- Haskell-Cafe - Haskell.org

Embedding compiled Haskell Platform in custom application
by blackbox.dev.ml 23 Sep '13

23 Sep '13

Hi! I'm writing a tool that generates haskell code, build it with cabal and launch it. I want to deliver that tool to clients, but I don't want to force them, to install system wide any specific ghc or cabal version. How can I embed compiled ghc, cabal and selected libraries (for specific platform) in installer of my application?

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PSA: do not install xcode 5 if you are using ghc 7.6
by Carter Schonwald 23 Sep '13

23 Sep '13

Hey everyone, if you are actively using ghc 7.6 on your mac, for now please do not install xcode 5. It will break your ghc install, because 7.6 doesn't know how to correctly use Clang for the CPP work. (ghc head / and thus 7.8 will work fine with xcode 5, thanks to some outstanding work by Austin Seipp, 7.6 does not) if you do not need xcode 5, and you're actively using ghc 7.6, stay with xcode 4.6 for now. if you installed xcode 5 because its there, and now your ghc 7.6 is occasionally giving you strange errors involving CPP parse failures on fragments like "#-}", you should go to the apple developers website, download, and reinstall the xcode 4.6 CLI tools. if you need both xcode 5 and ghc in working order *right now, tomorrow*, either a) live on the wildside: test out using ghc head: also means you could play with ghc-ios too! b) if you need both in working order now, and stabilish, Darin Morrison has a set of mac-homebrew taps that should be you use https://github.com/darinmorrison/homebrew-haskell these taps should be regarded as more "official" and "canonical" than the formula's that brew provides (the normal brew ones recurrently have problems induced by folks who aren't haskell devs) c) wait a wee bit till 7.8 lands in all its glory, and have both the freshest of xcodes, and the newest of awesome ghcs tl;dr if you don't need xcode 5, having xcode 4.6 CLI tools installed will stand you in good stead. if you are on os x mavericks, or absolutely need xcode 5 installed, and you want a ghc thats already released, use darin's brew formulae https://github.com/darinmorrison/homebrew-haskell Darin and I plan to spend some time next month preparing an unofficial patched version of ghc 7.6 that should play nice with clang / xcode 5, though at such a time ghc 7.8 will be in RC status at the very least. cheers -Carter

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A thought on the LinkedIn spam and an "upstream spam filter"
by damodar kulkarni 23 Sep '13

23 Sep '13

Hello, Sorry for dwelling on a "spammy" topic. If you are NOT interested in this then please accept my regret and let me assure you that this is NOT to add to the existing spam. If you still are unconvinced, then the only thing I can tell you is "sorry, accept my apologies for wasting your time and please stop reading further." Okay, here is what I thought of it. Yesterday I sent a mail as a response to a spam from LinkedIn to the cafe. I don't know how, but part of my mail text was missing. (I must have pressed Ctrl-C instead of Ctrl-V to paste the text from another file.) I had thought of an idea which I call "upstream spam filter". Anyway here is the text: I thought, some people here on the list, who might have links with the higher-ups at linked-in might bring the issue to their notice and would make them *register* the Haskell-Cafe list on their server so that they never send a spam to the entire list. They should install such an "upstream spam filter". This "upstream spam filter" based solution would be more effective in culling spam as compared to solutions based on requesting/heckling individual linked-in subscribers to take some action at his/her end. Note that here the individual may or may not be doing intentional spamming BUT the linkedin is *hiding* behind the subscribers' ignorance. I propose that more *influential* people on the list demand that the linked-in company should provide a way to register some emails (e.g. mailing lists) which they SHOULD spare from their spamming machines. I have already tried communicating with them but was unsuccessful. Is there any DND like service, at least, to force these big companies (like linked-in), who are happily spamming the world, behave properly?[1] Please send such protest mails to the personal email ids of the linked-in (and other such companies) top brass or other linkedin top level technical staff, if you know them. If anybody on this list is working for linkedin, then this mail is for you too. [1] http://en.wikipedia.org/wiki/Do_Not_Disturb_%28telecommunications%29 Thanks and regards, -Damodar Kulkarni On Mon, Sep 23, 2013 at 12:43 AM, MigMit <miguelimo38(a)yandex.ru> wrote: > So, instead of emailing this guy and asking him to change the address in > his LinkedIn profile (which is simple, since he did write a lot to café), > you decided to continue spamming the mailing list. > > Nice > > Отправлено с iPad > > 22 сент. 2013 г., в 21:31, damodar kulkarni <kdamodar2000(a)gmail.com> > написал(а): > > What a surprise, I didn't know the real name of "Haskell Cafe" till date, > BUT today I came to know it: it is Minh Thu V. > > linked in sucks ... > > > Thanks and regards, > -Damodar Kulkarni > > > On Sun, Sep 22, 2013 at 2:53 PM, Kyle Hanson via LinkedIn < > member(a)linkedin.com> wrote: > >> >> [image: LinkedIn] >> <http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/hom/?hs=false&tok=1F1OVFpS1PWl…> >> >> >> >> >> Hi Minh Thu, >> >> I'd like to connect with you on LinkedIn. >> >> Accept<http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/XvIdBwmueHfd6vFMPXXdLaqreCbl5o…> >> >> View Profile<http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/rso/60831967/_LLG/name/2272454…> >> >> >> >> >> <http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/rso/60831967/_LLG/name/2272454…> >> >> Kyle Hanson<http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/rso/60831967/_LLG/name/2272454…> >> >> Engineer at eShares, Inc. >> >> Greater Chicago Area >> >> >> >> You are receiving Invitation emails. Unsubscribe<https://www.linkedin.com/e/uc6lxc-hlw276p4-5e/XvIdBwmueHfd6vFMPXXdLaqreCbl5…>. >> >> >> This email was intended for Minh Thu Vo (Core/Server Lead Developer at >> OpenERP). Learn why we included this<http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/plh/http%3A%2F%2Flinkedin%2Ecu…>. >> © 2013, LinkedIn Corporation. 2029 Stierlin Ct. Mountain View, CA 94043, >> USA >> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

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GSoC Result - Communicating with Mobile devices - Push Notifications
by Marcos Pividori 23 Sep '13

23 Sep '13

I am happy to announce the result of 3 months working on the GSoC project: "Communicating with mobile devices". After reading many documentation, looking for a good abstraction, learning about mobile apps and networks connections, and really valuable recommendations from my mentor, (I really want to thank Michael Snoyman for his availability and kindness) I succeeded in developing 3 libraries to make it easy to send push notifications to mobile devices. They are available on Hackage: ** push-notify-0.1.0.0 : *This library offers a simple API for sending notifications through APNS, GCM and MPNS. [1]<http://hackage.haskell.org/package/push-notify-0.1.0.0> ** push-notify-ccs-0.1.0.0 :* This library offers an API for sending/receiving notifications through CCS (XMPP - Google Cloud Messaging). [2] <http://hackage.haskell.org/package/push-notify-ccs-0.1.0.0> ** push-notify-general-0.1.0.0 : *This library offers a general API for sending/receiving notifications, and handling the registration of devices on the server. It provides a general abstraction which can be used to communicate through different services as APNS, GCM, MPNS, hiding as much as possible, the differences between them. [3]<http://hackage.haskell.org/package/push-notify-general> Now, it is easy to send/receive information with mobile devices, so you can develop server applications which interact with them. So, to clarify this, as part of this project, I developed many test examples, including Android/WPhone and Yesod apps. I really want to thank FPComplete for giving me the possibility of hosting the Yesod app. The code is available on GitHub: [4]<https://github.com/MarcosPividori/GSoC-Communicating-with-mobile-devices> and they are running online on: [5] <http://gsoc.marcospividori.com.ar/> , so can be downloaded and tested on mobile devices. (BackAndForth Messaging and Connect4 apps) ** BackAndForth Messaging:* In this example, I show how to use the push-general library to handle the registration/reception and sending of messages. From a Yesod app [5]<http://gsoc.marcospividori.com.ar/>, you can send notifications to devices registered and receive messages from them. It is avaliable for Android and WPhone on [6]<http://gsoc.marcospividori.com.ar/apps> . ** Connect 4:* I have been thinking of an app which lets me show how useful push notifications are. The advantage of this notifications is that you can receive information from server when it is available without needing to continually poll. So, I started to think about a multiplayers game. Every time a player does something, you let the rest know about the new movement. So, I ran into the board game: "Connect 4". Both, authenticated web players and users of the android app, can play one against each other. For actualizing the website [5] <http://gsoc.marcospividori.com.ar/> , I use long polling, while for the Android app, push notifications. The Android app is available on [6]<http://gsoc.marcospividori.com.ar/apps> . Every feedback is welcome! Thanks, Marcos [1] http://hackage.haskell.org/package/push-notify-0.1.0.0 [2] http://hackage.haskell.org/package/push-notify-ccs-0.1.0.0 [3] http://hackage.haskell.org/package/push-notify-general [4] https://github.com/MarcosPividori/GSoC-Communicating-with-mobile-devices [5] http://gsoc.marcospividori.com.ar [6] http://gsoc.marcospividori.com.ar/apps

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Cabal install build of scion-browser 0.2.18 fails when linking Persistent-sqlite1.21
by Stephen Taylor 22 Sep '13

22 Sep '13

Hi I'm a Haskell newbie. I just installed Haskell on Windows 7 x64 (Haskell Platform 2013.2.0.0 containing GHC 7.6.3), and have been using cabal-install to build/install from Hackage all the "helper executables" required and/or supported by EclipseFP, the Eclipse Haskell Plugin. All the helper exe's installed without any issues, except for one: scion-browser 0.2.18. All its dependencies seemed to build fine, and it built fine up until the near the end of the link phase when the link to Persistent-sqlite 1.2.1 failed. Here is the error message (path information elided): .... Loading package persistent-sqlite-1.2.1 ... ghc.exe: *Unknown PEi386 section name `.drectve'* (while processing:\persistent-sqlite-1.2.1\libHSpersistent-sqlite-1.2.1.a) ghc.exe: panic! (the 'impossible' happened) (GHC version 7.6.3 for i386-unknown-mingw32): loadArchive "persistent-sqlite-1.2.1\libHSpersistent-sqlite-1.2.1.a": failed Failed to install scion-browser-0.2.18 I understand what the message is saying, but I don't know how to go about resolving it. I have of course cleaned and retried a few times. But I get the same error. Any and all suggestions on how to resolve or work around this issue so that I can provide EclipseFP with a usable scion-browser, would be greatly appreciated. Thanks

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Minh Thu, please add me to your LinkedIn network
by Kyle Hanson via LinkedIn 22 Sep '13

22 Sep '13

LinkedIn ------------ Kyle Hanson requested to add you as a connection on LinkedIn: ------------------------------------------ Minh Thu, I'd like to add you to my professional network on LinkedIn. - Kyle Accept invitation from Kyle Hanson http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/XvIdBwmueHfd6vFMPXXdLaqreCbl5o… View profile of Kyle Hanson http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/rso/60831967/_LLG/name/2272454… ------------------------------------------ You are receiving Invitation emails. This email was intended for Minh Thu Vo. Learn why this is included: http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/plh/http%3A%2F%2Fhelp%2Elinked… (c) 2012, LinkedIn Corporation. 2029 Stierlin Ct, Mountain View, CA 94043, USA.

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type-level integers, type-level operators, and most specific overlapping instance
by TP 22 Sep '13

22 Sep '13

Hi everybody, I encouter some problem in my code in the following simple example: two instances overlap for the multiplication sign `*`. The `OverlappingInstances` extension is of no help because it seems GHC does not look at the instance context to decide which instance is the most specific. file:///usr/share/doc/ghc-doc/html/users_guide/type-class- extensions.html#instance-overlap How to make GHC realize that in the second instance below, the instance context is not satisfied, such that the first instance has to be used? (Indeed, a Scalar is a `Tensor 'Zero`, so the strict inequality `'Zero :< n` is not satisfied in the context). -------------------------------------------- {-# LANGUAGE DataKinds #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE StandaloneDeriving #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE FunctionalDependencies #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE OverlappingInstances #-} import Prelude hiding ((*)) data Nat = Zero | Succ Nat deriving ( Show, Eq, Ord ) type family (m::Nat) :< (n::Nat) :: Bool -- Here Bool is a kind. type instance m :< 'Zero = 'False type instance 'Zero :< ('Succ n) = 'True type instance ('Succ m) :< ('Succ n) = m :< n data Tensor :: Nat -> * where Tensor :: Tensor order Mult :: Scalar -> Tensor order -> Tensor order deriving instance Show (Tensor order) type Scalar = Tensor 'Zero class Multiplication a b c | a b -> c where (*) :: a -> b -> c instance Multiplication Scalar (Tensor n) (Tensor n) where s * t = Mult s t instance (('Zero :< n) ~ 'True) => Multiplication (Tensor n) Scalar (Tensor n) where t * s = Mult s t main = do let s = Tensor :: Scalar let a = s*s print a -------------------------------------------- that yields at compilation: Overlapping instances for Multiplication Scalar Scalar (Tensor 'Zero) arising from a use of `*' Matching instances: instance [overlap ok] Multiplication Scalar (Tensor n) (Tensor n) -- Defined at test_overlapping_instance_with_typelevelinteger_test.hs:31:10 instance [overlap ok] ('Zero :< n) ~ 'True => Multiplication (Tensor n) Scalar (Tensor n) -- Defined at test_overlapping_instance_with_typelevelinteger_test.hs:34:10 In the expression: s * s In an equation for `a': a = s * s In the expression: do { let s = ...; let a = s * s; print a } Thanks in advance, TP

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ANNOUNCE: New OpenGL packages
by Sven Panne 21 Sep '13

21 Sep '13

New versions of the OpenGL packages are available on Hackage: * OpenGLRaw 1.4.0.0 * GLURaw 1.4.0.0 * OpenGL 2.9.0.0 * GLUT 2.5.0.0 The mid-term goal is to make all these packages conform to the latest OpenGL 4.4 specification, and while we're not yet there, this release is nevertheless an important stepping stone towards that goal. The packages contain a few non-backwards compatible changes, something which is never nice for a public API, but it has been necessary: OpenGL has come a long way from its initial fixed function pipeline to its current form flexible form centered around shaders and buffers. Because of this, a few design decisions on the Haskell side were not a good fit anymore and simply had to change. Nevertheless, almost all changes needed in the applications and libraries using the OpenGL packages should be mechanical and straightforward. If not: hopengl(a)haskell.org is the place to get help if needed. Hopefully the new packages will make it into the next Haskell Platform release (2013.4.0.0), at least if I find out how to make it through the proposal process... ;-) Cheers, S. P.S.: Here a list of the changes for each package: ====================================================================== Changes in the OpenGLRaw package ====================================================================== * Added support for the following extensions: GL_ARB_occlusion_query2 GL_ARB_timer_query GL_ARB_draw_indirect GL_ARB_gpu_shader5 GL_ARB_tesselllation_shader GL_ARB_transform_feedback3 GL_ARB_ES2_compatibility GL_ARB_get_program_binary GL_ARB_separate_shader_objects GL_ARB_shader_atomic_counters GL_ARB_compute_shader GL_ARB_ES3_compatibility GL_ARB_framebuffer_no_attachments GL_ARB_shader_storage_buffer_object GL_ARB_query_buffer_object * Added GLfixed type from OpenGL 4.1. * Moved GLhandle type to Graphics.Rendering.OpenGL.Raw.ARB.ShaderObjects where it belongs and fixed its representation on Mac OS X. * Added new Graphics.Rendering.OpenGL.Raw.Type module which exports all GL types. Core31 and Core32 export only their respective subset now. * Correctly typed bitfield tokens as, well, GLbitfield instead of GLenum. * Consistently use ‘Ptr a’ for ‘void*’ which are not opaque. * Use ccall instead of stdcall on x86_64-windows. * Use the OpenGLES framework on iOS. ====================================================================== Changes in the GLURaw package ====================================================================== * Use ccall instead of stdcall on x86_64-windows. * Use the OpenGLES framework on iOS. ====================================================================== Changes in the OpenGL package ====================================================================== * Added sync object support. * Added full support for OpenGL 4.4 query objects, extending and changing the previous query object API a bit. * Split ObjectName class into ObjectName + GeneratableObjectName classes. Added single-name variants deleteObjectName and genObjectName, they are a very common use case. * Made BufferObject and TextureObject abstract. Now all GL objects names are abstract and have to be explicitly generated. The only exception is DisplayList, which is required to be non-abstract by the spec. * Shader is not a class anymore, but a data type with an ObjectName instance and a creation action. Added ShaderType and shaderType. * Added partial support for tessellation/geometry/compute shaders. * Program is not a GeneratableObjectName, but has a createProgram action now. Added attachShader and detachShader for incremental changes. * Deprecated shaderSource and added shaderSourceBS instead. Using ByteString is more efficient and forces the caller to think about encodings, e.g. via Data.Text.Encoding. * Added support for shader/program binaries and shader precision queries. * Revamped texture targets, adding partial support for texture buffer objects and texture arrays. * OpenGL 3.1 deprecated separate polygon draw modes, so use GL_FRONT_AND_BACK internally in polygonMode whenever possible. * Added missing Eq/Ord/Show instances for lots of data types. * Simplified TransformFeedbackVaryings API, making it a bit more similar to the one for activeAttribs and activeUniforms. * Exported ContextProfile’. * Renamed BlitFramebufferMask (to BlitBuffer) and its constructors. * Renamed BufferRangeAccessBit (to MapBufferUsage) and its constructors * Removed currentMatrix, genLists, deleteLists and isList, they have been deprecated for ages. * Full internal support for UTF-8. * Do not expose internal #hidden modules. * Lots of Haddock fixes and improvements. * Renamed IndexedTransformFeedbackBuffer to IndexedTransformFeedbackBuffer. * Fixed clip plane query. ====================================================================== Changes in the GLUT package ====================================================================== * Deprecated the misspelled ContinueExectuion constructor and added a new one correctly called ContinueExecution instead. * Use ccall instead of stdcall on x86_64-windows. * Do not expose internal #hidden modules.

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using "default" declaration for overloaded numeric operations
by TP 21 Sep '13

21 Sep '13

Hi, I try to develop an embedded domain specific language in Haskell. I don't want to type "::Rational" all the time, so I try to use a default declaration for my types. This works correctly in this simple example: ------------------------------------------ default (Integer, Double) -- "default default" mag :: Float -> Float -> Float mag x y = sqrt( x^2 + y^2 ) main = do print $ mag 1 1 ------------------------------------------ Indeed we obtain sqrt(2) as a result. If we replace the default declaration by: default () , we obtain errors at compilation as expected: the type of `2` is ambiguous. Now let us consider a more complicated example: ------------------------------------------ {-# LANGUAGE FlexibleInstances #-} import Prelude hiding ((^^)) import Data.Ratio default (Integer, Rational, Double) class (Num a) => Foo a where (^^) :: Num b => b -> a -> b instance Foo Rational where (^^) x r = x ^ n where n = 2*numerator r -- dummy calculation instance Foo Integer where (^^) x n = x ^ n mag :: Float -> Float -> Float mag x y = sqrt( x ^^ 2 + y ^^ 2 ) main = do print $ mag 1 1 ------------------------------------------ I would expect it to work correctly, but we obtain errors concerning the ambiguous type of `2`. Why? How to make my default declaration work? And if I want to give the priority to `Rational` instead of `Integer`? Indeed, this should be possible because we don't get any error below. $ ghci > import Data.Ratio > 2::Rational 2 % 1 Thanks in advance, TP

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Demarcating monad transformers.
by Nickolay Kudasov 20 Sep '13

20 Sep '13

Hi Café, Below I describe what I call «demarcating monad transformer». It works great for my purposes, though the construction feels a bit awkward. Perhaps, this is just an instance of a general case. For details and example, see [1] (single module package). Recently I got a challenge of manipulating transformed monadic values. In my case the value was of type t (Free f) a (or MonadFree m => t m a). The challange itself was to provide a function: transform :: (Functor f, MonadTrans t) => (forall b. f b -> t (Free f) b) -> t (Free f) a -> t (Free f) a The type t (Free f) a for my purposes can be read as «a program with low-level API specified with functor f and extra features specified with monad transformer t». transform takes a “basic transformation” phi and an abstract program p and applies phi whenever p “executes” command of free functor f. It turns out that this function is impossible (try StateT). The point is that you can't “get inside” of transformed monadic value. So I came up with idea of «demarcating» monad transformer. By «demarcating» I mean separating pure monadic computations (lifted m a) from transformed ones (t m a). Such separation can be made explicit with the help of free monads: data DemarcateF t m next = forall b. DemarcateMonad (m b) (b -> next) -- "pure" monadic computation | forall b. DemarcateTrans (t m b) (b -> next) -- transformed monadic computation instance Functor (Demarcate t m) where ... -- getting monad for freenewtype Demarcate t m a = Demarcate { unDemarcate :: Free (DemarcateF t m) a } instance Monad (Demarcate t m) where ...instance MonadTrans (Demarcate t) where ... With that I can define transform functions: -- transform arbitrary monadic computationtransformDemarcateM :: (forall b. m b -> Demarcate t m b) -> Demarcate t m a -> Demarcate t m a -- transform free monadic actionstransformDemarcateFree :: (forall b. f b -> Demarcate t (Free f) b) -> Demarcate t (Free f) a -> Demarcate t (Free f) atransformDemarcateFree phi = transformDemarcateM (iterM phi) The complete code is available at [1]. Check out examples/simple.hs for a use case. Now the questions are: - has anyone else encountered such a challenge? - is this solution an instance of a more general pattern? - is it sensible to use Demarcate t m a when m is not a free monad? - how Demarcate may affect the performance? Thanks in advance, Nick [1] <https://github.com/fizruk/demarcate>https://github.com/fizruk/demarcate

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