August 2004 - Haskell

Mixing monadic and non-monadic functions
by Sean E. Russell 17 Sep '05

17 Sep '05

Hello, I posted this question to comp.lang.functional, and someone suggested that I try this group instead. I'm struggling with monads. Well, not monads themselves, but mixing them with non-monadic functions. Here's my base case: someFunc :: String -> IO [a] ... ax <- someFunc a bx <- someFunc b assertBool "fail" $ length ax == length bx I don't like the assignments; the typing is redundant, if I have a lot of asserts like this, and the "variables" are temporary. What I'd much rather have is: ... assertBool "fail" $ (length $ someFunc a) == (length $ someFunc b) which is more readable, to my eye. The only solution which has been suggested that may work is liberal use of the liftM variants, but this gets *really* tedious and obtuse. Is there an elegant way to do what I want to do, or am I stuck with procedural-style assignments and bunches of temp vars? Thanks! -- ### SER ### Deutsch|Esperanto|Francaise|Linux|XML|Java|Ruby|Aikido ### http://www.germane-software.com/~ser jabber.com:ser ICQ:83578737 ### GPG: http://www.germane-software.com/~ser/Security/ser_public.gpg

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WS-FM 2004 Call For Participation
by Mario Bravetti 20 Jul '05

20 Jul '05

---------------------------------------------------------------------- We apologize if you receive multiple copies of this announcement. ---------------------------------------------------------------------- ====================================================================== 1st International Workshop on Web Services and Formal Methods (WS-FM 2004) February 23-24, 2004, Pisa, Italy Workshop affiliated to COORDINATION 2004, February 24-27, 2004 WS-FM 2004 homepage: http://www.cs.unibo.it/~lucchi/ws-fm04/ ====================================================================== - The technical program is available at: http://www.cs.unibo.it/~lucchi/ws-fm04/ - Information about registration, travel and accomodation can be found at the COORDINATION 2004 web site: http://www.di.unipi.it/Coordination2004/ If you intend to participate, we recommend you to register and book the hotel as soon as possible. The Coordination 2004 Organizing Committee informed us that hotels are going to be fully booked in short time.

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Announce: Cabal 0.1 (Library Infrastructure Project)
by Isaac Jones 01 Nov '04

01 Nov '04

Much thanks to all who've made this possible :) The Haskell Cabal The Common Architecture for Building Applications and Libraries. DOWNLOAD: The Haskell Cabal has reached pre-release stage, with a 0.1 version The community should use this release to evaluate the interfaces and explore the concepts of these tools. Download the Cabal here: http://www.haskell.org/cabal/download.html BUGS: Please report bugs and wish-list items here: http://sourceforge.net/tracker/?func=add&group_id=44807&atid=440922 Or email Isaac Jones: ijones(a)syntaxpolice.org ABOUT: The Haskell Cabal is meant to be a part of a larger infrastructure for distributing, organizing, and cataloging Haskell Libraries and Tools. It is an effort to provide a framework for developers to more effectively contribute their software to the Haskell community. Specifically, the Cabal describes what a Haskell package is, how these packages interact with the language, and what Haskell implementations must to do to support packages. The Cabal also specifies some infrastructure (code) that makes it easy for tool authors to build and distribute conforming packages. The Cabal is only one contribution to the larger goal. In particular, the Cabal says nothing about more global issues such as how authors decide where in the module name space their library should live; how users can find a package they want; how orphan packages find new owners; and so on. NOTES: This release is meant to provide the community with concrete information about how the interfaces are shaping up. This release does NOT fix the interfaces, we can't promise not to break anything that relies on these interfaces. We hope that Haskell authors will try to package their software using these tools, and let us know where they fall short. MORE INFORMATION: Please see the web site for the source code, interfaces, and especially the proposal, which will serve as documentation for this release: http://www.haskell.org/cabal/

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Newbie Question about Types
by David Greenberg 06 Sep '04

06 Sep '04

Hi, I very recently just came to Haskell from the Java and Perl worlds, so my understanding of Haskell's type system is still a little vague. The tutorial and Google didn't seem to have an answer to my question, so I am hoping someone here might be able to help me. I am writing some code comparable to the following: class Fooable a where foo1 :: a -> a -> a foo2 :: a -> a -> a type MyType a = String -> a data (Fooable (MyType a)) => AnotherType a = AnotherType {str :: String, myval :: (MyType a)} instance (Fooable (MyType a)) => Fooable (AnotherType a) where (AnotherType s1 m1) `foo1` (AnotherType s2 m2) = AnotherType "dummy string" (m1 `foo1` m2) The trick here is I want to be able to pass a value of type MyType to the AnotherType constructor without making MyType directly an instance of Fooable. In other words, I want some sort of sub-type of MyType to be an instance of Fooable. That way I can use it in the constructor of AnotherType. I understand that type inference might make a lot of this easier, but I am trying to make a very strict API out of my module(s), and feel that relying on inference at this stage could become buggy. Thanks in advance for any help that you all can give me. -David

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ANNOUNCE: Zinc Curry Compiler 0.9.1 released
by Diego Berrueta 31 Aug '04

31 Aug '04

I'm glad to announce the new release of the Zinc Curry Compiler. It is still under development, so many features may fail, but it should perform OK with simple programs. The Zinc Compiler is the result of an effort to write an experimental compiler for a version of the Curry functional logic programming language[1], extended with Haskell's type classes. The Zinc project is being developed at the University of Oviedo (Spain) by Diego Berrueta as a final year project, under the direction of Prof. Jose E. Labra. The compiler is written in Haskell, on the top of the Münster Curry Compiler[2]. The current release of the Zinc Compiler is 0.9.1. Sources and instructions can be grabbed from the project web site at http://zinc-project.sourceforge.net/ Any feedback will be greatly appreciated. [1] http://www.informatik.uni-kiel.de/~mh/curry/ [2] http://danae.uni-muenster.de/~lux/curry/ -- ________________ | Diego Berrueta \_______________________ | E-mail: <diego(a)berrueta.net> | | Jabber: berrueta(a)jabber.org | | AsturLiNUX: http://www.asturlinux.org/ | |________________________________________|

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Re: [Haskell] Dependent types, was:2-D Plots, graphical representation of massive data
by MR K P SCHUPKE 31 Aug '04

31 Aug '04

>I think you are confusing Dependent Types with Functional Dependencies. Actually the two are not that dissimilar... If we allow types to depend on types (which is what Functional Dependencies allow) IE: class a b | a -> b instance Int Float instance Float Int For example is really a function on the type level mapping a to b. All that is missing is a way to make types depend on values... which can be done with dictionary passing. Here is an example: class ReifyBool t w where reifyBool :: Prelude.Bool -> t -> w instance (Apply t AllTrue w,Apply t AllFalse w) => ReifyBool t w where reifyBool Prelude.True t = apply t AllTrue reifyBool Prelude.False t = apply t AllFalse The limitation here is that an 'instance' must exist for each possibility in the program, so we are limited to a finite range of values... although we can use type recursion in the class to make the code smaller, we still must have some limit known at compile time, for example Int: class (NotNegative m,NotPositive n) => ReifyNotPositive m t i n w where reifyNotPositive :: Integral i => m -> t -> i -> n -> w instance NotPositive n => ReifyNotPositive Zero t i n w where reifyNotPositive _ _ _ _ = error "Number to be reified exceeds maximum range." instance (NotPositive n,ReifyNotPositive m t i (Pre n) w,Ctrl.Apply t n w) => ReifyNotPositive (Suc m) t i n w where reifyNotPositive (Suc m) t i n | i<0 = reifyNotPositive m t (i+1) (Pre n) | otherwise = Ctrl.apply t n (I appologise if the code is a little verbose, but to avoid mistakes I have cut and pasted from a working project - but you can see the important features)... So by combining reification to a type level representation and functional dependancies we arrive at dependant types... Keean./

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ListMap example
by jeff polakow 31 Aug '04

31 Aug '04

Hello, Why is the following not an arrow? newtype ListMap i o = LM ([i] -> [o] instance Arrow ListMap where pure f = LM (map f) LM f >>> LM g = LM (g . f) first (LM f) = LM ((uncurry zip) . (cross f id) . unzip) thanks, Jeff

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BBEdit syntax highlighting for Haskell
by David Menendez 31 Aug '04

31 Aug '04

If anyone else is using BBEdit 8.0 on the Mac, I've put together a simple language module for highlighting Haskell syntax. <http://www.eyrie.org/~zednenem/sw/bbedit/haskell-syntax.plist> To install, download the file above to ~/Application Support/BBEdit/Language Modules and restart BBEdit. -- David Menendez <zednenem(a)psualum.com> | "In this house, we obey the laws <http://www.eyrie.org/~zednenem> | of thermodynamics!"

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2-D Plots, graphical representation of massive data
by Frédéric Nicolier 29 Aug '04

29 Aug '04

I have done some code in order to interface haskell and octave. It is actually very simple, but it works. The communication between octave and haskell is done via files. I'm planning to change this and use sockets. This file belongs to my project : use haskell for image/signal procesing algorithms. For my opinion, people (in image processing reseach) uses matlab/octave because it allow bad programmers to test new algorithms very easy. Haskell can do better in this task. Fred \begin{code} ----------------------------------------------------------------------------- -- | -- Module : HipsExternal -- Copyright : (c) Fred Nicolier 2004 -- License : GPL -- -- Maintainer : Fred Nicolier -- Stability : experimental -- Portability : portable -- -- Links to external computation engine (octave) -- -- Examples: -- -- >myCos :: Num a => a -> Double -- >myCos x = head.head.octaveFunc $ ["a=" ++ show x, -- > "export(cos(a))"] -- > -- >doubleOct :: Num a => [a] -> [Double] -- >doubleOct list = head.octaveFunc $ ["a=" ++ show list, -- > "export(2*a)"] -- -- >fftOct list -- > = octaveFunc ["s=" ++ show list, -- > "f=fft(s)", -- > "export(real(f),imag(f))"] ----------------------------------------------------------------------------- module HipsExternal (octaveExec, octaveSend, octaveFunc ) where import System import IO import System.IO.Unsafe -- --------------------------------------------------------- -- --------------------------------------------------------- octaveExec :: [String] -> IO String octaveExec cmds = do system ("./octaveshell \"" ++ cmd ++ "\"") readFile "export.dat" where cmd = foldr insertSep "" cmds insertSep a b = a ++ ";" ++ b octaveSend :: [String] -> IO ExitCode octaveSend cmds = do system ("./octaveshell \"" ++ cmd ++ "\" &") where cmd = foldr insertSep "" cmds insertSep a b = a ++ ";" ++ b octaveFunc :: [String] -> [[Double]] octaveFunc = (map $ (map read).words).lines.unsafePerformIO.octaveExec \end{code} octaveshell is just a excutable file containing : \begin{code} #!/bin/sh echo "$*" | octave -qf \end{code} Fred Nicolier ------------------------------------------------- This mail sent through IMP: http://horde.org/imp/

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RE: [Haskell] 2-D Plots, graphical representation of massive data
by Zabiyaka, Yuliya 28 Aug '04

28 Aug '04

>I would like to ask the original poster, who asked first about the >Matlab<->Haskell links >what are her/his *concrete* problems... I have a list of timestamps representing how long it takes a process to finish under different conditions. I also have a summary of the stages that process goes through. It is way too many numbers to make sense of them without some kind of graphical representation. I get all these information out of Haskell simulator. Therefore I would like to be able to do two things in Haskell: 1) analyze the data (mean, std dev etc) - that's the easy part and I more or less know how to do it in Haskell 2) display result of the analysis (pie charts, histograms, plots) Yulia

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