November 2007 - Haskell-Cafe

Pb builind hdbc-sqlite3 (suite)
by manu 28 Nov '07

28 Nov '07

Hello, Still trying to build hdbc-sqlite3 it appears that the hdbc-sqlite3 package on Hackage is missing the C header file It is included with the hdbc-sqlite3 package found at http:// software.complete.org/hdbc-sqlite3/downloads however. Now I have another pb : >>> Building HDBC-sqlite3-1.1.3.0... [3 of 7] Compiling Database.HDBC.Sqlite3.Utils ( dist/build/Database/ HDBC/Sqlite3/Utils.hs, dist/build/Database/HDBC/Sqlite3/Utils.o ) Database/HDBC/Sqlite3/Utils.hsc:74:8: parse error on input `import' manu:/Volumes/data/Downloads/HDBC/hdbc-sqlite3 manu$ >>> line 74 is : foreign import ccall unsafe "sqlite3.h sqlite3_errmsg" I've checked and I have a sqlite3.h file in /usr/include what is this "parse error on input `import'" about ??? Thanks M

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Re: is there a more concise way to generate helper functions for a datatype built on records?
by Benedikt Huber 28 Nov '07

28 Nov '07

Neil Mitchell wrote: > Hi > > Some of these can be automatically derived by the Data.Derive tool... > The derivations Set, Is, From, Has, LazySet all look useful. > ... > > On Nov 24, 2007 4:01 PM, Thomas Hartman <tphyahoo(a)gmail.com> wrote: >> I think I'm running into more or less the same issue discussed at >> >> http://bloggablea.wordpress.com/2007/04/24/haskell-records-considered-grung… >> >> Just wondering if I missed anything, or if any of the ideas >> considering better records setter/getters have been implemented in the >> meantime. Hi, the Ref deriviation (included in Data.Derive) seems to be a good way to solve some aspects of this problem; I have some questions on my own though. Here is a working example of updating the two player's state in the pong game: > {-# OPTIONS -cpp #-} > {-# OPTIONS_DERIVE --output=file.h #-} > module Main where > import Control.Arrow > #include "file.h" Refs as in (http://www.haskell.org/pipermail/haskell-cafe/2007-June/026477.html ): > type Upd a = a -> a > data Ref cx t > = Ref { select :: cx -> t , update :: Upd t -> Upd cx } > (@.) :: Ref a b -> Ref b c -> Ref a c > a @. b > = Ref { select = select b . select a, > update = update a . update b } The game model: > data Object2D > = Object2D { x :: Double, y :: Double } deriving (Show {-! Ref !-}) > data Player > = Player { points :: Int, pos :: Object2D } deriving (Show {-! Ref !-}) > data Game > = Game { p1 :: Player, p2 :: Player, ball :: Object2D } deriving (Show {-! Ref !-}) > sampleGame :: Game > sampleGame = Game { p1 = Player 0 (Object2D 5 0), p2 = Player 0 (Object2D 5 10), ball = Object2D 5 5 } Game update proceeds in several steps, we now consider the first one: Updating the 2 player's position - this happens, at least conceptually, *in paralell* (for example: both players might be aloud to have a look at the other players position in the last turn, but not at the updated position). Here's the update for one player: > updatePlayerPos :: Bool -> Upd Player > updatePlayerPos moveRight > = update (refPos @. refX) $ > case moveRight of > True -> ((min 10) . (+1)) > False -> ((max 0) . (+(-1))) If sequential update is ok for us, the game state update is simply: > updatePositions :: Bool -> Bool -> Upd Game > updatePositions move1 move2 = update refP1 (updatePlayerPos move1) . update refP2 (updatePlayerPos move2) To get it *actually* work in parallel we have to create a new reference for both players: > refPlayers :: Ref Game (Player,Player) > refPlayers = Ref { select = select refP1 &&& select refP2, > update = \pu g -> let (p1',p2') = pu (p1 g, p2 g) in g { p1 = p1', p2 = p2' } } While the select part of the Ref is expressed using &&&, I don't know how the paralell update can be expressed in terms of combinators. Any hints ? Now, the game state update in the parallel version is easy. Note that it would also be possible now to take one player's position into account when updating the other player's position: > updatePositionsPar move1 move2 = (update refPlayers) $ updatePlayerPos move1 *** updatePlayerPos move2 So, the Ref deriviation is really nice for sequential updates; paralell updates on the other hand need some work. Furthermore, I don't really know how well Refs work if updates need information on other parts of the state without modifying it. (e.g. the AI player needs to know where the ball is, but does not modify the ball). I'd really appreciate if anyone has some additional clues. thanks, benedikt

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Pb building HDBC-sqlite3
by manu 28 Nov '07

28 Nov '07

Hello still, trying to use a database with ghc 6.8.1 - patience running low however :) I now have troubles installing HDBC-sqlite3 the build fails like so : >>>>> $ runhaskell Setup.lhs build Preprocessing library HDBC-sqlite3-1.1.3.0... Utils.hsc:31:33: error: hdbc-sqlite3-helper.h: No such file or directory Utils.hsc: In function ‘main’: Utils.hsc:70:0: error: parse error before ‘finalizeonce’ compiling dist/build/Database/HDBC/Sqlite3/Utils_hsc_make.c failed command was: /usr/local/bin/ghc -c -package base-3.0.0.0 -package mtl-1.1.0.0 -package HDBC-1.1.3 -I. dist/build/Database/HDBC/Sqlite3/ Utils_hsc_make.c -o dist/build/Database/HDBC/Sqlite3/Utils_hsc_make.o >>>>> the hdbc-sqlite3-helper.h file is nowhere to be found on my system should it be part of the package ? Thanks M

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About garbage collecting
by Maurício 27 Nov '07

27 Nov '07

Hi, If available memory is low, is the garbage collector going to eliminate data that is still referenced, but it knows it can be recalculated when needed? Thanks, Maurício

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Building MissingH on Windows
by nionita＠lycos.de 27 Nov '07

27 Nov '07

Hi, I'm trying to build MissingH (0.18.6) on Windows, but it looks like (probably because of changes in Cabal) the Setup.hs is broken. Im using GHC 6.8.1. Following message: $ runhaskell Setup.hs configure Setup.hs:19:35: Couldn't match expected type `(Either GenericPackageDescription PackageDescription, HookedBuildInfo)' against inferred type `PackageDescription' In the first argument of `(confHook defaultUserHooks)', namely `mydescrip' In the expression: let mydescrip = case os of "mingw32" -> ... _ -> ... in (confHook defaultUserHooks) mydescrip flags In the definition of `customConfHook': customConfHook descrip flags = let mydescrip = ... in (confHook defaultUserHooks) mydescrip flags I'm new to Cabal and I couldn't see a fast way to fix it. Thanks, Nicu

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building a Haskell package on cygwin
by Galchin Vasili 27 Nov '07

27 Nov '07

Hello, What is involved in building a package on cygwin? Kind regards, Vasya

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about GADTs on ghci
by Yu-Teh Shen 27 Nov '07

27 Nov '07

i have seen the documents in http://www.haskell.org/haskellwiki/Generalised_algebraic_datatype but i can not run the following code on ghci ex: data Term x where K :: Term (a -> b -> a) S :: Term ((a -> b -> c) -> (a -> b) -> a -> c) Const :: a -> Term a (:@) :: Term (a -> b) -> (Term a) -> Term b infixl 6 :@ could any tell me how to run the code? Thanks a lot

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Re: [Haskell-cafe] A tale of three shootout entries
by Ryan Dickie 27 Nov '07

27 Nov '07

Oops forgot to hit reply-to-all.. resending.. N-body is looking good. I am running and amd64 3000+ on ghc 6.8.1. The debian shootout is showing a huge gap between ghc 6.6 and g++ but I am not seeing that gap. One concern though is that the code doesn't look very "haskellish". So much pointer manip. For the nbody c++ code I am getting: -0.169075164 -0.169031665 real 0m11.168s user 0m10.891s sys 0m0.043s and for the nbody haskell code I am getting: -0.169075164 -0.169031665 real 0m11.595s user 0m11.422s sys 0m0.044s On Nov 26, 2007 8:21 PM, Don Stewart <dons(a)galois.com> wrote: > s.clover: > > In some spare time over the holidays I cooked up three shootout > > entries, for Fasta, the Meteor Contest, and Reverse Complement. I > > Yay! > > > First up is the meteor-contest entry. > > > > http://shootout.alioth.debian.org/gp4/benchmark.php? > > test=meteor&lang=ghc&id=5 > > > > This is the clear win of the bunch, with significantly improved time > > thanks to its translation of the better algorithm from Clean. > > Well done! Though looks like we'll have to follow the C++ implementation > to be really competitive. > > > Next is reverse-complement. > > > > http://shootout.alioth.debian.org/gp4/benchmark.php ? > > test=revcomp&lang=ghc&id=3 > > Very good. I'm glad someone looked at that, since the old code was > moderately naive (first bytestring effort). > > > Finally, there's fasta. > > > > http://shootout.alioth.debian.org/gp4/benchmark.php? > > test=fasta&lang=ghc&id=2 > > Yeah, we should do something better here. Hmm. > > > p.s. It looks like they've depreciated chameneos in favor of a new > > version, chameneos-redux. As this was one of the places Haskell > > really rocked the competition, it would probably be worth updating > > Definitely. I note also we're beating Erlang on the new thread-ring > benchmark too, > > http://shootout.alioth.debian.org/gp4/benchmark.php?test=threadring&lang=all > > > the Haskell entry for the new benchmark. Also, the n-bodies benchmark > > seems like another that could be much improved. > > Yeah, that's a hard one. > > -- Don > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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the ability to talk to POSIX device drivers
by Galchin Vasili 27 Nov '07

27 Nov '07

Hello, I saw somewhere that in one of the Haskell libraries there is support to open, read, write, ioctl, etc. to POSIX drivers, but I don't see in the Haskell Report. ?? Kind regards, Vasili

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data-parallel prime sieve?
by Adam Megacz 27 Nov '07

27 Nov '07

Hello, Can anybody point me to a data-parallel implementation of the prime sieve -- or any other prime number enumerator? NESL/Nepal/DP-Haskell code would be nice, but anything fitting the data parallel model will do. I'm particularly looking for a solution that doesn't wind up being dominated by the I/O latency between the serial and parallel contexts -- especially as you get towards higher numbers where the distance between the primes becomes a significant fraction of the amount of storage in the parallel context. I found pseudocode for such a program in a set of NESL slides from 1995 (before it was released) as well as a paper about a CM-2 implementation, but neither is quite satisfactory. Thanks! - a -- PGP/GPG: 5C9F F366 C9CF 2145 E770 B1B8 EFB1 462D A146 C380

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