March 2009 - Haskell-Cafe

Re: [Haskell-cafe] OpenGL and Cabal installation
by Henk-Jan van Tuyl 18 Mar '09

18 Mar '09

On Wed, 18 Mar 2009 04:34:29 +0100, Mark Spezzano <mark.spezzano(a)chariot.net.au> wrote: > > configure: error: no GLUT header found, so this package cannot be built > > See `config.log' for more details. > > > Where is it looking for these glut.h files? I’ve tried putting them > everywhere in my PATH but msys won’t find them. Add an environment variable C_INCLUDE_PATH and assign it the value of the directory where you keep the header files; for instance, if the glut.h file is in: C:\usr\local\include\GLUT then do Set C_INCLUDE_PATH=C:\usr\local\include before compiling, or set this variable in Windows with System properties. Similarly, set LIBRARY_PATH for the libraries to link. -- Regards, Henk-Jan van Tuyl -- http://functor.bamikanarie.com http://Van.Tuyl.eu/ --

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Re: [Haskell-cafe] Re: Query on list comprehension
by Kalman Noel 18 Mar '09

18 Mar '09

Jon Fairbairn schrieb: > Melanie_Green <jac_legend_sas(a)hotmail.com> writes: >> What are the limitations of list comprehension. [...] >> a >> aa >> aaa > > I'm not clear what you mean by the question. Why do you want > to use list comprehensions? What if they aren't the best way > of getting the result you want? > > You can write > > [a | b <- [replicate n 'a' | n <- [1..]], a <- b ++ "\n"] > > but does that "replicate" fail to meet your specification? Since we're »holfing« again: fix $ \xs -> [ 'a':xs | xs <- []:xs ]

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ANN: regex-tdfa-1.1.0
by ChrisK 18 Mar '09

18 Mar '09

I have just uploaded the new regex-tdfa-1.1.0 to hackage. This version is a small performance update to the old regex-tdfa-1.0.0 version. Previously all text (e.g. ByteString) being search was converted to String and sent through a single engine. The new version uses a type class and SPECIALIZE pragmas to avoid converting to String. This should make adding support for searching other Char containers easy to do. The new version includes six specialized engine loops to take advantage of obvious optimizations of the traversal. The previous version had only a couple of such engines. The new code paths have been tested for correctness and no performance degradations have shown up. -- Chris

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Re: [Haskell-cafe] Design Patterns by Gamma or equivalent
by wren ng thornton 18 Mar '09

18 Mar '09

Mark Spezzano wrote: > Because Haskell is not OO, it is functional, I was wondering if there is > some kind of analogous “design pattern”/”template” type concept that > describe commonly used functions that can be “factored out” in a general > sense to provide the same kind of usefulness that Design Patterns do for > OOP. Basically I’m asking if there are any kinds of “common denominator” > function compositions that are used again and again to solve problems. If > so, what are they called? Most of the (particular) problems OO design patterns solve are non-issues in Haskell because the language is more expressive. The issues giving rise to patterns like Visitor and Factory are non-issues, so their "solutions" are trivial. A number of other patterns can actually be written down once and for all (in higher-order functions like foldr, map,...) instead of needing repetition. But that's not to say we don't have our own expressiveness deficiencies ;) The analogous term for the genre is "functional pearl", though the individual pearls don't tend to be as codified as in OOP. One example is using coproducts for open unions[1] which solves the dual problem to Visitor. Another is using open recursion[2]. A third example along the same track is using two-level types[3]. But again a lot of the patterns, once discovered, get turned into libraries that can be used off the shelf: e.g. the two-continuation solution for efficient and fair backtracking search[4], and list-fusion techniques[5]. There also a number of "idioms" which are similar in scope to the idioms that arise in other languages: using tail recursion, accumulators, continuation-passing transformations, closures over recursion[6], Schwartzian transforms, etc. And then there are some things like monoids which fall somewhere between idiom and pearl. Some specific OO patterns have direct analogues in "defunctionalization"[7]. For the most part defunctionalization is something best left to the compiler, but on occasion we want to be explicit about it and this too is an idiom/pearl border case IMO. And, of course, there's the entire cottage industry of using category theory for fun and profit. [1] http://www.cs.nott.ac.uk/~wss/Publications/DataTypesALaCarte.pdf [2] http://www.cs.utexas.edu/~wcook/Drafts/2006/MemoMixins.pdf [3a] http://web.cecs.pdx.edu/~sheard/papers/generic.ps [3b] http://web.cecs.pdx.edu/~sheard/papers/JfpPearl.ps [4a] http://okmij.org/ftp/papers/LogicT.pdf [4b] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/logict [5a] http://www.cse.unsw.edu.au/~dons/papers/CSL06.html [5b] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bytestring [5c] http://www.cse.unsw.edu.au/~dons/papers/CLS07.html [5d] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/stream-fusion [5e] http://homepages.inf.ed.ac.uk/wadler/papers/vanish/vanish.pdf [6] For lack of a better name. I mean doing this: > -- Here the a,b,c,d variables are captured in the closure for go > recursive a b c d = go > where > go 0 = ...a...b... > go n = ...c...d...go (n-1) instead of this: > -- ...instead of needing to be passed through the recursion each time > recursive a b c d 0 = ...a...b... > recursive a b c d n = ...c...d...recursive a b c d (n-1) [7a] http://blog.plover.com/prog/defunctionalization.html -- Live well, ~wren

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Re: [Haskell-cafe] Re: Haskell Logo Voting has started!
by Daniel Schüssler 18 Mar '09

18 Mar '09

Hi, > Even worse, the buttons for moving items up and down are buggy - at > least on my browser (Firefox 3.1 beta 2 on Linux). They sometimes > reorder my other votes! Even assuming that the list box code is not > buggy (which I now doubt), not being able to use the buttons makes this > form almost unusable! I guess it works like this: "Move down" on an element X will make the /smallest/ change (with respect to the abstract ordering) that makes X worse than it's current value. This may require changing more than one number, for example if we have: (105: ) (106: A) (107: X,B) (108: C,D) (109: E ) (110: ) moving down X will result in either (105: A) (106: B) (107: X ) (108: C,D) (109: D ) (110: ) or equivalently (105: ) (106: A) (107: B ) (108: X ) (109: C,D) (110: D) of course, maybe you already know that but you're saying that it is doing this wrongly ;) Btw, I really think the logos should be on the same page as the voting form. Hotkeys for the buttons would be good too. It's usable though if you (incorrectly) consider the numbers as a sort of reverse "star rating" to make a O(n) pass, possibly finetuning later. Greetings, Daniel

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Re: [Haskell-cafe] Who generates Haskell code and uses type information at runtime?
by Martin Hofmann 18 Mar '09

18 Mar '09

> GHC is the current state of the art, which will give you a full > Haskell AST enriched with type information. You can then just modify the > AST directly. I experimented with the AST from HscTypes.CoreModule in the ghc api. However, it seems that this representation is too far away from my theory. I would prefer something similar as Template Haskell. > The ghc-api is somewhat sparsely documented That might be the reason, why I have not seen how it can help me. > It really depends on what you are trying to do... Putting in a nutshell, I generalize an extensional defined function definition into a recursive one. This is done in a number of steps by modifying expressions and exploiting type information of sub-expressions. For example: rev [] = [] rev [a] = [a] rev [a,b] = [b,a] rev [a,b,c] = [c,b,a] ~~> rev x = y ~~> rev [] = [] rev (x:xs) = (y:ys) ~~> rev [] = [] rev (x:xs) = (last (x:xs)) : (reverse (x:xs)) The initial set of rules is given by the user (in a file, via IO, ...). The problem later is to infer the type of an intermediate variable, e.g. 'y'. Thanks, Martin

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Who generates Haskell code and uses type information at runtime?
by Martin Hofmann 18 Mar '09

18 Mar '09

I try to modify Haskell code, parsed from an external source, at runtime. Therefore I need type information about this code. Sometimes to this is referred to as treating "data as code" and "code as data". In homoiconic languages such as Lisp this would be less cumbersome, but in Haskell this seems to be not trivial. Therefore I would like to know how other people solved this. Do you, for example, * use ghc-as-api and manipulate the code snippet in GHC's core language? * use Language.Haskell.Syntax or Language.Haskell.TH and get your type information via IO (from Hint or ghc) as a String? * use your own language representation for code and type and use a tailored type inference/unification algorithm? * use your own language representation combined with Data.Typeable and Data.Dynamics, but what about polymorphic types? * ...? Thanks a lot, Martin

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Re: [Haskell-cafe] OpenGL Linking Issue
by Sean Lee 18 Mar '09

18 Mar '09

Hi Mark, >From what I remember -- I haven't used OpenGL for about a year -- you need something like ghc --make -package GLUT -lglut Test1.hs assuming that you have both HOpenGL haskell package and OpenGL c library. Cheers, Sean 2009/3/18 Mark Spezzano <mark.spezzano(a)chariot.net.au>: > Hi, > > > > I hope I’m posting to the right forum. > > > > I’ve got OpenGL up and running on my Windows Vista machine (finally!) and it > runs perfectly well under Eclipse, bringing up a window with a rendered > image as expected. > > > > The only issue starts when I try to compile the program without Eclipse > (using GHC rather than GHCi like Eclipse does). > > > > I type: > > > > C:\Users\Mark\workspace2\OpenGLPractice\src>ghc --make Test1.hs > > > > And get the following output > > > > Linking Test1.exe ... > > C:\Program > Files\Haskell\GLUT-2.1.1.2\ghc-6.10.1/libHSGLUT-2.1.1.2.a(Extensions. > > o):fake:(.text+0xcc): undefined reference to `glutGetProcAddress@4' > > collect2: ld returned 1 exit status > > > > What’s happening here? Obviously it’s a linking issue, but I was wondering > whether I need to include some library or file or option to ghc so that it > links correctly. > > > > Cheers, > > > > Mark Spezzano > > > > No virus found in this outgoing message. > Checked by AVG. > Version: 7.5.557 / Virus Database: 270.11.18/2008 - Release Date: 17/03/2009 > 4:25 PM > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > -- Sean Lee PhD Student Programming Language and Systems Research Group School of Computer Science and Engineering University of New South Wales

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OpenGL Linking Issue
by Mark Spezzano 18 Mar '09

18 Mar '09

Hi, I hope I’m posting to the right forum. I’ve got OpenGL up and running on my Windows Vista machine (finally!) and it runs perfectly well under Eclipse, bringing up a window with a rendered image as expected. The only issue starts when I try to compile the program without Eclipse (using GHC rather than GHCi like Eclipse does). I type: C:\Users\Mark\workspace2\OpenGLPractice\src>ghc --make Test1.hs And get the following output Linking Test1.exe ... C:\Program Files\Haskell\GLUT-2.1.1.2\ghc-6.10.1/libHSGLUT-2.1.1.2.a(Extensions. o):fake:(.text+0xcc): undefined reference to `glutGetProcAddress@4' collect2: ld returned 1 exit status What’s happening here? Obviously it’s a linking issue, but I was wondering whether I need to include some library or file or option to ghc so that it links correctly. Cheers, Mark Spezzano No virus found in this outgoing message. Checked by AVG. Version: 7.5.557 / Virus Database: 270.11.18/2008 - Release Date: 17/03/2009 4:25 PM

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Haskell on your system? Information wanted!
by Don Stewart 18 Mar '09

18 Mar '09

Hey all, I noticed we didn't have an easy page to find out how to get hold of the Haskell toolchain for various systems. So there's now a link from haskell.org to (existing) pages on how to obtain Haskell on windows, mac osx and linux and bsd. If you're a distro maintainer for these systems, please consider adding relevant pointers to the pages, so that users of these systems can find all the info they need. http://haskell.org/haskellwiki/Windows http://haskell.org/haskellwiki/OSX http://haskell.org/haskellwiki/GNU/Linux http://haskell.org/haskellwiki/BSD -- Don

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