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HXT/Practical/Weather.hs difficulties
by Brian Troutwine 05 Nov '08

05 Nov '08

Hello all, I'm working through the practical HXT examples and have gotten stumped with the weather example[1]. I'm using GHC 6.8.3 and HXT 8.1.0. I compile the example like so... > blt@doritos:~ > $ ghc --make weather.hs > [1 of 1] Compiling Main ( weather.hs, weather.o ) > Linking weather ... And execute it... > blt@doritos:~ > $ ./weather > > error: ""<!DOCTYPE HTML PUBLIC \"-//IETF//DTD HTML 2.0/..."" (line 1, column 16): > unexpected "P" > expecting white space, "[" or ">" > > Unable to parse weather data. Woops. Would someone be so kind as to explain why this is failing? I'm at rather a loss. [1] http://www.haskell.org/haskellwiki/HXT/Practical/Weather1 --Brian P.S. Is this question better suited to the haskell-beginner list?

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announce [("InfixApplicative", 1.0), ("OpenGLCheck", 1.0), ("obj", 0.1)]
by Thomas Davie 04 Nov '08

04 Nov '08

Dear Haskellers, I've just uploaded a few packages to Hackage which I have produced while working at Anygma. I thought that people might be interested in knowing about these: obj-0.1: A library for loading and writing obj 3D models. This is still an early version and rather limited, but it's a starting point. Features: • Load models, complete with normals, texture coordinates and materials • Compute normals where smoothing groups are specified • An example program to load an obj model and render it spinning on the screen. • Faster loading that Maya itself! Bugs: • Memory usage is rather large • The exposed API is rather limited To Dos: • Add support for loading groups • Support for smooth surfaces OpenGLCheck-1.0: A micro-package containing instances of Arbitrary for the data structures provided in Graphics.Rendering.OpenGL. InfixApplicative-1.0: A second micro-package containing a pair of functions -- (<^) and (^>) which can be used to provide an infix liftA2 thus: Suppose we wanted to calculate liftA2 (+) [1,2] [2,3], but are unhappy with the fact that (+) is no longer infix, we may now use [1,2] <^(+)^> [2,3] Thanks -- any comments are greatly appreciated! Tom Davie

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Syntax question regarding 'import'
by Maurício 04 Nov '08

04 Nov '08

Hi, About this teste code: module Main (main) where { import Foreign hiding (unsafePerformIO,Foreign.Ptr,Data.Bits,) ; blo = xor 10 10 :: Int ; main = return () } Data.Bits is in the 'hiding' list. According to the syntax reference, this seems not to be allowed. GHC allows it, but do allow following code to use 'xor' from Data.Bits. I think this is correct, since 'xor' was exported by Foreign unqualified, but does 'Data.Bits' in that list mean something or it's just ignored? Haskell syntax allows a comma at the end of names to be imported or exported, like in the second line. What does that mean? Thanks, Maurício

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Re: [Haskell-cafe] code generation
by Martin Hofmann 04 Nov '08

04 Nov '08

Sorry for referring to a post, a bit ago. > http://www-users.cs.york.ac.uk/~ndm/derive/ (Deriving Generic Functions > by Example). > Thanks for the pointer, it was already on my to-read-pile :-) > I think using Template Haskell for your work would fit very nicely, so > is a good choice to learn :-) > I already got used to TH a bit, but I am not sure if it is appropriate for my purpose, or at least not completely. I want to load Haskell code into my program at runtime in an abstract representation (as TH), modify it and then type-check it or coerce it into a value (or execute it). For me it looks like I need a combination of Hint and TH. However, Hint can only interpret strings and to get a string from a QExp I have to enter the IO Monad using runQ. So, wouldn't it deteriorate my performance to do it all in the IO? Is there another way? Thanks, Martin

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Network.FastCGI does not emit stderr outputs to lighttpd's error.log?
by Agent Zhang 04 Nov '08

04 Nov '08

Hi, I'm trying Network.FastCGI + lighttpd 1.4.9 to develop a RESTful service platform. I've found that stderr (especially those from Debug.Trace) get lost in the error.log file. But plain CGI mode with Network.CGI works perfectly (all stderr outputs appear in error.log). Besides, my Perl fastcgi script also logs stderr with the same lighttpd. So it does seem that my lighttpd's mod_fastcgi module is OK. Is this a known issue in the Haskell fastcgi library? Is there a workaround or a fix? Thanks in advance :) Cheers, -agentzh

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a minimal Windows program in Haskell?
by Nun Aurbiz 04 Nov '08

04 Nov '08

How do I make a minimal Windows application in Haskell? I know there are Win API bindings in the libraries, and of course the ffi lets you call into and out of C, but I have no sense of how to bring it all together. I can't find any samples either. Is the Haskell code the "main" application and you just ffi into the Win API? Or does it ffi into a win_main.c that I write? Or is the win_main.c the "main" application and it calls into Haskell? Here is what I am talking about by a "minimal Windows application" (written in psuedo C code). #define WIN32_LEAN_AND_MEAN #include <windows.h> LRESULT CALLBACK windowsProcedure(..) { switch(message) { case WM_CLOSE: PostQuitMessage(0); return 0; } return DefWindowProc(..); } int APIENTRY WinMain(..){ WNDCLASS window_class; RegisterClass(&window_class) window = CreateWindow(..); ShowWindow(..); while(true) { /* do whatever */ while(PeekMessage(..)) if(msg.message == WM_QUIT) return msg.wParam; else DispatchMessage(&msg); } return 0; }

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ANNOUNCE: Graphalyze-0.5 and SourceGraph-0.3
by Ivan Lazar Miljenovic 04 Nov '08

04 Nov '08

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I've just submitted my thesis this morning (w00t!!!) and as such I'm announcing the latest versions of Graphalyze [1,2] and SourceGraph [3,4], which fix a couple of bugs in the previous versions (these bugs were fixed whilst waiting for my supervisor to finish reading through my draft, and as such I had to re-write bits of my thesis that talked about the limitations of the software :s ). [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Graphalyze [2] http://code.haskell.org/Graphalyze [3] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/SourceGraph [4] http://code.haskell.org/SourceGraph Briefly, SourceGraph is a utility that uses the Graphalyze library to analyse Cabalized Haskell software. Its input/output is rather restrictive at the moment: it takes a single argument, which is the path to a .cabal file, and then produces an HTML report in: <project directory>/SourceGraph/<project name>.html This report contains visualisation of the code for each module, for the imports (similar to what graphmod [5] does) as well as the entire code base. Furthermore, the entire code base is also visualised with functions grouped by the modules they're defined in, as well some simple analyses (such as comparing the export list to what functions are actually roots, similar to the output for top-level functions returned by GHC when using -fwarn-unused-binds). Main changes in Graphalyze since version 0.4: * When writing my thesis, I found some obvious silly mistakes (such as copying the rootsOf function definition to leavesOf, but not changing the function definition). * Images in the document representation are now inline elements. * When using Pandoc [6] for document generation, the size of generated graphs is now customisable on a per-format basis; furthermore, for web pages graph visualisations link to larger versions. Also, graph visualisations can now be created in a sub-directory. Main changes in SourceGraph since version 0.2: * Now uses Cabal 1.6 * Improve visual layout of generated HTML report (still no CSS though). * "Smarter" analysis: don't show trivial analysis results, and when analysing the entire code base don't return cliques, etc. that contain functions all in the same module (as they would have been reported in the per-module section). Note, however, that the parsing limitations for version 0.2 still apply: cpp is still as-yet unsupported (as I'm not sure what I'll do about choosing cpp flags); Template Haskell, HaRP and HXML are still ignored and functions in class declarations/records are still ignored (the former because it's ambiguous which actual function you want, the latter because they're boring :p ). Also, SourceGraph is _still_ not a refactoring tool ;-) If anyone's interested, I'll soon be uploading the final version of my thesis to my blog. Also, if anyone is interested in hacking on any of this, feel free! I'll probably leave it for a while (I'm going to be doing Java coding over summer, blech :s ), but I intend to come back to it later on. - -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) iEYEARECAAYFAkkOcaAACgkQfEfFJ9JhvyjhIwCeM9VXsJeSVK2CdWURJDer6zoA A5YAoIfayHtjpw0qt/gyPZhhhypOwzSh =x+/X -----END PGP SIGNATURE-----

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Typeable and Dynamic
by minh thu 04 Nov '08

04 Nov '08

Hi, Given a TypeRep and a Dynamic value with type corresponding to the TypeRep, I'd like to be able to use fromDyn *without* specifying a type (given as an additional 'default' argument) (since it is somewhat known from the TypeRep). That is, I'd like an undefinedOf that can be used in extract :: Typeable a => TypeRep -> Dynamic -> a extract typerep dyn = fromDyn (undefinedOf typerep) dyn For instance, if TypeRep is Int, extract Int dyn = fromDyn (undefined::Int) dyn Is it possible to write "extract" ? Thanks, Thu

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Typeable and Dynamic
by oleg＠okmij.org 04 Nov '08

04 Nov '08

minh thu asked a tricky question, about writing > extract :: Typeable a => TypeRep -> Dynamic -> a The question here is what determines the type 'a'. One answer is that 'a' is determined from the context, e.g., (extract tr dyn) + 1.0 fixes 'a' to be an Int. In that case, extract is equivalent to `read' (indeed, String is a primitive sort of Dynamic). We do not need any argument TypeRep though as we obtain 'a' from the context. fromDynamic is sufficient there. One can also construe the question to be asking about writing an `inverse' of typeOf. Whereas, typeOf :: Typeable a => a -> TypeRep can give the TypeRep for any (Typeable) type, undefinedOf :: Typeable a => TypeRep -> a could give (an undefined) value for a given TypeRep. Now, the _type_ 'a' is determined by the _value_ of TypeRep: seemingly we need dependent types. To write function of exactly that signature, we need Template Haskell. Oftentimes, we can get away with a weaker function: > data Dyn = forall a. Typeable a => Dyn a > reflect :: TypeRep -> Dyn to be used to implement dynApply, dynFst, dynSnd, dynHead and other operations on Dynamics. Perhaps the following message may help then http://www.haskell.org/pipermail/haskell-cafe/2007-December/036820.html

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Problem while compiling ghc 6.8
by Magicloud 04 Nov '08

04 Nov '08

Hi, I got my ghc 6.8 by `darcs get --partial http://darcs.haskell.org/ghc-6.8/ghc`, and after `darcs-all get`, `sh boot`, `configure`, without any problem, I started to make it. Well, when compiling libraries/stm, it reports "Control/Concurrent/STM/TVar.hs:22:8: Not in scope: `readTVarIO'. I tried to reget the source without '--partial', still the same.

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