December 2010 - Beginners

GUI library for beginners?
by Venanzio Capretta 14 Dec '10

14 Dec '10

Hi, I've been trying to find out what is the best GUI library to use for a Haskell beginner. At first I adopted gtk2hs and it was going well. But the web page for it has disappeared during the Haskell site migration. So now I don't have access to the documentation and the examples any more. Next I tried with wxHaskell, but unfortunately it doesn't install on Ubuntu (I checked on the mailing list: other people had the same problem and I don't understand the solution). Is there a library for GUI in Haskell that is simple to use and well supported, something that is user friendly for a beginner Haskell programmer? Best wishes, Venanzio

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Re: [Haskell-beginners] Equivalence of Inheritance
by Russ Abbott 14 Dec '10

14 Dec '10

I'm also confused about how to do the equivalence of inheritance in Haskell. Here is a complete example below. It doesn't compile. The error message is Class `Person' used as a type If I write "(Person p) =>" instead, I get other diagnostics. I would very much appreciate seeing how this should be done in Haskell. ---------- Example (multiple files) ------------ --- Group.hs --- module Group where import Person data Group = Group { members :: [Person] } instance Show Group where show group = unlines $ map show $ members group --- Person.hs --- module Person ( Condition(Bad, OK, Good) , Person ) where class Person where age :: Person -> Int name :: Person -> String getGenderSpecificCondition :: Person -> Condition instance Show Person where show p = name p ++ "(" ++ age p ++ ", " ++ getGenderSpecificCondition p ++ ")" data Condition = Bad | OK | Good --- Man.hs --- module Man ( age , name , Man (Man) ) where import Person data Man = Man { name :: String , age :: Int , prostateCondition :: Condition } instance Person Man where getGenderSpecificCondition :: Person -> Condition getGenderSpecificCondition m = prostateCondition m --- Woman.hs--- module Woman ( age , name , Woman (Woman) ) where import Person data Woman = Woman { name :: String , age :: Int , ovaryCondition :: Condition } instance Person Woman where getGenderSpecificCondition :: Person -> Condition getGenderSpecificCondition w = ovaryCondition w ---------- End example (multiple files) ------------ Thanks *-- Russ * On Tue, Dec 14, 2010 at 12:11 AM, <beginners-request(a)haskell.org> wrote: > Date: Mon, 13 Dec 2010 22:09:25 -0600 > From: Antoine Latter <aslatter(a)gmail.com> > Subject: Re: [Haskell-beginners] Equivalent of inheritance in Haskell > To: C K Kashyap <ckkashyap(a)gmail.com> > Cc: beginners(a)haskell.org > Message-ID: > <AANLkTinE30iTwWs8qBvWAcDoqGvy2T2_qpQqbXZKrCcm(a)mail.gmail.com> > Content-Type: text/plain; charset=UTF-8 > > On Mon, Dec 13, 2010 at 9:10 PM, C K Kashyap <ckkashyap(a)gmail.com> wrote: > >> > >> But there is not a way to easily say (in Haskell) "type A is > >> everything that type B is plus these other things here ...". Haskell > >> is not an OO language. > > > > This captures what I had in mind. Using compound types seems ok but > > I'd still need to do some mechanical stuff if I had to provide a > > function that works on the compound type which is actually defined for > > a component type. > > > > If I understand you right .. you'd build a 'Man' type and 'Woman' type > > by using a 'Person' type. Lets say, there is a function called getName > > that is Person -> String > > I'd have to mechanically define a function getName :: Man -> String - > > that extracts the person inside and calls getName on it - did I > > understand it right? > > Or would you typically write extract functions that'll return the > > components and then the user could call the method on the component? > > As in .... getPerson :: Man -> Person ... then call getName on that. > > > > How do you deal with situations like that? > > > > Well, in this case I might just have a person type with a 'gender' > field :-) Then I get the polymorphism and code-reuse for free! > > But what you're talking about is something that OO-style programming > is particularly aligned towards, and functional programming generally > is not. > > One thing people do is use type-classes - this would be a bit like > having 'Car' and 'Truck' implement the same interface. The simple > building blocks would be duplicated, but the complex application-level > functionality could be written against the typeclass. > > Another approach is with functional lenses - these are libraries that > aim to make updating complex compound types easier. Off the top of my > head I know of fclabels[1], but I know there are others. If you're > interested in this approach you might be able to email the -cafe > mailing list to ask for more. > > Is there a particular problem you're trying to solve? we might be able > to take the conversation in a less speculative direction. > > Antoine

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Is this scope range problem?
by Sok H. Chang 14 Dec '10

14 Dec '10

Hello, everyone. Thank you so much to previous great answer! Now, I don't know how can I fix this. The error is, Haskell>ghc --make Temp.hs -o Temp.exe [1 of 1] Compiling Main ( Temp.hs, Temp.o ) Temp.hs:19:27: Not in scope: `inpStr' The code is, import System.IO import System.Random sentenceAry = [] main :: IO () main = do inh <- openFile "c:\\Documents and Settings\\shaegis\\inputFile.txt" ReadMode outh <- openFile "c:\\Documents and Settings\\shaegis\\outputFile.txt" WriteMode mainloop inh outh hClose inh hClose outh mainloop :: Handle -> Handle -> IO () mainloop inh outh = do ineof <- hIsEOF inh if ineof then do hPutStrLn outh inpStr return () else do inpStr <- hGetLine inh let sentenceAry = inpStr : [] mainloop inh outh I'm try to change like below, but I failed. mainloop :: Handle -> Handle -> IO () mainloop inh outh = do ineof <- hIsEOF inh if not ineof then do inpStr <- hGetLine inh let sentenceAry = inpStr : [] mainloop inh outh else do hPutStrLn outh inpStr return () I wonder why... Thank you. Sincerely, Sok Chang

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Re: [Haskell-beginners] GUI library for beginners?
by . 14 Dec '10

14 Dec '10

Hi Venanzio, I found this to be working: <http://hackage.haskell.org/package/gtk> As far as GUI toolkits are concerned, I have used gtk2hs myself (also being still quite a haskell beginner). I have used gtkmm from c++ before, which sure helps in understanding what's going on (doing things in Haskell is much more fun and more pleasing though). Haskell rocks! SCNR Christian On Tue, 2010-12-14 at 12:00 +0100, beginners-request(a)haskell.org wrote: > Send Beginners mailing list submissions to > beginners(a)haskell.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://www.haskell.org/mailman/listinfo/beginners > or, via email, send a message with subject or body 'help' to > beginners-request(a)haskell.org > > You can reach the person managing the list at > beginners-owner(a)haskell.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Beginners digest..." > > > Today's Topics: > > 1. GUI library for beginners? (Venanzio Capretta) > 2. Re: GUI library for beginners? (Tom Hobbs) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Tue, 14 Dec 2010 09:16:40 +0000 > From: Venanzio Capretta <vxc(a)Cs.Nott.AC.UK> > Subject: [Haskell-beginners] GUI library for beginners? > To: beginners(a)haskell.org > Message-ID: <4D0735F8.1010509(a)cs.nott.ac.uk> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > Hi, > I've been trying to find out what is the best GUI library to use for > a Haskell beginner. > At first I adopted gtk2hs and it was going well. But the web page for it > has disappeared during the Haskell site migration. So now I don't have > access to the documentation and the examples any more. > Next I tried with wxHaskell, but unfortunately it doesn't install on > Ubuntu (I checked on the mailing list: other people had the same problem > and I don't understand the solution). > Is there a library for GUI in Haskell that is simple to use and well > supported, something that is user friendly for a beginner Haskell > programmer? > Best wishes, > Venanzio > > > > ------------------------------ > > Message: 2 > Date: Tue, 14 Dec 2010 09:55:45 +0000 > From: Tom Hobbs <tvhobbs(a)googlemail.com> > Subject: Re: [Haskell-beginners] GUI library for beginners? > To: beginners(a)haskell.org > Message-ID: > <AANLkTimDxvCzJW77Wszwb9+S+kNm_iGDYora_4Diq0zG(a)mail.gmail.com> > Content-Type: text/plain; charset=ISO-8859-1 > > Hi Venanzio, > > I found the following sites very helpful when trying to understand > OpenGL + Haskell. > > - http://blog.mikael.johanssons.org/archive/2006/09/opengl-programming-in-has… > - http://myawesomeblag.blogspot.com/2007/03/opengl-tetris-in-haskell.html > > My site contains the commands I used to get everything install on > Ubuntu, it also has a link to my code on it, but you'll find that the > code is very similar to Mikael's above. > > http://whatimean.wordpress.com/2010/10/19/simple-cell-automata-in-haskell/ > > Good luck. > > Tom > > On Tue, Dec 14, 2010 at 9:16 AM, Venanzio Capretta <vxc(a)cs.nott.ac.uk> wrote: > > Hi, > > ?I've been trying to find out what is the best GUI library to use for a > > Haskell beginner. > > At first I adopted gtk2hs and it was going well. But the web page for it has > > disappeared during the Haskell site migration. So now I don't have access to > > the documentation and the examples any more. > > Next I tried with wxHaskell, but unfortunately it doesn't install on Ubuntu > > (I checked on the mailing list: other people had the same problem and I > > don't understand the solution). > > Is there a library for GUI in Haskell that is simple to use and well > > supported, something that is user friendly for a beginner Haskell > > programmer? > > Best wishes, > > ?Venanzio > > > > _______________________________________________ > > Beginners mailing list > > Beginners(a)haskell.org > > http://www.haskell.org/mailman/listinfo/beginners > > > > > > ------------------------------ > > _______________________________________________ > Beginners mailing list > Beginners(a)haskell.org > http://www.haskell.org/mailman/listinfo/beginners > > > End of Beginners Digest, Vol 30, Issue 21 > *****************************************

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Cheap lookup tables
by Paul Sargent 14 Dec '10

14 Dec '10

I've just done some profiling on my application, and I've found that about 50% of my time and allocations is taken by two functions. All these are a functions which return constants from tables. At the moment they look something like this (I'm using the dimensional package to handle SI Units, hence the *~ one): buehlmannGradient :: (Fractional a) => Gas -> Int -> Dimensionless a buehlmannGradient Nitrogen 1 = 1.7928 *~ one buehlmannGradient Nitrogen 2 = 1.5352 *~ one [...] buehlmannGradient Nitrogen 15 = 1.0414 *~ one buehlmannGradient Nitrogen 16 = 1.0359 *~ one buehlmannGradient Helium 1 = 2.0964 *~ one buehlmannGradient Helium 2 = 1.7400 *~ one [...] buehlmannGradient Helium 15 = 1.0850 *~ one buehlmannGradient Helium 16 = 1.0791 *~ one This one causes 36% of my time. The other is similar: buehlmannZeroPoint :: (Fractional a) => Gas -> Int -> Int -> Pressure a buehlmannZeroPoint Nitrogen 1 mode = ([29.6, 29.6, 29.6] *~~ msw) !! mode - buehlmannGradient Nitrogen 1 * (10 *~ msw) [...] Again, 16 Cases times two gases. This one uses 14.5%. They tend to be called in pairs, and the first function is called about 100,000 times. The second about 50,000 times (which then causes 50,000 of the first function). What's my best strategy for optimising these functions? Is it the pattern match that's hurting me? Can I write them in a better way, or do I need to look at how I'm using them? Obviously calling them less often would help, but I'm not sure what I'd do to my code to achieve this. These constants are used in lots of fairly diverse areas of my code, and they're encapsulated into functions to stop magic numbers flying around. Thanks Paul

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Parse error. Please, Help me.
by Sok H. Chang 13 Dec '10

13 Dec '10

Hello, everyone. I write my second code... but when I compile this, I got an error... (My first code works. of course, at that time, I got an indentation error, but I could fix it.) Haskell>ghc --make Temp.hs -o Temp.exe [1 of 1] Compiling Main ( Temp.hs, Temp.o ) Temp.hs:7:0: parse error (possibly incorrect indentation) Temp.hs is made using by jEdit on Window XP. I install Haskell Platform. code is ... import System.IO import System.Random let sentenceAry = [] main :: IO () main = do inh <- openFile "c:\\Documents and Settings\\shaegis\\inputFile.txt" ReadMode outh <- openFile "c:\\Documents and Settings\\shaegis\\outputFile.txt" WriteMode mainloop inh outh hClose inh hClose outh mainloop :: Handle -> Handle -> IO () mainloop inh outh = do ineof <- hIsEOF inh if ineof then do hPutStrLn outh inpStr return () else do inpStr <- hGetLine inh let sentenceAry = inpStr : [] mainloop inh outh Please, help me. Thank you. Sincerely, Sok Chang

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Haskell For C Programmers
by Brian Shannon 13 Dec '10

13 Dec '10

Does anyone have a working link for the Haskell For C Programmers book? I get a 404 from the link [1] which is on the wiki. [2][3] Thanks, Brian [1] http://www.haskell.org/~pairwise/intro/intro.html [2] http://www.haskell.org/haskellwiki/Learning_Haskell [3] http://www.haskell.org/haskellwiki/Meta-tutorial

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Enum/Bounded question
by Patrick LeBoutillier 13 Dec '10

13 Dec '10

Hi, I'm looking for a function to make a list of all the constructors in a type that derives both Enum and Bounded, i.e. enumAll :: (Bounded a, Enum a) => [a] enumAll = [minBound .. maxBound] Does this function exists in the standard modules? Patrick -- ===================== Patrick LeBoutillier Rosemère, Québec, Canada

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Re: [Haskell-beginners] Beginners Digest, Vol 30, Issue 17
by Russ Abbott 13 Dec '10

13 Dec '10

Is there no way to make the class approach (or something like it) work? That's how I would do it in Java--define the component as an interface as far as the structure is concerned and then define the component itself to implement the interface. * -- Russ* On Sun, Dec 12, 2010 at 3:00 AM, <beginners-request(a)haskell.org> wrote: > Send Beginners mailing list submissions to > beginners(a)haskell.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://www.haskell.org/mailman/listinfo/beginners > or, via email, send a message with subject or body 'help' to > beginners-request(a)haskell.org > > You can reach the person managing the list at > beginners-owner(a)haskell.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Beginners digest..." > > > Today's Topics: > > 1. Re: Linking modules (Brent Yorgey) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Sat, 11 Dec 2010 15:37:23 -0500 > From: Brent Yorgey <byorgey(a)seas.upenn.edu> > Subject: Re: [Haskell-beginners] Linking modules > To: beginners(a)haskell.org > Message-ID: <20101211203723.GB9265(a)seas.upenn.edu> > Content-Type: text/plain; charset=iso-8859-1 > > On Sat, Dec 11, 2010 at 08:56:23PM +0100, Chadda? Fouch? wrote: > > On Sat, Dec 11, 2010 at 7:37 PM, Russ Abbott <russ.abbott(a)gmail.com> > wrote: > > > I have two modules Structure and Component. ?Module Structure defines > > > ?? ? data Structure = Component ... > > > Module Component defines > > > ?? ?data Component = ... > > > I would like Structure to import Component. ?But Component > > > includes?functions?that take a Structure as an argument. So I have (or > would > > > like) something like this organization. > > > > > > [snip] > > > > > > The functions in Component are really very Component related and should > not > > > be moved to Structure. So how can I set up this circular relationship? > > > > GHC allows you to compile mutually recursive modules, see > > > http://www.haskell.org/ghc/docs/latest/html/users_guide/separate-compilatio… > > for how to do it. > > Yes, this is possible, but it has always seemed sort of fragile and > ugly to me. Another suggestion is to put the definitions of the > Structure and Component data types into a separate module called > Types, and then import Types into both the Structure module (which > defines functions over Structures) and the Component module (which > defines functions over Components). Then no circularity is needed. > > -Brent > > > > ------------------------------ > > _______________________________________________ > Beginners mailing list > Beginners(a)haskell.org > http://www.haskell.org/mailman/listinfo/beginners > > > End of Beginners Digest, Vol 30, Issue 17 > ***************************************** >

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If I only had a brain
by Amy de Buitléir 12 Dec '10

12 Dec '10

I have a class with some functions that have type signatures of the form (RandomGen g) => some parameter types -> RandT g (State [Neuron]) something For example: stimulate :: (RandomGen g) => Int -> [Double] -> RandT g (State [Neuron]) () That "RandT g (State [Neuron])" is my implementation of a "brain", so I'd like to call it that. I tried: data (RandomGen g) => Brain g a = RandT g (State [Neuron]) a But I got this error: `State [Neuron]' is not applied to enough type arguments Expected kind `?', but `State [Neuron]' has kind `* -> *' In the type `State [Neuron]' In the definition of data constructor `RandT' In the data type declaration for `Brain' Do I need higher ranked types or existential types in order to do that? Or am I going about this the wrong way? Thank you in advance, Amy

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