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Re: [Haskell-beginners] problem cabal install'ing hmatrix
by Alberto Ruiz 27 Apr '09

27 Apr '09

Hi Erik, Probably a dependency not mentionend in extra-libraries is missing. There is not a standard way to link -llapack. For instance, in Ubuntu/Debian we only need gsl and lapack: $ ld -lgsl -llapack ld: warning: cannot find entry symbol _start; not setting start address This means that everything is ok, but in other systems we may also need some of -l[gsl]cblas, -lgfortran, or -lf77blas, -latlas, -lgcc_s, etc. Try to find the correct libraries with $ ld -lgsl -llapack -lgslcblas or other combinations, and modify the extra-libraries field in hmatrix.cabal. In any case, I will try to add cabal flags to cover common situations. (There is also a possible issue with ghc-6.8 that must be fixed, but the library should work ok with 6.10). Alberto PS: I CC the list for reference. Erik Quaeghebeur wrote: > Alberto, > > Original message: >>> >>> $ cabal install hmatrix >>> Resolving dependencies... >>> Configuring hmatrix-0.5.1.1... >>> Preprocessing library hmatrix-0.5.1.1... >>> running dist/build/Numeric/GSL/Special/Internal_hsc_make failed >>> command was: dist/build/Numeric/GSL/Special/Internal_hsc_make >>> > dist/build/Numeric/GSL/Special/Internal.hs >>> cabal: Error: some packages failed to install: >>> hmatrix-0.5.1.1 failed during the building phase. The exception was: >>> exit: ExitFailure 1 >>> >>> What should I do to diagnose/resolve this problem? > > On Tue, 21 Apr 2009, Alberto Ruiz wrote: >> >> Erik, do you have the same problem with a previous version? >> >> cabal install hmatrix-0.5.0.1 > > Thanks for your (speedy) reply. Yes it gives the same problem: > > $ cabal install hmatrix-0.5.0.1 > Resolving dependencies... > Configuring hmatrix-0.5.0.1... > Preprocessing library hmatrix-0.5.0.1... > running dist/build/Numeric/GSL/Special/Internal_hsc_make failed > command was: dist/build/Numeric/GSL/Special/Internal_hsc_make >> dist/build/Numeric/GSL/Special/Internal.hs > cabal: Error: some packages failed to install: > hmatrix-0.5.0.1 failed during the building phase. The exception was: > exit: ExitFailure 1 > > Also, suggested by Heinrich Apfelmus: > > $ cabal install hmatrix --verbose > /usr/bin/ghc --numeric-version > looking for package tool: ghc-pkg near compiler in /usr/bin > found package tool in /usr/bin/ghc-pkg > /usr/bin/ghc-pkg --version > /usr/bin/ghc --supported-languages > Reading installed packages... > /usr/bin/ghc-pkg list > Reading available packages... > Resolving dependencies... > selecting hmatrix-0.5.1.1 (hackage) and discarding hmatrix-0.1.0.0, > 0.1.1.0, > 0.2.0.0, 0.2.1.0, 0.3.0.0, 0.4.0.0 and 0.5.0.1 > selecting base-3.0.1.0 (installed) > selecting rts-1.0 (installed) > selecting storable-complex-0.2 (installed or hackage) and discarding > storable-complex-0.1 > selecting haskell98-1.0.1.0 (installed or hackage) and discarding > haskell98-1.0 > selecting process-1.0.0.0 (installed or hackage) and discarding > process-1.0.1.1 > selecting unix-2.3.0.0 (installed or hackage) and discarding unix-2.0, > 2.2.0.0, 2.3.1.0 and 2.3.2.0 > selecting directory-1.0.0.0 (installed or hackage) and discarding > directory-1.0.0.3 > selecting filepath-1.1.0.0 (installed or hackage) and discarding > filepath-1.0, > 1.1.0.1 and 1.1.0.2 > selecting array-0.1.0.0 (installed or hackage) and discarding array-0.2.0.0 > selecting QuickCheck-1.2.0.0 (installed or hackage) and discarding > QuickCheck-1.0, 1.1.0.0, 2.1 and 2.1.0.1 > selecting random-1.0.0.0 (installed or hackage) and discarding > random-1.0.0.1 > selecting old-time-1.0.0.0 (installed or hackage) and discarding > old-time-1.0.0.2 > selecting old-locale-1.0.0.0 (installed or hackage) and discarding > old-locale-1.0.0.1 > selecting HUnit-1.2.0.3 (installed or hackage) and discarding HUnit-1.1, > 1.2.0.0, 1.2.0.1 and 1.2.0.2 > In order, the following would be installed: > hmatrix-0.5.1.1 (new package) > hmatrix-0.5.1.1 has already been downloaded. > Extracting > /home/equaeghe/.cabal/packages/hackage.haskell.org/hmatrix/0.5.1.1/hmatrix-0.5.1.1.tar.gz > > to /tmp/hmatrix-0.5.1.16320... > Configuring hmatrix-0.5.1.1... > Flags chosen: unsafe=False, accelerate=False, mkl=False, splitbase=True > Dependency HUnit -any && ==1.2.0.3: using HUnit-1.2.0.3 > Dependency QuickCheck -any && ==1.2.0.0: using QuickCheck-1.2.0.0 > Dependency array -any && ==0.1.0.0: using array-0.1.0.0 > Dependency base >=3 && ==3.0.1.0: using base-3.0.1.0 > Dependency haskell98 -any && ==1.0.1.0: using haskell98-1.0.1.0 > Dependency storable-complex -any && ==0.2: using storable-complex-0.2 > Using Cabal-1.6.0.3 compiled by ghc-6.8 > Using compiler: ghc-6.8.2 > Using install prefix: /home/equaeghe/.cabal > Binaries installed in: /home/equaeghe/.cabal/bin > Libraries installed in: /home/equaeghe/.cabal/lib/hmatrix-0.5.1.1/ghc-6.8.2 > Private binaries installed in: /home/equaeghe/.cabal/libexec > Data files installed in: /home/equaeghe/.cabal/share/hmatrix-0.5.1.1 > Documentation installed in: /home/equaeghe/.cabal/share/doc/hmatrix-0.5.1.1 > No alex found > Using ar found on system at: /usr/bin/ar > No c2hs found > No cpphs found > No ffihugs found > Using gcc version 4.3.2 found on system at: /usr/bin/gcc > Using ghc version 6.8.2 found on system at: /usr/bin/ghc > Using ghc-pkg version 6.8.2 found on system at: /usr/bin/ghc-pkg > No greencard found > No haddock found > No happy found > No hmake found > Using hsc2hs version 0.66 found on system at: /usr/bin/hsc2hs > No hscolour found > No hugs found > No jhc found > Using ld found on system at: /usr/bin/ld > No nhc98 found > Using pkg-config version 0.23 found on system at: /usr/bin/pkg-config > Using ranlib found on system at: /usr/bin/ranlib > Using strip found on system at: /usr/bin/strip > Using tar found on system at: /bin/tar > /usr/bin/gcc /tmp/6320.c -o /tmp/6320 -D__GLASGOW_HASKELL__=608 -I. > -DFINIT -I/usr/lib64/ghc-6.8.2/lib/process-1.0.0.0/include > -I/usr/lib64/ghc-6.8.2/lib/unix-2.3.0.0/include > -I/usr/lib64/ghc-6.8.2/lib/directory-1.0.0.0/include > -I/usr/lib64/ghc-6.8.2/lib/old-time-1.0.0.0/include > -I/usr/lib64/ghc-6.8.2/lib/base-3.0.1.0/include > -I/usr/lib64/ghc-6.8.2/include -lgsl -llapack > Creating dist/build (and its parents) > Creating dist/build/autogen (and its parents) > Preprocessing library hmatrix-0.5.1.1... > Creating dist/build/Numeric/GSL/Special (and its parents) > /usr/bin/hsc2hs --cc=/usr/bin/gcc --ld=/usr/bin/gcc > --cflag=-D__GLASGOW_HASKELL__=608 --cflag=-DFINIT --lflag=-lgsl > --lflag=-llapack > --cflag=-I/usr/lib64/ghc-6.8.2/lib/process-1.0.0.0/include > --cflag=-I/usr/lib64/ghc-6.8.2/lib/unix-2.3.0.0/include > --cflag=-I/usr/lib64/ghc-6.8.2/lib/directory-1.0.0.0/include > --cflag=-I/usr/lib64/ghc-6.8.2/lib/old-time-1.0.0.0/include > --cflag=-I/usr/lib64/ghc-6.8.2/lib/base-3.0.1.0/include > --cflag=-I/usr/lib64/ghc-6.8.2/include > --lflag=-L/home/equaeghe/.cabal/lib/storable-complex-0.2/ghc-6.8.2 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/haskell98-1.0.1.0 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/process-1.0.0.0 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/unix-2.3.0.0 --lflag=-lutil > --lflag=-ldl --lflag=-L/usr/lib64/ghc-6.8.2/lib/directory-1.0.0.0 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/filepath-1.1.0.0 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/array-0.1.0.0 > --lflag=-L/home/equaeghe/.cabal/lib/QuickCheck-1.2.0.0/ghc-6.8.2 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/random-1.0.0.0 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/old-time-1.0.0.0 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/old-locale-1.0.0.0 > --lflag=-L/home/equaeghe/.cabal/lib/HUnit-1.2.0.3/ghc-6.8.2 > --lflag=-L/usr/lib64/ghc-6.8.2/lib/base-3.0.1.0 > --lflag=-L/usr/lib64/ghc-6.8.2 --lflag=-lm --lflag=-lgmp --lflag=-ldl > --lflag=-lrt -o dist/build/Numeric/GSL/Special/Internal.hs > lib/Numeric/GSL/Special/Internal.hsc > running dist/build/Numeric/GSL/Special/Internal_hsc_make failed > command was: dist/build/Numeric/GSL/Special/Internal_hsc_make >> dist/build/Numeric/GSL/Special/Internal.hs > cabal: Error: some packages failed to install: > hmatrix-0.5.1.1 failed during the building phase. The exception was: > exit: ExitFailure 1 > > I still have to test the version in the Gentoo Haskell overlay. That > should work (but then I wouldn't use cabal install). > > Regards, > > Erik >

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Re: [Haskell-beginners] generating the set of all finite-valued [...]
by Erik Quaeghebeur 27 Apr '09

27 Apr '09

> 2009/4/23 Erik Quaeghebeur <equaeghe(a)nospammail.net> > >> I'd like to lazily generate the set of all {-1,0,1}-valued functions on >> {'a','b','c'}? How should I best approach this. I was thinking about >> generalizing the power set definition >> >> powerset :: [a] -> [[a]] >> powerset = filterM (const [True, False]) >> >> but clearly don't know enough about filterM and the like to do it this way. >> >> Erik On Mon, 27 Apr 2009, Haroldo Stenger wrote: > > i got curious about this one. Can you elaborate ? Well, elaborate about my ultimate goal, or about the powerset definition? The latter I can tell little about, I found it on-line and recognized it as a starting point. The former: generalizing http://users.ugent.be/~equaeghe/constraints.php to previsions from probabilities; C++ is a little too heavy, so I thought I'd try out Haskell. Erik

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data constructors
by Michael Mossey 27 Apr '09

27 Apr '09

This is probably a side-effect of coming from OO land, but I'm confused about how to organize my data. Let's say I want to model musical information that occurs on a single staff. A staff consists of a list of StaffItem which occurs at specific times. type Time = Double type Staff = [(Time,StaffItem)] A StaffItem can be one of several things. Let's say it can be a "chord" or a "control". I might like to define Chord and Control first: data Chord = Chord { duration :: Double, notes :: [Note] } data Control = DynamicMark Int | TempoMark Int Okay, so now I want to express the idea a StaffItem can be a Chord or a Control. data StaffItem = StaffItemChord Chord | StaffItemControl Control My problem is the awkward need for separately named constructors "StaffItemChord" and "StaffItemControl". Is there a better way? (Is this even right?) Thanks, Mike

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music layout problem
by Michael Mossey 25 Apr '09

25 Apr '09

I'm continuing to work on this music layout problem, and I'm trying another angle. A page of music is made of many individual symbols and graphical items like lines and arcs. I decided to call a drawable symbol/item a Grapheme. so type MusicPage = [Grapheme] The program also maintains the more fundamental description of music in conceptual form---that is, notes, chords, time signatures, tempo indications, etc. I decided to call bits of information about music Datemes. type MusicScore = [Dateme] A function to lay out a musical page would have this signature: layoutPage :: [Dateme] -> [Grapheme] Now let's think about the structure of a page of music for a moment. It's made of *systems*, which are groups of notes read from left to right. A page consists of a number of systems stacked vertically (like a page of text has lines of text stacked vertically). The layout algorithm will fit as many systems as it can into a page. When it runs out of space, it will stop (even if there are Dateme left). A layout algorithm in imperative pseudocode would look something like: - initialize the list remainingDateme to the input list of Dateme - loop - looking at the list of remainingDateme, make a system - try to fit the system to the page - if the system doesn't fit, break out of the loop - add the system to the page - drop the used Dateme from remainingDateme - if remainingDateme is empty, break out of the loop - go to top of loop I tried to write this in Haskell, and it seem awkward. It would be something like: -- layout page, produce list of Grapheme and also list of -- unused Dateme layoutPage :: PageDimensions -> [Dateme] -> ( [Grapheme], [Dateme] ) layoutPage dim dateme = layoutPage' dim [] dateme layoutPage' :: PageDimensions -> [Grapheme] -> [Dateme] -> ( [Grapheme], [Dateme] ) layoutPage' dim graphemeSoFar [] = ( graphemeSoFar, [] ) layoutPage' dim graphemeSoFar remainingDateme = let ( newGrapheme, remainingDateme', dim' ) = layoutSystem dim remainingDateme in if null newGrapheme then ( graphemeSoFar, remainingDateme ) else layoutPage' dim' (graphemeSoFar ++ newGrapheme) remainingDateme' We assume this is defined elsewhere: -- layoutSystem takes as input the current page dimensions (think of -- the "current page dimensions" as the room *remaining* on the page), -- and a list of Dateme, and returns the triple: -- ( [Grapheme] for the new system, or null list if no additional system -- can fit on the page, -- remaining [Dateme] that are not consumed, -- new page dimensions ) layoutSystem :: PageDimensions -> [Dateme] -> ( [Grapheme], [Dateme], PageDimensions )

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parser comparison question
by Walck, Scott 25 Apr '09

25 Apr '09

I've been comparing Graham Hutton's simple parser with Parsec. Here is some example code. -- Comparison of Hutton's simple parser with Parsec -- Hutton's simple parser is available at -- http://www.cs.nott.ac.uk/~gmh/Parsing.lhs -- Hutton simple parser called H -- Parsec called P import qualified Parsing as H import qualified Text.ParserCombinators.Parsec as P exH = H.parse (H.string "hi") "hiho" exP = P.parse (P.string "hi") "" "hiho" charH = H.parse (H.char 'a' H.+++ H.char 'b') "bbb" charP = P.parse (P.char 'a' P.<|> P.char 'b') "" "bbb" choiceH = H.parse (H.string "hoo" H.+++ H.string "ho") "hono" choiceP1 = P.parse (P.string "bb" P.<|> P.string "ba") "" "bbb" choiceP2 = P.parse (P.string "ba" P.<|> P.string "bb") "" "bbb" choiceP22 = P.parse (P.try (P.string "ba") P.<|> P.string "bb") "" "bbc" I am interested if anyone could comment on the design of the Parsec 'try' function. For example, choiceP2 fails and returns Left error, while choiceP22 succeeds. Hutton's simple parser doesn't need try. It seems so simple and elegant. I'm wondering why Parsec requires me to use 'try' for a string parse that might fail. Thanks, Scott Scott N. Walck Associate Professor of Physics Lebanon Valley College

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WWAAA... I hate monads
by Daniel Carrera 25 Apr '09

25 Apr '09

I hate monads. I love 90% of Haskell. The functional stuff is beautiful, easy to understand, crystal clear, elegant, etc. But I'm having a mighty hard time getting my head around monads. Consider the following explanation of a monad: "A monad is represented as a type constructor (call it m), a function that builds values of that type (a -> m a), and a function that combines values of that type with computations that produce values of that type to produce a new computation for values of that type". 1) I know what a type is, but not a "type constructor". I don't normally think of an Int or even a complex type as being "constructed" except in the sense of OOP which I know is not what the author means. 2) Just *read* the paragraph... "a type constructor, a function that builds value of that type, and a function that combines values of that type with computations that produce values of that type to produce a computation of values of that type" Ugh.... Can anyone recommend a simple and clear explanation of monads? You can assume that I know basic math and basic Haskell syntax. So, for example, "a -> b" is much more clear than "a function that takes input of one type and has an output of a different type". Any help would be appreciated. Daniel.

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doing state right
by Floptical Logic 24 Apr '09

24 Apr '09

I am using a PPM library to generate a square image where each white pixel represents a prime number. The PPM library takes a function (Int -> Int -> Colour) to create the image. This interface isn't ideal but it is what I have to work with. I am convinced that using a sieve is faster than testing every pixel in the image for primality, but the (Int -> Int -> Colour) interface makes this awkward. The code below attempts to treat the list of prime numbers as a stack via global mutable state, popping the head whenever the pixel is prime. Obviously this is not idiomatic Haskell. What is the correct approach of dealing with state here? Thanks for reading. import ONeillPrimes import PPM6 import Colour import Data.IORef import System.IO.Unsafe limit = 2000 slimit = limit*limit primeList = takeWhile (<=slimit) primes p :: IORef [Int] p = unsafePerformIO (newIORef primeList) pcol n = unsafePerformIO $ do xs <- readIORef p if null xs then return black else if n == head xs then do writeIORef p (tail xs) return white else return black main = quick_ppm "foo.ppm" (\i j -> pcol ((i-1)*limit+j)) limit limit -- quick_ppm :: FilePath -> (Int -> Int -> Colour.Colour) -> Int -> Int -> IO ()

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computation vs function
by Daniel Carrera 23 Apr '09

23 Apr '09

Hello, I have finished the tutorial at http://ertes.de/articles/monads.html and my understanding of monads has increased greatly. I still need to cement some concepts in my mind. What exactly is the difference between a computation and a function? Monads revolve around computations, so I'd like to understand computations better. Thanks for the help. Daniel.

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Type families with kind * -> *
by Marco Túlio Gontijo e Silva 23 Apr '09

23 Apr '09

Hello, I read the type families example at http://haskell.org/haskellwiki/GHC/Indexed_types and I wanted to do something similar to the Collects example, but using a type of kind * -> *: > class StateFunctor sf where > type SFMonad sf > type SFValue sf > sfmap :: (SFValue sf -> SFValue sf) -> sf -> SFMonad sf () I wrote the instance as: > instance StateFunctor (ListStore a) where > type SFMonad (ListStore a) = IO > type SFValue (ListStore a) = a > sfmap function listStore > = listStoreGetSize listStore >>= listStoreSfmap function listStore > listStoreSfmap :: (a -> a) -> ListStore a -> Int -> IO () > listStoreSfmap _function _listStore 0 = [] > listStoreSfmap function listStore size > = listStoreGetValue listStore index > >>= listStoreSetValue listStore index . function > >> listStoreSfmap function listStore index > where > index :: Int > index = pred size I'm getting: DistroCreator/GUI/List.hs:51:47: Kind error: `SFMonad' is applied to too many type arguments In the type `SFMonad sf ()' In the type `sf -> SFMonad sf ()' In the type `(SFValue sf -> SFValue sf) -> sf -> SFMonad sf ()' Failed, modules loaded: none. How can I use type families with types * -> *? Greetings. -- marcot http://marcot.iaaeee.org/

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Help with types
by Daniel Carrera 23 Apr '09

23 Apr '09

Hi, I want to make a simple "average" function: average xs = (sum xs)/(length xs) When I try that on ghci I get the following error: No instance for (Fractional Int) arising from a use of `/' at <interactive>:1:17-36 Possible fix: add an instance declaration for (Fractional Int) In the expression: (sum xs) / (length xs) In the definition of `average': average xs = (sum xs) / (length xs) Ok, so 'sum' is of type (Num a => [a] -> a), length is of type ([a] -> Int) and (/) is of type (Fractional a => a -> a -> a). Can someone explain how I can "add an instance declaration" to my function so as to make all these types compatible? Thanks, Daniel.

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