December 2008 - Haskell-Cafe

Haskell project proposals reddit
by Don Stewart 11 Dec '08

11 Dec '08

I'd like to echo Jason's remarks earlier. http://www.reddit.com/r/haskell_proposals/ We've tried for a couple of years now to efficiently track 'wanted libraries' for the community, but never with much success. In particular, two approaches have been tried: * a wiki page * the 200{6,7,8} summer of code trac neither proved workable long term, likely because no one knew about them, they're harder to contribute to and other factors. Now I know there's a lot of spare Haskell capacity in this community. 3000 mailing list readers, but only 70 new libraries a week being uploaded to Hackage --- that's not how we take over the world! So this is your chance to contribute: * propose new libraries, and explain why you'd want them * vote on things you'd like to see * pick up tasks that sound interesting Let's try to make this work! -- Don

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unsafeThawByteArray#
by Patrick Perry 11 Dec '08

11 Dec '08

I've noticed that there is no longer an "unsafeThawByteArray#" function in GHC.Prim. Looking through the darcs history, I found a patch with description: [project @ 2000-03-13 12:11:43 by simonmar] simonmar**20000313121144 Remove unsafeThawByteArray# primop (which was a no-op), and use unsafeCoerce# instead. ] Is the following code safe? data IntArray = IntArray !Int (ByteArray#) data STIntArray s = STIntArray !Int (MutableByteArray# s) unsafeThaw :: IntArray -> ST s (STIntArray s) unsafeThaw (IntArray n arr#) = ST $ \s1# -> let coerceArray :: State# s -> MutableByteArray# s coerceArray _ = unsafeCoerce# arr# marr# = coerceArray s1# marr = STIntArray n marr# in (# s1#, marr #) Thanks, Patrick

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Re: [Haskell-cafe] A curios monad
by Andrew Coppin 11 Dec '08

11 Dec '08

Alberto G. Corona wrote: > but because keys and data must be of the same type, you are restricted > to instances of Eq and Ord. Itsn´n true? > > 2008/12/11 Andrew Coppin <andrewcoppin(a)btinternet.com > <mailto:andrewcoppin@btinternet.com>> > > Alberto G. Corona wrote: > > Well, you have not to use typeable, but instead you need to > use instances of Eq and Ord. This is because the values and > the keys must be of the same type. this is the tradeoff. > > > Not really, no. The *keys* need Eq and Ord, but the values I'm > storing don't. The values I'm storing don't need any specific > properties at all. That's what I like about it. > > No. Keys are of type "Key v", where "v" can be anything. It's a phantom type, so it's not used for anything (except knowing what to coerce the value back to when it's looked up). "Key v" is just an alias to Int, which *is* in Eq and Ord, as required. There are no constraints on "v" at all.

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problems configuring hs-plugins 1.3.1 in windows
by Alberto G. Corona 11 Dec '08

11 Dec '08

I have problems compiling plugins 1.3.1 in windows at the configure phase configure: error C compiler cannot create executables I use ghc 6.8.2 I know that plugins is nor much tested under windows but I´m trying anyway. I think that this problem is very common also in Linux. I tried to find references to this error ut all of then are old (for plugins 1.2) and it is supposed to be solved. Do you have any workaround? By the way the reported compiler used is gcc Responder Responder a todos Reenviar

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Re: [Haskell-cafe] A curios monad
by Andrew Coppin 11 Dec '08

11 Dec '08

Alberto G. Corona wrote: > it is safe to use unsafeCoherce in your context? I mean, I think you > need to use instances of Data.Typeable (or some with the same > functionality) to make it safe. Like in Data.Dynamic... The *only* way for you to generate a Key value is to use the function I provide - which conviniently tags it with the type of value it's supposed to retreive. That means the type cast is guaranteed to cast it back to the type it was in the first place. ...unless you can muddle keys from other state threads up. In that case, all bets are off. I looked at using Data.Dynamic, but that only works for a few types. I wanted something that will work for *any* type.

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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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