- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] [QuickCheck] Fwd: an idea for improving 'shrink'
by Petr Pudlák 17 Sep '14

17 Sep '14

Hi Nick, you're right, this example is indeed problematic. I'll try to think about it how to get around that, keeping backward compatibility. Petr Dne 11. 9. 2014 21:37 "Nick Smallbone" <nicsma(a)chalmers.se> napsal(a): > Hi Petr, > > My attitude has always been "just use the shrink instance for tuples". > I don't think there's all that much difference between: > shrink (C x y) = [ C x' y' | (x', y') <- shrink (x, y) ] > and: > shrink (C x y) = C <$> shrink x <*> shrink y > The second is certainly nicer, but neither way is really very painful. > > However, your shrinkOne example shows a case where shrinking tuples > doesn't work and you really need a shrinking Applicative. > So this is a good reason to add a shrinking Applicative to QuickCheck > and I would probably like to do it at some point. > > There is a problem with your current patch, though. Namely the default > implementation of shrinkA: > shrinkA = pure > If someone defines shrink but not shrinkA, then shrinkA will not > shrink! In fact, one of your examples exhibits this bug: > shrinkA (Branch x l r) = > Branch <$> shrinkA x <*> shrinkA l <*> shrinkA r > If the Arbitrary instance for whatever x is defines shrink but not > shrinkA, then this will do the wrong thing. > > So we can't provide a default implementation for shrink in terms of > shrinkA, or vice versa, because we want the user to be able to define > either. We can't even define both in terms of the other because then > the default implementation will loop instead of returning []. > > Probably we would just have to move shrinkA outside of the Arbitrary > class. This does make using the Applicative more cumbersome, e.g.: > shrink (C x y) = fromShrink (C <$> shrinkA x <*> shrinkA y) > shrinkOne shr = fromShrink . traverse (Shrink . shr) > but maybe this would still be useful for defining trickier shrink > functions. > > Anyway, this is the only worry I have - how to integrate the > traditional and applicative-based shrinking without too much syntactic > overhead. If we can come up with a good solution for that then I'd be > very eager to add this to QuickCheck. Or maybe calling fromShrink > isn't so painful and we should add it anyway. I will think it over a > bit... > > Nick > > On Saturday 06 September, 2014 at 11:17 am, Petr Pudlák wrote: > > 2014-09-05 18:22 GMT+02:00 Bryan O’Sullivan <bos(a)serpentine.com>: > > > > > > > On Thu, Sep 4, 2014 at 1:06 PM, Petr Pudlák <petr.mvd(a)gmail.com> > wrote: > > > > > >> since I got no response from the QuickCheck mail address, so I'm > > >> resending it here, if someone wants to comment on the idea. > > >> > > > > > > I don't think it pays its way: it makes shrink a bit tidier, at the > cost > > > of breaking backwards compatibility in a widely used library. > > > > > That’s a problem. But I believe it the patch addresses it. QuickCheck > > always uses ‘shrink’, not ‘shrinkA’, and as the default implementation of > > ‘shrink’ is defined in terms of ‘shrinkA’, then it’s possible to define > > instances both using ‘shrink’ and using ‘shrinkA’. So both old code and > new > > code that wants to take advantage of the Applicative interface work. > > > > I believe that in the long term this change would pay off: Compare the > old > > code > > > > shrinkOne [] = [] > > shrinkOne (x:xs) = [ x':xs | x' <- shr x ] > > ++ [ x:xs' | xs' <- shrinkOne xs ] > > > > shrink (x, y) = > > [ (x', y) | x' <- shrink x ] > > ++ [ (x, y') | y' <- shrink y ] > > > > shrink (x, y, z) = > > [ (x', y', z') > > | (x', (y', z')) <- shrink (x, (y, z)) ] > > > > against the improved piece > > > > traverse shr xs -- replaces the whole shrinkOne > > shrinkA (x, y) = liftA2 (,) (shrinkA x) (shrinkA y) > > shrinkA (x, y, z) = liftA3 (,,) (shrinkA x) (shrinkA y) (shrinkA z) >

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ANN: HacBerlin - Haskell Hackathon in Berlin, 26-28 Sep 2014
by Stefan Wehr 17 Sep '14

17 Sep '14

Hi everyone, this is just a quick reminder: The Haskell Hackathon in Berlin starts in 9 days and there are very few places left. Please register now: http://goo.gl/aLfnWu Where: Berlin, Germany When: Fri 26 - Sun 28 September 2014 We will do lots of Haskell hacking and listen to two excellent talks: * Beyond Parsec -- Revisiting Parser Combinators, by Andres Löh * Chordify: Advanced Functional Programming for Fun and Profit, by José Pedro Magalhães Meet in Berlin, discuss, hack together and improve the Haskell infrastructure. We welcome all programmers interested in Haskell, beginners and experts! For all details, visit our wiki page (http://www.haskell.org/haskellwiki/HacBerlin2014) and make sure to register now! Cheers, Stefan

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a question about cabal files
by Kazu Yamamoto 17 Sep '14

17 Sep '14

Hi cafe, I'm developing a library. In this package, some tools for development are included. I would like to compile these tools when I'm developing but I don't want users to compile them. Are there any ways to express such modes in cabal files? ("Executable" cannot be located under "if".) Or should I prepare a separated package for the development tools? Regards, --Kazu

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Re: [Haskell-cafe] Categorical description for vector-space instance of AdditiveGroup (Maybe a)
by trevor cook 17 Sep '14

17 Sep '14

Jason, John, Thanks for the in depth descriptions, it was just what I was looking for. Trevor

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Hackage package "synopsis" sections
by Richard Lewis 17 Sep '14

17 Sep '14

Hi there, If any of you have ever used CPAN you may agree with me that the synopsis sections customarily included in each package's POD are generally invaluable for getting a quick overview of how to use the facilities provided by that package. I wonder if we might be able to encourage the Hackage community to do something similar? Perhaps in the cabal description authors could include a synopsis with a few code examples? Obviously, I ought to start the ball rolling but I don't actually have any code published on Hackage. Any thoughts? Richard -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Richard Lewis @lewisrichard http://web.rjlewis.me.uk/ -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

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Hello and type-level SKI
by Tslil Clingman 17 Sep '14

17 Sep '14

Greetings all, I've been reading this list for a short while and I thought I'd like to begin to contribute where possible. This message pretty much serves to say: - Hello, Haskell! - This community is great, and it's always been a great pleasure to read the newsgroup(s) - Here is a small and likely multiply re-re-discovered `proof' of why the type system is Turing Complete > {-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, > FlexibleInstances, FlexibleContexts, UndecidableInstances #-} > data S2 x y > data S1 x > data S > data K1 x > data K > data I > class Apply a b c | a b -> c > instance Apply K x (K1 x) > instance Apply S x (S1 x) > instance Apply (S1 x) y (S2 x y) > instance Apply I x x > instance Apply (K1 x) y x > instance (Apply x z xz, Apply y z yz, Apply xz yz a) => Apply (S2 x y) z a > -- The core function > apply :: (Apply a b c) => a -> b -> c > apply _ _ = undefined > -- Hereendeththelesson -- > -- For `ease of use', but not strictly necessary > data X > data Y > data Z > s = undefined :: S > k = undefined :: K > i = undefined :: I > x = undefined :: X > y = undefined :: Y > z = undefined :: Z > -- Example > reverse = apply (apply s (apply k (apply s i))) k I just thought I'd share this snippet here, but if this is not the right place, or it's too long or something please don't hesitate to let me know. Thanks for your attention, Yours &c., Tslil

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Re: [Haskell-cafe] Temporarily taking over hdevtools on Hackage
by Schell Scivally 16 Sep '14

16 Sep '14

I talked with Erik the admin@hackage about taking over hdevtools and he suggested waiting another week before invading. In the meantime he suggested asking a hackage trustee to please upload this git branch to hackage (https://github.com/schell/hdevtools/tree/cabal-support-ghc7.8) Thank you and let me know if there is anything else I can do to help! -- Schell Scivally | github <https://github.com/schell> | twitter <http://twitter.com/schellsan> | blog <http://efnx.com> | wiki <http://wiki.zyghost.com>

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Re: [Haskell-cafe] Hackage package "synopsis" sections
by Britt Mathis 16 Sep '14

16 Sep '14

I meant to post this about 30 minutes ago, but I accidentally sent it only to Michael Snoyman. It seems to me that there are two use cases here - documentation inside code and documentation that stands alone. I agree with you, Michael, that there is no reason why you shouldn't be able to use whichever documentation method you prefer in your readme file. Since it stands alone, it should be trivial to include support for a multitude of formats and display the resulting documentation on Hackage. I think where Mateusz' opinion differs is on the inclusion of markdown in source files (correct me if I am wrong): > More importantly, Markdown > is not suited for documenting code. We'd have to introduce new > identifiers if we wanted to link to some functions from our synopsis. > 16th standard aside, this is quickly starts looking like Haddock. As he says, there are problems with using markdown this way. I think it would be beneficial to have a defacto standard for documentation that lives inside source files - this would prevent it from changing from file to file and provide consistency across the community's code-base. Because the haskell community controls haddock it is in a better position to evolve to our needs. Some flavor of markdown that has a user-base outside the haskell community may not be willing to incorporate changes that make it a better fit for living inside haskell source files, so we would have to maintain our own fork of it anyway. Why duplicate the work that has already been done? I think if the community has a problem with haddock syntax that can be discussed and, if need be, changed. But I do believe that there should be consistency in source file documentation. The last problem I see is the cabal problem. It seems that cabal has trouble handling edge cases, and I think that is again something we can work on (I may even look into it myself - I have been looking for a project). It seems like it would be a good idea to only include small blurbs about the project in the .cabal file, and to separate the larger documentation into a README file, like is done on github. The reasoning behind this is two-fold: 1) Cabal files are human readable. They give us insight into the dependencies a project requires, and including full documentation here would make it harder to get a quick overview of the project (I know most people use hackage for this, but cabal was chosen over formats like XML specifically because it was meant to be read and understood by humans). 2) Separating the README file allows users to choose their favorite format, and be certain that it will be formatted as it was intended (cabal can't be expected to handle every edge case of every format - there are far too many, and Pandoc already does a great job translating between formats).

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[ANN] accelerate-0.15
by Trevor L. McDonell 16 Sep '14

16 Sep '14

Friends, I am pleased to announce the release of the Accelerate 0.15 family of packages. Accelerate defines an embedded language of array computations for high performance computing in Haskell. Computations on multi-dimensional, regular arrays are expressed in the form of parameterised collective operations, such as maps, reductions, and permutations. These computations may then be online compiled and executed on a range of architectures, such as GPUs. This release brings mainly bug fixes and performance improvements. The following packages are available on Hackage: accelerate The language definition and reference implementation accelerate-cuda A high performance parallel backend targeting NVIDIA GPUs accelerate-io Fast conversion between Accelerate arrays and other formats, including ‘vector’ and ‘repa’. accelerate-fft Discrete Fourier transforms, backed by CUFFT where available accelerate-examples Computational kernels and applications showcasing Accelerate The code can be found on GitHub, where you can also submit issues: https://github.com/AccelerateHS https://github.com/AccelerateHS/accelerate/issues Finally, there is also a mailing list that can be used for both use and development discussions: accelerate-haskell(a)googlegroups.com http://groups.google.com/group/accelerate-haskell -The Accelerate Team

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Type union
by Dmitry Bogatov 15 Sep '14

15 Sep '14

Hello! I am trying to create type safe boolean formula representation. Main operation is substion of particular value, to get another formula, and function that accept formula to calculate it's value. So target is: a = Conjunction (Var X) (Var Y) is 2 variable formula value (apply (X, True) . apply (Y, True) $ a) -- True and neither value a apply (X, True) . apply (X, False) $ a typechecks. How can I archive it? class Union a b c instance (a ~ b) => Union a b b instance Union a b (a, b) data P = P deriving Show data Q = Q deriving Show class (Show a) => Variable a instance Variable P instance Variable Q data Formula t where Prop :: (Variable b) => b -> Formula b Conjunction :: (Union t1 t2 t3) => Formula t1 -> Formula t2 -> Formula t3 deriving instance Show (Formula t) main = print (Conjunction (Prop P) (Prop Q) :: Int) This complains on ambitious t3. Attempt by typefamilies fails, since type family Union t1 t2 :: * data Void type instance Union a a = a type instance Union (a, b) a = (a, b) type instance Union (a, b) b = (a, b) type instance Union (a, b) c = (a, b, c) type instance Union a (a, b) = (a, b) type instance Union b (a, b) = (a, b) type instance Union c (a, b) = (a, b, c) type instance Union (a, b, c) a = (a, b, c) type instance Union (a, b, c) b = (a, b, c) type instance Union (a, b, c) c = (a, b, c) type instance Union (a, b, c) d = Void type instance Union a (a, b, c) = (a, b, c) type instance Union b (a, b, c) = (a, b, c) type instance Union c (a, b, c) = (a, b, c) type instance Union d (a, b, c) = Void this is somewhy conflicting instances. I am out of ideas. -- Best regards, Dmitry Bogatov <KAction(a)gnu.org>, Free Software supporter, esperantisto and netiquette guardian. GPG: 54B7F00D

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Using cabal repl with tests
by Arnaud Bailly 15 Sep '14

15 Sep '14

Hello, I have a classical project with cabal file split between a library, an executable and a test-suite. When I run `cabal repl` I got all modules from the library loaded, which is somewhat logical. I would like to launch a repl with test modules loaded, how can I achieve this? Adding `--enable-tests` does not help for the repl... Thanks, -- Arnaud Bailly FoldLabs Associate: http://foldlabs.com

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Control.Monad.Error deprecated?
by Karl Voelker 15 Sep '14

15 Sep '14

Hello everyone, I just discovered that Control.Monad.Error [1] has recently become deprecated in favor of Control.Monad.Except [2], and I am curious about what motivated the change. Can anyone explain? Thanks, Karl 1: http://hackage.haskell.org/package/mtl-2.2.1/docs/Control-Monad-Error.html 2: http://hackage.haskell.org/package/mtl-2.2.1/docs/Control-Monad-Except.html

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ANN: haskell-src-exts-1.16.0
by Roman Cheplyaka 13 Sep '14

13 Sep '14

I am pleased to announce the release of haskell-src-exts-1.16.0! Hackage: https://hackage.haskell.org/package/haskell-src-exts-1.16.0 GitHub: https://github.com/haskell-suite/haskell-src-exts This release brings many bugfixes, as well as the following language features: * DoRec * Closed type families * GADT records * ExplicitNamespaces * Type equality constraints * PolyKinds * DataKinds * Default associated types * Instance signatures * OVERLAP pragma * Parallel arrays * MINIMAL pragma * Default signatures * Safe Haskell * Binary literals * Qualified record puns * Type splices The full changelog is available at https://github.com/haskell-suite/haskell-src-exts/blob/1.16.0/CHANGELOG This release is brought to you by: Alan Zimmerman Erik de Castro Lopo klapaucius Lars Corbijn Leonid Onokhov Peter A. Jonsson phischu Roman Cheplyaka Stefan Wehr Stijn van Drongelen yuriy0 Special thanks to Peter Jonsson who has done an incredible job for this release and fixed many of the longstanding issues in haskell-src-exts. Roman

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policy for new packages
by Corentin Dupont 13 Sep '14

13 Sep '14

Hi guys, In my software I developped some piece of code that I think are sufficiently generic to be useful for others (some datatypes and typeclasses). Should I put them in a separate package and annonce them? What is the best pratice here? Namely it's a datatype called Data.Todo allowing to keep track of actions left to do to complete a computation, and the other is a typeclass called Control.Shortcut designed for computations that can be run in parralel and shortcuted if necessary. So they are small (but useful) things, I'm wondering if creating one package for each is worth it, or another policy can apply. Cheers, Corentin

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XML <--> Haskell Data Structure using HXT
by Han Joosten 11 Sep '14

11 Sep '14

I would like to write code to enable importing data to and fro from a Haskell data structure. It makes sense to have some XSD or so that specifies how the XML should be structured. The HDS is already in place. I have been looking into hte HXT library and I think it could be used for this job. However, I am not familiar (yet) with Arrows and the like. Also the use of picklers is new to me. It would help me a lot if someone has a neat example of how coversion between XML and some Haskell data structure can be implemented in het HXT-style. Do such examples exist? Where can I find them? For those interested: Here is the Haskell Data Structure: https://sourceforge.net/p/ampersand/code/HEAD/tree/trunk/src/lib/Database/D… Cheers & Thanks for reading! Han Joosten

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understanding cloud Haskell serialization
by felipe zapata 11 Sep '14

11 Sep '14

Dear Cafe, I'm trying to understand the implementation of Cloud Haskell, specially the closures. According to the documentation, the serialization of a function uses a map from Label to values (RemoteTable), where Remotable is implemented as: newtype RemoteTable = RemoteTable (Map String Dynamic) Where Dynamic is given by, data Dynamic = Dynamic TypeRep GHC.Any The question is then, How does this Dynamic data type encodes functions? And how is related this Dynamic type to the decoder function? closure :: Static (ByteString -> a) -- Decoder -> ByteString -- Encoded closure environment -> Closure a Static provides two function, one function related to the label to lookup at the RemoteTable and one used for composition. But how is this related to Dynamic? Any guide will be appreciated. Felipe Z.

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HaLVM Talk in NYC on Monday
by Adam Wick 11 Sep '14

11 Sep '14

Howdy - For those of you in the New York City area, I’ll be giving a talk this coming Monday, the 15th, on Galois’s use of the HaLVM — the Haskell Lightweight Virtual Machine — over the last many years. The talk ("Unikernels: Who, What, Where, When, Why") will be part of the Xen User Summit at the Lighthouse Executive Conference Center: http://events.linuxfoundation.org/events/xen-project-user-summit/program/sc… I believe you can get 50% off using the offer code “XenUser50off”. The talk will mostly about the general concept of unikernels like the HaLVM, and how we’ve used them well (and poorly!) on various projects, and so will be light on technical details. But if you’d like to chat with me about any aspect of the HaLVM, stop on by, and we can talk functional languages at a system’s conference. It’ll be great. - Adam

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Cabal doesn't reset the search-path when invoking GHC: potential subtleties
by Phil Ruffwind 11 Sep '14

11 Sep '14

It seems that even when invoked via Cabal, GHC will look in the local directory *first* and then in the list of modules and dependencies supplied by Cabal. I was aware of this behavior subconsciously but I hadn't realized the implications until now. Normally, it's not a big problem, other than for the occasional situation where I forget to add those local modules to 'other-modules'. This would cause 'cabal sdist' to generate an incomplete package, even though 'cabal build && cabal install' works just fine! But there are more subtle "bugs": it breaks if the executable and library share the same directory, but the library has some hidden modules stashed away in a different directory! The conditions required to reproduce this is somewhat difficult to explain, so let me show a simple example: 1. Make a Cabal package: -- ./foo.cabal name: foo version: 0.0.0.0 build-type: Simple cabal-version: >=1.8 library exposed-modules: Exposed other-modules: Hidden build-depends: base hs-source-dirs: ., hidden executable main main-is: Main.hs build-depends: base, foo 2. Add a library with two modules at the given paths: -- ./Exposed.hs module Exposed where import Hidden -- ./hidden/Hidden.hs module Hidden where 3. Add an executable: -- ./Main.hs module Main where import Exposed main = return () 4. Now run `cabal build`. This would cause an error message akin to: > Could not find module Hidden The problem is that despite the dependency on the library `foo` being specified in Cabal, GHC still chose the *local* `Exposed` module over the `Exposed` module in the library `foo`. This means when it tries to recompile the `Exposed` module, it is unaware that `Hidden` is located in another directory. The error message is unhelpful because it doesn't point to the actual cause of the problem and led me astray thinking that something was wrong with my Cabal configuration. In the end, the problem has to do with GHC deciding to look up packages in locations outside Cabal's control. There are many other ways to trigger this problem -- the above was only one that I just happened to run into. For now, a workaround would be to use `-i` with all the executables to avoid this subtle issue in the future. RF

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Categorical description for vector-space instance of AdditiveGroup (Maybe a)
by trevor cook 11 Sep '14

11 Sep '14

Hi Haskell Cafe, In Vector-space-0.8.7, there is the cited inconsistency of the definition of AdditiveGroup (Maybe a). I've posted the source, including comment, below for reference. Following the logic of the counterexample and Conal's (and or Andy Gill's) comment, the problem hinges on the equality, Nothing = Just (zeroV :: a). I'm curious about the catigorical description of this situation. Does this mean that the category of Additive Groups and Maybe Additive Groups are equivalent as categories? I'm not proposing that this is somehow a resolution to vector-space, but rather trying to gain some insight into equivalence, naturalitity, adjunction, etc. My thinking as to why equivalence is that if we have the instance below defined using: zeroV = Just zeroV and making appropriate changes following that new decision. Nothing ^+^ Nothing = zeroV a ^+^ Nothing = a Nothing ^+^ b = b negateV Nothing = zeroV negateV a = fmap negateV then we pretty much defer the group structure of (Maybe a) to be based totally on the structure of a. And since `a` and `Maybe a` are not isomorphic then "hey, I just learned about this new thing so maybe its that." Its a horrible argument, hopefully the cafe will show some better thinking for me. Regards, Trevor -- Maybe is handled like the Maybe-of-Sum monoidinstance AdditiveGroup a => AdditiveGroup (Maybe a) where zeroV = Nothing Nothing ^+^ b' = b' a' ^+^ Nothing = a' Just a' ^+^ Just b' = Just (a' ^+^ b') negateV = fmap negateV{-Alexey Khudyakov wrote: I looked through vector-space package and found lawless instance. Namely Maybe's AdditiveGroup instance It's group so following relation is expected to hold. Otherwise it's not a group. > x ^+^ negateV x == zeroV Here is counterexample: > let x = Just 2 in x ^+^ negateV x == zeroV False I think it's not possible to sensibly define group instance for Maybe a at all.I see that the problem here is in distinguishing 'Just zeroV' fromNothing. I could fix the Just + Just line to use Nothing instead of JustzeroV when a' ^+^ b' == zeroV, although doing so would require Eq a andhence lose some generality. Even so, the abstraction leak would probablyshow up elsewhere.Hm.-}

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Haskell Weekly News: Issue 304
by Daniel Santa Cruz 11 Sep '14

11 Sep '14

Welcome to issue 305 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers from August 31 to September 06, 2014 Quotes of the Week * srhb: segfaults sure are easier to come by doing FFI stuff Top Reddit Stories * Pandoc author working with industry on Markdown spec Domain: standardmarkdown.com, Score: 68, Comments: 7 Original: [1] http://goo.gl/JBte8k On Reddit: [2] http://goo.gl/LWT42a * ICFP 2014 Talks Domain: youtube.com, Score: 56, Comments: 0 Original: [3] http://goo.gl/2zRte4 On Reddit: [4] http://goo.gl/NvWBBa * ICFP 2014 Workshops (Videos) Domain: youtube.com, Score: 53, Comments: 6 Original: [5] http://goo.gl/gpfI8T On Reddit: [6] http://goo.gl/Bj5SwB * Let's Build a Browser Engine in Haskell Domain: hrothen.github.io, Score: 45, Comments: 18 Original: [7] http://goo.gl/FkOM49 On Reddit: [8] http://goo.gl/rXM38x * Open type families are not modular Domain: blog.ezyang.com, Score: 41, Comments: 52 Original: [9] http://goo.gl/XO1bVK On Reddit: [10] http://goo.gl/ROxxUA * IDE for Haste projects Domain: haskell-web.blogspot.com.es, Score: 36, Comments: 5 Original: [11] http://goo.gl/uvjZUC On Reddit: [12] http://goo.gl/3Ra4dt * Real world one-liner examples Domain: github.com, Score: 33, Comments: 7 Original: [13] http://goo.gl/E5wFiW On Reddit: [14] http://goo.gl/9gipjb * Planning Yesod 1.4 Domain: yesodweb.com, Score: 32, Comments: 8 Original: [15] http://goo.gl/7Kul02 On Reddit: [16] http://goo.gl/erCRmZ * Practical Machines: A simple tutorial for the Machines streaming library Domain: statusfailed.com, Score: 32, Comments: 24 Original: [17] http://goo.gl/bmRQot On Reddit: [18] http://goo.gl/0QSdOL * Anecdotes and Advice on Hiring Junior or Summer/Co-Op Students for Haskell Work Domain: self.haskell, Score: 32, Comments: 29 Original: [19] http://goo.gl/M7NOJO On Reddit: [20] http://goo.gl/M7NOJO * Write your compiler passes in Coq for great good! Domain: megacz.com, Score: 30, Comments: 13 Original: [21] http://goo.gl/l7MU6n On Reddit: [22] http://goo.gl/oSqi3Z * IntelliJ IDEA haskell-idea-plugin + Hasklig Domain: self.haskell, Score: 28, Comments: 3 Original: [23] http://goo.gl/cNWkLh On Reddit: [24] http://goo.gl/cNWkLh * Upcast, a declarative cloud infrastructure orchestration tool that leverages Nix Domain: github.com, Score: 27, Comments: 12 Original: [25] http://goo.gl/vPpXcn On Reddit: [26] http://goo.gl/MHj0Le * Ray Marching Distance Fields with Haskell and GLSL Domain: github.com, Score: 27, Comments: 13 Original: [27] http://goo.gl/HZSjFq On Reddit: [28] http://goo.gl/w0IZ0w * A Pretty-Printer that Says What It Means (or, Why Idris's Pretty-Printer is a Functor) Domain: davidchristiansen.dk, Score: 25, Comments: 14 Original: [29] http://goo.gl/vfdISz On Reddit: [30] http://goo.gl/mHU49x * The Ivory Language is an eDSL for safe systems programming. You can think of Ivory as a safer C, embedded in Haskell. Domain: ivorylang.org, Score: 23, Comments: 3 Original: [31] http://goo.gl/xJJ68c On Reddit: [32] http://goo.gl/RLljxg * Pre-published the slide "Writing NetBSD Sound Drivers in Haskell" for Haskell Symposium 2014. #icfp2014 Domain: slideshare.net, Score: 23, Comments: 4 Original: [33] http://goo.gl/gsENVq On Reddit: [34] http://goo.gl/mWH3zH * Haskell 2014 talk: Reflection without Remorse: Revealing a hidden sequence to speed up monadic reflection Domain: youtube.com, Score: 23, Comments: 8 Original: [35] http://goo.gl/Dffhnx On Reddit: [36] http://goo.gl/UFPUu3 * Wadler's Blog: Howard on Curry-Howard Domain: wadler.blogspot.com, Score: 21, Comments: 0 Original: [37] http://goo.gl/Fz90FG On Reddit: [38] http://goo.gl/P5kemv Top StackOverflow Questions * Infinite lazy bitmap votes: 11, answers: 2 Read on SO: [39] http://goo.gl/4zDwFX * Correct terminology for continuations votes: 11, answers: 4 Read on SO: [40] http://goo.gl/QHVRWI * How do I make MonadRandom a Functor? votes: 9, answers: 1 Read on SO: [41] http://goo.gl/vvD7bR * Why does Haskell's foldr NOT stackoverflow while the same Scala implementation does? votes: 9, answers: 4 Read on SO: [42] http://goo.gl/zdxgAM Until next time, [43]+Daniel Santa Cruz References 1. http://standardmarkdown.com/ 2. http://www.reddit.com/r/haskell/comments/2fgtuu/pandoc_author_working_with_… 3. https://www.youtube.com/playlist?list=PL4UWOFngo5DVBqifWX6ZlXJ7idxWaOP69 4. http://www.reddit.com/r/haskell/comments/2f8o3x/icfp_2014_talks/ 5. http://www.youtube.com/playlist?list=PL4UWOFngo5DXuUiMCNumrFhaDfMx54QgV 6. http://www.reddit.com/r/haskell/comments/2f60hd/icfp_2014_workshops_videos/ 7. http://hrothen.github.io/2014/09/05/lets-build-a-browser-engine-in-haskell/ 8. http://www.reddit.com/r/haskell/comments/2flosm/lets_build_a_browser_engine… 9. http://blog.ezyang.com/2014/09/open-type-families-are-not-modular/ 10. http://www.reddit.com/r/haskell/comments/2fi4zc/open_type_families_are_not_… 11. http://haskell-web.blogspot.com.es/2014/09/ide-for-haste-projects.html 12. http://www.reddit.com/r/haskell/comments/2fk91p/ide_for_haste_projects/ 13. https://github.com/sjoerdvisscher/blog/blob/master/2014/2014-09-03%20real%2… 14. http://www.reddit.com/r/haskell/comments/2feen3/real_world_oneliner_example… 15. http://www.yesodweb.com/blog/2014/09/planning-yesod-1-4 16. http://www.reddit.com/r/haskell/comments/2f4kym/planning_yesod_14/ 17. http://statusfailed.com/blog/2014/09/02/practical-machines-in-60-seconds.ht… 18. http://www.reddit.com/r/haskell/comments/2fao00/practical_machines_a_simple… 19. http://www.reddit.com/r/haskell/comments/2fj0v5/anecdotes_and_advice_on_hir… 20. http://www.reddit.com/r/haskell/comments/2fj0v5/anecdotes_and_advice_on_hir… 21. http://www.megacz.com/berkeley/coq-in-ghc/ 22. http://www.reddit.com/r/haskell/comments/2f8bu9/write_your_compiler_passes_… 23. http://www.reddit.com/r/haskell/comments/2fb1j5/intellij_idea_haskellideapl… 24. http://www.reddit.com/r/haskell/comments/2fb1j5/intellij_idea_haskellideapl… 25. https://github.com/zalora/upcast 26. http://www.reddit.com/r/haskell/comments/2f2meq/upcast_a_declarative_cloud_… 27. https://github.com/blitzcode/ray-marching-distance-fields 28. http://www.reddit.com/r/haskell/comments/2ffmys/ray_marching_distance_field… 29. http://www.davidchristiansen.dk/2014/09/06/pretty-printing-idris/ 30. http://www.reddit.com/r/haskell/comments/2fntec/a_prettyprinter_that_says_w… 31. http://ivorylang.org/ 32. http://www.reddit.com/r/haskell/comments/2f6p2h/the_ivory_language_is_an_ed… 33. http://www.slideshare.net/master_q/writing-netbsd-sound-drivers-in-haskell 34. http://www.reddit.com/r/haskell/comments/2fd02w/prepublished_the_slide_writ… 35. https://www.youtube.com/watch?v=_XoI65Rxmss&index=31&list=UUP9g4dLR7xt6KzCY… 36. http://www.reddit.com/r/haskell/comments/2fnj6p/haskell_2014_talk_reflectio… 37. http://wadler.blogspot.com/2014/08/howard-on-curry-howard.html 38. http://www.reddit.com/r/haskell/comments/2f9v8e/wadlers_blog_howard_on_curr… 39. http://stackoverflow.com/questions/25621889/infinite-lazy-bitmap 40. http://stackoverflow.com/questions/25648332/correct-terminology-for-continu… 41. http://stackoverflow.com/questions/25622571/how-do-i-make-monadrandom-a-fun… 42. http://stackoverflow.com/questions/25622959/why-does-haskells-foldr-not-sta… 43. https://plus.google.com/105107667630152149014/about

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Re: [Haskell-cafe] api-tools questions
by Karsten Gebbert 10 Sep '14

10 Sep '14

Chris, thank you for the pointer, that is really helpful indeed! I see that you are using Haskell types for some fields, rather than types defined in your API. When I, for instance, try to use Map as field type, with String as both key and value type, I get an error: myrec :: MyRec // a map = record myfield :: Map String String Exception when trying to run compile-time code: Syntax error at line 345, column 20 (@8596): [(AlexPn 8596 345 20,TypeIden "String"),(AlexPn 8603 345 27,TypeIden "String")] I suspect this is only the case with types that are parameterized over others, as a type synonym seems to make this possible anyways. Is there a better way to deal with this than the one I mentioned? Thanks for your help, karsten Chris Dornan <chris(a)chrisdornan.com> writes: > You might also find the keystore[0] package useful as it makes use of > This technique in several places. See, for example the definition of > Pattern in the `Data.Keystore.Types.Schema`[1] and > `Data.Keystore.Types`[2]. > > Chris > > [0] http://hackage.haskell.org/package/keystore > [1] > https://github.com/cdornan/keystore/blob/master/src/Data/KeyStore/Types/Sch > ema.hs#L179 > [2] > https://github.com/cdornan/keystore/blob/master/src/Data/KeyStore/Types.hs# > L68 > [3] http://hackage.haskell.org/package/keystore-0.5.0.4 > > > On 09/09/2014 17:20, "Karsten Gebbert" <k(a)ioctl.it> wrote: > >>Excellent, thanks a lot Adam. I'll open a PR when I'm through with this >>project :) >> >>Adam Gundry <adam(a)well-typed.com> writes: >> >>> Hi Karsten, >>> >>> This isn't very well documented, but there is a (hidden) feature of >>> api-tools that should do what you want. If you say something like >>> >>> mt :: MyTime = basic string with inj_MyTime, prj_MyTime >>> >>> then you can define your own type MyTime and give conversion functions >>> inj_MyTime and prj_MyTime to convert back and forth from a >>> newtype-wrapped Text. (In fact, you could probably use UTCTime as >>> MyTime...). More precisely, api-tools will generate something like >>> >>> newtype REP__MyTime = REP__MyTime Text >>> >>> and you will need to implement >>> >>> inj_MyTime :: REP__MyTime -> ParserWithErrs MyTime >>> prj_MyTime :: MyTime -> REP__MyTime >>> >>> I hope this helps, and further questions or documentation contributions >>> are very welcome! >>> >>> Cheers, >>> >>> Adam >>> >>> >>> On 09/09/14 14:02, Karsten Gebbert wrote: >>>> Hi All, >>>> >>>> I have a question concerning the api-tools package. >>>> >>>> Its not clear from the tests, sources or the tutorial how I can use >>>> other date/time formats that the default `utc` type can handle. I'm >>>> trying to wrap a JSON API that is not under my control, so I have to >>>> adhere to whatever I get back from it. Could anybody with experience >>>> with the package point me to some example, relevant bits in the sources >>>> or a tip how to do it? >>>> >>>> I'm planning to create some more documentation around the package to >>>> contribute back once I figured out a few more details, because I think >>>> its quite a useful abstraction when dealing with (foreign) APIs IMO. >>>> >>>> Thanks already for any hints, >>>> >>>> karsten >>> >>> >>> -- >>> Adam Gundry, Haskell Consultant >>> Well-Typed LLP, http://www.well-typed.com/ >>_______________________________________________ >>Haskell-Cafe mailing list >>Haskell-Cafe(a)haskell.org >>http://www.haskell.org/mailman/listinfo/haskell-cafe

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Use Haskell shared library with foreign exports with dlopen/dlsym
by Tobias Neumann 10 Sep '14

10 Sep '14

Hello Cafe, I am trying to use a Haskell shared library with foreign exports from Haskell again via dlopen/dlsym. Sadly it segfaults, and the segfaults happen on dlclose during garbage collection points (as figured out by monochrom in #haskell). So right now I can only open a library once and may not dlclose it. Can someone point me to a mistake I made, or is this rather a ghc (7.8.3) bug? Please see attached minimal example. Regards, Tobias test.hs: module Main where import qualified System.Posix.DynamicLinker as DL import Foreign foreign import ccall "dynamic" mkTest :: FunPtr Int -> Int main = do DL.withDL ("./libtest.so") [DL.RTLD_NOW] $ \dl -> do dimPtr <- DL.dlsym dl "test" let test = mkTest dimPtr print test libtest.hs: module Test() where import Foreign foreign export ccall test :: Int test :: Int test = 124 build with: ghc --make -shared -dynamic -fPIC libtest.hs -o libtest.so ghc --make -dynamic test.hs

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Re: [Haskell-cafe] Categorical description for vector-space instance of AdditiveGroup (Maybe a)
by trevor cook 10 Sep '14

10 Sep '14

Here's that vector-space code, formatted better. -- Maybe is handled like the Maybe-of-Sum monoid instance AdditiveGroup a => AdditiveGroup (Maybe a) where zeroV = Nothing Nothing ^+^ b' = b' a' ^+^ Nothing = a' Just a' ^+^ Just b' = Just (a' ^+^ b') negateV = fmap negateV {- Alexey Khudyakov wrote: I looked through vector-space package and found lawless instance. Namely Maybe's AdditiveGroup instance It's group so following relation is expected to hold. Otherwise it's not a group. > x ^+^ negateV x == zeroV Here is counterexample: > let x = Just 2 in x ^+^ negateV x == zeroV False I think it's not possible to sensibly define group instance for Maybe a at all.I see that the problem here is in distinguishing 'Just zeroV' fromNothing. I could fix the Just + Just line to use Nothing instead of JustzeroV when a' ^+^ b' == zeroV, although doing so would require Eq a andhence lose some generality. Even so, the abstraction leak would probablyshow up elsewhere.Hm. -}

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cabal-install fails (osx 10.10)
by Michael Trotter 10 Sep '14

10 Sep '14

I'm having trouble getting cabal-install to work. I used homebrew (brew install cabal-install), which successfully installed the ghc dependency and then attempted to install cabal-install. The problem looks like it's either with my ghc install or maybe an issue with cabal-install and osx 10.10. This is my first haskell experience though, so I'm not really sure how to proceed. Here's the console output: setup: Error: Could not find module: Distribution.Compat.CreatePipe with any suffix: ["dyn_hi"] in the search path: ["dist/build"] cabal: Error: some packages failed to install: Cabal-1.20.0.2 failed during the final install step. The exception was: ExitFailure 1 cabal-install-1.20.0.3 depends on Cabal-1.20.0.2 which failed to install.

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LinkedIn job ad link for openings for several enthusiastic great Haskell developers (geoloc. globally) at Swedish spin-off Functor Group with subsidiaries + three Scala developer (geoloc. Sweden) with spear-edge / very strong qualifications and high-end industry salary for Functor Consulting AB
by Johan Glimming 10 Sep '14

10 Sep '14

Dear Haskell developers, type theory developers, Agda/Epigram/Idris/Coq developers/enthusiasts abound in this community, We are searching the planet for great Haskell and Scala programmers right now for a really interesting spin-off now growing and flourishing after 2.5 years since it was founded. If you are a functional programmer this might be the most exciting job around with e.g. a very exciting customer "as close as a space station as you can get", and industrially entirely unique heavily research-based technology that we have developed now for several years. » https://www.linkedin.com/jobs2/view/19207355 You would help us develop our products further, the new constructive programming paradigm based on type theory carrying languages including domain-specific languages as never done before in the software industry … ( And yes, we are entirely based on (Martin-Löf) type theory, that's what we are all about. And we use Haskell for our development internally almost entirely, with some Ocaml etc on top ... ) We look for three experienced Scala developers (for being based in Sweden, Stockholm-area) at Functor Group AB, Functor AB and Functor Consulting AB. These developers are recruited into Functor Consulting AB which is to become the spear-edge partner to Typesafe in Scandinavia, specifically Sweden, while interacting with our other two teams at Functor AB to a certain extent, focusing on DSL development, DDD and more. We bring type theory to the industry in the new constructive programming paradigm and with a new static analysis technique combined with testing and dependent types, all based on the same core technology … The three Scala developers, for extreme FP consultancy, are offered very competitive Swedish salary, plus added potential for also other benefits via Functor Group AB and the product company Functor AB. Experience from Scala development and documented skills with Scala and related technologies (such as Java) is must be considerable to be considered for these three positions. If you are not based in Sweden, we would assist as much as possible in moving to Stockholm/Uppsala, Sweden, where these three Scala spear-edge developers will be based, with a consultancy manager of considerable experience handling administration and co-ordination in what we expect to be an otherwise quite self-organised business targeting the hardest and most challenging projects at any given time. You can apply on LinkedIn — or, if you prefer, email your resumé, references, credentials, and cover letter to jobs(a)functorgroup.com. » https://www.linkedin.com/jobs2/view/19207355. Best wishes, Johan Glimming — Company website: http://www.functorgroup.com Twitter feeds to follow: @FunctorGroup @Functors @FunctorTech

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Persistent Journal/Event queue Implementation
by Arnaud Bailly 10 Sep '14

10 Sep '14

Hello Cafe, I am looking for a Haskell implementation (or library binding) to some persistent journal/event queue software, something like Apache Kafka. My google-fu is lacking so I was not able to find anything but I might have been doing it wrong. Thanks, -- Arnaud Bailly FoldLabs Associate: http://foldlabs.com

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Re: [Haskell-cafe] FFI question
by Vasili I. Galchin 10 Sep '14

10 Sep '14

On Tue, Sep 9, 2014 at 10:36 PM, Vasili I. Galchin <vigalchin(a)gmail.com> wrote: > Adam, > > Did a find/grep under my posix-realtime directory .. no > definition of MCL_CURRENT, MCL_FUTURE or MCL_CURRENTandFUTURE!! But If > I comment out the case arm MCL_CURRENTandFUTURE in my LockMem.hsc file > and run "cabal build" from the directory where my *.cabal file lives > .. clean compile ... Sigh!??!! > > Vasya > > On Mon, Sep 8, 2014 at 7:36 AM, adam vogt <vogt.adam(a)gmail.com> wrote: >> Hi Vasili >> >> Does the sys/mman.h or another included header actually define >> MCL_CURRENTandFUTURE? >> >> Regards, >> Adam >> >> On Sep 8, 2014 4:45 AM, "Vasili I. Galchin" <vigalchin(a)gmail.com> wrote: >>> >>> Following is a fragment generated by hsc2hs from LockedMem.hsc: >>> >>> #line 93 "LockedMem.hsc" >>> hsc_const (MCL_CURRENTandFUTURE); >>> hsc_fputs (")\n" >>> "", hsc_stdout()); >>> hsc_line (94, "LockedMem.hsc"); >>> hsc_fputs ("\n" >>> "foreign import ccall unsafe \"sys/mman.h mlockall\"\n" >>> " c_mlockall :: CInt -> IO CInt\n" >>> "\n" >>> "\n" >>> "-- | unlock all mapped pages of a process!\n" >>> "unlockAllMemory :: IO () \n" >>> "unlockAllMemory = do\n" >>> " throwErrnoIfMinus1 \"unlockAllMemory\" (c_munlockall)\n" >>> " return ()\n" >>> "\n" >>> "foreign import ccall unsafe \"sys/mman.h munlockall\"\n" >>> " c_munlockall :: IO CInt\n" >>> "", hsc_stdout()); >>> return 0; >>> >>> On Mon, Sep 8, 2014 at 2:11 AM, Vasili I. Galchin <vigalchin(a)gmail.com> >>> wrote: >>> > Hello, >>> > >>> > I need memory refreshing about FFI because I need to fix a bug >>> > (plus I got down a rat hole because of Ukraine war :-(). Following a >>> > snippet of something I wrote: >>> > >>> > -- | lock all of the memory space of a process >>> > lockAllMemory :: LockAllFlags -> IO () >>> > lockAllMemory flags = do >>> > throwErrnoIfMinus1 "lockAllMemory" (c_mlockall cflags) >>> > return () >>> > where >>> > cflags = case flags of >>> > CURRENT -> (#const MCL_CURRENT) >>> > FUTURE -> (#const MCL_FUTURE) >>> > CURRENTandFUTURE -> (#const MCL_CURRENTandFUTURE) >>> > >>> > >>> > it is a file called LockedMem.hsc and the third arm CURRENTandFUTURE I >>> > just added to fix the this bug .. >>> > >>> > MCL_CURRENTandFUTURE ends up in LockedMem_make.c(sp??) but I get a >>> > undeclared nasty message when I try to build LockedMem.hsc... my >>> > bad... . Please help so I can go back to help Ukraine. >>> > >>> > Kind regarsd, >>> > >>> > Vasya >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> Haskell-Cafe(a)haskell.org >>> http://www.haskell.org/mailman/listinfo/haskell-cafe

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2014 haskell cabal update hangs on mac
by Madhu Babu 09 Sep '14

09 Sep '14

I initially installed haskell platform ( 2013 version; 7.6.3 ghc ) on my mac. Everything was working great. Just now saw the haskell platform website again and found new version was released ( Haskell Platform 2014.2.0.0 for Mac OS X, 64bit ). I installed it, and un-installed the older version using uninstall-hs. Now when i type "cabal" or "cabal update" on my terminal, it hangs. Actually when i look into Activity Monitor, i can see that it is invoking some "sh script & possibly some find command" infinitely. I initially guess may be it is building some indexes. but it has been running for an hr or so. I have Xcode 5, gcc and other command line tools installed properly Please advice. I cannot install any other package using cabal.

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Reversing a fixed-length vector
by Cristiano Paris 09 Sep '14

09 Sep '14

Hi, I'm playing around with Type Families so I decided to implement a simple fixed-length Vect of Integers. Here is my straightforward implementation (ghc 7.8.3): https://gist.github.com/anonymous/d838e68ce6a02412859f As you can see, I'm trying to implement a reverse function for my vectors which guarantees that the output vector is the same size as the input one. I tried to express this constraint at the type level. The problem is that I can't have ghc to type check the reverse function in the non-trivial case: _________________ Could not deduce (Plus n1 (S m) ~ S (Plus n1 m)) from the context (n ~ S n1) bound by a pattern with constructor CV :: forall n. Int -> Vect n -> Vect (S n), in an equation for ‘vecReverse’ at vect3.hs:30:13-18 Expected type: Vect (Plus n m) Actual type: Vect (Plus n1 (S m)) _________________ Iit has to do with the fact that the type checker can't deduce that: Plus n1 (S m) ~ S (Plus n1 m) ~ Plus (S n1) m ~Plus n m I tried to insert the following instance to the family: Plus n (S m) = S (Plus n m) but to no avail. Any clue? Thanks. C. -- GPG Key: 4096R/C17E53C6 2010-02-22 Fingerprint = 4575 4FB5 DC8E 7641 D3D8 8EBE DF59 B4E9 C17E 53C6

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Warnings for unhandled exceptions
by Henk-Jan van Tuyl 09 Sep '14

09 Sep '14

L.S., I was reading about the Aardvark language [0] and the robustness they intend to implement in it by, amongst others, catching each possible exception. I wonder, is it possible to implement compiler warnings for unhandled exceptions in Haskell? One of the strong points of Haskell is the type checking and clearly identifying functions with side effects, but exceptions are not reflected by the type of a function. It would be useful if the compiler gave a warning for each type of exception, for each expression, that is not handled by the program. Regards, Henk-Jan van Tuyl [0] http://aardvarklanguage.sourceforge.net/ -- Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://folding.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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Specifying build flags in cabal depencies
by Pedro Vasconcelos 09 Sep '14

09 Sep '14

Hello, I've run across an annoyance with a Haskell project of mine that requires Snap built with SSL: I couldn't find a way to specify the flag "-fopensll" to pass when building the snap-server package. This means that building on a new machine requires either manually installing the right version of snap-server with -fopenssl or re-installing with after the Cabal build. Is there a better way to do this? Thanks, Pedro

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Re: [Haskell-cafe] Parallel interruptible computations
by Julian K. Arni 09 Sep '14

09 Sep '14

Are you looking for something like amb/unamb? [0] In particular, if you look at the comments in the source for 'race', it should be pretty intuitive how to go from there to "run x computations, kill the remaining ones after y return". You just need to fiddle with the MVar, possibly adding another thread and MVar that represents whether the calculation can already be completed. [0] https://hackage.haskell.org/package/unamb-0.2.5/docs/src/Data-Unamb.html#amb

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End of support for test-framework-smallcheck and test-framework-golden
by Roman Cheplyaka 08 Sep '14

08 Sep '14

I'm going to stop maintaining the test-framework-smallcheck and test-framework-golden packages. I recommend switching to tasty's tasty-smallcheck and tasty-golden, respectively. If you are interested in taking over these test-framework packages, let me know. Otherwise, I will continue supporting them for the next 3 months and abandon/deprecate them afterwards. Roman

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Can't create a static Linux executable when using hmatrix
by Kai Zhang 08 Sep '14

08 Sep '14

Hi Cafe, I am trying to build a static exec to be run on another machine, and I failed probably due to hmatrix. How can I fix this? Thanks! Test code: import Numeric.LinearAlgebra.Data main = print (fromLists [[2,3,3], [2,3,3]] :: Matrix Double) When complied with "ghc -O2 -static -optc-static -optl-static test.hs -optl-pthread", gave me lots of errors: /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgees.o): In function `dgees_': (.text+0xbc4): undefined reference to `dcopy_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgees.o): In function `dgees_': (.text+0xed9): undefined reference to `dswap_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgees.o): In function `dgees_': (.text+0x1304): undefined reference to `dswap_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgees.o): In function `dgees_': (.text+0x1377): undefined reference to `dswap_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgeev.o): In function `dgeev_': (.text+0xf9a): undefined reference to `dnrm2_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgeev.o): In function `dgeev_': (.text+0xfd4): undefined reference to `dnrm2_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgeev.o): In function `dgeev_': (.text+0x1022): undefined reference to `dscal_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgeev.o): In function `dgeev_': (.text+0x103b): undefined reference to `dscal_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgeev.o): In function `dgeev_': (.text+0x109c): undefined reference to `idamax_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgeev.o): In function `dgeev_': (.text+0x1125): undefined reference to `drot_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgeev.o): In function `dgeev_': (.text+0x12aa): undefined reference to `dnrm2_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgeev.o): In function `dgeev_': (.text+0x12e4): undefined reference to `dnrm2_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgeev.o): In function `dgeev_': (.text+0x1332): undefined reference to `dscal_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgeev.o): In function `dgeev_': (.text+0x134b): undefined reference to `dscal_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgeev.o): In function `dgeev_': (.text+0x13ac): undefined reference to `idamax_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgeev.o): In function `dgeev_': (.text+0x143d): undefined reference to `drot_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgeev.o): In function `dgeev_': (.text+0x148e): undefined reference to `dnrm2_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgeev.o): In function `dgeev_': (.text+0x14bc): undefined reference to `dscal_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgeev.o): In function `dgeev_': (.text+0x14fe): undefined reference to `dnrm2_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgeev.o): In function `dgeev_': (.text+0x152c): undefined reference to `dscal_' /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/liblapack.a(dgehrd.o): In function `dgehrd_': (.text+0x65d): undefined reference to `dtrmm_' . . .

4 7

ANNOUNCE: buildable-0.1.0.0
by Ivan Lazar Miljenovic 08 Sep '14

08 Sep '14

Have you ever wanted to deal with the builders for various data types in a polymorphic/overloaded fashion? I'm needing to do so and couldn't find any existing code that did so, so I decided to rectify this: http://hackage.haskell.org/package/buildable As a (very contrived) example: λ> build ((365 :: Dec Int) <| fromValue (Char7 ' ') |> (365 :: BigEndian Int16) |> (" omega=𝟂 " :: Utf8 String) |> Utf16 (LE ("hello" :: LT.Text))) :: SB.ByteString "365 \SOHm omega=\240\157\159\130 h\NULe\NULl\NULl\NULo\NUL" -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

1 0

Re: [Haskell-cafe] Parallel interruptible computations
by Corentin Dupont 08 Sep '14

08 Sep '14

Hi guys, thanks for the nice answers! I'll give you a little bit more context: I'm designing an event engine. I have instances for Applicative, Alternative, Monad, MonadPlus. It's like that: -- | Composable events data Event a where SumEvent :: Event a -> Event a -> Event a -- The first event to fire will be returned. AppEvent :: Event (a -> b) -> Event a -> Event b -- Both events should fire, and then the result is returned. PureEvent :: a -> Event a -- Create a fake event. The result is useable with no delay. EmptyEvent :: Event a -- An event that is never fired. BindEvent :: Event a -> (a -> Event b) -> Event b -- The first event should fire, then a second event is created using the result. BaseEvent :: BaseEvent a -> Event a -- Embed a base event. ShortcutEvents :: [Event a] -> ([Maybe a] -> Maybe b) -> Event b -- The function is called each time an event fires, as soon as the result can be computed from the available data, it is returned, dismissing the events that haven't fired yet. instance Functor Event where fmap f a = pure f <*> a instance Applicative Event where pure = PureEvent (<*>) = AppEvent instance Alternative Event where (<|>) = SumEvent empty = EmptyEvent instance Monad Event where (>>=) = BindEvent return = PureEvent instance MonadPlus Event where mplus = SumEvent mzero = EmptyEvent The Applicative instance is good if you have two events and you want both of them to fire ("and"). The Alternative instance is good if you have two events and you need only one to fire ("or"). But what if you have several events, but you need only a part of them to fire in order to construct a final result? Say you have 10 events, but the 5 first to fire will give you enough data to construct a result. You cannot do that with Applicative/Alternative because with Applicative, you need *all* events results, with Alternative you need *only one*. That's why I added this primitive "ShortcutEvents" in my DSL, but I'm not convinced by it. So my questions are: 1. is ShortcutEvents expressible in term of Applicative/Alternative/Monad/MonadPlus? 2. if not is their a well known typeclass that covers this case? 3. if not is their a better way to write it? I especially don't like the list of Event, I'd prefer a more generic writing. What if I want a structure containing the events, instead of a list? What if I want event of various types (say a pair (Event a, Event b) for example)? Note that I'm not working with streams of events (like in traditional FRP frameworks): just with single events (the "BaseEvents") that I want to combine with each other. Those "BaseEvents" will fire only once. The final result of the combination of events will trigger a callback. Cheers, Corentin

3 6

FFI question
by Vasili I. Galchin 08 Sep '14

08 Sep '14

Hello, I need memory refreshing about FFI because I need to fix a bug (plus I got down a rat hole because of Ukraine war :-(). Following a snippet of something I wrote: -- | lock all of the memory space of a process lockAllMemory :: LockAllFlags -> IO () lockAllMemory flags = do throwErrnoIfMinus1 "lockAllMemory" (c_mlockall cflags) return () where cflags = case flags of CURRENT -> (#const MCL_CURRENT) FUTURE -> (#const MCL_FUTURE) CURRENTandFUTURE -> (#const MCL_CURRENTandFUTURE) it is a file called LockedMem.hsc and the third arm CURRENTandFUTURE I just added to fix the this bug .. MCL_CURRENTandFUTURE ends up in LockedMem_make.c(sp??) but I get a undeclared nasty message when I try to build LockedMem.hsc... my bad... . Please help so I can go back to help Ukraine. Kind regarsd, Vasya

1 1

[ANN] haddock-2.15-0, haddock-api-2.15-0, haddock-library-1.1.1
by Mateusz Kowalczyk 07 Sep '14

07 Sep '14

Hello, I'd like to announce the release of Haddock 2.15.0. Before we dive in, I'd like to announce that Haddock development has moved out of the GHC tree and is now done against the latest compiler release. If in the past you wanted to contribute but were intimidated by having to make sure it works against GHC HEAD then here's your chance. Additionally, it now should also work with GHC 7.8.2 so if for whatever reason you're forced to use that, you can now get the latest Haddock features. If you want to contribute then please let us know, we're understaffed! Come chat at #haddock or send us an e-mail. If you have been using 2.14.x, you should be good to simply ‘cabal install haddock’. Now the changes: This is an API-breaking bugfix release so any tickets originally scheduled for 2.15.0 were pushed towards 2.16. Perhaps the biggest change is that ‘cabal install haddock’ will now only give you the Haddock binary. To use Haddock API, please depend on ‘haddock-api’ from now on. I have sent out an e-mail about this couple of weeks in advance to any reverse dependencies of ‘haddock’. This is to workaround cabal's inability to pass flags to dependencies from the cabal file. ‘haddock-library’ only got a minor bump, 1.1.0 → 1.1.1 improving its output. The Monoid instance for DocH is gone however as it was ill-formed to begin with. Changes in version 2.15.0 * Always read in prologue files as UTF8 (#286 and Cabal #1721) * parser: don't wrap headers in DocParagraph (#307) * parser: don't mangle append order for nested lists (pandoc #1346) * parser: preserve list ordering in certain scenarios (#313) * parser: update the attoparsec version used internally giving slight parsing performance boost. * Move development to be against latest GHC release and not GHC HEAD. * Further split up the package to separate the executable from the library, necessary by things like GHCJS. We now have ‘haddock-library’ which are the parts that don't use GHC API, ‘haddock-api’ which are (some of) the parts that do use GHC API and ‘haddock’ which merely provides the executable. * Export few extra functions in the API. * Add compatibility with GHC 7.8.2. * Omit unnecessary ‘forall’s (#315 and #86) * Remove some files which were really old or did not belong in the repository in the first place. Once again, we'd love to have more people on board be it for the HTML backend, refactoring, LaTeX/Hoogle backend, parser improvements, test writing, new feature implementation or bug fixing. Our issue tracker[1] is up to date if you are interested. Thanks! [1]: https://github.com/haskell/haddock/issues -- Mateusz K.

3 5

Re: [Haskell-cafe] Parallel interruptible computations
by Corentin Dupont 07 Sep '14

07 Sep '14

Nobody on those parallel interruptible computations/events? I believe this is related to FRP: we register on several events but only a part of them is enough to compute the result. But I don't see such operator in FRP frameworks such as reactive-banana... On Fri, Sep 5, 2014 at 12:59 PM, Corentin Dupont <corentin.dupont(a)gmail.com> wrote: > Hi guys! > I'm wondering if there is an abstraction (for example a typeclass) for > parallel interruptible computations. > I want several things to be computed in parallel. Those computations will > not finish at the same time, but as soon as enough result is gathered, the > remaining computations can be cancelled and the final result computed. > Clearly a Monad is not suited here: Monad are by definition for sequential > computation (since the result of the first computation is fed to the next). > > -> So the question is: is there an abstraction for parallel computations? > > Note that I'm not interrested with real implementations (such as with > threads) but with the abstraction. > For now I came up with: > > ShortcutEvents :: [Event a] -> ([a] -> Maybe b) -> Event b > > This takes a list of events and a function. The events can fire at > whatever moment, and as soon as one of the events fires, the function is > called with the results available so far. If the function returns Just, the > remaining events are cancelled and the final result is returned. > This is working fine, but I'd like a way to generalize this, especially to > generalize the list to any structure... > > The use case is a voting system: people can vote at whatever moment, but > sometime the result of the vote is known even if not everybody voted yet. > > Thanks! > Corentin >

3 2

Fwd: an idea for improving 'shrink'
by Petr Pudlák 06 Sep '14

06 Sep '14

Hi, since I got no response from the QuickCheck mail address, so I'm resending it here, if someone wants to comment on the idea. Best regards, Petr ---------- Forwarded message ---------- From: Petr Pudlák <petr.mvd(a)gmail.com> Date: 2014-07-06 20:13 GMT+02:00 Subject: an idea for improving 'shrink' To: QuickCheck developers <quickcheck(a)projects.haskell.org> Hi, I was learning about 'shrink' lately and I was trying to create some instances. It felt quite awkward until I realized that the operation for producing shrunk tuples is an applicative functor. I was playing with the idea for a while and I'm sending an experimental patch against QuickCheck master that shows the basics of the idea and how it can help constructing 'shrink' instances. If you feel that this is a good idea, let me know, I'll work on a full patch. Best regards, Petr

2 3

Functional dependency failure
by Alexander Pakhomov 06 Sep '14

06 Sep '14

Hi! I have following code: STRead.hs: import Control.Monad.Reader import Control.Monad.ST import qualified Data.Vector.Mutable as MV import qualified Data.Vector as V type ReadVecMonad s = ReaderT (MV.MVector s Int) (ST s) freezeV :: ReadVecMonad s (V.Vector Int) freezeV = ask >>= lift V.freeze Trying to compile this I have "Couldn't match type ... When using functional dependencies to combine" error following with kind mismatch and type with literaly the same type mismatch. How can I work this around? There's full error message: STRead.hs:9:11: Couldn't match type `V.MVector s Int' with `(->) (V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int)' When using functional dependencies to combine MonadReader r (ReaderT r m), arising from the dependency `m -> r' in the instance declaration in `Control.Monad.Reader.Class' MonadReader ((->) (V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int)) (ReaderT (V.MVector s Int) (ST s)), arising from a use of `ask' at STRead.hs:9:11-13 In the first argument of `(>>=)', namely `ask' In the expression: ask >>= lift V.freeze STRead.hs:9:19: Couldn't match kind `* -> *' with `*' Expected type: (->) (V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int) -> ReaderT (V.MVector s Int) (ST s) (V.Vector Int) Actual type: (->) (V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int) -> ReaderT (V.MVector s Int) (ST s) (V.Vector Int) Kind incompatibility when matching types: (->) (V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int) :: * -> * (->) (V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int) :: * In the return type of a call of `lift' In the second argument of `(>>=)', namely `lift V.freeze' STRead.hs:9:24: Couldn't match kind `*' with `* -> *' Expected type: V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int -> ReaderT (V.MVector s Int) (ST s) (V.Vector Int) Actual type: V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int -> ReaderT (V.MVector s Int) (ST s) (V.Vector Int) Kind incompatibility when matching types: (->) (V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int) :: * (->) (V.MVector (Control.Monad.Primitive.PrimState (ReaderT (V.MVector s Int) (ST s))) Int) :: * -> * In the first argument of `lift', namely `V.freeze' In the second argument of `(>>=)', namely `lift V.freeze'

2 2

Maintaining test-suite dependencies with cabal
by Bram Neijt 06 Sep '14

06 Sep '14

Dear reader, I have a single executable package in Cabal[1] and I have added a test for it using an example configuration from the ltc package[2]. With my test on my executable I can't depend on the main package, but I seem to have to repeat the dependencies of my executable, or split off functionality into a library. [3] Can I easily depend on the dependencies of another package or should I create a library and depend on that in my test and executable? All source is at: https://github.com/bneijt/after/ Greetings, Bram [1] https://github.com/bneijt/after/blob/master/after.cabal [2] https://github.com/scvalex/ltc/blob/master/ltc.cabal [3] A part of my cabal file added below executable after main-is: Main.hs build-depends: base >=4.7 && <4.8, options ==1.*, directory ==1.2.*, parallel-io ==0.3.*, filepath ==1.3.*, unix ==2.7.* hs-source-dirs: src ghc-options: -Wall default-language: Haskell2010 test-suite afterTests hs-source-dirs: test src main-is: AfterTest.hs type: exitcode-stdio-1.0 build-depends: base >=4.7 && <4.8, unix ==2.7.*, -- Here because of after depending on it directory ==1.2.*, -- Here because of after depending on it filepath ==1.3.*, -- Here because of after depending on it test-framework, test-framework-hunit, HUnit default-language: Haskell2010

6 6

Elm-like IDE for Haste projects
by Alberto G. Corona 05 Sep '14

05 Sep '14

Following the thread on lightweight Web interfaces for Haskell: http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/112586 I finished an Elm-like IDE for Haste projects. The software is at: https://github.com/agocorona/tryhplay Running in a heroku instance: http://tryplayg.herokuapp.com Besides to edit-compile and run, it can also import , compile and run haste projects from git repositories (Although this, like the rest of the project is experimental). I use it for my hplayground framework but it can run any haste project. Using playground is easy to translate console programs to the browser and have reactive effects A simple example: http://tryplayg.herokuapp.com/try/console.hs/edit the hello-haste example: http://tryplayg.herokuapp.com/try/hello-haste.hs/edit Or something more complicated: the todo application, from todoMVC.com written in Haste and hplayground: http://tryplayg.herokuapp.com/try/todo.hs/edit rename the programs if you modify them. Follow the instructions to download the HTML generated, that include the Javascript generated. At this time there are no permission controls so it is more or less like a wiki, but heroku from time to time will reset the application. It is a free instance on heroku so expect delays and request timeouts when many people access to the application. I do not know what will happen. Feedback welcome My heroku instance is limited but It is easy to create your own instance in heroku. Follow the install instructions. Haste: https://github.com/valderman/haste-compiler http://haste-lang.org hplayground: https://github.com/agocorona/hplayground -- Alberto.

2 1

Parallel evaluation of code dependencies
by felipe zapata 04 Sep '14

04 Sep '14

Hi Cafe, Suppose that I have a representation of a DSL in Haskell (a physical number crunching simulation using quasiquoting for instance) and I want to evaluate the resulting Haskell representation by splitting it into chunks and send these chunk to some cluster, a supercomputer, etc. It doesn't matter for the moment the distribution protocol. My advisor suggested me that the best way of doing such a thing, is through a call by value strategy. Where I simply evaluate in parallel all the arguments of the functions. The problem with this alternative is that I must manipulate the Haskell representation and use some library ( or write some code) to identify the dependencies and evaluate them in parallel. Can please someone suggest me the best way to tackle this problem? I really appreciate any help. Felipe Z.

2 1

Re: [Haskell-cafe] diagrams fails to install
by Roger Mason 04 Sep '14

04 Sep '14

Hello Mike, Mike Meyer <mwm(a)mired.org> writes: > You should have a /usr/local/llvm32 directory. If so, try: > > PATH=/usr/local/llvm32/bin:$PATH cabal install diagrams. > > I have llvm34 installed, and it worked for me using > /usr/local/llvm34/bin:$PATH. > Thank you, that worked. best wishes, Roger

1 0

diagrams fails to install
by Roger Mason 04 Sep '14

04 Sep '14

Hello, I'm trying to install Diagrams on FreeBSD 10. It fails thus: cabal install diagrams Resolving dependencies... Configuring arithmoi-0.4.1.1... Building arithmoi-0.4.1.1... Preprocessing library arithmoi-0.4.1.1... [ 1 of 34] Compiling Math.NumberTheory.Primes.Sieve.Indexing ( Math/NumberTheory/Primes/Sieve/Indexing.hs, dist/build/Math/NumberTheory/Primes/Sieve/Indexing.o ) <no location info>: Warning: Couldn't figure out LLVM version! Make sure you have installed LLVM ghc: could not execute: opt Failed to install arithmoi-0.4.1.1 cabal-install: Error: some packages failed to install: arithmoi-0.4.1.1 failed during the building phase. The exception was: ExitFailure 1 diagrams-1.2 depends on arithmoi-0.4.1.1 which failed to install. diagrams-contrib-1.1.2.1 depends on arithmoi-0.4.1.1 which failed to install. ghc --info reports: [("Project name","The Glorious Glasgow Haskell Compilation System") ,("GCC extra via C opts"," -fwrapv") ,("C compiler command","gcc47") ,("C compiler flags"," -fno-stack-protector -Wl,--hash-size=31 -Wl,--reduce-memory-overheads") ,("ar command","/usr/bin/ar") ,("ar flags","clqs") ,("ar supports at file","NO") ,("touch command","touch") ,("dllwrap command","/bin/false") ,("windres command","/bin/false") ,("perl command","/usr/bin/perl") ,("target os","OSFreeBSD") ,("target arch","ArchX86") ,("target word size","4") ,("target has GNU nonexec stack","True") ,("target has .ident directive","True") ,("target has subsections via symbols","False") ,("LLVM llc command","llc") ,("LLVM opt command","opt") ,("Project version","7.6.3") ,("Booter version","7.6.3") ,("Stage","2") ,("Build platform","i386-portbld-freebsd") ,("Host platform","i386-portbld-freebsd") ,("Target platform","i386-portbld-freebsd") ,("Have interpreter","YES") ,("Object splitting supported","YES") ,("Have native code generator","YES") ,("Support SMP","YES") ,("Unregisterised","NO") ,("Tables next to code","YES") ,("RTS ways","l debug thr thr_debug thr_l thr_p dyn debug_dyn thr_dyn thr_debug_dyn") ,("Leading underscore","NO") ,("Debug on","False") ,("LibDir","/usr/local/lib/ghc-7.6.3") ,("Global Package DB","/usr/local/lib/ghc-7.6.3/package.conf.d") ,("Gcc Linker flags","[\"-Wl,--hash-size=31\",\"-Wl,--reduce-memory-overheads\"]") ,("Ld Linker flags","[\"--hash-size=31\",\"--reduce-memory-overheads\"]") ] opt is installed as /usr/local/bin/opt32, so I tried symlinking /usr/local/bin/opt to it, but the error remains. Is there some workaround? Thanks, Roger

1 0

Jobs at the University of Kent
by Simon Thompson 04 Sep '14

04 Sep '14

We've been doing functional programming at Kent for more than thirty years, and it would be great to recruit more people in FP, theory, type theory, programming languages, verification, concurrency ... Details of three positions here: https://jobs.kent.ac.uk/fe/tpl_kent01.asp?s=4A515F4E5A565B1A&jobid=38618,12… If you're interested in discussing, just send us an email. Simon Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

1 0

heroku-buildpack-haste
by Alberto G. Corona 04 Sep '14

04 Sep '14

Just to let you know that I created an heroku buildpack that install GHC and Haste in the running environment, so that web applications can invoke ghc, cabal, hastec haste-inst etc. I use it for the creation of an Haste IDE. But it may have other uses. https://github.com/agocorona/heroku-buildpack-haste -- Alberto.

2 2

Package bounds approximation
by Ernesto Rodriguez 04 Sep '14

04 Sep '14

Dear Cafe, I was wondering if there exists a tool to approximate what would be the minimal versions of the dependencies required by a package. I know that calculating this exactly is a bit intractable, but I was considering whether a tool that works as follows would work: 1) Compile the package with known to work dependencies 2) For each version of dependency as d: For each function in d used by My Package: * Perform unification of the resulting type when compiled with known to work dependencies and the type exported by the api of the version of the dependency in consideration. If all unifications succeeds, mark the version as compatible, incompatible otherwise This approximation is obviously not complete. Nevertheless, I would like to get opinions about whether this would be a good/useful/feasible approximation? Does the current GHC api export enough functionality for this package to be feasible? Are there alternatives? I was consider doing this as my `hack` during the high energy, intense no-sleep jacobsHack! <http://jacobshack.com> hackathon, do you think it would be a good idea? Thank you for the opinions and best regards, Ernesto Rodriguez -- Ernesto Rodriguez Masters Student Computer Science Utrecht University www.netowork.me github.com/netogallo

4 6

ANN: Ray Marching Distance Fields with Haskell and GLSL
by Tim C. Schroeder 04 Sep '14

04 Sep '14

https://github.com/blitzcode/ray-marching-distance-fields "This project is a Haskell and GLSL program containing my distance field / ray marching related experiments. The Haskell viewing application is doing the pre-processing, functioning as a development and debugging aid, allowing different shaders to be explored. It automatically reloads and recompiles shaders when they change, showing an overlay displaying any errors. There's a flexible frame buffer system, supporting under and super sampling and saving of screenshots. Tiled rendering avoids shader timeouts and unresponsive UI. It also features offline convolution of environment maps with a filter kernel to enable fast lighting of diffuse and glossy surfaces. Finally, there's an implementation of the Mandelbulb fractal as well as several simpler ones like Mandelbrot and Julia sets. There's some more functionality in the program, try it out and / or visit my website." Cheers, Tim

1 0