July 2013 - Haskell-Cafe

Liber Amicorum for Doaitse Swierstra.
by Jurriaan Hage 03 Jul '13

03 Jul '13

Dear all, Prof. Doaitse Swierstra is retiring on August 1 of this year, and is leaving the very functional programming minded Software Technology group that he has led for many decades. We have compiled a Liber Amicorum in his honour that we handed to him after his farewell speech on May 30th. You can find a download of this book at: http://www.cs.uu.nl/people/jur/liberdoaitseswierstra.pdf Not all contributions are ``technical'', and not all of them are in English, but counting up the pages, I guess about 75 percent is. best, Jurriaan Hage

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Re: [Haskell-cafe] some questions about Template Haskell
by oleg＠okmij.org 03 Jul '13

03 Jul '13

TP wrote: > pr :: Name -> ExpQ > pr n = [| putStrLn $ (nameBase n) ++ " = " ++ show $(varE n) |] The example is indeed problematic. Let's consider a simpler one: > foo :: Int -> ExpQ > foo n = [|n + 1|] The function f, when applied to an Int (some bit pattern in a machine register), produces _code_. It helps to think of the code as a text string with the source code. That text string cannot include the binary value that is n. That binary value has to be converted to the numeric text string, and inserted in the code. That conversion is called `lifting' (or quoting). The function foo is accepted because Int is a liftable type, the instance of Lift. And Name isn't. BTW, the value from the heap of the running program inserted into the generated code is called `cross-stage persistent'. The constraint Lift is implicitly generated by TH when it comes across a cross-stage persistent identifier. You can read more about it at http://okmij.org/ftp/ML/MetaOCaml.html#CSP Incidentally, MetaOCaml would've accepted your example, for now. There are good reasons to make the behavior match that of Haskell.

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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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