October 2013 - Beginners

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=xu5Tg3_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+hbxrsejHYMwZWXWhMEnH7NJf-Bo=VhB=xe7UYO6388igEw(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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Setting x-range in haskell-chart
by Nathan Hüsken 07 Oct '13

07 Oct '13

Hey, I plot a chart where I use LocalTime for the x plot value. I want to define what the range of the x axis is. So I try: layout1_bottom_axis . laxis_generate .~ scaledAxis def (xmin,xmax) where xmin, xmax :: LocalTime. This fails with: No instance for (RealFloat LocalTime) Anyone knows how I set the xrange correctly in chart? Thanks! Nathan

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best performance with foldl
by Roland Leißa 06 Oct '13

06 Oct '13

Hi all, for a benchmark I'd like to write code like this: foldl (+) [0 100000000] how do I get the best performance out of it? However, It is important for me to rely on a higher-order function. Is it possible to be en par with the C version? int64_t result = 0; for (int64_t i = 0; i <= 100000000; ++i) result += i; Many thanks in advance for helping out, Roland

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ghci and module with FFI code
by Nathan Hüsken 04 Oct '13

04 Oct '13

Hey, I wrote a little package which gives bindings to a C++ library (to the random forest from vigra). Works fine! But when I try to load a module using it in ghci, and run an function (which is unrelated to the FFI bindings) I get: /lib/hsVigraRF-0.1.0.0/ghc-7.6.2/HShsVigraRF-0.1.0.0.o: unknown symbol `_ZGVZN5vigra10rf_defaultEvE6result' _ZGVZN5vigra10rf_defaultEvE6result is a symbol from vigra. So why do I get this in ghci and not when compiling/running? What can I do about this? Thanks! Nathan

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auto set objects imported
by Nathan Hüsken 04 Oct '13

04 Oct '13

Hey, It seems to be good practice, to explicitly say, which objects one wants to import in an import statement: import SomeModule (someFunc) while this is good documentation, it can be cumbersome to maintain. So I was wondering: Is there some tool, that automaticly finds out which functions I use from which module and modifies my import statements? That would be most usefull! Regards, Nathan

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Defaulting the following constraint ....
by Alan Buxton 03 Oct '13

03 Oct '13

Hi I have something like this - purpose is that I need to drop redundant .0 in a whole number - so to show 1.2345 as 1.2345 and to show 1.0 as 1 module Test where niceShow x = if (isInt x) then show (floor x) else show x isInt x = x == fromInteger (floor x) But the hlint in my vim plugin keeps warning me that test.hs|3 col 38 warning| Defaulting the following constraint(s) to type `Integer' || (Integral a0) arising from a use of `floor' at /tmp/test.hs:3:38-42 || (Show a0) arising from a use of `show' at /tmp/test.hs:3:32-35 || In the first argument of `show', namely `(floor x)' || In the expression: show (floor x) || In the expression: if (isInt x) then show (floor x) else show x What does this mean? And what would I need to do in order to prevent this warning?

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