Re: [Haskell-cafe] Grok Monad Transformers - some help needed
On 02/01/2012 06:12, Arseniy Alekseyev wrote: I don't know what to actually do with this after putting it in a *.lhs file. You can :load *.lhs into ghci the same way you load .hs-files. I swear I tried this before, but now it suddenly works. Must be the chaos of stupid random assumptions making me do stupid things - I go through this phase with anything new. I have no idea what I was doing to screw things up, but I'm pretty there's no conspiracy to drive me nuts. Though now I think of it... hmmm... I wonder... The errors I was getting from GHC mostly referred to the monomorphism restriction - at least for test1 and test2. The errors for test3 were much longer and scarier. I'll try to figure out what's different going from GHC to GHCi later - for the moment, I'm getting back to those transformers. BTW - interesting how the signatures of test1 and test2 are reported - I hadn't realised monad transformers were relevant there. Of course it does seem a bit silly to implement both StateT and State when StateT can implement State for you. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to split this string.
I want to write a function whose behavior is as follows: foo string1\nstring2\r\nstring3\nstring4 = [string1, string2\r\nstring3, string4] Note the sequence \r\n, which is ignored. How can I do this? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to split this string.
Doesn't the function lines handle different line-endings? (In the Prelude and in Data.List) If not, doing this with parsec would be easy (yet maybe slightly overkill...) 2012/1/2 max m...@mtw.ru I want to write a function whose behavior is as follows: foo string1\nstring2\r\nstring3\nstring4 = [string1, string2\r\nstring3, string4] Note the sequence \r\n, which is ignored. How can I do this? ___ 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] How to split this string.
В Mon, 2 Jan 2012 10:45:18 +0100 Yves Parès limestr...@gmail.com пишет: Prelude lines string1\nstring2\r\nstring3\nstring4 [string1,string2\r,string3,string4] Doesn't the function lines handle different line-endings? (In the Prelude and in Data.List) If not, doing this with parsec would be easy (yet maybe slightly overkill...) 2012/1/2 max m...@mtw.ru I want to write a function whose behavior is as follows: foo string1\nstring2\r\nstring3\nstring4 = [string1, string2\r\nstring3, string4] Note the sequence \r\n, which is ignored. How can I do this? ___ 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] How to split this string.
Doesn't the function lines handle different line-endings? (In the Prelude and in Data.List) It does not ignore \r\n. Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On the purity of Haskell
Conal Elliott cites Steve Horne: I look at this World parameter as purely hypothetical, a trick used to gain an intuition. Whereas Jerzy (I think) uses it to claim Haskell is referentially transparent - those differing x and y values come from different worlds, or different world-states. I don't see this interpretation in Jerzy's words, and I'd be very surprised if he had that sort of argument in mind. I don't think either having used the 'World' model as an argument of the referential transparency. The main reason is that I don't know what does it mean, the referential transparency of the real world. There is a philosophical issue involved: the problem of IDENTITY, which is as old as the humanity, and it will survive it... We simply don't know what does it mean: the same... But I disagree quite strongly with the idea of /World parameter as purely hypothetical, a trick used to gain an intuition/. I mentioned the language Clean (no reaction, seems that Haskellians continue to ignore it...) In Clean this IS the IO model. You have such entities as FileSystem, which has the Unique Access property, etc. You can put all that in an equivalent of the IO Monad, constructed within Clean itself, not as a primitive. Jerzy ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Dutch FP day 2012, January 6; ; reminder, and happy new year to all of you
We are happy to announce that the next Dutch functional programming day will take place on January 6, 2012, at the university campus de Uithof of Utrecht University. The program, participants registered thus far, and further details can be found at: http://www.cs.uu.nl/wiki/bin/view/FPDag2012/WebHome If you are aware of people who might not be on the mailing list and might be interested (e.g. your students), please point this information out to them. Please do not forget to tell me that you whether you want to go to the dinner too. Best, hoping to see you all, Doaitse ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to split this string.
Am 02.01.2012 10:44, schrieb max: I want to write a function whose behavior is as follows: foo string1\nstring2\r\nstring3\nstring4 = [string1, string2\r\nstring3, string4] Note the sequence \r\n, which is ignored. How can I do this? replace the sequence by something unique first, i.e. a single \r (and revert this change later). (Replacing a single character is easier using concatMap). HTH Christian -- | replace first (non-empty) sublist with second one in third -- argument list replace :: Eq a = [a] - [a] - [a] - [a] replace sl r = case sl of [] - error replace: empty list _ - concat . unfoldr (\ l - case l of [] - Nothing hd : tl - Just $ case stripPrefix sl l of Nothing - ([hd], tl) Just rt - (r, rt)) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On the purity of Haskell
A perhaps acceptable notion of the property we want (purity etc.) is that all the extensions of the purely functional core language of Haskell (say the lazy lambda calculus extended with data constructors, etc) are _conservative_, that is all the equations that hold in the pure core language still hold in the extended language. For a part of Concurrent Haskell such a conservativity result is shown in D.Sabel , M. Schmidt-Schauß. On conservativity of Concurrent Haskell. Frank report 47, 2011. http://www.ki.informatik.uni-frankfurt.de/papers/frank/frank-47.pdf It also shows that with arbitrary use of unsafeInterleaveIO conservativity does not hold. And of course the result does not capture any IO-operation (only takeMVar, putMVar and spawning threads are considered), but it may be extended to more operations ... Just my two cents, David On 30.12.2011 02:07, Conal Elliott wrote: I wrote that post to point out the fuzziness that fuels many discussion threads like this one. See also http://conal.net/blog/posts/notions-of-purity-in-haskell/ and the comments. I almost never find value in discussion about whether language X is functional, pure, or even referentially transparent, mainly because those terms are used so imprecisely. In the notions-of-purity post, I suggest another framing, as whether or not a language and/or collection of data types is/are denotative, to use Peter Landin's recommended replacement for functional, declarative, etc. I included some quotes and a link in that post. so people can track down what denotative means. In my understanding, Haskell-with-IO is not denotative, simply because we do not have a (precise/mathematical) model for IO. And this lack is by design, as explained in the toxic avenger remarks in a comment on that post. I often hear explanations of what IO means (world-passing etc), but I don't hear any consistent with Haskell's actual IO, which includes nondeterministic concurrency. Perhaps the difficulties could be addressed, but I doubt it, and I haven't seen claims pursued far enough to find out. - Conal On Thu, Dec 29, 2011 at 4:42 PM, Steve Horne sh006d3...@blueyonder.co.uk mailto:sh006d3...@blueyonder.co.uk wrote: On 30/12/2011 00:16, Sebastien Zany wrote: Steve Horne wrote: I haven't seen this view explicitly articulated anywhere before See Conal Elliott's blog post The C language is purely functional http://conal.net/blog/posts/the-c-language-is-purely-functional. Thanks - yes, that's basically the same point. More concise - so clearer, but not going into all the same issues - but still the same theme. ___ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to split this string.
On 02/01/2012 09:44, max wrote: I want to write a function whose behavior is as follows: foo string1\nstring2\r\nstring3\nstring4 = [string1, string2\r\nstring3, string4] Note the sequence \r\n, which is ignored. How can I do this? Doing it probably the hard way (and getting it wrong) looks like the following... -- Function to accept (normally) a single character. Special-cases -- \r\n. Refuses to accept \n. Result is either an empty list, or -- an (accepted, remaining) pair. parseTok :: String - [(String, String)] parseTok = [] parseTok (c1:c2:cs) | ((c1 == '\r') (c2 == '\n')) = [(c1:c2:[], cs)] parseTok (c:cs) | (c /= '\n')= [(c:[], cs)] | True = [] -- Accept a sequence of those (mostly single) characters parseItem :: String - [(String, String)] parseItem = [(,)] parseItem cs = [(j1s ++ j2s, k2s) | (j1s,k1s) - parseTok cs , (j2s,k2s) - parseItem k1s ] -- Accept a whole list of strings parseAll :: String - [([String], String)] parseAll [] = [([],)] parseAll cs = [(j1s:j2s,k2s) | (j1s,k1s) - parseItem cs , (j2s,k2s) - parseAll k1s ] -- Get the first valid result, which should have consumed the -- whole string but this isn't checked. No check for existence either. parse :: String - [String] parse cs = fst (head (parseAll cs)) I got it wrong in that this never consumes the \n between items, so it'll all go horribly wrong. There's a good chance there's a typo or two as well. The basic idea should be clear, though - maybe I should fix it but I've got some other things to do at the moment. Think of the \n as a separator, or as a prefix to every item but the first. Alternatively, treat it as a prefix to *every* item, and artificially add an initial one to the string in the top-level parse function. The use tail etc to remove that from the first item. See http://channel9.msdn.com/Tags/haskell - there's a series of 13 videos by Dr. Erik Meijer. The eighth in the series covers this basic technique - it calls them monadic and uses the do notation and that confused me slightly at first, it's the *list* type which is monadic in this case and (as you can see) I prefer to use list comprehensions rather than do notation. There may be a simpler way, though - there's still a fair bit of Haskell and its ecosystem I need to figure out. There's a tool called alex, for instance, but I've not used it. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to split this string.
On Mon, Jan 2, 2012 at 3:14 PM, max m...@mtw.ru wrote: I want to write a function whose behavior is as follows: foo string1\nstring2\r\nstring3\nstring4 = [string1, string2\r\nstring3, string4] Note the sequence \r\n, which is ignored. How can I do this? Here's a simple way (may not be the most efficient) - import Data.List (isSuffixOf) split = reverse . foldl f [] . lines where f [] w = [w] f (x:xs) w = if \r `isSuffixOf` x then ((x++\n++w):xs) else (w:x:xs) Testing - ghci split ab\r\ncd\nefgh\nhijk [ab\r\ncd,efgh,hijk] -- Anupam ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to split this string.
On Mon, Jan 02, 2012 at 12:44:23PM +0300, max wrote:
I want to write a function whose behavior is as follows:
foo string1\nstring2\r\nstring3\nstring4 = [string1,
string2\r\nstring3, string4]
Note the sequence \r\n, which is ignored. How can I do this?
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unixLines :: String - [String]
unixLines xs = reverse . map reverse $ go xs []
where
go [] l ls = l:ls
go ('\r':'\n':xs) l ls = go xs ('\n':'\r':l) ls
go ('\n':xs) l ls = go xs (l:ls)
go (x:xs) l ls = go xs (x:l) ls
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Re: [Haskell-cafe] On the purity of Haskell
On 02/01/2012 10:03, Jerzy Karczmarczuk wrote: But I disagree quite strongly with the idea of /World parameter as purely hypothetical, a trick used to gain an intuition/. I mentioned the language Clean (no reaction, seems that Haskellians continue to ignore it...) I don't know about others, but I intend to learn one language at a time. In any case, that's Clean, not Haskell. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to split this string.
Okay, so it doesn't handle different line-endings. I have a more general solution (statefulSplit) http://hpaste.org/55980 I cannot test it as I don't have an interpreter at hand, but if someone has, I'd be glad to have comments. (It might be more readable by using the State monad) 2012/1/2 max m...@mtw.ru В Mon, 2 Jan 2012 10:45:18 +0100 Yves Parès limestr...@gmail.com пишет: Prelude lines string1\nstring2\r\nstring3\nstring4 [string1,string2\r,string3,string4] Doesn't the function lines handle different line-endings? (In the Prelude and in Data.List) If not, doing this with parsec would be easy (yet maybe slightly overkill...) 2012/1/2 max m...@mtw.ru I want to write a function whose behavior is as follows: foo string1\nstring2\r\nstring3\nstring4 = [string1, string2\r\nstring3, string4] Note the sequence \r\n, which is ignored. How can I do this? ___ 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] How to split this string.
max m...@mtw.ru writes: I want to write a function whose behavior is as follows: foo string1\nstring2\r\nstring3\nstring4 = [string1, string2\r\nstring3, string4] Note the sequence \r\n, which is ignored. How can I do this? cabal install split then do something like import Data.List (groupBy) import Data.List.Split (splitOn) rn '\r' '\n' = True rn _ _ = False required_function = fmap concat . splitOn [\n] . groupBy rn (though that might be an abuse of groupBy) -- Jón Fairbairn jon.fairba...@cl.cam.ac.uk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to split this string.
On Mon, Jan 02, 2012 at 12:44:23PM +0300, max wrote: I want to write a function whose behavior is as follows: foo string1\nstring2\r\nstring3\nstring4 = [string1, string2\r\nstring3, string4] Note the sequence \r\n, which is ignored. How can I do this? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe A short yet requiring regex solution: import Text.Regex.PCRE match (makeRegex (?:[^\r\n]+|\r\n)+ :: Regex) b\nc\r\n\n\r\n\nd :: [[String]] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Grok Monad Transformers - some help needed
On Mon, Jan 2, 2012 at 03:32, Steve Horne sh006d3...@blueyonder.co.ukwrote: BTW - interesting how the signatures of test1 and test2 are reported - I hadn't realised monad transformers were relevant there. Of course it does seem a bit silly to implement both StateT and State when StateT can implement State for you. If you're using the mtl1 library, State is separate from StateT. With the transformers library (or mtl2, which is a wrapper for transformers) State is defined as StateT Identity. Part of the reason for this is that older ghc didn't optimize very well with something like StateT Identity; part is simply because monad transformers came later and nobody bothered to go back and rework the standalone monads as transformers over an Identity monad. The original Monad library included non-transformer-based multi-monads such as RWS (Reader+Writer+State) as well, since nobody has worked out transformers as a concept yet. -- brandon s allbery allber...@gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to split this string.
В Mon, 02 Jan 2012 11:12:49 + Jon Fairbairn jon.fairba...@cl.cam.ac.uk пишет: max m...@mtw.ru writes: I want to write a function whose behavior is as follows: foo string1\nstring2\r\nstring3\nstring4 = [string1, string2\r\nstring3, string4] Note the sequence \r\n, which is ignored. How can I do this? cabal install split then do something like import Data.List (groupBy) import Data.List.Split (splitOn) rn '\r' '\n' = True rn _ _ = False required_function = fmap concat . splitOn [\n] . groupBy rn (though that might be an abuse of groupBy) This is the simplest solution of the proposed, in my opinion. Thank you very much. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to split this string.
On Mon, Jan 2, 2012 at 10:12 AM, max m...@mtw.ru wrote: This is the simplest solution of the proposed, in my opinion. Thank you very much. Better yet, don't use String and use Text. Then you just need T.splitOn \r\n [1]. Cheers, [1] http://hackage.haskell.org/packages/archive/text/0.11.1.12/doc/html/Data-Text.html#v:splitOn -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to split this string.
On Mon, Jan 2, 2012 at 5:52 PM, Felipe Almeida Lessa felipe.le...@gmail.com wrote: On Mon, Jan 2, 2012 at 10:12 AM, max m...@mtw.ru wrote: This is the simplest solution of the proposed, in my opinion. Thank you very much. Better yet, don't use String and use Text. Then you just need T.splitOn \r\n [1]. That is actually the opposite of what the OP wants, however it's interesting that Text has a function like that and not the String functions in the standard library. -- Anupam ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] space-efficient, composable list transformers [was: Re: Reifying case expressions]
Sebastian Fischer wrote: Your `ListTo` type achieves space efficiency for Applicative composition of list functions by executing them in lock-step. Because of the additional laziness provided by the `Fmap` constructor, compositions like interpret a . interpret b can also be executed in constant space. However, we cannot use the space efficient Applicative combinators again to form parallel compositions of sequential ones because we are already in the meaning type. We could implement composition for the `ListTo` type as follows (.) :: ListTo b c - ListTo a [b] - ListTo a c a . b = interpret a $ b But if we use a result of this function as argument of *, then the advantage of using `ListTo` is lost. While interpret ((,) $ andL * andL) runs in constant space, interpret ((,) $ (andL . idL) * (andL . idL)) does not. The ListTransformer type supports composition in lock-step via a category instance. The meaning of `ListTransformer a b` is `[a] - [b]` with the additional restriction that all functions `f` in the image of the interpretation function are incremental: xs `isPrefixOf` ys == f xs `isPrefixOf` f ys [..] The Applicative instance for `ListTransformer` is different from the Applicative instance for `ListTo` (or `ListConsumer`). While interpret ((,) $ idL * idL) is of type `[a] - ([a],[a])` transformList ((,) $ idL * idL) is of type `[a] - [(a,a)]`. [..] Ah, so ListTransformer is actually quite different from ListTo because the applicative instance yields a different type. Then again, the former can be obtained form the latter via unzip . I have a gut feeling that the laziness provided by the `Fmap` constructor is too implicit to be useful for the kind of lock-step composition provided by ListTransformer. So I don't have high hopes that we can unify `ListConsumer` and `ListTransformer` into a single type. Do you have an idea? Well, the simple solution would be to restrict the type of (.) to (.) :: ListTo b c - ListTransformer a b - ListTo a c so that the second argument is guaranteed to be incremental. Of course, this is rather unsatisfactory. Fortunately, there is a nicer solution that keeps everything in the ListTo type. The main problem with Fmap is that it can be far from incremental, because we can plug in any function we like: example :: ListTo a [a] example = Fmap reverse Without an explicit guarantee that the function is incremental, we can't do anything here. But we can just add another constructor to that effect if we turn ListTo into a GADT: data ListTo a b where CaseOf :: b - (a - ListTo a b) - ListTo a b Fmap :: (b - c) - ListTo a b - ListTo a c FmapCons :: b - ListTo a [b] - ListTo a [b] The interpretation for this case is given by the morphism interpret (FmapCons x g) = fmap (x:) $ interpret g and sequential composition reads -- sequential composition -- interpret (a . b) = interpret $ interpret a $ b (.) :: ListTo b c - ListTo a [b] - ListTo a c (CaseOf _ cons) . (FmapCons y b) = cons y . b (Fmap f a) . (FmapCons y b) = Fmap f $ a . (FmapCons y b) (FmapCons x a) . (FmapCons y b) = FmapCons x $ a . (FmapCons y b) a . (CaseOf nil cons) = CaseOf (interpret a nil) ((a .) . cons) a . (Fmap f b)= fmap (interpret a . f) b Of course, the identity has to be redefined to make use of the new guarantee idL :: ListTo a [a] idL = caseOf [] $ \x - FmapCons x idL I'm going to omit the new definition for the applicative instance, the full code can be found here: https://gist.github.com/1550676 With all these combinators in place, even examples like liftA2 (,) (andL . takeL 3) (andL . idL) should work as expected. While nice, the above solution is not perfect. One thing we can do with ListTransformer type is to perform an apply first and then do a sequential composition. a . (b * c) This only works because the result of * is already zipped. And there is an even more worrisome observation: all this work would have been superfluous if we had *partial evaluation*, i.e. if it were possible to evaluate expressions like \xs - f (4:xs) beneath the lambda. Then we could dispense with all the constructor yoga above and simply use a plain type ListTo a b = [a] - b with the applicative instance instance Applicative (ListTo a) where pure b = const b (f * x) cs = case cs of [] - f [] $ x [] (c:cs) - let f' = f . (c:); x; = x . (c:) in f' `partialseq` x' `partialseq` (f' * x') to obtain space efficient parallel and sequential composition. In fact, by using constructors, we are essentially doing partial evaluation by hand. Best regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org
[Haskell-cafe] Experiments in Haskell Packaging
Hi All, The http://justhub.org Haskell distribution for Enterprize Linux (RHEL/CentOS 5 6) is now live. The distribution deviates from current practice. When you upgrade to a new Platform from justhub.org you add the new platform to your Haskell infrastructure rather than replacing the old platform with a new one. Why? **Stability**: Enterprise Linux places a strong emphasis on stability and updating packages should not break things. (This has provided some challenges for us as RHEL 5 is still using GCC 4.1.2 and Binutils 2.17.50.) **Flexibility**: Different projects will in general need to work with different versions of the platform and toolkits and upgrade according to their own schedules. I believe Haskell’s strong-typing sharpens the need for this. Production projects will need to upgrade according to their own schedules while other projects will want to stay up-to-date. In general when you check out a source tree you want to build with the tools and libraries that it has been tested with and move on according to the project’s timetable. **Sandboxes**: The same mechanism for managing the multiple toolkits and platforms can be adapted to provide an integrated sandbox utility. The logic that dictates that projects have different tool-chain requirements applies to the user packages too. (‘Handbox’ doesn’t really work so we use **Hubs** instead.) **Package Deletion**: The infrastructure can also be expanded to complete the package management tools with package removal and garbage collection of library code. **The Catalogue**: All of the GHC releases can be added as they become available. In general the distribution works just like any other – after an upgrade invoking ‘ghc’ without any other configuration will invoke the compiler for that latest platform, which should behave as it would on any other (working) distribution. But after an upgrade: o any projects configured to work with specific tool chains and libraries will continue undisturbed; o you can create a new hub based on the new platform and experiment with it on newly-checked-out source tree without disturbing an existing working tree (or just swap the hub into an existing work tree and back out again if things don’t work out); o even on release of a new version of a package (or if you want to experiment with your existing packages) you can easily duplicate an existing hub and delete, upgrade and add packages on a topic branch. Of course ‘serious developers’ have been doing this with home-brew infrastructure for ever. Nevertheless I have found doing it with well-integrated tools to be quite liberating. It might also help new users to make the transition to serious developers more quickly. Thoughts anyone? Chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] proxy settings with simpleHttp
Hi, I am fiddling around with the package http-enumerator to download web pages. I was used to `simpleHttp` do do that. However, I would like to infuence the proxy settings, because sometimes I am behind a firewall. Is there a simple way to do this? Thanks! Han. -- View this message in context: http://haskell.1045720.n5.nabble.com/proxy-settings-with-simpleHttp-tp5114946p5114946.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] proxy settings with simpleHttp
On Mon, Jan 2, 2012 at 6:31 PM, hanjoosten han.joos...@atos.net wrote: Hi, I am fiddling around with the package http-enumerator to download web pages. I was used to `simpleHttp` do do that. However, I would like to infuence the proxy settings, because sometimes I am behind a firewall. Is there a simple way to do this? Thanks! Han. -- View this message in context: http://haskell.1045720.n5.nabble.com/proxy-settings-with-simpleHttp-tp5114946p5114946.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 You'll need to drop down one layer and use httpLbsRedirect. You can look at the code of simpleHttp[1] and add your proxy settings there. Do people think it would be a good idea to expose an extra function that has the same semantics as simpleHttp but takes a Request instead of a String? Any ideas on names? Michael [1] http://hackage.haskell.org/packages/archive/http-conduit/1.0.0/doc/html/src/Network-HTTP-Conduit.html#simpleHttp ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Experiments in Haskell Packaging
[I am sorry for if get two copies of this -- no sign of the first copy.] The justhub.org Haskell distribution for Enterprise Linux (RHEL/CentOS 5 6) is now live. The distribution deviates from current practice. When you upgrade to a new Haskell Platform you add the new platform to your Haskell infrastructure rather than replacing the old platform with a new one. Why? • Stability: Enterprise Linux places a strong emphasis on stability and updating packages should not break things. (This has provided some challenges for us as RHEL 5 is still using GCC 4.1.2 and Binutils 2.17.50.) • Flexibility: Different projects will in general need to work with different versions of the platform and toolkits and upgrade according to their own schedules. I believe Haskell’s strong-typing sharpens the need for this. Production projects will need to upgrade according to their own schedules while other projects will want to stay up-to-date. In general when you check out a source tree you want to build with the tools and libraries that it has been tested with and move on according to the project’s timetable. • Sandboxes: The same mechanism for managing the multiple toolkits and platforms can be adapted to provide an integrated sandbox utility. The logic that dictates that projects have different tool-chain requirements applies to the user packages too. (‘Handbox’ doesn’t really work so we use Hubs instead.) • Package Deletion: The infrastructure can also be expanded to complete the package management tools with package removal and garbage collection of library code. • The Catalogue: All of the GHC releases can be added as they become available. In general the distribution works just like any other – after an upgrade invoking ‘ghc’ without any other configuration will invoke the compiler for that latest platform, which should behave as it would on any other (working) distribution. But after an upgrade: • any projects configured to work with specific tool chains and libraries will continue undisturbed; • you can create a new hub based on the new platform and experiment with it on newly-checked-out source tree without disturbing an existing working tree (or just swap the hub into an existing work tree and back out again if things don’t work out); • even on release of a new version of a package (or if you want to experiment with your existing packages) you can easily duplicate an existing hub and delete, upgrade and add packages on a topic branch. Of course ‘serious developers’ have been doing this with home-brew infrastructure for ever. Nevertheless I have found doing it with well-integrated tools to be quite liberating. It might also help new users to make the transition to serious developers more quickly. Thoughts anyone? Chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to split this string.
String is really for small strings. Text is more efficent and also has more functionality, including most, if not all, of the functions defined for String. On Mon, Jan 2, 2012 at 3:12 PM, Anupam Jain ajn...@gmail.com wrote: On Mon, Jan 2, 2012 at 5:52 PM, Felipe Almeida Lessa felipe.le...@gmail.com wrote: On Mon, Jan 2, 2012 at 10:12 AM, max m...@mtw.ru wrote: This is the simplest solution of the proposed, in my opinion. Thank you very much. Better yet, don't use String and use Text. Then you just need T.splitOn \r\n [1]. That is actually the opposite of what the OP wants, however it's interesting that Text has a function like that and not the String functions in the standard library. -- Anupam ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Markus Läll ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] space-efficient, composable list transformers [was: Re: Reifying case expressions]
Hi, On Jan 2, 2012, at 2:34 PM, Heinrich Apfelmus wrote: Without an explicit guarantee that the function is incremental, we can't do anything here. But we can just add another constructor to that effect if we turn ListTo into a GADT: data ListTo a b where CaseOf :: b - (a - ListTo a b) - ListTo a b Fmap :: (b - c) - ListTo a b - ListTo a c FmapCons :: b - ListTo a [b] - ListTo a [b] I did not follow your discussion but how about using an additional GADT for the argument of Fmap, that is data Fun a b where Fun :: (a - b) - Fun a b Cons :: a - Fun [a] [a] data ListTo a b where CaseOf :: b - (a - ListTo a b) - ListTo a b Fmap :: Fun b c - ListTo a b - ListTo a c and provide a function to interpret this data type as well interpretFun :: Fun a b - a - b interpretFun (Fun f) = f interpretFun (Cons x) = (x:) for the sequential composition if I am not mistaken. (.) :: ListTo b c - ListTo a [b] - ListTo a c (CaseOf _ cons) . (Fmap (Cons y) b) = cons y . b (Fmap f a) . (Fmap g b) = Fmap f $ a . (Fmap g b) a . (CaseOf nil cons)= CaseOf (interpret a nil) ((a .) . cons) a . (Fmap f b) = fmap (interpret a . interpretFun f) b -- functor instance instance Functor (ListTo a) where fmap f = normalize . Fmap (Fun f) normalize :: ListTo a b - ListTo a b normalize (Fmap (Fun f) (Fmap (Fun g) c)) = fmap (f . g) c normalize x = x Cheers, Jan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On the purity of Haskell
On 2012/1/1 Ertugrul Söylemez e...@ertes.de wrote: Steve Horne sh006d3...@blueyonder.co.uk wrote: Of course even the bind operator arguably isn't primitive. We could translate to get rid of those too, and see what lies underneath. This is where we start seeing functions of type... World - (x, World) Problem - this level of abstraction is hypothetical. It is not part of the Haskell language. Haskell specifically defines the IO monad to be a black box. And that's fine, because IO is an embedded DSL. A better view of IO is a GADT like: data IO :: * - * where GetLine :: IO String PutStrLn :: String - IO () ... This is still hypothetical, but it shows how even IO is easily referentially transparent (as long as you don't use unsafe* cheats). What?? I see how a definition like this one shows how something else that you call IO can be denotative RT. I don't see how what that conclusion has to do with Haskell's IO. I also wonder whether you're assuming that all of the IO primitives we have in Haskell treat their non-IO arguments denotationally/extensionally, so that there cannot be operations like isWHNF :: a - IO Bool. - Conal ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] porting feed to xml-enumerator
Hi Sigbjorn (and Don), I'm back for another reason. feed leaks and uses a lot of memory due to the xml package. Rather than fix xml I ported feed to xml-enumerator, which is used by yesod and more actively maintained than xml. This seems to have fixed the problem so I'm thinking of uploading this version to hackage as feed-1.0 (which I'll use for rss2irc and hackagebot.) Please let me know whether you agree. Also you might be interested in moving your repo (http://code.galois.com/cgi-bin/gitweb?p=feed.git;a=summary) to github ? This would make it easier to publish my changes, either to the main repo or a branch or fork. Otherwise I'll need to get them to your repo somehow. Thanks again, -Simon On Feb 21, 2011, at 5:14 PM, Simon Michael wrote: thanks for feed. I'm just investigating a bug with rss2irc, and I think I'm seeing problems in the current feed on hackage. It lookas as if there's no way to get item updated date as opposed item published date, and getItemPublishDate actually gets the updated date in the case of an atom feed (http://hackage.haskell.org/packages/archive/feed/0.3.8/doc/html/src/Text-Feed-Query.html#getItemPublishDate). I'd like to contribute a fix. Would you be able to make feed's repo public, eg on darcsden.com or github ? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] porting feed to xml-enumerator
If I may: I'm about to upload a new version of xml-enumerator that will state that it's officially deprecated in favor of xml-conduit. My guess is you'll be able to migrate to the latter by just changing the package name in your cabal file. On Mon, Jan 2, 2012 at 8:54 PM, Simon Michael si...@joyful.com wrote: Hi Sigbjorn (and Don), I'm back for another reason. feed leaks and uses a lot of memory due to the xml package. Rather than fix xml I ported feed to xml-enumerator, which is used by yesod and more actively maintained than xml. This seems to have fixed the problem so I'm thinking of uploading this version to hackage as feed-1.0 (which I'll use for rss2irc and hackagebot.) Please let me know whether you agree. Also you might be interested in moving your repo (http://code.galois.com/cgi-bin/gitweb?p=feed.git;a=summary) to github ? This would make it easier to publish my changes, either to the main repo or a branch or fork. Otherwise I'll need to get them to your repo somehow. Thanks again, -Simon On Feb 21, 2011, at 5:14 PM, Simon Michael wrote: thanks for feed. I'm just investigating a bug with rss2irc, and I think I'm seeing problems in the current feed on hackage. It lookas as if there's no way to get item updated date as opposed item published date, and getItemPublishDate actually gets the updated date in the case of an atom feed (http://hackage.haskell.org/packages/archive/feed/0.3.8/doc/html/src/Text-Feed-Query.html#getItemPublishDate). I'd like to contribute a fix. Would you be able to make feed's repo public, eg on darcsden.com or github ? ___ 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] porting feed to xml-enumerator
Hi Simon and all, You might want to consider using xml-conduit instead of xml-enumerator. Michael Snoyman has shifted his attention to this new alternative. Cheers, Aristid 2012/1/2 Simon Michael si...@joyful.com: Hi Sigbjorn (and Don), I'm back for another reason. feed leaks and uses a lot of memory due to the xml package. Rather than fix xml I ported feed to xml-enumerator, which is used by yesod and more actively maintained than xml. This seems to have fixed the problem so I'm thinking of uploading this version to hackage as feed-1.0 (which I'll use for rss2irc and hackagebot.) Please let me know whether you agree. Also you might be interested in moving your repo (http://code.galois.com/cgi-bin/gitweb?p=feed.git;a=summary) to github ? This would make it easier to publish my changes, either to the main repo or a branch or fork. Otherwise I'll need to get them to your repo somehow. Thanks again, -Simon On Feb 21, 2011, at 5:14 PM, Simon Michael wrote: thanks for feed. I'm just investigating a bug with rss2irc, and I think I'm seeing problems in the current feed on hackage. It lookas as if there's no way to get item updated date as opposed item published date, and getItemPublishDate actually gets the updated date in the case of an atom feed (http://hackage.haskell.org/packages/archive/feed/0.3.8/doc/html/src/Text-Feed-Query.html#getItemPublishDate). I'd like to contribute a fix. Would you be able to make feed's repo public, eg on darcsden.com or github ? ___ 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] On the purity of Haskell
On Jan 2, 2012, at 1:30 PM, Conal Elliott wrote: On 2012/1/1 Ertugrul Söylemez e...@ertes.de wrote: And that's fine, because IO is an embedded DSL. A better view of IO is a GADT like: data IO :: * - * where GetLine :: IO String PutStrLn :: String - IO () ... This is still hypothetical, but it shows how even IO is easily referentially transparent (as long as you don't use unsafe* cheats). What?? I see how a definition like this one shows how something else that you call IO can be denotative RT. I don't see how what that conclusion has to do with Haskell's IO. Whether you say such a beast is IO or something else that you call 'IO', I don't see the problem with positing an open GADT of this form, new constructors of which are introduced by built-in magic and/or by 'foreign import', and letting the denotation of IO be terms in the free algebraic theory on the resulting signature. It is then the job of the compiler, linker, et al, to implement a model of that algebraic theory in the machine language. Foreign imports introduce new external names - constructors of the GADT - and the linker connects those names to their implementations - giving them denotations as terms in the target machine's language. Maybe I'm missing something but, in the presence of FFI, how can the world-interfacing portion of a programming language possibly be any more denotative than that? Once you cross that threshold, I'd much rather have an operational semantics anyway. Ultimately, programming a computer is about making the computer _do_ things. No matter what sort of denotational semantics you come up with, I don't see any way to avoid it eventually bottoming out at some abstract representation which must then either have an operational semantics or an informal everyone who matters knows what that means semantics. Eventually, the denotation of anything that potentially involves interaction with the real world must be a program in some real or imaginary machine's language. This model chooses a very reasonable place to sever the infinite tower of turtles because it produces a language that is universal: it is the free algebra of the signature specified by the GADT. Incidentally, this model also addresses a concern I've heard voiced before that IO isn't demonstrably a monad. The whole point of IO is, as I understand it, that it is a monad _by construction_ - specifically, it is the monad whose Kleisli category is the category of contexts and substitutions in the free algebraic theory generated on this signature. There are even at least 2 published implementations of this construction in Haskell - the MonadPrompt and operational packages - and it has been shown that it does, in fact, form a monad. I would assert that if there is any sense in which the IO type _implementation_ fails to be a monad, it is a bug and not a flaw in the concept of an IO monad. I also wonder whether you're assuming that all of the IO primitives we have in Haskell treat their non-IO arguments denotationally/extensionally, so that there cannot be operations like isWHNF :: a - IO Bool. Correct me if I'm wrong, but it appears the implication here is that [[isWHNF x]] /= [[isWHNF]] [[x]]. I don't think this is necessarily true though. Somewhere in any formal model of any language which takes the real world into account, there must be some translation from a denotational semantics to an operational one. If the denotational semantics is not computable, that translation necessarily must introduce some kind of accidental extra state. The denotational semantics will generally include no concept of this state, so no denotation can mention it. But I see no problem in there being a value in the denotation which is translated to an operation which does make use of this state. In this model, [[isWHNF x]] is something like IsWHNF [[x]], which the compiler then translates into some code that, at run time, checks the progress of the attempt to compute the denotation of x. At no point is there a term whose denotation depends on that state; instead, there is a computation which chooses how to proceed to do based on that state. This does not infect the denotation with the forbidden knowledge, it only allows you to denote operations which are aware of the mechanism by which the denotation is computed. Similarly, the operations 'peek' and 'poke' allow you to denote operations which may do unspeakably evil things at runtime, including entirely subverting that mechanism. That doesn't mean the denotation is wrong, it means the machine has a back door. Certainly it would be better, all other things being equal, if the translation did not open the back door like that but, as is so often the case, all other things are not equal. The FFI and the occasional heinous performance hack are far too useful for most people to ever consider throwing out. This may mean
[Haskell-cafe] More cabal install problems
I've been trying to install threadscope on my macbook pro runing OSX 10.7 (Lion). This hasn't been easy. Thanks to help here, I finally got glib installed, but now one of the hangups is in installing the package gio. The following happens: Building gio-0.12.2... Building library... creating dist/build /usr/bin/ghc --make -package-name gio-0.12.2 -hide-all-packages -fbuilding-cabal-package -i -idist/build -i. -idist/build/autogen -Idist/build/autogen -Idist/build -Idist/build/autogen -Idist/build -I/opt/local/include/glib-2.0 -I/opt/local/lib/glib-2.0/include -I/opt/local/include -optP-include -optPdist/build/autogen/cabal_macros.h -odir dist/build -hidir dist/build -stubdir dist/build -package-id array-0.3.0.2-143060371bda4ff52c270d1067551fe8 -package-id base-4.3.1.0-239d76b73f466dc120129098b3472858 -package-id bytestring-0.9.1.10-5bb17614aed376ea31b721a9272770b1 -package-id containers-0.4.0.0-b4885363abca642443ccd842502a3b7e -package-id glib-0.12.2-185c12da89238d25c489c0b80fc015c5 -package-id mtl-2.0.1.0-5b7a9cce5565d8cc8721ba4f95becf1b -O -XHaskell98 -XForeignFunctionInterface System.GIO System.GIO.Enums System.GIO.Types System.GIO.Async.AsyncResult System.GIO.Signals System.GIO.Async.Cancellable System.GIO.File.AppInfo System.GIO.File.ContentType System.GIO.File.FileAttribute System.GIO.File.File System.GIO.File.FileEnumerator System.GIO.File.FileInfo System.GIO.File.FileMonitor System.GIO.File.IOError System.GIO.File.MountOperation System.GIO.Icons.Emblem System.GIO.Icons.EmblemedIcon System.GIO.Icons.FileIcon System.GIO.Icons.Icon System.GIO.Icons.ThemedIcon System.GIO.Volumes.Drive System.GIO.Volumes.Mount System.GIO.Volumes.Volume System.GIO.Volumes.VolumeMonitor command line: cannot satisfy -package-id mtl-2.0.1.0-5b7a9cce5565d8cc8721ba4f95becf1b (use -v for more information) World file is already up to date. cabal: Error: some packages failed to install: gio-0.12.2 failed during the building phase. The exception was: ExitFailure 1 --- However, cabal list tells me: * mtl Synopsis: Monad classes, using functional dependencies Default available version: 2.0.1.0 Installed versions: 2.0.1.0 License: BSD3 which tells me that the version of mtl that's desired is already installed. Any suggestions? Victor ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] More cabal install problems
On Mon, Jan 2, 2012 at 21:36, Victor Miller victorsmil...@gmail.com wrote: command line: cannot satisfy -package-id mtl-2.0.1.0-5b7a9cce5565d8cc8721ba4f95becf1b (use -v for more information) However, cabal list tells me: * mtl Synopsis: Monad classes, using functional dependencies Default available version: 2.0.1.0 Installed versions: 2.0.1.0 License: BSD3 The right version, but possibly not the right ABI hash. Also, it might be broken by some other dependency; try ghc-pkg list which should give you an idea about both issues. ghc is regrettably not very good about saying *why* it cannot satisfy a package dependency. -- brandon s allbery allber...@gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] More cabal install problems
Brandon, Thanks again. That put me on the right track. When I did a ghc-pkg list it added a message saying that the cache was out of date and that I should run ghc-pkg recache. I did that and gio appears to installing. Victor On Mon, Jan 2, 2012 at 9:49 PM, Brandon Allbery allber...@gmail.com wrote: On Mon, Jan 2, 2012 at 21:36, Victor Miller victorsmil...@gmail.comwrote: command line: cannot satisfy -package-id mtl-2.0.1.0-5b7a9cce5565d8cc8721ba4f95becf1b (use -v for more information) However, cabal list tells me: * mtl Synopsis: Monad classes, using functional dependencies Default available version: 2.0.1.0 Installed versions: 2.0.1.0 License: BSD3 The right version, but possibly not the right ABI hash. Also, it might be broken by some other dependency; try ghc-pkg list which should give you an idea about both issues. ghc is regrettably not very good about saying *why* it cannot satisfy a package dependency. -- brandon s allbery allber...@gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Avoiding parametric function binding
On Sun, 01 Jan 2012 05:29:42 -0700, Sebastian Fischer fisc...@nii.ac.jp wrote: On Sat, Dec 31, 2011 at 4:09 PM, Kevin Quick qu...@sparq.org wrote: onVarElem :: forall a . (Show a) = (Maybe a - String) - Var - String The problem is the scope of the quantification of the type variable 'a'. You can use higher-rank types (via the Rank2Types or RankNTypes language extension) to achieve what you want. Change the type of 'onVarElem' to onVarElem :: (forall a . (Show a) = Maybe a - String) - Var - String Thanks to both Sebastian and Sean for the solution (abbreviated from Sebastian's reponse above). -Kevin P.S. Sorry for the late followup: some minor system issues prevented checking email for a little while. The delay notwithstanding, *all* of the responses were much appreciated. -- -KQ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
