December 2006 - Libraries

a cabal/database lib experience (was: [Haskell-cafe] Trivial database access in Haskell)
by Claus Reinke 14 Dec '06

14 Dec '06

>> if you're using Haskell at all, you *are* the Haskell community. > [..lots of "I searched, I found, I tried, I got this error, I thought, > I tried this workaround, I got to this point, now I'm stuck here..] I just wanted to comment that I find this kind of "experience report" very helpful, especially if someone does not give up at the first hurdle, and goes through the trouble of writing up all the frustrating steps and thoughts rather than summarizing ("it didn't work"/"I got it to work after some fiddling") - thanks! The problem with mindsets is that minds get set in them, and not only do people outside find it very difficult to "get in", but the people inside find it very difficult to understand what it is like "outside". While you are looking for documentation of the supposedly easy first steps to get you started on your more detailed investigation, so you have just provided the rest of the community with some documentation of what its works currently look like. That situation seems to be slightly embarrassing (if only because we are tempted to think that we have no time for the traditional README and INSTALL files - after all, all darcs/cabal stuff is self-explanatory, isn't it, and has been discussed to death somewhere, hasn't it, and the library does the obvious thing, doesn't it, and isn't quite ready for prime time yet anyway, at which time it is going to be carved in stone and documented thoroughly by a team of Pulitzer-price-winning authors?-) Seriously, and as Simon PJ has been fond of reminding us: the user is always right, so I very much hope that those of us involved with the projects mentioned in your report will take note and do something about it (for easy reference I repeat it at the end of this message;-). Some suggestions, gleaned from your experience (perhaps you could comment on whether they'd have been of any use?): cabal: - the separation into interpreter/compiler and resource as Setup does not set up the right mindset in users. for instance, you can "runhaskell Setup.hs --help" as for most unixy tools, but who'd think of that in this situation, and how much does it help? + add a dedicated command "cabal", which does nothing more than "runhaskell Setup", but is more memorable and suggestive + when anything goes wrong, also mention "cabal --help" in the error message + in "cabal --help", explicitly and prominently mention the typical usage cycle (configure/build/install); also point to cabal home page, with more documentation, bug reports, newest version and known problem info, downloads, .. - the three step separation into configure/build/install is traditional and has good justifications, but is unhelpful for the most typical use case (I need a library for a part of my work, it isn't installed by default, it doesn't have an installer, so I have to do this cabal thing to get on with my work). if someone types "cabal install" as the first command, cabal might engage in a simple dialogue: "would you like to configure then build then install <program/library name> with default options [yes/no]?" y <cabal configure output> "please check configuration defaults [ok, continue/no, change]" n "thank you - no files were built or installed. please run 'cabal --help' and 'cabal configure --help' for details on how to change the configuration defaults" - cabal/darcs/haddock are no replacement for minimal help texts: cabal should require the existence of a README (darcs should complain if there is a *.cabal, but no README..). that might be too specific a request for darcs, but perhaps the useful, but increasingly lengthy resource http://www.haskell.org/haskellwiki/How_to_write_a_Haskell_program might start with a motivational section 0 on "the intended user experience" ?-) the database libraries: - the cabal/README points above seem to apply, according to the experience report below, so getting started is more difficult than it needs to be - comparative evaluation/individual feature sets appear to be difficult, according to earlier email - sample code for "trivial queries" (aka, I know about databases, but I need to see the way this particular library handles things, so that I can figure out whether it is the right one for me) is not obvious to find - distributions are bare-boned: > - following the HDBC link on the Haskell Wiki leads to a huge list of > tar.gz files, with no indication of which one I might want :-( > > Option 2, Takusen, leads to a file listing, but no downloadable package. > > Option 3, HSQL, leads to a page which doesn't mention Oracle support > (even though the Wiki page does) so I'm put off trying further... - installing database libraries is not the main activity, it just gets in the way of running SQL queries from Haskell, and may well be the first experience with getting/building/installing 3rd party libs for Haskell - other languages and their bindings are tempting if potential users get stuck I hope this summary/rephrasing of Paul's report is helpful. what do users and implementors think (cc-ed to libraries list)? Claus > OK, thanks for the gentle push. After a bit of digging, I decided that > the takusen link looked like a darcs repository, and I downloaded > darcs and got takusen. I installed GHC 6.6 in a spare VM (no PC round > I can install stuff on just now, I'll do this properly later). On the > assumption that the takusen.cabal file means I should look at Cabal, I > had a dig and found the incantation "runhaskell setup.hs". > > I got the error: > > F:\takusen>runhaskell setup.hs > > setup.hs:11:7: > Could not find module `Distribution.Compat.FilePath': > it is hidden (in package Cabal-1.1.6) > > I assume this relates to the note in setup.hs "For ghc-6.6 you will > need to first install Cabal-1.1.6.1", but as I got GHC from a Windows > binary install, I'm not sure where to go from here. I found the Cabal > webpage and downloaded 1.1.6.1. Trying to install it, I got the > following: > > F:\cabal-1.1.6.1>runhaskell Setup.lhs install > Setup.lhs: error reading ./.setup-config; run "setup configure" command? > > > F:\cabal-1.1.6.1>runhaskell Setup.lhs configure > Configuring Cabal-1.1.6.1... > configure: Dependency base-any: using base-2.0 > configure: Using install prefix: C:\Program Files > configure: Binaries installed in: C:\Program Files\Haskell\bin > configure: Libraries installed in: C:\Program > Files\Haskell\Cabal-1.1.6.1\ghc-6.6 > configure: Private binaries installed in: C:\Program Files\Cabal-1.1.6.1 > configure: Data files installed in: C:\Program Files\Common Files\Cabal-1.1.6.1 > configure: Using compiler: c:\ghc\ghc-6.6\bin\ghc.exe > configure: Compiler flavor: GHC > configure: Compiler version: 6.6 > configure: Using package tool: c:\ghc\ghc-6.6\bin\ghc-pkg.exe > configure: Using ar found on system at: c:\ghc\ghc-6.6\bin\ar.exe > configure: No haddock found > configure: No pfesetup found > configure: No ranlib found > configure: Using runghc found on system at: c:\ghc\ghc-6.6\bin\runghc.exe > configure: No runhugs found > configure: No happy found > configure: No alex found > configure: Using hsc2hs: c:\ghc\ghc-6.6\bin\hsc2hs.exe > configure: No c2hs found > configure: No cpphs found > configure: No greencard found > > F:\cabal-1.1.6.1>runhaskell Setup.lhs install > Installing: C:\Program Files\Haskell\Cabal-1.1.6.1\ghc-6.6 & > C:\Program Files\Haskell\bin Cabal-1.1.6.1... > Setup.lhs: Error: Could not find module: Distribution.Compiler with any suffix: > ["hi"] > > OK, that's as far as I can go. Remember, what I *want* to do is to run > some SQL against my database to get some data into a Haskell program. > I'm not up to debugging a Cabal install. (At this point, if I was > doing this for "real work", I'd be off to the Python website like a > shot...) > > Can anyone help? I promise, I will document what I end up with! > > Paul. > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

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Re[2]: [Haskell-cafe] Re: a cabal/database lib experience
by Bulat Ziganshin 13 Dec '06

13 Dec '06

Hello Paul, Tuesday, December 12, 2006, 4:48:55 PM, you wrote: >> ./Setup.lhs configure -p >> ./Setup.lhs build >> ./Setup.lhs install > I come from a Python background, and Python's distutils (which feels > very like cabal - or should that be the other way round?) tends to > have later commands include earlier ones. So, i suggest you to write simple script that automates this. i've attached makefile which i include with all my libs that does this - you need to run only "make install". i propose to all library developers to include such makefile with their libs -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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Request for improvements
by Chris Kuklewicz 13 Dec '06

13 Dec '06

I have written a thin but useful layer on top of parts of Control.Concurrent and Control.Exception to aid in forking new threads. I think I have written it correctly and understand the guarantees (when running under GHC 6.4 or 6.6). It is useful when * you need to be able to check whether a thread has finished running * you need to be able to wait until a thread has finished running * when you want to run within the scope of 'block' * you need to run in another thread with ** an exception handler (catch) ** a finally clause ** bracket commands But it may need improving, especially if I have missed a subtle blocking or race condition. And suggestions on improved names are welcome. The code is on the wiki at http://haskell.org/haskellwiki/WrapConc -- Chris

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Re: Data.List documentation improvements
by Andriy Palamarchuk 12 Dec '06

12 Dec '06

It's not yet checked in. Any takers? Andriy ----- Original Message ---- From: Andriy Palamarchuk <apa3a(a)yahoo.com> To: libraries(a)haskell.org Sent: Wednesday, December 6, 2006 9:17:31 PM Subject: Re: Data.List documentation improvements The deadline for this update is up. Can somebody commit the changes for me? Here is the ticket with the patch: http://hackage.haskell.org/trac/ghc/ticket/1034 Andriy ____________________________________________________________________________________ Want to start your own business? Learn how on Yahoo! Small Business. http://smallbusiness.yahoo.com/r-index ____________________________________________________________________________________ Do you Yahoo!? Everyone is raving about the all-new Yahoo! Mail beta. http://new.mail.yahoo.com

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The Data.Array.* hierarchy is unsafe (or, Segfaulting for fun and profit)
by Spencer Janssen 11 Dec '06

11 Dec '06

I've discovered a problem in the array libraries that allows one to read arbitrary memory locations without the use of any unsafeFoo functions. Both GHC and Hugs are affected. > import Data.Array.IArray > import Data.Array.Unboxed Here is a poorly behaved instance of Ix: inRange and index ignore the bounds supplied. > newtype EvilIx = E Int deriving (Eq, Ord) > instance Ix EvilIx where > inRange _ _ = True > index _ (E i) = i > range (E x, E y) = map E $ range (x, y) One can read arbitrary memory locations, eventually indexing far enough to cause a segmentation fault. > main = print [a ! E (2^i) | i <- [0..]] > where > a :: UArray EvilIx Int > a = array (E 0, E 0) [] This problem is not specific to UArrays: > main' = print [a ! E (2^i) | i <- [0..]] > where > a :: Array EvilIx String > a = array (E 0, E 0) [] The issue is that the array operators trust the Ix instance to manage boundaries correctly. The solution is to double check the value returned by index with the actual length of the array. I volunteer to write the fix, if I can extract some hints from more knowledgeable folk. There's sizeOfByteArray#, is there an analog for an Array#? I need to know how to find the length of Hugs array primitives too. Cheers, Spencer Janssen

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Wanted: documentation for STM
by dons＠cse.unsw.edu.au 11 Dec '06

11 Dec '06

Could someone who's used the STM subsystem submit a haddock documentation patch. Looking here: http://www.haskell.org/ghc/docs/latest/html/libraries/stm/Control-Concurren… is embarrassing. -- Don

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Library name choice for network accept loop module under development
by Cat Dancer 11 Dec '06

11 Dec '06

I am working on a library module to implement a network accept loop with graceful shutdown. (See http://code.catdancer.ws/acceptloop/) This code is tricky to get right, so if I am successful, it will be useful to projects such as web or database servers which accept network connections and would like to be able to restart gracefully without dropping or losing connections. Is "Network.AcceptLoop" a good name for this module in the hierarchical library namespace?

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darcs patch: Add documentation for TChan (and 1 more)
by Spencer Janssen 11 Dec '06

11 Dec '06

Mon Dec 11 01:12:01 CST 2006 Spencer Janssen <sjanssen(a)cse.unl.edu> * Add documentation for TChan Mon Dec 11 01:43:18 CST 2006 Spencer Janssen <sjanssen(a)cse.unl.edu> * Add documentation for TMVar.

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darcs patch: Fix missing comma in Fractional documentation
by Alec Berryman 11 Dec '06

11 Dec '06

Fri Dec 1 12:32:37 EST 2006 Alec Berryman <alec(a)thened.net> * Fix missing comma in Fractional documentation

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Library docs on Debian
by Yitzchak Gale 10 Dec '06

10 Dec '06

It used to be that the Haddock docs for all of the standard libraries were automatically installed on my Debian system together with GHC. I could browse them conveniently through a single consolidated index. But now that I have upgraded to GHC 6.6, many of them are gone. The packages that I most yearn for are mtl and network. What is the new Right Way to install these docs on a Debian system? Thanks, Yitz

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