the parse. Thanks, Joel -- http://wagerlabs.com/

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Re: [Haskell-cafe] operating on a hundred files at once
by Chad Scherrer 10 Apr '07

10 Apr '07

Hi Jeff, > I have a series of NxM numeric tables I'm doing a quick > mean/variance/t-test etcetera on. The cell t1 [i,j] corresponds exactly > to the cells t2..N [i,j], and so it's perfectly possible to read one > item at a time from each of the 100 files and compute the mean/variance > etcetera on all cells that way. So after mapping openAndProcess, you have a 100xNxM "array" (really a list-of-lists-of-lists), right? And then when you take means and variances, which index are you doing this with respect to? As I read it, you seem to be trying to eliminate the first axis, and end up with an NxM "array". If this is the case, let's say we have mean, variance :: [Double] -> Double openAndProcess :: String -> IO (Matrix String) Here, defining type Matrix a = [[a]] makes it easier to keep the types straight. Then you have these building blocks: (map . map . map) read :: [Matrix String] -> [Matrix Double] transpose2 :: [Matrix Double] -> Matrix [Double] (a couple of lines, maybe even a one-liner, if you use that [a] is a monad) (map . map) mean :: Matrix [Double] -> Matrix Double Composing these gives a function [Matrix String] -> Matrix Double, so once we get to [Matrix String], we're effectively done. you also use map OpenAndProcess :: [String] -> [IO (Matrix String)] You can use sequence to get the IO outside the list, so now you have IO [Matrix String]. All you have to do now is use liftM on your function [Matrix String] -> Matrix Double, which turns it into a function IO [Matrix String] -> IO (Matrix Double). -- Chad Scherrer "Time flies like an arrow; fruit flies like a banana" -- Groucho Marx

1 0

Parsec: buildExpressionParser of a different type than parsed term
by Joel Reymont 10 Apr '07

10 Apr '07

Folks, I'm trying to parse NumExpr > NumExpr (example) which should return a logical expression while parsing numeric terms. I can't figure out how to make buildExpressionParser do this for me since it takes the type of the term parser given to it. If I supply a parser for numeric terms then I cannot return a logical expression. How can this be resolved? Note that I do not want to put all expressions into the same Expr type since it makes generating valid random ASTs with QuickCheck impossible. Thanks, Joel -- http://wagerlabs.com/

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[Beginner's Question] How to read filenames from a DirStream
by Albert Lee 10 Apr '07

10 Apr '07

Newbie's question: I want to ls the filenames of a directory. The program in C is something like: #include <direnet.h> int main(){ DIR *dp; struct dirent *dirp; dp = opendir("/"); while((dirp = readdir(dp)) != NULL) printf("%s\n", dirp->d_name); closedir(dp); } and I write that in haskell: ----- import System.Posix import System.IO main = do dp <- openDirStream "/" df <- readDirStream dp putStrLn df closeDirStream dp ------ It can print the first entry of the dir, but how can we list it all like the C prog? map ? list comperhension?

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runInteractiveCommand
by Sergey Perminov 10 Apr '07

10 Apr '07

I wished to get output of unix commands in haskell code. So i wrote: ---------------------------------------------------------------------------------- import System.IO import System.Process eval :: String -> IO String eval s = do (_,hOutput,_,hProcess) <- runInteractiveCommand s sOutput <- hGetContents hOutput waitForProcess hProcess return sOutput ---------------------------------------------------------------------------------- 'eval' works well if output of evaluated command is less than 64Kb. If not - 'eval' never ends. What may cause this problem? Is it possible to use 'runInteractiveCommand' when command's output size is longer than 64Kb? -- Best regards, Sergey Perminov

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Re: [Haskell-cafe] runInteractiveCommand
by Dave Feustel 09 Apr '07

09 Apr '07

I tried the code below with both ghc 6.2.2 and hugs march 2005. ghc: "The last statement in a 'do' construct must be an expression" Hugs ERROR "interactive.hs" - Can't find imported module "System.Process" . >---------------------------------------------------------------------------------- >import System.IO >import System.Process > >eval :: String -> IO String >eval s = do (_,hOutput,_,hProcess) <- runInteractiveCommand s > sOutput <- hGetContents hOutput > waitForProcess hProcess > return sOutput >---------------------------------------------------------------------------------- http://RepublicBroadcasting.org - Because You CAN Handle The Truth! http://iceagenow.com - Because Global Warming Is A Scam!

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Re: Fwd: Yi pre-release
by Dominic Steinitz 09 Apr '07

09 Apr '07

JP, I deleted the lot and re-installed. make emacs then worked. Three things. 1. ~/usr/bin isn't on my path. Clearly I can fix. 2. Where should YiConfig.hs live? I know it's in examples but I don't want to copy it into every directory. > dom@heisenberg:~> ~/usr/bin/yi test.hs > > <command line>: > Could not find module `YiConfig': > Use -v to see a list of the files searched for. > error: YiConfig not loaded > > > * "*messages*" L5 C0 100% > > > - "test.hs" L1 C0 0% > error: YiConfig not loaded > dom@heisenberg:~> ls yi/yi/examples/ -ltr > total 24 > -rw-r--r-- 1 dom users 367 2007-04-09 07:17 YiConfig.hs > -rw-r--r-- 1 dom users 1148 2007-04-09 07:17 DynamicReconf.hs > -rw-r--r-- 1 dom users 276 2007-04-09 07:17 HaskellVim.hs 3. Even when YiConfig.hs is there, I get the following error and can't do any editing > dom@heisenberg:~/yi/yi/examples> ~/usr/bin/yi test.hs > > > User configuration finished. > error: Keymap not defined, type 'q' to quit. README file may help you. Dominic.

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Fwd: [Haskell-cafe] Yi pre-release
by Dominic Steinitz 09 Apr '07

09 Apr '07

> dom@heisenberg:~/yi/yi> make > ghc --make Setup.*hs -o setup > [1 of 1] Compiling Main ( Setup.hs, Setup.o ) > Linking setup ... > ./setup configure --user --with-haddock=/home/dom/usr//bin/haddock > --prefix=/home/dom/usr/ --datadir=--prefix=/home/dom/usr/ > --disable-haddock-use-packages > --haddock-args="--read-interface=http://haskell.org/ghc/docs/latest/html/li >braries/base,/home/jp/haskell/ghc/libraries/base/base.haddock > --read-interface=http://haskell.org/ghc/docs/latest/html/libraries/QuickChe >ck,/home/jp/haskell/ghc/libraries/QuickCheck/QuickCheck.haddock > --source-module=%{MODULE}.hs.html --source-entity=%{FILE///.}.html#%{NAME} > --comments-base=http://haskell.org/haskellwiki/Talk:yi/Library > --comments-module=http://haskell.org/haskellwiki/Talk:yi/Library/%{MODULE/. >//}" configure: searching for ghc in path. > configure: Using alex: /usr/local/bin/alex > /usr/lib/gcc/i586-suse-linux/4.1.2/../../../../i586-suse-linux/bin/ld: > cannot find -lreadline collect2: ld returned 1 exit status > make: *** [build] Error 1 So make finds alex but make emacs doesn't. > dom@heisenberg:~/yi/yi> make emacs > make -C packages/yi-vty install > make[1]: Entering directory `/home/dom/yi/yi/packages/yi-vty' > ./setup build --with-ghc=/usr/bin/ghc > Preprocessing library yi-vty-0.2... > setup: ../../Yi/Syntax/Haskell.x: no alex preprocessor available > make[1]: *** [build] Error 1 > make[1]: Leaving directory `/home/dom/yi/yi/packages/yi-vty' > make: *** [yi-vty] Error 2 Dominic.

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Fwd: [Haskell-cafe] Yi pre-release
by Dominic Steinitz 09 Apr '07

09 Apr '07

---------- Forwarded Message ---------- > setup: Unrecognised flags: --disable-haddock-use-packages > make[1]: *** [.setup-config] Error 1 > make[1]: Leaving directory `/home/dom/yi/yi/packages/yi-vty' ------------------------------------------------------- > dom@heisenberg:~/yi/yi> make emacs > make -C packages/yi-vty install > make[1]: Entering directory `/home/dom/yi/yi/packages/yi-vty' > ./setup build --with-ghc=/usr/bin/ghc > Preprocessing library yi-vty-0.2... > setup: ../../Yi/Syntax/Haskell.x: no alex preprocessor available > make[1]: *** [build] Error 1 > make[1]: Leaving directory `/home/dom/yi/yi/packages/yi-vty' > make: *** [yi-vty] Error 2 JP, I assume this is the sort of feedback you want? Dominic.

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Stubborn memory leak
by Oren Ben-Kiki 09 Apr '07

09 Apr '07

I've minimized my problem to a short test program I pasted at http://hpaste.org/1314 The problem seems to be in forcing strict evaluation at just the right place, but all my attempts in doing so have causes the program to stop streaming and start consuming memory again - this time in un-emitted tokens. Any help would be appreciated, Oren.

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Yi pre-release
by Dominic Steinitz 09 Apr '07

09 Apr '07

> setup: Unrecognised flags: --disable-haddock-use-packages > make[1]: *** [.setup-config] Error 1 > make[1]: Leaving directory `/home/dom/yi/yi/packages/yi-vty'

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Yi pre-release
by Jean-Philippe Bernardy 09 Apr '07

09 Apr '07

Hello folks, More that two years after the 0.1.0 release, I would like to attract people's attention to recent developments on the Yi editor. This preview release is an attempt to gather more users, testers and hopefully contributors for an upcoming "stable" release. Yi is a text editor written and extensible in Haskell. The goal of Yi is to provide a flexible, powerful and correct editor core dynamically scriptable in Haskell. * Yi is an haskell interpreter. Much like emacs is a Lisp interpreter, Yi is an haskell interpreter. This is implemented by binding to the GHC API. This permits hacking of the editor behaviour at runtime. Tools and goodies written in haskell are also readily available from the editor. * Frontends. Yi can use either gtk2hs or vty as frontends, so users can choose their favourite interface. * "Emulation modes". The primary emulation modes for Yi are vi and emacs. Keybindings for vim, mg and nano and other are also provided. Other editor interfaces can be written by the user to extend Yi. More information is available on: http://haskell.org/haskellwiki/Yi Darcs repo: http://www.cse.unsw.edu.au/~dons/yi/ Yi homepage: http://www.cse.unsw.edu.au/~dons/yi.html Patches, comments, criticism welcome... as always! -- Jean-Philippe Bernardy

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Function call by string
by Philipp Volgger 09 Apr '07

09 Apr '07

Hello everybody! Can me somebody say how I can call a function by string? Thus I want to have a function that has as argument a string (name of a function to call) and then tries to call that function, a kind of: functionCall :: String -> [String] -> RetVal functionCall functionName arguments = ... Thanks

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