October 2009 - Haskell-Cafe

dsl and gui toolkit
by Andrew U. Frank 07 Oct '09

07 Oct '09

thanks for the connection to the gui runner - it is interesting and worthwile, but a different approach. my approach is strictly declarative and does not describe sequences of process. it describes screens and links operations to buttons. then it takes inputs from the screen and runs the operations and posts the result on the screen. some operations open new screens etc. i started with the idea that ontologies describe the semantics of data in a static way; this should be (nearly) enough to create the user interface - which is all about semantics of the data. of course, you have to include in the ontology the semantics of the operations (as class with functions). the implementation is close to a reactive framework - adding a representation of all what is visible on the screen (the universer of discourse) in a format usable by the operations. then you have only to connect this 'universe of discourse' to the programs which operate on the data and post their reaction in the UoD and map the UoD to the screen the details are messy as i attempted to construct the internal data structures etc. as automatically as possible and with minimal designer input I did not use template haskell, yet, but will need to (i think). i am happy to share it with interested parties and hear the comments and perhaps somebody can help me with using templates to reduce the . it is IMHO not yet ready for posting in a library - but this is certainly the goal.

6 7

New to Haskell - List Comprehension Question
by Steven1990 07 Oct '09

07 Oct '09

Hi, I'm currently learning Haskell, and I've been trying to work out a function for the following problem for a couple of days now. I want to use a list comprehension method to change the first letter of a string to upper case, and the rest of the string to lower case. Eg: "heLLo" -> "Hello" As I'm trying to learn this, I would appreciate hints rather than the explicit solution if possible? I'm sure I'm close to a solution, I must be missing something though. Driving me crazy! My attempts are something similar to this: upperCase :: String -> String upperCase xs = [toUpper(x):toLower(xs) | x <- xs] I think 'toLower' expects a single character rather than the list which is one place I'm going wrong? Thanks in advance, Steven -- View this message in context: http://www.nabble.com/New-to-Haskell---List-Comprehension-Question-tp257941… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

5 4

Finally tagless - stuck with implementation of "lam"
by Günther Schmidt 07 Oct '09

07 Oct '09

Hi all, I'm playing around with finally tagless. Here is the class for my Syntax: class HOAS repr where lam :: (repr a -> repr b) -> repr (a -> b) app :: repr (a -> b) -> repr a -> repr b fix :: (repr a -> repr a) -> repr a let_ :: repr a -> (repr a -> repr b) -> repr b int :: Int -> repr Int add :: repr Int -> repr Int -> repr Int sub :: repr Int -> repr Int -> repr Int mul :: repr Int -> repr Int -> repr Int and here is one instance of that class for semantics. newtype I a = I { unI :: IO a } instance HOAS I where app e1 e2 = I (do e1' <- unI e1 e2' <- unI e2 return $ e1' e2') int i = I (putStrLn ("setting an integer: " ++ show i) >> return i) add e1 e2 = I (do e1' <- unI e1 e2' <- unI e2 putStrLn (printf "adding %d with %d" e1' e2') return $ e1' + e2') sub e1 e2 = I (do e1' <- unI e1 e2' <- unI e2 putStrLn (printf "subtracting %d from %d" e1' e2') return $ e1' - e2') mul e1 e2 = I (do e1' <- unI e1 e2' <- unI e2 putStrLn (printf "multiplying %d with %d" e1' e2') return $ e1' * e2') I'm stuck with the "lam" method, for 2 days now I've been trying to get it right, but failed. Is there a possibility that it isn't even possible? Günther

6 11

Re: [Haskell] ANNOUNCE: GPipe-1.0.0: A functional graphics API for programmable GPUs
by Petr Pudlak 07 Oct '09

07 Oct '09

Hi Tobias, (I'm completely new to GPU programming, so my question may be completely stupid or unrelated. Please be patient :-).) Some time ago I needed to perform some large-scale computations (searching for first-order logic models) and a friend told me that GPUs can be used to perform many simple computations in parallel. Could GPipe be used for such a task? I.e. to program some non-graphical, parallelized algorithm, which could be run on a GPU cluster? Thanks for your answer, Petr On Sun, Oct 04, 2009 at 08:32:56PM +0200, Tobias Bexelius wrote: > I'm proud to announce the first release of GPipe-1.0.0: A functional graphics > API for programmable GPUs. > > GPipe models the entire graphics pipeline in a purely functional, immutable > and typesafe way. It is built on top of the programmable pipeline (i.e. > non-fixed function) of OpenGL 2.1 and uses features such as vertex buffer > objects (VBO's), texture objects and GLSL shader code synthetisation to create > fast graphics programs. Buffers, textures and shaders are cached internally to > ensure fast framerate, and GPipe is also capable of managing multiple windows > and contexts. By creating your own instances of GPipes classes, it's possible > to use additional datatypes on the GPU. > > You'll need full OpenGL 2.1 support, including GLSL 1.20 to use GPipe. Thanks > to OpenGLRaw, you may still build GPipe programs on machines lacking this > support. > > The package, including full documentation, can be found at: > http://hackage.haskell.org/package/GPipe-1.0.0 > > Of course, you may also install it with: > cabal install gpipe > > > Cheers! > Tobias Bexelius > > ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ > kolla in resten av Windows LiveT. Inte bara e-post - Windows LiveT är mycket > mer än din inkorg. Mer än bara meddelanden

2 1

better way to do this?
by Michael Mossey 07 Oct '09

07 Oct '09

I'm looking for a hint to write the following code with less redundancy. I have a constructor called BoxBounds, and I want to make one with random values. randomBox :: IO BoxBounds randomBox = do x <- getStdRandom (randomR (-10,10)) y <- getStdRandom (randomR (-70,70)) t <- getStdRandom (randomR (5,10)) b <- getStdRandom (randomR (5,10)) l <- getStdRandom (randomR (5,10)) r <- getStdRandom (randomR (5,10)) return (BoxBounds x y l r t b)

16 28

Network.Curl and posting XML data
by Erik de Castro Lopo 07 Oct '09

07 Oct '09

Hi all, I need to do a HTTP post of XML data (Content-type == "text/xml") to a HTTP (eventually HTTPS) server and to retrieve both the response code and some returned XML data. I have had an extensive read of the haskell-curl docs: http://hackage.haskell.org/packages/archive/curl/1.3.5/doc/html/Network-Cur… as well as playing around with some code, but haskell-curl doesn't seem to support this. I've tried curlPost which along with not returning a response also insists on encoding my XML data as application/x-www-form-urlencoded which simply doesn't work. Anyone ben able to get something like this to work? Are there any alternatives to haskell-curl which will work for my application? Cheers, Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/

4 8

Dutch HUG: meeting next week (October 12th) in Utrecht
by Tom Lokhorst 07 Oct '09

07 Oct '09

I'd like to invite functional programmers in The Netherlands to the Dutch Haskell User Group [1, 2] meeting next Monday at 19:00. Each meeting I see new faces, so that's why I continue to send these invitations to several mailing lists; it's working! At this meeting we'll have two talks. Andres Löh will talk about lhs2TeX, a tool for typesetting Haskell code using LaTeX. Yaakov Nemoy will talk about the status of Haskell packaging in Fedora and how to do it yourself. Like last month, the meeting will be in the Booth Hall [3] of the Utrecht University Library. There's free car parking [4] at the library, and it's easily accessible by bike and bus [5]. Unfortunately, I won't be able to attend, but I hope you will! - Tom Lokhorst [1]: http://www.haskell.org/haskellwiki/Dutch_HUG [2]: http://groups.google.com/group/dutch-hug [3]: http://www.uu.nl/EN/library/contact/university_library/zaalverhuur/Pages/de… [4]: http://www.uu.nl/EN/library/contact/university_library/Parkeren/Pages/defau… [5]: http://www.uu.nl/EN/library/contact/university_library/plattegrondenrou/Pag…

1 0

Creating an alias for a function
by michael rice 07 Oct '09

07 Oct '09

How do I create an alias for a function, like giving CAR the same functionality as HEAD. I know I can do it by creating a definition (see below), but is there a better way, like Scheme's (define head car) car :: [a] -> a car x = head x The reason for doing this is to more closely mirror legacy code. Michael

8 13

RETURNED MAIL: SEE TRANSCRIPT FOR DETAILS
by svens＠gmx.de 07 Oct '09

07 Oct '09

נ��55��7y�9(ߖ��! ��B��уN�(�a� h\H D�D Ĵ��׏��ɔ�2Qlo�q� ]u��\$`�.�,j~��E�M�{� ��;�{>v'�g��뱤�t��3D磻�y�b �hY((�[2TUm�1��[P�3�K��u��B�Uݠ�a�C�<�#�0�С�~�ŉ�|��8�l�~'Rf��("�LG�ǜ�2y��2��Zݑ�$Zss��Y51��V:�j�� [g1��9Z4o2��s�� laۛ�H!�ߤ4�&W�hM�4�S��"z��o}d��l:qi�D�H�$mRm3Vf�WG��'� �>��]�tA�� :Q�8��ɪ��yT[�!�)鶞i��3Go�R��㯂��R�.<�<ɗ��^e��.��.�b��Cj�� _��-3]��"��Q®��o_�"S_&�3U��"��i��3nҖ�h�B�j�3�ٺ�J �U�t�B��|<�m�y�XE� /a>"�>��e��Ȏe]��ʂ��嚕��Ei��Ocf��I$�דcM3��Ս5E�7��Y�$gV[�0~�Fo��4CA��/�h'z�BؿO��GM ��o, �]�[.�:�u'K�>Z��T�Eb̈́"ᧈk��9��_i\�!L�k�!9��Ki�H�탊e$&K�.*u��-�� f ��&_j\��p�"�Eq:<b0 M'�l�t�C��<�_��IV蓲QW��A��q� ��4��p��`��Z.'t[��c?��z�#�/[��u��hG��HG�� ą?iC�4 R2[X~�;,��12:P2 �U\i��*n�%�{ �"ZX^�W�Ⱦ� M��QZ��)�]�cՅi�X�`��S��h��LbI��#$cY~ЁB�k�E��*�dXK��~X�DļHRZɜ��SԨϘ�P�L�� :�4?�V�3<��9E�3�ϟY�(K��/�Y��ShD��ց��E��R�w}�a|e�&-��Q_P�^j��6�W}8*m��-��ڃ�ck3�/�,?�%h�h�2 ѝY�О��C��w��5�X� �MK U<�#�2<a T<zRe��91��>k�Ϛ� f�?u�� 6x8Y8F'�:> �0Zq�fh��A��U߲��7(�E�t�r(G��O �[8)mk6�_�$d��^k8�K��W젧�u/��҆�So�z6�[آ��r��f��u"�ae��-� �Oc��a72Z�jwz��gq�$�Q�~�-{��:g��!SX 2c�(��Zm~��Ǘ��U��K?�s�;�/G&��(��|�:��Rd�{��K��>��$N�e�EW9��0�qa��Jsy�!Ix�� wA#�[wq\o٘.��1�ZhIT� n8˖�I�� :��k<��`�Z�Ơ��#9��͜߆��L�jb��gM�e��R1N��ؘ͐�pN 6��o�;�X��O\/��d��*�L��ʁ ��Dݸ�&:$0��[a�x��vğC'Dua��ҕ�k �w� 2C�B��D�R�Va9]��#zn��n-K|�k�%��:�I��9J� 1:��ѡ>'�9�^��"Jo�~�dΐV�US��x}��B�lō�궼�^��\�ghM��pP\�#d�Z� ��9��*��k�#�P�d��*'��-�R�� iC�m�œﵜM�>`<n/E�� 8��;u��l�� CH�pմrHl��^w��B��_��e��,��iyv�c�3�vƵ�-L%�.��t~��W��Mo��7�-4�$�J��G"]�WS��8âp��9�}��A"�O�6N*��J��&.�:R�� /�uu�捎KϬ�(�EoS�To�tF'�zLz��:�o��'*2\O��2Iad�r��W�`hp�W]�SVʫ9��Lݼ��{&6��ժ#��(�݇��Jڿ�bM<��T� ţ�I�3ӃͲu�eW� \��?�!�� ş�$(��\%�(D�e�9��PX��x�AI�-j��J�SUi��o��qI�� Pp��PD�(Rΐ��g�d��mȇ��Vgu1:��Ż��04a�}"�-u3�"w̪��x��c�� g��g�p��5�,Ю��}�P�oK�H�x��T ;�k��̽�*�?��7�4��]/�94��$�֋ӘU�ޖHBe��p��<��9��˓!U��{�Aϻfb�y��stl��9, 5d�r"Q�&8f .d mcqݟv�.Hڈ��s� N��z�9i��R1��8~0.~��p��-#��v�ny�U��5ʪ��'��W�N��T�!�H3Rt oY�3��$��TV6�T/�,A�oDbQ�fO��X�赁w�r)��h �2��t��S�HQ�k��#m�0��M�R�x\��*��<� �e)�~��g��i��:��|toL��#J'tL��0�ڰ�.Ie�7��VZ�� `�rdg�K�H�v;�� <�~0d� D�7BC�R��P��\H4�7X��9�G(�e,�� "��T�M��Ԉ1��ꮞ��f_L� �勥��;�n$蛮��`��]��ǝtp�|[�{��b`�ɑ�K�bϋD#�Q�G;�x{��c��3�E��JV,�X�U��X?/j&Qt�G\��?o$.J �W�� !��'��enC��f�\��[U/��m& �� ԉ�]�o#}��㜥s{e��Q��zJ�, �0�YE��cRt��ӗ�CW�PD`��s4��&�A!��Uy�o�lB��>?��V��u %�;��s�^�䕘]��~�˫8.��{��|m��d-�AȪ�UqFF�� .��%��U䵛$��a�oK�*��n�n�|g�~��jI��2-u~�Ǳ��r��y�3և��98�i��da�cH�� ;h��3N�Jw$T�a��5ezD\z��x�z��7HM�� K8v&Mm�,v��ޚ�\��Ə��$p0<�mo�D��m#3}�f�\Q

1 0

Fwd: [Haskell-cafe] I read somewhere that for 90% of a wide class of computing problems, you only need 10% of the source code in Haskell, that you would in an imperative language.
by Alberto G. Corona 07 Oct '09

07 Oct '09

May be because consciousness is relatively new and thus, not optimized. Sequentiallity is somehow related with lack of information and lack or resources. There is nothing more sequential than a Turing machine. The Von Newman architecture is designed to make as much as possible with a few more resources. The older parts of the brain are fast and parallel because they have a long history of optimizations by natural selection., The new cortex still struggles, step by step, to deduce new information from the available internal and external information at the pace they arrive. 2009/10/1 Tom Tobin <korpios(a)korpios.com> On Thu, Oct 1, 2009 at 3:26 AM, Andrew Coppin > <andrewcoppin(a)btinternet.com> wrote: > > It might be a better argument to say that human thinking is fundamentally > > sequential; parallel computers have been around for a little while now... > > Perhaps *conscious* human thinking is sequential — yet our brains are > massively parallel processors, and have been around for quite a long > time. ;-) > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

2 1