Re: [Haskell-cafe] displaying conetents of a list
Even more succinctly: sequence_ . map is mapM_, and putStrLn . show is print, so you get: mapM_ print films Dan On Sun, May 10, 2009 at 9:59 PM, Alex MDC alex@gmail.com wrote: 2009/5/11 applebiz89 applebi...@hotmail.com I know to use show and putStrLn but I just don't know how to put them into the function correctly Well I hope we're not doing your homework for you but... As putStrLn is in the IO monad, listFilms should at least have a signature like this: listFilms :: [Film] - IO () Now you know you want to call putStrLn on each item in the list. That means you want to join a bunch of functions return IO (). That sounds like a job for sequence_: listFilms films = sequence_ $ map (putStrLn.show) films Or the same thing more verbosely: listFilms [] = return () listFilms (film:films) = do putStrLn (show film) listFilms films Hope that helps, Alex ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [ANNOUNCE] Bindings for libguestfs
I added some partial bindings for libguestfs[1] here: http://git.et.redhat.com/?p=libguestfs.git;a=blob;f=haskell/Guestfs.hs;hb=HEAD Some very simple example programs which use these bindings: http://git.et.redhat.com/?p=libguestfs.git;a=tree;f=haskell;hb=HEAD Any comments welcome. My Haskell skills are pretty terrible, so I'm sure there are many ways these can be improved. If someone wants to look at binding the rest of the API, then please send me some patches. (Note that the Guestfs.hs file is automatically generated). BTW, I found the documentation on writing FFIs very contradictory and incomplete. For example, I was completely defeated trying to find ways to do simple stuff like passing in integers or returning booleans. *Potentially* Haskell's FFI seems like it might be one of the best out of the languages I've used so far, but it needs way more documentation and examples. Rich. [1] http://et.redhat.com/~rjones/libguestfs/ -- Richard Jones, Emerging Technologies, Red Hat http://et.redhat.com/~rjones virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://et.redhat.com/~rjones/virt-df/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Decoupling OpenAL/ALUT packages from OpenGL
Sven Panne wrote: Regarding Functor/Applicative: The obvious instances for e.g. a 2-dimensional vertex are: data Vertex2 a = Vertex2 a a instance Functor Vertex2 where fmap f (Vertex2 x y) = Vertex2 (f x) (f y) instance Applicative Vertex2 where pure a = Vertex2 a a Vertex2 f g * Vertex2 x y = Vertex2 (f x) (g y) They fulfill all required laws, but are these the only possible instances? If not, are they at least the most canonical ones in a given sense? And finally: Does somebody have a real-world example where the Applicative instance is useful? Usages of the Functor instance are much more obvious for me. I'd say those are the right instances. Some obvious uses (perhaps more useful for Vector2 than Vertex2, but still) are: liftA2 (+) (Vertex2 1 3) (Vertex2 4 5) == Vertex2 5 8 pure 0 == Vertex2 0 0 The latter being a useful shorthand to get a vertex for the origin. Also, if you define Foldable: foldl1 (+) . liftA2 (*) v w == dotProduct v w The useful thing being that that definition of dotProduct is the same for 2-, 3- and 4- dimensional things, and for vertexes and vectors. So possible additions to your type-class list are Foldable and maybe Traversable (no harm, although I'd have to reach further for an example for this). I guess the tricky decision might be whether to provide a Num instance (again, probably more suitable for Vector2)? instance Num a = Num (Vertex2 a) where (+) = liftA2 (+) (-) = liftA2 (-) (*) = liftA2 (*) abs = fmap abs signum = fmap signum negate = fmap negate fromInteger = pure . fromInteger Even if you don't want to define Num, note how easy having the Applicative instance makes defining some of the operators :-) Thanks, Neil. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Classes: functional dependency (type - value)
2009/05/10 Belka lambda-be...@yandex.ru: Some real code using wished feature: This code has multiple issues: . It is nearly unreadable as formatted. . There are actual errors that would prevent it from compiling (pattern match on `Left` and `Just` in the same `case` expression!). Please amend the code so it is easier to read and test. -- Jason Dusek ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Decoupling OpenAL/ALUT packages from OpenGL
Sven, Am Montag, 4. Mai 2009 13:33:33 schrieb David Duke: Decoupling basic primitives for geometric modelling from OpenGL would be useful. [...] Even just data constructors and instances of these within Functor and Applicative are a useful starting point. [...] This leads me to the conclusion that I should only lift the data types for vectors and matrices out of the OpenGL package, including only instances for standard type classes like Eq, Ord, Functor, etc. This means that the new package will *not* include type classes for things like scalars, vector spaces, etc. These can be defined by the other packages in their own type class language. That seems a reasonable step. If and when consensus does emerge on packaging vector matrix operations, that could be added as a further package. Regarding Functor/Applicative: The obvious instances for e.g. a 2-dimensional vertex are: data Vertex2 a = Vertex2 a a instance Functor Vertex2 where fmap f (Vertex2 x y) = Vertex2 (f x) (f y) instance Applicative Vertex2 where pure a = Vertex2 a a Vertex2 f g * Vertex2 x y = Vertex2 (f x) (g y) They fulfill all required laws, but are these the only possible instances? If not, are they at least the most canonical ones in a given sense? And finally: Does somebody have a real-world example where the Applicative instance is useful? Usages of the Functor instance are much more obvious for me. The Vertex constructor and Applicative operators don't seem to admit anything different that is also sensible (unless someone has a use for * with function and/or args permuted). As to real-world example, if you interpret a vertex as a (position) vector and want to apply that to another vertex, liftA2 (+) is neat. For working with sampled data, we have something like class Interp b where interpolate :: Float - b - b - b with suitable instances for types in the numeric hierarchy, and then instance (Interp a, Applicative f) = Interp (f a) where interp t = liftA2 (interp t) If vertex is an instance of applicative, we then immediately have interpolation between coordinates (we use it in contour and surface extraction, others may find it useful in animation or distortion). David -- Dr. David Duke E: d...@comp.leeds.ac.uk School of Computing W: www.comp.leeds.ac.uk/djd/ University of Leeds T: +44 113 3436800 Leeds, LS2 9JT, U.K. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re[2]: [Gtk2hs-users] ANN: Gtk2HS 0.10.1 released
Hello Peter, Monday, May 11, 2009, 5:40:20 PM, you wrote: GHC 6.10.1 is now supported. 6.10.2/6.10.3? Yes, those versions are supported as well. GHC 6.10.1 changed the way finalizers are handled, and as a result, Gtk2HS programs were crashing. I don't think anything that affects Gtk2HS was changed in GHC 6.10.[23]. no, you mixed things a bit :) 6.10.1 was out in Nov 2008. gtk2hs 0.10 supports it the change in finalizers was made in 6.10.2, issued in Apr 2009 and BIG THANKS to entire gtk2hs team: i'm really happy to finally get production-level ghc 6.10 together with new gtk2hs -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Data.Map lookup signature
Hi everyone. The docs in the web on http://www.haskell.org/ghc/docs define Data.Map.lookup as follows: http://www.haskell.org/ghc/docs lookup :: Ord k = k - Map k a - Maybe a but my version of ghci does i like that: Data.Map.lookup :: (Ord k, Monad m) = k - Data.Map.Map k a - m a but i need the 1. one. my version of ghci is 6.8.2 regards ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: ANN: Gtk2HS 0.10.1 released
Peter Gavin pga...@gmail.com writes: Hi everyone, I'd like to announce the release of Gtk2HS 0.10.1! This release includes mostly bug fixes and other small improvements. Most notably, GHC 6.10.1 is now supported. The source tarball may be downloaded from: http://sourceforge.net/project/showfiles.php?group_id=49207package_id=42440 A Windows installer will be provided soon. Thanks to all the contributors! Now i use gtk2hs develop GUI program, and it's very nice integrate GTK and Haskell. Thanks gtk2hs team! :) Hope gtk2hs will support *all* functional of GTK (newest version) in the feature. -- Andy ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Fundep Curiosity
I've noticed that a large majority of fundeps I see in other people's libraries are written: class C a b | b - a Where the dependent parameter appears first in the MPTC. Is there a reason for this? AFAIK, there isn't any semantic significance to the order of parameters in an MPTC. Why do many haskellers find this configuration more intuitive? Friendly, --Lane ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ANN: Gtk2HS 0.10.1 released
I vaguely remember there being some finalizer behavior that changed in 6.10.2 that might affect this package. Not sure though. On Sun, May 10, 2009 at 12:10 PM, Andy Stewart lazycat.mana...@gmail.com wrote: Bulat Ziganshin bulat.zigans...@gmail.com writes: Hello Peter, Sunday, May 10, 2009, 7:43:38 PM, you wrote: I'd like to announce the release of Gtk2HS 0.10.1! This release includes mostly bug fixes and other small improvements. Most notably, GHC 6.10.1 is now supported. 6.10.2/6.10.3? I think 6.10.1 compatible with 6.10.2/6.10.3 6.10.2/6.10.3 just fix some bug of 6.10.1 -- Andy ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Data.Map lookup signature
Oh sorry. It was probalby changed in one of the latest versions I downloaded the latest and now i'm finde. 2009/5/11 Nico Rolle nro...@web.de: Hi everyone. The docs in the web on http://www.haskell.org/ghc/docs define Data.Map.lookup as follows: http://www.haskell.org/ghc/docs lookup :: Ord k = k - Map k a - Maybe a but my version of ghci does i like that: Data.Map.lookup :: (Ord k, Monad m) = k - Data.Map.Map k a - m a but i need the 1. one. my version of ghci is 6.8.2 regards ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hoogle: converting binary .hoo into text?
On Mon, May 11, 2009 at 10:25 AM, Neil Mitchell ndmitch...@gmail.comwrote: Hi Peter, I would like to use the Hoogle text format in C#. Out of curiosity, why? I'm just interested to know what work you're doing. Sure. We're building with a graphical representation of a Haskellish language (a tiny subset of Haskell actually). The target audience is graphical artists and designers. For testing, I would like to populate the library with primitives taken from the Haskell base libraries. I tried using the GHC API for it, but got stuck. I got the advice in #haskell to parse the Hoogle format, which indeed looks simple enough for the task. Hoogle on Hackage comes with a bunch of binary *.hoo files. Can these be converted to text/xml? If not, is the binary format documented? The binary format is documented in the code, and there is a show command. Try: hoogle +base --dump However the binary format is not an encoding of the text format, it throws away lots of data, and precomputes interesting tables etc. If you want the original, the binary is probably not that useful. I do have a complete set of text files though. I can upload them to the Hoogle website, or I can distribute them with the hackage package. I could just email them to you privately. What seems the best option for everyone? I'm not everyone but I guess it would be useful in general. From within Haskell, ideally one would just use the GHC API (or Cabal API) to extract all information I guess, but for usage in other languages, an easy to parse format is better no? (maybe even XML, but that is bulky :-) I know I can build hoo files using cabal haddock --hoogle. But doing this on the BASE package (which I need) from Hackage fails (I'm on Windows, using MSYS): configure: creating ./config.status config.status: error: cannot find input file: include/HsBaseConfig.h.in Does anyone have an easy solution? Maybe I just need to switch to Linux to get this working? :-) I have a small pile of hacks to get the base library building with Hoogle. You are welcome to look at them (data/generate in the Hoogle repo). Caution: these hacks may make your eyes bleed, and certainly won't work for anything but the GHC/base version pair that I last did it on. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hoogle: converting binary .hoo into text?
Hi Sure. We're building with a graphical representation of a Haskellish language (a tiny subset of Haskell actually). The target audience is graphical artists and designers. For testing, I would like to populate the library with primitives taken from the Haskell base libraries. I tried using the GHC API for it, but got stuck. I got the advice in #haskell to parse the Hoogle format, which indeed looks simple enough for the task. You might be able to use haskell-src-exts (plus a little bit of preprocessing) to parse the declarations. I deliberately tried to follow Haskell syntax where possible. Hoogle on Hackage comes with a bunch of binary *.hoo files. Can these be converted to text/xml? If not, is the binary format documented? The binary format is documented in the code, and there is a show command. Try: hoogle +base --dump However the binary format is not an encoding of the text format, it throws away lots of data, and precomputes interesting tables etc. If you want the original, the binary is probably not that useful. I do have a complete set of text files though. I can upload them to the Hoogle website, or I can distribute them with the hackage package. I could just email them to you privately. What seems the best option for everyone? I'm not everyone but I guess it would be useful in general. From within Haskell, ideally one would just use the GHC API (or Cabal API) to extract all information I guess, but for usage in other languages, an easy to parse format is better no? (maybe even XML, but that is bulky :-) Writing a converting from text files to XML is fine by me - Hoogle already has the textual format parser, so if you add a patching adding a dump XML option I'll happily apply. I'll send you the .txt files by private email. It seems like you want them now, but don't care about keeping them up to date, since it's only a demo. Hence fast and quick, but not long term provided, seems a good short-term compromise. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] caml build
Hello, I have forgotten whether I sent this posting out. Sorry if I did (I didn't see on Haskell cafe archive). I am building Swish and getting an error. I want to follow the progress of swish build ... I don't see an additional parameter like verbose mode that will tell which swish component is being built. ??? Regards, Vasili ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Kind of confusing
GHC amused me today with this error (context omitted): Couldn't match kind `(* - *) - * - *' against `?? - ? - *' When matching the kinds of `t :: (* - *) - * - *' and `(-) :: ?? - ? - *' It was a silly mistake: I had used 'lift' where I intended to use 'liftM'. But I'm thinking Haskell compilers should have some sort of option which, when the ratio of punctuation to alphanumerics in an error message exceeds a certain level, just responds to the user with a more readily comprehensible message such as WTF, dude? Serious question: what is the significance of the question mark and double question marks in those signatures, or better yet, where can I read about it? Anton ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Developing 3 dimensional interactive environments/functional objects
Does any programmer on this mailing list have experience with developing 3 dimensional interactive environments/functional objects within them, au Second Life? Is Haskell useful for such an endeavor? With best wishes, Paul ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: OT: Languages
Tillmann Rendel wrote: wren ng thornton wrote: Indeed. The proliferation of compound words is noteworthy, but it's not generally considered an agglutinative language. From what (very little) German I know compounds tend to be restricted to nouns, as opposed to languages like Turkish, Japanese, Korean,... Yes, compounds are restricted to nouns in German. But as I understand it, agglutinative relates more to the inflection system than to the lexicon anyway. In general, I'm not sure I draw a distinction there. What belongs in the grammar vs what belongs in the lexicon is rather fluid and depends on both the language and the theory in question; whereas the phenomenon is, I think, easily identifiable (if not always easily definable). That is, the distinction between agglutinative vs fusional is typological rather than theoretical. The distinction has to do with information content per morpheme (or compositional vs idiomatic information construction). For determining this, root/base morphemes are included just as much as inflectional morphemes. The distinction between what is root vs what is inflection is a spectrum and not always clear cut, especially in agglutinative languages. In languages like Japanese which lacks spaces, this difficulty is highlighted by the fact that it's not always clear whether something is a word or a phrase (and hence whether the latter major segment contains base morphemes, or is only inflection). Though yes, the distinction is most clearly observed by looking at verbal inflections. And now we're really far off topic :) -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Stream-fusion without the lists
Hi everyone, With stream-fusion, we can write functions which construct and destruct lists, such as (this is the main example from the Stream Fusion paper[1]) f :: Int - Int f n = sum [k * m | k - [1..n], m - [1..k]] and the rewrite rules in stream-fusion replace these operations on lists with fusible operations on the Stream (non-recursive) datatype. In this example, the domain and codomain of the function don't mention the list datatype. There seem to be many functions like this: the lists are being used internally as composable loops rather than as data-structures. The Stream datatype seems to be much better suited to representing loops than the list datatype is. So, instead of programming with the lists, why don't we just use the Stream datatype directly? For example: In Data.Stream (from the stream-fusion package) we can find most of the Prelude list functions but with Stream in all the types instead of []. For example, Data.Stream.sum :: Num a = S.Stream a - a Using this module, we can rewrite f without mentioning lists. We first need a Monad instance for Data.Stream.Stream: import qualified Data.List.Stream as S instance Monad S.Stream where return = S.return (=) = S.concatMap Now we can write f :: Int - Int f n = S.sum $ do k - S.enumFromToInt 1 n m - S.enumFromToInt 1 k return (k*m) which is essentially the same as the original f, although lacking the syntactic sugar of the list comprehension. To me, it seems that Stream is more sensible data type to use than [] when the algorithm being expressed is just a loop (rather than something which needs a [] as a cache/buffer), for the following reasons: 1. If I am programming with lists and I need some function which I can't express with Prelude functions, I have to write it myself. I will probably lose fusion in this case, because I will write it recursively in terms of lists. On the other hand, if I am programming with Streams, I will write it myself in terms of Streams, and it should be easier to maintain fusion because it won't be recursive. 2. Holding on to a [] too long can cause a space leak. This is not the case for Stream, because a Stream only ever contains one state. More generally, the memory use of Stream is more easily predictable than that of [], since running a Stream only holds on to one state at a time, and we often know how big the state is. 3. Fusion doesn't rely on rewrite rules firing. I consider this point less significant than the other two. So, thoughts? Do people program with Streams directly? What have I not considered? Cheers, Reiner [1] http://www.cse.unsw.edu.au/~dons/papers/stream-fusion.pdf ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Inferred typing?
In the code below, is the type returned by the return functions inferred from the result type in the function type signature, i.e., just change the result type to Maybe Int and the code will return a Maybe monad, (Just 4), instead of a List monad? Michael = import Monad fn :: [Int] - [Int] fn l = mzero `mplus` (return (head l)) `mplus` (return (last l)) *Main :l test5 [1 of 1] Compiling Main ( test5.hs, interpreted ) Ok, modules loaded: Main. *Main fn [4,5,6,7,8] [4,8] *Main ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] OT: Is conference dead?
Hello all, I'm sorry for the OT post, is the conference dead? I've got no mail since yeasterday afternoon. And that is quite unusual. Best regards, Dusan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Classes: functional dependency (type - value)
Hello! The problem is that it's impossible to infer the SomeClass instance from the type SomeRole. If you do print role, which instance should it use? I can think of two ways around it: -- 1. (dummy parameter) -- data SomeRole a = Role1 | Role2 | Role3 deriving Show class SomeClass a where role :: SomeRole a data Foo = Foo data Bar = Bar instance SomeClass Foo where role = Role1 instance SomeClass Bar where role = Role2 main = do print (role :: SomeRole Foo) print (role :: SomeRole Bar) -- 2. (dummy argument) -- data SomeRole = Role1 | Role2 | Role3 deriving Show class SomeClass a where role :: a - SomeRole data Foo = Foo data Bar = Bar instance SomeClass Foo where role _ = Role1 instance SomeClass Bar where role _ = Role2 main = do print (role (undefined :: Foo)) print (role (undefined :: Bar)) -- On Sunday 10 May 2009 15:21:39 Belka wrote: Hello, communion people! I seek for your advice in a matter, where it's really hard for me to determine a good programming style. Here's the problem. I'm generalizing multiple authorization procedures to one, using class definition. (if of any interest, the code is in the end.) The problem essense is folowing: data SomeRole = Role1 | Role2 | Role3 class SomeClass a b c | a - b, c where f1 :: ... f2 :: ... ... fn :: ... role :: SomeRole -- -- here is the problem I want to have a fuctional dependency from a type a on a value of *role*, so that I could easily inspect the *role* from within any other class members. Is it possible? Or do I rougly violate some style traditions? Some real code using wished feature: --- data AuthentificationPurpose = JustValidateInput | JustGenerateForOutput | ValidateInputAndGenerateForOutput type AuthSucceded = Bool class AuthentificationStructure t_env t_realInput t_assumption t_keySet | t_realInput - t_assumptionInput, t_keySet where authentificationPurpose :: AuthentificationPurpose makeAssumption :: t_env - t_realInput - IO (Either ErrorMessage t_assumption) makeFinalKeySet :: (t_realInput, t_assumption) - t_keySet validateRealKeySet_with_Assumed :: t_realInput - t_keySet - Maybe ErrorMessage tryLogTheValidKey :: t_env - (t_realInput, t_assumption) - IO (Maybe ErrorMessage) tryLogTheAuthTry :: t_env - (t_realInput, t_assumption, AuthSucceded) - IO (Maybe ErrorMessage) authentificate :: AuthentificationStructure t_env t_realInput t_assumptionInput t_keySet = t_env - t_businessInput - IO (Either ErrorMessage (t_assumption, t_keySet)) authentificate env realInput = do err_or_assumption - makeAssumption env realInput case err_or_assumption of Left err_msg - return $ Left Error! Assumption maker failed. Lower level error message: ++ err_msg Just assumption - do key_set - makeFinalKeySet (realInput, assumption) err_or_keyset1 - case authentificationPurpose of JustGenerateForOutput - return $ Right key_set JustValidateInput - do mb_failure - validateRealKeySet_with_Assumed t_realInput key_set case mb_failure of Just err_msg - return $ Left Error! Invalid set of auth keys. Lower level error message: ++ err_msg Nothing - return $ Right key_set ValidateInputAndGenerateForOutput err_or_keyset2 - case err_or_keyset1 of Left err_msg - return err_or_keyset1 Right key_set - do mb_failure - tryLogTheValidKey env (realInput, assumption) case mb_failure of Just err_msg - return $ Left Error! Could not log valid key. Lower level error message: ++ err_msg Nothing - return err_or_keyset1 mb_failure - tryLogTheAuthTry env (realInput, assumption, isRight err_or_keyset2) case mb_failure of Just err_msg1 - case err_or_keyset2 of Left err_msg2 - return $ Left (1. ++ err_msg2 ++ \n2. ++ err_msg1) Right _ - return $ Left err_msg1 Nothing - case err_or_keyset2 of Left err_msg - return $ Left err_msg Right key_set - return $ Right (assumption, key_set) - Best regards, Belka ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org
[Haskell-cafe] Re: [Gtk2hs-users] ANN: Gtk2HS 0.10.1 released
On Sun, May 10, 2009 at 11:52 AM, Bulat Ziganshin bulat.zigans...@gmail.com wrote: Hello Peter, Sunday, May 10, 2009, 7:43:38 PM, you wrote: I'd like to announce the release of Gtk2HS 0.10.1! This release includes mostly bug fixes and other small improvements. Most notably, GHC 6.10.1 is now supported. 6.10.2/6.10.3? Yes, those versions are supported as well. GHC 6.10.1 changed the way finalizers are handled, and as a result, Gtk2HS programs were crashing. I don't think anything that affects Gtk2HS was changed in GHC 6.10.[23]. Pete ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: AAIP Workshop on ICFP Deadline Extension
AAIP Workshop on ICFP Deadline Extension Please note that the submission deadline for the 3rd Workshop on Approaches and Applications of Inductive Programming has been extended to May 25. The workshop takes place for the first time at the 14th ACM SIGPLAN International Conference on Functional Programming (ICFP 2009) in Edinburgh, Scotland. If a sufficient number of high quality papers is submitted, there will be a Post-Workshop Proceedings Volume published at Springer LNCS. The workshop will present three invited speakers from the research area of functional programming who have done excellent work to make use of inductive programming techniques. The full Call for Papers and further information are available at http://www.cogsys.wiai.uni-bamberg.de/aaip09/ Submit to the workshop and help to tighten the link between the functional programming and the inductive programming community! Best regards, Ute Schmid, Rinus Plasmeijer and Emanuel Kitzelmann ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: OT: Is conference dead?
On 12/05/2009 08:04, Dušan Kolář wrote: I'm sorry for the OT post, is the conference dead? I've got no mail since yeasterday afternoon. And that is quite unusual. We had a full disk on haskell.org over the weekend. We freed up some space yesterday, but it seems the lists were still stuck. I've restarted mailman and the mail now seems to be flowing, but there's a large backlog. Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Kind of confusing
Hi Anton, AFAIK the only place this is documented is in GHC source code. Please see the section called Main data types representing Kinds at http://hackage.haskell.org/packages/archive/ghc/6.10.2/doc/html/Type.html. Basically, they are all members of GHC's internal subkind hierarchy, which is used to distinguish between the representation of types. For example, the error function can be instantiated to have the type String - Int# - Int# whereas every polymorphic function you write will only be able to be instantiated at lifted types like Int. This reflects the fact that internally the type variable in the type of error has (IIRC) kind ?. I don't know why they showed up in your error message! Cheers, Max 2009/5/12 Anton van Straaten an...@appsolutions.com: GHC amused me today with this error (context omitted): Couldn't match kind `(* - *) - * - *' against `?? - ? - *' When matching the kinds of `t :: (* - *) - * - *' and `(-) :: ?? - ? - *' It was a silly mistake: I had used 'lift' where I intended to use 'liftM'. But I'm thinking Haskell compilers should have some sort of option which, when the ratio of punctuation to alphanumerics in an error message exceeds a certain level, just responds to the user with a more readily comprehensible message such as WTF, dude? Serious question: what is the significance of the question mark and double question marks in those signatures, or better yet, where can I read about it? Anton ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [darcs-users] [Haskell-cafe] Darcs as undo/redo system?
Am Freitag, 8. Mai 2009 18:43 schrieb Jason Dagit: If you wanted to work on this, I would encourage you to read more about patch theory[1,2,3,4] and also try out libdarcs[5]. Is libdarcs the same as the darcs library package on Hackage (which exports the darcs API)? Best wishes, Wolfgang ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: OT: Languages
wren ng thornton w...@freegeek.org wrote: That is, the distinction between agglutinative vs fusional is typological rather than theoretical. Though yes, the distinction is most clearly observed by looking at verbal inflections. And now we're really far off topic :) No, we aren't. A couple of days ago, I considered replacing a couple of highly regular function definitions by three lists and two calls to *, but didn't do it as I would still have to name the resulting functions by hand, to use them, and TH seemed utter overkill. -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Inferred typing?
michael rice nowg...@yahoo.com wrote: In the code below, is the type returned by the return functions inferred from the result type in the function type signature, i.e., just change the result type to Maybe Int and the code will return a Maybe monad, (Just 4), instead of a List monad? Yes. Prelude :m Control.Monad Prelude Control.Monad let fn l = mzero `mplus` (return (head l)) `mplus` (return (last l)) Prelude Control.Monad fn [1,3] :: Maybe Int Just 1 Prelude Control.Monad fn [1,3] :: Maybe Float Just 1.0 Prelude Control.Monad fn [1,2,3] :: [Int] [1,3] -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Classes: functional dependency (type - value)
Belka wrote:
Hello, communion people!
I seek for your advice in a matter, where it's really hard for me to
determine a good programming style.
Here's the problem. I'm generalizing multiple authorization procedures to
one, using class definition. (if of any interest, the code is in the end.)
The problem essense is folowing:
data SomeRole = Role1 | Role2 | Role3
class SomeClass a b c | a - b, c where
f1 :: ...
f2 :: ...
...
fn :: ...
role :: SomeRole -- -- here is the problem
I want to have a fuctional dependency from a type a on a value of *role*,
so that I could easily inspect the *role* from within any other class
members.
Is it possible? Or do I rougly violate some style traditions?
The problem is that when you write
role
there is no way to choose the right instance? That is, where does the
compiler get a, b, c from when looking just at an invocation of role
? Therefore, the type of role has to involve a , for example as in
class SomeClass a b c ... where
...
role :: a - SomeRole
and used as
role (undefined :: Foo)
That being said, I think that type classes are not what you want here. I
suggest to simply use a regular data type
data SomeThing a b c = SomeThing {
f1 :: ...
, f2 :: ...
...
, fn :: ...
, role :: SomeRole
}
Remember that f1, f2, ... can be functions, this is a functional
language, after all! Instances are then simply a concrete value, like
for example
thething :: SomeThing Foo Bar Baz
thething = SomeThing {
f1 = id
, f2 = filter (3) . map length
, ...
, role = Role1
}
Regards,
apfelmus
--
http://apfelmus.nfshost.com
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Re: [Haskell-cafe] Stream-fusion without the lists
On 12/05/2009, at 14:45, Reiner Pope wrote: The Stream datatype seems to be much better suited to representing loops than the list datatype is. So, instead of programming with the lists, why don't we just use the Stream datatype directly? I think the main reason is that streams don't store data and therefore don't support sharing. That is, in let xs = map f ys in (sum xs, product xs) the elements of xs will be computed once if it is a list but twice if it is a stream. Roman ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] commending Design concepts in programming languages
Am Freitag, 8. Mai 2009 14:31 schrieb Daniel Fischer: Though I had no contact with algebraists in the 1980s, I also hadn’t. However, nowadays I have contact with someone who was an algebraist in the 1980s. It’s my boss (professor), by the way. :-) I think, also category theorists often wrote (write?) composition with the first morphism on the left, i.e., “the other way round”. Yeah, I heard that, too. It's a field where the advantages of postfix notation show clearly and a young one, so for them it was relatively easy to switch. However, I fear that all those other mathematicians who define f . g = \x - f(g(x), have made the category theorists switch to this suboptimal notation (first morphism on the right). At least, I cannot remember seeing the other notation (first morphism on the left) in category theory literature so far. It’s just that my above-mentioned professor told me that category theorists would use the first-morphism-on-the-left notation. Best wishes, Wolfgang ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Inferred typing?
On Mon, May 11, 2009 at 10:59:01PM -0700, michael rice wrote: In the code below, is the type returned by the return functions inferred from the result type in the function type signature, i.e., just change the result type to Maybe Int and the code will return a Maybe monad, (Just 4), instead of a List monad? Indeed, it is. Try it! =) -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell Weekly News: Issue 117 - May 12, 2009
--- Haskell Weekly News http://sequence.complete.org/hwn/20090512 Issue 117 - May 12, 2009 --- Welcome to issue 117 of HWN, a newsletter covering developments in the [1]Haskell community. The Haskell Platform is here! Announcements The Haskell Platform. Don Stewart [2]announced the first release of the [3]Haskell Platform: a single, standard Haskell distribution for every system. The Haskell Platform is a blessed library and tool suite for Haskell culled from Hackage, along with installers for a wide variety of systems. It saves developers work picking and choosing the best Haskell libraries and tools to use for a task. GHC version 6.10.3. Ian Lynagh [4]announced the release of [5]GHC 6.10.3. This release contains a handful of bugfixes relative to 6.10.2 and better line editing support in GHCi, so updating is recommend. See the [6]release notes for more details. Bindings for libguestfs. Richard W.M. Jones [7]announced some [8]partial bindings for [9]libguestfs. Heads up: Conflicting versions of network-2.2.1. Johan Tibell [10]announced a heads-up that the version of network-2.2.1 that shipped with GHC 6.10 differs from the one on Hackage. If you want the API additions that are present in network-2.2.1 on Hackage, be sure to use network-2.2.1.1 instead. hpc-strobe-0.1: Hpc-generated strobes for a running Haskell program. Thorkil Naur [11]announced the initial release of [12]hpc-strobe, a rudimentary library that demonstrates the possibility of using Hpc (Haskell Program Coverage) to inspect the state of a running Haskell program. hpc-strobe uses the basic machinery provided by Hpc to produce multiple tix files, also called strobes, representing the coverage at different times while the program is running. By subtracting such two tix files, again using Hpc machinery, a tix file representing the expressions used between the times of recording the subtracted tix files is produced. This may be used, for example, to get a better idea of what a long-running program is doing. It could also be used as a profiling tool, getting information about how many times individual expressions are used. BUG FIX release of regex-tdfa-1.1.2. ChrisK [13]announced version 1.1.2 of [14]regex-tdfa, a bug-fix release. Silkworm game. Duane Johnson [15]announced the release of [16]Silkworm, a game written in Haskell using [17]Hipmunk and GLFW. Discussion Platform policy question: API compatibility in minor releases. Duncan Coutts began a [18]discussion on versioning policies for major and minor releases, for packages included in the Haskell Platform. See also the [19]newly started discussion on the purpose of Haskell Platform releases. Blog noise [20]Haskell news from the [21]blogosphere. Blog posts from people new to the Haskell community are marked with , be sure to welcome them! * Magnus Therning: [22]Vim haskellmode packaged for Arch. * Manuel M T Chakravarty: [23]Instant Generics: Fast and Easy.. * Bjorn Buckwalter: [24]May 2009 HCAR Submissions. * Gtk2HS: [25]Gtk2HS 0.10.1 Released. * Magnus Therning: [26]Arch and Haskell, on little snag. * Mikael Vejdemo Johansson (DrSyzygy): [27]Gröbner bases for operads - Or What I did in my vacation. * Mads Lindstrøm: [28]WxGeneric 0.6.0. * Osfameron: [29]Is currying monadic?. * James Iry: [30]A Brief, Incomplete, and Mostly Wrong History of Programming Languages. * Duane Johnson: [31]Visualizing Typed Functions. * Well-Typed.Com: [32]Next steps for the Haskell Platform. * Don Stewart (dons): [33]The Haskell Platform. * Luke Palmer: [34]Lazy Partial Evaluation. * Christopher Lane Hinson: [35]Vec is Good. * LHC Team: [36]Constructor specialization and laziness.. * Lee Pike: [37]An Atomic Fibonacci Server: Exploring the Atom (Haskell) DSL. * John Van Enk: [38]Atom Arduino :: First Program (pt. 2). * Chris Forno: [39]Is Haskell a Good Choice for Web Applications?. * Sparky: [40]Haskell and Eclipse [Part 2]. * Brit Butler: [41]Playing with Haskell. * Duane Johnson: [42]Silkworm Game written in Haskell. * Matthew Podwysocki: [43]Functional Composition and Partial Application . * Takashi: [44]A Prolog In Haskell. * mokehehe: [45]Using DirectX from Haskell. * mokehehe: [46]AO bench in Haskell. Quotes of the Week * jfredett: My haskell-spider senses were tingling, I just overshot RT and went for the Halting Problem. * NeilBrown: I heard that if you chant I don't think this can be done in Haskell three times in front of a text editor, Don Stewart appears and implements it in one line... * bos: The last couple
Re: [Haskell-cafe] caml build
Excerpts from Vasili I. Galchin's message of Tue May 12 00:27:26 +0200 2009: Hello, I have forgotten whether I sent this posting out. Sorry if I did (I didn't see on Haskell cafe archive). I am building Swish and getting an error. I want to follow the progress of swish build ... I don't see an additional parameter like verbose mode that will tell which swish component is being built. ??? I don't get the relation with the subject of your post, can you elaborate? Best regards, -- Nicolas Pouillard ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Fundep Curiosity
Am Montag 11 Mai 2009 18:36:54 schrieb Christopher Lane Hinson:
I've noticed that a large majority of fundeps I see in other people's
libraries are written:
class C a b | b - a
Where the dependent parameter appears first in the MPTC. Is there a
reason for this?
Yes. Generalised newtype deriving (perhaps others, but that's what jumped at
me).
Consider
class MonadState s m | m - s where ...
newtype State s a = State { runState :: s - (a,s) }
instance Monad (State s) where ...
instance MonadState s (State s) where ...
newtype MySpecialState s a = MSS (State (s,Int) a)
deriving (Monad, MonadState (s,Int))
AFAIK, there isn't any semantic significance to the order of parameters in
an MPTC. Why do many haskellers find this configuration more intuitive?
Friendly,
--Lane
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Re: [Haskell-cafe] Inferred typing?
Am Dienstag 12 Mai 2009 07:59:01 schrieb michael rice: In the code below, is the type returned by the return functions inferred from the result type in the function type signature, i.e., just change the result type to Maybe Int and the code will return a Maybe monad, (Just 4), instead of a List monad? You can find out such things yourself, just remove the type signature and ask ghci/hugs what they think: *MType :t fn fn :: (MonadPlus m) = [a] - m a Michael = import Monad fn :: [Int] - [Int] fn l = mzero `mplus` (return (head l)) `mplus` (return (last l)) *Main :l test5 [1 of 1] Compiling Main ( test5.hs, interpreted ) Ok, modules loaded: Main. *Main fn [4,5,6,7,8] [4,8] *Main ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] OT: Is conference dead?
Am Dienstag 12 Mai 2009 09:04:46 schrieb Dušan Kolář: Hello all, I'm sorry for the OT post, is the conference dead? I've got no mail since yeasterday afternoon. And that is quite unusual. I didn't get anything yesterday afternoon either. On Saturday, posts reached my mailbox typically one hour after sending, Sunday it was 2+ hours, yesterday noon I got what was sent up to 8am GMT, nothing after that. Today things are much delayed again. It seems the mail server at haskell.org is seriously acting up. Does anybody know whom one can ask to look into it? Best regards, Dusan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Kind of confusing
On Mon, 2009-05-11 at 20:43 -0400, Anton van Straaten wrote: Serious question: what is the significance of the question mark and double question marks in those signatures, or better yet, where can I read about it? I've forgotten where to find the details (try the GHC manual if you haven't already?), but IIRC they're part of how GHC handles boxing. -- Philippa Cowderoy fli...@flippac.org ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] List of exports of a module - are there alternatives?
Hi, When we want to list which declarations are exported by a module we do: module Mod ( list of exports ) where ... Are there propositions to alternatives to that (I could not find one)? Like, say, add a do export or do not export tag to declarations we want to (not) export? (I think something like that could be nice when we have modules with 200 declarations and just a few are (not) going to be exported.) Thanks, Maurício ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Problem with text and text-icu packages
Hi, I'm struggling with text-0.1 and text-icu-0.1, as announced at http://www.serpentine.com/blog/2009/02/27/finally-fast-unicode-support-for-haskell/ The code in http://pastebin.com/m7d8d9f91 is intended to read in a UTF-8 file a1.txt, reverse it twice, and write it out to another UTF-8 file a2.txt, which I would have thought should make a2.txt identical to a1.txt. Mostly it is, but sometimes it isn't, e.g.: % echo a a1.txt % tryicu # - my code % cat a2.txt ࠋ퐤 Specifically, a1.txt contains bytes 97 and 10, while a2.txt contains bytes 224 160 139 237 144 164. Have I misconstrued things, or is this a bug? I am running ghc 6.10.2 and ICU 4.0.1 on SuSE. Thanks for any help David ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Fundep Curiosity
Christopher Lane Hinson wrote: I've noticed that a large majority of fundeps I see in other people's libraries are written: class C a b | b - a Where the dependent parameter appears first in the MPTC. Is there a reason for this? AFAIK, there isn't any semantic significance to the order of parameters in an MPTC. Why do many haskellers find this configuration more intuitive? The order of parameters in an MPTC is significant if you want to use newtype deriving, which can only be used with the last parameter, by explicitly providing all other parameters. Tillmann ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [ANNOUNCE] Bindings for libguestfs
rjones: I added some partial bindings for libguestfs[1] here: http://git.et.redhat.com/?p=libguestfs.git;a=blob;f=haskell/Guestfs.hs;hb=HEAD Some very simple example programs which use these bindings: http://git.et.redhat.com/?p=libguestfs.git;a=tree;f=haskell;hb=HEAD Any comments welcome. My Haskell skills are pretty terrible, so I'm sure there are many ways these can be improved. If someone wants to look at binding the rest of the API, then please send me some patches. (Note that the Guestfs.hs file is automatically generated). Very cool. Are you likely to upload to hackage? BTW, I found the documentation on writing FFIs very contradictory and incomplete. For example, I was completely defeated trying to find ways to do simple stuff like passing in integers or returning booleans. *Potentially* Haskell's FFI seems like it might be one of the best out of the languages I've used so far, but it needs way more documentation and examples. Perhaps read the FFI chapter of RWH (online?) What resources were you using to grok the FFI? Cheers, Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] International Summer School on Advances in Programming Languages (precedes ICFP'09)
International Summer School on Advances in Programming Languages 25th-28th August, 2009 Heriot-Watt University, Edinburgh, Scotland http://www.macs.hw.ac.uk/~greg/ISS-AiPL Overview This four-day residential International Summer School on Advances in Programming Languages has a major theme of Concurrency, Distribution, and Multicore. Intended primarily for postgraduate research students, the School offers lectures and practical sessions on an engaging blend of cutting edge theoretical and practical techniques from international experts. The Summer School is supported by the Scottish Informatics and Computer Science Alliance (http://www.sicsa.ac.uk/), a Scottish Funding Council Research Pool. Participants from SICSA member institutions may attend at no cost. Confirmed Topics/Speakers * Static and dynamic languages, Prof Philip Wadler, University of Edinburgh * Compiler technology for data-parallel languages, Dr Sven-Bodo Scholz, University of Hertfordshire * New applications of parametricity, Dr Janis Voigtlander, Technical University of Dresden * Automatic vectorising compilation, Dr Paul Cockshott, University of Glasgow * Foundational aspects of size analysis, Prof Marko van Eekelen / Dr Olha Shakaravska, Radboud University Nijmegen * Context oriented programming, Dr Pascal Costanza, Vrije Universiteit Brussels * Multi-core programming, Dr Phil Trinder, Heriot-Watt University * Multi-core compilation, Dr Alastair Donaldson, Codeplay Software Ltd * Principles and Applications of Refinement Types, Dr Andrew D. Gordon, Microsoft Research, Cambridge * Resource aware programming in Hume, Prof Greg Michaelson, Heriot-Watt University / Prof Kevin Hammond, University of St Andrews * Haskell concurrency parallelism, Dr Satnam Singh, Microsoft Research, Cambridge Location The Summer School is at Heriot-Watt University's Riccarton campus, set in pleasant parkland to the west of Edinburgh, with easy access to the airport, city and central Scotland (http://www.hw.ac.uk/welcome/directions.htm). The Summer School immediately precedes the 2009 International Conference on Functional Programming (http://www.cs.nott.ac.uk/~gmh/icfp09.html) and takes place during the Edinburgh International Festival (http://www.eif.co.uk/) , and the associated Edinburgh Festival Fringe (http://www.edfringe.com/) and Edinburgh International Book Festival (http://www.edbookfest.co.uk/) Steering Committee ~~ Prof Prof Greg Michaelson, Heriot-Watt University (Convenor), g.michael...@hw.ac.uk Prof Kevin Hammond, University of St Andrews Dr Patricia Johann, University of Strathclyde Prof Philip Wadler, University of Edinburgh Fee ~~~ Full rate: £400; (free for SICSA students) Includes: four nights single room, en-suite accommodation with breakfast, lunch and dinner, plus coffee breaks and session materials. Day rate: £200; (free for SICSA students) Includes: lunch, coffee breaks, session materials Registration of Interest If you are interested in attending the International Summer School, please complete the form available from (http://www.macs.hw.ac.uk/~greg/ISS-AiPL/ISS-AiPL%20register.doc) or below, and return it to: iss-aipl-regis...@macs.hw.ac.uk ** International Summer School on Advances in Programming Languages 25th-28th August, 2009 Heriot-Watt University, Edinburgh, Scotland Registration of Interest Name: Address: Email: Phone: SICSA Uni: Yes / No Rate: Full / Day Accessibility requirements: Dietary requirements: Return to: iss-aipl-regis...@macs.hw.ac.uk ** ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Developing 3 dimensional interactive environments/functional objects
paulfrancis: Does any programmer on this mailing list have experience with developing 3 dimensional interactive environments/functional objects within them, au Second Life? Is Haskell useful for such an endeavor? Mm.. Anygma http://www.anygma.com/JobOfferA.html gamr7 http://www.gamr7.com/ Both use Haskell to some extent. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [ANNOUNCE] Bindings for libguestfs
On Tue, May 12, 2009 at 08:18:08AM -0700, Don Stewart wrote: rjones: I added some partial bindings for libguestfs[1] here: http://git.et.redhat.com/?p=libguestfs.git;a=blob;f=haskell/Guestfs.hs;hb=HEAD Some very simple example programs which use these bindings: http://git.et.redhat.com/?p=libguestfs.git;a=tree;f=haskell;hb=HEAD Any comments welcome. My Haskell skills are pretty terrible, so I'm sure there are many ways these can be improved. If someone wants to look at binding the rest of the API, then please send me some patches. (Note that the Guestfs.hs file is automatically generated). Very cool. Are you likely to upload to hackage? I think it should be a bit more complete before uploading it. It only covers about half the interface. BTW, I found the documentation on writing FFIs very contradictory and incomplete. For example, I was completely defeated trying to find ways to do simple stuff like passing in integers or returning booleans. *Potentially* Haskell's FFI seems like it might be one of the best out of the languages I've used so far, but it needs way more documentation and examples. Perhaps read the FFI chapter of RWH (online?) What resources were you using to grok the FFI? Well, Real World Haskell was one of the resources: http://book.realworldhaskell.org/read/interfacing-with-c-the-ffi.html (And it's fine, one of the better resources as an introduction. But not thorough enough to cover the booleans / returning complex structs problems I had). The others, as I remember it, were: http://www.haskell.org/haskellwiki/FFI_Introduction http://www.haskell.org/haskellwiki/FFICookBook (Made me think it was simple, but doesn't really cover much once I got down to the details) http://www.cse.unsw.edu.au/~chak/haskell/ffi/ the documentation for 'Foreign' etc in the Haddock-generated library docs. Rich. -- Richard Jones, Emerging Technologies, Red Hat http://et.redhat.com/~rjones virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://et.redhat.com/~rjones/virt-df/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [ANNOUNCE] Bindings for libguestfs
rjones: On Tue, May 12, 2009 at 08:18:08AM -0700, Don Stewart wrote: rjones: I added some partial bindings for libguestfs[1] here: http://git.et.redhat.com/?p=libguestfs.git;a=blob;f=haskell/Guestfs.hs;hb=HEAD Some very simple example programs which use these bindings: http://git.et.redhat.com/?p=libguestfs.git;a=tree;f=haskell;hb=HEAD Any comments welcome. My Haskell skills are pretty terrible, so I'm sure there are many ways these can be improved. If someone wants to look at binding the rest of the API, then please send me some patches. (Note that the Guestfs.hs file is automatically generated). Very cool. Are you likely to upload to hackage? I think it should be a bit more complete before uploading it. It only covers about half the interface. BTW, I found the documentation on writing FFIs very contradictory and incomplete. For example, I was completely defeated trying to find ways to do simple stuff like passing in integers or returning booleans. *Potentially* Haskell's FFI seems like it might be one of the best out of the languages I've used so far, but it needs way more documentation and examples. Perhaps read the FFI chapter of RWH (online?) What resources were you using to grok the FFI? Well, Real World Haskell was one of the resources: http://book.realworldhaskell.org/read/interfacing-with-c-the-ffi.html (And it's fine, one of the better resources as an introduction. But not thorough enough to cover the booleans / returning complex structs problems I had). The others, as I remember it, were: http://www.haskell.org/haskellwiki/FFI_Introduction http://www.haskell.org/haskellwiki/FFICookBook (Made me think it was simple, but doesn't really cover much once I got down to the details) http://www.cse.unsw.edu.au/~chak/haskell/ffi/ the documentation for 'Foreign' etc in the Haddock-generated library docs. Very good. I wonder if /you/ could note down (maybe on the wiki) the things you need to work out - then we would have a tutorial from someone learning on the job. That could then be fleshed out into a fuller tutorial? -- Donn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [darcs-users] [Haskell-cafe] Darcs as undo/redo system?
Wolfgang Jeltsch wrote: Am Freitag, 8. Mai 2009 18:43 schrieb Jason Dagit: If you wanted to work on this, I would encourage you to read more about patch theory[1,2,3,4] and also try out libdarcs[5]. Is libdarcs the same as the darcs library package on Hackage (which exports the darcs API)? Yes. Ganesh === Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html === ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] haskell cuda?
Hi, Does anyone know if there's a compiler from Data-Parallel Haskell to GPU code? I saw a paper on it a while back, but Google hasn't turned up any code. Cheers, - Dan begin:vcard fn:Daniel K. Cook n:Cook;Daniel K. email;internet:danielkc...@gmail.com tel;cell:+44 (0) 7949 125 491 x-mozilla-html:TRUE version:2.1 end:vcard ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Structural sharing in haskell data structures?
So I've been reading a lot about a (relatively) new language called Clojure. One of its goals is to make concurrency easier via a built-in home-grown STM. Anyway, one of the ways it tries to do this is to have completely immutable data structures. Every time I read a tutorial about this in Clojure, it says ...yes, it sounds awful to think that your whole data structure gets copied every time you want to make a change to it, but it's sane because of a technique called structural sharing. Yet every time I hear immutability talked about in Haskell, what I hear is ...yes, it sounds awful to think that your whole data structure gets copied every time you want to make a change to it, but it's sane because of laziness...unless you need the whole data structure So I'm just curious, does GHC use structural sharing or something similar? Do other implementations? Does it matter? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Main function error
I have compiled each function independently and they have compiled the only problem is the main function.. I keep getting the error 'films not defined' and I am not sure why [code] type Title = String type Director = String type Year = Int type Fan = String data Film = Film Title Director Year [Fan] deriving Show -- List of films testDatabase :: [Film] testDatabase = [ (Film Casino Royale Martin Campbell 2006 [Garry, Dave, Zoe])] -- Function filmsInGivenYear :: Year - [Film] - [String] filmsInGivenYear year' films = [ title | (Film title director year fans) - films, year == year'] doFilmsInGivenYear :: [Film] - IO () doFilmsInGivenYear films = do putStrLn which year? text - getLine let year' = read text :: Int let answer = filmsInGivenYear year' films print answer main :: IO () main = do doFilmsInGivenYear films main [/code] if the other functions are compiling without this error im not sure as to why the main function does not compile because of the films...any light on this? Thanks -- View this message in context: http://www.nabble.com/Main-function-error-tp23506481p23506481.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Stream-fusion without the lists
rl: On 12/05/2009, at 14:45, Reiner Pope wrote: The Stream datatype seems to be much better suited to representing loops than the list datatype is. So, instead of programming with the lists, why don't we just use the Stream datatype directly? I think the main reason is that streams don't store data and therefore don't support sharing. That is, in let xs = map f ys in (sum xs, product xs) the elements of xs will be computed once if it is a list but twice if it is a stream. The other issue is reminding developers to preserve stream invariants, so as not to break the heavy duty rewriting that's going to happen to their code. Still, if someone finds a use for it, proceed! -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Stream-fusion without the lists
On Tue, May 12, 2009 at 1:39 PM, Roman Leshchinskiy r...@cse.unsw.edu.au wrote: let xs = map f ys in (sum xs, product xs) the elements of xs will be computed once if it is a list but twice if it is a stream. If you're using lists for loops rather than data, that's what you want (what you probably really want is cfoldl' ((,) $ sumF * productF) xs, in terms of combinable folds). Roman --Max ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] commending Design concepts in programming languages
On Tue, May 12, 2009 at 1:41 PM, Wolfgang Jeltsch g9ks1...@acme.softbase.org wrote: At least, I cannot remember seeing the other notation (first morphism on the left) in category theory literature so far. It’s just that my above-mentioned professor told me that category theorists would use the first-morphism-on-the-left notation. I've seen the notation f;g for g.f somewhere (and Wikipedia mentions it). I think it's less ambiguous than just fg (which I've seen for f.g too), but in Haskell we have the option of . A flipped application might be nice to go with it. How about $ ? --Max ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Inferred typing?
I was looking at some code and couldn't figure out how it was returning a list since there were no list constructors present. Thanks! Michael --- On Tue, 5/12/09, Brent Yorgey byor...@seas.upenn.edu wrote: From: Brent Yorgey byor...@seas.upenn.edu Subject: Re: [Haskell-cafe] Inferred typing? To: haskell-cafe@haskell.org Date: Tuesday, May 12, 2009, 7:50 AM On Mon, May 11, 2009 at 10:59:01PM -0700, michael rice wrote: In the code below, is the type returned by the return functions inferred from the result type in the function type signature, i.e., just change the result type to Maybe Int and the code will return a Maybe monad, (Just 4), instead of a List monad? Indeed, it is. Try it! =) -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Stream-fusion without the lists
Roman Leshchinskiy wrote: On 12/05/2009, at 14:45, Reiner Pope wrote: The Stream datatype seems to be much better suited to representing loops than the list datatype is. So, instead of programming with the lists, why don't we just use the Stream datatype directly? This is more or less the conclusion I came to myself the other day when I sat down and tried to implement stream fusion myself (just for giggles). I think the main reason is that streams don't store data and therefore don't support sharing. That is, in let xs = map f ys in (sum xs, product xs) the elements of xs will be computed once if it is a list but twice if it is a stream. ...and I hadn't thought of this part! ;-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [ANNOUNCE] Bindings for libguestfs
Richard, I added some partial bindings for libguestfs[1] here: http://git.et.redhat.com/?p=libguestfs.git;a=blob;f=haskell/Guestfs.hs;hb=HEAD Terrific! Partial bindings are great. Thanks for releasing it. I haven't taken the time to look at your code, but... BTW, I found the documentation on writing FFIs very contradictory and incomplete. For example, I was completely defeated trying to find ways to do simple stuff like passing in integers or returning booleans. *Potentially* Haskell's FFI seems like it might be one of the best out of the languages I've used so far, but it needs way more documentation and examples. Can you be more specific about what needs improvement? I wrote a partial Haskell binding for Net-SNMP recently, and I got along pretty well using the API docs at http://www.haskell.org/ghc/docs/latest/html/libraries/index.html, and an example in RWH using hsc2hs. What did you see that was contradictory? Regards, John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] List of exports of a module - are there alternatives?
I think that it's not nice to export 200 declarations from a single module. On 12 May 2009, at 18:05, Maurício wrote: Hi, When we want to list which declarations are exported by a module we do: module Mod ( list of exports ) where ... Are there propositions to alternatives to that (I could not find one)? Like, say, add a do export or do not export tag to declarations we want to (not) export? (I think something like that could be nice when we have modules with 200 declarations and just a few are (not) going to be exported.) Thanks, Maurício ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] List of exports of a module - are there alternatives?
On Tue, May 12, 2009 at 10:05 AM, Maurício briqueabra...@yahoo.com wrote: snip (I think something like that could be nice when we have modules with 200 declarations and just a few are (not) going to be exported.) Thanks, Maurício Uh, show me such a module, and I'll show you a module that's quite bloated and desperately needs to be refactored. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Map lookup signature
Maybe is an instance of Monad; the second signature is just more general than the first. class Monad m where return :: a - m a (=) :: m a - (a - m b) - m b fail :: String - m a Map lookup only uses return and fail; for Maybe these are defined as follows: return x = Just x fail s = Nothing So it's really the same thing. -- ryan On Mon, May 11, 2009 at 8:37 AM, Nico Rolle nro...@web.de wrote: Hi everyone. The docs in the web on http://www.haskell.org/ghc/docs define Data.Map.lookup as follows: http://www.haskell.org/ghc/docs lookup :: Ord k = k - Map k a - Maybe a but my version of ghci does i like that: Data.Map.lookup :: (Ord k, Monad m) = k - Data.Map.Map k a - m a but i need the 1. one. my version of ghci is 6.8.2 regards ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Stream-fusion without the lists
Sure, but this definition leaks space, which I think is one of the points that Reiner made. -- ryan On Tue, May 12, 2009 at 5:39 AM, Roman Leshchinskiy r...@cse.unsw.edu.au wrote: On 12/05/2009, at 14:45, Reiner Pope wrote: The Stream datatype seems to be much better suited to representing loops than the list datatype is. So, instead of programming with the lists, why don't we just use the Stream datatype directly? I think the main reason is that streams don't store data and therefore don't support sharing. That is, in let xs = map f ys in (sum xs, product xs) the elements of xs will be computed once if it is a list but twice if it is a stream. Roman ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] IO trouble
Hi, I can't really describe it in the subject. So let me try to do it here. I have two functions f :: a - b g :: (a - b) - c - d and I use them as gf :: c - d gf = g f Now I want to handle exceptions in f and redefine f as in f' f' :: a - IO (Either e b) So my question is how to define gf' now to use f' instead of f? gf' :: c - IO (Either e d) Thanks in advance. Xiao-Yong -- c/*__o/* \ * (__ */\ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskell cuda?
Lee, Chakravarty et al Data Parallelism in Haskell : ICFP PC Portland 2009 http://bit.ly/17EQcl The other thing to look for is Obsidian, from Chalmers danielkcook: Hi, Does anyone know if there's a compiler from Data-Parallel Haskell to GPU code? I saw a paper on it a while back, but Google hasn't turned up any code. Cheers, - Dan begin:vcard fn:Daniel K. Cook n:Cook;Daniel K. email;internet:danielkc...@gmail.com tel;cell:+44 (0) 7949 125 491 x-mozilla-html:TRUE version:2.1 end:vcard ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] caml build
Hi Nicolas, I am starting a caml build. I want line by line which module is being built so when I get an error I have a context to reason about to fix the problem. Got it? Regards, Vasili On Tue, May 12, 2009 at 7:23 AM, Nicolas Pouillard nicolas.pouill...@gmail.com wrote: Excerpts from Vasili I. Galchin's message of Tue May 12 00:27:26 +0200 2009: Hello, I have forgotten whether I sent this posting out. Sorry if I did (I didn't see on Haskell cafe archive). I am building Swish and getting an error. I want to follow the progress of swish build ... I don't see an additional parameter like verbose mode that will tell which swish component is being built. ??? I don't get the relation with the subject of your post, can you elaborate? Best regards, -- Nicolas Pouillard ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Structural sharing in haskell data structures?
wagner.andrew: So I've been reading a lot about a (relatively) new language called Clojure. One of its goals is to make concurrency easier via a built-in home-grown STM. Anyway, one of the ways it tries to do this is to have completely immutable data structures. Every time I read a tutorial about this in Clojure, it says ...yes, it sounds awful to think that your whole data structure gets copied every time you want to make a change to it, but it's sane because of a technique called structural sharing. Yet every time I hear immutability talked about in Haskell, what I hear is ...yes, it sounds awful to think that your whole data structure gets copied every time you want to make a change to it, but it's sane because of laziness...unless you need the whole data structure So I'm just curious, does GHC use structural sharing or something similar? Do other implementations? Does it matter? Purity allows our data structures to have a lot of sharing. This is separate to laziness. Laziness lets us build up interesting structures that have unusual sharing. Actually, what kind of persistant structures does Clojure have at this stage? I was under the impression they were reusing Java data structures. E.g. some of the nicer ones on hackage are zippers, patricia tries, finger trees, which I can't imaging have been ported. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskell cuda?
Try reaching Manuel Chakravarty, http://justtesting.org/ and his colleague Sean Lee at Galois. Slides from his talk on GPU.gen : Just gave my talk on Data Parallelism in Haskell at PSU; here the slides: http://bit.ly/17EQcl and slides from an earlier Galois talk: http://www.galois.com/blog/2008/08/29/gpugen-bringing-the-power-of-gpus-into-the-haskell-world/ --ts On May 12, 2009, at 9:18 AM, Dan wrote: Hi, Does anyone know if there's a compiler from Data-Parallel Haskell to GPU code? I saw a paper on it a while back, but Google hasn't turned up any code. Cheers, - Dan danielkcook.vcf___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Main function error
applebiz89 wrote: main :: IO () main = do doFilmsInGivenYear films main You pass as argument to 'doFilmsInGivenYear' the value 'films', which is not defined. Instead, I think you meant 'testDatabase'. All the best, -- Jochem Berndsen | joc...@functor.nl GPG: 0xE6FABFAB ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problem with text and text-icu packages
On Tue, May 12, 2009 at 7:16 AM, David Carter david.m.car...@gmail.comwrote: Specifically, a1.txt contains bytes 97 and 10, while a2.txt contains bytes 224 160 139 237 144 164. Have I misconstrued things, or is this a bug? It's probably a bug, and it has (I hope) already been found and fixed. Please try the darcs version of text instead: http://code.haskell.org/text/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskell cuda?
Sean and Manuel are both at Univ. New South Wales http://www.cse.unsw.edu.au/~seanl/ http://www.cse.unsw.edu.au/~chak/ On May 12, 2009, at 2:36 PM, Scott A. Waterman wrote: Try reaching Manuel Chakravarty, http://justtesting.org/ and his colleague Sean Lee at Galois. Slides from his talk on GPU.gen : Just gave my talk on Data Parallelism in Haskell at PSU; here the slides: http://bit.ly/17EQcl and slides from an earlier Galois talk: http://www.galois.com/blog/2008/08/29/gpugen-bringing-the-power-of-gpus-into-the-haskell-world/ --ts On May 12, 2009, at 9:18 AM, Dan wrote: Hi, Does anyone know if there's a compiler from Data-Parallel Haskell to GPU code? I saw a paper on it a while back, but Google hasn't turned up any code. Cheers, - Dan danielkcook.vcf___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskell cuda?
Doesn't look like there's code out there - will try e-mailing the authors of the various papers/presentations. This e-mail also counts as an open plea to those compiler wizards working on this stuff: feel free to put beta buggy versions of your code online :) Thanks, - Dan Scott A. Waterman wrote: Try reaching Manuel Chakravarty, http://justtesting.org/ and his colleague Sean Lee at Galois. Slides from his talk on GPU.gen : Just gave my talk on Data Parallelism in Haskell at PSU; here the slides: http://bit.ly/17EQcl and slides from an earlier Galois talk: http://www.galois.com/blog/2008/08/29/gpugen-bringing-the-power-of-gpus-into-the-haskell-world/ --ts On May 12, 2009, at 9:18 AM, Dan wrote: Hi, Does anyone know if there's a compiler from Data-Parallel Haskell to GPU code? I saw a paper on it a while back, but Google hasn't turned up any code. Cheers, - Dan danielkcook.vcf___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe begin:vcard fn:Daniel K. Cook n:Cook;Daniel K. email;internet:danielkc...@gmail.com tel;cell:+44 (0) 7949 125 491 x-mozilla-html:TRUE version:2.1 end:vcard ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Structural sharing in haskell data structures?
Purity allows our data structures to have a lot of sharing. This is separate to laziness. Ah, so haskell does do it. Interesting that it so rarely comes up, whereas it's frequently mentioned in clojure. Laziness lets us build up interesting structures that have unusual sharing. Actually, what kind of persistant structures does Clojure have at this stage? I was under the impression they were reusing Java data structures. E.g. some of the nicer ones on hackage are zippers, patricia tries, finger trees, which I can't imaging have been ported. It has some built-in persistent data structures: lists, vectors (arrays), maps, and sets. It also has strong interoperability with Java, so that any existing Java library can easily be used in Clojure code. In some ways, that makes it a VERY mature language already. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Structural sharing in haskell data structures?
wagner.andrew: Purity allows our data structures to have a lot of sharing. This is separate to laziness. Ah, so haskell does do it. Interesting that it so rarely comes up, whereas it's frequently mentioned in clojure. I think it is just assumed, since that's been the case for 20 years or more now. Sharing is kind of exciting to the ex-Java people looking at Clojure, I guess, since it's a new idea. So they talk about it. Laziness lets us build up interesting structures that have unusual sharing. Actually, what kind of persistant structures does Clojure have at this stage? I was under the impression they were reusing Java data structures. E.g. some of the nicer ones on hackage are zippers, patricia tries, finger trees, which I can't imaging have been ported. It has some built-in persistent data structures: lists, vectors (arrays), maps, and sets. It also has strong interoperability with Java, so that any existing Java library can easily be used in Clojure code. In some ways, that makes it a VERY mature language already. Certainly the JVM and its libraries are mature. Looks like yet another example of tech incubation in Haskell, then dispersal outwards to other langs. The more the better. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Main function error
What would you expect the program to output? You probably mean 'testDatabase' instead of 'films'. /jve On Tue, May 12, 2009 at 12:59 PM, applebiz89 applebi...@hotmail.com wrote: I have compiled each function independently and they have compiled the only problem is the main function.. I keep getting the error 'films not defined' and I am not sure why [code] type Title = String type Director = String type Year = Int type Fan = String data Film = Film Title Director Year [Fan] deriving Show -- List of films testDatabase :: [Film] testDatabase = [ (Film Casino Royale Martin Campbell 2006 [Garry, Dave, Zoe])] -- Function filmsInGivenYear :: Year - [Film] - [String] filmsInGivenYear year' films = [ title | (Film title director year fans) - films, year == year'] doFilmsInGivenYear :: [Film] - IO () doFilmsInGivenYear films = do putStrLn which year? text - getLine let year' = read text :: Int let answer = filmsInGivenYear year' films print answer main :: IO () main = do doFilmsInGivenYear films main [/code] if the other functions are compiling without this error im not sure as to why the main function does not compile because of the films...any light on this? Thanks -- View this message in context: http://www.nabble.com/Main-function-error-tp23506481p23506481.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Main function error
On Tue, May 12, 2009 at 9:59 AM, applebiz89 applebi...@hotmail.com wrote: I have compiled each function independently and they have compiled the only problem is the main function.. I keep getting the error 'films not defined' and I am not sure why [code] type Title = String type Director = String type Year = Int type Fan = String data Film = Film Title Director Year [Fan] deriving Show -- List of films testDatabase :: [Film] testDatabase = [ (Film Casino Royale Martin Campbell 2006 [Garry, Dave, Zoe])] -- Function filmsInGivenYear :: Year - [Film] - [String] filmsInGivenYear year' films = [ title | (Film title director year fans) - films, year == year'] doFilmsInGivenYear :: [Film] - IO () doFilmsInGivenYear films = do putStrLn which year? text - getLine let year' = read text :: Int let answer = filmsInGivenYear year' films print answer main :: IO () main = do doFilmsInGivenYear films main [/code] if the other functions are compiling without this error im not sure as to why the main function does not compile because of the films...any light on this? Thanks When you say 'doFilmsInGivenYear films', where does the variable 'films' come from? It's not defined anywhere in your program. That's what the compiler is complaining about. Alex ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Main function error
Am Dienstag 12 Mai 2009 18:59:47 schrieb applebiz89: I have compiled each function independently and they have compiled the only problem is the main function.. I keep getting the error 'films not defined' and I am not sure why [code] type Title = String type Director = String type Year = Int type Fan = String data Film = Film Title Director Year [Fan] deriving Show -- List of films testDatabase :: [Film] testDatabase = [ (Film Casino Royale Martin Campbell 2006 [Garry, Dave, Zoe])] -- Function filmsInGivenYear :: Year - [Film] - [String] filmsInGivenYear year' films = [ title | (Film title director year fans) - films, year == year'] doFilmsInGivenYear :: [Film] - IO () doFilmsInGivenYear films = do putStrLn which year? text - getLine let year' = read text :: Int let answer = filmsInGivenYear year' films print answer main :: IO () main = do doFilmsInGivenYear films main There is no top level definition of films in your module, main doesn't take any parameter, so films is not in scope in main. You probably meant testDatabase. However, main is not good even if you fix that, because every iteration of main, you work on the same database, you can't add new films or fans to films. You should do something like main :: IO () main = loop testDatabase loop db = do actionToRun - selectAction newDB - actionToRun db loop newDB selectAction = do putStrLn $ Select action to run:\n 1-print films from given year\n 2-add fan for some film\n ... ln - getLine let n = read ln act = case n of 1 - doFilmsInGivenYear 2 - becomeFan return act doFilmInGivenYear :: [Film] - IO [Film] doFilmInGivenYear films = do (your code) return films becomeFan :: [Film] - IO [Film] becomeFan films = do who - ask for name of fan whichFilm - ask for film let newFilms = makeFan who whichFilm films return newFilms then you can alter your database and have the modified database available in the next iteration of loop. [/code] if the other functions are compiling without this error im not sure as to why the main function does not compile because of the films...any light on this? The other functions receive films as a parameter. Thanks ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Developing 3 dimensional interactive environments/functional objects
You might want to contact the author of RogueStar GL http://roguestar.downstairspeople.org/ On Tue, May 12, 2009 at 5:21 PM, Don Stewart d...@galois.com wrote: paulfrancis: Does any programmer on this mailing list have experience with developing 3 dimensional interactive environments/functional objects within them, au Second Life? Is Haskell useful for such an endeavor? Mm.. Anygma http://www.anygma.com/JobOfferA.html gamr7 http://www.gamr7.com/ Both use Haskell to some extent. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Removing mtl from the Haskell Platform
I wanted to pass this idea around the cafe to get some thoughts before submitting a trac on this topic. I'd like to see the mtl removed from the Haskell Platform. The mtl was a tremendous step forward when it was developed. However, we have learned a few things about monad transformers since the development of the mtl, and it is time that we moved forward. There are at least 3 significant problem with the mtl. 1) `pass' should not be a member functions of the MonadWriter class. It is my understanding that there is no `MonadWriter w m = MonadWriter w (ContT s m)' instance because the `pass' function cannot be implemented. I'm also highly suspicious of some other methods too (I'm looking at you `local'). 2) The `StateT s (Cont r a)' instance of callCC is wrong. The paper on modular monad transformers http://www.cs.nott.ac.uk/~mjj/pubs/mmt/mmt.pdf describes why this is wrong. 3) I am told by many people that the order of the state and value pair in `State' is backwards. Actually, I'm not entirely sure what the issue is here, but I trust the people who say this. I think that use of the mtl should be deprecated so that we move on to improved monad transformer libraries. Having the mtl in the Haskell Platform does the opposite by further entrenching its use, possibly to the point where we may not be able to get rid of it for years. If I had to recommend a replace library, I would pick monadLib. However, there are other libraries, such as the mmtl and transformers and it's related packages that I haven't looked at, and may also make fine replacements for the mtl. -- Russell O'Connor http://r6.ca/ ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.'' ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] List of exports of a module - are there alternatives?
I would like to see this too. Maybe just a private keyword that would make everything after it invisible to the outside (or until a public keyword appeared)? On Tue, May 12, 2009 at 10:05 AM, Maurício briqueabra...@yahoo.com wrote: Hi, When we want to list which declarations are exported by a module we do: module Mod ( list of exports ) where ... Are there propositions to alternatives to that (I could not find one)? Like, say, add a do export or do not export tag to declarations we want to (not) export? (I think something like that could be nice when we have modules with 200 declarations and just a few are (not) going to be exported.) Thanks, Maurício ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Structural sharing in haskell data structures?
Hi, Andrew Wagner wrote: So I'm just curious, does GHC use structural sharing or something similar? Structural sharing is not a feature of implementations, but of libraries. Consider this example: -- a function to change the head of a list replaceHead y xs = y : tail xs -- a big list xs = [1..1] -- two new list with changed head ys = replaceHead 42 xs zs = replaceHead 27 xs -- the length of our lists n = length xs + length ys + length zs In this example, n will be 3, but even after evaluation xs, ys and zs, we have only 10002 cons cells allocated, because cons cells are shared between xs, ys and zs. This happens automatically in every language with references or pointers. However, it is only sane to do with immutable data structures, so programmers have to add extra code to explicitly avoid structural sharing in impure languages. Another example: xs = 1 : xs This list is infinite, but we have only one cons cell allocated. Tillmann ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Main function error
applebiz89 wrote: I have compiled each function independently and they have compiled the only problem is the main function.. I keep getting the error 'films not defined' and I am not sure why Well, because it is not defined :) type Title = String type Director = String type Year = Int type Fan = String data Film = Film Title Director Year [Fan] deriving Show -- List of films testDatabase :: [Film] testDatabase = [ (Film Casino Royale Martin Campbell 2006 [Garry, Dave, Zoe])] -- Function filmsInGivenYear :: Year - [Film] - [String] filmsInGivenYear year' films = [ title | (Film title director year fans) - films, year == year'] doFilmsInGivenYear :: [Film] - IO () doFilmsInGivenYear films = do putStrLn which year? text - getLine let year' = read text :: Int let answer = filmsInGivenYear year' films print answer main :: IO () main = do At this point, the following names are defined: - testDatabase - filmsInGivenYear - doFilmsInGivenYear - main - (and names from libraries) doFilmsInGivenYear films main Here you use three names: - doFilmsInGivenYear (ok, is defined) - films (oups, not defined) - main (ok, is defined) So ghc tries to figure out what you mean with films, and fails, because it was not defined. Try using one of the defined names instead of films. Tillmann ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] IO trouble
On Tue, May 12, 2009 at 04:59:36PM -0400, Xiao-Yong Jin wrote: f :: a - b g :: (a - b) - c - d gf :: c - d gf = g f Now I want to handle exceptions in f and redefine f as in f' f' :: a - IO (Either e b) So my question is how to define gf' now to use f' instead of f? gf' :: c - IO (Either e d) Use Control.Monad.Error.ErrorT, it's exactly for this. You have to monadize g to be able to pass f' as an argument to it. f' :: a - ErrorT e IO b g' :: Monad m = (a - m b) - c - m d gf' :: c - ErrorT e IO d gf' = g' f' Here e should be some fixed instance of Error. HTH. Lauri ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Darcs as undo/redo system?
Wolfgang Jeltsch g9ks1...@acme.softbase.org writes: Am Freitag, 8. Mai 2009 18:43 schrieb Jason Dagit: If you wanted to work on this, I would encourage you to read more about patch theory[1,2,3,4] and also try out libdarcs[5]. Is libdarcs the same as the darcs library package on Hackage (which exports the darcs API)? The Darcs package (both on Hackage and elsewhere) builds two things: the darcs(1) binary, and libHSdarcs. The latter is what Jason was referring to. Note that currently it just exposes all our internal functions, rather than providing a coherent (or stable!) API. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Kind of confusing
On Tue, 2009-05-12 at 14:09 +0100, Philippa Cowderoy wrote: On Mon, 2009-05-11 at 20:43 -0400, Anton van Straaten wrote: Serious question: what is the significance of the question mark and double question marks in those signatures, or better yet, where can I read about it? I've forgotten where to find the details (try the GHC manual if you haven't already?), but IIRC they're part of how GHC handles boxing. http://hackage.haskell.org/trac/ghc/wiki/IntermediateTypes ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] forall vs =
What is the difference between forall as in: runSThttp://www.haskell.org/ghc/docs/6.10-latest/html/libraries/base/Control-Monad-ST.html#v%3ArunST:: ( forall s. SThttp://www.haskell.org/ghc/docs/6.10-latest/html/libraries/base/Control-Monad-ST.html#t%3ASTs a) - a and the = as in evalStateThttp://www.haskell.org/ghc/docs/6.6/html/libraries/mtl/Control-Monad-State.html#v%3AevalStateT:: Monadhttp://www.haskell.org/ghc/docs/6.6/html/libraries/base/Control-Monad.html#t%3AMonadm = StateThttp://www.haskell.org/ghc/docs/6.6/html/libraries/mtl/Control-Monad-State.html#t%3AStateTs m a - s - m a thanks daryoush ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
