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Re: [Haskell] ANNOUNCE: Visual Haskell prerelease 0.2
by Johannes Waldmann 01 Dec '06

01 Dec '06

> > Not only the interfaces [Visual Studio vs. Eclipse] > > are completely different, but an entirely new > > set of interoperability problems would need to be solved. ... I still don't see what would be the fundamental difference. (Except perhaps that the Eclipse interfaces are easily available and well documented so it is at least possible to describe the interface problems...) The main advantage (Visual Haskell over eclipsefp) at the moment is that VH uses incremental (on-the-fly) typechecking/compilation while eclipsefp calls the compiler for whole modules? What source text transformations (refactorings) does VH support? Best regards, -- -- Johannes Waldmann -- Tel/Fax (0341) 3076 6479/80 -- ---- http://www.imn.htwk-leipzig.de/~waldmann/ -------

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Re: How to get subset of a list?
by oleg＠pobox.com 01 Dec '06

01 Dec '06

Huazhi (Hank) Gong wrote: > Like given a string list s="This is the string I want to test", I want to get > the substring. In ruby or other language, it's simple like s[2..10], but how > to do it in Haskell? Quite simply, actually: > infixl 1 %% > str %% idxs = map (str !!) idxs That is it. Not the most efficient, but gets the job done. > tstring = "This is the string I want to test" > test1 = tstring %% [2..10] *Sub> test1 "is is the" > However, like I want to choose s[1,3,6,10] or something like this. > Are there some straightforward function or operator for doing this > job? Yes, see above. > test2 = tstring %% [1,3,6,10] *Sub> test2 "hsse" Indices don't have to be in the increasing order > test3 = tstring %% [10,6,3,1] *Sub> test3 "essh" or in any order... > test4 = tstring %% [10,6,3,1]++[2..10] *Sub> test4 "esshis is the" Of course if one cares about the overhead of running code (rather than the overhead of writing code), one would probably ask, as several posters did, if the list of characters is the right data structure and if the problem indeed calls for random access to the elements of the list.

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Building Binaries with Cabal
by John Goerzen 30 Nov '06

30 Nov '06

Hi folks, I'm in need of some Cabal assistance. I want to build the unit tests for MissingH using Cabal. According to the docs, this should require me to list all of the exposed modules from the library as other modules to the binary. Since there are dozens of these, I thought a simple hook could do the trick. I tried hooking into the confHook (which I have already used successfully to add "unix" as a build-dep on non-Windows platforms), and thought I could just pull the exposedModules list from the package and add those as otherModules to the executable. But it had no effect. So I tried hooking in to customBuildHook to do the same thing. Again, no effect. Here's the code I've tried. Suggestions appreciated. import Distribution.Simple import Distribution.PackageDescription import Distribution.Version import System.Info import Data.Maybe winHooks = defaultUserHooks {confHook = customConfHook} customConfHook descrip flags = let mydescrip = case System.Info.os of "mingw32" -> descrip _ -> descrip {buildDepends = (Dependency "unix" AnyVersion) : buildDepends descrip} in (confHook defaultUserHooks) mydescrip flags customBuildHook descrip lbi uh flags = let myexecutables = map bdfix (executables descrip) bdfix exe = exe {buildInfo = (buildInfo exe) {otherModules = exposedModules . fromJust . library $ descrip}} mydescrip = descrip {executables = myexecutables} in (buildHook defaultUserHooks) mydescrip flags main = defaultMainWithHooks winHooks

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New Name for MissingH?
by John Goerzen 30 Nov '06

30 Nov '06

Quick feedback time... One comment people made in the Future of MissingH thread was that the name isn't very suggestive of what the library does. I'm planning to follow the advice of many people and split the major MissingH components off into smaller bits (ConfigParser, HVFS, etc). MissingH itself will then contain any small utility functions (probably mainly string and list-related) that for whatever reason aren't suitable to go into base. What should it be called? Should it keep the MissingH name? The alternative I've been thinking of is something like Haskell Utility Library (HUL). Ideas?

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Command line utility that shrinks/simplifies functions applications ?
by Nicola Paolucci 30 Nov '06

30 Nov '06

Hi All! Haskell newbie here with a very simple question because google and hoogle are of no help. On the IRC channel #haskell (which I cannot access now from work) I saw somebody using a tool which automatically simplifies expressions,composition of multiple functions to the bare minimum. It was a query to lambdabot I think. Is that tool/library also standalone ? What's its name ? Where can I find it ? That really rocked ... Thanks, Nick

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[Redirect] polymorphism and existential types
by dons＠cse.unsw.edu.au 30 Nov '06

30 Nov '06

Redirected to haskell-cafe(a)haskell.org, the right list. -- Don ----- Forwarded message from Louis-Julien Guillemette <guillelj(a)iro.umontreal.ca> ----- Date: Mon, 27 Nov 2006 16:15:26 -0500 (EST) From: Louis-Julien Guillemette Subject: [Haskell] polymorphism and existential types Supposing a polymorphic value (of type, say, forall a . ExpT a t) is stored inside an existential package (of type, say, forall a . Exp a), I wonder how to recover a polymorphic value when eliminating the existential. The ``natural way'' to write this doesn't work: {-# OPTIONS -fglasgow-exts #-} data ExpT a t data Exp a = forall t . Exp (ExpT a t) f :: (forall a . ExpT a t) -> () f e = () g :: (forall a . ExpT a t) -> () g e = let e1 :: forall a . Exp a e1 = Exp e in case e1 of Exp e' -> f e' {- Test.hs:18:17: Inferred type is less polymorphic than expected Quantified type variable `a' is mentioned in the environment: e' :: ExpT a t (bound at Test.hs:18:11) In the first argument of `f', namely `e'' In the expression: f e' In a case alternative: Exp e' -> f e' Failed, modules loaded: none. -} In particular, the solution of pushing the forall inside doesn't work for me (it breaks other parts of my code...) : data Exp' = forall t . Exp' (forall a . ExpT a t) g' :: (forall a . ExpT a t) -> () g' e = let e1 :: Exp' e1 = Exp' e in case e1 of Exp' e' -> f e' Any help welcome! Louis-Julien _______________________________________________ Haskell mailing list Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell

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The Future of MissingH
by John Goerzen 30 Nov '06

30 Nov '06

Hi, Josef Svenningsson posted a comment on my blog today that got me to thinking. He suggested that people may be "intimidated by the size of MissingH, confused by the undescriptive name, and don't quite know what's in there." And I think he's right. I've been passively thinking about what MissingH should be for awhile now, and wonder if you all would have some suggestions. First, let me back up and describe a bit of what MissingH is. It gets its name because I think that it has useful functions that are "missing" from the standard Haskell libraries. But I can see how it's not very descriptive. The major features are: * A general-purpose modular logging infrastructure * A virtual filesystem component (similar to VFS in Gnome, but written in Haskell) * A configuration file parser, compatible with Python's and Perl's, which can also modify and generate config files and do variable interpolation * A bunch of tools for setting up pipes to/from processes * Tools to format numbers as quantities, with default configs for the SI system (1000-based) and binary system (1024-based) * Tools to track the progress of long-running actions and display a status bar on the terminal * Pure-Haskell un-gzip code, *DBM infrastructure, etc * Assorted list, string, regexp, bit, pointer, etc. utilities * MIME and email parsers. I wrote most of the code myself, but did pull some large chunks from others where licenses were compatible. The API reference is at http://gopher.quux.org:70/devel/missingh/html/index.html So, some of the questions are: Should this all be one library? I initially wrote it that way to make resolving dependencies easier for end users. Also, it still has utility because modules make use of each other's features. The list and string functions are used almost everywhere, for instance. HVFS support is also fairly pervasive. Should the module naming scheme be changed? Modules are currently named things like MissingH.List, MissingH.IO.HVFS, MissingH.ProgressMeter, etc. I guess these could go to System.ListExt, System.IO.HVFS, System.Console.ProgressMeter, etc. Could, and should, any of this be integrated into the Haskell libraries project? (That set of libraries formerly known as fptools) A few bits of code have already found their way into them. But I bet there could be a lot more. Maybe even the majority of it. How could greater community participation be encouraged, while still encouraging quality control? I have received some very good contributions to MissingH from people, and that's been great. I've also received some that just aren't that great -- they don't have Haddock docs, the code is opaque, they don't come with unit tests, etc. But by and large, I've been maintaining it mostly myself. Whenever I write some code, I think about whether this is generic code that could be useful in other projects. If so, I consider whether it would be appropriate for MissingH (and it usually is). It would be wonderful if others would be interested in contributing code that solves some need as well. There is a public darcs repo already, and I have received some darcs patches from people (thanks!) I'm not trying to rid myself of MissingH, but I think that it could be a nice resource for small tools from the entire community, if we can maintain a structure and QA footprint to it. What else should be done to make this a valuable resource for Haskell programmers? And a showcase for what is possible with Haskell? The floor's open... Thanks, -- John

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Lazy data from pipe using MissingH module
by Dougal Stanton 30 Nov '06

30 Nov '06

Newbie here working on a little program for fetching podcasts. I've been using the MissingH.Cmd module in concert with curl to download the RSS feeds like this: > fetchFeed :: Subscription -> IO (Either Error [Episode]) > fetchFeed sub = do > (pid, feed) <- pipeFrom "curl" (curlOpts ++ > ["--url", (slocation sub)]) > let eps = parseEpisodes (stitle sub) feed > forceSuccess pid > return eps According to the API docs I have to forceSuccess pid *after* I use the data. Will this construct do that, or does the compiler have free reign to move the line beginning 'let ...' wherever it feels? It seems to work occasionally for me but then just hangs, so I thought this might be the problem. Cheers, D. -- Dougal Stanton <ithika(a)gmail.com> <http://brokenhut.livejournal.com> Word attachments considered harmful.

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generating javascript
by jeff p 30 Nov '06

30 Nov '06

Hello, Are there any Haskell tools to generate javascript? Has anyone made a combinator library for javascript? thanks, Jeff

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SimonPJ and Tim Harris explain STM - video
by Bayley, Alistair 30 Nov '06

30 Nov '06

http://channel9.msdn.com/Showpost.aspx?postid=231495 The links to the video are a couple of yellow buttons at the bottom of the article: "Watch" or "Download". I haven't watched this yet (it's nearly an hour long, I think). Found via reddit (http://reddit.com) Haskeller's on TV (sort of...) woot woot! Alistair ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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