January 2009 - Haskell-Cafe

GLUT (glutGet undefined reference)
by Paul Keir 22 Jan '09

22 Jan '09

Hi all, I was hoping to introduce my old pal OpenGL with my new chum, Haskell. I used cabal to install GLUT on my 64-bit Ubuntu machine with GHC 6.8.2 (installed via apt-get/synaptic). I followed the wiki OpenGLTutorial1 until: ghc -package GLUT HelloWorld.hs -o HelloWorld at which point my screen is filled with errors. The errors begin with: /home/paul/.cabal/lib/GLUT-2.1.1.2/ghc-6.8.2/libHSGLUT-2.1.1.2.a(Begin.o): In function `szEn_info': (.text+0x26c): undefined reference to `glutGet' This surprised me a little because I've already seen these same errors recently on two separate Windows boxes. Somehow I'd got the idea it was (on Windows) due to installing from a binary; though I guess the story is the same with apt-get. Should I look for an apt-get switch to reinstall GHC from source instead? Regards, Paul

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tensor product of dynamic-sized bits
by Ahn, Ki Yung 22 Jan '09

22 Jan '09

For some reasons, I am trying to write a small Haskell code for tensor products (See http://en.wikipedia.org/wiki/Tensor_product) of bits, which can expand or shrink their size and dimension as needed. Has anyone already done similar or more general work before? If so, I'd be happy use/consult that and cite the work. Otherwise, I should think about cleaning up and packaging this as a library. My code is like this right now: > data Bits = O -- all 1 bits of any size and dimension > | I -- all 0 bits of any size and dimension > | Bs [Bits] -- row of bits possibly nested > | Rep Bits -- repeating of bits (e.g. O = Rep O = Bs [O,O]) > deriving (Eq,Show) bitwise-and > O .& _ = O > _ .& O = O > (Rep O) .& _ = O > _ .& (Rep O) = O > (Bs (O:xs)) .& _ | all (O==) xs = O > _ .& (Bs (O:xs)) | all (O==) xs = O > I .& y = y > x .& I = x > (Rep I) .& y = y > x .& (Rep I) = x > (Bs (I:xs)) .& y | all (I==) xs = y > x .& (Bs (I:ys)) | all (I==) ys = x > (Bs xs) .& (Bs ys) = reduce $ Bs (zipWith (.&) xs ys) > (Rep x) .& (Bs ys) = reduce $ Bs (xs .&. ys) where xs=repeat x > (Bs xs) .& (Rep y) = reduce $ Bs (xs .&. ys) where ys=repeat y > (Rep x) .& (Rep y) = reduce $ Rep (x .& y) > > (.&.) = zipWith (.&) bitwise-or > O .| y = y > x .| O = x > (Rep O) .| y = y > x .| (Rep O) = x > (Bs (O:xs)) .| y | all (O==) xs = y > x .| (Bs (O:ys)) | all (O==) ys = x > I .| _ = I > _ .| I = I > (Rep I) .| _ = I > _ .| (Rep I) = I > (Bs (I:xs)) .| _ | all (I==) xs = I > _ .| (Bs (I:ys)) | all (I==) ys = I > (Bs xs) .| (Bs ys) = reduce $ Bs (xs .|. ys) > (Rep x) .| (Bs ys) = reduce $ Bs (xs .|. ys) where xs=repeat x > (Bs xs) .| (Rep y) = reduce $ Bs (xs .|. ys) where ys=repeat y > (Rep x) .| (Rep y) = reduce $ Rep (x .| y) > > (.|.) = zipWith (.|) tensor product > O .* _ = O > _ .* O = O > (Rep O) .* _ = O > _ .* (Rep O) = O > (Bs (O:xs)) .* _ | all (O==) xs = O > _ .* (Bs (O:ys)) | all (O==) ys = O > I .* I = I > I .* (Rep y) = I .* y > (Rep I) .* y = I .* y > (Bs (I:xs)) .* y | all (I==) xs = I .* y > I .* y = reduce $ Rep y > x .* (Rep I) = x .* I > x .* (Bs (I:xs)) | all (I==) xs = x .* I > x .* I = x > (Bs xs) .* (Bs ys) = reduce $ Bs (xs .*. ys) > (Bs xs) .* (Rep y) = reduce $ > Bs (map (reduce . Rep) $ xs .*. [y]) > (Rep x) .* y = reduce $ Rep (x .* y) > > [] .*. _ = [] > (x:xs) .*. ys = (reduce $ Bs [x .* y | y<-ys]) : (xs .*. ys) reducing from Bs [O,O,..] to O and from Bs [I,I,..] to I > reduce (Bs (x:xs)) | all (x==) xs = x > reduce (Rep x@(Rep _)) = x > reduce x = x Some example run on Hugs: Main> Bs [I,O] Bs [I,O] Main> Bs [I,O] .| Bs [O,Bs [I,I,I,I] .* Bs [I,O,O,O,O]] Bs [I,Rep (Bs [I,O,O,O,O])] Main> Bs [I,O] .| Bs [O, Bs [I,I,I,I] .* Bs [I,O,O,O,O]] .| Bs [O, Bs [I,O,O,O] .* Bs [I,I,I,I,I]] Bs [I,Bs [I,Bs [I,O,O,O,O],Bs [I,O,O,O,O],Bs [I,O,O,O,O]]] Main> Bs [I,O] .| Bs [O, Bs [I,I,I,I] .* Bs [I,O,O,O,O]] .| Bs [O, Bs [I,O,O,O] .* Bs [I,I,I,I,I]] .| Bs [O, Bs [O,I,I,O] .* Bs [O,I,I,O,O]] Bs [I,Bs [I,Bs [I,I,I,O,O],Bs [I,I,I,O,O],Bs [I,O,O,O,O]]] Main> Bs [I,O] .| Bs [O, Bs [I,I,I,I] .* Bs [I,O,O,O,O]] .| Bs [O, Bs [I,O,O,O] .* Bs [I,I,I,I,I]] .| Bs [O, Bs [O,I,I,O] .* Bs [O,I,I,O,O]] .| Bs [O, Bs [O,I,I,I] .* Bs [O,O,O,I,I]] Bs [I,Bs [I,I,I,Bs [I,O,O,I,I]]] Main> Bs [I,O] .| Bs [O, Bs [I,I,I,I] .* Bs [I,O,O,O,O]] .| Bs [O, Bs [I,O,O,O] .* Bs [I,I,I,I,I]] .| Bs [O, Bs [O,I,I,O] .* Bs [O,I,I,O,O]] .| Bs [O, Bs [O,I,I,I] .* Bs [O,O,O,I,I]] .| Bs [O, Bs [O,O,I,I] .* Bs [O,I,I,O,O]] I

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Re: [Haskell-cafe] A pattern type signature cannot bind scoped type variables `t'
by George Pollard 22 Jan '09

22 Jan '09

On Mon, 2009-01-12 at 20:24 -0200, rodrigo.bonifacio wrote: > Hi all, > > I'm trying to build a library that has the following code: > > hasTypeOf (TermRep (dx,_,_)) (x::t) > = ((fromDynamic dx)::Maybe t) > Could you do something like this? Enforce the types with a signature: hasTypeOf :: (Typeable t) => Dynamic -> t -> Maybe t hasTypeOf x _ = fromDynamic x > hasTypeOf (toDyn (2::Int)) (undefined::Integer) Nothing > hasTypeOf (toDyn (2::Int)) (undefined::Int) Just 2 Or if you just want boolean result: hasTypeOf x y = typeOf y == dynTypeRep x

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1000 libraries
by Don Stewart 21 Jan '09

21 Jan '09

We've done it! http://hackage.haskell.org/cgi-bin/hackage-scripts/stats 274 users have uploaded 3161 versions of 1000 packages. Thanks everyone who has written a library or tool or app and released it, for making hackage and cabal a success! This has gone further, perhaps more than anything else, towards making it possible to use Haskell in industry. The lucky 1000th package is: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/threadPool-0.1 threadPool: Runs other programs in the manner of a thread pool Takes a single, optional argument which is the number of threads (the default is three). Give it the commands to run, one per line, through standard input. Author Brian Jaress Now, onto 10k libraries! -- Don

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Re: Why monoids will abide...
by Andrzej Jaworski 21 Jan '09

21 Jan '09

Monads are monoids in categories of functors C -> C Arrows are monoids in subcategories of bifunctors (C^op) x C -> C Trees are a playing ground for functors in general:-)

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Applicative/Monad for Either
by Tony Morris 21 Jan '09

21 Jan '09

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 In the code below, the Applicative instance accumulates on the Left constructor using Monoid/mappend. Is it possible to write an equivalent Monad such that ap = (<*>) ? I'm finding difficulty in proving to myself either way. import Control.Monad.Instances import Control.Applicative import Data.Monoid newtype Z e a = Z { either :: Either e a } instance Functor (Z e) where fmap f (Z e) = Z (f `fmap` e) instance (Monoid e) => Applicative (Z e) where pure = Z . Right (Z (Left e1)) <*> (Z (Left e2)) = Z (Left (e1 `mappend` e2)) (Z (Left e1)) <*> (Z (Right _)) = Z (Left e1) (Z (Right _)) <*> (Z (Left e2)) = Z (Left e2) (Z (Right f)) <*> (Z (Right a)) = Z (Right (f a)) instance (Monoid e) => Monad (Z e) where return = pure (Z e) >>= f = error "todo" -- ? - -- Tony Morris http://tmorris.net/ S, K and I ought to be enough for anybody. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFJd5vImnpgrYe6r60RAoUNAJ4jn0GfC6zsP9giPGop1ILExiHrLQCfSoc2 0QXf533sWb3HyrL0pQNjMww= =R36O -----END PGP SIGNATURE-----

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Haddock bug for strict unpacked fields?
by Stephan Friedrichs 21 Jan '09

21 Jan '09

Hi, using haddock-2.4.1 and this file: > module Test where > > data Test > = NonStrict Int > | Strict !Int > | UnpackedStrict {-# UNPACK #-} !Int The generated documentation looks like this: data Test Constructors NonStrict Int Strict !Int UnpackedStrict !!Int Note the double '!' in the last constructor. This is not intended behaviour, is it? //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr

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Existencial quantification and polymorphic datatypes
by Mauricio 21 Jan '09

21 Jan '09

Hi, I'm trying, without success, to understand the difference between existencial quantification and polymorphic datatypes. Can you give me a hint, or an example where one is valid and the other is not? Thanks, Maurício

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Re: [Haskell-cafe] haskell-src-meta Package
by Matt Morrow 21 Jan '09

21 Jan '09

Hi, I managed to miss not one, but two separate emails containing patches to haskell-src meta. My sincere apologies to those who've sent me patches. I'll be applying them among other improvement to src-meta and will update the package on hackage in short time (today :). Matt

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(no subject)
by Matt Morrow 21 Jan '09

21 Jan '09

Hi, I managed to miss not one, but two separate emails containing patches to haskell-src meta. My sincere apologies to those who've sent me patches. I'll be applying them among other improvement to src-meta and will update the package on hackage in short time (today :). Matt

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