October 2013 - Beginners

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=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 >> _______________________________________________ >> 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=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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confusing type signature with sections
by Patrick Redmond 03 Oct '13

03 Oct '13

I wrote code to shift and scale the range [-1, 1] to [0, 1] and mapped it on a list. Prelude> map (\n -> ((n + 1) / 2)) [-1, 0, 1] [0.0,0.5,1.0] I thought using sections would better express the simplicity of this operation. Prelude> :t (+ 1) (+ 1) :: Num a => a -> a Prelude> :t (/ 2) (/ 2) :: Fractional a => a -> a Given the types of those sections, I thought it sensible for me to compose them like this. Prelude> :t ((+ 1) / 2) ((+ 1) / 2) :: (Fractional (a -> a), Num a) => a -> a This didn't work of course, and its type baffles me. Though it ends with "Num a) => a -> a", it gives an error when given a number. I don't understand what "(Fractional (a -> a), ...) =>" really means. It seems like I've asked Haskell to perform "/" on the arguments "(+ 1)" and "2", but that ought to be disallowed by the type of "/". I eventually realized I should use the composition operator (below), but I'm still curious what I created with "((+ 1) / 2)". Prelude> :t (/ 2) . (+ 1) (/ 2) . (+ 1) :: Fractional c => c -> c Thanks! Patrick

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Num instnace for [Double]
by Nathan Hüsken 03 Oct '13

03 Oct '13

Hey, I am working a lot with timeseries (with instances at discrete moments) of doubles. So I use [Double]. Now I want to be able to do stuff like timeSeries3 = timeSeries1 + timeSeries2 So I was thinking, I create a newtype newtype TimeSeries a = TimeSeries [a] Now, can I somehow autoderive List, Monad, MonadPlus for TimeSeries? Also I would like to derive from Num. Most of the things can be done pointwise! What about fromInteger??? Should that just be a list with one element? Or does it simple not make sense? Thanks! Nathan

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My own State Monad and State Arrow
by Thiago Negri 03 Oct '13

03 Oct '13

I think I did understand Monads and Arrows. So I put it to the test: I tried to write my own State Monad and an State Arrow without looking at the real implementation. This is what I got: http://lpaste.net/93801 Please take a look on line 146 where I try to define a State Monad that is represented with a full function (state+result -to- state+result -- like my Arrow implementation). Things got hairy with the bind operator (line 153) and I just hit the keyboard until I hit the correct types and got it to compile. Yet, I can't fully understand my own bind implementation. Using the result "a" twice seems to be wrong, but I couldn't write a test to prove it.

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Creating arrays in Haskell
by Michal Kawalec 02 Oct '13

02 Oct '13

Hello, I want to use the FFT library in Haskell and for that I need to create an array. However, when I input array (1,100) [(i, i*i) | i <- [1..100]] in ghci, I get an error saying: No instance for (Enum e0) arising from the arithmetic sequence `1 .. 100' The type variable `e0' is ambiguous Possible fix: add a type signature that fixes these type variable(s) Note: there are several potential instances: instance Enum Double -- Defined in `GHC.Float' instance Enum Float -- Defined in `GHC.Float' instance Integral a => Enum (GHC.Real.Ratio a) -- Defined in `GHC.Real' ...plus 15 others In the expression: [1 .. 100] In a stmt of a list comprehension: i <- [1 .. 100] In the second argument of `array', namely `[(i, i * i) | i <- [1 .. 100]]' Could you please tell me how to add the type signature? -- Michal

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Haskell book
by Michael Loegering 02 Oct '13

02 Oct '13

I am looking for a general Haskell book with syntax reference to self-teach. I have a computer science background, so technical and theoretical is fine. Something similar in size and scope as the Camel book is to perl would be ideal - covering basic language idioms, with a decent language reference, but by no means exhaustive. I have looked at Learn You a Haskell and Real World Haskell online, both of which were accessible but were difficult to follow beyond the basics. I'm not sure if it's the organization of the material or just the learning curve, so I'm open to both if these are hands-down the favorites. Thanks, -Mike

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Libzip for Haskell under Window
by Riaan 02 Oct '13

02 Oct '13

I am using the Haskell Libzip package [ http://hackage.haskell.org/package/LibZip] to unzip a password protected file. This works great in OSX but I now need to build the application using this package for Windows. I have not been able to figure out how to get libzip [ http://www.nih.at/libzip/index.html] installed under windows so that cabal can install the package. I don't seem to be able to find a compiled binary anywhere. Can anyone help? Thanks Riaan

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Why html in platform?
by q 01 Oct '13

01 Oct '13

HP includes the html package, but everything I've seen that produces html uses blaze-html. Is html included for some historical reason?

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scotty installation error
by Ovidiu D 01 Oct '13

01 Oct '13

I'm trying to write a small web application starting from here: http://adit.io/posts/2013-04-15-making-a-website-with-haskell.html Resolving dependencies... Configuring scotty-0.2.0... Building scotty-0.2.0... Preprocessing library scotty-0.2.0... Web/Scotty.hs:35:8: Could not find module `Control.Monad.Trans.Resource' It is a member of the hidden package `resourcet-0.4.8'. Perhaps you need to add `resourcet' to the build-depends in your .cabal file. Use -v to see a list of the files searched for. Failed to install scotty-0.2.0 My build-depends clause is the following: build-depends: base ==4.5.* , wai ==1.3.* , warp ==1.3.* , http-types ==0.7.* , resourcet , scotty , text , bytestring , blaze-html , persistent , persistent-template , persistent-sqlite , persistent-postgresql , heroku , transformers ==0.3.0.0 , wai-middleware-static ==0.3.2 , wai-extra , time , monad-logger ==0.2.4 Any idea what is wrong with it? I also tried to use the dependencies list without any versions and I get the same error Thanks ovidiu

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