- Beginners - Haskell.org

Control.Exception.bracket-like for MonadIO ?
by Olivier Iffrig 14 Oct '13

14 Oct '13

Hello, I'm trying to build an application with a monad encapsulating its state, environment, ... For the sake of simplicity, let's say data MyState type Main = StateT MyState IO But I would like to use something like bracket with my Main monad, and I did not find how to to it. I'm looking for something like bracket' :: MonadIO m => m a -> (a -> m b) -> (a -> m c) -> m c or in my case myBracket :: Main a -> (a -> Main b) -> (a -> Main c) -> Main c Searching for that on hoogle did not give me anything interesting... Did someone encounter this problem, and have a solution ? -- Olivier

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Turing machine that decides if a string is an element of an-bn-cn
by Costello, Roger L. 13 Oct '13

13 Oct '13

Hi Folks, I implemented, in Haskell, a Turing Machine that decides if a string is a member of the language consisting of an equal number of a's, b's, and c's, i.e., anbncn. http://www.xfront.com/Turing-Machines/an-bn-cn/TM.hs.txt /Roger

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daemons and signals
by Jeff Lasslett 13 Oct '13

13 Oct '13

Hello, I'm trying to write a daemon that handles some signals. My problem is currently with the handling of posix signals. I don't think my signal handlers are being run. All they do at present is write to syslog and a file (for diagnostic purposes). I'm not seeing anything in /var/log/system.log (I'm on a mac). My code is attached. Any advice would be greatly appreciated. Thanks, Jeff

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cabal issues
by emacstheviking 12 Oct '13

12 Oct '13

Fresh install via homebrew on osx, brew doctor reports no problems. After installing ghc and cabal-install I then tried a cabal update and it failed because of permissions issues in the ~/.cabal folder I fixed that as stated on the brew site and tried again, no joy... Last 10 lines of the build log ( /Users/seancharles/.cabal/logs/OpenGLRaw-1.4.0.0.log ): cabal: /Users/seancharles/.cabal/logs/OpenGLRaw-1.4.0.0.log: permission denied I also did a Verify and Repair from Disk Utilities just in case, that fixed some things but no this. Have I done something wrong or is there an issue with cabal because every time I do a cabal update it seems to me the problem keeps coming back?!?! This is very frustrating because I initially installed the latest Haskell Platform for OSX .pkg file and had exactly the same problems. Sometimes I despair at how hard it seems to get a working Haskell installation...I never have these problems on Linux, only OSX and I don't know why! Thanks in advance. Sean. Some information (I did notice that seancharles:staff and seancharles:admin are in existence) that may help. I have no idea about :staff and :admin, not seen that before! all of the log file: Installing library in /Users/seancharles/.cabal/lib/x86_64-osx-ghc-7.6.3/OpenGLRaw-1.4.0.0 setup-Cabal-1.16.0-x86_64-osx-ghc-7.6.3: dist/build/HSOpenGLRaw-1.4.0.0.o: permission denied ghc --version The Glorious Glasgow Haskell Compilation System, version 7.6.3 Seans-iMac:~ seancharles$ cabal --version cabal-install version 1.18.0.2 using version 1.18.1 of the Cabal library Folder permissions: drwxr-xr-x 9 seancharles staff 306 12 Oct 20:37 .cabal brew folder: drwxr-xr-x 6 seancharles admin 204 12 Oct 20:34 Cellar

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Re: [Haskell-beginners] Error when starting GHCI (Arie van Wingerden)
by Arie van Wingerden 12 Oct '13

12 Oct '13

Hi Howard, thanks for your help. I guess this is a nasty problem which may take quit some time to solve. Since I only wish to learn a new functional language, I'll try my hands on F# for now. Perhaps later on this problem is solved and I will retry starting with Haskell. For now i wish you luck and say goodbye. 2013/10/11 Arie van Wingerden <xapwing(a)gmail.com> > C:\Windows\system32>cabal update > Downloading the latest package list from hackage.haskell.org > cabal: Failed to download > http://hackage.haskell.org/packages/archive/00-index.tar.gz : ErrorMisc > "Unsucessful HTTP code: 404" > > Which is another error; sigh... > > I already uninstalled 2 applications that might have interfered; but the > problems remain. > > > 2013/10/11 Howard B. Golden <howard_b_golden(a)yahoo.com> > > Arie, >> >> Try this from the command line: >> >> cabal update >> cabal install hs-dotnet >> >> That should install hs-dotnet. (I'm not sure that will solve your ghci >> problem, but it's worth a try.) >> >> Howard >> >> ------------------------------ >> *From:* Arie van Wingerden <xapwing(a)gmail.com> >> *To:* Howard B. Golden <howard_b_golden(a)yahoo.com> >> *Cc:* "beginners(a)haskell.org" <beginners(a)haskell.org> >> *Sent:* Friday, October 11, 2013 1:03 AM >> >> *Subject:* Re: [Haskell-beginners] Error when starting GHCI (Arie van >> Wingerden) >> >> Hi Howard, >> >> maybe you are spot on! >> I only have this: "C:\Users\Arie\AppData\Roaming\ghc" only containing >> ghci_history !! >> But how to repair this? >> >> The install gave me no errors. >> >> Kind regards, >> Arie >> >> >> 2013/10/10 Howard B. Golden <howard_b_golden(a)yahoo.com> >> >> Arie, >> >> The only difference I have with your output on my computer is a line >> after the "Using binary package database..." line: >> >> Using binary package database: >> C:\Users\hgolden\AppData\Roaming\ghc\i386-mingw32-7.6.3\package.conf.d\package.cache >> >> That package cache contains hs-dotnet-0.4.0. >> >> I have no idea if this is why you are getting the error message at the >> end ("Loading package base ... "). >> >> Did you get any error messages when you installed the Haskell Platform? >> >> Howard >> >> ------------------------------ >> *From:* Arie van Wingerden <xapwing(a)gmail.com> >> *To:* Howard B. Golden <howard_b_golden(a)yahoo.com>; The >> Haskell-Beginners Mailing List - Discussion of primarily beginner-level >> topics related to Haskell <beginners(a)haskell.org> >> *Sent:* Wednesday, October 9, 2013 11:41 AM >> *Subject:* Re: [Haskell-beginners] Error when starting GHCI (Arie van >> Wingerden) >> >> Hi, >> following Howards guidance I tried to start GHCI with the -v option and >> get: >> >> GHCi, version 7.6.3: http://www.haskell.org/ghc/ :? for help >> Glasgow Haskell Compiler, Version 7.6.3, stage 2 booted by GHC version >> 7.4.1 >> Using binary package database: C:\Program Files\Haskell >> Platform\2013.2.0.0\lib\ >> package.conf.d\package.cache >> wired-in package ghc-prim mapped to >> ghc-prim-0.3.0.0-9d603ae4e062e1401099a3daa89 >> 31d0f >> wired-in package integer-gmp mapped to >> integer-gmp-0.5.0.0-4093e6ff1e8ebdba04ec8 >> 92df9ac108f >> wired-in package base mapped to >> base-4.6.0.1-f0c2cc6dcf0e12bf75312a2e7f354095 >> wired-in package rts mapped to builtin_rts >> wired-in package template-haskell mapped to >> template-haskell-2.8.0.0-42f1e6e5551 >> 1ef4dff7e4249580faf8f >> wired-in package dph-seq not found. >> wired-in package dph-par not found. >> Hsc static flags: -static >> Loading package ghc-prim ... linking ... done. >> Loading package integer-gmp ... linking ... done. >> *** gcc: >> "C:\Program Files\Haskell Platform\2013.2.0.0\lib/../mingw/bin/gcc.exe" >> "-fno-st >> ack-protector" "-Wl,--hash-size=31" "-Wl,--reduce-memory-overheads" >> "-LC:\Progra >> m Files\Haskell Platform\2013.2.0.0\lib\base-4.6.0.1" "--print-file-name" >> "wsock >> 32.dll" >> *** gcc: >> "C:\Program Files\Haskell Platform\2013.2.0.0\lib/../mingw/bin/gcc.exe" >> "-fno-st >> ack-protector" "-Wl,--hash-size=31" "-Wl,--reduce-memory-overheads" >> "-LC:\Progra >> m Files\Haskell Platform\2013.2.0.0\lib\base-4.6.0.1" "--print-file-name" >> "user3 >> 2.dll" >> *** gcc: >> "C:\Program Files\Haskell Platform\2013.2.0.0\lib/../mingw/bin/gcc.exe" >> "-fno-st >> ack-protector" "-Wl,--hash-size=31" "-Wl,--reduce-memory-overheads" >> "-LC:\Progra >> m Files\Haskell Platform\2013.2.0.0\lib\base-4.6.0.1" "--print-file-name" >> "shell >> 32.dll" >> Loading package base ... ghc.exe: : Kan opgegeven module niet vinden. >> *** Deleting temp files: >> Deleting: >> *** Deleting temp dirs: >> Deleting: >> <command line>: can't load .so/.DLL for: (addDLL: could not load DLL) >> >> Any ideas why this happens? >> TIA, >> Arie >> >> >> 2013/10/8 Howard B. Golden <howard_b_golden(a)yahoo.com> >> >> Hi Arie, >> >> My guess is that you don't have a necessary library in your path. Here >> are the Haskell libraries I have in my path (change as necessary for your >> setup): >> >> C:\Program Files\Haskell Platform\2013.2.0.0\lib\extralibs\bin >> C:\Program Files\Haskell Platform\2013.2.0.0\bin >> C:\Program Files\Haskell Platform\2013.2.0.0\mingw\bin >> >> HTH, >> >> Howard >> >> ------------------------- >> Message: 2 >> >> Date: Tue, 8 Oct 2013 18:12:41 +0200 >> From: Arie van Wingerden <xapwing(a)gmail.com> >> To: beginners(a)haskell.org >> Subject: [Haskell-beginners] Error when starting GHCI >> Message-ID: >> <CADkALSHpG7s89tT7rXJw56q7hkDyEcwv1%3Dxu5Tg3_qLqoqtDxg(a)mail.gmail.com> >> Content-Type: text/plain; charset="iso-8859-1" >> >> Hi, >> >> today I downloaded the Haskell platform for 32 bits Windows >> (HaskellPlatform-2013.2.0.0-setup.exe) and installed it. >> >> The first time I started GHCI all worked perfectly. >> >> When I closed GHCI and later tried to start it again I constantly get >> however: >> C:\Users\Arie>ghci >> GHCi, version 7.6.3: http://www.haskell.org/ghc/ :? for help >> Loading package ghc-prim ... linking ... done. >> Loading package integer-gmp ... linking ... done. >> Loading package base ... ghc.exe: : Kan opgegeven module niet vinden. >> <command line>: can't load .so/.DLL for: (addDLL: could not load DLL) >> WHERE Kan opgegeven module niet vinden MEANS Can't find the specified >> module >> >> Any ideas? >> >> Kind regards, >> Arie >> _______________________________________________ >> Beginners mailing list >> Beginners(a)haskell.org >> http://www.haskell.org/mailman/listinfo/beginners >> >> >> >> >> >> >> >> >> >> >

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Re: [Haskell-beginners] Error when starting GHCI (Arie van Wingerden)
by Howard B. Golden 09 Oct '13

09 Oct '13

Hi Arie, My guess is that you don't have a necessary library in your path. Here are the Haskell libraries I have in my path (change as necessary for your setup): C:\Program Files\Haskell Platform\2013.2.0.0\lib\extralibs\bin C:\Program Files\Haskell Platform\2013.2.0.0\bin C:\Program Files\Haskell Platform\2013.2.0.0\mingw\bin HTH, Howard ------------------------- Message: 2 Date: Tue, 8 Oct 2013 18:12:41 +0200 From: Arie van Wingerden <xapwing(a)gmail.com> To: beginners(a)haskell.org Subject: [Haskell-beginners] Error when starting GHCI Message-ID: <CADkALSHpG7s89tT7rXJw56q7hkDyEcwv1%3Dxu5Tg3_qLqoqtDxg(a)mail.gmail.com> Content-Type: text/plain; charset="iso-8859-1" Hi, today I downloaded the Haskell platform for 32 bits Windows (HaskellPlatform-2013.2.0.0-setup.exe) and installed it. The first time I started GHCI all worked perfectly. When I closed GHCI and later tried to start it again I constantly get however: C:\Users\Arie>ghci GHCi, version 7.6.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... ghc.exe: : Kan opgegeven module niet vinden. <command line>: can't load .so/.DLL for: (addDLL: could not load DLL) WHERE Kan opgegeven module niet vinden MEANS Can't find the specified module Any ideas? Kind regards, Arie

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Javascript with Haskell
by Franco 09 Oct '13

09 Oct '13

Hello mailing list, I am developing a small text adventure game, which now runs nicely on a Linux terminal. I was going to ask a friend of mine to compile it on Windows, but then I thought: "Wouldn't it be awesome if people could run that in their browser?" I searched a bit and found this little example game [1]. As you can see it was written in Haskell but you can play it in your browser. Now, to the problem: it seems to me that the code requires UHC (Utrecht Haskell Compiler), which I don't have (I use GHC). What are the alternatives (if any)? As stated above, I am not going to code anything complex graphic wise, so the simpler the merrier! Thanks -F [1] http://jshaskell.blogspot.de/2012/09/breakout.html

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RankNTypes + ConstraintKinds to use Either as a "union"
by Thiago Negri 09 Oct '13

09 Oct '13

Is there a way to compile this code? If not, why? {-# LANGUAGE RankNTypes, ConstraintKinds #-} -- This compiles bar :: (Num a, Num b) => (forall c. Num c => c -> c) -> Either a b -> Either a b bar f (Left a) = Left (f a) bar f (Right b) = Right (f b) bar' = bar (+ 2) -- This doesn't compile because foo' does not typecheck foo :: (tc a, tc b) => (forall c. tc c => c -> c) -> Either a b -> Either a b foo f (Left a) = Left (f a) foo f (Right b) = Right (f b) foo' = foo (+ 2)

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Error when starting GHCI
by Arie van Wingerden 08 Oct '13

08 Oct '13

Hi, today I downloaded the Haskell platform for 32 bits Windows (HaskellPlatform-2013.2.0.0-setup.exe) and installed it. The first time I started GHCI all worked perfectly. When I closed GHCI and later tried to start it again I constantly get however: C:\Users\Arie>ghci GHCi, version 7.6.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... ghc.exe: : Kan opgegeven module niet vinden. <command line>: can't load .so/.DLL for: (addDLL: could not load DLL) WHERE Kan opgegeven module niet vinden MEANS Can't find the specified module Any ideas? Kind regards, Arie

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Error when starting GHCI
by Arie van Wingerden 08 Oct '13

08 Oct '13

??? <CADkALSHpG7s89tT7rXJw56q7hkDyEcwv1=xu5Tg3_qLqoqtDxg at mail.gmail.com> Content-Type: text/plain; charset="iso-8859-1" Hi, today I downloaded the Haskell platform for 32 bits Windows (HaskellPlatform-2013.2.0.0-setup.exe) and installed it. The first time I started GHCI all worked perfectly. When I closed GHCI and later tried to start it again I constantly get however: C:\Users\Arie>ghci GHCi, version 7.6.3: http://www.haskell.org/ghc/??:? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... ghc.exe: : Kan opgegeven module niet vinden. <command line>: can't load .so/.DLL for:? (addDLL: could not load DLL) WHERE Kan opgegeven module niet vinden MEANS Can't find the specified module Any ideas? Kind regards, ???Arie >From franco00 at gmx.com Tue Oct 8 20:30:44 2013 From: franco00 at gmx.com (Franco) Date: Tue, 8 Oct 2013 22:30:44 +0200 Subject: [Haskell-beginners] Javascript with Haskell Message-ID: <20131008203044.GA10796@efikamx> X-List-Received-Date: Sat, 12 Oct 2013 07:40:54 -0000 X-List-Received-Date: Sat, 12 Oct 2013 07:40:54 -0000 Hello mailing list, I am developing a small text adventure game, which now runs nicely on a Linux terminal. I was going to ask a friend of mine to compile it on Windows, but then I thought: "Wouldn't it be awesome if people could run that in their browser?" I searched a bit and found this little example game [1]. As you can see it was written in Haskell but you can play it in your browser. Now, to the problem: it seems to me that the code requires UHC (Utrecht Haskell Compiler), which I don't have (I use GHC). What are the alternatives (if any)? As stated above, I am not going to code anything complex graphic wise, so the simpler the merrier! Thanks -F [1] http://jshaskell.blogspot.de/2012/09/breakout.html >From jeff.lasslett at gmail.com Wed Oct 9 01:50:57 2013 From: jeff.lasslett at gmail.com (Jeff Lasslett) Date: Wed, 9 Oct 2013 12:50:57 +1100 Subject: [Haskell-beginners] daemons and signals Message-ID: <CAK6%2BhbxrsejHYMwZWXWhMEnH7NJf-Bo%3DVhB%3Dxe7UYO6388igEw(a)mail.gmail.com> X-List-Received-Date: Sat, 12 Oct 2013 07:40:54 -0000 X-List-Received-Date: Sat, 12 Oct 2013 07:40:54 -0000 Hello, I'm trying to write a daemon that handles some signals. My problem is currently with the handling of posix signals. I don't think my signal handlers are being run. All they do at present is write to syslog and a file (for diagnostic purposes). I'm not seeing anything in /var/log/system.log (I'm on a mac). My code is attached. Any advice would be greatly appreciated. Thanks, Jeff

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