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Re: [Haskell] ANN: Yi 0.6.2.2
by Jeff Wheeler 25 Mar '10

25 Mar '10

On Thu, Mar 25, 2010 at 7:48 AM, John Lato <jwlato(a)gmail.com> wrote: > Will it work if you set data-accessor-template < 0.2.1.3 in the .cabal > file? I think that version is acceptable to both ghc-6.10 and 6.12. It seems so, yes. Unfortunately, I've already made other changes to HEAD that are incompatible with 6.10. -- Jeff Wheeler Undergraduate, Electrical Engineering University of Illinois at Urbana-Champaign

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phonetic dictionnary
by Dupont Corentin 25 Mar '10

25 Mar '10

Hello, sorry if i ask a lot of questions these days! Do you know of a phonetic dictionnary? i'm very fond of enigmas. To solve certain enigmas, i've made a little program that search into a french dictionnary. But it would be much better if i could search into a phonetic dictionnary... The goal is to answer questions like "Wich word would rhyme with aligator?" Corentin

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explicit big lambdas
by Paul Brauner 25 Mar '10

25 Mar '10

Hi again, is there a way in some haskell extension to explicit (system F's) big lambdas and (term Type) applications in order to help type inference? If not: is there a way to provide ghc directly with core code before the type checking phase? Paul

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Re[Haskell-cafe] mote invocations in Haskell?
by Yves Parès 25 Mar '10

25 Mar '10

Hello, Is there a way to perform some kind of remote method invocation in haskell? (Or, "remote object", but I prefer not to use this term, as there are no "objects" strictly speaking in Haskell) I would like to use a higher level API than sockets for network programing. ----- Yves Parès Live long and prosper -- View this message in context: http://old.nabble.com/Remote-invocations-in-Haskell--tp28006793p28006793.ht… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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breadth first search one-liner?
by Johannes Waldmann 25 Mar '10

25 Mar '10

Dear all, there is this neat "one-line" BFS implementation bfs :: Eq a => ( a -> [a] ) -> a -> [a] bfs next start = let xs = nub $ start : ( xs >>= next ) in xs but it has a problem: it only works for infinite graphs. This is fine: take 20 $ bfs ( \ x -> [2*x, x+1] ) 1 but this is not: take 20 $ bfs ( \ x -> filter (>0) [ div x 2, x - 1 ] ) 10 Is there a nice way to repair this? (I know how to code a BFS but here I'm asking for a one-liner.) J. W.

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ANN: Salvia-1.0.0
by Sebastiaan Visser 25 Mar '10

25 Mar '10

Hi all, Straight from Zurihac: I'm very pleased to announce the 1.0.0 release of the Salvia web server. Salvia is a feature rich web server and web application framework that can be used to write dynamic websites in Haskell. From the lower level protocol code up to the high level application code, everything is written as a Salvia handler. This approach makes the framework extremely modular and extensible. This release include the following stack of packages: * salvia-protocol: Protocol stack containing URI, HTTP, Cookie and Mime. * salvia: Basic server interface and implementation. * salvia-extras: Additional server handlers and back end implementation. * salvia-sessions: Session and user management support. * salvia-websocket: Cutting edge HTML5 web socket support. * salvia-demo: Demo servers showing how to use Salvia. All the code is on Hackage[1] and the source repositories can be found on GitHub[2]. Most of the basic ideas of the previous Salvia release are still in these package, but all the code has been cleaned up considerably. There is now a very strong separation between interface and implementation making it more easy to plug-in new back-ends for your web application. To do a full install first run `cabal update' followed by `cabal install salvia-demo'. Now you can run the salvia-demo command and point your browser to http://localhost:8080/ . Thanks to the people that helped me with coding, suggestions and bug-reports. Any comments/suggestions are welcome! Have fun, -- Sebatiaan Visser [1] http://hackage.haskell.org/package/salvia (-protocol, -demo, etc) [2] http://github.com/sebastiaanvisser/salvia (-protocol, -demo, etc)

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Using Get monad to efficiently parse byte-stuffed data
by Pom Monico 25 Mar '10

25 Mar '10

Hello all, I'm struggling to use the Get monad to efficiently parse the some binary data of the format below. I simply can't find a way to use the monad to parse it efficiently. Binary data is terminated by a 0xFF marker. If the data itself contains an 0xFF, a 0x00 is byte-stuffed after it to indicate it is part of the data. An 0xFF followed by a non-zero byte indicates that it is a real marker and terminates the data and the 0xFF is not part of the data. Going through the data using getWord8 is a no-go. It is just too slow. My solution so far has been to get the underlying bytestring and work with that, but obviously defeats the purpose of using the Get monad. What might be a better solution? Pom.

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Fwd: [Haskell-cafe] Graphical representation of Haskell code
by Miguel Vilaca 24 Mar '10

24 Mar '10

Hi all, Concerning INblobs, it's again online; a fire damaged the cable that links the university to the world!! I don't update the tool for a long time... but I'll take a look on that. Concerning visual functional programming, see this small chapter of my thesis about some of the existing languages. There are more subtleties on the visual side than those expected!! If you also consider debugging tools, take a look on Ghood http://hackage.haskell.org/package/GHood best regards Miguel Vilaça A 2010/03/23, às 05:31, Ronald Guida escreveu: > On Mon, Mar 22, 2010 at 7:02 PM, Dupont Corentin > <corentin.dupont(a)gmail.com> wrote: >> Hello, I’m relatively new to Haskell. >> I’m wondering if it exist a tool to graphically represent Haskell code. > ... >> Let’s try to do it on a simple example, as an exercise: >> f = Map (+1) > > Your graphic for "f = map (+1)" seems much more complex than the > corresponding code. I would agree with Ivan Miljenovic: >> I'm of the opinion that unless you just use it on small snippets, >> the generated images will be too large and unwieldy. > > The first question I would ask is /why/ would you like to visualize > some Haskell code? If you want to see the high-level structure of > a complex program, try SourceGraph. (I have never used it though.) > > On the other hand, if you are trying to visualize Haskell as part of > your efforts to learn the language, then I believe it would be best to > draw diagrams by hand, rather than relying on an automated tool. > The kinds of things that you'll want to depict are probably going to > vary considerably, depending on what you're trying to understand. > > Consider a few different implementations of the "map" function: > > -- version 1: recursion > map1 :: (a -> b) -> [a] -> [b] > map1 f [] = [] > map1 f (x:xs) = (f x) : map1 f xs > > -- version 2: fold > map2 :: (a -> b) -> [a] -> [b] > map2 f = foldr ((:) . f) [] > > -- version 3: continuation passing style > map3 :: (a -> b) -> [a] -> [b] > map3 f xs = map' (\x y -> f x : y) xs > where > map' k [] = [] > map' k (y:ys) = k y (map' k ys) > > -- version 4: list comprehension > map4 :: (a -> b) -> [a] -> [b] > map4 f xs = [f x | x <- xs] > > -- version 5: list monad > map5 :: (a -> b) -> [a] -> [b] > map5 f xs = xs >>= (return . f) > > These all do exactly the same thing, but each one uses different > techniques. If I'm trying to learn (or teach) Haskell, I would > probably need a slightly different visual "language" for each one > in order to capture the most relevant concepts in a useful way. > How would you visualize them? > > @Mihai Maruseac: > I think a visual debugger would be a wonderful idea. You may want > to consider how a visual debugger would work with each of these > versions of map. > > :-) You might also consider several versions of factorial :-) > http://www.willamette.edu/~fruehr/haskell/evolution.html > > -- Ron > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

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Fwd: [Haskell-cafe] Graphical representation of Haskell code
by Miguel Vilaca 24 Mar '10

24 Mar '10

Hi all, Concerning INblobs, it's again online; a fire damaged the cable that links the university to the world!! I don't update the tool for a long time... but I'll take a look on that. Concerning visual functional programming, see this small chapter of my thesis about some of the existing languages. There are more subtleties on the visual side than those expected!! If you also consider debugging tools, take a look on Ghood http://hackage.haskell.org/package/GHood best regards Miguel Vilaça A 2010/03/23, às 05:31, Ronald Guida escreveu: > On Mon, Mar 22, 2010 at 7:02 PM, Dupont Corentin > <corentin.dupont(a)gmail.com> wrote: >> Hello, I’m relatively new to Haskell. >> I’m wondering if it exist a tool to graphically represent Haskell code. > ... >> Let’s try to do it on a simple example, as an exercise: >> f = Map (+1) > > Your graphic for "f = map (+1)" seems much more complex than the > corresponding code. I would agree with Ivan Miljenovic: >> I'm of the opinion that unless you just use it on small snippets, >> the generated images will be too large and unwieldy. > > The first question I would ask is /why/ would you like to visualize > some Haskell code? If you want to see the high-level structure of > a complex program, try SourceGraph. (I have never used it though.) > > On the other hand, if you are trying to visualize Haskell as part of > your efforts to learn the language, then I believe it would be best to > draw diagrams by hand, rather than relying on an automated tool. > The kinds of things that you'll want to depict are probably going to > vary considerably, depending on what you're trying to understand. > > Consider a few different implementations of the "map" function: > > -- version 1: recursion > map1 :: (a -> b) -> [a] -> [b] > map1 f [] = [] > map1 f (x:xs) = (f x) : map1 f xs > > -- version 2: fold > map2 :: (a -> b) -> [a] -> [b] > map2 f = foldr ((:) . f) [] > > -- version 3: continuation passing style > map3 :: (a -> b) -> [a] -> [b] > map3 f xs = map' (\x y -> f x : y) xs > where > map' k [] = [] > map' k (y:ys) = k y (map' k ys) > > -- version 4: list comprehension > map4 :: (a -> b) -> [a] -> [b] > map4 f xs = [f x | x <- xs] > > -- version 5: list monad > map5 :: (a -> b) -> [a] -> [b] > map5 f xs = xs >>= (return . f) > > These all do exactly the same thing, but each one uses different > techniques. If I'm trying to learn (or teach) Haskell, I would > probably need a slightly different visual "language" for each one > in order to capture the most relevant concepts in a useful way. > How would you visualize them? > > @Mihai Maruseac: > I think a visual debugger would be a wonderful idea. You may want > to consider how a visual debugger would work with each of these > versions of map. > > :-) You might also consider several versions of factorial :-) > http://www.willamette.edu/~fruehr/haskell/evolution.html > > -- Ron > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

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State of the Haskell Web Application Stack
by Ozgun Ataman 24 Mar '10

24 Mar '10

Greetings all. I have been for quite some time trying to assess the feasibility of using Haskell in relatively large, high volume, high availability, long-running web application projects. I have enjoyed learning and using Haskell very much for the past year and I often find myself missing various language features when reasoning about alternatives like Ruby (on Rails). If I can identify the right set of tools for the job, I would really like to take the plunge and make Haskell my standard go-to language in web applications. Here are the couple of key questions that I wanted get your feedback on: Do you consider Haskell and its environment of libraries ready for prime time in web app development as defined above? What collection of libraries would you use in such an effort? What are the up and coming packages/technologies in Haskell-land you would watch out for? Also, here are some core requirements that I would define for such a project: Ease/speed of development in both back and front-ends, minimal boilerplate Extendability and flexibility in iterative development Robustness and reliability in production environment High performance Scalability Ability to interface with new technologies in the future: Cassandra, Redis, memcached, etc. Ease of implementing common/reusable features across web applications: user authentication, S3 file uploads, thumbnail/image handling, exception notifications, etc. In terms of libraries, I can think of a few key components (as pointed out by several others before) that one would need to arrange: Choice of server (happstack vs. alternatives) Templating (xhtml vs. file templates vs. newer efforts like BlazeHtml) Data/storage layer: HDBC vs. HaskellDB vs. others I know this is a common topic in Haskell-Cafe, but I have failed to identify conclusive opinions from experienced Haskellers out there in previous discussions. My apologies in advance if this is a blatantly redundant post. All the best, Ozgun

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Fwd: [Haskell-cafe] Bytestrings and [Char]
by Alberto G. Corona 24 Mar '10

24 Mar '10

2010/3/24 Stephen Tetley <stephen.tetley(a)gmail.com> > If you consider containers as the containers package, the data > structures are all (?) functorial - but they have different shapes, > so e.g. a cons operation makes sense on the linear ones > (Data.Sequence, Data.List) but not on Data.Map, Data.Tree. 'cons' is > analogous to 'insert' but 'insert' exactly describes the operation on > maps whereas 'cons' doesn't, similarly 'insert' doesn't describe the > 'cons' operation on lists exactly as it doesn't indicate the position > of where it adds to the list. > Some operations like insert in list could be inefficient, some operations like cons in maps could be an inefficient hack, but at this does not means that a list can do create, insert, map , lookup faster that a Map in the case of sort lists, for example. A generalized cons applied to a Map can make less sense, but a program made for lists with occasional cons's can happen to perform better with Maps and so on. So a library with generality in mind can perform optimally in two or more different scenarios with different instances/implementations. . A genetic algoritm can have the opportunity to detect this. I think also that a complex list of class hierarchies is neither necessary nor recommended. We are not talking about mathemathical concepts. This is a performance issue. Even if a definitive class hierarchy is a problem, hopefully it may be worth to define tentative and temporal classes for performance testing purposes, that warps the common primitives with the sole purpose of executing the testing algorithm for different instance implementations, compilation flags and fusion rules. > > Now, if you partition the type classes into small groups you get over > the fact that some operations make sense on certain 'shapes' of data > structure, but there are still subtle type differences that aren't > conducive to type classes - e.g. ByteString and Data.Text aren't > functorial so map is type restricted: > > map :: (Word8 -> Word8) -> ByteString -> ByteString > > For this purpose, specific testing classes for Word8 data -with no claim to be "official" can be defined by the programmer, leaving to the library user to run the testing process for the different instances in his particular program. I know that this add extra work and that not many would do this extra level of abstraction, but perhaps this is less work than spending even more time exchanging emails, discussing low level issues, performing tests, trying to figure out what will be the most common sceniarios for wich the library could be used, testing manually what is the container that has the most performance here and now, not tomorrow for these scenarios, to worry about the obsolescence of the library for reasons not related with the library algorithm etc Regards

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Fwd: [Haskell-cafe] Bytestrings and [Char]
by Alberto G. Corona 24 Mar '10

24 Mar '10

---------- Forwarded message ---------- From: Alberto G. Corona <agocorona(a)gmail.com> Date: 2010/3/24 Subject: Re: [Haskell-cafe] Bytestrings and [Char] To: Stephen Tetley <stephen.tetley(a)gmail.com> 2010/3/24 Stephen Tetley <stephen.tetley(a)gmail.com> Hi Alberto > > I rather doubt a valuable set of type classes that is suitable for all > containers exists, I'm afraid. > > If you consider containers as the containers package, the data > structures are all (?) functorial - but they have different shapes, > so e.g. a cons operation makes sense on the linear ones > (Data.Sequence, Data.List) but not on Data.Map, Data.Tree. 'cons' is > analogous to 'insert' but 'insert' exactly describes the operation on > maps whereas 'cons' doesn't, similarly 'insert' doesn't describe the > 'cons' operation on lists exactly as it doesn't indicate the position > of where it adds to the list. > Some operations like insert in list could be inefficient, some operations like cons in maps could be an inefficient hack, but at this does not means that a list can do create, insert, map , lookup faster that a Map in the case of sort lists, for example. A generalized cons applied to a Map can make less sense, but a program made for lists with occasional cons's can happen to perform better with Maps and so on. So a library with generality in mind can perform optimally in two or more different scenarios with different instances/implementations. . A genetic algoritm can have the opportunity to detect this. I think also that a complex list of class hierarchies is neither necessary nor recommended. We are not talking about mathemathical concepts. This is a performance issue. Even if a definitive class hierarchy is a problem, hopefully it may be worth to define tentative and temporal classes for performance testing purposes, that warps the common primitives with the sole purpose of executing the testing algorithm for different instance implementations, compilation flags and fusion rules. > > Now, if you partition the type classes into small groups you get over > the fact that some operations make sense on certain 'shapes' of data > structure, but there are still subtle type differences that aren't > conducive to type classes - e.g. ByteString and Data.Text aren't > functorial so map is type restricted: > > map :: (Word8 -> Word8) -> ByteString -> ByteString > > For this purpose, specific testing classes for Word8 data -with no claim to be "official" can be defined by the programmer, leaving to the library user to run the testing process for the different instances in his particular program. I know that this add extra work and that not many would do this extra level of abstraction, but perhaps this is less work than spending even more time exchanging emails, discussing low level issues, performing tests, trying to figure out what will be the most common sceniarios for wich the library could be used, testing manually what is the container that has the most performance here and now, not tomorrow for these scenarios, to worry about the obsolescence of the library for reasons not related with the library algorithm etc Also, while ListLike does provide default definitions for many ops I'm > guessing its more important for performance to redefine them, so the > defaults definitions aren't adding much. > > There might be a couple of useful new type classes waiting in the > wings, e.g a destroy one as per view in Data.Sequence, but I doubt > that a proliferation of classes will generally make programs clearer > or more efficient and it would introduce more instances of problems > that we already have with Num type class. > > class Destroy f where > destroy :: f a -> (a, Maybe (f a)) > > Best wishes > > Stephen > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Re: [Haskell-cafe] Graphical representation of Haskell code
by Dupont Corentin 24 Mar '10

24 Mar '10

Hello! Thanks for the welcome! Ivan: Too overcome the problem of large and messy images, i propose too have a system to navigate into the code. You could zoom in and out, occulting unecessary details while zooming out. My big graphic of map (+1) could easely be summed up to: (Embedded image moved to file: pic36782.jpg) My idea is to provide an efficient system of zooming, as you can zoom in a fractal picture, showing more or less details! Such a tool, if created, could be implemented as a part of, or used by SourceGraph. In the first place i thought the GHC API would be great to infer each function's type. But indeed haskell-src-exts seems to be more appropriate as you get the structure of the program. Lyndon: Wahou this page (MockingBirds) his very interresting and funny! Mihai: That's funny we had the same idea quite the same time. I guess that idea is "in the air" and as said one contributor on your Reddit, "a well explored territory": It has major pitfalls and the reason why we heard little about that wild territory is because many explorers never returned :) By the way, i'm interrested and i could contribute on the little spare time i have. My idea is to make it as a library that display code as graphs. That library could be used for several purposes: debugging as you proposes, but also education, shows, audit (with SourceGraph), and why not construction... I think this kind of visual tool could be a "plus" in Haskell popularity. Despite not being that efficient, it is spectacular. Ronald: I agree big graphs are confusing. The big point of the project is to find or adapt an algorithm to simplify the graph and make it valuable. I'll have to make little graphics for each of your versions of map, this may be instructive to me... Stephen: I'll have a look at those interaction nets! But the home page for INBlobs seems to be down. Thank you all for you kind responses. Corentin

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how to make it faster ?
by 国平张 24 Mar '10

24 Mar '10

Hi, I wrote a type program to compute fibonacci series, if the max value is big, then it becomes very slow. like take 100 fib How can I make it faster :-) >>>>>>>>>>>>>>>> fibo 0 = 0 fibo 1 = 1 fibo (n+2) = (fibo n) + (fibo (n+1)) fib :: [Int] fib = [fibo i | i <- [0..]]

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Re: [Haskell-cafe] Bytestrings and [Char]
by John Lato 24 Mar '10

24 Mar '10

Hi Alberto, To some extent this already exists, it's just that nobody uses it. I believe it's the approach taken by the Edison libraries. Also the ListLike package provides the type classes ListLike, StringLike, and a few others. Neither seems to have become very popular despite having well-respected authors (Okasaki and Goerzon, respectively). Some container functions are already provided by other classes, namely Foldable, Traversable, and Monoid. The first bit, creating a tree of type classes suitable for all containers, is probably a few hours work. An automated system to determine the best implementation is significantly more difficult; I can't say if the scope would be appropriate for SoC. Best, John > From: "Alberto G. Corona " <agocorona(a)gmail.com> > > Just a dream: > -separate interface and implementation for all containers, via type classes > -develop, by genetic programming techniques + quickcheck, a system that find > the best container implementation for a particular program. > > Is that suitable for a Google Summer of Code project? > > 2010/3/23 Alberto G. Corona <agocorona(a)gmail.com> > > The question can be generalized via type classes: Is there any common set of >> primitives encapsulated into a single type class that has instances for >> Strings (Data.List) ByteStrings, Data.Text, Lazy bytestrings, Arrays, >> vectors and wathever container that can store an boxed, unboxed, packed >> unpacked sequence of wathever including chars? All of them have folds, >> heads, tails and a lot of common functions with the same name, but since >> there is not a single type class, the library programmer can not abstract >> his code when it is possible, so the library user can chose the particular >> instance for his particular problem.

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really difficult for a beginner like me...
by Ivan Amarquaye 24 Mar '10

24 Mar '10

Hi everyone, this is my first posting on here and this was what drove me here and the quest to know more as i anticipate a lot of help and direction in this quite new and different environment haskell.I have this paper that i'm working on and need to solve these scenarios/ cases based on some sample codes: Scenarios/cases: 1) Allow words to be hyphenated and treat the hyphenated word as a single word (including the hyphen). 2) As for no. 2 but if the hyphen is the last character on a line treat the hyphenated word as a single word without the hyphen. 3) Treat a capitalised word (one or more capital letters) the same as lower case, i.e. only the lower case word appears in the index. 4) Treat a word ending in an ‘s’ as a plural and thus the same as the singular, i.e. only the singular appears in the index. 5) As for no. 5 but (a) treat suffix ‘ss’ as not a plural; and (b) treat the plural suffixes ‘sses’, ‘zzes’, ‘oes’, ‘xes’, ‘shes’, ‘ches’ the same as the singular, i.e. without the ‘es’, e.g. “branches” (except for 4- and 5-letter plurals with suffices ‘oes’ and ‘ches’, e.g. “floes”, and 4-letter plural suffix ‘xes’); and (c) treat the plural suffix ‘ies’ (except for 4-letter plurals, e.g. “pies”) as the singular suffix ‘y’. 6) Make the output more readable in the form of an index table. 7) Use an output file 8) Include a user-friendly menu by which the user can choose input and output file names. This is the code i'm supposed tomodify and in some cases create new functions to support.I also need some explanation as the various approaches in solving them.............................................................................................. The function makeIndex given a document produces a list of entries. Each entry is a word and a list of line numbers (for words > 4 letters) Type definitions: import Prelude -- hiding (Word) -- predefined Word hidden, so we can define ours -- type String = [Char] defined in Prelude type Doc = String type Line = String type Word = String -- our version makeIndex :: Doc -> [ ([Int], Word) ] A data-directed design considers a sequence of functions (i.e using composition operator ‘.’) to transform the document of type, Doc, into an index of type, [ ([Int], Word) ]. splitUp the document, doc, into a list of lines, [Line]. numLines pairs each line with a line number, [(Int, Line)]. allNumWords splits lines into words and line no., [(Int, Word)]. sortLs sorts words into alphabetical order, [(Int, Word)]. makeLists makes a list for each line number, [([Int], Word)]. amalgamate nos. into a list of nos. for each word, [([Int], Word)]. shorten into a list for words > 4 letters, [([Int], Word)]. makeIndex = shorten . -- [([Int], Word)] -> [([Int], Word)] amalgamate . -- [([Int], Word)] -> [([Int], Word)] makeLists . -- [(Int, Word)] -> [([Int], Word)] sortLs . -- [(Int, Word)] -> [(Int, Word)] allNumWords . -- [(Int, Line)] -> [(Int, Word)] numLines . -- [Line] -> [(Int, Line)] splitUp -- Doc -> [Line] Last -- [a] -> [a ] splitUp function splitUp :: Doc -> [Line] splitUp [] = [] splitUp text = takeWhile (/='\n') text : -- first line (splitUp . -- splitup other lines dropWhile (==’\n’) . -- delete 1st newline(s) dropWhile (/='\n')) text -- other lines Example: splitUp “hello world\n\nnext world” => [“hello world”, “next world”] numLines function: numLines :: [Line] -> [(Int, Line)] numLines lines -- list of pairs of = zip [1 .. length lines] lines -- line no. & line Example: numLines [“hello world”, “next world”] => [(1, “hello world”), (2, “next world”)] splitWords function: -- for each line -- a) split into words -- b) attach line no. to each word splitWords :: Line -> [Word] -- a) splitWords [ ] = [ ] splitWords line = takeWhile isLetter line : -- first word in line (splitWords . -- split other words dropWhile (not.isLetter && Last ==’-’) . -- delete separators dropWhile isLetter) line -- other words where isLetter ch = (‘a’<=ch) && (ch<=’z’) || (‘A’<=ch) && (ch<=’Z’) Example: splitWords “hello world” => [“hello”, “world”] allNumWords function: numWords :: (Int, Line) -> [(Int, Word)] -- b) numWords (number, line) = map addLineNum ( splitWords line) -- all line pairs where addLineNum word = (number, word) -- a pair allNumWords :: [(Int, Line)] -> [(Int, Word)] allNumWords = concat . map numWords -- doc pairs Examples: addLineNum “hello” => (1, “hello”) numWords (1, “hello world”) => [(1, “hello”), (1, “world”)] allNumWords [(1, “hello world”), (2, “next world”)] => [(1, “hello”), (1, “world”), (2, “next”), (2, “world”)] SortLs function: sortLs :: [(Int, Word)] -> [(Int, Word)] sortLs [ ] = [ ] sortLs (a:x) = sortLs [b | b <- x, compare b a] -- sort 1st half ++ [a] ++ -- 1st in middle sortLs [b | b <- x, compare a b] -- sort 2nd half where compare (n1, w1) (n2, w2) = (w1 < w2) -- 1st word less || (w1 == w2 && n1 < n2) -- check no. Example: sortLs [(1, “hello”), (1, “world”), (2, “next”), (2, “world”)] => [(1, “hello”), (2, “next”), (1, “world”), (2, “world”)] makeLists function: makeLists :: [(Int, Word)] -> [([Int], Word)] makeLists = map mk -- all pairs where mk (num, word) = ([num], word) -- list of single no. Examples: mk (1, “hello”) => ([1], “hello”) makeLists [(1, “hello”), (2, “next”), (1, “world”), (2, “world”)] => [([1], “hello”), ([2], “next”), ([1], “world”), ([2], “world”)] Amalgamate function: amalgamate :: [([Int], Word)] -> [([Int], Word)] amalgamate [ ] = [ ] amalgamate [a] = [a] amalgamate ((n1, w1) : (n2, w2) : rest) -- pairs of pairs | w1 /= w2 = (n1, w1) : amalgamate ((n2, w2) : rest) | otherwise = amalgamate ((n1 ++ n2, w1) : rest) -- if words are same grow list of numbers Example: amalgamate [([1], “hello”), ([2], “next”), ([1], “world”), ([2], “world”)] => [([1], “hello”), ([2], “next”), ([1, 2], “world”)] Shorten function: shorten :: [([Int], Word)] -> [([Int], Word)] shorten = filter long -- keep pairs >4 where long (num, word) = length word > 4 -- check word >4 Example: shorten [([1], “hello”), ([2], “next”), ([1, 2], “world”)] => [([1], “hello”), ([1, 2], “world”)] _________________________________________________________________ Connect to the next generation of MSN Messenger http://imagine-msn.com/messenger/launch80/default.aspx?locale=en-us&source=…

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derivable type classes
by Ozgur Akgun 24 Mar '10

24 Mar '10

Can a user define a derivable type class of her own? If yes, how? Cheers, -- Ozgur Akgun

4 4

Syntax programming with lexemes rather than trees?
by Stephen Tetley 24 Mar '10

24 Mar '10

Hello All Modern functional programming languages give you algebraic data types that are mighty convenient for programming with syntax trees. However, I'm working in a domain (music typesetting) where modelling syntax with trees can be problematic and I'm wondering whether I should work at a lower level - essentially a list / stream of lexemes and some notion of a context stack for processing, tracking when I'm inside a tuplet and the metrical calculation is scaled, for example. Does anyone know of any previous work that takes a "lexical" view of syntax rather than an abstract syntax tree view? Any domain is good - I can't imagine there's any prior work on music typesetting. Pointers to papers would be more digestible than code but either is fine. Similarly, implementation in any functional language is fine. Thanks Stephen

4 6

Problem with Haskell Platform website
by Dietrich Epp 24 Mar '10

24 Mar '10

There's a problem with the Haskell Platform website. I'm posting the message here because I gave up looking for contact information for the site, maybe someone here can forward the message or tell me who to forward it to? The specific page is http://hackage.haskell.org/platform/mac.html Being one of the few who still use the PPC architecture, I expect to have to build my own packages from source. Imagine my surprise when the Haskell platform uses the "Universal Binary" logo on the Mac download. Nowhere on the Mac download page does it specify an architecture. However, the binary is i386 only and not PPC. So I just wasted time downloading something I can't install on my computer. This page shows the "Universal Binary" logo: http://hackage.haskell.org/platform/ Here is Apple's "Universal Binary" page, which describes what the logo means: http://www.apple.com/universal/ It would be nice to get rid of the "Universal Binary" logo and to mark the packages as i386. --Dietrich Epp

2 1

Syntax programming with lexemes rather than trees?
by Max Rabkin 24 Mar '10

24 Mar '10

[Sorry for the accidental off-list reply, Neil] On Tue, Mar 23, 2010 at 10:43 PM, Neil Mitchell <ndmitchell(a)gmail.com> wrote: > It actually sounds like your representation has structure, but you > dislike structure because it's hard to work with. It seems to me like the data has structure, but that data is not treelike! Is a performance a collection of measures or a collection of instruments? A tree-like structure makes you choose, but in truth it is both. I'm not sure I've seen a good solution to this kind of problem in FP. --Max

3 3

Are there any web server framework ?
by zaxis 24 Mar '10

24 Mar '10

Erlang has yaws (http://yaws.hyber.org/) Scala has lift (http://liftweb.net/) Python has django (http://www.djangoproject.com/) Ruby has rails (http://rubyonrails.org/) How about haskell ? Is there any similar framework, which should be steady, powerful and easy to use, in haskell ? Sincerely! ----- fac n = let { f = foldr (*) 1 [1..n] } in f -- View this message in context: http://old.nabble.com/Are-there-any-web-server-framework---tp27926433p27926… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

8 7

Cabal Compiler Flag Problem
by Ben Derrett 24 Mar '10

24 Mar '10

Hi, I'm trying to install the Haskell cgi module, as per here http://passingcuriosity.com/2009/haskell-fastcgi-with-apache/. When I type cabal install cgi, I get the following error (on a Fedora instance): cabal install cgi Resolving dependencies... Configuring MonadCatchIO-mtl-0.3.0.0... Preprocessing library MonadCatchIO-mtl-0.3.0.0... Building MonadCatchIO-mtl-0.3.0.0... [1 of 1] Compiling Control.Monad.CatchIO ( Control/Monad/CatchIO.hs, dist/build/Control/Monad/CatchIO.o ) Control/Monad/CatchIO.hs:146:34: Illegal signature in pattern: E.SomeException Use -XPatternSignatures to permit it cabal: Error: some packages failed to install: MonadCatchIO-mtl-0.3.0.0 failed during the building phase. The exception was: exit: ExitFailure 1 cgi-3001.1.8 depends on MonadCatchIO-mtl-0.3.0.0 which failed to install. So, I modified my /root/.cabal/config with: -- flags: -XPatternSignatures This doesn't seem to resolve the problem. What do I need to do to change the compiler flags? Thanks, Ben

3 4

installing Network on windows
by gladstein＠gladstein.com 24 Mar '10

24 Mar '10

7 6

Timeouts that don't cause data growth.
by David Leimbach 24 Mar '10

24 Mar '10

Trying to understand why the code here: http://moonpatio.com/fastcgi/hpaste.fcgi/view?id=8823#a8823 exhausts memory. I need to have timeouts in a program I'm writing that will run an interactive polling session of some remote resources, and know when to give up and handle that error. Unfortunately this code dies pretty quickly and produces an -hc graph like the one attached. It seems that System.Timeout can't be used for this. I should note that if the code is changed to use an inifnite timeout (-1) that this problem doesn't occur. Is this a bug in System.Timeout, or is there something I should be doing to keep the data size down? Dave

4 10

ANNOUNCE: Bravo-0.1.0
by Matthias Reisner 24 Mar '10

24 Mar '10

Hello, I'm pleased to announce the first release of Bravo, a static text template generation library, on Hackage: http://hackage.haskell.org/package/Bravo. Bravo is a text template library that provides parsing and generation of templates at compile time. Templates can be read from strings or files and for each a new record data type is created, allowing convenient access to all template variables in a type-safe manner. Since all templates are processed at compile time, no extra file access or error handling at runtime is necessary. Bravo is inspired by the PHP template engine Smarty and the Haskell template library chunks. Compared to chunks, Bravo provides additional features like conditional template evaluation, embedding of Haskell expressions and customized data type generation. I'm going to add further information to the HaskellWiki page (http://www.haskell.org/haskellwiki/Bravo) later. Bravo is still highly experimental and not well-tested, so bug reports and additional feedback are very welcome. I'd also like to hear if you feel the package dependencies are to restrictive. Regards, Matthias Reisner

4 7

Bytestrings and [Char]
by Johann Höchtl 23 Mar '10

23 Mar '10

Hello, I was recentyl playing with Haskell (GHC that is) IO and text processing. Bytestrings and Lazy Bytestrings allow for fast and memory eficient string (well, bytestring) handling, yet a lot of libraries do not support them (yet) Given the incredibly inneficient memory representation of [Char] (16 bytes? per cell) I wonder wheather String should default to lazy batestring altogether instead of [Char]. The levenshtein distance as is on hackage uses e.g. String ([Char]) and as such is unneccessarily slow. My question or discussion point: Why not depreciate [Char] altogether and favour of lazy Bytestrings? Regards, Johann

16 23

Fwd: [Haskell-cafe] Bytestrings and [Char]
by Alberto G. Corona 23 Mar '10

23 Mar '10

Just a dream: -separate interface and implementation for all containers, via type classes -develop, by genetic programming techniques + quickcheck, a system that find the best container implementation for a particular program. Is that suitable for a Google Summer of Code project? 2010/3/23 Alberto G. Corona <agocorona(a)gmail.com> The question can be generalized via type classes: Is there any common set of > primitives encapsulated into a single type class that has instances for > Strings (Data.List) ByteStrings, Data.Text, Lazy bytestrings, Arrays, > vectors and wathever container that can store an boxed, unboxed, packed > unpacked sequence of wathever including chars? All of them have folds, > heads, tails and a lot of common functions with the same name, but since > there is not a single type class, the library programmer can not abstract > his code when it is possible, so the library user can chose the particular > instance for his particular problem. > > 2010/3/23 Johann Höchtl <johann.hoechtl(a)gmail.com> > > On 22.03.2010 14:15, Ivan Miljenovic wrote: >> >>> On 23 March 2010 00:10, Johan Tibell<johan.tibell(a)gmail.com> wrote: >>> >>> >>>> A sequence of bytes is not the same thing as a sequence of Unicode >>>> code points. If you want to replace String by something more efficient >>>> have a look at Data.Text. >>>> >>>> >>> Though Data.Text still has the disadvantage of not being as nice to >>> deal with as String, since you can't pattern match on it, etc. >>> >>> Whilst it may degrade performance, treating String as a list of >>> characters rather than an array provides you with greater flexibility >>> of how to deal with it. >>> >>> >>> >> But doesn't this basically mean sacrifice performance / applicability for >> algorithmic beauty? Sure, pattern match comes in handy, but in the case of >> strings at a high price >> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > >

1 0

Re: [Haskell-cafe] Bytestrings and [Char]
by Iustin Pop 23 Mar '10

23 Mar '10

On Tue, Mar 23, 2010 at 05:53:00PM +0000, Vincent Hanquez wrote: > On 23/03/10 17:11, Iustin Pop wrote: > >Data.ByteString.Lazy (bytestring readFile + length) -< 10 miliseconds, > >incorrect length (as expected). > > > >Data.ByteString.Lazy.UTF8 (system readFile + fromString + length) - 11 > >seconds, correct length. > > Why would you use system readFile and not bytestring readFile in the > second case ? > > using the later i got a ~48x slowdown, not a >1100x slowdown, and > the length is correct too. Hmm… because I didn't think of that :) iustin

1 0

RE: [Haskell-cafe] Cabal source installation
by Chris Dornan 23 Mar '10

23 Mar '10

> Have you tried? > > cabal unpack <package-name> Thanks if I understand rightly, that 'cabal unpack' be used to build the shell script I have in mind. But I really want an option to Cabal to request it to install the source code of a package in a source-tree edition of the installed binary package. Chris -----Original Message----- From: Colin Paul Adams [mailto:colin@colina.demon.co.uk] Sent: 23 March 2010 11:35 AM To: Chris Dornan Subject: Re: [Haskell-cafe] Cabal source installation Have you tried? cabal unpack <package-name> -- Colin Adams Preston Lancashire

1 0

Cabal source installation
by Chris Dornan 23 Mar '10

23 Mar '10

I am using Cabal on Windows and Haskell Platform 2009.2.0.2 and have been trying get it to install the package source code with no success, so I am considering writing a script to unpack the tar archive and install it in my own package source repository. Is there an easier way to do this? Chris

1 0

"Improve Cabal's test support" for Google summer of code
by Mujtaba Boori 23 Mar '10

23 Mar '10

Hello I'm thinking of project for my google proposal . I found "improve Cabal's test support' is really interesting .I have a decent knowledge about Haskell programming and testing methods . I was wondering if this project is suitable for me and what skill I required to have. I would be very thankful if you give me advice for resources to look and understand it. Thank you -- Mujtaba Ali Alboori

1 0

openFile and portability
by Ketil Malde 23 Mar '10

23 Mar '10

Hi, For convenience, I often build binaries with -optl-static, and distribute them. Except for the slightly annoying necessity of adding -optl-pthread as well, this works great. Now I just upgraded my Ubuntu box from 9.10 (Karmic) to 10.4 (Lucid), and suddently static binaries refuse to work on other machines, specifically I get: openFile: invalid argument (Invalid argument) This seems to happen for any program trying to read a file, for instance: main = readFile "/etc/passwd" >>= putStrLn The program will compile and work as expected, but fails if I move it to a computer with an older distribution (I've tested RHEL and CentOS 5.4 so far). I tried strace, and the call to open appears to be similar, and succeed in all cases. Any ideas? -k -- If I haven't seen further, it is by standing in the footprints of giants

1 0

Graphical representation of Haskell code
by Dupont Corentin 23 Mar '10

23 Mar '10

Hello, I’m relatively new to Haskell. I’m wondering if it exist a tool to graphically represent Haskell code. Look at the little graphics at: http://www.haskell.org/arrows/index.html (and following pages) from Ross Paterson. <http://www.haskell.org/arrows/index.htm> If found these very useful to understand the Arrow monad. Why not automatise this in a tool? Such a tool could draw a graphic from the code of a program. This could be done entirely automatically from the types of the functions. Let’s try to do it on a simple example, as an exercise: f = Map (+1) How does this function could be represented? It contains the (+) function. This function has the type (+) :: Num a => a -> a -> a. >From this type we could deduce the graphic: [image: Haskell schematic_html_m20060f13.gif] Or a curried version: [image: Haskell schematic_html_5155f0eb.gif] The function (+1) then is: [image: Haskell schematic_html_m68795eb7.gif] The function map could be drawn like this : [image: Haskell schematic_html_m28c92a58.gif] Or like this: [image: Haskell schematic_html_m6ae433ea.gif] And the entire function map (+1) could be represented as: [image: Haskell schematic_html_macb1643.gif] Thanks to the advanced type system of Haskell, everything could be deduced from the type signatures. Such a tool would be recreational and educational. One could zoom in and out in a program, to display more or less details. This could help understand a program, globally or locally. We could even imagine a constructive version of the tool, where the programmer would draw functions from a toolbox, and stick them into the graphic! Does a tool approaching this already exist? If not, would it be a good project? Cheers, Corentin

6 5

Hackape package lackage
by Dougal Stanton 23 Mar '10

23 Mar '10

Hackage seems to be down again. $ cabal update Downloading package list from server 'http://hackage.haskell.org/packages/archive' ^Ccabal: interrupted $ ping -c3 hackage.haskell.org PING abbot.galois.com (69.30.63.204) 56(84) bytes of data. --- abbot.galois.com ping statistics --- 3 packets transmitted, 0 received, 100% packet loss, time 2012ms

4 3

ICFP 2010: Final Call for Papers
by Wouter Swierstra 23 Mar '10

23 Mar '10

===================================================================== Final Call for Papers ICFP 2010: International Conference on Functional Programming Baltimore, Maryland, 27 -- 29 September 2010 http://www.icfpconference.org/icfp2010 ===================================================================== Important Info ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Submission: 2 April 2010 Author response: 24 -- 25 May 2010 Notification: 7 June 2010 Final papers due: 12 July 2010 All deadlines are at 14:00 UTC. Submission is now open at http://icfp2010.seas.upenn.edu/ Scope ~~~~~ ICFP 2010 seeks original papers on the art and science of functional programming. Submissions are invited on all topics from principles to practice, from foundations to features, from abstraction to application. The scope includes all languages that encourage functional programming, including both purely applicative and imperative languages, as well as languages with objects or concurrency. Particular topics of interest include * Language Design: type systems; concurrency and distribution; modules; components and composition; metaprogramming; relations to object-oriented or logic programming; interoperability * Implementation: abstract machines; compilation; compile-time and run-time optimization; memory management; multi-threading; exploiting parallel hardware; interfaces to foreign functions, services, components or low-level machine resources * Software-Development Techniques: algorithms and data structures; design patterns; specification; verification; validation; proof assistants; debugging; testing; tracing; profiling * Foundations: formal semantics; lambda calculus; rewriting; type theory; monads; continuations; control; state; effects * Transformation and Analysis: abstract interpretation; partial evaluation; program transformation; program calculation; program proof * Applications and Domain-Specific Languages: symbolic computing; formal-methods tools; artificial intelligence; systems programming; distributed-systems and web programming; hardware design; databases; XML processing; scientific and numerical computing; graphical user interfaces; multimedia programming; scripting; system administration; security; education * Functional Pearls: elegant, instructive, and fun essays on functional programming The conference also solicits Experience Reports, which are short papers that provide evidence that functional programming really works or describe obstacles that have kept it from working in a particular application. Abbreviated instructions for authors ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ By 2 April 2010, 14:00 UTC, submit an abstract of at most 300 words and a full paper of at most 12 pages (6 pages for an Experience Report), including bibliography and figures. The deadline will be strictly enforced and papers exceeding the page limits will be summarily rejected. Authors have the option to attach supplementary material to a submission, on the understanding that reviewers may choose not to look at it. A submission will be evaluated according to its relevance, correctness, significance, originality, and clarity. It should explain its contributions in both general and technical terms, clearly identifying what has been accomplished, explaining why it is significant, and comparing it with previous work. The technical content should be accessible to a broad audience. Functional Pearls and Experience Reports are separate categories of papers that need not report original research results and must be marked as such at the time of submission. Detailed guidelines on both categories are on the conference web site. Each submission must adhere to SIGPLAN's republication policy, as explained on the web at http://www.acm.org/sigplan/republicationpolicy.htm. Proceedings will be published by ACM Press. Authors of accepted submissions are expected to transfer the copyright to the ACM. Presentations will be videotaped and released online if the presenter consents by signing an additional permission form at the time of the presentation. Formatting: Submissions must be in PDF format printable in black and white on US Letter sized paper and interpretable by Ghostscript. If this requirement is a hardship, make contact with the program chair at least one week before the deadline. Papers must adhere to the standard ACM conference format: two columns, nine-point font on a ten-point baseline, with columns 20pc (3.33in) wide and 54pc (9in) tall, with a column gutter of 2pc (0.33in). A suitable document template for LATEX is available from SIGPLAN at http://www.acm.org/sigs/sigplan/authorInformation.htm. Submission: Submissions will be accepted electronically at a URL to be named later. Improved versions of a paper may be submitted at any point before the submission deadline using the same web interface. Author response: Authors will have a 48-hour period, starting at 14:00 UTC on 24 May 2010, to read and respond to reviews. Special Journal Issue: There will be a special issue of the Journal of Functional Programming with papers from ICFP 2010. The program committee will invite the authors of select accepted papers to submit a journal version to this issue. Organization ~~~~~~~~~~~~ Conference Chair Paul Hudak, Yale University Program Chair Stephanie Weirich, University of Pennsylvania Program Committee: Umut Acar, Max Planck Institute for Software Systems Zena Ariola, University of Oregon James Cheney, University of Edinburgh Peter Dybjer, Chalmers University of Technology Robert Bruce Findler, Northwestern University Andy Gill, Kansas University Fritz Henglein, University of Copenhagen Michael Hicks, University of Maryland, College Park Patricia Johann, University of Strathclyde Andres Löh, Utrecht University Simon L. Peyton Jones, Microsoft Research Didier Rémy, INRIA Paris-Rocquencourt John Reppy, University of Chicago Manuel Serrano, INRIA Sophia-Antipolis Matthieu Sozeau, Harvard University

1 0

CUFP mailing list
by Günther Schmidt 22 Mar '10

22 Mar '10

Hi everyone, is there a mailing list for CUFP-lers? I have some questions that are related to commercial software development (in Haskell) which I don't think fit well on this list. Günther

4 7

Zarathustra
by Günther Schmidt 22 Mar '10

22 Mar '10

Hi Cliff, here is a link which might interest you http://en.wikipedia.org/wiki/Zoroastrianism Love Günther

1 0

Strange typing?
by Ozgur Akgun 22 Mar '10

22 Mar '10

Hi Cafe! Disclaimer: I know what I'm going to ask is now available as a language feature normally. And sorry for the subject of this message, I couldn't compe up with a good&descriptive subject. Is there any way to limit a functions type, not by a data type but by a group of constructors of a data type? If not, what would be the *right* thing to do to achieve this level of type safety? data DT1 = X | Y | Z data DT2 = A | B | C | D func1 :: DT1 -> DT2 -- instead of this func1' :: (X|Y) -> (B|C) -- i want sth. like this. (| means or) Only think I can think of is having the constructors, as seperate data types, introducing new type classes to group every possible subset of [X,Y,Z] and [A,B,C,D] and use those type classes when defining the functions. But as you can imagine, this is not the only place I want to use this thing, and the code will start to look cryptic if I do so. I must add, I want to use this *disjunction of constructors* thingy in data type declerations as well. A little bit brainstorming maybe? Thanks in advance, -- Ozgur Akgun

6 7

RFC: only-read-or-write-vars
by Bas van Dijk 22 Mar '10

22 Mar '10

Hello, I've written a tiny package for restricting access to mutable variables to be read-only or write-only: http://code.haskell.org/~basvandijk/code/only-read-or-write-vars/ This is a Request For Comments, so any comments / patches / +1s / -1s about anything are more than welcome before I upload it to hackage (sometime this weekend). regards, Bas

2 3

ANN: Three package announcements
by Mario Blažević 22 Mar '10

22 Mar '10

There are three new packages on Hackage: - monad-parallel 0.5 (http://hackage.haskell.org/package/monad-parallel) - monad-coroutine 0.5 (http://hackage.haskell.org/package/monad-coroutine) - Streaming Component Combinators 0.5 (http://hackage.haskell.org/package/scc) The first two packages are completely new. Their functionality has been present in SCC 0.4, but I thought they might be useful on their own. I'm keeping all the version numbers in sync for now, and the source code for all three packages is in a single Darcs repository at http://code.haskell.org/SCC/. The monad-parallel library defines two Monad subclasses, MonadParallel and MonadFork, that enable monadic computations to be executed in parallel and their results combined. The library also exports a subset of the Control.Monad interface (ap, sequence, and related functions), adjusted to exploit the parallelism. The only currently defined MonadParallel instances are IO, Maybe, [], and Identity. More instances could be added, but I didn't want the package to depend on MTL or transformers. The library design was heavily influenced by the discussion in this Cafe thread: http://www.mail-archive.com/haskell-cafe@haskell.org/msg68581.html The monad-coroutine package exports a generic monad transformer Coroutine: Functor s => MonadTrans (Coroutine s). A Coroutine-transformed monad can suspend at any point, returning its resumption wrapped in the functor s. There are also some functions for manipulating and running coroutines, as well as a couple of useful suspension functors such as Yield and Await. Finally, version 0.5 of Streaming Component Combinators (a.k.a. SCC) comes with some significant code refactoring (as the two aforementioned packages prove), simplifications, and performance enhancements. No new features have been added since the 0.4 release.

1 0

ANNOUNCE: AusHac2010
by Ivan Lazar Miljenovic 22 Mar '10

22 Mar '10

Dreading the end of ZuriHac? Wish the Haskellian camaraderie could continue? Well, if you're able to make your way to Sydney, Australia between the 16th and 18th of July, then AusHac2010 is for _you_! It will be held at the School of Computer Science and Engineering at the University of New South Wales (thanks to Manuel Chakravarty and Ben Lippmeier for offering to organise the rooms!). If you are wanting to attend the inaugural Australian Hackathon, please register at http://axman6.wufoo.com/forms/aushac-2010-sign-up/ . For more information, see http://www.haskell.org/haskellwiki/AusHac2010 We will shortly be adding an extended version of the "Who" table; please also add your details there as well as which projects you would be interested in hacking in. Hoping to see you there! -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

1 0

Occurs check error, help!
by boblettoj 22 Mar '10

22 Mar '10

Hi i am writing a shuffle function which takes in a random number i and a list and then produces a jumbled up version of the list at the end. Here is what i have at the moment (i'm not sure if it works yet as it won't compile! --function used to shuffle cards --list equals random member of array plus the rest of the array --i is randomly generated from range of length equal to that of cards. shuffle :: int -> [a] -> [a] shuffle i [] = [] shuffle i [cards] = (cards!!i) + (shuffle (randomR (0, ((length cards)-2))) (delete (cards!!i) cards)) I get this error message when i try to compile: Occurs check: cannot construct the infinite type: a = [[a]] I'm very new to haskell so you'll have to excuse any ignorance! thanks -- View this message in context: http://old.nabble.com/Occurs-check-error%2C-help%21-tp27966341p27966341.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

8 20

RE: No warning in GHC
by Simon Peyton-Jones 22 Mar '10

22 Mar '10

[Redirecting to haskell-cafe] Try http://www.haskell.org/ghc/docs/latest/html/users_guide/flag-reference.html… With -Wall I get bash-3.2$ ghc -c -Wall Foo.hs Foo.hs:3:0: Warning: Definition but no type signature for `func' Inferred type: func :: forall t t1. (Num t1) => t -> t1 Foo.hs:3:5: Warning: Defined but not used: `x' Foo.hs:4:10: Warning: This binding for `x' shadows the existing binding bound at Foo.hs:3:5 | -----Original Message----- | From: cvs-ghc-bounces(a)haskell.org [mailto:cvs-ghc-bounces@haskell.org] On Behalf Of | Grigory Sarnitskiy | Sent: 21 March 2010 19:37 | To: cvs-ghc(a)haskell.org | Subject: No warning in GHC | | Hello! I wonder, why GHC shows no warning in situations like | | func x = x | where x = 5 | | Sometimes I forget about argument names used, and use the same names in let or where. | And it can take me quite a lot time to understand what is wrong. I think it would be | nice to warn users if the argument is "redefined" in let/where clause. Shall I report | a bug/feature request? I'm using ghc 6.10.4. | | btw, I couldn't post to IRC: #ghc :Cannot send to channel | | _______________________________________________ | Cvs-ghc mailing list | Cvs-ghc(a)haskell.org | http://www.haskell.org/mailman/listinfo/cvs-ghc

1 0

Bubble sort algorithm implementations (Haskell vs. C)
by Yasir Arsanukaev 22 Mar '10

22 Mar '10

Hello. I have written 2 implementation of bubble sort algorithm in C and Haskell. Haskell implementation: module Main where main = do contents <- readFile "./data" print "Data loaded. Sorting.." let newcontents = bubblesort contents writeFile "./data_new_ghc" newcontents print "Sorting done" bubblesort list = sort list [] False rev = reverse -- separated. To see rev2 = reverse -- who calls the routine sort (x1:x2:xs) acc _ | x1 > x2 = sort (x1:xs) (x2:acc) True sort (x1:xs) acc flag = sort xs (x1:acc) flag sort [] acc True = sort (rev acc) [] False sort _ acc _ = rev2 acc I've compared these two implementations having run both on file with size of 20 KiB. C implementation took about a second, Haskell — about 1 min 10 sec. I have also profiled the Haskell application: Compile for profiling: C:\Temp> ghc -prof -auto-all -O --make Main Profile: C:\Temp> Main.exe +RTS -p and got these http://hpaste.org/fastcgi/hpaste.fcgi/view?id=24190#a24190 This is a pseudocode of the algorithm: procedure bubbleSort( A : list of sortable items ) defined as: do swapped := false for each i in 0 to length(A) - 2 inclusive do: if A[i] > A[i+1] then swap( A[i], A[i+1] ) swapped := true end if end for while swapped end procedure The performance may suffer from the memory allocation for the list. I wonder if it's possible to make Haskell implementation work faster without changing the algorithm (there's are actually a few tricks to make it work faster, but neither implementations have these optimizations). I'm interested not in particular algorithm performance but rather in performance of its implementations in various languages. I compiled the Haskell implementation in GHC (Haskell Platform 2009.2.0.2), which is the latest available from the site.

5 6

Google summer of code idea.
by Mujtaba Boori 22 Mar '10

22 Mar '10

Hello I would like to discuss my idea for google summer of code. I'm an active Haskell programmer . I have read the idea list . I think Improve Cabal's test support really suit my ability of haskell. I would like to give me advice about my idea . and how to improve my proposal . Thank you. -- Mujtaba Ali Alboori

2 1

Data.Number.BigFloat/Fixed
by H. 21 Mar '10

21 Mar '10

Hello, With ghc-6.10.4 the following results are produced with numbers 2009.8.9: (7e-3 :: BigFloat Prec50) < (6e-4 :: BigFloat Prec50) False (7e-3 :: BigFloat Prec50) < (8e-4 :: BigFloat Prec50) True where in the sourecode is written: data BigFloat e = BF (Fixed e) Integer deriving (Eq, Ord) and import Data.Ratio newtype Fixed e = F Rational deriving (Eq, Ord, Enum, Real, RealFrac) H.

5 6

How to set a breakpoint in GHCi
by Gracjan Polak 21 Mar '10

21 Mar '10

Hi all, Tried to use :break today, without success: guestbook-session-bug>ghci -DMIN_VERSION_template_haskell(a,b,c)=1 -isrc Main -i../happstack/happstack-ixset/src GHCi, version 6.12.1: http://www.haskell.org/ghc/ :? for help ... ... [10 of 13] Compiling Happstack.Data.IxSet ( ..\happstack\happstack-ixset\src\Happstack\Data\IxSet.hs, interpreted ) ... ... *Main> :m +Happstack.Data.IxSet *Main Happstack.Data.IxSet> :bre getOrd No breakpoints found at that location. *Main Happstack.Data.IxSet> What now? -- Gracjan

1 0

Re: [Haskell-cafe] ANN: fixed-list -- A fixed length list library
by Casey McCann 21 Mar '10

21 Mar '10

Job Vranish <job.vranish(a)gmail.com> wrote: > Its main advantages are: > Very easy to use. > Almost entirely Haskell98 (the non Haskell98 pieces are not critical, just > nice) > The datatype is a member of Foldable, Traverable, Applicative, Monad, > etc... > Then length of the list is encoded in the type in a natural way. Unfortunately, it's very easy to get a context reduction stack overflow from GHC this way, which makes using such datatypes awkward for anything but very short lists. Explicit type annotations will often make things work, but at that point the type class isn't helping you anyway. For example, assuming the default stack size: import Data.FixedList fixed18 :: FixedList18 Int fixed18 = fromFoldable' [1..] -- this works fixed20 = 20 :. 20 :. fixed18 -- this works fixed22 :: FixedList22 Int fixed22 = 22 :. 22 :. fixed20 -- this only works with a type annotation show18 = show fixed18 -- this works -- this doesn't work: -- show20 = show fixed20 show20' :: FixedList20 Int -> String show20' list20 = show list20 show20 = show20' fixed20 -- this does work Using head and tail on longer lists fails likewise. I expect there's some way to make it work without simply increasing the stack depth, but I'm not sure how. Any thoughts? - C.

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Parallel Pi
by Artyom Kazak 21 Mar '10

21 Mar '10

Hello! I tried to implement the parallel Monte-Carlo method of computing Pi number, using two cores: --PROGRAM module Main where import Random import Data.Ratio import Data.List import System.IO import GHC.Conc main = do putStrLn "pi 1" putStr "n: " hFlush stdout t <- getLine piMonte (read t) >>= (putStrLn . show) piMonte n = do (g1, g2) <- split `fmap` getStdGen let r1 = r (n `div` 2) g1 r2 = r (n `div` 2 + n `mod` 2) g2 in return (ratio (r1 `par` (r2 `pseq` (merge r1 r2)))) where r n g = (length (filter id lAll), n) where l = take n . randomRs (0, 1) inCircle :: Double -> Double -> Bool inCircle a b = a*a + b*b <= 0.25 lAll = zipWith inCircle (l g1) (l g2) (g1, g2) = split g ratio :: (Int, Int) -> Double ratio (a, b) = fromRational (toInteger a % toInteger b * 16) merge (a, b) (c, d) = (a + c, b + d) --END But it uses only on core: C:\>ghc --make -threaded Monte.hs -fforce-recomp [1 of 1] Compiling Main ( Monte.hs, Monte.o ) Linking Monte.exe ... C:\>monte +RTS -N2 -s monte +RTS -N2 -s pi 1 n: 1000000 3.143616 2,766,670,536 bytes allocated in the heap 1,841,300 bytes copied during GC 5,872 bytes maximum residency (1 sample(s)) 23,548 bytes maximum slop 2 MB total memory in use (0 MB lost due to fragmentation) Generation 0: 5285 collections, 5284 parallel, 0.64s, 0.31s elapsed Generation 1: 1 collections, 1 parallel, 0.00s, 0.00s elapsed Parallel GC work balance: 1.00 (454838 / 454676, ideal 2) MUT time (elapsed) GC time (elapsed) Task 0 (worker) : 0.00s ( 9.33s) 0.00s ( 0.00s) Task 1 (worker) : 0.63s ( 9.33s) 0.00s ( 0.00s) Task 2 (worker) : 6.00s ( 9.34s) 0.64s ( 0.31s) Task 3 (worker) : 0.00s ( 9.34s) 0.00s ( 0.00s) SPARKS: 1 (0 converted, 1 pruned) INIT time 0.02s ( 0.00s elapsed) MUT time 6.63s ( 9.34s elapsed) GC time 0.64s ( 0.31s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 7.28s ( 9.66s elapsed) %GC time 8.8% (3.2% elapsed) Alloc rate 416,628,033 bytes per MUT second Productivity 91.0% of total user, 68.6% of total elapsed We see that our one spark is pruned. Why? And another question. I compiled it also with -O: C:\>ghc --make -threaded Monte.hs -O -fforce-recomp [1 of 1] Compiling Main ( Monte.hs, Monte.o ) Linking Monte.exe ... C:\>monte +RTS -N2 -s monte +RTS -N2 -s pi 1 n: 1000000 3.148096 2,642,947,868 bytes allocated in the heap 1,801,952 bytes copied during GC 5,864 bytes maximum residency (1 sample(s)) 18,876 bytes maximum slop 2 MB total memory in use (0 MB lost due to fragmentation) Generation 0: 5077 collections, 5076 parallel, 0.08s, 0.05s elapsed Generation 1: 1 collections, 1 parallel, 0.00s, 0.00s elapsed Parallel GC work balance: 1.00 (445245 / 444651, ideal 2) MUT time (elapsed) GC time (elapsed) Task 0 (worker) : 3.94s ( 14.02s) 0.00s ( 0.00s) Task 1 (worker) : 0.00s ( 14.02s) 0.00s ( 0.00s) Task 2 (worker) : 5.61s ( 14.03s) 0.08s ( 0.05s) Task 3 (worker) : 0.00s ( 14.05s) 0.00s ( 0.00s) SPARKS: 1 (0 converted, 0 pruned) INIT time 0.02s ( 0.02s elapsed) MUT time 9.55s ( 14.03s elapsed) GC time 0.08s ( 0.05s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 9.64s ( 14.09s elapsed) %GC time 0.8% (0.3% elapsed) Alloc rate 276,386,705 bytes per MUT second Productivity 99.0% of total user, 67.7% of total elapsed We see, that with -O, 2 worker threads were doing some job, but overall performance is not better. >From one spark, zero - converted, zero - pruned. Is it a bug?

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ANN: regular-web 0.1 | generic web programming in Haskell
by Chris Eidhof 21 Mar '10

21 Mar '10

From the ZuriHac hackathon, I am happy to announce the first release of the regular-web package [1]. The package contains functions for generic web programming: generating HTML, JSON and Formlets. It is based on the regular generic programming library [2]. Generic HTML and forms are often not sufficient for real purposes, so we encourage the use of regular-web in combination with the fclabels package [3]. There is an example in the documentation of the Formlets module. Furthermore, there is a slightly larger example [4] on github that shows off some more features of the package. This is a preliminary release and the API will probably change. I am interested to see what other people think of this. So please send me your comments or fork the project on github. [1]: http://hackage.haskell.org/package/regular-web [2]: http://hackage.haskell.org/package/regular [3]: http://hackage.haskell.org/package/fclabels [4]: http://github.com/chriseidhof/regular-web/blob/master/Example.lhs

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