November 2007 - Haskell-Cafe

XMonad architecture paper?
by Galchin Vasili 09 Nov '07

09 Nov '07

Hello, I was watching Simon Peyton-Jones' video on "A Taste of Haskell" Part 1. .. Is there any paper discussing the architecture? I am not afraid to read code but sometimes a paper overview is good ... Regards, Vasya

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ByteString search code available in easy-to-digest form
by Bryan O'Sullivan 09 Nov '07

09 Nov '07

I've packaged up the fast Boyer-Moore and Knuth-Morris-Pratt code that Chris Kuklewicz posted a few months ago: http://article.gmane.org/gmane.comp.lang.haskell.libraries/7363 The consensus at the time was that the code was not ready for rolling into the bytestring package, but now it's easy to install and start working with. API docs: http://darcs.serpentine.com/stringsearch/dist/doc/html/stringsearch/ Patches against the darcs repo welcome: darcs get http://darcs.serpentine.com/stringsearch Credit to Justin Bailey, Daniel Fischer, and Chris Kuklewicz for their hard work. (Currently only tested against GHC 6.6.1, FYI.) <b

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[OT] GHC uninstall on Linux
by Dusan Kolar 09 Nov '07

09 Nov '07

Hello all, I use tar.bz2 binary distribution of GHC compiler as my distro does not use any supported packaging system. Everything is fine, but... I want to install the new version of the GHC compiler. Is there any (easy) way, how to get information about what was copied and where during installation? (./configure; make install) There seems to be no uninstall target in the Makefile. :-( And I want to uninstall the previous version of the compiler. Is it safe to delete files/folders just from /usr/local/lib/ghc-6.6.1 and /usr/local/bin/gh* ? Thanks for any hint Dusan P.S. Tried google with no usable results. D.

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Memory-mapped arrays?
by Joel Reymont 09 Nov '07

09 Nov '07

Is there such a thing as memory-mapped arrays in GHC? I'm looking for something that would let me memory-map a file of floats and access it as an array. Thanks, Joel -- http://wagerlabs.com

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ANN: FileManip 0.1, an expressive file manipulation library
by Bryan O'Sullivan 09 Nov '07

09 Nov '07

The FileManip package provides expressive functions and combinators for searching, matching, and manipulating files. It provides three modules. System.FilePath.Find lets you search a filesystem hierarchy efficiently: find always (extension ==? ".rb") >>= mapM_ remove System.FilePath.GlobPattern lets you perform glob-style pattern matching, without going through a regexp engine: "foo.c" ~~ "*.c" ==> True System.FilePath.Manip lets you rename files procedurally, edit files in place, or save old copies as backups: modifyWithBackup (<.> "bak") (unlines . map (takeWhile (/= ',')) . lines) "myPoorFile.csv"

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Fibbonachi numbers algorithm work TOO slow.
by gitulyar 08 Nov '07

08 Nov '07

Please help me. I'm new in Haskell programming, but wrote some things in Scheme. I make so function: fib 1 = 1 fib 2 = 2 fib n = fib (n-1) + fib (n-2) And when I call "fib 30" it works about 5 seconds. As for me it's really TOO SLOW. Tell me please if I have something missed, maybe some compiler (interpretaitor) options (I use ghc 6.6.1). P.S. As I understand function "fib n" should be calculated one time. For example if I call "fib 30" compiler builds tree in which call function "fib 28" 2 times and so on. But as for lazy calculation principle it should be calculated just ones and then it's value is used for all other calls of this function with the same argument. But it seems that this principle doesn't work in this algorithm. -- View this message in context: http://www.nabble.com/Fibbonachi-numbers-algorithm-work-TOO-slow.-tf4752338… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Re: [Haskell-cafe] Flymake Haskell
by Daisuke IKEGAMI 08 Nov '07

08 Nov '07

Hi, Thanks Thomas for your advice. The speed is improved very much. The latest code about Flymake Haskell will be developed and discussed on EmacsWiki:FlymakeHaskell. http://www.emacswiki.org/cgi-bin/emacs/FlymakeHaskell However, we can continue the discussion via email, too. Thomas wrote: > It seems you need multi-line pattern matching. Note that shim already > can do this, but it doesn't do it automatically. Unfortunately, shim > chokes on files that need pre-processing. There's probably a way to > integrate these two. You are right; the multi-line pattern matching is needed. However, I failed some tries, and finally I invoked ghci from Emacs as I did usually. Anyone helps? I don't know shim's work. Gwern wrote: > Is there further setup needed? I think your setting maybe wrong. > (defun flymake-Haskell-init () > (interactive) ; this line should be removed > brabra I didn't test Gwern's setting on XEmacs, however I wish it helps. Best wishes, Ike

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Composing trading strategies (was: Should I step into a minefield? / Writing a trading studio in Haskell)
by Greg Fitzgerald 08 Nov '07

08 Nov '07

> My idea is to write something like TradeStation [1] or NinjaTrader, only for the Mac. > It would be quite nifty to use SPJ's financial combinator approach I was experimenting with a Haskell EDSL for financial trading not too long ago. My favorite strategy so far is the parallel parser combinator approach. It allows users to run many parallel trading strategies in a nice single-threaded way that's easy to reason about and straightforward to compose new trading strategies. The idea is that the user composes an 'openPosition' and 'closePosition' trading strategies from a combinator library and gives them to the trading platform. The user's trading strategies are nothing more than a numeric parser combinators. With each incoming quote, the trading platform kicks off the user's 'openPosition' trading strategy. When a strategy succeeds (a successful parse), the trading platform opens a position for the user. Once a position is opened, the platform starts running the user's 'closePosition' strategy. The closePosition parser is run the same way and when it succeeds, the user's position is closed. To implement, I leveraged Twan van Laarhoven's ParseP library ( http://twan.home.fmf.nl/parsep/) which at least for my simple experiments, was incredibly complete and stable given its 0.1 version number. Why ParseP and not Parsec or ReadP? Parsec doesn't have an unbiased choice operator and ReadP only works on strings. Implementing context-free trading strategies like limit orders is very easy (limitOrder price = satisfy (>= price)), but context-sensitive strategies, such as "match the longest string of increasing numbers" is quite a bit more painful. Below are some of my experiments (also on hpaste: http://hpaste.org/3756) If anybody could offer more elegant solutions, I'd love to hear because this still feels overly complicated to me. 'testUpThenDown' matches an input stream that increases then decreases. 'testNumericFib' will try to match as much of the Fibonacci sequence as possible. import Text.ParserCombinators.ParseP import qualified Text.ParserCombinators.ParseP.Greedy as Greedy import Control.Applicative import Data.Monoid testUpThenDown = print $ runParser coaster [1, 2, 1] testNumericFib = print $ runParser (fib (Sum 1) (Sum 1)) (map Sum [2, 3, 5, 7, 1]) testAlphaFib = print $ runParser (fib "a" "b") ["ab", "bab", "cad"] fib :: (Eq a, Monoid a) => a -> a -> Parser a p [a] fib n1 n2 = Greedy.option [] (do n3 <- satisfy (== (n1 `mappend` n2)) ns <- fib n2 n3 return (n3:ns)) coaster :: Ord a => Parser a p ([a], [a]) coaster = do seed <- get up <- increasing seed down <- decreasing (last up) return (seed:up, down) increasing seed = trend (<) seed decreasing seed = trend (>) seed trend :: (Monad (Parser a p)) => (a -> a -> Bool) -> a -> Parser a p [a] trend f = many1WithContext (satisfy . f) manyWithContext p = Greedy.option [] . many1WithContext p many1WithContext p seed = do n <- p seed ns <- manyWithContext p n return (n:ns) Thanks, Greg On Nov 7, 2007 5:02 PM, Joel Reymont <joelr1(a)gmail.com> wrote: > I need to pick among the usual list of suspects for a commercial > product that I'm writing. The suspects are OCaml, Haskell and Lisp and > the product is a trading studio. My idea is to write something like > TradeStation [1] or NinjaTrader, only for the Mac. > > It would be quite nifty to use SPJ's financial combinator approach > and, for example, embed Yi (Haskell editor). > > One of the key features of the product would be the ability to model > your trading logic using a trading DSL. I'm thinking that this DSL > could well be Haskell but I'm concerned about stepping into a minefield. > > I will need to embed GHC into the app, for example, and I understand > that the GHC API does not offer unloading of code at the moment. I > would prefer not to bundle GHC separately so I don't think the hs- > plugins approach would work for me. Maybe I'm mistaken. > > Most of all, I'm concerned that my users will need to face the error > reports from GHC and could get tripped by laziness, i.e. write > something that would make the app run out of memory. Off the top of my > head I can't figure out a way to limit what my users can do without > analyzing the Haskell AST within the GHC API and complaining if > necessary. > > Can someone with experience in offering a Haskell DSL to their users > please comment? > > Notice that I'm not even mentioning being concerned with the > unpredictable effects of laziness. There's probably a reason why Jane > St Capital is using OCaml instead of Haskell. I'm not going to play in > that league but my knee-jerk reaction is to use OCaml or Lisp and > avoid laziness altogether. I just can't see how laziness can help in > processing real-time price data. > > Thanks, Joel > > [1] http://www.tradestation.com/default_2.shtm > [2] http://www.ninjatrader.com/webnew/index.htm > > -- > http://wagerlabs.com > > > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Re: [Haskell-cafe] Haskell performance question
by Dan Piponi 08 Nov '07

08 Nov '07

On Nov 8, 2007 11:36 AM, Paul Brown <paulrbrown(a)gmail.com> wrote: > All that said, I'm not sure where I got the GHC that I used to build > the 6.6.1 via MacPorts; I think it shipped with MacOS once upon a time. > sudo port install ghc . . . configure: error: GHC is required unless bootstrapping from .hc files. But I do have a plan... -- Dan

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Standalone PNG module?
by Peter Verswyvelen 08 Nov '07

08 Nov '07

I would like to load 32-bit images (RGB+alpha) for use with GLUT/OpenGL. I know GTK2HS has support for loading images, but does a standalone Haskell (wrapper) module exists for loading images? PNG or TGA would be enough for me. Yes, I could of course just use the GTK2HS OpenGL widget support, but I already have written most of my code on top of GLUT. Or I could use the SDL wrapper, but that one does not work with GHCI under Windows. Thanks, Peter

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