- Haskell-Cafe - Haskell.org

type error
by Cetin Sert 11 Dec '08

11 Dec '08

Hi, Why does this not function? Prelude> sequence [print 'a', print 2] 'a' 2 [(),()] *Prelude> let myprint = print* *Prelude> sequence [myprint 'a', myprint 2]* <interactive>:1:18: Couldn't match expected type `()' against inferred type `Char' In the first argument of `myprint', namely 'a' In the expression: myprint 'a' In the first argument of `sequence', namely `[myprint 'a', myprint 2]' Can providing some type annotations (interactively in ghci or in some .hs file) help solve the problem? Best Regards, CS

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Can my type be allowed as return type in FFI?
by Mauricio 11 Dec '08

11 Dec '08

Hi, When I do: foreign import "nameOfFunction" nameOfFunction :: IO MyType I can get a function that return MyType only if it's a pointer or some of the C* type family. Is it possible to write a new MyType and make it allowed as a return type from foreign functions? Is changing the compiler the only way to do that? Thanks, Maurício

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how to pipe in pure input with HSH? (Would be helpful for sending emails via sendmail/mailx via HSH interface)
by Thomas Hartman 11 Dec '08

11 Dec '08

{- I am trying to figure out a way to send email using HSH and I'm stumped. The problem is that there is no ShellCommand instance for a pure vanilla string, which can be piped into another ShellCommand. There is a ShellCommand String instance, but the string is a command to be executed. I defined PureInput wrapper around String in an attempt to get this working, but I'm stumped defining an fdInvoke method for it. class (Show a) => ShellCommand a where fdInvoke :: a -> System.Posix.Types.Fd -> System.Posix.Types.Fd -> [System.Posix.Types.Fd] -> IO () -> IO [InvokeResult] Can someone help out? Below is a stub. Thomas. -} import HSH newtype PureInput = PureInput { unpureinput :: String } deriving (Read,Show) -- This works fine, blah blah blah gets outputted demo1 = runIO $ ( ( ( ("echo blah blah blah") :: String) -|- ( "cat" :: String) ) :: PipeCommand String String ) -- This is what I want. Specify a pure input string, to be piped into another command. -- In this example it's cat, which isn't very usefuol. -- This would be useful, however, for sending email via sendmail or mailx, with variable input piped in. -- The result should be that "blah blah blah" is printed from cat, just as in demo1. demo2 = runIO $ (PureInput "blah blah blah") -|- ( "cat" :: String) -- How can/should this be done? instance ShellCommand PureInput where fdInvoke (PureInput justAString) ifd ofd closefd forkfunc = undefined

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Retrospective on 2008?
by Don Stewart 11 Dec '08

11 Dec '08

I've been kicking the idea around of a 2008 retrospective. How did we do this year? After all, it has been a dramatic growth period (we're close to 600 people a day in #haskell now, for example, and many new faces!) Some ideas: * 10 best new libraries * 10 best new apps * 10 most influential blog posts * best new library by category Determing this is an interesting task. To start with, I scanned hackage. Some stats: * Hackage currently holds 914 applications and libraries. * 601 of them were released on Hackage this year: http://galois.com/~dons/tmp/new-releases-2008.txt Which is rather impressive, I have to say. We're getting better at the production of new libraries and apps (I imagine all the releases are feeding into new apps and libs in new areas not easily reachable before). The last couple of months, we're averaging around 10 uploads a day, in fact. You can see the upload growth here, http://galois.com/~dons/images/hackage-daily-graph.png We've fundamentally transformed the suitability of Haskell and GHC in a range of domains through the production of these apps and libraries. Well done everyone! Now, as for determining which new things make the top 10, a chance to apply some heuristics? (Most voted on? Most downloaded? Most depended upon by other things?). Any thoughts? Anyone have their own top 10 list? Or other key events of the year? -- Don

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Projects that depend on the vty package?
by Corey O'Connor 11 Dec '08

11 Dec '08

Hello, For further development of the vty package I'm really only paying attention to the requirements that fall out of the Yi project. Are there any other projects that depend on the vty package? In addition, the vty project has it's own wiki: http://trac.haskell.org/vty/ Right now there isn't much information there but it is a great place to send bug reports or enhancement requests if you have them. Cheers, Corey O'Connor

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Re: Haskell-Cafe Digest, Vol 64, Issue 17
by Artyom Shalkhakov 11 Dec '08

11 Dec '08

Hello, 2008/12/10 Ben <midfield(a)gmail.com>: > do you have any plans for iteratee based IO? I would like to use it in XHB (X Haskell Bindings). We use ByteStrings ATM, but I find the code hard to read. > have you seen takusen? Actually, I only took a glance or two. Regards, Artyom Shalkhakov.

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Source code
by Andrew Coppin 10 Dec '08

10 Dec '08

The library documentation pages on Haskell.org used to have helpful links to the library source code. But they don't seem to be there any more. Anybody know why?

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ANNOUNCE: haskell-src-exts 0.4.4
by Niklas Broberg 10 Dec '08

10 Dec '08

Fellow Haskelleers, it is my pleasure to announce the new release of the haskell-src-exts package, version 0.4.4: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haskell-src-exts… darcs get http://code.haskell.org/HSP/haskell-src-exts The new feature in this release is support for pragmas. haskell-src-exts-0.4.4 supports all pragmas supported by GHC, with the exception of option-level pragmas (LANGUAGE, OPTIONS_GHC etc) that appear before the module header. The reason these are not yet supported is simply time, there's no real difficulty involved in supporting them too and I will surely get there eventually. 0.4.4 is backwards incompatible with 0.4.3 for two constructors: * The Module constructor (:: Module) now has an extra argument of type 'Maybe WarningText', used for deprecated modules. * The ImportDecl constructor (:: ImportDecl) now has an extra argument of type Bool, stating whether the SOURCE pragma has been used for the import. The full list of pragmas supported by 0.4.4 is: SOURCE, RULES, DEPRECATED, WARNING, INLINE, NOINLINE, SPECIALISE, CORE, SCC, GENERATED and UNPACK. Cheers and Happy Haskelling, /Niklas

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Re: Iteratee-based IO and lightweight monadic
by John Lato 10 Dec '08

10 Dec '08

> From: "Artyom Shalkhakov" <artyom.shalkhakov(a)gmail.com> > > Hello, > > Is anybody planning to use these shiny new ways for doing IO? > > I'm also interested in a fair comparison of ByteString/Binary > with iteratee-based IO. Has anybody done this? > I would like to use Iteratee-based IO, and have been doing some experiments with it recently for my problem domain (reading sound files). There has been a discussion recently on the haskell-art list about this specific topic. I posted some timing/memory data, and links to my test code, which you should be able to find in the archives if you're interested. I have found that, with my specific implementations and test case, Iteratee-based IO is slightly slower than the most performant ByteString/Binary code I used, however it uses significantly less memory and has nice composability. Also note that my ByteString-based reader actually reads strict ByteStrings and outputs a stream of UArr Doubles (from the uvector package) using unsafeInterleaveIO rather than using lazy ByteStrings directly. Other implementations made different choices, which I covered in some detail in the mentioned thread. Oleg has recently (after I did my tests) published a small library for reading TIFF files using Iteratees. This new code offers some significant advantages over what I was doing with Iteratees, and may offer performance benefits. More work for me... Unfortunately, neither approach (Iteratee nor ByteString) is yet competitive with hsndfile/libsndfile. However, an Iteratee layer that uses hsndfile to read could be implemented, giving the benefits of the Iteratee approach with high performance. I believe the hsndfile authors are interested in this. It should be very easy to implement.

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Re: [Haskell-cafe] File name encodings
by Don Stewart 10 Dec '08

10 Dec '08

Oh, perhaps you want to 'decode' the string that dirOpenDialog returns. redcom: > Hi Don, > > must be doing something wrong. > > The messed up string originates from calling Graphics.UI.WX.dirOpenDialog > and selecting a directory with Umlauts. > > The encode function doesn't seem to help here as it's too far at the end > of the chain. > > Günther > > Am 10.12.2008, 02:45 Uhr, schrieb Don Stewart <dons(a)galois.com>: > > >redcom: > >>Hi, > >> > >>how can I convert a file name with for example umlauts (ü, ä ... ) into > >>UTF8, or some other format that I can actually use it? > >> > >>Günther > >> > > > >Using the utf8-string package to encode the file name string. > > > > e.g. > > > > x <- readFile (encode "ኃይሌ ገብረሥላሴ") > > > > http://hackage.haskell.org/cgi-bin/hackage-scripts/package/utf8-string > >

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