- Haskell-Cafe - Haskell.org

ANNOUNCE: Vintage BASIC 1.0
by Lyle Kopnicky 13 Mar '09

13 Mar '09

I am pleased to announce the initial release of Vintage BASIC, an interpreter for microcomputer-era BASIC. Fully unit-tested, it faithfully implements the common elements of the language. On the web site, you can find 102 games from the classic book BASIC Computer Games, all of which run flawlessly. Have fun! This is a standalone interpreter, operating on text files. Although not an embedding, like Lennart Augustsson's clever implementation, it does use a custom BASIC monad in order to execute the code. A unique feature of this implementation is that control structures such as FOR are implemented using resumable exceptions: FOR is a handler and NEXT throws an exception. A Developer's Guide is included with the source. This is my first public release of open source software. I have been working on this project since 2003. Home page: http://www.vintage-basic.net Also available on Hackage<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/vintage-basic>and patch-tag.com <http://patch-tag.com/repo/vintage-basic/home>. Please e-mail me at lyle(a)vintage-basic.net with any questions/comments. - Lyle

2 1

Distributing Linux binaries
by Lyle Kopnicky 13 Mar '09

13 Mar '09

Hi folks, I've got an application to release. I'm releasing the source, but I also wanted to release binary versions for people that don't have GHC. I developed on Windows, so making a Windows executable was simple. I also have access to an Ubuntu Linux box, on which I can easily build and test my app. But, I'm a bit confused about how to release binaries for Linux. It's not so simple as on Windows. Or, maybe it is but I don't know it. What do people recommend as a way of distributing Linux binaries? I tried to make a Debian package and couldn't figure it out, but maybe that's overkill. GHC itself has some kind of tarball for the binary distributions, one for Debian and one for Red Hat. How would I make such a package and what would go into it? There's only one executable, so it shouldn't be too complicated. I figure the main issue on Linux is that when you compile it, it's linked to specific shared libraries. Don't have a Mac myself but I'm happy to have Mac folks submit binaries. I'll worry about that later. - Lyle

6 8

Natural Numbers: Best implementation?
by Mark Spezzano 13 Mar '09

13 Mar '09

Hi, I was wondering what the best way to implement Natural number would be. Is there a package which already does this? Here are some options: 1. Don’t bother. Just use Integer. 2. Use the type data Natural = Zero | Succ !Natural 3. Use the following definition taken from the Gentle Introduction to Haskell 98 newtype Natural = MakeNatural Integer toNatural ::Integer-> Integer toNatural x | x < 0 = error “Can’t create negative naturals!” | otherwise = MakeNatural x fromNatural :: Natural -> Integer fromNatural (MakeNatural i) = i and then... instance Num Natural where fromInteger = toNAtural x + y = toNatural (fromNatural x + fromNatural y) x – y = etc.. x * y = etc... Which method is best? So far, I’ve been picking option #1 – just leaving things as they are and using Integer to keep things simple. I’ve got that feeling that [2] would be fast and [3] would be slow. Comment appreciated on the merits of each. Cheers, Mark Spezzano No virus found in this outgoing message. Checked by AVG. Version: 7.5.557 / Virus Database: 270.11.12/1998 - Release Date: 12/03/2009 6:23 PM

1 0

Combining haddock documentation from multiple packages
by Heikki Aitakangas 13 Mar '09

13 Mar '09

Is it possible to generate a "unified" documentation tree similar to http://www.haskell.org/ghc/docs/latest/html/libraries/index.html from packages installed via cabal from hackage? And if so, how does one go about doing it? -- Heikki Aitakangas

1 0

Using a monad to decompose a function into functions
by Marcin Kosiba 13 Mar '09

13 Mar '09

Hi, I'm doing a bit of research into mobility models and I'm currently exploring implementation language choices for the simulator (yes, sadly it needs to be a custom one). I've been using Haskell here and there for some small tasks, and thought I should consider it as an implementation language for the simulator. While I already have an working implementation in Haskell, there is one thing that I would like to express in a more elegant way, but just can't figure out. The simulation algorithm requires expressing the node's mobility so that it is "stateless". The mobility model algorithm's type should be something like: mobility_model :: WorldState -> NodeState -> OtherInput -> (Action, NodeState) where Action can alter WorldState and the second NodeState is an altered input NodeState. I perform a form of speculative execution on mobility_model so sometimes I need to backtrack to a previous world and node state. This is all fairly simple stuff, and was just an introduction. What I do now is store an enum in NodeState and implement mobility_model as one big case statement. Yes, this is very imperative of me, I know. What I'd like to do is to express mobility_model, so that the code would look like: mobility_model world node input = do do_calculus emit_action if something then emit_action else emit_action do_calculus emit_action mobility_model world node input but I'd like to be able to alter world and node state before continuing from emit_action. I've tried to get this working by using the idea from http://www.haskell.org/pipermail/haskell/2005-April/015684.html but couldn't get the state-altering behavior I was looking for. I've also taken a look at http://monadicheadaches.blogspot.com/2008/01/python-25s-iterators-in-haskel…, the unified concurrency model and Control.Coroutine, but couldn't get the behavior I was going for. Thanks! Marcin Kosiba

2 1

DSLs with {in,}equalities
by Andrew Hunter 13 Mar '09

13 Mar '09

Several times now I've had to define an EDSL for working with (vaguely) numeric expressions. For stuff like 2*X+Y, this is easy, looking pretty much like: > data Expr = Const Integer | Plus Expr Expr | Times Expr Expr > > instance Num Expr where > fromInterger = Const > (+) = Plus > (*) = Times &c. This lets me get a perfectly nice AST, which is what I want. When I want to be able to express and work with inequalities and equalities, this breaks. Suppose I want to write 2*X + Y < 3. I either have to: a) Hide Prelude.(<) and define a simple < that builds the AST term I want. b) Come up with a new symbol for it that doesn't look totally awful. Neither of these work decently well. Hiding Eq and Ord operators, which is what I effectively have to do for a), is pretty much a nonstarter--we'll have to use them too much for that to be practical. On the other hand, b) works...but is about as ugly as it gets. We have lots and lots of symbols that are already taken for important purposes that are syntactically "near" <,<=,==, and the like: << and >> and >>= for monads, >>> for arrows, etc. There...are not good choices that I know of for the symbols that don't defeat the purpose of making a nice clean EDSL for expressions; I might as well use 3*X + Y `lessthan` 3, which is just not cool. Does anyone know of a good solution, here? Are there good substitutions for all the six operators that are important (<,>,>=,<=,==,/=), that are close enough to be pretty-looking but not used for other important modules? Better yet, though a little harder, is there a nice type trick I'm not thinking of? This works for Num methods but not for Ord methods because: (+) :: (Num a) => a -> a -> a (<) :: (Ord a) => a -> a -> Bool i.e. the return type of comparisons is totally fixed. I don't suppose there's a good way to...well, I don't know what the *right* answer is, but maybe define a new typeclass with a more flexible type for < that lets both standard types return Bool and my expressions return Expr? Any good solution would be appreciated. Thanks, AHH

8 10

Hand calculation of Bird's definition of zip using foldr
by R J 13 Mar '09

13 Mar '09

Can someone provide a complete hand calculation of zip [1,2,3] [4,5,6] using the following definition of zip, based on foldr: zip :: [a] -> [b] -> [(a, b)] zip = foldr f e where e ys = [] f x g [ ] = [] f x g (y : ys) = (x , y) : g ys foldr :: (a -> b -> b) -> b -> ([a] -> b) foldr _ e [] = e foldr f e (x : xs) = f x (foldr f e xs) This implementation of zip produces the expected result [(1, 4), (2, 5), (3, 6)], but I'm unable to do the hand calculation and don't understand why it works. Part of my problem is that "e" is defined as a function that takes one argument, I don't see how that fits in with the usual scheme for foldr, which, as I understand it, is: foldr f e [x1, x2, ...] = f x1 (f x2 (f x3 ...(f xn e)))... Thanks, as always, to all in this great community. _________________________________________________________________ Windows Live™: Life without walls. http://windowslive.com/explore?ocid=TXT_TAGLM_WL_allup_1a_explore_032009

3 2

Re: [Haskell-cafe] ThreadScope: Request for features for the performance tuning of parallel and concurrent Haskell programs
by Don Stewart 13 Mar '09

13 Mar '09

karel.gardas: > Don Stewart wrote: > > marlowsd: > >> Ben Lippmeier wrote: > >> > >>> On 12/03/2009, at 12:24 AM, Satnam Singh wrote: > >>>> Before making the release I thought it would be an idea to ask people > >>>> what other features people would find useful or performance tuning. > >>>> So if you have any suggestions please do let us know! > >>>> > >>> Is it available in a branch somewhere to try out? > >> There are three parts to it: > >> > >> - some patches to GHC to generate the log files. The patches are > >> not yet in, but I hope to get them in in the next couple of weeks. > > > > Just as a meta-point, it makes a *lot* of sense for the runtime to > > support proper logging -- it's practically a microkernel after all, so > > logging makes as much sense for GHC's rts as it does for regular > > kernels. > > > > Now we just need a /proc for the rts, so I can peek at GC stats live. > > Seeing this thread and discussion direction I cannot resist to > temptation to ask: is anybody going to write rts DTrace[1] provider? I think this is clear next step in the investigations. -- Don

1 0

Re: [Haskell-cafe] Dynamically typing TH.Exp at runtime
by Martin Hofmann 13 Mar '09

13 Mar '09

This is what hint does, isn't it? However, this still leaves it to me to infer what type [|a|] in [| reverse (a:b:[]) = (b:a:[]) |] is. Thanks a lot anyway. Martin On Thu, 2009-03-12 at 12:59 -0200, Daniel Gorín wrote: > would using ghc-as-a-library to type (strings with) haskell > expressions at runtime help? > > On Mar 12, 2009, at 12:37 PM, Martin Hofmann wrote: > > > I am doing meta-programming at runtime. So my program gets a full > > Haskell declaration in expression quotation ([d|...|]) modifies it and > > returns the modified expression. Therefore, I need type information of > > this expression, and any subexpression, at _runtime_ ! For example: > > > > [d| reverse x1 = y1 |] > > > > - rewrites_to -> > > > > [d| reverse x2:xs = y2:ys |] > > > > - rewrites_to -> > > > > [d| reverse x:xs = reverse xs ++ [x] |] > > > > reverse :: [a] -> [a] implies > > x2,y2 :: a > > x1,y1,xs,ys :: [a] > > > > TH.reify is not applicable, because I need the information at runtime > > and I am in IO. I suppose Data.Dynamic does not work either, because > > [| > > xs|] :: ExpQ and not [a]. > > > > So it looks like I need my own type checker and inference and tag each > > subexpression with its type. If so, I can even omit TH and use my own > > data type for the abstract syntax tree. This annoys me a bit, because > > for me it seems that all I need is already there. > > > > Did anybody have similar problems, because I shouldn't be the only one > > doing dynamic typing in a static language? Is there a Haskell > > implementation of the paper "Typing Dynamic Typing" by Baars and > > Swierstra (http://people.cs.uu.nl/arthurb/dynamic.html ), so I can try > > out if this helps me? > > > > Any help, comments, and how-to-suggestions are highly welcome. > > > > Thanks a lot, > > > > Martin > > > > > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe

1 0

Data.Binary patches?
by Denis Bueno 13 Mar '09

13 Mar '09

I've got a small patch for Data.Binary. Should I post it here, or is there some more appropriate forum? http://code.haskell.org/binary/ doesn't specify. Thanks, Denis

3 3

"The Curse of Our Times" in different languages
by Jamie 13 Mar '09

13 Mar '09

See Black-Scholes model/option formula being implemented in different languages including Haskell. http://www.espenhaug.com/black_scholes.html Jamie

1 0

ThreadScope: Request for features for the performance tuning of parallel and concurrent Haskell programs
by Satnam Singh 13 Mar '09

13 Mar '09

Donnie Jones, Simon Marlow and I have been working on infrastructure for logging run-time events and a graphical viewer program called ThreadScope. Hopefully these features will make it into the next release of GHC. We hope the event-log viewer ThreadScope will be useful for the performance tuning of parallel and concurrent Haskell programs. You can see a few screen shots at the program's website http://raintown.org/threadscope Before making the release I thought it would be an idea to ask people what other features people would find useful or performance tuning. So if you have any suggestions please do let us know! Cheers, Satnam Singh ________________________________ Satnam Singh Microsoft 7 JJ Thomson Avenue Cambridge CB3 0FB United Kingdom Email: satnams(a)microsoft.com<mailto:satnams@microsoft.com> UK tel: +44 1223 479905 Fax: +44 1223 479 999 UK mobile: +44 7979 648412 USA cell: 206 330 1580 USA tel: 206 219 9024 URL: http://research.microsoft.com/~satnams Live Messenger: satnam(a)raintown.org<mailto:satnam@raintown.org>

4 3

monadic logo
by Gregg Reynolds 13 Mar '09

13 Mar '09

At risk of becoming the most hated man in all Haskelldom, I'd like to suggest that the Haskell logo not use lambda symbols. Or at least not as the central element. Sorry, I know I'm late to the party, but the thing is there is nothing distinctive about lambda; it's common to all FPLs. Besides, Lisp/Scheme already have that franchise. What is distinctive about Haskell it's use of the monad. The Pythagorean monad symbol is wonderfully simple: http://en.wikipedia.org/wiki/Monad_(Greek_philosophy)<http://en.wikipedia.org/wiki/Monad_%28Greek_philosophy%29>. Something might also be done with the triad to reflect the fact that the monad in cat theory is actually a triple ( http://en.wikipedia.org/wiki/Triad_(Greek_philosophy)<http://en.wikipedia.org/wiki/Triad_%28Greek_philosophy%29> ). The "Cup or Monad" (http://www.sacred-texts.com/chr/herm/hermes4.htm) with a little bit of work, could be turned into an amusing Haskell manifesto. Lots of interesting imagery from the gnostic tradition ( http://www.sacred-texts.com/gno/th2/index.htm) although SICP seems already to have used something similar ( http://mitpress.mit.edu/images/products/books/0262011530-f30.jpg) Hermes Trismegistus = Thrice-great Hermes -> Haskell Trismegistus, Thrice-Glorious Haskell, etc. Might be too cute. There's also Leibniz' monadology - I can't think of any visual imagery to go with it, but he did end up with the "best of all possible worlds" hypothesis, which gives us a slogan sure to irritate: "Haskell - the best of all possible languages". Not to mention "Haskell Monadology" as a name for the official Haskell definition, etc. Hey, at least it isn't cute. -gregg

3 2

Dynamically typing TH.Exp at runtime
by Martin Hofmann 12 Mar '09

12 Mar '09

I am doing meta-programming at runtime. So my program gets a full Haskell declaration in expression quotation ([d|...|]) modifies it and returns the modified expression. Therefore, I need type information of this expression, and any subexpression, at _runtime_ ! For example: [d| reverse x1 = y1 |] - rewrites_to -> [d| reverse x2:xs = y2:ys |] - rewrites_to -> [d| reverse x:xs = reverse xs ++ [x] |] reverse :: [a] -> [a] implies x2,y2 :: a x1,y1,xs,ys :: [a] TH.reify is not applicable, because I need the information at runtime and I am in IO. I suppose Data.Dynamic does not work either, because [| xs|] :: ExpQ and not [a]. So it looks like I need my own type checker and inference and tag each subexpression with its type. If so, I can even omit TH and use my own data type for the abstract syntax tree. This annoys me a bit, because for me it seems that all I need is already there. Did anybody have similar problems, because I shouldn't be the only one doing dynamic typing in a static language? Is there a Haskell implementation of the paper "Typing Dynamic Typing" by Baars and Swierstra (http://people.cs.uu.nl/arthurb/dynamic.html ), so I can try out if this helps me? Any help, comments, and how-to-suggestions are highly welcome. Thanks a lot, Martin

1 0

Request: warn about language extensions that are not used
by Peter Verswyvelen 12 Mar '09

12 Mar '09

When I put {-# OPTIONS_GHC -Wall -Werror #-} in my source file, I don't get compiler (GHC) warnings about redundant language extensions that I enabled. It would be nice if the compiler gave warnings about this, since after refactoring, some language extensions might not be needed anymore, and hence should be removed since fewer language extensions mean more stable and portable code no? What do you think?

5 7

Haskell SDL
by michael millard 12 Mar '09

12 Mar '09

hi, im having trouble setting up the haskell sdl bindings for windows vista im trying to install using minGW but its just not installing correctly. does anyone know any good tutorials for this? _________________________________________________________________ Get 30 Free Emoticons for your Windows Live Messenger http://www.livemessenger-emoticons.com/funfamily/en-ie/

1 0

How to get program command line arguments in Unicode-aware way (Unix/Linux)?
by Dimitry Golubovsky 12 Mar '09

12 Mar '09

Hi, I am trying to process command line arguments that may contain Unicode (cyrillic in this example) characters. The standard GHC's getArgs seems to pass whatever was obtained from the underlying C library without any regard to encoding, e. g the following program (testarg.hs): module Main where import System.Environment main = do x <- getArgs mapM (putStrLn . show) x being invoked (ghc 6.10.1) runghc testarg -T 'при<в>ет' prints the following: "-T" "\208\191\209\128\208\184<\208\178>\208\181\209\130" (not correct, all bytes were passed without proper encoding) Is there any way to get program arguments in GHC Unicode-aware? Or at least assuming that they are always in UTF-8? Something like System.IO.UTF8, but for command line arguments? Thanks. PS: BTW runhugs testarg -T 'при<в>ет' prints: "-T" "\1087\1088\1080<\1074>\1077\1090" which is correct. -- Dimitry Golubovsky Anywhere on the Web

3 2

Loading 3D points & normals into OpenGL?
by Duane Johnson 12 Mar '09

12 Mar '09

Hi, I am considering writing a VRML (.wrl) parser so that I can load points and normals for a game I'm making in Haskell. Is there something around that will already do the trick? Or perhaps another format is preferred and already supported? Thanks, Duane Johnson (canadaduane) http://blog.inquirylabs.com/

4 4

Binary Parsing
by Rick R 12 Mar '09

12 Mar '09

I have basic beginning to a parser for the BSON spec: http://www.mongodb.org/display/DOCS/BSON It is basically a binary compressed form of JSON. The usage model should be general, but I intend to read this data over TCP. Currently my system is quite inefficient, I convert leading bytes to Int then switch based on that type that that Int represtents. I was wondering if there is a tool set that exists for this purpose. For instance, should I use Data.Binary and make my Binary instance of get and put use the BSON protocol? Or is that not correct? I also looked at Parsec.ByteString, but that seems to only have a file input mechanism, and tcp buffers may be out of its scope. Are there any other tools that I should look at? I'm sure similar things have been done before. Can anyone point me to some open, successful implementations that I could mimick? -- We can't solve problems by using the same kind of thinking we used when we created them. - A. Einstein

2 1

generic sum for an UArr
by Manlio Perillo 12 Mar '09

12 Mar '09

Hi. I have an array (Data.Array.Vector.UArr) of Word8 elements. Elements are stored as Word8 to keep memory usage down. Now I need to compute the sum of all the array elements; what is the best method? The sum must be of type Int. How efficient is to simply convert to an UArr Int, using: mapU fromIntegral v :: UArr Int ? What about, instead, of something like: genericSumU :: (UA e, Integral e) => UArr e -> Int genericSumU = foldU add 0 where add x y = x + fromIntegral y ? Unfortunately the latter does not compile: Couldn't match expected type `Int' against inferred type `e' `e' is a rigid type variable bound by the type signature for `genericSumU' at bin/process-data-1.hs:64:19 In the expression: foldU add 0 In the definition of `genericSumU': genericSumU = foldU add 0 where add x y = x + fromIntegral y Moreover, this is not really a generic version. I would like to have: genericSumU :: (Num i, UA e, Num e) => UArr e -> i is this possible? Thanks Manlio

2 2

How to insert character key self in sourceView?
by Andy Stewart 12 Mar '09

12 Mar '09

Hi all, I use gtk2hs develop editor. I use below function handle key press event. keyPressHandler :: Event -> IO Bool keyPressHandler (Key {eventKeyName = keyName}) = do case keyName of "Escape" -> do mainQuit >> return True _ -> do -- How to insert character self? return True I need handle key press event, and insert itself if key is character (like: 'a' 'b' 'c'). How to insert character self in sourceView buffer? Below are complete source code: ------------------------------> source code start <------------------------------ import Graphics.UI.Gtk import Graphics.UI.Gtk.SourceView import Graphics.UI.Gtk.Abstract.Widget import Graphics.UI.Gtk.Gdk.Events import Text.Printf import Control.Monad main :: IO () main = do -- Init. initGUI -- Root frame. rootFrame <- windowNew onDestroy rootFrame mainQuit -- quit main loop when root frame close -- Root frame status. -- windowFullscreen rootFrame -- fullscreen windowSetPosition rootFrame WinPosCenter -- set init position windowSetDefaultSize rootFrame 400 300 -- set init size -- Main box. mainBox <- vBoxNew False 0 containerAdd rootFrame mainBox -- Source view box. sourceViewBox <- vBoxNew False 0 containerAdd mainBox sourceViewBox -- Source view. sourceView <- sourceViewNew boxPackStart sourceViewBox sourceView PackNatural 0 -- Echo area box. echoAreaBox <- vBoxNew False 0 echoAreaAlign <- alignmentNew 0 1 1 1 containerAdd echoAreaBox echoAreaAlign containerAdd mainBox echoAreaBox -- Echo area. echoArea <- statusbarNew boxPackStart echoAreaBox echoArea PackNatural 0 -- Display. widgetShowAll rootFrame -- Handle keystroke. onKeyPress rootFrame $ keyPressHandler -- Update echo area. updateEchoArea sourceView echoArea -- Loop mainGUI keyPressHandler :: Event -> IO Bool keyPressHandler (Key {eventKeyName = keyName}) = do case keyName of "Escape" -> do mainQuit >> return True _ -> do return True updateEchoArea :: SourceView -> Statusbar -> IO () updateEchoArea sv sb = do buf <- textViewGetBuffer sv mark <- textBufferGetInsert buf iter <- textBufferGetIterAtMark buf mark line <- textIterGetLine iter col <- textIterGetLineOffset iter statusbarPop sb 1 statusbarPush sb 1 $ printf "Line %4d, Column %3d" (line + 1) (col + 1) return () ------------------------------> source code end <------------------------------ Any help? Thanks! -- Andy

2 2

advice on a parsing function
by Manlio Perillo 12 Mar '09

12 Mar '09

Hi. I'm still working on the Netflix Prize; now I have managed to implement a parsing function for the qualifying data set (or quiz set). The quiz set is in the format: 1: 10 20 30 2: 100 200 3: 1000 2000 3000 4000 5000 Where 1, 2, 3 are movie ids, and the others are user ids. The parsing program is at: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=2300 The program reads the file using lazy IO. One of the feature I want is, for the quiz function, to be a *good producer*. I'm quite satisfied with the result (this is the first "complex" parsing function I have written in Haskell), and I have also managed to avoid the use of an accumulator. However I'm interested to know it there is a more efficient solution. The qualifying.txt file is 51MB, 2834601 lines. On my laptop, the function performance are: real 1m14.117s user 0m2.496s sys 0m0.136s CPU usage is about 3%, system load is about 0.20, memory usage is 4956 KB. What I'm worried about is: quiz' ((id, ":") : l) = (id, quiz'' l) : quiz' l quiz' ((id, _) : l) = quiz' l the problem here is that the same elements in the list are processed multiple times. I have written alternate versions. The first using foldl http://hpaste.org/fastcgi/hpaste.fcgi/view?id=2303 (that, however, builds the entire data structure in memory, and in reverse order) The latter using foldr http://hpaste.org/fastcgi/hpaste.fcgi/view?id=2304 (that, however, is incorrect and I'm unable to fix). The performances of the foldr version are very similar to the performances of the first implementation (it make use, however, of 3704 KB, and it is about 3 seconds faster). P.S: the expected result for the sample quiz set I have posted is: [(1,[10,20,30]),(2,[100,200]),(3,[1000,2000,3000,4000,5000])] The foldl version produces: [(3,[5000,4000,3000,2000,1000]),(2,[200,100]),(1,[30,20,10])] The foldr version produces: [(1,[]),(2,[10,20,30]),(3,[100,200]),(5000,[1000,2000,3000,4000])] Thanks Manlio Perillo

2 7

ByteString in patterns
by Manlio Perillo 12 Mar '09

12 Mar '09

Hi. Using normal String type I can define a pattern like: > let foo "baz" = 777 > foo "baz" 777 But if I want to use ByteString, what should I do? This seems impossible, since ByteString data constructor is not available. Thanks Manlio Perillo

5 12

View patterns and warnings about overlapping or non-exhaustive patterns
by Stephan Friedrichs 12 Mar '09

12 Mar '09

Hi, I'm working on a data structure that uses Data.Sequence a lot, so views are important and I tried to simplify my code using view patterns. The problem is, that I keep getting warnings about both overlapping and non-exhaustive pattern matches. A simple test case: ===============================T.hs=============================== {-# LANGUAGE ViewPatterns #-} import Data.Sequence test :: Seq a -> Seq b -> String test (viewl -> EmptyL) (viewl -> EmptyL) = "empty, empty" test (viewl -> EmptyL) (viewl -> _ :< _) = "empty, non-empty" test (viewl -> _ :< _) (viewl -> EmptyL) = "non-empty, empty" test _ _ = "non-empty, non-empty" ================================================================== > ghci -Wall T.hs GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Main ( T.hs, interpreted ) T.hs:6:0: Warning: Pattern match(es) are overlapped In the definition of `test': test ((viewl -> EmptyL)) ((viewl -> EmptyL)) = ... test ((viewl -> EmptyL)) ((viewl -> _ :< _)) = ... test ((viewl -> _ :< _)) ((viewl -> EmptyL)) = ... test _ _ = ... T.hs:6:0: Warning: Pattern match(es) are non-exhaustive In the definition of `test': Patterns not matched: Ok, modules loaded: Main. *Main> test empty (singleton 'a') "empty, non-empty" *Main> test (singleton 'b') (singleton 'a') "non-empty, non-empty" *Main> test (singleton 'b') empty "non-empty, empty" *Main> test empty empty "empty, empty" There are warnings about non-exhaustive and overlapping pattern matches, but the tests show that this isn't the case. So what's the problem? I don't want to turn off or ignore warnings. //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr

3 3

QC 2.0 missing some stuff I need
by John Goerzen 11 Mar '09

11 Mar '09

Hi, QuickCheck 1.x had this function: evaluate :: Testable a => a -> Gen Result which I used in TestPack to help wrap a QuickCheck test as a HUnit test case. QuickCheck 2.x seems to have no pure evaluate-like function at all; all of its functions are in the IO monad and also write their result to stdout, according to the docs. Am I missing something? Thanks, -- John

2 1

Using FosSyDe to translate haskell to VHDL.
by wanghanyi 11 Mar '09

11 Mar '09

Dear all, I have used ForSyDe to translate a Haskell script to VHDL for a while, and I have one problem by applying where-clause during the translation. I wrote a small function Plus2.hs which is implied as following addTwof :: ProcFun (Int32 -> Int32) addTwof = $(newProcFun [d|addTwof :: Int32 -> Int32 addTwof n = addOnef+1 where addOnef = n +1 |]) *Plus2> writeVHDL plus2SysDef *** Exception: VHDL Compilation Error: Untranslatable function: where constructs are not supported in functions: where addOnef_0 = n_1 GHC.Num.+ 1 in process function `addTwof' (created in Plus2) used by process `plus2Proc' belonging to system definition `plus2' (created in <unkown>) The compiling process was fine, but the script could not be translated into VHDL, like the error i mentioned above. Is there any way to solve this problem if a where-clause is a must. Thanks all. Hanyi _________________________________________________________________ Live Search视频搜索，快速检索视频的利器！ http://www.live.com/?scope=video

2 2

Re: [Haskell-cafe] Design Patterns by Gamma or equivalent
by Sean Leather 11 Mar '09

11 Mar '09

Hi Mark, Because Haskell is not OO, it is functional, I was wondering if there is > some kind of analogous “design pattern”/”template” type concept that > describe commonly used functions that can be “factored out” in a general > sense to provide the same kind of usefulness that Design Patterns do for > OOP. Basically I’m asking if there are any kinds of “common denominator” > function compositions that are used again and again to solve problems. If > so, what are they called? > Look at Jeremy Gibbons' publications. All of the ones that have "pattern" or "origami" in the title describe design patterns in Haskell. Some of them relate to the translation of Gang-of-Four patterns. http://www.comlab.ox.ac.uk/people/publications/date/Jeremy.Gibbons.html Regards, Sean

1 0

Re: Design Patterns by Gamma or equivalent
by Achim Schneider 11 Mar '09

11 Mar '09

"Mark Spezzano" <mark.spezzano(a)chariot.net.au> wrote: > Basically I___m asking if there are any kinds of ___common denominator___ > function compositions that are used again and again to solve > problems. If so, what are they called? > Haskellers tend to cast their design patterns into functions and libraries. What they're supposed to be called is a zealously heated discussion, there's, for example, return == pure == point and fmap == map == (.) == liftM [1] OTOH, we're said to not care at all: | Don't underrate Haskell programmers. The ones I know have the kind of | minds where if you switched the names to pig latin, they wouldn't skip | a beat. -- [2] If you're looking for a text that could be named "The N most (use|success)ful Haskell Design Patterns", I recommend having a look at the Typeclassopedia[3]. [1]well, at least there _could_ be. [2]http://www.mail-archive.com/boost@lists.boost.org/msg08898.html [3]http://byorgey.wordpress.com/2009/02/16/the-typeclassopedia-request-for-f… -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited.

1 0

Re: [Haskell-cafe] Design Patterns by Gamma or equivalent
by Robin Green 11 Mar '09

11 Mar '09

The concept of "design pattern" tends not to be used by Haskell programmers - it brings a lot of baggage with it (like being formally documented in a particular way, being "proven" by being used in production several times, etc.) and it doesn't seem to be particularly useful for us in this heavyweight form. However, we do have a more lightweight concept of an "idiom" and "idiomatic Haskell". See http://www.haskell.org/haskellwiki/Category:Idioms (Not all of these pages should probably be in this category, but it gives you an idea.) -- Robin On Wed, 11 Mar 2009 21:28:52 +1030 "Mark Spezzano" <mark.spezzano(a)chariot.net.au> wrote: > Hi, > > > > I’m very familiar with the concept of Design Patterns for OOP in Java > and C++. They’re basically a way of fitting components of a program > so that objects/classes fit together nicely like Lego blocks and it’s > useful because it also provides a common “language” to talk about > concepts, like Abstract Factory, or an Observer to other programmers. > In this way one programmer can instantly get a feel what another > programmer is talking about even though the concepts are > fundamentally abstract. > > > > Because Haskell is not OO, it is functional, I was wondering if there > is some kind of analogous “design pattern”/”template” type concept > that describe commonly used functions that can be “factored out” in a > general sense to provide the same kind of usefulness that Design > Patterns do for OOP. Basically I’m asking if there are any kinds of > “common denominator” function compositions that are used again and > again to solve problems. If so, what are they called? > > > > Cheers, > > > > Mark Spezzano > > > > > > > No virus found in this outgoing message. > Checked by AVG. > Version: 7.5.557 / Virus Database: 270.11.9/1993 - Release Date: > 10/03/2009 7:19 AM >

1 0

Re: [Haskell-cafe] Design Patterns by Gamma or equivalent
by minh thu 11 Mar '09

11 Mar '09

2009/3/11 Mark Spezzano <mark.spezzano(a)chariot.net.au>: > Hi, > > > > I’m very familiar with the concept of Design Patterns for OOP in Java and > C++. They’re basically a way of fitting components of a program so that > objects/classes fit together nicely like Lego blocks and it’s useful because > it also provides a common “language” to talk about concepts, like Abstract > Factory, or an Observer to other programmers. In this way one programmer can > instantly get a feel what another programmer is talking about even though > the concepts are fundamentally abstract. > > > > Because Haskell is not OO, it is functional, I was wondering if there is > some kind of analogous “design pattern”/”template” type concept that > describe commonly used functions that can be “factored out” in a general > sense to provide the same kind of usefulness that Design Patterns do for > OOP. Basically I’m asking if there are any kinds of “common denominator” > function compositions that are used again and again to solve problems. If > so, what are they called? Hi, A particular instance of what can replace the idea of design pattern is given by this now famous post : http://blog.sigfpe.com/2009/01/haskell-monoids-and-their-uses.html You'll see that what 'speaks' to the haskell programmers, maybe in the same way you say design patterns speak to another oo programmer, is much more fitted to the language in haskell. At a lower scale, the reusability of some simple functions like fold or map is reflected at a higher scale by the reusability of concepts like monoids (whih 'exist' in the language, as type classes, while a pattern doesn't). Cheers, Thu

1 0

Design Patterns by Gamma or equivalent
by Mark Spezzano 11 Mar '09

11 Mar '09

Hi, I’m very familiar with the concept of Design Patterns for OOP in Java and C++. They’re basically a way of fitting components of a program so that objects/classes fit together nicely like Lego blocks and it’s useful because it also provides a common “language” to talk about concepts, like Abstract Factory, or an Observer to other programmers. In this way one programmer can instantly get a feel what another programmer is talking about even though the concepts are fundamentally abstract. Because Haskell is not OO, it is functional, I was wondering if there is some kind of analogous “design pattern”/”template” type concept that describe commonly used functions that can be “factored out” in a general sense to provide the same kind of usefulness that Design Patterns do for OOP. Basically I’m asking if there are any kinds of “common denominator” function compositions that are used again and again to solve problems. If so, what are they called? Cheers, Mark Spezzano No virus found in this outgoing message. Checked by AVG. Version: 7.5.557 / Virus Database: 270.11.9/1993 - Release Date: 10/03/2009 7:19 AM

1 0

Re: [Haskell-cafe] Generics Versus Parametric Polymorphism
by Bulat Ziganshin 11 Mar '09

11 Mar '09

Hello Mark, Wednesday, March 11, 2009, 9:11:42 AM, you wrote: > Just wondering if Generics and Parametric polymorphism are one and the same in Haskell. haskell Parametric polymorphism is the same type of thing as Java Generics :) haskell Generics provides ability to define procedures polymorphic by *any* data type with just a fixed number of definitions there are at least dozen of various tools/libraries supporting Generics in some way in haskell, so indeed we are interested to have at least one with guaranteed availability google for "scrap your boilerplate" paper for a description of one of the most popular Generics implementation -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

2 2

Re: [reactive] FRP + physics / status of hpysics
by Wolfgang Jeltsch 11 Mar '09

11 Mar '09

Am Freitag, 6. März 2009 14:34 schrieb Daniel Bünzli: > > without using recursive signal functions, > > If this is because there's this limitation in the frp system you use It is. > then better fix the system. The system is Grapefruit, by the way. And I’m its developer, by the way. :-) I have to say that it’s hard, if not impossible, to combine recursive signal definitions with other features, I want to have. The point of recursive definitions is that you want to turn recursive equations from your problem domain directly into Haskell definitions. This is nice from a user’s point of view but hard from a programmers point of view. Standard Haskell already shows that. While it is possible to define an infinite list of ones by ones = 1 : ones, it is not possible to do the same for sequences of type Seq. The above definition of ones relies very much on the structure of lists. Analogously, the ability to define signals recursively restricts the set of possible signal implementations seriously. Haskell’s recursive definitions are very general. They have to find fixpoints of arbitrary functions over arbitrary type. Therefore, their semantics are rather weak. They give you the least defined fixpoint. The consequence is that you get bottom if you use something like x = 0 * x although x = 0 might be what you prefered. What I want to say is that coming up with a signal implementation that allows Haskell recursion and has other advantages at the same time is a big challenge. There are three features, you might want from a signal implementation: 1. support for recursive signal definitions using Haskell equations 2. memoization (for avoiding time leaks, for example) 3. signals which may depend on external sources I tried hard to support 2 and 3 well in Grapefruit. Fran has 1 but has problems with 2 and 3. I don’t know whether Reactive has a solution for 2 in the context of recursive definitions, i.e., whether the space and time leak problems of Fran were solved. I think, it has at least problems with 3. For me, 2 and 3 are more important than 1. One reason is that 1 has other problems than being in conflict with 2 and 3. The result of a recursively defined signal depends on when sampling occurs. Since a recursive definition tends to result in accumulation of values, errors introduced by sampling may accumulate too. So you have to use clever approximation algorithms in addition. My new idea is to view the problem in a different way. Let’s take the problem where the position of a ball is the integral of the difference between the mouse position and the ball position. As far as I can see, the transformation of the mouse position signal into the ball position signal forms a linear system. So the ball position signal is the mouse position signal convoluted with another signal. If we would have a function that performes convolution, we could probably implement many problems using this function. Using convolution would let us get rid of the problems with accumulating errors. I suppose that most of the recursive definitions you would use in FRP are differential or integral equations. Let’s look at the equation for the ball-following-the-mouse example: ballPos = integral (mousePos - ballPos) ballPos can be represented in terms of mousePos as follows: ballPos = (exp . negate) * mousePos where * means convolution. We could provide a library which supports common stuff like distance-dependent acceleration, friction etc. Of course, you could say that now the programmer isn’t able anymore to enter his equations directly which isn’t nice. However, this situation is not different to other areas. For example, you cannot write x = 5 - x / 2 and expect x to be 10 / 3. Instead, you have to transform the equation first. > Soon or later it you'll want it elsewhere. A recursive reactive signal just > means that some of what your reactive program computed will be > usefull/necessary for the next step. You can do this with convolution, I think. By the way, continuous signals don’t have steps. These are just introduced by sampling. > You'll see that happen very quickly (e.g. any simple reactive state > machine). “State machine” sounds like a discrete problem. You can use accumulation over event sequences here (as, for example, provided by the scan function in FRP.Grapefruit.Signal.Discrete). By the way, the adress of the Grapefruit mailing list is grapefruit(a)projects.haskell.org, not grapefruit(a)haskell.org. Best wishes, Wolfgang

1 2

Re: [Haskell-cafe] Generics Versus Parametric Polymorphism
by Sean Leather 11 Mar '09

11 Mar '09

Hi Mark, > Just wondering if Generics and Parametric polymorphism are one and the same > in Haskell. > > I read (somewhere!) an article stating that generics might be included in > Haskell Prime but I thought that they’re already included as parametric > polymorphism. > To see the current status of Haskell Prime, visit the Trac page: http://hackage.haskell.org/trac/haskell-prime/ > Did I misread something? Or is generics in Haskell referring to something > completely different. > I'm not sure which article you read, but there is a lot of ambiguity in the term "generics." Depending on whom you talk to, it means a different thing. But I can give you some pointers to where you can learn about many of the possible interpretations. The following paper gives a useful vocabulary for describing the different types of "generics." Just by reading section 2 you can see how confusing it is when so many techniques are referred to as generic programming. For example, parametric polymorphism is an example of genericity by type here. In the Haskell world, (as Don said) it's not considered generics, but in Java (as Alp remarked), it's called generics. http://www.comlab.ox.ac.uk/jeremy.gibbons/publications/dgp.pdf There's a comparison paper from 2003 that presents language support for generics in C++, ML, Haskell, Eiffel, Java, and C#. Things have changed a bit since then, but it's an interesting read. http://ece-www.colorado.edu/~siek/pubs/comparing_generic_programming03.pdf "Generics" in Haskell has come to be known as datatype-generic programming. In the past, it has been labeled polytypism, structural polymorphism, or typecase. This refers to the technique of writing functions or programs that work for many types and have knowledge about the structure of the type (mentioned by Bulat). Generic Haskell is a (non-standard) language extension to Haskell. It was used to explore the possibilities of datatype-generic programming (DGP) with Haskell. The following paper compares varying approaches of DGP to Generic Haskell. http://people.cs.uu.nl/johanj/publications/ComparingGP.pdf In the last few years, people have seen the power of Haskell's type system, and GHC has developed some interesting extensions to that type system. As a result of this and the difficulty with maintaining language extensions external to a compiler (e.g. Generic Haskell), libraries for DGP in Haskell have become much more common and powerful. The following article compares a large number of these libraries. http://www.cs.uu.nl/wiki/Alexey/ComparingLibrariesForGenericProgrammingInHa… Lastly, since I started working in this area over a year ago, I've been collecting references to published research. My citations are on CiteULike: http://www.citeulike.org/user/spl There are tags for "generics" and "datatype-generic" that give you a narrower view on the collection. http://www.citeulike.org/user/spl/tag/generics http://www.citeulike.org/user/spl/tag/datatype-generic Hope this helps to answer your questions. Regards, Sean

1 0

FRP + physics / status of hpysics
by Peter Verswyvelen 11 Mar '09

11 Mar '09

Regarding hpysics, did anybody did some experiments with this? The blog seems to be inactive since december 2008; has development ceased? Do alternatives exist? Maybe good wrappers (hopefully pure...) around existing engines? Integrating hpysics with Grapefruit might be a good topic for the Hackaton, trying to make a simple game (e.g. Pong or Breakout) without using recursive signal functions, but with correct collision response and better-than-Euler integration, all handled by the physics engine. Other FRP engines could be tried, but Grapefruit hacking is already a topic on the Hackaton, so it would combine efforts. It feels as if none of the current FRP engines can handle physics correctly, since a typical physics implementations requires "time backtracking", in the sense that when you want to advance the current simulation time by a timestep, collision events can happen during that time interval, and hence the FRP engine can only advance time until the earliest collision event. So to do physics *with* an FRP engine, the implementation and maybe even semantics of the FRP system might need to be changed. *Using* a physics engine as a blackbox inside an FRP system might make more sense. Thanks to Wolfgang Jeltsch and Christopher Lane Hinson for having a discussion with me that lead to this. Interestingly a similar discussion was help by other people in the Reactive mailing list at the same time :-) Cheers, Peter Verswyvelen

7 13

do nmergeIO or mergeIO preserve order?
by Anatoly Yakovenko 11 Mar '09

11 Mar '09

do nmergeIO or mergeIO preserve order? or not preserve order?

3 7

Re: [Haskell-cafe] Generics Versus Parametric Polymorphism
by Don Stewart 11 Mar '09

11 Mar '09

mark.spezzano: > Hi, > > Just wondering if Generics and Parametric polymorphism are one and the same in > Haskell. > > I read (somewhere!) an article stating that generics might be included in > Haskell Prime but I thought that they’re already included as parametric > polymorphism. > > Did I misread something? Or is generics in Haskell referring to something > completely different. Parametric polymorphism is kinda boring in Haskell -- since it's been there since the beginning. We tend to reserve the term "generics" for higher order, and fancier, polymorphism. These kinds of things: http://hackage.haskell.org/packages/archive/pkg-list.html#cat:generics -- Don

2 1

Generics Versus Parametric Polymorphism
by Mark Spezzano 11 Mar '09

11 Mar '09

Hi, Just wondering if Generics and Parametric polymorphism are one and the same in Haskell. I read (somewhere!) an article stating that generics might be included in Haskell Prime but I thought that they’re already included as parametric polymorphism. Did I misread something? Or is generics in Haskell referring to something completely different. Cheers, Mark Spezzano No virus found in this outgoing message. Checked by AVG. Version: 7.5.557 / Virus Database: 270.11.9/1993 - Release Date: 10/03/2009 7:19 AM

1 0

Re: [Haskell-cafe] Parallel programming (threads, cores, processors)
by Sterling Clover 11 Mar '09

11 Mar '09

On Mar 10, 2009, at 10:38 PM, Mark Spezzano wrote: > Hi, > > I’m an experienced software developer, but a bit of a newbie when > it comes to parallel processing in any language. > > Question 1: > > Is there any programmatic change in dealing with multiple threads > as opposed to multiple cores in most languages (specifically Haskell)? > > That is, to write multiple threads you normally “spin-off” a new > thread which runs in parallel along with other threads. Is Haskell > smart enough to do this by magic by itself, or would I need to tell > it explicitly : Run thread A whilst running thread B > > Also, what about multicore architectures? Do I have to tell the > language to spin off two separate programs to run on each core and > then somehow use some kind of communications to exchange data? > GHC's parallel runtime, which is what we're really talking about when we're talking about Haskell concurrency, operates roughly like this: Threads at the language level are "green" -- i.e. they are conceptually threads, and the runtime schedules them as it sees fit, but they aren't tied to any given core for execution. You can create (using the forkIO primitive) as many new threads as you like. If you then execute your program with runtime options (i.e. +RTS -N 2 for two cores) that specify how many actually operating system threads you want, the runtime will then map your set of green threads onto OS threads (and presumably cores) in what it thinks is an efficient manner. Communication between threads is via MVars, which are like one-item mailboxes, and are one concurrency primitive, or TVars, which are for Software Transactional Memory. > I also assume that, in theory it would be possible to have multiple > threads running on each core. Say, 3 threads spawned from program 1 > running on core 1 and 5 threads on program 2 running on core 2 > Generally, the runtime system moves threads between cores as it sees fit. However, you can tie threads to particular cores using other concurrency primitives (i.e. runInBoundThread). See the documentation for Control.Concurrent (http://www.haskell.org/ ghc/docs/latest/html/libraries/base/Control-Concurrent.html) and Control.Concurrent.STM (http://www.haskell.org/ghc/docs/latest/html/ libraries/stm/Control-Concurrent-STM.html) for more details. > Likewise I would suppose that it would be possible to have > multiprocessors, each potentially multicore, each core running > multiple threads. > Yep, see above, although I don't know of any way to distinguish between cores and processors as you're really just mapping to OS threads (i.e. capabilities) and relying on the OS to distribute these among cores and processors reasonably. > Question 2: > > In light of the above statement, is the programmatic change > DIFFERENT for dealing with each of > > a) Multithreading in Haskell versus > > b) Multicores in Haskell verus > > c) Multiprocessors in Haskell > Generally, you'll want to write concurrent Haskell code as an abstraction to think about things that are "naturally" concurrent -- i.e. which are best thought of as happening at the same time. At runtime, you specify how many OS capabilities you want to map onto. For algorithms where you want computations to happen in parallel, there's an entirely different set of operations, based around `par` (see Control.Parallel [http://www.haskell.org/ghc/docs/latest/html/ libraries/parallel/Control-Parallel.html] and Control.Parallel.Strategies). In neither case should you need, generally, to concern yourself with the details of threads vs. cores vs. processors. Cheers, Sterl.

1 0

Parallel programming (threads, cores, processors)
by Mark Spezzano 11 Mar '09

11 Mar '09

Hi, I’m an experienced software developer, but a bit of a newbie when it comes to parallel processing in any language. I’ve done some multithreading in Java and C++ on a single processor, single core architecture only. First, let me define some terms: Multithreading: this is multiple processes running on one processor and is the conventional way to do parallel programming Multicore: this is when we have two (or more) cores within the one CPU Multiprocessor: this is when we have multiple CPUs Question 1: Is there any programmatic change in dealing with multiple threads as opposed to multiple cores in most languages (specifically Haskell)? That is, to write multiple threads you normally “spin-off” a new thread which runs in parallel along with other threads. Is Haskell smart enough to do this by magic by itself, or would I need to tell it explicitly : Run thread A whilst running thread B Also, what about multicore architectures? Do I have to tell the language to spin off two separate programs to run on each core and then somehow use some kind of communications to exchange data? I also assume that, in theory it would be possible to have multiple threads running on each core. Say, 3 threads spawned from program 1 running on core 1 and 5 threads on program 2 running on core 2 Likewise I would suppose that it would be possible to have multiprocessors, each potentially multicore, each core running multiple threads. Question 2: In light of the above statement, is the programmatic change DIFFERENT for dealing with each of a) Multithreading in Haskell versus b) Multicores in Haskell verus c) Multiprocessors in Haskell References or info appreciated. Just curious. Mark No virus found in this outgoing message. Checked by AVG. Version: 7.5.557 / Virus Database: 270.11.9/1993 - Release Date: 10/03/2009 7:19 AM

1 0

Parallel programming in Haskell (threads, cores, processors)
by Mark Spezzano 11 Mar '09

11 Mar '09

Hi, I’m an experienced software developer, but a bit of a newbie when it comes to parallel processing in any language. I’ve done some multithreading in Java and C++ on a single processor, single core architecture only. First, let me define some terms: Multithreading: this is multiple processes running on one processor and is the conventional way to do parallel programming Multicore: this is when we have two (or more) cores within the one CPU Multiprocessor: this is when we have multiple CPUs Question 1: Is there any programmatic change in dealing with multiple threads as opposed to multiple cores in most languages (specifically Haskell)? That is, to write multiple threads you normally “spin-off” a new thread which runs in parallel along with other threads. Is Haskell smart enough to do this by magic by itself, or would I need to tell it explicitly : Run thread A whilst running thread B Also, what about multicore architectures? Do I have to tell the language to spin off two separate programs to run on each core and then somehow use some kind of communications to exchange data? I also assume that, in theory it would be possible to have multiple threads running on each core. Say, 3 threads spawned from program 1 running on core 1 and 5 threads on program 2 running on core 2 Likewise I would suppose that it would be possible to have multiprocessors, each potentially multicore, each core running multiple threads. Question 2: In light of the above statement, is the programmatic change DIFFERENT for dealing with each of a) Multithreading in Haskell versus b) Multicores in Haskell verus c) Multiprocessors in Haskell References or info appreciated. Just curious. Mark No virus found in this outgoing message. Checked by AVG. Version: 7.5.557 / Virus Database: 270.11.9/1993 - Release Date: 10/03/2009 7:19 AM

1 0

Horner's Rule, foldl, and direct recursion
by R J 11 Mar '09

11 Mar '09

Given a list of decimal digits represented by Integers between 0 and 9--for example, the list [1,2,3, 4]--with the high-order digit at the left, the list can be converted to a decimal integer n using the following formula, an instance of Horner's rule: n = 10 * 10 * 10 * 1 + 10 * 10 * 2 + 10 * 3 + 4 = 10 * (10 * 10 * 1 + 10 * 2 + 3) + 4 = 10 * (10 *(10 * 1 + 2) + 3) + 4 In Haskell, the foldl function neatly captures this pattern: horner :: [Integer] -> Integer horner = myFoldl timesPlus 0 where timesPlus x y = 10 * x + y What is the direct recursive calculation of this function without using the call to foldl? In other words, what's the second equation of: horner2 :: [Integer] -> Integer horner2 [] = 0 horner2 (x : xs) = ? Given that we've already got the definition using foldl, it ought to be easy to express the second equation, but it's eluding me. Thanks. _________________________________________________________________ Windows Live™ Groups: Create an online spot for your favorite groups to meet. http://windowslive.com/online/groups?ocid=TXT_TAGLM_WL_groups_032009

2 1

TASE 2009 - CALL FOR POSTER PRESENTATIONS
by CRACIUN F. 11 Mar '09

11 Mar '09

TASE 2009 - CALL FOR POSTER PRESENTATIONS ****************************************** * 3rd IEEE International Symposium on * Theoretical Aspects of Software Engineering * (TASE 2009) * 29-31 July 2009, Tianjin, China * http://www.dur.ac.uk/ieee.tase2009 * * For more information email: IEEE.TASE2009(a)durham.ac.uk ********************************************************** TASE 2009 will include a poster session during the conference. The session aims to give students and researchers an opportunity to present their research to the community, and to get responses from other researchers. SCOPE: Poster presentations are sought in all theoretical aspects of software engineering, including (but not limited to): * Requirements Engineering * Specification and Verification * Program Analysis * Software Testing * Model-Driven Engineering * Software Architectures and Design * Aspect and Object Orientation * Embedded and Real-Time Systems * Software Processes and Workflows * Component-Based Software Engineering * Software Safety, Security and Reliability * Reverse Engineering and Software Maintenance * Service-Oriented Computing * Semantic Web and Web Services * Type System and Theory * Program Logics and Calculus * Dependable Concurrency * Software Model Checking SUBMISSION PROCESS: A Poster proposal consists of: - a 50 word or less short abstract that summarizes the content of the poster - a set of keywords describing the technical area of the work - a two-page extended abstract, suitable for inclusion in the TASE 2009 conference proceedings. All abstracts must adhere to the two-column IEEE format. All Poster proposals are to be submitted by email to IEEE.TASE2009(a)durham.ac.uk. The file containing the two-page extended abstract must be in .pdf or .ps format. Upon acceptance, at least one of the authors must register with the TASE2009 conference in order to have their extended abstract included in the conference proceedings. Once registered, a bulletin board space of A1 paper size (594 mm wide and 841 mm high) will be provided for each presentation. In addition to the camera-ready version of the extended abstract, the authors are also requested to submit their poster of A1 paper size (594 mm wide and 841 mm high) for backup. An A1 poster sample template is available at http://www.dur.ac.uk/ieee.tase2009/poster.a1.ppt for authors to download. The authors can prepare 8 individual slides, save them in .jpg format and then place them on the above A1 sample. The Poster presenter will need to print out their Poster in advance and bring it to the conference for the Poster session. POSTER CONTENT: A small selection committee led by the Poster Chair will evaluate the poster proposals based on their contributions and on how effectively they communicate those contributions. All posters should include the following information: - The purpose and goals of the work. - Any background and motivation information needed to understand the work. - A summary of the contribution and/or results, in sufficient detail for a viewer to understand the work and/or results; especially key details, results and contributions, or the anticipated contributions if the work is at an early stage. - The relationship to other related efforts, where appropriate. - Where to find additional information. This should include (but is not restricted to): a web site where viewers can go to find additional information about the work, how to contact the authors (including email addresses), citations for any papers, books, or other materials that provide additional information. POSTER COMPETITION: A poster competition will be organised during the poster session. A panel of experts will be formed as referees for the competition. Awards will be given to the winners of the competition. IMPORTANT DATES: Poster proposals submission: April 22, 2009 Acceptance/rejection notification: May 6, 2009 Camera-ready version and Poster due: May 13, 2009 TASE 2009 Conference: July 29-31, 2009 CONTACT: For questions or requests, please contact the TASE 2009 poster chair, Florin Craciun (IEEE.TASE2009(a)durham.ac.uk) Please mention "poster session" in the subject of your email.

1 0

Haskell Logo Voting will start soon!
by Eelco Lempsink 11 Mar '09

11 Mar '09

Hi there! It's been quiet for a while around the 'new logo' competition, but here is how it is going to work: The list with options can be found here (for now): http://community.haskell.org/~eelco/poll.html Notice that some (very) similar logos are grouped as one option (thanks to Ian Lynagh) All submissions compete, so that still makes more than a 100 options! The voting system we'll use is the Condorcet Internet Voting System (http://www.cs.cornell.edu/andru/civs.html ). The poll won't be public, but every subscriber to Haskell-Cafe will get a (private) voting ballot by email. The poll will (probably) start March 16 and run for about a week (don't worry, there will be a strict deadline communicated). When the poll is over, the results will be viewable by everybody. The CIVS allows easy grouping and ordering, so the task of ordering 100 options should be doable within 5-10 minutes. If you're in a hurry you can do it a lot faster, just pick your favorite and put it first. If you want to learn more about condorcet voting, the CIVS site and Wikipedia are your friends. I'll supervise the poll and make sure it's started, stopped and all Haskell-Cafe subscribers get a ballot (Simon Marlow provided the email addresses). Since I'm going on a (probably internet deprived) holiday for a week _and_ to make sure I haven't overlooked anything, I'm announcing it now but won't start the poll till March 16. Of course, I'd love to hear about anything that I missed and/or that might influence the voting process in a significant way. (There are probably some people subscribed with multiple addresses, but I'll be using the subscriber list from yesterday, so signing up now with lots of addresses won't get you more ballots ;) -- Regards, Eelco Lempsink

18 28

digest and zlib on Windows
by Tillmann Rendel 11 Mar '09

11 Mar '09

Hi Eugene, I run into some troubles with the digest package on Windows. On unix, digest binds to zlib, but on Windows, the relevant c files from zlib are included. However, in digest-0.0.0.4, two header files were missing which were needed for compilation on my machine. With these header files added (from digits-0.0.0.3), digest compiles fine. Unfortunately, the zlib package has the same approach of including c files from zlib on Windows. That means that I could not use both zlib and digest together, because they contained conflicting symbols. Unfortunately, pandoc requires both zlib and digest. I solved the problem by removing the cbits from digest, and instead require the zlib on Windows. In other words, I deleted the cbits subdirectory, and changed the last few lines of digest.cabal from if !os(windows) extra-libraries: z else c-sources: cbits/adler32.c cbits/crc32.c include-dirs: cbits install-includes: zlib.h to the following: if !os(windows) extra-libraries: z else build-depends: zlib With this change, everything seems to work fine for me. Tillmann

1 0

ANNOUNCE: torch-0.1
by Yusaku Hashimoto 11 Mar '09

11 Mar '09

Hello, I have wrote and uploaded my unit test library (or framework) torch-0.1 on Hackage. With torch, We can write simple unit test and run like this: > import Test.Torch > > main = run $ do > ok (odd 1) "assertion" > is 42 (7*6) "equality assertion" > isBottom (error undefined) "check whether value is bottom" > ans <- liftIO (putStr "\n5 + 7 = " >> readLn) > is ans 12 "sanity check :)" Despite QuickCheck and HUnit, Why I wrote unit test library now? There is two reasons. 1. QuickCheck is not all-round QuickCheck is awesome. But I often can't write Property when I want to test things, like not pure function. Even for pure function, I can't write Property by thinking _laws_ behind that with probability about 0.5. When I can't write Property, I want to write unit test using HUnit. But for me, HUnit does not fit to my hands. Because it is annoying that writing list of test literally in source code and confusing operators (I still can't remember distinction between (@=?) and (@?=)) This means when I read test written in HUnit, I can't read this without Documentation. And I got an idea for expressing structure of tests from a blog post about Monoid and Writer Monad. 2. Try to realize an idea that Writer monad can be treated as Monoid (and list of Test is Monoid) I read sigfpe's great blog post (http://blog.sigfpe.com/2009/01/ haskell-monoids-and-their-uses.html) and hit upon the idea that considering Writer as Monoid, list of tests can be expressed with Monad. And I tried to realize it, and want to sympathize this idea with Haskellers. I think almost complete realizing this idea in the library. Those is why I wrote this library. And It is my first package on Hackage, I apologize for any wrong about packaging. I hope you'll enjoy this! Thanks, nonowarn

1 1

ANN: sparsebit 0.5 - Sparse Bitmaps for Pattern Match Coverage
by Ahn, Ki Yung 10 Mar '09

10 Mar '09

sparsebit - Sparse Bitmaps for Pattern Match Coverage http://hackage.haskell.org/cgi-bin/hackage-scripts/package/sparsebit This library packages the functional peal paper 'Sparse Bitmaps for Pattern Match Coverage' submitted to ICFP 2009 by Ki Yung Ahn and Tim Sheard. You can look up the tutorial-like paper and the talk slides, which are availabel at: http://kyagrd.dyndns.org/wiki/SparseBitmapsForPatternMatchCoverage Abstract: Pattern matching coverage over Algebraic Data Types(ADTs) has most often been studied in the context of pattern compilation algorithms. However, it is worth considering the pattern matching coverage problem in isolation, since general solutions will be independent of the specifics of any implementation or language. We define an intuitive and mathematically well-established bit masking semantics for pattern match coverage. We design and implement a sparse bitmap data structure, which realizes this semantics in a compact and flexible manner. This bitmap data structure supports computing coverage solutions of large programs incrementally from coverage solutions of sub-programs. It can also be used as a common data representation for pattern coverage shared between different tools (e.g., compilers, linting tools, software analysis tools) that need pattern match coverage information. Additional source files Type.hs and TestType.hs packaged with this library provides the examples and QuickCheck extracted from the paper to demonstrate how to use this library. ==================================================================== Some additional notes: Personally, I am very happy to upload my first project on Hackage. If you are looking for simple and elegant way of describing pattern match coverage or testing exhaustiveness of pattern matching, we hope this may give you a better insight. This is a reference implementation, but I think it is still usable to some extent. One might want to define monadic version of the library functions and operators since the type representation in the program analysis tools might be monadic for implementation reasons (easy to generate fresh type variables) and performance reasons (to exploit sharing while unification of type variables). And in such cases, more optimized implementation of tensor product may be possible as well. And there are some other issues discussed in the paper as well. I was not able to make the haddock documentation appear in Hackage, although I have no problem generating documentation using "cabal haddock" locally. It would be nice if there is a way to see some diagnose of warning or error messages why haddock failed on Hackage. -- Ahn, Ki Yung

2 1

Re: [Haskell-cafe] Sugestion for a Haskell mascot
by Gregory Michael Travis 10 Mar '09

10 Mar '09

Maur??cio <briqueabraque(a)yahoo.com> sed: > Hi, > > Here in Brazil we have a forest animal we name 'preguiça' -- literally, > lazyness. What better mascot we could have for Haskell? It lives (and > sleeps) in trees, and if you see the main picture in wikipedia articles > you can easily imagine the tree branch beeing replaced by a lambda: > > http://en.wikipedia.org/wiki/Sloth > > http://pt.wikipedia.org/wiki/Bicho-pregui%C3%A7a Perfect!

1 0

Re: [Haskell] Google Summer of Code 2009
by Johan Tibell 10 Mar '09

10 Mar '09

On Tue, Feb 10, 2009 at 3:26 PM, Malcolm Wallace <Malcolm.Wallace(a)cs.york.ac.uk> wrote: > Gentle Haskellers, > > The Google Summer of Code will be running again this year. Once again, > haskell.org has the opportunity to bid to become a mentoring > organisation. (Although, as always, there is no guarantee of > acceptance.) > > If you have ideas for student projects that you think would benefit the > Haskell community, now is the time to start discussing them on mailing > lists of your choice. We especially encourage students to communicate > with the wider community: if you keep your ideas private, you have a > much worse chance of acceptance than if you develop ideas in > collaboration with those who will be your "customers", end-users, or > fellow-developers. This is the open-source world! > > The timeline is that Haskell.org will apply for GSoC membership between > 9-13 March, and if we are successful, students can submit applications > between 23 March - 3 April. Google is now accepting applications: http://google-opensource.blogspot.com/2009/03/google-summer-of-code-applica…

2 2

Mystified by Cabal
by Colin Paul Adams 10 Mar '09

10 Mar '09

I have just attempted Cabal-izing my program (splitting it into a library and main program as well), and I'm mystified by some problems I am having. First, when I try to build the library I get: [colin@susannah game-tree]$ runhaskell Setup build Preprocessing library game-tree-1.0.0.0... Building game-tree-1.0.0.0... Data/Tree/Game/Negascout.hs:31:0: Unrecognised pragma [1 of 2] Compiling Data.Tree.Game.Tree ( Data/Tree/Game/Tree.hs, dist/build/Data/Tree/Game/Tree.o ) Data/Tree/Game/Tree.hs:1:0: Failed to load interface for `Prelude': it is a member of package base-3.0.3.0, which is hidden That mystifies me. Googling, it appears to be a common error in the past, but none of the reasons apparently apply to my case. Incidentally, Tree.hs imports nothing. It just looks like: -- | Nodes in game trees -- Copyright 2009 Colin Adams -- -- This file is part of game-tree. -- -- Game-tree is free software: you can redistribute it and/or modify -- it under the terms of the GNU General Public License as published by -- the Free Software Foundation, either version 3 of the License, or -- (at your option) any later version. -- Game-tree is distributed in the hope that it will be useful, -- but WITHOUT ANY WARRANTY; without even the implied warranty of -- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the -- GNU General Public License for more details. -- You should have received a copy of the GNU General Public License -- along with game-tree. If not, see <http://www.gnu.org/licenses/>. module Data.Tree.Game.Tree where -- | Nodes in a game search tree class Tree a where -- | Is this a game-terminating node (e.g. checkmate)? is_terminal :: a -> Bool -- | Heuristic value of node node_value :: a -> Int -- | Child nodes in the game tree (positions more deeply searched) children :: a -> [a] So I couldn't build my program using runhaskell, as I couldn't install the library. Instead, i tried ghc --make instead with the -idir option. It looks in the right place, but still doesn't recognise the module: Chasing modules from: *Chu-shogi.hs Generator.hs:27:7: Could not find module `Data.Tree.Game.Tree': locations searched: Data/Tree/Game/Tree.hs Data/Tree/Game/Tree.lhs dirs=../game-tree/Data/Tree/Game/Tree.hs dirs=../game-tree/Data/Tree/Game/Tree.lhs What am I doing wrong? Perhaps Cabal should be named Caballa instead. -- Colin Adams Preston Lancashire

7 12