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Reflective capabilities of Haskell (cont'd)
by Martin Hofmann 13 Mar '08

13 Mar '08

I am trying to port a programme written in Maude, which is a reflective language based on rewriting logic ( http://maude.cs.uiuc.edu/ ), to Haskell. I thought using Template Haskell might be a good idea, but I got stuck and now I am wondering if this is really possible in Haskell. Let me give an example of a Maude module defining the function last over a list of Peano numbers. fmod LAST is sorts Peano PeanoList . op 0 : -> Peano [ctor] . op s : Peano -> Peano [ctor] . op [] : -> PeanoList [ctor] . op cons : Peano PeanoList -> PeanoList [ctor] . op last : PeanoList -> Peano . vars X Y : Peano . var Xs : PeanoList . eq last(cons(X,[])) = X . eq last(cons(X,cons(Y,Xs))) = last(cons(Y,Xs)) . endfm So, last(cons(s(0),cons(s(s(0)),cons(s(s(s(0))),[])))) would reduce to s(s(s(0))). The cool thing about Maude is, that terms, modules, ... can be lifted to the meta level. For example: upModule('LAST, false) would yield fmod 'LAST is including 'BOOL . sorts 'Peano ; 'PeanoList . none op '0 : nil -> 'Peano [ctor] . op '`[`] : nil -> 'PeanoList [ctor] . op 'cons : 'Peano 'PeanoList -> 'PeanoList [ctor] . op 'last : 'PeanoList -> 'Peano [none] . op 's : 'Peano -> 'Peano [ctor] . none eq 'last['cons['X:Peano,'`[`].PeanoList]] = 'X:Peano [none] . eq 'last['cons['X:Peano,'cons['Y:Peano,'Xs:PeanoList]]] = last['cons[ 'Y:Peano,'Xs:PeanoList]] [none] . endfm I also have access, e.g. to the defined type constructors. So upOpDecls('LAST,false). yields op '0 : nil -> 'Peano [ctor] . op '`[`] : nil -> 'PeanoList [ctor] . op 'cons : 'Peano 'PeanoList -> 'PeanoList [ctor] . op 'last : 'PeanoList -> 'Peano [none] . op 's : 'Peano -> 'Peano [ctor] . Given an arbitrary function, I have access to its definition, its types and the type constructors, all as ADTs. Is this possible with Template Haskell, or in some other way? Thanks a lot, Martin

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Re: unification
by Christian Maeder 13 Mar '08

13 Mar '08

andrea wrote: >> data Tipo = Var Int | Const String | Tipo :-> Tipo deriving (Show, Eq) >> > But now how can I do to make the set of Const fixed?? > I want just a few base types, like "int" and "string", how could I > define it? your base types could be: Const "String" :: Tipo Const "Int" :: Tipo and the polymorphic type of the identity function could be: Var 1 :-> Var 1 :: Tipo (and with "infixr :->") the type of binary function like (+) Const "Int" :-> Const "Int" :-> Const "Int" Note: the data type does not support type constructors like "List". I recommend from: http://www.haskell.org/haskellwiki/Research_papers/Type_systems Typing Haskell in Haskell The first few pages will be enough (substitution is on page 7) However, the link http://www.cse.ogi.edu/~mpj/pubs/thih.html does not work for me Could someone correct that link? Christian

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floating point operations and representation
by Don Stewart 13 Mar '08

13 Mar '08

> I am under the restriction that I need to write Haskell programs using > Double which mimic existing C/C++ programs or generated data sets, and > get the same answers. (It's silly, but take it as a given > requirement.) If the C programs are using "log2", then I need "log2" > in the Haskell, or else I run the risk of not producing the same > answers. Hey Jacob, Just to make life super simple, I packaged up a binding to the basic math.h library for Doubles. You can find the library here: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/cmath For example, Prelude> Foreign.C.Math.Double.log10 5 0.6989700043360189 Prelude> log 5 / log 10 0.6989700043360187 Enjoy! -- Don

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Re: Reflective capabilities of Haskell (cont'd)
by oleg＠okmij.org 13 Mar '08

13 Mar '08

Martin Hofmann wrote: > Thanks a lot, this helps a bit, but access to function bodies is exactly > what I need. Then perhaps you might like the method of reconstructing bodies (of possibly compiled) functions http://okmij.org/ftp/Computation/Generative.html#diff-th in the form of AST -- the template Haskell AST. The reconstructed bodies of functions can be arbitrarily manipulated (e.g., _symbolically_ differentiated or algebraically simplified) and then converted `back' to the compiled code.

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[GSoC] A data parallel physics engine
by Roman Cheplyaka 13 Mar '08

13 Mar '08

I'm looking for interesting project to work on during Google Summer of Code. So I found [1]"A data parallel physics engine" ticket and got excited about it. I'd like to know interested mentors and community opinion about the complexity of such project. I have not very deep knowledge about both NDP and physics engines. Is it feasible to learn all the necessary stuff during these 2 month before SoC starts? 1. http://hackage.haskell.org/trac/summer-of-code/ticket/1535 -- Roman I. Cheplyaka :: http://ro-che.info/ ...being in love is totally punk rock...

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linker question
by Galchin Vasili 13 Mar '08

13 Mar '08

Hello, I have made modifications against an existing Haskell library and installed in my --prefix=$HOME. How do I specify to link against this test .a and not the "global" archive? Regards, vasili

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Java interfacing and ghc-6.8?
by Marc Weber 12 Mar '08

12 Mar '08

Hi, I've read on haskell org about gcjni Haskel/Java VM bridge Lambada (< ghc 6.6.1) Do you know wether any of them can be compiled with ghc-6.8 ? If not does it need much effort to patch them? Sincerly Marc Weber

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Constructing Data.Map from ByteString
by Dave Tapley 12 Mar '08

12 Mar '08

Hi all, I've been plugging away at this all day and some discussion in #haskell has been fruitless. Perhaps you have the inspiration to see what's happening! Concerning this minimal example: http://hpaste.org/6268 It works as required, loading K/V pairs into a Data.Map, the concern is the amount of memory used. Pausing (using a getLine) after the readFile one can see (through 'ps v') that the whole file 'f' is loaded in to memory. However once the Map is created the memory footprint swells to around five times the size. Surely this can't be just overhead from Map? My reasoning was that by using ByteString and getting the whole file into memory a small and linear increase would be seen for Map overhead.. I have tried using both Data.ByteString.Char8 and Data.ByteString.Lazy.Char8 with negligible difference. For a hoot I tried it with String and yes, it's ridiculous :) Cheers, Dave

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Reminder: 4th Haskell Hackathon, April 11-13 in Gothenburg
by Bjorn Bringert 12 Mar '08

12 Mar '08

------------------------------------------------------------------------ Hac4 4th Haskell Hackathon April 11-13, 2008 Gothenburg, Sweden http://haskell.org/haskellwiki/Hac4 Sponsored by Credit Suisse and Galois. ------------------------------------------------------------------------ This is a reminder to register for the 4th Haskell Hackathon. The event will be held over 3 days, April 11-13, at Chalmers University of Technology in Gothenburg, Sweden. == NEWS == * Lunches and at least one dinner for the Hackathon attendees will be provided through our generous sponsors Credit Suisse and Galois. * If you plan to start a new project on community.haskell.org, please request an account and project in advance, so as to save valuable Hackathon time. See http://community.haskell.org/admin/ for more details. == What it is == The plan is to hack on Haskell infrastructure, tools, libraries and compilers. To attend please register, and get ready to hack those lambdas! Code to hack on: * Hackage * Cabal * Porting foreign libraries * Bug squashing * You decide! Before you attend, do start thinking and familiarizing yourself with 1 or 2 projects you wish to work on, to ensure no wasted effort during the Hackathon. A list of possible projects is available on the website. == Registration == We ask that you register your interest. Follow the instructions on the registration page: http://haskell.org/haskellwiki/Hac4/Register Once you've registered, do add your info to the attendees self-organizing page, http://haskell.org/haskellwiki/Hac4/Attendees if you are looking to share costs, or meet up prior to the hackathon, with other attendees. N.B. if you already expressed interest via the wiki, do confirm by registering `officially' anyway. == Important dates == Hackathon: April 11-13, 2008 == Organizers == Björn Bringert (local) Thomas Schilling (local) Lennart Kolmodin (local) Krasimir Angelov (local) Jean-Philippe Bernardy (local) Ian Lynagh Duncan Coutts

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Re: [Haskell-cafe] simple Haskell question - List comprehensions
by Philip Müller 12 Mar '08

12 Mar '08

Dan Licata schrieb: > Does that help? > Yeah, it did - Thanks! - Philip

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