- Haskell-Cafe - Haskell.org

News about the GSoC Project : Communicating with mobile devices
by Marcos Pividori 02 Jul '13

02 Jul '13

Hi, I am working this summer on the project "Communicating with mobile devices" for the GSoC. I have started a blog to show the progress. To show a simple usage of the API for GCM, I developed a simple test example of a Yesod server, where devices can register to receive GCM messages and users can send messages through the web service. More information: http://gsoc2013cwithmobiledevices.blogspot.com.ar/ Every feedback is welcome!! Thanks, Marcos

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Upgrading GHC 7.6.3 global packages to latest versions
by Rouan van Dalen 02 Jul '13

02 Jul '13

Hi, I am trying to install the latest version of some hackage packages I use often in GHC 7.6.3. However, I am having some problems with packages like [containers] and [time], which are shipped with GHC as global packages. Now when I try to install the latest version of the [time] package, I have 2 time packages, 1 in the global package db (the older version), and 1 in the user package db (the newer version). Now I would like subsequent installed packages to always use the latest version of the [time] package. But if i try to install the [plugins] package, cabal says: #In order, the following would be installed: #ghc-paths-0.1.0.9 (new package) #random-1.0.1.1 (reinstall) changes: time-1.4.1 -> 1.4.0.1 #plugins-1.5.3.0 (new package) So I guess I have 2 options here: 1. unregister all the global packages so that I can install the latest versions of all the global packages. 2. force cabal to only look at latest packages in user package db (not sure if this is possible). Can anyone please point me in the right direction here. I have read about [cabal-dev], but I am not sure if it can be used to solve my problem. Regards --Rouan

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cabal-dev: installing/running with profiling enabled
by Ömer Sinan Ağacan 02 Jul '13

02 Jul '13

Hi all, I want to profile a Haskell program. I have tons of libraries installed without profiling enabled, and some of them are installed with my Linux distribution's package mangaer. So I tried installing the program in a fresh cabal-dev environment with profiling enabled, so that all dependencies would be also installed with profiling enabled. But for some reason even after installing with `cabal-dev install --enable-executable-profiling -prof` I still can't run this program with `caba-dev/bin/program +RTS -p`, it fails with 'program: the flag -p requires the program to be built with -prof'. Can anyone help me on installing/running in cabal-dev with profiling enabled? --- Ömer Sinan Ağacan http://osa1.net

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Spam on list??
by Vlatko Basic 02 Jul '13

02 Jul '13

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Installing Z3 on OS X 10.8.4 ( Off topic )
by mukesh tiwari 02 Jul '13

02 Jul '13

Hello all, Not directly related to Haskell but I am trying to install Z3 to use SBV package[1]. I followed the instructions[2] to install it. *Mukeshs-MacBook-Pro:SMT mukeshtiwari$ git clone https://git01.codeplex.com/z3 -b unstable Cloning into 'z3'... remote: Counting objects: 16070, done. remote: Compressing objects: 100% (3928/3928), done. remote: Total 16070 (delta 12057), reused 16070 (delta 12057) Receiving objects: 100% (16070/16070), 7.62 MiB | 287 KiB/s, done. Resolving deltas: 100% (12057/12057), done.* After installing Z3 *Running python example.py in z3/examples/python gives this result. * *Mukeshs-MacBook-Pro:python mukeshtiwari$ python example.py sat [y = 4, x = 2]* but when I am running sbv package, I am getting this error. *Mukeshs-MacBook-Pro:site-packages mukeshtiwari$ ghci -XScopedTypeVariables GHCi, version 7.6.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Prelude> :m Data.SBV.Bridge.Z3 Prelude Data.SBV.Bridge.Z3> prove $ \(x::SWord8) -> x `shiftL` 2 .== 4*x Loading package pretty-1.1.1.0 ... linking ... done. Loading package array-0.4.0.1 ... linking ... done. Loading package deepseq-1.3.0.1 ... linking ... done. Loading package filepath-1.3.0.1 ... linking ... done. Loading package old-locale-1.0.0.5 ... linking ... done. Loading package time-1.4.0.1 ... linking ... done. Loading package bytestring-0.10.0.0 ... linking ... done. Loading package unix-2.6.0.0 ... linking ... done. Loading package directory-1.2.0.0 ... linking ... done. Loading package process-1.1.0.2 ... linking ... done. Loading package old-time-1.1.0.1 ... linking ... done. Loading package containers-0.5.0.0 ... linking ... done. Loading package random-1.0.1.1 ... linking ... done. Loading package template-haskell ... linking ... done. Loading package QuickCheck-2.5.1.1 ... linking ... done. Loading package transformers-0.3.0.0 ... linking ... done. Loading package mtl-2.1.2 ... linking ... done. Loading package syb-0.3.7 ... linking ... done. Loading package sbv-2.10 ... linking ... done. *** An error occurred. *** Unable to locate executable for z3 *** Executable specified: "z3" Prelude Data.SBV.Bridge.Z3> * I have posted every details on installation on pastebin[3]. The documentation file says that[4] it will install *2) Building Z3 using make/g++ and Python Execute: autconf ./configure python scripts/mk_make.py cd build make sudo make install It will install z3 executable at /usr/bin, libraries at /usr/lib, and include files at /usr/include.* Mukeshs-MacBook-Pro:z3 mukeshtiwari$ echo $PATH /usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Users/mukeshtiwari/Programming/GHC/ghc-7.6.1/bin:/Users/mukeshtiwari/.cabal/bin:/Users/mukeshtiwari/Erlang/bin:/Users/mukeshtiwari/Programming/Scala/scala-2.10.0/bin:/usr/local/smlnj-110.75/bin:/Users/mukeshtiwari/.rvm/bin Could some one please tell me how to solve this problem. Regards, Mukesh Tiwari [1] http://hackage.haskell.org/package/sbv [2] http://z3.codeplex.com/wikipage?title=Building%20the%20unstable%20%28workin… [3] http://pastebin.com/K5rq3jCF [4] http://z3.codeplex.com/SourceControl/latest#README

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question about indentation conventions
by Richard Cobbe 02 Jul '13

02 Jul '13

I hope I'm not starting a holy war with this, but I'm curious about an aspect of coding style that's been bugging me for a while, and I'm not finding much discussion of this question on the web or in the mailing list archives. Two questions: 1) Are there wide-spread conventions in the Haskell community for how to indent an application expression that's split across multiple lines? For how to indent an expression that uses infix operators? Or does everyone pretty much do their own thing? 2) If there is such a convention, how do I make Emacs's haskell-mode do it? By default, in most cases Emacs's haskell-mode with turn-on-haskell-indentation does function firstArgument (second argument) thirdArgument Personally, I'd prefer some indentation on the 2nd and 3rd lines to indicate that they're continuing an expression begun on a previous line. I can use parens around the entire application to force haskell-mode to indent subsequent lines (and of course this is necessary in some contexts, like a 'do' expression), but haskell-mode only indents that by a single space: do (function firstArgument (second argument) thirdArgument) nextAction I'd find a larger indent---even just 2 spaces---to be more readable. My inclination to indent the second and following lines of a multi-line application expression is informed by my long experience in Scheme, Racket, and Lisp, whose S-expressions lend themselves to fairly straightforward (and automatable!) indentation conventions. If the Haskell community does things differently, though, I'm happy to adapt. This is the sort of thing that one picks up from the community, as in other languages. I don't, however, have a whole lot of contact with that community outside this list -- thus the post, despite the dangers inherent in discussing subjective stuff like this that people often feel strongly about. Thanks, Richard

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Re: [Haskell-cafe] Subclass or no subclass?
by Patrick Browne 01 Jul '13

01 Jul '13

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some questions about Template Haskell
by TP 29 Jun '13

29 Jun '13

Hi everybody, I am trying to learn Template Haskell, and I have two independent questions. 1/ First, the following code (which is not in its final version, but it is a test) does not compile: ------------------- {-# LANGUAGE TemplateHaskell #-} module Pr where import Language.Haskell.TH pr :: Name -> ExpQ pr n = [| putStrLn $ (nameBase n) ++ " = " ++ show $(varE n) |] ------------------- I obtain: ------------------- No instance for (Lift Name) arising from a use of `n' Possible fix: add an instance declaration for (Lift Name) In the first argument of `nameBase', namely `n' ------------------- Why? Indeed, there is no typeclass constraint on n in the definition of nameBase: ghci> :t nameBase nameBase :: Name -> String Contrary to lift for example: ghci> :t lift lift :: Lift t => t -> Q Exp 2/ If I define in a module: j = 3 and then define in another module: ------------------- h x = $([|j|]) main = do print $ h undefined ------------------- I obtain "3" as expected. However, I do not achieve to make this system work with an infix declaration: infix $([| j |]) + I obtain: parse error on input `$(' What is the problem? Thanks in advance, TP

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Subclass or no subclass?
by Patrick Browne 29 Jun '13

29 Jun '13

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Improving GHC's LLVM Backend
by Alex Ford 29 Jun '13

29 Jun '13

Hello, I'm interested in improving the LLVM backend of GHC by using the existing Haskell LLVM bindings to the C API, as suggested by option 1 in the LLVM FAQ: http://llvm.org/docs/FAQ.html#i-d-like-to-write-a-self-hosting-llvm-compile… At the moment, the backend uses the option 2: emitting LLVM assembly code which is then assembled to LLVM bitcode, optimised, and compiled to machine code by standard LLVM tools. Changing this to use the Haskell FFI bindings to the LLVM C API would allow better tracking of any changes to the LLVM IR, and hopefully a reasonable speed increase by avoiding the overhead of first emitting LLVM Assembly to be assembled. In his bachelor's thesis, David Terei considered this approach when initially writing the LLVM backend, but dismissed it due to the existing Haskell bindings being too large and high level to use with GHC. I have not personally looked at the high level Haskell bindings in much depth, but the low level (llvm-base) bindings appear to be somewhat incomplete with respect to LLVM 3.3. Therefore, I plan to extend the FFI bindings to cover more or all of the C API, and then to modify the GHC LLVM backend to use these bindings to call into the LLVM libraries directly. http://hackage.haskell.org/trac/ghc/wiki/Commentary/Compiler/Backends/LLVMc… a link to David's thesis, as well as documentation of the LLVM backend. I'd really appreciate it if anyone who knows about the Haskell LLVM bindings or about the GHC LLVM backend could give any advice regarding what sort of work needs to be done with the LLVM bindings to make them more appropriate for use within GHC, or how to approach modifying the existing LLVM backend. Many thanks, Alex

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