June 2009 - Haskell-Cafe

Re: Scary type inference for monadic function definitions
by Ahn, Ki Yung 04 Jun '09

04 Jun '09

Ahn, Ki Yung 쓴 글: > Scary type inference for monadic function definitions > (or, why you'd want to annotate types for monadic function definitions) > > This is a real example that I've experienced. > > I defined the following function. > >> checkOneVerseByLineWith readLine v = >> do mg <- readLine >> case mg of >> Just g -> return Just (v==g) >> Nothing -> return Nothing > > My intention was to use it something like this: > > checkOneVerseByLineWith (readline "% ") > > where readline is the library function from System.Console.Readline. > > As you can see, there is an obvious mistake which I forgot to > group (Just (v==g)) in parenthesis. However, GHC or any other > Haskell 98 compliant implementation will infer a type for you > and this will type check! Try it yourself if in doubt. > > Of course, checkOneVerseByLineWith (readline "% ") won't type check > because checkOneVerseByLineWith has strange type. The reason why > the above definition type checks is because ((->) r) is an instance > of Monad. Oh, I happened to be importing Control.Monad.Trans somehow, it just doesn't work with Prelude import itself. And, there were already some discussions on this last year: [Haskell-cafe] The danger of Monad ((->) r) http://www.mail-archive.com/haskell-cafe@haskell.org/msg23680.html Tomasz Zielonka Tue, 15 May 2007 03:05:30 -0700

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ANN: HSH 2.0.0
by John Goerzen 03 Jun '09

03 Jun '09

Hi, I'm pleased to announce the release of version 2.0.0 of HSH, the Haskell shell scripting library. This version features a complete rewrite of the core. Since System.Process has finally become capable enough to be the low-level of HSH, HSH has been reimplemented in terms of it. This has produced a dramatic reduction in code size and complexity. It also gains cross-platform support; HSH now works on Windows. Finally, the API is both simpler and more flexible. The 180-test suite for HSH continues to run and pass with only minor tweaks for the new API. Optional support for setting environment variables on commands to be run has been added as well. It will stay out of your way unless you need it, in which case it is easy. As a reminder, HSH lets you easily set up shell command pipelines. You can also pipe data between Haskell functions and shell commands with complete ease. The package also provides Haskell versions of a number of familiar shell primitives to help you get up and running quickly. HSH 2.0.0 has been uploaded to Hackage. -- John

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Re: [Haskell-cafe] Cabal/primes
by michael rice 03 Jun '09

03 Jun '09

Excellent! Thanks. Michael --- On Wed, 6/3/09, Don Stewart <dons(a)galois.com> wrote: From: Don Stewart <dons(a)galois.com> Subject: Re: [Haskell-cafe] Cabal/primes To: "michael rice" <nowgate(a)yahoo.com> Cc: "brian" <briand(a)aracnet.com>, haskell-cafe(a)haskell.org Date: Wednesday, June 3, 2009, 6:40 PM nowgate: > Got it working. > > I downloaded two packages, primes and Numbers. Since Numbers has the three > functions I want to use, primes, isPrime and isProbablyPrime, how do I > uninstall the primes package so there won't be a conflict? Easy! $ ghc-pkg unregister primes -- Don

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ANN: atom-0.0.5
by Tom Hawkins 03 Jun '09

03 Jun '09

A few bug fixes and doc improvements. Thanks to John Van Enk and Brian Lewis for the patches! http://hackage.haskell.org/cgi-bin/hackage-scripts/package/atom -Tom

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type checking that I can't figure out ...
by Vasili I. Galchin 03 Jun '09

03 Jun '09

Hi Andrew (Bromage), I reversed the parameter order to Data.Map.lookup and calling fromJust to pull out value from Maybe wrapper ... all as you suggested: > remLookupFwd :: (ReVars m t) => SimplRe t -> ReM m t (ReInfo t) > remLookupFwd re > = do fwd <- gets resFwdMap > let { Just reinfo = fromJust(M.lookup re fwd) } -- PROBLEM > return reinfo I am still getting a type mismatch: Swish\HaskellRDF\Dfa\Dfa.lhs:162:29: Couldn't match expected type `Maybe t' against inferred type `ReInfo t1' In the expression: fromJust (M.lookup re fwd) In a pattern binding: Just reinfo = fromJust (M.lookup re fwd) In the expression: do fwd <- gets resFwdMap let Just reinfo = fromJust (M.lookup re fwd) return reinfo Vasili

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Using type families to define runtime representation and evaluation strategy?
by Corey O'Connor 03 Jun '09

03 Jun '09

I'm interested in the feasibility of extending the compiler using a construct similar to type synonym families to determine runtime representation and evaluation strategy for types. Can anybody point me to existing work in this area? I'm not sure of the exact terminology to be using here so my description is going to be fuzzy and probably off the mark on a few points. If anybody could help me clarify what I'm trying to described that would be appreciated. What I imagine is an open construct that be evaluated at compile time to determine: - How the data for a type is represented in memory. Whether values are boxed or unboxed etc. - How an expression should be represented. As a lazy evaluation thunk (weak head normal form?) or evaluated to normal form. - How a expression should be reduced. Since "the best" evaluation strategy depends on the application the equations should be open. For one application a data structure should be evaluated the normal form but not another. This is why the construct should be open much like type synonym families. One application could define an instance that declares the value should be reduced to HNF when defined while the other application could define an instance that declares the value to be reduced to WHNF. Still, the library implementor needs the ability to define reasonable defaults. If the construct was closed I don't think these requirements could be satisfied. This resembles extending the Control.Parallel.Strategies evaluation strategies and adaptive-container's container representation to be represented by type level equations. Control.Parallel.Strategies has a good interface but littering the equations with expressions declaring the evaluation strategy seems awkward. Preferably the evaluation strategy should be definable in parallel to the equations when possible. Strictness annotations already resemble the start of such a construct. And any such construct would have to be able to take the place of strictness annotations. Cheers, Corey O'Connor

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ANN: new version of uu-parsinglib
by S. Doaitse Swierstra 03 Jun '09

03 Jun '09

A new version of the uu-parsinglib has been uploaded to hackage. It is now based on Control.Applicative where possible. Be warned that functions like some and many will be redefined in the future. Doaitse Swierstra

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Re: [Haskell-cafe] Cabal/primes
by michael rice 03 Jun '09

03 Jun '09

This is working differently than it did last night, when at least import was working. Michael [michael@localhost ~]$ ghci GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Prelude> import Data.Numbers.Primes Could not find module `Data.Numbers.Primes': it was found in multiple packages: Numbers-0.2.1 primes-0.1.1 Prelude> :m + Data.Numbers.Primes Could not find module `Data.Numbers.Primes': it was found in multiple packages: Numbers-0.2.1 primes-0.1.1 Prelude> Data.Numbers.Primes> :browse <interactive>:1:21: parse error on input `:' Prelude> isPrime 3525266 <interactive>:1:0: Not in scope: `isPrime' Prelude> ========== [michael@localhost ~]$ cd .cabal [michael@localhost .cabal]$ ls -l total 20 -rw-rw-r-- 1 michael michael 1729 2009-06-02 18:59 config drwxrwxr-x 4 michael michael 4096 2009-06-02 22:14 lib drwxrwxr-x 2 michael michael 4096 2009-06-02 19:05 logs drwxrwxr-x 3 michael michael 4096 2009-06-02 18:59 packages drwxrwxr-x 3 michael michael 4096 2009-06-02 19:05 share [michael@localhost .cabal]$ cd packages [michael@localhost packages]$ ls -l total 4 drwxrwxr-x 4 michael michael 4096 2009-06-02 22:14 hackage.haskell.org [michael@localhost packages]$ cd hackage.haskell.org [michael@localhost hackage.haskell.org]$ ls -l total 12464 -rw------- 1 michael michael 11735040 2009-06-02 22:14 00-index.tar -rw------- 1 michael michael 992994 2009-06-02 22:14 00-index.tar.gz -rw-rw-r-- 1 michael michael 418 2009-06-02 22:14 build-reports.log drwxrwxr-x 3 michael michael 4096 2009-06-02 22:14 Numbers drwxrwxr-x 3 michael michael 4096 2009-06-02 19:05 primes [michael@localhost hackage.haskell.org]$ [michael@localhost hackage.haskell.org]$ pwd /home/michael/.cabal/packages/hackage.haskell.org [michael@localhost hackage.haskell.org]$ ============= --- On Wed, 6/3/09, brian <briand(a)aracnet.com> wrote: From: brian <briand(a)aracnet.com> Subject: Re: [Haskell-cafe] Cabal/primes To: "michael rice" <nowgate(a)yahoo.com> Cc: haskell-cafe(a)haskell.org Date: Wednesday, June 3, 2009, 10:46 AM Prelude> :m + Data.Numbers.Primes Prelude Data.Numbers.Primes> :browse isPrime :: Integer -> Bool isProbablyPrime :: (System.Random.RandomGen g) => Integer -> g -> (Bool, g) primes :: [Integer] Prelude Data.Numbers.Primes> isPrime 3525266 Loading package syb ... linking ... done. Loading package base-3.0.3.0 ... linking ... done. Loading package old-locale-1.0.0.1 ... linking ... done. Loading package old-time-1.0.0.1 ... linking ... done. Loading package random-1.0.0.1 ... linking ... done. Loading package Numbers-0.2.1 ... linking ... done. False Prelude Data.Numbers.Primes> On Jun 3, 2009, at 6:57 AM, michael rice wrote: > OK, I downloaded Numbers. Still missing the three functions I wanted, which are primes, isPrime, and isProbablyPrime. How do I get these? > > Michael > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

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Linkage errors in scenegraph
by Gregory D. Weber 03 Jun '09

03 Jun '09

I'd like to get the scenegraph package (http://hackage.haskell.org/cgi-bin/hackage-scripts/package/scenegraph) to work, but am encountering linkage errors. I installed scenegraph 0.1.0.1 for ghc-6.10.1 on Fedora 10 Linux. # runghc Setup configure --prefix=/opt # runghc Setup build # runghc Setup install Then I created this little program based on the example at http://www.haskell.org/haskellwiki/SceneGraph (in file SGTest.hs): module Main where import Graphics.SceneGraph import Control.Monad.Identity main :: IO () main = runScene $ osgt $ myScene myScene :: OSGT Identity SceneNode myScene = cube 0.5 `colour` Green `scale` v1x 40 `translate` vy 2 <+> camera `translate` vy (-10) <+> light `translate` vz 10 Then I compiled it and got a long list of linker errors; here are the first few lines: ghc --make SGTest Linking SGTest ... /opt/lib/scenegraph-0.1.0.1/ghc-6.10.1/libHSscenegraph-0.1.0.1.a(Basic__210.o): In function `sdE1_info': (.text+0x8d): undefined reference to `scenegraphzm0zi1zi0zi1_GraphicsziSceneGraphziMatrix_translateM_closure' /opt/lib/scenegraph-0.1.0.1/ghc-6.10.1/libHSscenegraph-0.1.0.1.a(Basic__210.o): In function `scenegraphzm0zi1zi0zi1_GraphicsziSceneGraphziBasic_translate_srt': (.data+0x0): undefined reference to `scenegraphzm0zi1zi0zi1_GraphicsziSceneGraphziMatrix_translateM_closure' /opt/lib/scenegraph-0.1.0.1/ghc-6.10.1/libHSscenegraph-0.1.0.1.a(Basic__207.o): In function `sdDq_info': (.text+0x7e): undefined reference to `scenegraphzm0zi1zi0zi1_GraphicsziSceneGraphziMatrix_scaleM_info' /opt/lib/scenegraph-0.1.0.1/ghc-6.10.1/libHSscenegraph-0.1.0.1.a(Basic__207.o): In function `scenegraphzm0zi1zi0zi1_GraphicsziSceneGraphziBasic_scale_srt': (.data+0x0): undefined reference to `scenegraphzm0zi1zi0zi1_GraphicsziSceneGraphziMatrix_scaleM_closure' /opt/lib/scenegraph-0.1.0.1/ghc-6.10.1/libHSscenegraph-0.1.0.1.a(Basic__491.o):(.text+0x27): undefined reference to `__stginit_scenegraphzm0zi1zi0zi1_GraphicsziSceneGraphziUtils_' Also with this command, same result but a lot more detail: ghc --make -v -package scenegraph SGTest With -v, the output includes gcc -v -o SGTest -DDONT_WANT_WIN32_DLL_SUPPORT SGTest.o -L/opt/lib/scenegraph-0.1.0.1/ghc-6.10.1 -L/opt/lib/hmatrix-0.5.1.1/ghc-6.10.1 -L/opt/lib/storable-complex-0.2/ghc-6.10.1 ... -lHSscenegraph-0.1.0.1 -lHShmatrix-0.5.1.1 -lgsl -llapack -lHSstorable-complex-0.2 -lHSQuickCheck-1.2.0.0 ... which seems to show that the proper -L and -l options are included. If I'm decoding the first "undefined reference" symbol -- (.text+0x8d): undefined reference to `scenegraphzm0zi1zi0zi1_GraphicsziSceneGraphziMatrix_translateM_closure' -- correctly, then the missing symbol is in the scenegraph-0.1.0.1 package, in module Graphics.SceneGraph.Matrix, and is associated with the translateM function defined in that module. I looked for this symbol with nm: # pwd /opt/lib/scenegraph-0.1.0.1/ghc-6.10.1 # nm HSscenegraph-0.1.0.1.o | grep translateM U scenegraphzm0zi1zi0zi1_GraphicsziSceneGraphziMatrix_translateM_closure U scenegraphzm0zi1zi0zi1_GraphicsziSceneGraphziMatrix_translateM_info # nm libHSscenegraph-0.1.0.1.a | grep translateM U scenegraphzm0zi1zi0zi1_GraphicsziSceneGraphziMatrix_translateM_closure U scenegraphzm0zi1zi0zi1_GraphicsziSceneGraphziMatrix_translateM_info but I understand the "U" means that it is referenced by some other function in these files, but is undefined in them. Since the module Graphics.SceneGraph.Matrix does not declare any exports, I thought that might be the reason the symbol was undefined. But looking back at the Haskell 98 language definition, I found that the absence of an export declaration in a module means that all the symbols of the module are exported. Also, I notice that in the cabal file for scenegraph, the list of exposed modules Exposed-Modules: Graphics.SceneGraph, Graphics.SceneGraph.Basic, Graphics.SceneGraph.Vector, Graphics.SceneGraph.Render, Graphics.SceneGraph.SimpleViewport, Graphics.SceneGraph.GraphViz, Graphics.SceneGraph.Library, Graphics.SceneGraph.Dump, Graphics.SceneGraph.Textures does not include Graphics.SceneGraph.Matrix, but that should only mean that I can't call functions of that module directly -- not that the other SceneGraph modules can't call them -- right? So, why is this symbol undefined? And how can I get it to work? Oh by the way: I can actually use this package if I move into its src directory, add a main function to Examples.hs, and compile and run it right there. Just can't use it as an installed library, it seems. -- ___ ___ __ _ / _ \ / _ \| | | | Gregory D. Weber, Associate Professor / /_\// / | | | /\ | | Indiana University East / /_\\/ /__| | |/ \| | http://mypage.iu.edu/~gdweber/ \____/\_____/\___/\__/ Tel. (765) 973-8420; FAX (765) 973-8550

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GSoC update: sneak peek at the live heap profiler
by Patai Gergely 03 Jun '09

03 Jun '09

Hello everyone, finally there's a bit of eye candy for anyone interested in the heap profiling project: http://just-bottom.blogspot.com/ Feel encouraged to comment and check out the project page too, where you can already see the beginnings of the core library. Gergely -- http://www.fastmail.fm - The way an email service should be

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