February 2010 - Haskell-Cafe

ANN: ForSyDe DSL v3.1
by Seyed Hosein Attarzadeh Niaki 25 Jun '10

25 Jun '10

Dear All, A new version of the ForSyDe DSL is uploaded to the Hackage database. "The ForSyDe (Formal System Design) methodology has been developed with the objective to move system design to a higher level of abstraction and to bridge the abstraction gap by transformational design refinement. This library provides ForSyDe's implementation as a Haskell-embedded Domain Specific Language (DSL). For more information, please see ForSyDe's website: http://www.ict.kth.se/forsyde/." In addition to compatibility with base 4 and GHC 6.10.x, the new version provides more freedom for declaration of process functions (e.g., support for when and let blocks). BR/ Hosein Attarzadeh

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ANN: parameterized-data library v0.1.4
by Seyed Hosein Attarzadeh Niaki 25 Jun '10

25 Jun '10

Dear Haskell developers, A new version of the parameterized-data library providing fixed-sized vectors (based on the type-level library) is pushed into the repository and uploaded to the Hackage database. This is only a minor update to fix the compatibility issues with base 4, GHC>=6.10 and cabal-install (not backward compatible). Bests, Hosein Attarzadeh

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Help with Bird problem 3.3.3
by Peter Hilal 11 Jun '10

11 Jun '10

I'm working my way through Bird's _Introduction to Functional Programming Using Haskell_. I'd appreciate any help with problem 3.3.3, which is: "Division of natural numbers can be specified by the condition (n * m) / n = m for all positive n and all m. Construct a program for division and prove that it meets the specification." The required construction relies on the following definitions: data Nat = Zero| Succ Nat (+) :: Nat -> Nat m + Zero = m m + Succ n = Succ (m + n) (*) :: Nat -> Nat m * Zero = Zero m * Succ n = m * n + m Proceeding as Bird does in Sec. 3.2.2, where he derives the definition of "-" from the specification "(m + n) - n = m", I've so far gotten the first case, in which m matches the pattern "Zero", simply by (i) substituting Zero for m in the specification, (ii) substituting Succ n for n in the specification (solely because n is constrained to be positive), and (iii) reducing by applying the first equation of "*": Case Zero: (Succ n * Zero) / Succ n = Zero ≡ {first equation of "*"} Zero / Succ n = Zero Easy enough, and completely intuitive, since we expect Zero divided by any non-Zero finite number to be Zero. The next case, in which m matches the pattern "Succ m", is where I get stuck, and I really have no intuition about what the definition is supposed to be. My first step is to substitute "Succ m" for "m" in the given specification, and to substitute Succ n for n in the specification (for the same reason, as above, that n is constrained to be positive), and then to use the definition of "*" to reduce the equation: Case Succ m: Succ n * Succ m / Succ n = Succ m ≡ {second equation of "*"} (Succ n * m + Succ n) / Succ n = Succ m Where do I go from here? Thank you so much.

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GHC 6.12 on OS X 10.5
by Conor McBride 08 May '10

08 May '10

Hi I thought I'd record my upgrade exerience (so far) in case anyone else finds it useful, and (more selfishly) in case anyone has some helpful advice. Summary of situation * I got 6.12 working. * It took a lot of fumbling around. * The eventual "fix" (renaming /opt/local/lib/libiconv.dylib) was a bit dodgy, but is holding for now. Long rambling narrative follows. Various features of GHC 6.12 made it very tempting to go for an earlier upgrade than I normally would. (SHE really needs GADT-style data families; everything I do needs deriving Traversable (deriving HalfZip would be nice too!).) Already there was a handy installer for Intel+Leopard macs (is anybody on the PPC+Leopard case? if not, I will be soon...). I thought "go for it". Installation, no problem. Compiling something: whoops, no mtl. OK, cabal install mtl: whoops, no acceptable cabal. Fair dos, if I'd read the warnings I'd have known that my cabal-install would be useless and tried to build the new one. QUESTION: Is the sensible upgrade path to build cabal-install 0.8 with your old GHC, before installing 6.12? Does this even work? At one point, I tried this and had some peculiar issues involving zlib... Anyhow, I've got 6.12 and I need cabal-install 0.8. Can I find it? Tricky, and http://haskell.org/cabal/ didn't help much. I'm very tolerant of busy people not quite getting round to it, and I can use google, so I find the darcs version and get cracking. This happens: ----------------------------------------------------------------------------- bash-3.2$ ./bootstrap.sh Checking installed packages for ghc-6.12.1... parsec-2.1.0.1 will be downloaded and installed. network-2.2.1.5 will be downloaded and installed. Cabal is already installed and the version is ok. mtl-1.1.0.2 will be downloaded and installed. HTTP-4000.0.8 will be downloaded and installed. zlib-0.5.2.0 will be downloaded and installed. Downloading parsec-2.1.0.1... % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 15430 100 15430 0 0 12743 0 0:00:01 0:00:01 --:--:-- 19312 [1 of 1] Compiling Main ( Setup.hs, Setup.o ) Linking Setup ... Undefined symbols: "_iconv_close", referenced from: _hs_iconv_close in libHSbase-4.2.0.0.a(iconv.o) "_iconv", referenced from: _hs_iconv in libHSbase-4.2.0.0.a(iconv.o) "_iconv_open", referenced from: _hs_iconv_open in libHSbase-4.2.0.0.a(iconv.o) ld: symbol(s) not found collect2: ld returned 1 exit status Error during cabal-install bootstrap: Compiling the Setup script failed ----------------------------------------------------------------------------- At lthis point, I suspected a linker/dylib problem, but foolishly, I wanted the problem to be pretty much anything else, so I spent far too long looking the wrong way. I thought that if I could just get cabal-install working somehow, I'd be ok. I tried installing parsec with runhaskell Setup.hs {configure,build,install} but each of these commands appeared content to do precisely nothing: I found this perplexing. I tried reverting to 6.10.4 and compiling cabal-install. This made more progress, but died with some sort of zlib version snafu. (I'm sorry, I should have recorded the details but didn't.) The zlib-0.5.2.0 package did install successfully, but somehow the build for cabal-install itself went awry with an "even though this is the right version I can't find X" sort of a problem. I uninstalled 6.10.4, deleted my .cabal directory, nuked a few other relics showing up from what's probably a dumb choice of PATH setting. I had another go at 6.12, and this time I tried compiling a wee program of my own with no exciting package dependencies. Should have done that straight away, of course. Same iconv problem. This left no alternative. I found I had a /usr/lib/libiconv.dylib etc and an /opt/local/lib/libiconv.dylib etc, so I renamed the latter to opt/local/lib/moolibiconv.dylib, and suddenly, GHC became capable of linking stuff. The darcs version of cabal-install then built just fine; SHE rebuilt ok; Epigram needed a few extra LANGUAGE pragmas, but no trouble. I'm almost back where I was. I worry about this. (1) What have I broken by shifting the opt/local/lib copy of libiconv? (2) Why did that break things anyway? (3) How come I ended up with a broken library setup? (4) What else is broken? (What's worse than finding a maggot in your apple? Finding half a maggot in your apple.) I'm not at all a mac expert (I use a mac because I'm too stupid to maintain a linux installation -- the Nottingham grad students (all grown up now) told me they were fed up fixing my computer back in 04.) This dylib nonsense seems quite common. Is it MacPorts messing things up? Is there a more principled fix than the brutal thing I did? I wonder if it might be possible to build some sort of diagnostic tool to check paths and libraries for conflicts and omissions. Anyhow, sorry for the dreariness of this story, but it ends in an acceptable configuration, for the moment. I hope it can be of some small help. Happy hols Conor

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DLL on Windows
by Serguey Zefirov 20 Apr '10

20 Apr '10

I tried the way described in http://www.haskell.org/ghc/docs/latest/html/users_guide/win32-dlls.html and i got this error message: -------------------------------------------------------------------------------------------- ghc -shared -o test.dll --make test.hs [1 of 1] Compiling Test ( test.hs, test.o ) ghc.exe: panic! (the 'impossible' happened) (GHC version 6.10.3 for i386-unknown-mingw32): link: GHC not built to link this way: LinkDynLib Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug -------------------------------------------------------------------------------------------- How can I fix it?

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Cabal update problem
by Maciej Podgurski 12 Apr '10

12 Apr '10

Hi, after updating to cabal-install-0.8.0/Cabal-1.8.0.2 with GHC 6.10.4, I always get an error when updating the package list: > cabal update Downloading the latest package list from hackage.haskell.org cabal: Codec.Compression.Zlib: premature end of compressed stream Is there a way to fix this without rebuilding from the latest darcs repo? Best wishes, Maciej

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passing cpp options to c2hs from cabal
by Chris Casinghino 11 Apr '10

11 Apr '10

Hi all, I have a question about cpp, c2hs and cabal. The short version: What can I put in my cabal file to get "-cppopts=-U__BLOCKS__" passed as an argument in calls to c2hs? Longer story: I need to set up my cabal file so that c2hs gets this extra option to make things build smoothly on some macs. If I run cabal from the command line, I can pass it: cabal install --c2hs-options='--cppopts=-U__BLOCKS__' And this works great. I need to make my .cabal file do this, but c2hs-options doesn't seem to be accepted there. I tried: cpp-options: "-U__BLOCKS__" But if I run cabal install -v I can see this isn't being passed on to c2hs: ... /home/ccasin/.cabal/bin/c2hs --include=dist/build --cppopts=-D__GLASGOW_HASKELL__=610 --cppopts=-Icontrib/libpuz/include --output-dir=dist/build --output=Codec/Game/Puz/Internal.hs ./Codec/Game/Puz/Internal.chs ... Thanks! --Chris Casinghino

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Time for a San Francisco Hackathon?
by Bryan O'Sullivan 04 Apr '10

04 Apr '10

I'm thinking it might be a good idea to organise a Haskell Hackathon for people in (and who'd like to visit) the Bay Area. The tentative date I have in mind is the first weekend in May (conveniently May 1). If you'd be interested in attending or helping to organise, please let me know.

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Profiling
by Andrew Coppin 03 Apr '10

03 Apr '10

Two small questions: 1. Is Thread Scope any use for profiling single-threaded programs? 2. I tried to compile my program with -prof, but GHC just whines at me that the packages I'm using haven't been compiled for profiling. Do I really need to go recompile every single package I'm using with profiling support before I can profile my program? How do I tell Cabal to install the necessary code? (I really hope this doesn't involve uninstalling and reinstalling everything...)

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Has "Try Haskell! An interactive tutorial in your browser" been announced yet?
by DekuDekuplex＠Yahoo.com 28 Mar '10

28 Mar '10

There is a link to "Try Haskell! -- an interactive, online Haskell interpreter" (see http://tryhaskell.org/) under "February 2010" under "1 Headlines" on the "Haskell - HaskellWIki" Web page (see http://www.haskell.org/) While I could be mistaken, there do not seem to be any announcements for February 2010 concerning this interactive tutorial on either the Haskell or Haskell-Cafe mailing lists. Has it been announced yet? If not, can I go ahead and announce it on the Haskell mailing list? -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^

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