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ANN: clash-0.1.3.0 (Functional Hardware Descriptions)
by Christiaan Baaij 25 Mar '11

25 Mar '11

Hello, I am pleased to announce an incremental update to CLaSH, version 0.1.3.0. CLaSH can translate a (semantic) subset of Haskell to RTL-style VHDL. Instead of being an embedded DSL like Lava or ForSyDe, CLaSH takes are more 'traditional' approach to synthesis/compilation. It uses the GHC API as a front-end for parsing, type-checking and desugaring the Haskell source. It then exhaustively applies a list of meaning-preserving transformations to the intermediate GHC Core representation until it is in the desired normal form. The normalized Core/System Fc is then 'trivially' translated to RTL-style VHDL. The new version of CLaSH has the following updates: - Support for simulation and synthesis of multi-clock hardware [6] - Significant synthesis speed-up (4x to 10x) CLaSH already supported synthesis of: - User-defined Higher-Order functions [1] - User-defined ADTs (GADTs are not tested, but *might* work) - All of Haskell's choice constructs (Guards, Pattern Matching, etc.) - Lambda-abstraction / Anonymous Functions You can use CLaSH as a library, but the use of the adapted GHC interpreter (added the :vhdl command) is recommended. The interpreter can be found on the CLaSH website [2], where you will also find examples, papers, tutorials, etc. The library can be downloaded from Hackage [3]. I recently gave a demo of CLaSH at the DATE'11 conference in grenoble, this demo already made use of the multi-clock feature (and is actually the only reference if you want to experiment with multi-clock hardware yourself). The source for the demo (audio spectrum analyzer programmed on an Altera Cyclone II FPGA board) can be downloaded from my github page [4]. Do note that CLaSH only works when you have the 6.12.* branch of GHC installed! I am currently analyzing the impact of the GHC API changes made in the 7.0.* brach, and hope to make the transition to the new API within the next month. Although the compiler is already used by 2 other phd's in our group [5], it is not a thoroughly tested product, so your coding style might not be anticipated by the current version of CLaSH ;-) -- Christiaan Baaij [1] There is hard-coded support for a set of recursively defined higher-order functions such as map, fold, zipWith, etc. [2] http://clash.ewi.utwente.nl [3] http://hackage.haskell.org/package/clash-0.1.3.0 [4] http://github.com/christiaanb/DE1-Cyclone-II-FPGA-Board-Support-Package [5] http://caes.ewi.utwente.nl [6] Simulation does not show meta-stability, you will have to take care of synchronization (dual flipflop) yourself

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package cache being out of date
by Wolfgang Jeltsch 25 Mar '11

25 Mar '11

Hi, I have a freshly installed Haskell Platform 2010.2.0.0 on Windows 7. When I run ghc-pkg list, I get the following message (besides the expected package info): WARNING: cache is out of date: C:/Program Files (x86)/Haskell Platform/2010.2.0.0\lib\package.conf.d\package.cache use 'ghc-pkg recache' to fix. What does this mean? Is this harmful? (In principal, I could just run ghc-pkg recache, but the installation is replicated on about 20 machines, and I don’t have admin rights on these.) Best wishes, Wolfgang

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ANNOUNCE: Multiplate 0.0.1
by roconnor＠theorem.ca 25 Mar '11

25 Mar '11

Multiplate is a lightweight generic library for mutually recursive data types that won't make Conor lose his lunch. Multiplate is an alternative extension of the Uniplate/Compos core design to support mutually recursive datatypes in a way that is as powerful as Compos, almost as easy to use as Uniplate, and more portable than both of them. Multiplate does not require you to rewrite your data type, does not require run-time reflection, does not require GADTs, and does not even require multi-parameter type classes. It only requires rank 3 polymorphism. <http://hackage.haskell.org/package/multiplate-0.0.1> A more detailed paper is forthcoming, but the library is available to try right now. -- Russell O'Connor <http://r6.ca/> ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.''

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threading question for ghc 7.0.2
by Oliver Mueller 25 Mar '11

25 Mar '11

hello, i'm a bit lost here so i hope s.o. can help me here: seems i have a problem in my code when compiled with ghc-7.0.2: what i try to do: serverside: -listen on a socket and reply to requests client-side: -send a request to that server -wait for a response (with a timeout) any ideas on how i can make this work again without using the -threaded flag? is there is a better way for what i'm trying to achieve? many thanks, oliver the simplified code is available at https://gist.github.com/882770 explanation: the code forks of a lightweight thread (not an OS thread) that will listen for incoming responses. the main thread will go on to push out a message and then wait for the receiver thread to finish. i used to compile my application with the -threaded option but ran into some obscure FFI problems after upgrading from ghc-6.12.3 to ghc-7.0.2. so i tried to remove the -threaded option. but now the message does not get pushed out until the receiver-thread has finished. what is strange to me is that this worked without problems on 6.12.3 but not on 7.0.2. also the behavior is a little different on mac os X with 7.0.2: here i get a "resource vanished (Connection reset by peer)" see the output of the program below ([S] marks output from the main thread, [R] from the receiver thread) compiled on ghc-7.0.2/ubuntu 64bit, without -threaded "running all things..." [R]listening for response... [R]wait for data with timeout:2000 ms ......................................................................................................................................................................................................... [R]no message available [S]pushing out the message [S]sending --> "\EOT\ETX" "[S]going on..." Nothing compiled on ghc-7.0.2/ubuntu 64bit, using -threaded "running all things..." [S]pushing out the message [R]listening for response... [S]sending --> "\EOT\ETX" [R]wait for data with timeout:2000 ms "[S]going on..." ..................................................Just "\ETX\EOT" and...also very strange: when i introduce a putStrLn in the main thread (not a print !) it will work again...only a lot (see code snipped line38: putStrLn "[S]hickup" "running all things..." [S]hickup [R]listening for response... [S]pushing out the message [S]sending --> "\EOT\ETX" [R]wait for data with timeout:2000 ms "[S]going on..." ..................................................Just "\ETX\EOT"

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STM, newArray, and a stack overflow?
by Ketil Malde 25 Mar '11

25 Mar '11

Hi, I'm seeing some weirdness here. My code does this: omap <- atomically $ (newArray_ (0,n-1) :: STM (TArray Int Int)) This gives a stack overflow when n is one million. The equivalent code in the ST monad doesn't show this behavior, and works as expected. I'm not sure what is going on here, so I thought I'd ask in case anybody can put me on the right track. -k -- If I haven't seen further, it is by standing in the footprints of giants

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Haskell programming 3 month internship in Tokyo
by employment 25 Mar '11

25 Mar '11

Tsuru Capital has an opening for an intern for three months starting next month in Tokyo. We are looking for people with moderate experience with Haskell or another functional programming language. Evidence of work written in Haskell is a big plus. More details can be found here. There is a small coding task on the site. Please send this code with your application. http://www.tsurucapital.com/en/jobs.html Any who have applied before but would like to be considered again, please feel free to send a reminder of your availability along with the code sample. Interested candidates please send resumes with code to jobs(a)tsurucapital.com . The package includes flights, and accommodation plus some salary while here.

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Tying the recursive knot
by Joshua Ball 24 Mar '11

24 Mar '11

{- - Hi all, - - I'm having trouble tying the recursive knot in one of my programs. - - Suppose I have the following data structures and functions: -} module Recursion where import Control.Monad.Fix import Data.Map ((!)) import qualified Data.Map as M import Debug.Trace newtype Key = Key { unKey :: String } deriving (Eq, Ord, Show) data Chain = Link Int Chain | Trace String Chain | Ref Key deriving (Show) reduce :: M.Map Key Chain -> Key -> [Int] reduce env k = follow (env ! k) where follow (Link i c) = i : follow c follow (Ref k) = reduce env k follow (Trace message c) = trace message (follow c) -- Now I want a "force" function that expands all of the chains into int sequences. force1, force2 :: M.Map Key Chain -> M.Map Key [Int] -- This is pretty easy to do: force1 mp = M.fromList (map (\k -> (k, reduce mp k)) (M.keys mp)) -- But I want the int sequences to be lazy. The following example illustrates that they are not: example = M.fromList [(Key "ones", Link 1 . Trace "expensive computation here" . Ref . Key $ "ones")] -- Run "force1 example" in ghci, and you will see the "expensive computation here" messages interleaved with an infinite -- list of ones. I would prefer for the "expensive computation" to happen only once. -- Here was my first attempt at regaining laziness: fixpointee :: M.Map Key Chain -> M.Map Key [Int] -> M.Map Key [Int] fixpointee env mp = M.fromList (map (\k -> (k, reduce env k)) (M.keys mp)) force2 env = fix (fixpointee env) main = print $ force2 example {- - However, this gets stuck in an infinite loop and doesn't make it past printing "fromList ". - (It was not difficult for me to see why, once I thought about it.) - - How do I recover laziness? A pure solution would be nice, but in the actual program - I am working on, I am in the IO monad, so I am ok with an impure solution. - It's also perfectly ok for me to modify the reduce function. - - Thanks in advance for you help, - Josh "Ua" Ball -}

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GHC 7/Cabal request for help
by John Goerzen 24 Mar '11

24 Mar '11

Hi folks, I don't have a GHC 7 environment running yet (it's on my list...) but I received a bug report pointing me at this build failure: http://hackage.haskell.org/packages/archive/testpack/2.0.1/logs/failure/ghc… Among other things, this noted: Dependency QuickCheck >=2.1.0.3: using QuickCheck-2.4.0.1 and the errors were: [1 of 3] Compiling Test.QuickCheck.Instances ( src/Test/QuickCheck/Instances.hs, dist/build/Test/QuickCheck/Instances.o ) src/Test/QuickCheck/Instances.hs:39:10: Duplicate instance declarations: instance Arbitrary Word8 -- Defined at src/Test/QuickCheck/Instances.hs:39:10-24 instance Arbitrary Word8 -- Defined in Test.QuickCheck.Arbitrary src/Test/QuickCheck/Instances.hs:42:10: Duplicate instance declarations: instance CoArbitrary Word8 -- Defined at src/Test/QuickCheck/Instances.hs:42:10-26 instance CoArbitrary Word8 -- Defined in Test.QuickCheck.Arbitrary Now, that's fairly standard, and in fact, in my code, is wrapped with: #if MIN_VERSION_QuickCheck(2,3,0) -- we have Word8 instances here #else instance Arbitrary Word8 where arbitrary = sized $ \n -> choose (0, min (fromIntegral n) maxBound) instance CoArbitrary Word8 where coarbitrary n = variant (if n >= 0 then 2 * x else 2 * x + 1) where x = abs . fromIntegral $ n #endif And that code has been working to support modern QuickCheck versions for some time. It would appear that something in Cabal, GHC 7, or QuickCheck is breaking this check. Ideas? -- John

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Blocking problem reading a handle
by Daniel Díaz 24 Mar '11

24 Mar '11

Hi, cafe, all I want is to read the unread portion of a handle, without blocking waiting for an EOF or a newline. My first attempt was to try with hGetBufNonBlocking from System.IO, and other functions that use it in its definition (directly or indirectly). But, unfortunately: hGetBufNonBlocking doesn't work on Windows: http://hackage.haskell.org/trac/ghc/ticket/806 This was a bad surprise. How can achieve my purpose without hGetBufNonBlocking? Thanks in advance, Daniel Díaz

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Haskell Weekly News: Issue 174
by Daniel Santa Cruz 24 Mar '11

24 Mar '11

Welcome to issue 174 of the HWN, a newsletter covering developments in the [1]Haskell community. This release covers the week of March 13-19. You can find the HTML version at: http://bit.ly/hLu36R Announcements JP Moresmau [2]announced a new release of EclipseFP with support for ghc 7! S. Doaitse Swierstra [3]announced the release of version 2.7.0 to the uu-parsinglib library to hackage. Vincent Gerard [4]informed us that he has taken over maintainership of hsmagick, which is "a FFI bindings library to ImageMagick." He is pleased to announce the 0.5 release of the library. Malte Harder [5]announce the first release of the Craftwerk graphics library for 2d vector graphics. Corey O'Connor [6]annouced a new release of his VTY library. Brent Yorgey [7]announced the release of the special Poetry and Fiction Edition of The Monad.Reader. Thanks for putting this together Brent! Gregory D. Weber [8]announced version 1.2.4 of his Sifflet and sifflet-lib. "This is a compatibility release for HXT >= 9.1." Edward Kmett [9]remminded us that the Google Summer of Code is upon us. Follow the link to see the sign up information. Quotes of the Week * ddarius: *ddarius is more of a glass SUM_n (-1)^n full person. * monochrom: some kind of lazy evaluation is already known to highschool kids. teachers tell you that in a*(b+c), "evaluate b+c first", right? well, I challenge you to take 0*(389238493+97283748) and find one single student who faithfully evaluate 389238493+97283748 first. * hpc: in soviet russia, yoda speaks flawless english * lambdabot: trololololo * hpc: jokes are subject to an incompleteness theorem; if you can prove they are funny, they were never good jokes to begin with * hpc: when all you have is Haskell, everything looks like a research paper * Edward Kmett:Clearly we need some sort of xbox live-like achievement system for these. Achievement Unlocked: Stumped Oleg! Top Reddit Stories * Haskell.org has been accepted for the 2011 Google Summer of Code From (twitter.com) scored 48 with 1 comments. Read on [10]reddit. Read the [11]original post. * Haskell's Niche: Hard Problems From (cdsmith.wordpress.com) scored 47 with 17 comments. Read on [12]reddit. Read the [13]original post. * A little care and feeding can go a long way From (serpentine.com) scored 39 with 6 comments. Read on [14]reddit. Read the [15]original post. * The reception of monads circa 1995... From (self.haskell), scored 35 with 1 comments. Read on [16]reddit. * BlazeHtml: a blazingly fast HTML combinator library From (skillsmatter.com) scored 29 with 18 comments. Read on [17]reddit. Read the [18]original post. * Simon Peyton Jones: Managing parallelism: embrace diversity, but control side effects From (skillsmatter.com) scored 28 with 12 comments. Read on [19]reddit. Read the [20]original post. * EZYang: Mutation is frequently not what people expect ; mutation is not modular, and mutation is complicated. From (blog.ezyang.com) scored 26 with 0 comments. Read on [21]reddit. Read the [22]original post. * Functor is to Lens as Applicative is to Biplate: Introducing Multiplate From (front.math.ucdavis.edu) scored 25 with 19 comments. Read on [23]reddit. Read the [24]original post. * Monad.Reader special poetry and fiction edition From (themonadreader.wordpress.com) scored 23 with 1 comments. Read on [25]reddit. Read the [26]original post. * Functional flocks : modelling and visualizing flocking behavior in Haskell From (syntacticsalt.com) scored 22 with 0 comments. Read on [27]reddit. Read the [28]original post. Top StackOverflow Answers * [29]Why does application of `sequence` on List of Lists lead to computation of its Cartesian Product? votes: 12 This works because using lists as monads in Haskell makes them model indeterminism. Consider: sequence [[1,2],[3,4]] By definition this is the same as: do x <- [1,2] y <- [3,4] return [x,y] Just read it as "First a choice between 1 and 2, then a choice between 3 and 4". The list monad will now accumulate all possible outcomes - hence the ... * [30]In GHCi, why does the kind of the function arrow `:kind (->)` include question marks `(->) :: ?? -&ht; ? -> *`? votes: 11 The ? and ?? kinds refer to GHC extensions, specifically unboxed types. http://hackage.haskell.org/trac/ghc/wiki/IntermediateTypes has a diagram showing relationships between the extended kinds ? (all possible types), # (unboxed types), ?? (boxed or normal unboxed types â "least upper bound of # and *"), (#) (unboxed tuples, which can only be used in a ... * [31]How to use (->) instances of Monad and confusion about (->) votes: 11 For a given type r, the function of type r -> a can be thought of as a computation delivering an a using an environment typed r. Given two functions r -> a and a -> (r -> b), it's easy to imagine that one can compose these when given an environment (again, of type r). But wait! That's exactly what monads are about! So we can create an instance ... * [32]How and why is ap defined as liftM2 id in Haskell votes: 10 The type variable a from id can be instantiated at any type, and in this case that type is a -> b. So we are instantiating id at (a -> b) -> (a -> b). Now the type variable a1 from liftM2 is being instantiated at (a -> b), a2 is being instantiated at a, and r is being instantiated at b. Putting it all together, liftM2 is instantiated at ... * [33]What "reify" and "reification" means in the context of (functional?) programming? votes: 8 So I read up on this, and it is pretty much what it means: taking an abstract concept and making it concrete. Or, there is a proxy that represents the abstract concept. For example, in Lisp, the concept of procedure abstraction and application is reified when you use lambdas. Reification by itself is a broad concept and not just applicable to functional ... Top StackOverflow Questions * [34]What "reify" and "reification" means in the context of (functional?) programming? votes: 17, answers: 6 * [35]How to use (->) instances of Monad and confusion about (->) votes: 12, answers: 2 * [36]In GHCi, why does the kind of the function arrow `:kind (->)` include question marks `(->) :: ?? -> ? -> *`? votes: 12, answers: 1 * [37]Haskell-like type system in C votes: 11, answers: 2 * [38]Write a Maximum Monoid using Maybe in Haskell votes: 9, answers: 1 About the Haskell Weekly News To help create new editions of this newsletter, please send stories to dstcruz(a)gmail.com. I'm in dire need of finding good "quotes of the week". If you happen to come across any, please don't hesitate to send it along. Until next time, Daniel Santa Cruz References 1. http://haskell.org/ 2. http://jpmoresmau.blogspot.com/2011/03/eclipsefp-204-released-supports-ghc-… 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/87205 4. http://article.gmane.org/gmane.comp.lang.haskell.general/18564 5. http://article.gmane.org/gmane.comp.lang.haskell.general/18568 6. http://article.gmane.org/gmane.comp.lang.haskell.general/18574 7. http://article.gmane.org/gmane.comp.lang.haskell.general/18572 8. http://article.gmane.org/gmane.comp.lang.haskell.general/18584 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/87399 10. http://www.reddit.com/r/haskell/comments/g6nwe/haskellorg_has_been_accepted… 11. http://twitter.com/haskellorg/status/48838580029755392 12. http://www.reddit.com/r/haskell/comments/g382d/haskells_niche_hard_problems/ 13. http://cdsmith.wordpress.com/2011/03/13/haskells-niche-hard-problems/ 14. http://www.reddit.com/r/haskell/comments/g6a01/a_little_care_and_feeding_ca… 15. http://www.serpentine.com/blog/2011/03/18/a-little-care-and-feeding-can-go-… 16. http://www.reddit.com/r/haskell/comments/g4f1m/the_reception_of_monads_circ… 17. http://www.reddit.com/r/haskell/comments/g7akc/blazehtml_a_blazingly_fast_h… 18. http://skillsmatter.com/podcast/scala/blazehtml-a-blazingly-fast-html-combi… 19. http://www.reddit.com/r/haskell/comments/g7ajj/simon_peyton_jones_managing_… 20. http://skillsmatter.com/podcast/scala/talk-by-haskell-expert-simon-peyton-j… 21. http://www.reddit.com/r/haskell/comments/g3dsw/ezyang_mutation_is_frequentl… 22. http://blog.ezyang.com/2011/03/killer-mutants-attack-mutation-gone-wrong/ 23. http://www.reddit.com/r/haskell/comments/g56xw/functor_is_to_lens_as_applic… 24. http://front.math.ucdavis.edu/1103.2841 25. http://www.reddit.com/r/haskell/comments/g4r6e/monadreader_special_poetry_a… 26. http://themonadreader.wordpress.com/2011/03/15/special-poetry-and-fiction-e… 27. http://www.reddit.com/r/haskell/comments/g2v75/functional_flocks_modelling_… 28. http://syntacticsalt.com/2011/03/10/functional-flocks/ 29. http://stackoverflow.com/questions/5299295/why-does-application-of-sequence… 30. http://stackoverflow.com/questions/5359707/in-ghci-why-does-the-kind-of-the… 31. http://stackoverflow.com/questions/5310203/how-to-use-instances-of-monad-an… 32. http://stackoverflow.com/questions/5358868/how-and-why-is-ap-defined-as-lif… 33. http://stackoverflow.com/questions/5314884/what-reify-and-reification-means… 34. http://stackoverflow.com/questions/5314884/what-reify-and-reification-means… 35. http://stackoverflow.com/questions/5310203/how-to-use-instances-of-monad-an… 36. http://stackoverflow.com/questions/5359707/in-ghci-why-does-the-kind-of-the… 37. http://stackoverflow.com/questions/5290408/haskell-like-type-system-in-c 38. http://stackoverflow.com/questions/5344164/write-a-maximum-monoid-using-may…

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