Re: [Haskell-cafe] Mathematics and Statistics libraries
Tom Doris tomdo...@gmail.com writes: If you're interested in UI work, ideally we'd have something similar to RStudio as an environment, a simple set of windows encapsulating an editor, a repl, a plotting panel and help/history, this sounds superficial but it really has an impact when you're exploring a data set and trying stuff out. I agree, this sounds really nice. I really disagree that we need a data frame type structure; they're an abomination in R, they try to accommodate event records and time series, and do neither well. Just to clarify (since I think the original suggestion was mine), I don't want to copy R's data frame (which I never quite understood, anyway), but I'd like some standardized data structure, ideally with an option to label columns, and functions to slice and join. The underlying structure can just be a list of columns (Vector) or whatever. -k -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What happened with goa package repo?
On 26 March 2012 07:24, Dmitry Malikov malikov@gmail.com wrote: Cloning into bare repository '/usr/portage/distfiles/egit-src/goa.git'... fatal: The remote end hung up unexpectedly * ERROR: dev-haskell/goa- failed (unpack phase): * git-2_initial_clone: can't fetch from git://github.com/chrisdone/goa.git https://github.com/chrisdone/goa returns 404. So it seems like Chris dropped that repo. Did someone have clone of it? It will be nice to put it back on github. This has been entirely unmaintained for some time. The repo is up there now, but I haven't used it or maintained it in nearly a year. Please clone this if you want the commits, but otherwise it is available on hackage. I will remove it eventually. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Mathematics and Statistics libraries
On 26/03/2012, at 8:35 PM, Ketil Malde wrote: Just to clarify (since I think the original suggestion was mine), I don't want to copy R's data frame (which I never quite understood, anyway) A data.frame is - a record of vectors all the same length - which can be sliced and diced like a 2d matrix It's not unlike an SQL table (think of a column-oriented data base so a table is really a collection of named columns, but it _looks_ like a collection of rows). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] adding the elements of two lists
Le 26/03/2012 02:41, Chris Smith a écrit : Of course there are rings for which it's possible to represent the elements as lists. Nevertheless, there is definitely not one that defines (+) = zipWith (+), as did the one I was responding to. What? The additive structure does not define a ring. The multiplication can be a Legion, all different. Over. Jerzy K ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Execute only one step in Hood-Melville Real time queue.
Hi, I read the Hood-Melville real time queue realization in [1]. There are 2 lists maintained in queue, front and rear. When the queue gets unbalanced due to push/pop, it amortized the f ++ reverse r incrementally to build the new front list based on the below mechanism reverse r = reverse' r [] where reverse' [] acc = acc reverse' (x:xs) = reverse' xs (x:acc) and f ++ reverse r == reverse (reverse f) ++ reverse r == reverse' (reverse f) [] ++ reverse r == reverse' (reverse' f []) (reverse' r []) And the re-balance happens once | f | + 1 = | r |. Let's denote m = |f|. incremental f ++ reverse r takes total 2*m + 2 steps. In the the realization mentioned in [1], it execute 2 steps every push and pop to make sure the incremental computation finish before next queue re-balancing. However, I found it's possible to execute only one step per push/pop. because: 1. Next re-balance happens at earliest | f' | + 1 = |r|+|f|+1+1 = 2*m + 2 times by continuously push operation; 2. If we keep a copy of f, and a counter of how many elements left in f, which need to be incrementally 'appended', by continuously m times popping operation. we can finish the f ++ reverse r (actually, only reverse r is needed, as all elements in f are popped) Based on this fact, I rewrite the program as the following: data State a = Empty | Reverse Int [a] [a] [a] [a] -- n, f', acc_f' r, acc_r | Append Int [a] [a] -- n, rev_f', acc | Done [a] -- result: f ++ reverse r deriving (Show, Eq) -- front, length of front, on-goint reverse state, rear, length of reverse data RealtimeQueue a = RTQ [a] Int (State a) [a] Int deriving (Show, Eq) -- we skip the empty error for pop and front empty = RTQ [] 0 Empty [] 0 isEmpty (RTQ _ lenf _ _ _) = lenf == 0 -- O(1) time push push (RTQ f lenf s r lenr) x = balance f lenf s (x:r) (lenr + 1) -- O(1) time pop pop (RTQ (_:f) lenf s r lenr) = balance f (lenf - 1) (abort s) r lenr front (RTQ (x:_) _ _ _ _) = x balance f lenf s r lenr | lenr = lenf = step f lenf s r lenr | otherwise = step f (lenf + lenr) (Reverse 0 f [] r []) [] 0 -- execute f ++ reverse r step by step step f lenf s r lenr = case s' of Done f' - RTQ f' lenf Empty r lenr s' - RTQ f lenf s' r lenr where s' = if null f then next $ next s else next s next (Reverse n (x:f) f' (y:r) r') = Reverse (n+1) f (x:f') r (y:r') next (Reverse n [] f' [y] r') = Append n f' (y:r') next (Append 0 _ acc) = Done acc next (Append n (x:f') acc) = Append (n-1) f' (x:acc) next s = s -- Abort unnecessary appending as the element is popped abort (Append 0 _ (_:acc)) = Done acc -- Note! we rollback 1 elem abort (Append n f' acc) = Append (n-1) f' acc abort (Reverse n f f' r r') = Reverse (n-1) f f' r r' abort s = s Note the 'where' clause in step function. This is because we need an extra step to change the state from (Append 0 _ xs) to (Done xs). I tested this program with invariant testing with QuickCheck. The behavior is correct as other queue implementation. The program can be found here: https://github.com/liuxinyu95/AlgoXY/blob/algoxy/datastruct/elementary/queue/src/RealtimeQueue.hs Reference: [1]. Chris Okasaki. ``Purely functional data structures''. P102. Section 8.2.1. Cambridge University Press. ISBN 0521663504 -- Larry, LIU Xinyu https://sites.google.com/site/algoxy/ https://github.com/liuxinyu95/AlgoXY ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Using HaXml
Thanks! Apparently some also have problems to find tutorials/help with HaXml [1]. I'm curious to hear how HaXml compares to HXT / HXML / TagSoup. I'm curious too. I've read that HXML is old and not longer maintained. I believe besides the rewriting of the API to use arrows, HaXml adds checking capabilities like use of RelaxNG. [1] http://stackoverflow.com/questions/6082350/how-to-access-some-xml-data-with-haskell-using-haxml Le 25 mars 2012 11:06, aditya bhargava bluemangrou...@gmail.com a écrit : I don't know much about HaXml, but HXT is based on it and comes with a tutorial: http://www.haskell.org/haskellwiki/HXT I also show some basic functionality of HXT in this blog post: http://adit.io/posts/2012-03-10-building_a_concurrent_web_scraper_with_haskell.html I'm curious to hear how HaXml compares to HXT / HXML / TagSoup. Adit On Sun, Mar 25, 2012 at 1:34 AM, Yves Parès yves.pa...@gmail.com wrote: Hello café, Provided what I read, HaXml seems to be the recommended library for parsing XML files (I'm trying to browse and alter spreadsheets (ODS) and possibly release a package when I'm done), is there somewhere tutorials on how to use it? I used 'xml' package by the past, but HaXml is more substantial. Thanks. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- adit.io ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] difficulty building (some) TH packages with ghc-7.4.1
Hello, I've run into an odd problem when building certain packages that use Template Haskell with GHC-7.4.1. For example, RepLib: $ cabal --version cabal-install version 0.13.3 using version 1.14.0 of the Cabal library $ cabal install -O2 -w ~/.ghc-7.4.1/bin/ghc RepLib --reinstall Resolving dependencies... Configuring RepLib-0.5.2... Building RepLib-0.5.2... Preprocessing library RepLib-0.5.2... [ 1 of 12] Compiling Generics.RepLib.R ( Generics/RepLib/R.hs, dist/build/Generics/RepLib/R.o ) [ 2 of 12] Compiling Generics.RepLib.R1 ( Generics/RepLib/R1.hs, dist/build/Generics/RepLib/R1.o ) [ 3 of 12] Compiling Generics.RepLib.Derive ( Generics/RepLib/Derive.hs, dist/build/Generics/RepLib/Derive.o ) [ 4 of 12] Compiling Generics.RepLib.PreludeReps ( Generics/RepLib/PreludeReps.hs, dist/build/Generics/RepLib/PreludeReps.o ) Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package type-equality-0.1.0.2 ... linking ... done. Loading package array-0.4.0.0 ... linking ... done. Loading package deepseq-1.3.0.0 ... linking ... done. Loading package containers-0.4.2.1 ... linking ... done. Loading package pretty-1.1.1.0 ... linking ... done. Loading package template-haskell ... linking ... done. Loading package transformers-0.2.2.0 ... linking ... done. Loading package mtl-2.0.1.0 ... linking ... done. cabal: Error: some packages failed to install: RepLib-0.5.2 failed during the building phase. The exception was: ExitFailure 11 This is without library profiling enabled. If I enable library profiling, the unprofiled build is fine but the profiled build exits with the same error, at the same location. If I pass the -v argument to cabal-install, the package builds fine with profiling disabled. The -v flag makes no difference with profiling enabled, although some packages (but not RepLib) work with -v2 I haven't seen this with ghc-7.2.*, but I'm guessing this is some sort of cabal-install bug. Has anyone else witnessed anything like this? Thanks, John L. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: Latest package versions on Hackage as JSON/JSONP
Hi, I provide a relation between /package name/ and /latest version/ on Hackage as both JSON and JSONP. http://www.typeful.net/~tbot/hackage/ This are static files, and they are regenerated whenever new packages are uploaded (with a delay of about one minute). Two simple usage examples are given in the README[1]. Feel free to access this information for whatever purpose! Cheers, Simon [1] https://github.com/sol/hackage-jsonp#readme ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] adding the elements of two lists
This is interesting because it seems to be a counterexample to the claim that you can lift any Num through an Applicative (ZipList, in this case). It seems like maybe that only works in general for monoids instead of rings? On Mar 25, 2012 8:43 PM, Chris Smith cdsm...@gmail.com wrote: Jerzy Karczmarczuk jerzy.karczmarc...@unicaen.fr wrote: Le 26/03/2012 01:51, Chris Smith a écrit : instance (Num a) = Num [a] where xs + ys = zipWith (+) xs ys You can do this in the sense that it's legal Haskell... but it is a bad idea [...] It MIGHT be a ring or not. The real problem is that one should not confuse structural and algebraic (in the classical sense) properties of your objects. Of course there are rings for which it's possible to represent the elements as lists. Nevertheless, there is definitely not one that defines (+) = zipWith (+), as did the one I was responding to. By the time you get a ring structure back by some *other* set of rules, particularly for multiplication, the result will so clearly not be anything like a general Num instance for lists that it's silly to even be having this discussion. -- Chris Smith ___ 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] adding the elements of two lists
Jerzy Karczmarczuk jerzy.karczmarc...@unicaen.fr wrote: Le 26/03/2012 02:41, Chris Smith a écrit : Of course there are rings for which it's possible to represent the elements as lists. Nevertheless, there is definitely not one that defines (+) = zipWith (+), as did the one I was responding to. What? The additive structure does not define a ring. The multiplication can be a Legion, all different. I'm not sure I understand what you're saying there. If you were asking about why there is no ring on [a] that defines (+) = zipWith (+), then here's why. By that definition, you have [1,2,3] + [4,5] = [5,7]. But also [1,2,42] + [4,5] = [5,7]. Addition by [4,5] is not one-to-one, so [4,5] cannot be invertible. -- Chris Smith ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] good lightweight web-framework like sinatra?
On 21 March 2012 03:45, serialhex serial...@gmail.com wrote: i'm looking for something lightweight, that dosnt need it's own server, can easily run on cgi on an apache with minimal work, and dosn't have many dependancies. i was looking at yesod, but it is bigger than i need for my site (at this point) and would take too much work to get running on my webhost. though i am looking forward to learning it and using it in the future, i just need something that will play nicely with apache cgi... You could use WAI without warp/yesod? There's a CGI handler in wai-extra. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] adding the elements of two lists
Le 26/03/2012 16:31, Chris Smith a écrit : If you were asking about why there is no ring on [a] that defines (+) = zipWith (+), then here's why. By that definition, you have [1,2,3] + [4,5] = [5,7]. But also [1,2,42] + [4,5] = [5,7]. Addition by [4,5] is not one-to-one, so [4,5] cannot be invertible. So, * the addition* is not invertible, why did you introduce rings to this discussion, if the additive group within is already lousy?... OK I see now. You are only interested in the explicitly ambiguous usage of the element-wise addition which terminates at the shortest term... But I don't care about using (+) = zipWith (+) anywhere, outside of a programming model / framework, where you keep the sanity of your data. In my programs I KNEW that the length of the list is either fixed, or of some minimal size (or infinite). Your [4,5] simply does not belong to MY rings, if I decided to keep the other one. Jerzy K. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] adding the elements of two lists
On Mon, Mar 26, 2012 at 10:18 AM, Jerzy Karczmarczuk jerzy.karczmarc...@unicaen.fr wrote: So, * the addition* is not invertible, why did you introduce rings ... My intent was to point out that the Num instance that someone suggested for Num a = Num [a] was a bad idea. I talked about rings because they are the uncontroversial part of the laws associated with Num: I think everyone would agree that the minimum you should expect of an instance of Num is that its elements form a ring. In any case, the original question has been thoroughly answered... the right answer is that zipWith is far simpler than the code in the question, and that defining a Num instance is possible, but a bad idea because there's not a canonical way to define a ring on lists. The rest of this seems to have devolved into quite a lot of bickering and one-ups-manship, so I'll back out now. -- Chris Smith ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] adding the elements of two lists
On 3/26/12 8:16 AM, Jake McArthur wrote: This is interesting because it seems to be a counterexample to the claim that you can lift any Num through an Applicative (ZipList, in this case). It seems like maybe that only works in general for monoids instead of rings? I'm not so sure about that. The Applicative structure of ZipLists is specifically defined for infinite lists (cf., pure = repeat). And in the case of infinite lists the (+) = zipWith(+) definition works just fine, since we don't have to worry about truncation. I wasn't aware that Num was supposed to be liftable over any Applicative, but this doesn't seem like a counterexample... -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Is there a generic way to detect mzero?
Hi, I was writing a code trying to use MonadPlus to detect some error cases (representing missing values etc. in pure code). With the Maybe monad, I can do this: can0 :: (a - Maybe b) - a - Bool can0 f x = case f x of Nothing - False Just x - True And I got the expected result: *Main can0 (\x - Just x) 1 True But, when I try to generalize this using MonadPlus, as follows: can :: (MonadPlus m) = (a - m b) - a - Bool can f x = case f x of mzero - False _ - True I got a warning: __testError.hs:31:11: Warning: Pattern match(es) are overlapped In a case alternative: _ - ... Ok, modules loaded: Main. And the result is also not as intended (see also can0): *Main can (\x - Just x) 1 False Can anyone help to explain why this wouldn't work or if there is a workaround to use Monadplus and mzero (or Monad and fail) to achieve this? Thanks in advance for your help Ting ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is there a generic way to detect mzero?
can :: (MonadPlus m) = (a - m b) - a - Bool can f x = case f x of mzero - False _ - True I got a warning: __testError.hs:31:11: Warning: Pattern match(es) are overlapped In a case alternative: _ - ... Ok, modules loaded: Main. The problem here is that when you match on f x, your first match is an identifier that matches anything at all, and binds it to mzero. I think what you're looking for is can f x = case f x of x' | x' == mzero - False _ - True Jeff ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is there a generic way to detect mzero?
On 26 March 2012 20:33, Ting Lei tin...@hotmail.com wrote: can :: (MonadPlus m) = (a - m b) - a - Bool can f x = case f x of mzero - False _ - True In the first pattern `mzero' is just a variable and matches anything, as does `_'. So, naturally, both patterns overlap. I don't see any way to write this without requiring `Eq m'. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is there a generic way to detect mzero?
On 26 March 2012 21:11, Jeff Shaw shawj...@msu.edu wrote: can :: (MonadPlus m) = (a - m b) - a - Bool can f x = case f x of mzero - False _ - True I got a warning: __testError.hs:31:11: Warning: Pattern match(es) are overlapped In a case alternative: _ - ... Ok, modules loaded: Main. The problem here is that when you match on f x, your first match is an identifier that matches anything at all, and binds it to mzero. I think what you're looking for is can f x = case f x of x' | x' == mzero - False _ - True can f x = f x /= mzero ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is there a generic way to detect mzero?
On Mon, Mar 26, 2012 at 1:33 PM, Ting Lei tin...@hotmail.com wrote: Hi, I was writing a code trying to use MonadPlus to detect some error cases (representing missing values etc. in pure code). With the Maybe monad, I can do this: can0 :: (a - Maybe b) - a - Bool can0 f x = case f x of Nothing - False Just x - True And I got the expected result: *Main can0 (\x - Just x) 1 True But, when I try to generalize this using MonadPlus, as follows: can :: (MonadPlus m) = (a - m b) - a - Bool can f x = case f x of mzero - False _ - True I got a warning: __testError.hs:31:11: Warning: Pattern match(es) are overlapped In a case alternative: _ - ... Ok, modules loaded: Main. Well, you can sort of do it with only MonadPlus - but it really depends on your choice of Monad whether or not it does anything like what you want: can :: (MonadPlus m) = (a - m ()) - a - m Bool can f x = (f x return True) | return false For 'Maybe' this works great, but for something like 'List' I couldn't even tell you what it would do without reasoning through it. So you might be better off with the suggestion from Tobias using Eq Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is there a generic way to detect mzero?
Jeff, I don't think your code works in general, since it is not guaranteed that x' == mzero is allowed unless (m b) is an instance of Eq. I'm unsure if you are able to test for mzero in general. Harry On Mon, Mar 26, 2012 at 3:11 PM, Jeff Shaw shawj...@msu.edu wrote: can :: (MonadPlus m) = (a - m b) - a - Bool can f x = case f x of mzero - False _ - True I got a warning: __testError.hs:31:11: Warning: Pattern match(es) are overlapped In a case alternative: _ - ... Ok, modules loaded: Main. The problem here is that when you match on f x, your first match is an identifier that matches anything at all, and binds it to mzero. I think what you're looking for is can f x = case f x of x' | x' == mzero - False _ - True Jeff __**_ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/**mailman/listinfo/haskell-cafehttp://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] Is there a generic way to detect mzero?
* Ting Lei tin...@hotmail.com [2012-03-26 11:33:16-0700] I was writing a code trying to use MonadPlus to detect some error cases (representing missing values etc. in pure code). You are probably looking for the MonadError class. There's also the MonadLogic class (which allows to literally detect mzero), but if you simply need to catch errors, it is not as appropriate as MonadError. -- Roman I. Cheplyaka :: http://ro-che.info/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is there a generic way to detect mzero?
On Mon, Mar 26, 2012 at 21:24, Antoine Latter aslat...@gmail.com wrote: On Mon, Mar 26, 2012 at 1:33 PM, Ting Lei tin...@hotmail.com wrote: Hi, I was writing a code trying to use MonadPlus to detect some error cases (representing missing values etc. in pure code). With the Maybe monad, I can do this: can0 :: (a - Maybe b) - a - Bool can0 f x = case f x of Nothing - False Just x - True And I got the expected result: *Main can0 (\x - Just x) 1 True But, when I try to generalize this using MonadPlus, as follows: can :: (MonadPlus m) = (a - m b) - a - Bool can f x = case f x of mzero - False _ - True I got a warning: __testError.hs:31:11: Warning: Pattern match(es) are overlapped In a case alternative: _ - ... Ok, modules loaded: Main. Well, you can sort of do it with only MonadPlus - but it really depends on your choice of Monad whether or not it does anything like what you want: can :: (MonadPlus m) = (a - m ()) - a - m Bool can f x = (f x return True) | return false For 'Maybe' this works great, but for something like 'List' I couldn't even tell you what it would do without reasoning through it. So you might be better off with the suggestion from Tobias using Eq Well, if you accept the following MonadPlus laws: mzero = f == mzero mzero `mplus` m == m Then you can say that for a well-behaving MonadPlus, mzero will return (only) False in that function. However, I don't think it's guaranteed that a non-mzero value will give (only) True. In fact, the list monad will always return the final False. Erik ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: Latest package versions on Hackage as JSON/JSONP
Looks cool! One suggestion: make it a webservice I can use like: typeful.net/~tbot/hackage/[package name] example: typeful.net/~tbot/hackage/aeson So that I don't have to download an 83k file for every request. Adit On Mon, Mar 26, 2012 at 4:12 AM, Simon Hengel s...@typeful.net wrote: Hi, I provide a relation between /package name/ and /latest version/ on Hackage as both JSON and JSONP. http://www.typeful.net/~tbot/hackage/ This are static files, and they are regenerated whenever new packages are uploaded (with a delay of about one minute). Two simple usage examples are given in the README[1]. Feel free to access this information for whatever purpose! Cheers, Simon [1] https://github.com/sol/hackage-jsonp#readme ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- adit.io ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is there a generic way to detect mzero?
Hi Antoine and Tobias (and everyone else), Thanks a lot for your answers. They are really helpful Can you please show me how to use the (Eq m) constraint to do this? Also, my general question (probably novice-level) is that in monadic programming, you can convert not necessarily monadic codes into monadic ones. I know for many cases, it is impossible to do the reverse conversion, e.g. you can't make a function involving real IO operations into a pure code. In other cases, for example, I may need to using things like Nothing as the null value as in other programming languages, just to represent a special missing value outside the regular type. Is mzero a reasonable replacement for this or is there any reasonable (abstract) approximation in Haskell for doing this? (Like null, I need the ability to detect it.) Thanks, Ting From: aslat...@gmail.com Date: Mon, 26 Mar 2012 14:24:09 -0500 Subject: Re: [Haskell-cafe] Is there a generic way to detect mzero? To: tin...@hotmail.com CC: haskell-cafe@haskell.org On Mon, Mar 26, 2012 at 1:33 PM, Ting Lei tin...@hotmail.com wrote: Hi, I was writing a code trying to use MonadPlus to detect some error cases (representing missing values etc. in pure code). With the Maybe monad, I can do this: can0 :: (a - Maybe b) - a - Bool can0 f x = case f x of Nothing - False Just x - True And I got the expected result: *Main can0 (\x - Just x) 1 True But, when I try to generalize this using MonadPlus, as follows: can :: (MonadPlus m) = (a - m b) - a - Bool can f x = case f x of mzero - False _ - True I got a warning: __testError.hs:31:11: Warning: Pattern match(es) are overlapped In a case alternative: _ - ... Ok, modules loaded: Main. Well, you can sort of do it with only MonadPlus - but it really depends on your choice of Monad whether or not it does anything like what you want: can :: (MonadPlus m) = (a - m ()) - a - m Bool can f x = (f x return True) | return false For 'Maybe' this works great, but for something like 'List' I couldn't even tell you what it would do without reasoning through it. So you might be better off with the suggestion from Tobias using Eq Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] adding the elements of two lists
On 27/03/2012, at 5:18 AM, Jerzy Karczmarczuk wrote: But I don't care about using (+) = zipWith (+) anywhere, outside of a programming model / framework, where you keep the sanity of your data. In my programs I KNEW that the length of the list is either fixed, or of some minimal size (or infinite). Your [4,5] simply does not belong to MY rings, if I decided to keep the other one. And *that* is why I stopped trying to define instance Num t = Num [t]. If I KNEW that the length of the lists is ... fixed ... then the type wasn't *really* [t], but some abstract type that happened to be implemented as [t], and that abstract type deserved a newtype name of its own. Naming the type - makes the author's intent clearer to readers - lets the compiler check it's used consistently - lets you have instances that don't match instances for other abstract types that happen to have the same implementation - provides a natural place to document the purpose of the type - gives you a way to enforce the intended restrictions all for zero run-time overhead. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is there a generic way to detect mzero?
On Mon, Mar 26, 2012 at 4:25 PM, Ting Lei tin...@hotmail.com wrote: Hi Antoine and Tobias (and everyone else), Thanks a lot for your answers. They are really helpful Can you please show me how to use the (Eq m) constraint to do this? Also, my general question (probably novice-level) is that in monadic programming, you can convert not necessarily monadic codes into monadic ones. I know for many cases, it is impossible to do the reverse conversion, e.g. you can't make a function involving real IO operations into a pure code. In other cases, for example, I may need to using things like Nothing as the null value as in other programming languages, just to represent a special missing value outside the regular type. Is mzero a reasonable replacement for this or is there any reasonable (abstract) approximation in Haskell for doing this? (Like null, I need the ability to detect it.) I think using 'Maybe' (with Nothing) is perfect for this - this function should come in handy: http://hackage.haskell.org/packages/archive/base/latest/doc/html/Data-Maybe.html#v:isNothing Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] adding the elements of two lists
Well, ZipList's pure is indeed repeat, but there is nothing about ZipList restricting it to infinite lists. As long as pure is repeat, I'm pretty sure any other value can still be finite without violating Applicative's laws. On Mar 26, 2012 1:02 PM, wren ng thornton w...@freegeek.org wrote: On 3/26/12 8:16 AM, Jake McArthur wrote: This is interesting because it seems to be a counterexample to the claim that you can lift any Num through an Applicative (ZipList, in this case). It seems like maybe that only works in general for monoids instead of rings? I'm not so sure about that. The Applicative structure of ZipLists is specifically defined for infinite lists (cf., pure = repeat). And in the case of infinite lists the (+) = zipWith(+) definition works just fine, since we don't have to worry about truncation. I wasn't aware that Num was supposed to be liftable over any Applicative, but this doesn't seem like a counterexample... -- Live well, ~wren __**_ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/**mailman/listinfo/haskell-cafehttp://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] Need a backup GSOC to apply for? Last minute new proposal -- memory reuse analysis for GHC
Hi potential GSOC'ers, If there are multiple students interested in the project you're applying to it's a good idea to put in more than one application. This is a project proposal that would focus on performance analysis -- in particular in reusing some of the tools for analyzing memory access patterns in the context of Haskell: http://hackage.haskell.org/trac/summer-of-code/ticket/1619 I think this project would yield pretty good bang for the buck because almost all the pieces are already there. They just need to be combined, polished, documented, and evangelized. Cheers, -Ryan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is there a generic way to detect mzero?
On Tue, Mar 27, 2012 at 11:03 AM, Antoine Latter aslat...@gmail.com wrote: On Mon, Mar 26, 2012 at 4:25 PM, Ting Lei tin...@hotmail.com wrote: Hi Antoine and Tobias (and everyone else), Thanks a lot for your answers. They are really helpful Can you please show me how to use the (Eq m) constraint to do this? Also, my general question (probably novice-level) is that in monadic programming, you can convert not necessarily monadic codes into monadic ones. I know for many cases, it is impossible to do the reverse conversion, e.g. you can't make a function involving real IO operations into a pure code. In other cases, for example, I may need to using things like Nothing as the null value as in other programming languages, just to represent a special missing value outside the regular type. Is mzero a reasonable replacement for this or is there any reasonable (abstract) approximation in Haskell for doing this? (Like null, I need the ability to detect it.) I think using 'Maybe' (with Nothing) is perfect for this - this function should come in handy: http://hackage.haskell.org/packages/archive/base/latest/doc/html/Data-Maybe.html#v:isNothing Ting, It's often not good style to check Nothing explicitly, rather, it's better to use monads to thread it through automatically. If you have many functions that return a Maybe, then you can chain them together using do syntax: frobnicate = do foo - function1 bar - function2 foo return (bar + 1) If any of the functions in the chain return Nothing, then the monad will short circuit and the whole expression will result in Nothing. The - acts like an automatic null check. Chris Antoine ___ 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] good lightweight web-framework like sinatra?
Here's another Miku / Sinatra-like framework that looks interesting: https://github.com/xich/scotty From the README: My issue with miku is that it uses the Hack2 interface instead of WAI (they are analogous, but the latter seems to have more traction), and that it is written using a custom prelude called Air Adit On Mon, Mar 26, 2012 at 8:09 AM, dag.odenh...@gmail.com dag.odenh...@gmail.com wrote: On 21 March 2012 03:45, serialhex serial...@gmail.com wrote: i'm looking for something lightweight, that dosnt need it's own server, can easily run on cgi on an apache with minimal work, and dosn't have many dependancies. i was looking at yesod, but it is bigger than i need for my site (at this point) and would take too much work to get running on my webhost. though i am looking forward to learning it and using it in the future, i just need something that will play nicely with apache cgi... You could use WAI without warp/yesod? There's a CGI handler in wai-extra. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- adit.io ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
