October 2006 - Libraries

RE: Idea to allow people to comment on Haskell docs
by Simon Peyton-Jones 09 Jan '07

09 Jan '07

| I've had a go at patching Haddock to put a link on the page for each | module. It's controlled by an optional --wiki=URL flag. | | As an example, I used this with the (devel version of the) Gtk2Hs docs: | | http://haskell.org/gtk2hs/docs/devel/ | | For example this page: | | http://haskell.org/gtk2hs/docs/devel/Graphics-Rendering-Cairo-SVG.html It looks great! But I'd never have found the link if you hadn't pointed me at it. Rather than "Wiki" say "User comments". And I think the per-entry [User comment] link is essential. Typically people are going to be looking at a particular thing. For example, here http://haskell.org/gtk2hs/docs/devel/Graphics-Rendering-Cairo-SVG.html#v %3AsvgRenderFromString is where I'd look for the link for svgRenderFromString. Does MediaWiki support anchors in the middle of a page? That's essential here -- we want one Wiki page for one Haddock page. On a closely related matter, Benjamin Pierce told me how often he wished that there was a link from the Haddock documentation to the source code for a function. Especially for Prelude functions, he's dead right. So another really useful Haddock enhancement would be the ability to add links to the source code from the Haddock docs --- again on a per-function basis. Do you feel like adding that too? Where should the code live? I'd suggest snap-shoting it at the moment that the Haddock docs are generated, and putting the files with the Haddock docs. Simon

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Re: [GHC] #974: Add isLeft, isRight, fromLeft, fromRight, and splitEithers to Data.Either
by dons＠cse.unsw.edu.au 07 Dec '06

07 Dec '06

ndmitchell: > Hi > > >#974: Add isLeft, isRight, fromLeft, fromRight, and splitEithers to > >Data.Either > > Woohoo! Finally! > > >This proposal would add basic functionality to `Either` similar to that > > for `Maybe`. The `splitEithers` function of type `[Either a b] -> > > ([a],[b])` is unique; however, it seems to be a widely useful function. > > This (in my mind) is a parallel to unzip? unzipEithers to me gives a > much clearer picture of what is going on here. yeah, if its an unzip, then unzipEithers makes more sense. -- Don

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Success Story: Cabal and Dlls
by Jason Dagit 01 Dec '06

01 Dec '06

Hello, I would like to report that I was able to use Cabal with Visual Haskell to build Dlls in windows. I have posted the details about this on the Haskell wiki (and started an extremely minimal Cabal page). If my content is in the wrong place, please feel free to move it (or edit it or whatever). http://www.haskell.org/haskellwiki/Cabal The trick was to take the final HSfoo-0.1.o file generated by the normal build process (and linked with the DllMain.c code) and tell ghc to build a dll. I use -package with each of the dependencies in the cabal file to link with the needed libraries. The resulting dll seems to be working. This approach is a bit hackish and while I've tried to implement as much of it as I can in a general way it requires you to hack your Setup.lhs file if you want to 1) build static 2) specify your exports 3) specify the name of the resulting dll. Also, it's only been tested on my setup which uses Visual Haskell so it may not be fit for general consumption. Finally, I just started really looking at Cabal yestarday so I may not have considered things which an experienced Cabal user would think about. Is it possible to get this functionality built directly into Cabal so that I tell it I want a DLL built from a library and it knows how to make it happen? Thanks, Jason

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Re: [Haskell-cafe] deepSeq vs rnf
by Cale Gibbard 27 Nov '06

27 Nov '06

On 22/10/06, Chad Scherrer <chad.scherrer(a)gmail.com> wrote: > Hi, > > I had posted this question a while back, but I think it was in the > middle of another discussion, and I never did get a reply. Do we > really need both Control.Parallel.Strategies.rnf and deepSeq? Should > we not always have > > x `deepSeq` y == rnf x `seq` y > ? > > Maybe there's a distinction I'm missing, but it seems to me they're > basically the same. I agree, they are the same. The Strategies library also gives much more general operations for working with strictness and parallelisation. That library seems to need more love, I think it's a great idea, but it doesn't really get noticed all that much. The Hierarchical libraries documentation for it is a little lacking -- it doesn't even provide a reference or link to the paper, and many of the combinators, as well as the general idea of how to use it are undocumented from there. It also spuriously contains an Assoc datatype, which if I recall correctly, was an example from the paper, but doesn't really belong in the library as far as I can tell. It would also be really nice to see the list of instances for the NFData class expanded to include other datatypes in the libraries, possibly also with compiler support for deriving, since it's mostly boilerplate. Speaking of boilerplate and the scrapping thereof, Data.Generics could theoretically also be used to write a relatively generic rnf/deepSeq, but in my attempts, it seems to be much much slower than using a specific normal form class. Here's my code from quite a while back. As I recall, it's semantically correct, but ran about an order of magnitude slower. There might be a much better way to do it, I don't really know Data.Generics all that well. rnf :: (Data a) => a -> () rnf x = everything (\x y -> x `seq` y) (\x -> x `seq` ()) x deepSeq x y = rnf x `seq` y f $!! x = rnf x `seq` f x - Cale

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darcs patch: Implementation of aton and ntoa outside ... (and 1 more)
by Robert Marlow 16 Nov '06

16 Nov '06

Mon Sep 25 16:55:55 JST 2006 Robert Marlow <bobstopper(a)bobturf.org> * Implementation of aton and ntoa outside the IO monad This is a second attempt at the earlier patch inet_ntoa and inet_aton can be implemented purely to avoid the need for the IO monad. Additionally, inet_addr is currently incorrect due to using the inet_addr C function which is considered obsolete due to incorrectly failing while converting 255.255.255.255 as an address. Mon Sep 25 17:12:52 JST 2006 Robert Marlow <bobstopper(a)bobturf.org> * Fixed bugs in names of aton and ntoa

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Data.List.join
by Josef Svenningsson 15 Nov '06

15 Nov '06

Hi, I'd like to propose to include the following function in Data.List: join :: [a] -> [[a]] -> [a] join x xs = concat (intersperse x xs) I find that every time I use intersperse I also concat the result. And it seems that I'm not alone: http://www.google.com/codesearch?q=file%3A%5C.hs+intersperse&btnG=Search+Co… A clear majority of all the uses of intersperse also use concat on the result. I think it seems worthwhile to give a name to that idiom. The name 'join' was taken from Data.ByteString, where a similar function exists. All the best, Josef Svenningsson

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Guidelines for proposing library changes
by dons＠cse.unsw.edu.au 10 Nov '06

10 Nov '06

After some discussion on the libraries list, I've put up the suggested 'best practice' for proposing library changes, here: http://haskell.org/haskellwiki/Library_submissions The idea is to reduce the number of 'bikeshed' discussions we're having, ensure that submissions are not dropped, and generally improve productivity. People should refer to this when proposing new functions for the core libraries, at risk of not having the suggestion adopted or considered ;) Cheers, Don

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Speaking of small functions
by Cale Gibbard 03 Nov '06

03 Nov '06

Speaking of small functions, Kleisli composition should at least be in Control.Monad. It's a simple thing, and not commonly explicitly used at the moment, but rather important conceptually. (@@) :: (Monad m) => (b -> m c) -> (a -> m b) -> (a -> m c) g @@ f = \x -> f x >>= g

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hs-plugins: dynamic linking error with .ctors section
by Cyril Schmidt 03 Nov '06

03 Nov '06

I am using hs-plugins to load some Haskell modules dynamically. It all goes well until I try to load a module that uses a package with some C++ code in the implementation. The module in question, A.hs, uses a package named RGPack, which consists of some C++ code and a single Haskell module that provides the necessary `foreign import' declarations. The package (including the C++ code) is built by GHC. When I try to load A.hs using hs-plugins, I get the following error: Unknown PEi386 section name `.ctors' (while processing: C:\Program Files\Haskell\RGPack-0.0\ghc-6.4.2/HSRGPack-0.0.o) When I link A.hs statically (using `import A' in my main module), it works fine. I am fairly sure that the problem is somehow related to the usage of the C++ code in the package (because .ctors section is C++-specific), but I have no idea how I can remedy this. Rewriting the C++ code to pure C is an obvious workaround, but I'd prefer to try something else before I resort to this ;-) For the record, I use GHC 6.4.2 on Windows, hs-plugins-1.0-rc0. I will greatly appreciate any hints. Cheers, Cyril

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Re: [GHC] #971: Add intercalate and split to Data.List
by Christian Maeder 02 Nov '06

02 Nov '06

> = Split = > Bulat Ziganshin suggested also adding a function split which is a right > inverse of intercalate. Donald Steward seemed to agree with this decision. > No one else raised their voice about this so it seems uncontroversial. I also agree to add a split function. The problem was to agree which variant should be called split (wrt. to treatment of multiple and final separators as well as to "Eq" context or predicate argument). http://article.gmane.org/gmane.comp.lang.haskell.libraries/4862 http://article.gmane.org/gmane.comp.lang.haskell.libraries/4869

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