September 2007 - Haskell-Cafe

"Functional dependencies conflict between instance declarations"
by Peter Verswyvelen 12 Sep '07

12 Sep '07

The Haskell mailing list seems to be filled with people requesting information about this error, so I cannot resist to include myself in it ;-) I've read the information about funcdeps in the GHC user guide, and I think I understand how it works, but I get the error a lot, without having a clue why. Sometimes I get the error even when all the types of all the type parameters are completely different, so even when all parameters would be one-to-one dependent, I still don't get why I would get a conflict error. Does a wiki exists with possible reasons why this error occured and how to fix it? Thanks, Peter

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Re: [Haskell-cafe] Re: Is "take" behaving correctly?
by PR Stanley 12 Sep '07

12 Sep '07

>Hi > > > The same should apply to head and tail. head or tail of [] should be []. > > > > What does the list think? > >Disagree, strongly. Its not even possible for head, since [a] -> a. >Wadler's theorems for free states that if head is given an empty list >the _only_ thing it can do is crash. What's the logic behind this? Thanks, Paul

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Haddock/hscolour integration broken on Hackage?
by David Menendez 12 Sep '07

12 Sep '07

I was looking at the Data.Binary documentation[1] on Hackage, and I've noticed some problems with the associated source listings[2]. First, none of the "Source" links work. They all refer to fragment IDs (e.g., "#Binary") that are not defined. I'm not sure if this is a problem with hscolor, haddock, or hackage. Second, the source listing itself[2] is invalid HTML[3]. The W3C validator lists 678 errors. Of these, 677 are have to do with the line number anchors, all of which start with parentheses. This is bad not only because HTML requires fragment ids to start with a letter, but because parentheses are not allowed to occur in URIs. As a result, links to line numbers will come out looking like "Data-Binary.html#%28line100%29". [1] <http://hackage.haskell.org/packages/archive/binary/0.3/doc/html/Data-Binary…> [2] <http://hackage.haskell.org/packages/archive/binary/0.3/doc/html/src/Data-Bi…> [3] <http://validator.w3.org/check?uri=http%3A%2F%2Fhackage.haskell.org%2Fpackag…>

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Re: Tiny documentation request
by manu 12 Sep '07

12 Sep '07

On Sep 11, 2007, Simon Marlow wrote: > > Please, please, someone do this for me. I tried, and failed, to > get the > layout right for the contents list in all browsers at the same > time. The > semantics of CSS is beyond my comprehension. > > Cheers, > Simon Hi Simon, On the page http://www.haskell.org/ghc/docs/latest/html/libraries/ index.html, you only need tables to display the foldable lists of modules (HTML tables were commonly used to display many "things" on a same line), but they can be replaced by nested lists with a bit of CSS : Check this page out : http://la.di.da.free.fr/haddock/ I can help further, if need be. Emmanuel

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Developing XPCOM components (Firefox extensions) in Haskell
by Pasqualino 'Titto' Assini 12 Sep '07

12 Sep '07

Hello, I wondered if anyone could advice on how to develop XPCOM components in Haskell. I am aware that HDirect supports COM and that there are some similarities with XPCOM but I do not have the time to extend/fix HDirect to support XPCOM. Would using FFI directly be simpler? What problems should I expect? Would you anticipate platform specific issues ? The components should work under both Linux and Windows and ideally Mac as well. Thanks in advance, titto

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Re: Tiny documentation request
by manu 12 Sep '07

12 Sep '07

On Sep 11, 2007, at 9:58 PM, Miguel Mitrofanov wrote: > > > Well, I'm not a web designer, but I did work with few of them, and it > seems to me that you either create a table design in two hours or > spend three days trying to create a CSS one and THEN create a table > design in two hours. That's an exaggeration. It's widely accepted than tables can straightforwardly be dropped in most cases. They are intented to be used to present tabular datas, NOT for layout. (This ideas is not new, Zeldman talked about it in 2001) It does require a bit of CSS-Fu, however, as CSS support in browsers varies... But hey, you've got to occupy these HTML-CSS guys ! Emmanuel

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GraphicsMagick binding for Haskell
by Tim Chevalier 11 Sep '07

11 Sep '07

As a Hackathon project, I'm thinking of trying to write a Haskell binding for the GraphicsMagick image manipulation library (http://www.graphicsmagick.org/) Has anyone done this already? If not, would anyone else besides me use it? If you think there's a better library out there that serves a similar purpose, feel free to tell me about it as well. Cheers, Tim -- Tim Chevalier * catamorphism.org * Often in error, never in doubt "Work is there when love is gone" -- Greg Brown

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"Prime" monads?
by Greg Meredith 11 Sep '07

11 Sep '07

Haskellians, Is there a characterization of "prime" monads? Here the notion of factorization i'm thinking about is decomposition into adjoint situations. For example, are there monads for which there are only the Kleisli and Eilenberg-Moore decompositions into adjoint situations? Would this be a characterization of quintessentially "free" or "generative"? Best wishes, --greg -- L.G. Meredith Managing Partner Biosimilarity LLC 505 N 72nd St Seattle, WA 98103 +1 206.650.3740 http://biosimilarity.blogspot.com

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Licenses and Libraries
by H. 11 Sep '07

11 Sep '07

Hello, I have some questions connected more with the licenses and libraries as the language itself: Is it possible to: - publish Haskell source code under the BSD3 license - provide an executable binary together with the code "including" (compiled e.g. with 'ghc --make') "standard" (in the ghc compiler download) libraries of the base and/or other packages - publish Haskell source code under the BSD3 license which will work with GTK2HS - provide an executable binary together with the code compiled with 'ghc -- make' - does there have to be any special flags set to do so - does there have to be included further notes about the libraries and/or there license -- Thanks in advance, H.

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Tiny documentation request
by Andrew Coppin 11 Sep '07

11 Sep '07

I have the following page bookmarked: http://haskell.org/ghc/docs/latest/html/libraries/ I'd like to ask 2 things. 1. Would it be possible to make the *huge* list of package names at the top collapsable? (That way I don't have to scroll through several pages of uninteresting text to get to the bit I actually want.) 2. Could we make is so all items are collapsed initially? (Currently they're all expended initially - which makes it take rather a long time to find anything.) Just thought I'd ask...

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