- Haskell-Cafe - Haskell.org

"Segmentation fault/access violation" when working with FFI
by Leza Morais Lutonda 07 Jan '14

07 Jan '14

Hi, I has trying to use the portaudio [1] package to play some sound, and running the examples [2] and it results in the "Segmentation fault/access violation" error. Any idea? Thanks. [1] http://hackage.haskell.org/package/portaudio [2] https://github.com/sw17ch/portaudio/blob/master/examples/Example1.h

2 2

Associated types, kind constraints & typelits
by Nicolas Trangez 07 Jan '14

07 Jan '14

All, While toying with typelits I wanted to get the following to work, but failed to. Is it intended not to work at all, should I change something to get it to work, or is this something which needs some GHC support? Note I obviously tried to add the constraint mentioned in the compiler error, but failed to: I seem to add too many type arguments to SingI, which somewhat puzzles me. Thanks, Nicolas {-# LANGUAGE TypeFamilies, DataKinds #-} module Main where import GHC.TypeLits class C a where type T a :: Nat data D = D instance C D where type T D = 10 {- This is not allowed, as intended: data E = E instance C E where type T E = Int -} -- This works: tOfD :: D -> Integer tOfD D = fromSing $ (sing :: Sing (T D)) {- This doesn't work: - Could not deduce (SingI Nat (T a1)) arising from a use of `sing' - from the context (C a) tOf :: C a => a -> Integer tOf _ = fromSing $ (sing :: Sing (T a)) -} main :: IO () main = return ()

3 4

Please fix documentation for you Hackage packages!
by Mateusz Kowalczyk 06 Jan '14

06 Jan '14

Greetings café, As some of you might have noticed recently, there seems to be quite a few packages with broken documentation on Hackage recently. If you are an owner of such package, please consider fixing it. There's a thread on cabal-devel about this if you're interested in details. Here's a list of packages uploaded since beginning of 2013 for which the documentation was broken as of yesterday: http://fuuzetsu.co.uk/misc/sorted.txt If your package is on that list, your documentation is broken. Only the most recent versions of packages were being considered. I outline how to fix your documentation (in most cases this means uploading it by hand) in a blog post I just published. Please refer to: http://fuuzetsu.co.uk/blog/posts/2014-01-06-Fix-your-Hackage-documentation.… The post contains a link to as script which naively attempts to automate the burden of uploading the docs manually. If your package can't be built simply with ‘cabal configure && cabal build && cabal haddock --hyperlink-source’, you'll have to adapt it to your situation. Thanks. I hope to see fewer packages with broken documentation in the future. -- Mateusz K.

11 21

Re: [Haskell-cafe] preprocessor, how to?
by Erik Hesselink 06 Jan '14

06 Jan '14

I don't quite understand why you can't just use pathSeparator (or </>) here. The code in the quotes is still Haskell, and it's going to compile on the same platform it's going to run on, right? Erik On Mon, Jan 6, 2014 at 9:13 AM, Kees Bleijenberg <k.bleijenberg(a)lijbrandt.nl> wrote: > In a program I use a lot of hamlet files. All these hamlet files are in a > submap of the source map. In code: > allHtml = Mconcat [ $(hamletFile "hamlet\\belastingen.hamlet") renderUrl > ,$(hamletFile "hamlet\\winddruk.hamlet") renderUrl > .. > ,$(hamletFile "hamlet\\berekeningDruk.hamlet") > renderUrl > ,$(hamletFile "hamlet\\drukNaarBuigTrek.hamlet") > renderUrl] > This is a Windows program. > > For another project I want to use this piece of code on Linux. The code > should now be: > .. $(hamletFile "hamlet/winddruk.hamlet") renderUrl > > I can't use pathSeparator here, because this is all happening at compile > time. So I think I need a preprocessor. > I would like to have a kind of hamletDir macro and change the code to > something like: > > #ifdef Win32 > hamletDir = "hamlet\\" > #else > hamletDir = "hamlet/" > #endif > ... > $(hamletFile "{hamletDir}winddruk.hamlet") renderUrl > Is it possible in Haskell and how do I it? > > All examples of preprocessing in Haskell I found are something like this: > #ifdef xxx > aaaa > #else > Bbbbb > #endif > I could use that. But a user defined macro is less code. > > Kees > > > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

1 0

Infelicity in StdGen?
by Rob Arthan 06 Jan '14

06 Jan '14

Either I am misunderstanding something or there is an infelicity in the implementation of StdGen. The documentation on mkStdGen says that distinct arguments should be likely to produce distinct generators. This made me think that I would get a reasonable pseudo-random function to simulate n rolls of a die by using n to seed the random number generator: import System.Random roll :: Int -> String roll n = take n . randomRs ('1', '6') . mkStdGen $ n However, this produces a string beginning with a '6' for 0 <= n <= 53667. In fact the dependency of the first value on the seed seems to be far from random: map (\l -> (head l, length l)) . group . map (fst . randomR (1, 6) . mkStdGen) $ [0..25*53668+6] returns: [(6,53668),(5,53668),(4,53668),(3,53669),(2,53668),(1,53668),(6,53669),(5,53668),(4,53668),(3,53669),(2,53668),(1,53668),(6,53668),(5,53669),(4,53668),(3,53668),(2,53669),(1,53668),(6,53668),(5,53669),(4,53668),(3,53668),(2,53669),(1,53668),(6,53668)] The behaviour seems to be related to the length of the range. You get similar behaviour for ranges of length 2, 3, 6 and 9 for example, but not for 4, 5, 7 or 8. If it is relevant, I am using ghc version 7.6.3. Regards, Rob.

3 4

Re: [Haskell-cafe] Please fix documentation for you Hackage packages!
by timmy tofu 06 Jan '14

06 Jan '14

With authors (no emails), quick and dirty: http://lpaste.net/raw/98035 Date: Sun, 5 Jan 2014 20:47:27 -0500 > From: Clark Gaebel <cgaebel(a)uwaterloo.ca> > To: Mateusz Kowalczyk <fuuzetsu(a)fuuzetsu.co.uk> > Cc: haskell-cafe <haskell-cafe(a)haskell.org> > Subject: Re: [Haskell-cafe] Please fix documentation for you Hackage > packages! > Message-ID: > <CA+aES6NVWY_EJKzpWSTap1b3BTEWVzh2=+ > qTchiCMeLgtjeFbw(a)mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > Is there any way you could tag that list with the author so that we can > Ctrl+f ourselves? > > > On Sun, Jan 5, 2014 at 8:37 PM, Mateusz Kowalczyk > <fuuzetsu(a)fuuzetsu.co.uk>wrote: > > > Greetings caf?, > > > > As some of you might have noticed recently, there seems to be quite a > > few packages with broken documentation on Hackage recently. If you are > > an owner of such package, please consider fixing it. There's a thread on > > cabal-devel about this if you're interested in details. > > > > Here's a list of packages uploaded since beginning of 2013 for which the > > documentation was broken as of yesterday: > > http://fuuzetsu.co.uk/misc/sorted.txt > > > > If your package is on that list, your documentation is broken. Only the > > most recent versions of packages were being considered. > > > > I outline how to fix your documentation (in most cases this means > > uploading it by hand) in a blog post I just published. Please refer to: > > > > > http://fuuzetsu.co.uk/blog/posts/2014-01-06-Fix-your-Hackage-documentation.… > > > > The post contains a link to as script which naively attempts to automate > > the burden of uploading the docs manually. If your package can't be > > built simply with ?cabal configure && cabal build && cabal haddock > > --hyperlink-source?, you'll have to adapt it to your situation. > > > > Thanks. I hope to see fewer packages with broken documentation in the > > future. > > -- > > Mateusz K. > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > > > -- > Clark. > > Key ID : 0x78099922 > Fingerprint: B292 493C 51AE F3AB D016 DD04 E5E3 C36F 5534 F907 >

1 0

Cloud Haskell, spawn, link and spawnLink
by Alexander Alexeev 06 Jan '14

06 Jan '14

Hi. Let's consider the following code: pid <- spawnLocal ... link pid Is it true, that a parent process will always be terminated when child process terminates, even if child process will be terminated between calls of spawnLocal and link? I wrote a test program and it seems to be so. But I wanted to be sure, that this is not some coincidence, but a real Cloud Haskell semantics. Is the same true for monitors? -- Best regards, Alexander Alexeev http://eax.me/

1 1

Re: [Haskell-cafe] preprocessor, how to?
by Chris Wong 06 Jan '14

06 Jan '14

You can use forward slashes in Windows as well. On Jan 6, 2014 9:13 PM, "Kees Bleijenberg" <k.bleijenberg(a)lijbrandt.nl> wrote: > In a program I use a lot of hamlet files. All these hamlet files are in a > submap of the source map. In code: > allHtml = Mconcat [ $(hamletFile "hamlet\\belastingen.hamlet") renderUrl > ,$(hamletFile "hamlet\\winddruk.hamlet") renderUrl > .. > ,$(hamletFile "hamlet\\berekeningDruk.hamlet") > renderUrl > ,$(hamletFile "hamlet\\drukNaarBuigTrek.hamlet") > renderUrl] > This is a Windows program. > > For another project I want to use this piece of code on Linux. The code > should now be: > .. $(hamletFile "hamlet/winddruk.hamlet") renderUrl > > I can't use pathSeparator here, because this is all happening at compile > time. So I think I need a preprocessor. > I would like to have a kind of hamletDir macro and change the code to > something like: > > #ifdef Win32 > hamletDir = "hamlet\\" > #else > hamletDir = "hamlet/" > #endif > ... > $(hamletFile "{hamletDir}winddruk.hamlet") renderUrl > Is it possible in Haskell and how do I it? > > All examples of preprocessing in Haskell I found are something like this: > #ifdef xxx > aaaa > #else > Bbbbb > #endif > I could use that. But a user defined macro is less code. > > Kees > > > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

2 1

Turning off warning in ghc-mod (in vim)
by Magnus Therning 06 Jan '14

06 Jan '14

On the command line I can do the following: % ghc-mod check -g -isrc -g dist/build/autogen src/Main.hs | grep Top-level Binary file (standard input) matches % ghc-mod check -g -isrc -g dist/build/autogen -g -fno-warn-missing-signatures src/Main.hs | grep Top-level % That is, there is no output on the second call, just as expected. However, I can't work out out to turn off the warning in Vim. AFAIU the following should work: g:ghcmod_ghc_options = ['-isrc', '-idist/build/autogen', '-fno-warn-missing-signatures'] but it doesn't. I'm obviously missing something, but what? /M -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus Beauty is more important in computing than anywhere else in technology because software is so complicated. Beauty is the ultimate defence against complexity. -- David Gelernter

1 1

preprocessor, how to?
by Kees Bleijenberg 06 Jan '14

06 Jan '14

In a program I use a lot of hamlet files. All these hamlet files are in a submap of the source map. In code: allHtml = Mconcat [ $(hamletFile "hamlet\\belastingen.hamlet") renderUrl ,$(hamletFile "hamlet\\winddruk.hamlet") renderUrl .. ,$(hamletFile "hamlet\\berekeningDruk.hamlet") renderUrl ,$(hamletFile "hamlet\\drukNaarBuigTrek.hamlet") renderUrl] This is a Windows program. For another project I want to use this piece of code on Linux. The code should now be: .. $(hamletFile "hamlet/winddruk.hamlet") renderUrl I can't use pathSeparator here, because this is all happening at compile time. So I think I need a preprocessor. I would like to have a kind of hamletDir macro and change the code to something like: #ifdef Win32 hamletDir = "hamlet\\" #else hamletDir = "hamlet/" #endif ... $(hamletFile "{hamletDir}winddruk.hamlet") renderUrl Is it possible in Haskell and how do I it? All examples of preprocessing in Haskell I found are something like this: #ifdef xxx aaaa #else Bbbbb #endif I could use that. But a user defined macro is less code. Kees

1 0