- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] Very crazy
by Andrew Coppin 25 Sep '07

25 Sep '07

Chaddaï Fouché wrote: > 2007/9/25, Andrew Coppin <andrewcoppin(a)btinternet.com>: > >> Forget PrintfType - I can't even understand the haddoc page yet! >> >> (printf performs I/O, yet it is outside the I/O monad. It seems to >> accept an arbitrary number of arguments, which is obviously impossible. >> It's *almost* as scary as the original. Although the original will crash >> your program is you use it wr... oh, so does this one. Cool.) >> > > printf don't always perform IO : if you ask it for a String it will > happily turn into sprintf for you, if you use it in the IO Monad, it > will indeed perform IO, but there's nothing fundamentally IO bound in > printf logic. > That's even *more* impossible... o_O > Well printf crash your program because it can't check if you're > arguments correspond to the chain at compile time (quite obviously > since the chain itself can be dynamic), but it won't corrupt memory or > anything from this kind, so it's arguably much better than the C one. > All I know is that in C, any attempt to use printf() has an 80% probability of causing the machine to dump the entire contents of RAM to stdout until it happens upon a zero byte. Probably the most annoying part was all the 0x07 bytes in there. Do you know what a room full of beeping PCs is like? I do... Sometimes when we got bored, we would "race" our PCs to see which one would stop beeping first. (But they stopped that when I worked out how to make mine "win" every race...)

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bindings to the xmms_remote API, GList and something more
by Andrea Rossato 25 Sep '07

25 Sep '07

Hi, I think there's a huge flaw in the Haskell design: if you conceive such a powerful and expressive programming language, one that empowers even the most ignorant computer user to write complex applications, instead of sticking to basic shell scripting - the only domain graspable by such stupid pseudo-coders -, well you end up with messages like this one flooding the mailing list you are providing for your users. This is what I call inevitability... To make a short story long, I needed some client for the Audacious media player, something I could use to remote control it and, since I'm addicted to Haskell, instead of surfing the web to find a suitable client I surfed the web to find the API documentation. With the FFI, in a matter of half an hour I had the client with all the commands I needed. (The long introduction was written just to let you know that you'd better not waste too much time with what follows...;-) So far so good, but, since everything was so easy, I thought: "Why not packaging a library (and the client) for Hackage? Maybe others may be willing to use it, maybe..." And then the problems start, problems due to my basic ignorance of the C language ("How comes you dare to import in Haskell functions written in a language you don't even understand?" you should replay!). Basically there are two C types I'm having problem with: 1. GList: even though I read the gtk2hs code I do not exactly understand how to create a GList to feed to this function: void xmms_remote_playlist_add(gint session, GList * list); As far as I understand this function takes a session number and a list of files' names. Still I seem not to be able to create a wrapper function around the imported one. 2. what a "gchar ** list" is? As far as my C goes, it should be an array of strings, right? What should I use on the Haskell side, newArray? void xmms_remote_playlist(gint session, gchar ** list, gint num, gboolean enqueue); 3. c2hs v. hsc2hs? Which should I prefer? In c2hs I write {#pointer * GList#}. What is the equivalent in hsc2hs? 4. As I said, I solved my personal problem: I imported enough functions to create the client I needed. Releasing the library is just something I would like to do, to give something back to the Haskell community. So this is something useful if I can provide robust and well designed code. This is a name space question: what is the name of the exported module? Sound.XMMS, Sound.XmmsRemote? Is the some kind of convention I should be referring to? Sorry if I was too long. Moreover I'm asking help I need just to publish a piece of software that is probably useless. Do not waste your time. But if you do, well... thank you, I really appreciate. Andrea

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PROPOSAL: Rename haskell@ to haskell-announce@
by Neil Mitchell 25 Sep '07

25 Sep '07

Hi I've just replied to another first poster with "wrong list". Its entirely not their fault, but its also probably a bit off-putting that your very first post gets a (very polite) "you got it wrong" message. To steal the reasons and explanations from Ian: --------------------- pretty much what would be haskell-announce@ anywhere else, and haskell-cafe@ what would be haskell@ elsewhere. A haskell-cafe@ list elsewhere would probably be where the haskell@ people discuss things which aren't actually related to Haskell (like e.g. the demon.local newsgroup). I think the number of posts in the wrong place would be lower if these were more conventionally named (although there aren't a lot of them anyway). I think it would make sense to: * Rename haskell@ to haskell-announce@, and redirect mails from haskell@ to haskell-announce@ for some period. (more, but can be done step by step in the future) --------------------- I suggest that following somewhat the http://www.haskell.org/haskellwiki/Library_submissions we allow 4 weeks for discussion, and depending on the result we then move the mailing list. Bug to track: http://hackage.haskell.org/trac/ghc/ticket/1732 Deadline: 23 October 2007 Thanks Neil

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non POSIX/Win32 API support
by Galchin Vasili 25 Sep '07

25 Sep '07

Hello, I want to provide support for another OS. How are the POISIX modules implemented? E.g. in terms of Green Card? Kind regards, Bill Halchin

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Re:[Haskell] Math behind Haskell
by Tomas Caithaml 25 Sep '07

25 Sep '07

Hi and thanks for that many replies! > The haskell-cafe@ mailing list is more appropriate for messages such > as this. haskell@ is just for announcements (it should be called > haskell-annouce@ !) Sorry for misposting. > I'd add: > * Discrete Maths - booleans, relations, functions etc. > * Type theory > * Logic programming (Prolog) > * Semantics > Most of these are computer science courses, rather than maths ones. My formulation was somewhat unfortunate on this point. I wasn't strictly looking for math courses, so Type Theory a Semantics seems to be a very good suggestions. Alas, I do not recall any course named "Type Theory" being taught here. But thanks for these hints. I should have probably also noted that I am not new to university (4th year), so I have already taken some courses. Notably: several semesters of real analysis Linear algebra, Algebra Discrete mathematics and graph theory few algorithm and datastructure courses, Logic Programming introduction courses into: Propositional and Predicate logic Computability theory Computational complexity theory Set Theory And I think I have enough of basic mathematical fluency to be able to follow (at least to some degree) any math course if it is not extra hard or if it does not heavily depend on other courses. >Just take the computer science courses that the fewest of your fellow > students see any point to. Well, there are too many of those :-) Thanks, Tom.

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Re: [Haskell-cafe] PROPOSAL: Rename haskell@ to haskell-announce@
by Simon Michael 25 Sep '07

25 Sep '07

The gmane newsgroups corresponding to haskell mail lists can be found eg at: http://gmane.org/find.php?list=haskell

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Complexity question
by Andrew Coppin 25 Sep '07

25 Sep '07

Greetings. Anybody happen to know what the time complexity of "transpose" is?

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Re: [Haskell] Math behind Haskell
by Neil Mitchell 24 Sep '07

24 Sep '07

Hi The haskell-cafe@ mailing list is more appropriate for messages such as this. haskell@ is just for announcements (it should be called haskell-annouce@ !) > * Lambda calculus - the basis of functional languages > > * Category theory - where all these mysterious things like monads, > arrows, and functors come from. I'd add: * Discrete Maths - booleans, relations, functions etc. * Type theory * Logic programming (Prolog) * Semantics Most of these are computer science courses, rather than maths ones. Thanks Neil

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PROPOSAL: Rename haskell@ to haskell-announce@
by Andrzej Jaworski 24 Sep '07

24 Sep '07

Sorry guys for joining the thread of sinners on haskell@ today. Forgot to check if guests had not moved to cafe;-) It is a good example though how insufficient this verbal principles are, since I have myself raised the need to revise names of the lists here. On second thought, with rising traffic the problem should be approached by introducing AI automation - sort of scunning, learning, summerising and sending tagged abstracts onto haskel@. In other words the only possible input onto haskell list should be robotic:-) Be brave guys, you are ment to make history:-) Cheers, -Andrzej Jaworski

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Noob question and sequence of operations (print then do something else)
by John Wicket 24 Sep '07

24 Sep '07

I am still in an imperative way of thinking. In this example here; how would I call "putStrLn" and then set the function with a value. Eg: aa :: String -> IO () aa instr = do putStrLn "abc" putStrLn "abc" return "123" --- The error I am getting. Couldn't match expected type `()' against inferred type `[Char]' In the first argument of `return', namely `"123"' In the expression: return "123" In the expression: do putStrLn "abc" putStrLn "abc" return "123"

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