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ANN: variable-precision floating point
by Claude Heiland-Allen 16 May '12

16 May '12

Hi all, I'm pleased to announce variable-precision-0.2: http://hackage.haskell.org/package/variable-precision There was no announcement for previous versions, as I quickly found their flaws to be too irritating in practice. --8<-- excerpt from the hackage page Software floating point with type-tagged variable mantissa precision, implemented using a strict pair of Integer and Int scaled alike to decodeFloat. Instances of the usual numeric type classes are provided, along with additional operators (with carefully chosen fixities) to coerce, adjust and reify precisions. --8<-- end excerpt Known shortcomings of this release: * no implementation of (inverse) (hyperbolic) trigonometric functions * no support for negative zero * no support for rounding modes * accuracy has not been extensively verified * termination of algorithms has not been proven The intention of this package is to be simple yet useable in the meantime until there is a version of hmpfr[1] or fixed-precision[2] that work without requiring a custom-compiled GHC. The design of variable-precision was inspired by the latter, and variable-precision is probably inferior, but the lifetime of the variable-precision package is hopefully going to be short. [1] http://hackage.haskell.org/package/hmpfr [2] http://hackage.haskell.org/package/fixed-precision I'm currently mainly using variable-precision for exploring the Mandelbrot Set, particularly in algorithms using Newton's method (for example, tracing external rays, where more precision is needed the closer you get to the boundary of the set). Thanks, Claude PS: --8<-- excerpt from ghci session Prelude Numeric.VariablePrecision> (pi :: F24) .@$ 200 $ show . (pi -) "1.5815072737072126433832795028841971693993751058209749096292229e-6" Prelude Numeric.VariablePrecision> (pi :: F53) .@$ 200 $ show . (pi -) "4.1192675685652988632476805983544532308209749096292228904414057e-15" Prelude Numeric.VariablePrecision> (2 :: F53) .@$ 200 $ show . log "0.69314718055994530941723212145817656807550013436025525413214402" Prelude Numeric.VariablePrecision> log 2 0.6931471805599453 Prelude Numeric.VariablePrecision> (2 :: F53) .@$ 200 $ show . exp "7.3890560989306502272304274605750078131803155705518473240869941" Prelude Numeric.VariablePrecision> exp 2 7.38905609893065 --8<-- end excerpt

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Can't prevent memoizing in simple code
by Yves Parès 16 May '12

16 May '12

The buffer http://hpaste.org/68595 presents a simple code I tried to profile. I spotted what I strongly think to be an abusive memoization. The problem is that I don't see how to (simply) get rid of it. Compiled with -O2, it consumes 130MB of memory, however lines A and B executed separately consume each only 1MB. The infinite list (l 1), whatever I do, keeps being shared between lines A and B. I tried to wrap it in a function, as you can see, I also tried to make it explicitely polymorphic (bypassing monomorphic restriction), nothing solves it, GHC is just to good at memoizing. NB: When compiled without optimisations, the sharing does not happen (side note: but then lack of strictness analysis -- which is what I was testing at the first place -- makes line A (call to suminit2) consume a lot of memory, but this is normal).

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Call for AusHac 2012
by Ivan Lazar Miljenovic 15 May '12

15 May '12

For any Australian Haskellers (or indeed anyone that feels willing to come from wherever you may hail) who have _not_ yet received an email, seen it on Reddit or Google+ but is interested in attending AusHac 2012, we are currently trying to determine which weekend in July best suits everyone. So if you're interested in coming, please fill out the form at http://tinyurl.com/AusHac2012PreferredDates This year we're going to hold AusHac in central Sydney (thanks to Atlassian putting their offices at our disposal!) rather than UNSW, which should make transport and accommodation easier for people. AusHac is open to anyone interested in Haskell, from a complete newbie to one of the Simons. We don't have any specific themes or projects to work on; instead just come along and hack on whatever takes your fancy. -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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hackage & hackage accounts
by Dmitry Malikov 15 May '12

15 May '12

Good day. Recently, in irc://#haskell you can see very often replicas of people, who are tired of waiting their hackage accounts. After next release of any package from hackagebot, some depressed people definitely comes out and starts telling to everybody how hard life is without having hackage account. 11:15 * hackagebot shakespeare 1.0.0.2 - A toolkit for making compile-time interpolated templates http://hackage.haskell.org/package/shakespeare-1.0.0.2 (MichaelSnoyman) 11:15 <|> I'm still waiting for my Hackage account... ... 15:12 * hackagebot hspec-discover 0.0.0 - Automatically discover and run Hspec tests http://hackage.haskell.org/package/hspec-discover-0.0.0 (SimonHengel) 15:13 <|> Still haven't got my hackage account And so on and so on. Yes, you can tolerate, that a lot of people considered in the order of things for asking lambdabot in public window every day, every hour. Yes, you can tolerate, that every five minutes some another notification from hackagebot will be be appeared, or maybe two or even three in a time. But how can you tolerate, that adding to all that stuff there is a permanent disturbances from the people, who can't submit their packages to hackage because they have no hackage account (frankly speaking, I'm also do not have one, but I've send 5 letters to Ross)? Previously, #haskell's log was really like something readable and interesting. But now it's a robot-like speeches with 2 bots, minimal slightly mixed with something really meaningfull. This raises some questions: 1) Did anyone successfully get their hackage account in last 2 months? Because it's really strange to see some "still don't have my hackage account"-message and another Ross answer in HC. 2) You should give hackage account for all of ther requiring people or remove hackagebot from #haskell. 3) Could I finally have my hackage account in the amount of all others, please? Dmitry Malikov

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How to use Jacobian from levmar lib?
by Martin Hilbig 15 May '12

15 May '12

hi, i'm using the nice levmar package like this [1]. why is there such a big difference in 'infNorm2E' between using/not using the Jacobian? thanks in advance martin hilbig [1]: http://hpaste.org/68537

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Safe Haskell at the export symbol granularity?
by Ryan Newton 14 May '12

14 May '12

Separate from whether or not we actually want this -- is it feasible? Here's my situation. When working on parallel programming libraries in Haskell there are very often unsafe operations one wants to do within an otherwise pure model. For example, Accelerate currently violates safe haskell because it trusts the user to provide an associative function to parallel "fold". No associativity, no referential transparency. The solution is to put fold in a separate namespace and mark that module as Unsafe. Likewise for certain monad-par operations that are unsafe. But this factoring can have a serious impact. Not only are extra modules required, but extra type classes as well. For example, if Accelerate is ever refactored for "Safe Haskell" then the following ParAccelerate type class probably should be as well: https://github.com/simonmar/monad-par/blob/5cc656bc45dc473d7a185ec99bb15619… I.e. ParAccelerate & ParAccelerateUnsafe for the "unsafeHybrid" operation. But this starts to be death by a thousand organizational factorings! - The package, abstract-par-accelerate, is already factored out from abstract-par just to avoid an unnecessary Accelerate dependency (which used to mean CUDA errors). (And *another* factoring is possibly warranted for whether or not the module depends on accelerate-io.) - The file would be separate to mark it as Safe Haskell. - The type class ParAccelerateUnsafe would be separate so as to put it in a separate file. What's a possible solution? If, in addition to "Safe" and "Unsafe" modules, there were "Partially Safe" modules, which exported a mix of safe and unsafe identifiers, then this could all be much cleaner. The simple rule is that any reference whatsoever to an unsafe identifier disqualifies the client code. For example, in the above ParAccelerate type class we would mark the unsafeHybrid binding with something like {-# UNSAFE unsafeHybrid #-}. We wouldn't even have to factor it out of the type class. Likewise, Accelerate could mark "fold" as unsafe (providing safe variants as well) without introducing module namespace bloat and confusion. What do you think? -Ryan

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[ANN] Accelerate version 0.12: GPU computing with Haskell
by Manuel M T Chakravarty 14 May '12

14 May '12

We just released version 0.12 of Data.Array.Accelerate, the GPGPU[1] library for Haskell: http://justtesting.org/gpu-accelerated-array-computations-in-haskell This is a beta release. The library is not perfect, but it is definitely usable, and we are looking for early adopters. Manuel [1] Currently only NVIDIA GPUs are supported via NVIDIA's CUDA framework.

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Bug in SYB, SYB-documentation or GHC-API (or I messed up somewhere)
by "Philip K. F. Hölzenspies" 13 May '12

13 May '12

Dear Haskelers, Since I don't quite know whether this is a SYB-thing or a GHC-specific thing, I figured this report should go here. If not, kindly redirect. I am trying to write a program, using the GHC-API to refactor some parts of the GHC-code (initially, I want to add a type variable to the types in the AST to express the representation of types, as noted to be a Good Thing at [1]). To do this, I first search for all definitions of and references to type constructors. I do this using SYB. Consider these functions: type OccurrenceTable = [(RdrName, (SrcSpan,Bool))] locTyNames :: SrcSpan -> Bool -> HsType RdrName -> OccurrenceTable locTyNames l p (HsTyVar n ) = [(n, (l, p))] <… HSType-specific traversal cases omitted for brevity …> extTyNamesDef :: Data a => SrcSpan -> a -> OccurranceTable extTyNamesDef l x = gmapQl (++) [] (extTyNames l) x extTyNamesTy :: SrcSpan -> HsType RdrName -> OccurranceTable extTyNamesTy l x = locTyNames l True x extTyNames l x = (extTyNamesDef l x `mkQ` extTyNamesTy l) x The OccurrenceTable type collects for every type constructor (RdrName) the location of its occurrence (either definition or reference, SrcSpan) and whether adding a type variable (formal or actual) requires parenthesis (Bool). This works fine, although now, we always find the same SrcSpan for everything. When traversing an AST, whenever we find anything that's Located, we want to continue the traversal with this new location information. To this end, we define: extTyNamesLoc :: Data a => Located a -> OccurrenceTable extTyNamesLoc (L l x) = extTyNames l x and modify the universal entry point to: extTyNames l x = (extTyNamesDef l x `mkQ` extTyNamesTy l `ext1Q` extTyNamesLoc) x However, it turns out that this never leads to an evaluation of extTyNamesLoc. I've come as far as to see that, since "Located a" is a synonym for "GenLocated SrcSpan a", the type we're looking for really has a binary constructor, thus we should use ext2Q. This made things work: We first modify the function we apply to Located things: extTyNamesLoc :: (Data loc, Data a) => SrcSpan -> GenLocated loc a -> OccurrenceTable extTyNamesLoc l (L l' x) = case cast l' of Just l'' -> extTyNames l'' x Nothing -> extTyNames l x and define the universal entry point to be: extTyNames l x = (extTyNamesDef l x `mkQ` extTyNamesTy l `ext2Q` extTyNamesLoc l) x Even though I see why this works, I'm not completely sure why the former version does not. Is there no currying with type constructors (for SYB)? The cast I perform always succeeds, because all types that occur in the traversal are "Located x" and never "GenLocated NonSrcSpanType x". The extensions to extX functions (i.e. ext1Q, ext2Q, ext1T, etc.) are not very extensively documented. Their discussion in the ICFP04 paper only discusses their relation to TypeableX classes, but not to the partiality of type constructor application and/or synonyms. (As a side-note on that discussion in ICFP04, the remark that we're generally interested in type constructors with arguments of kind * sounded fine, until I started to try and parameterise the AST in the location-annotation-type as well; it made my brain hurt.) Apologies for the waffling, but comments would be greatly appreciated. Regards, Philip [1] http://hackage.haskell.org/trac/ghc/wiki/Commentary/Compiler/HsSynType

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ANN: Patterns 0.0.3
by Tobias Schoofs 12 May '12

12 May '12

Hi! I am pleased to announce patterns-0.0.3. On Hackage: http://hackage.haskell.org/package/patterns The Patterns package implements communication patterns that are often used in distributed, message-oriented applications. The package implements a set of basic patterns and a device to connect basic patterns through routers, brokers, load balancers, etc. The package is based on the zeromq library, but abstracts from the notion of sockets, on which zeromq is built. Cheers Tobias

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Linear Diaphantine equation solver bug
by John D. Ramsdell 12 May '12

12 May '12

I uploaded a new version of the ACU unifier in package cmu. It includes a Linear Diaphantine equation solver that now handles inhomogeneous equations. What's interesting is the algorithm is based on a paper by Contejean and Devie. That paper includes a proof of correctness of their algorithm. Yet I found an example in which following the steps in the order they gave, the algorithm produces extra answers. I had to switch the order of the steps in the algorithm to get the right answer. I wonder if anyone else knows of this issue. The example is given in the module documentation on Hackage. John http://hackage.haskell.org/packages/archive/cmu/1.6/doc/html/Algebra-Commut…

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