Re: [Haskell-cafe] Roman Numeral Problem
Hi Christopher, I made a small library to convert between strings and roman numerals [1]. It didn't use much abstraction. I mainly used some type-classes so multiple string-like types can be parsed. The numerals themselves are basically a concatenation of value symbols. The order from high to low is not even strictly necessary in order to parse a roman numeral. One insight was to handle exceptions like "IV", "IX", "XL" etc. as separate symbols. It would be interesting if you could parse roman numerals using a dedicated parsing library and come up with something shorter and/or more elegant/readable than my little library. Regards, Roel 1 - http://hackage.haskell.org/package/roman-numerals On 24 June 2013 08:43, Christopher Howard wrote: > Hi. I am working on some practice programming problems, and one is the > Roman numeral problem: write a program that converts Roman numerals into > their (arabic) numeral equivalent. I imagine I could hack something > together, but I was trying to think about the problem a bit more deeply. > I don't know much about parsing, but I was wondering if this problem > matched up with some kind of parsing or grammar or other generic > approach to thinking about the problem. (I once read something about > Context Free Grammars, which was rather interesting.) I can do more of > my own research if I can get some initial guidance. > > -- > frigidcode.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] putting the result of a function in `infix` declaration
Related to Karl's Template Haskell suggestion you could also have a look at quasiquotation: http://www.haskell.org/haskellwiki/Quasiquotation The GHC documentation has an example of a expression quoter: http://www.haskell.org/ghc/docs/latest/html/users_guide/template-haskell.html#th-quasiquotation On 23 June 2013 22:22, Karl Voelker wrote: > On Sun, Jun 23, 2013 at 6:36 AM, TP wrote: > >> In a more general way, let us suppose I have a Haskell library able to >> perform some calculations: how to use it in a pre-processing step, before >> compilation of the executable? > > > You are looking for Template Haskell. > > http://www.haskell.org/haskellwiki/Template_Haskell > > I'm not sure how up-to-date the wiki is, but it should give you the > general idea. > > -Karl V. > > ___ > 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] Incrementation fails
> problem = replaceBasedIdx "X" ["b","d","f"] "aXcXeXgX" > -- "abcdefg*** Exception: Prelude.(!!): index too large This problem occurs because you never check if 'counter' is a valid index in the 'replaceStrList'. You can solve it by not using the !! operator at all. The solution is to also pass 'replaceStrList' in the recursion. That way you can check whether you have exhausted all strings in that list and as a bonus you do not need your counter anymore: > replaceBasedIdx :: String -> [String] -> String -> String > replaceBasedIdx findStr replaceStrList myText = loop replaceStrList myText > where > loop :: [String] -> String -> String > loop rs [] = [] > -- Check for empty list of replacements > loop [] text = text > -- Pattern match on the list of replacements to get both the > -- entire list rs, the first element r and the tail rs'. > loop rs@(r:rs') text = > let (prefix, rest) = splitAt n text > in if findStr == prefix > then r ++ loop rs' rest > else head text : loop rs (tail text) > > n :: Int > n = length findStr 2013/5/8 Roel van Dijk > I stared at the code some more and deduced what I think is the > intented meaning. Occurences of 'findStr' in 'myText' are replaced > with the strings in 'replaceStrList'. > > So replaceBasedIdx "X" ["b","d","f"] "aXcXeXg" = "abcdefg" > > The reason your counter didn't increment is because it was defined as > an argument to 'replaceBasedIdxSub'. That means its value is fixed > once you evaluate that function. Its value will not change no matter > how many times the inner 'loop' function is evaluated. The solution is > to pass the counter as an argument to said 'loop' function. Now when > 'loop' enters the recursion you can pass a different value, such as > counter + 1. > > > replaceBasedIdx :: String -> [String] -> String -> String > > replaceBasedIdx findStr replaceStrList myText = replaceBasedIdxSub > findStr replaceStrList myText > > > replaceBasedIdxSub :: String -> [String] -> String -> String > > replaceBasedIdxSub findStr replaceStrList myText = loop 0 myText > > where > > loop :: Int -> String -> String > > loop counter [] = [] > > loop counter myText = > > let (prefix, rest) = splitAt n myText > > in if findStr == prefix > > then (replaceStrList !! counter) ++ loop (counter + 1) rest > > else head myText : loop counter (tail myText) > > > > n :: Int > > n = length findStr > > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Incrementation fails
I stared at the code some more and deduced what I think is the intented meaning. Occurences of 'findStr' in 'myText' are replaced with the strings in 'replaceStrList'. So replaceBasedIdx "X" ["b","d","f"] "aXcXeXg" = "abcdefg" The reason your counter didn't increment is because it was defined as an argument to 'replaceBasedIdxSub'. That means its value is fixed once you evaluate that function. Its value will not change no matter how many times the inner 'loop' function is evaluated. The solution is to pass the counter as an argument to said 'loop' function. Now when 'loop' enters the recursion you can pass a different value, such as counter + 1. > replaceBasedIdx :: String -> [String] -> String -> String > replaceBasedIdx findStr replaceStrList myText = replaceBasedIdxSub findStr replaceStrList myText > replaceBasedIdxSub :: String -> [String] -> String -> String > replaceBasedIdxSub findStr replaceStrList myText = loop 0 myText > where > loop :: Int -> String -> String > loop counter [] = [] > loop counter myText = > let (prefix, rest) = splitAt n myText > in if findStr == prefix > then (replaceStrList !! counter) ++ loop (counter + 1) rest > else head myText : loop counter (tail myText) > > n :: Int > n = length findStr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Incrementation fails
Hi John, Can you tell us what your function is supposed to do? It appears to be some kind of search-and-replace for strings. What is the relationship between 'findStr', 'replaceStrList' and 'myText'? 2013/5/8 John > Hello All, > > I'm in a big trouble with incrementation of a counter in this code. It > doesn't increment. > > Could you please tell me where the problem ist and how can I solve it? > > replaceBasedIdx:: String -> [String] -> String -> String > replaceBasedIdxfindStr replaceStrList myText = replaceBasedIdxSub > findStr replaceStrList myText 0 > > replaceBasedIdxSub :: String -> [String] -> String -> Int -> String > replaceBasedIdxSub findStr replaceStrList myText counter = loop myText > where > loop [] = [] > loop myText = > let (prefix, rest) = splitAt n myText > in > if findStr == prefix-- found an > occurrence? > then (replaceStrList !! (counter+1)) ++ loop rest -- yes: replace > it > > else head myText : loop (tail myText) -- no: keep > looking > n = length findStr > > Thank you very mutch! > > Greetings! > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Inject cabal version or VCS version as a CPP macro
For each package "myPackage" Cabal generates a module containing, among other things, the package's version as a Haskell value: > import Paths_myPackage ( version ) > import Data.Version ( showVersion ) > main = showVersion version See also "Accessing data files from package code" in http://www.haskell.org/cabal/users-guide/ I do not now how to expose information from the VCS. 2012/2/22 Eugene Kirpichov : > Hi, > > I'd like my program to print something like "this is $program 1.0.4 git > 45fea6b" when invoked with --version, or at least just the 1.0.4 part. > > Can Cabal expose the version as a preprocessor macro by default, or do I > have to use Build-Type: Custom and add a preprocessing step of my own? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to increase performance using concurrency for sequential producer-consumer problem
Hello, I have a program which I believe can benefit from concurrency. But I am wondering if the mechanisms I need already exist somewhere on Hackage. Here is a sketch of my program, in literate Haskell: > module Problem where > import Control.Monad ( forM_ ) The producer produces values. It blocks until there are now more values to produce. Each value is given to a callback function. > type Producer a = (a -> IO ()) -> IO () The converter does some work with a value. This work is purely CPU and it is the bottleneck of the program. The amount of work it has to do is variable. > type Converter a b = a -> b The consumer does something with the value calculated by the converter. It is very important that the consumer consumes the values in the same order as they are produced. > type Consumer b = b -> IO () Dummy producer, converter and consumer: > producer :: Producer Int > producer callback = forM_ [1..10] callback > converter :: Converter Int Int > converter = (*10) > consumer :: Consumer Int > consumer = print A simple driver. Does not exploit concurrency. > simpleDriver :: Producer a -> Converter a b -> Consumer b -> IO () > simpleDriver producer converter consumer = producer (consumer . converter) > current_situation :: IO () > current_situation = simpleDriver producer converter consumer Ideally I would like a driver that spawns a worker thread for each core in my system. But the trick is in ensuring that the consumer is offered results in the same order as they are generated by the producer. I can envision that some kind of storage is necessary to keep track of results which can not yet be offered to the consumer because it is still waiting for an earlier result. Is there any package on Haskell that can help me with this problem? Or do I have to implement it using lower level concurrency primitives? Regards, Roel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] zlib 0.5.3.2 broken?
bzlib-0.5.0.2 suffers from the exact same problem. I send a bug report to the author a few days ago, but I can imagine he's very busy. It might help if we can send patches that fix the compile error. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to "show" a utf8 string?
Have you tried using putStrLn? Small GHCI example: Prelude> putStrLn "\29579" 王 I believe the Show instances for chars and strings escape all characters with a codepoint > 127. 2012/1/10 Magicloud Magiclouds : > Hi, > I am using LDAP hackage to do some ldap searching. I am not sure if > this is its problem. All Chinese chars returned like "\29579". > How to convert it to the actual Chinese char? I thought it was my > terminal's fault, so tried to use System.IO.UTF8 to put the result > into a file and viewed by firefox, no luck. > -- > 竹密岂妨流水过 > 山高哪阻野云飞 > > ___ > 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] ANNOUNCE: vector-bytestring-0.0.0.0
2011/10/18 Roel van Dijk : > Maybe we [can] create an example program which would fail with the > more general type. Migrating the function "foo" from bytestring to vector-bytestring would fail with more general types: > import Data.ByteString > foo = print empty Ok, modules loaded: Test. With vector: > import Data.Vector.Storable > foo = print empty Ambiguous type variable `a0' in the constraints: (Show a0) arising from a use of `print' at /home/roelvandijk/development/test.hs:5:7-11 (Storable a0) arising from a use of `empty' at /home/roelvandijk/development/test.hs:5:13-17 Probable fix: add a type signature that fixes these type variable(s) In the expression: print empty In an equation for `foo': foo = print empty Failed, modules loaded: none. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: vector-bytestring-0.0.0.0
2011/10/18 Christian Maeder : > you could re-export VS.empty, VS.singleton, etc. directly. The vector singleton and the vector-bytestring singleton don't have the same type. vector: > singleton :: a -> Vector a vector-bytestring: > singleton :: Word8 -> Vector Word8 By choosing the more general type you risk that a previously correct program becomes ambiguous. (When migrating from bytestring to vector-bytestring). I'm not sure if this will actually occur in practive or that it holds for all the little functions that you could theoretically re-export directly. Maybe we create an example program which would fail with the more general type. Proving the opposite (that the more general type is always safe) will be more difficult. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to compile this example code?
{- forgot to reply to list -}
This isn't Haskell syntax. Atleast not directly. It is either
hsc2hs[1] or c2hs [2]. Also see [3] for the difference between the
two. Soin order to compile that code you first have to run it through
aspecial preprocessor.
1 - http://www.haskell.org/ghc/docs/7.2.1/html/users_guide/hsc2hs.html2
- http://www.cse.unsw.edu.au/~chak/haskell/c2hs/3 -
http://stackoverflow.com/questions/6009031/difference-between-hsc2hs-and-c2hs
2011/10/3 Magicloud Magiclouds :
> Hi,
> I am learning to use data-flags, and got this example code:
> import Data.Flags
> newtype MyFlags = MyFlags CInt deriving (Eq, Flags)
> #{enum MyFlags, MyFlags
> , myFlag1 = C_FLAG1
> , myFlag2 = C_FLAG2
> , myFlag3 = C_FLAG3
> }
>
> I modified it trying to compile it. Well, I got illegal syntax at "#{e".
> In fact, I am not quite know the syntax here. Any clue?
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Re: [Haskell-cafe] hackage library info
Unfortunately the bifunctor.homelinux.net domain stopped working. The reverse dependencies can now be found at: http://revdeps.hackage.haskell.org/ The reverse dependency algorithm needs some love. Some packages have -1 reverse dependencies, which is somewhat strange. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Strange No instance error with cabal install
I see the aeson version with the stricter dependency on deepseq < 1.2 is now also released on hackage: http://hackage.haskell.org/package/aeson-0.3.2.12 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Strange No instance error with cabal install
I believe this is because of aeson depending on *any* version of deepseq. This was very recently fixed in the development version: https://github.com/mailrank/aeson/pull/25 2011/9/20 Rune Harder Bak : > Sometimes when one of our developers (using Arch-linux) tries to cabal > install packages he gets > a "no instance for" error. > Code that compiles fine on my computer, and other computers I try it > on. Even some packages on hackage > (trying to install aeson-native for instance gives Data/Aeson/Types.hs:196:22: > No instance for (NFData Object) > arising from a use of `rnf' > Possible fix: add an instance declaration for (NFData Object) > In the expression: rnf o > In an equation for `rnf': rnf (Object o) = rnf o > In the instance declaration for `NFData Value') > I tried removing the .ghc and .cabal folder, even reinstalled ghc-7.04 > and cabal-install (most recent), but the problem persisted (might not > have been a clean install though, I'm no Arch expert) > I know this is kind of vauge, and not in she shape of filling a bug > report, heck I can't even reproduce the error on my computer. > But perhaps somebody else has run in to this strange behavior before? > > Best, > Rune > > ___ > 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] ANN: numerals
> Are you familiar with the Grammatical Framework [1]? It is a Haskell > library and language for natural language parsing and translation -- > If you need to do a lot of translation or string localization, you > should take a look at it as much of the complexity has been addressed > there. Yes. Someone mentioned it to me in the Haskell IRC channel approximately a year ago when I was discussing some problems I had with my numerals package. I am not really in need to translation or string localization. The numerals package is merely a hobby project that got a bit out of hand :-) > That said, the numeral libraries for GF are somewhat limited (and/or > somewhat undocumented) so there is probably a lot your experience and > library could bring to that project. I am interested in the ways the two projects could work together. Maybe they could check each other's results. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: numerals
Hello everyone, I would like to announce the release of the numerals and numerals-base packages. * Numerals The numerals package contains functions to convert numbers to number words in a number of languages. For now the package only supports cardinal numbers. Example: >>> import qualified Text.Numeral.Language.EN as EN >>> EN.uk_cardinal 123 :: Maybe String Just "one hundred and twenty-three" You can also inspect the underlying structure of a number word: >>> import Text.Numerals >>> EN.shortScaleStruct 123 :: Exp Add (Mul (Lit 1) (Lit 100)) (Add (Mul (Lit 2) (Lit 10)) (Lit 3)) Compare this structure with the number word: 1 (one) * 100 (hundred) + (and) 2 (twen) * 10 (ty) + 3 (three) The package also comes with a test suite: >>> cabal configure --enable-tests >>> cabal build >>> ./dist/build/test-numerals/test-numerals --hide-successes I recommend the "--hide-successes" option of test-framework (>=0.4) because there are many tests (3383). * Numerals-base The numerals-base package contains all the machinery upon which numerals is build. Using this package you can write conversion functions for your own language(s). It is documented, although the documentation can be improved. For now the numerals package is probably the best documentation. * Resources: Hackage: http://hackage.haskell.org/package/numerals http://hackage.haskell.org/package/numerals-base Github: http://github.com/roelvandijk/numerals http://github.com/roelvandijk/numerals-base * Help wanted Currently I support 24 languages. But I only have some experience with 4 of them. The rest is scraped together with information I found online. For most languages I can find online how to form the first 100 cardinal numbers. But after that information is sparse. You can help by checking and expanding the test suite. This is very simple because the test suite consists only of numbers combined with the expected cardinal number word. Regards, Roel van Dijk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] TypeOperators and Unicode
2011/9/12 Brandon Allbery : > Don't all infix constructors have to start with a colon? Yes that is true. You can of course use Unicode symbols as infix type variables: (⋙) :: Category ⇝ => (α ⇝ β) -> (β ⇝ γ) -> α ⇝ γ But a constructor must always begin with a capital letter or with a colon. UnicodeSyntax is only required if you want to replace existing Haskell syntax with Unicode. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haddock chokes on function arguments
Does it help if you format it like this: -- |Apply a given function over all elements of a list and select one of the -- results. selector :: (Arbitrary b) => [a] -- ^ Elements to select from -> (a -> b) -- ^ Constructor to apply to selected element -> Gen b selector list ctor = oneof (map (return . ctor) list) So placing the => and -> before the lines instead of after them? 2011/8/25 Arnaud Bailly : > Hello, > while trying to generate Haddock documentation (Haddock version 2.9.2, (c) > Simon Marlow 2006), it chokes on the following fragment > > -- |Apply a given function over all elements of a list and select one of the > -- results. > selector :: (Arbitrary b) => > [a] -> -- ^ Elements to select from > (a -> b) -> -- ^ Constructor to apply to selected element > Gen b > selector list ctor = oneof (map (return . ctor) list) > > with the following error message: > > ' parse error on input `-- ^ Elements to select from > > I am puzzled as this is exactly how arguments are supposed to be documented, > according to http://www.haskell.org/haddock/doc/html/ch03s02.html#id565220 > > Any clues ? > > Arnaud > > ___ > 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] The Lisp Curse
On 20 May 2011 12:46, Markus Läll wrote: > What's stopping it from being put on the official hackage? I use it quite a > lot to find well established packages and/or example code, and am quite fond > of it. But it is only visible when you know that this exists. Poor timing. I wrote the patch when there was significant work being done for the new version of hackage [1]. So the feeling was that the current hackage (which is a bunch of cgi programs) would soon be replaced by the new hackage-server (based on happstack). I also stated in my initial announcement that I would look into writing a version of my reverse dependencies for the new server. I haven't done that yet. Since at least July of 2010 the new server has some support for reverse dependencies. Unfortunately hackage-server seems to have lost a bit of momentum. It is now almost 3 years old. Looking at "darcs show authors" I'd say there are about 4 main contributors, with the main author being Duncan Coutts. The last patches are from December 2010. I think the best solution is to get more people contributing to hackage-server. It is superior to the current hackage in many ways. 1 - http://code.haskell.org/hackage-server/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] The Lisp Curse
On 19 May 2011 20:50, Serguey Zefirov wrote: > The solution... I think that some ratings, like "used directly by ### > packages/projects and indirectly by ###" would be nice, but not much. Maybe my reverse dependencies mirror of hackage could be useful here: http://bifunctor.homelinux.net/~roel/hackage/packages/hackage.html The mirror was intended to show the workings of a patch for the old (current) hackage. It is updated daily. The algorithm needs some attention so don't trust it blindly, but in general it is quite accurate. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Those damned parentheses
On 10 May 2011 09:47, Andrew Butterfield wrote: > Why not indeed ? > (-->) = flip (.) > f = Main.id --> show --> (++ " = message received") --> putStrLn -- (>>>) :: Category cat => cat a b -> cat b c -> cat a c import Control.Category ( (>>>) ) f = Main.id >>> show >>> (++ " - message received") >>> putStrLn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Storing failing testcases for QuickCheck
On 24 April 2011 01:49, wren ng thornton wrote: > I would *love* there to be a tool which (a) automatically saves failing > QuickCheck values to disk, and (b) automates using HUnit to load those in > and test them. I'm not so sure that QuickCheck should be doing the second > step of that since that'd really mess with the QuickCheck infrastructure; > once you have the code for reading from disk, it'd be trivial to just use > HUnit. Maybe this is a job for test-framework? I think the API's of QuickCheck and HUnit expose enough information for this to be possible. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] IO and Cont as monads
On 13 April 2011 21:26, Tim Chevalier wrote: > IO doesn't obey the monad laws, due to the presence of seq in Haskell. > Sad but true... See also a previous discussion about IO and the Monad laws: http://www.haskell.org/pipermail/haskell-cafe/2010-March/074001.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Encoding of Haskell source files
On 5 April 2011 07:04, Mark Lentczner wrote: > I'm not on that mailing list, so I'll comment here: I recommend joining the prime list. It is very low traffic and the place where language changes should be discussed. > My only caveat is that the encoding provision should apply when Haskell > source is presented to the compiler as a bare stream of octets. Where > Haskell source is interchanged as a stream of Unicode characters, then > encoding is not relevant -- but may be likely governed by some outer > protocol - and hence may not be UTF-8 but nonetheless invisible at the > Haskell level. My intention is that every time you need an encoding for Haskell sources, it must be UTF-8. At least if you want to call it Haskell. This is not limited to compilers but concerns all tools that process Haskell sources. > Two examples where this might come into play are: > 1) An IDE that stores module source in some database. It would not be > relevant what encoding that IDE and database choose to store the source in > if the source is presented to the integrated compiler as Unicode characters. An IDE and database are free to store sources any way they see fit. But as soon as you want to exchange that source with some standards conforming system it must be encoded as UTF-8. > 2) If a compilation system fetches module source via HTTP (I could imagine a > compiler that chased down included modules directly off of Hackage, say), > then HTTP already has a mechanism (via MIME types) of transmitting the > encoding clearly. As such, there should be no problem if that outer protocol > (HTTP) transmits the source to the compiler via some other encoding. There > is no reason (and only potential interoperability restrictions) to enforce > that UTF-8 be the only legal encoding here. This is an interesting example. What distinguishes this scenario from others is that there is a clear understanding between two parties (client and server) how a file should be interpreted. I could word my proposal in such a way that it only concerns situations where such a prior agreement doesn't or can't exist. For example, when storing source on a file system. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Encoding of Haskell source files
I made an official proposal on the haskell-prime list: http://www.haskell.org/pipermail/haskell-prime/2011-April/003368.html Let's have further discussion there. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Encoding of Haskell source files
2011/4/4 Ketil Malde : > I think the safest thing to do is to require source to be ASCII, and > provide escapes for code points >127... I do not think that that is the safest option. The safest is just writing down whatever GHC does. Escape codes for non-ASCII would break a lot of packages and make programming really painful. Consider the following, utf-8 encoded, file: http://code.haskell.org/numerals/test/Text/Numeral/Language/ZH/TestData.hs I don't want to imagine writing that with escape characters. It would also be very error prone, not being able to readily read what you write. But the overall consensus appears to be UTF-8 as the default encoding. I will write an official proposal to amend the haskell language specification. (Probably this evening, utc+1). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Encoding of Haskell source files
On 4 April 2011 12:22, Michael Snoyman wrote: > Firstly, I personally would love to insist on using UTF-8 and be done with > it. I see no reason to bother with other character encodings. This is also my preferred choice. > There *is* an algorithm for determining the encoding of an XML file based on > a combination of the BOM (Byte Order Marker) and an assumption that the file > will start with a XML declaration (i.e., ). But this isn't > capable of determining every possible encoding on the planet, just > distinguishing amongst varieties of UTF-(8|16|32)/(big|little) endian and > EBCIDC. It cannot tell the difference between UTF-8, Latin-1, and > Windows-1255 (Hebrew), for example. I think I was confused between character encodings in general and Unicode encodings. > I think the implication of "Unicode encoding formats" is something in the > UTF family. An encoding like Latin-1 or Windows-1255 can be losslessly > translated into Unicode codepoints, but it's not exactly an encoding of > Unicode, but rather a subset of Unicode. That would validate Colin's point about there not being that many encodings. > My guess is that a large subset of Haskell modules start with one of left > brace (starting with comment or language pragma), m (for starting with > module), or some whitespace character. So it *might* be feasible to take a > guess at things. But as I said before: I like UTF-8. Is there anyone out > there who has a compelling reason for writing their Haskell source in > EBCDIC? I think I misinterpreted the word 'leading'. I thought Colin meant "most used". The set of characters with which Haskell programmes start is indeed small. But like you I prefer no guessing and just default to UTF-8. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Encoding of Haskell source files
2011/4/4 Colin Adams : > Not from looking with your eyes perhaps. Does that matter? Your text editor, > and the compiler, can surely figure it out for themselves. I am not aware of any algorithm that can reliably infer the character encoding used by just looking at the raw data. Why would people bother with stuff like if automatically figuring out the encoding was easy? > There aren't many Unicode encoding formats >From casually scanning some articles about encodings I can count at least 70 character encodings [1]. > and there aren't very many possibilities for the > leading characters of a Haskell source file, are there? Since a Haskell program is a sequence of Unicode code points the programmer can choose from up to 1,112,064 characters. Many of these can legitimately be part of the interface of a module, as function names, operators or names of types. [1] - http://en.wikipedia.org/wiki/Character_encoding ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Encoding of Haskell source files
Hello,
The Haskell 2010 language specification states that "Haskell uses
the Unicode character set" [1]. I interpret this as saying that,
at the lowest level, a Haskell program is a sequence of Unicode
code points. The standard doesn't say how such a sequence should
be encoded. You can argue that the encoding of source files is
not part of the language. But I think it would be highly
practical to standardise on an encoding scheme.
Strictly speaking it is not possible to reliably exchange Haskell
source files on the byte level. If I download some package from
hackage I can't tell how the source files are encoded from just
looking at the files.
I propose a few solutions:
A - Choose a single encoding for all source files.
This is wat GHC does: "GHC assumes that source files are ASCII or
UTF-8 only, other encodings are not recognised" [2]. UTF-8 seems like
a good candidate for such an encoding.
B - Specify encoding in the source files.
Start each source file with a special comment specifying the encoding
used in that file. See Python for an example of this mechanism in
practice [3]. It would be nice to use already existing facilities to
specify the encoding, for example:
{-# ENCODING #-}
An interesting idea in the Python PEP is to also allow a form
recognised by most text editors:
# -*- coding: -*-
C - Option B + Default encoding
Like B, but also choose a default encoding in case no specific
encoding is specified.
I would further like to propose to specify the encoding of haskell
source files in the language standard. Encoding of source files
belongs somewhere between a language specification and specific
implementations. But the language standard seems to be the most
practical place.
This is not an official proposal. I am just interested in what the
Haskell community has to say about this.
Regards,
Roel
[1] -
http://www.haskell.org/onlinereport/haskell2010/haskellch2.html#x7-150002.1
[2] -
http://www.haskell.org/ghc/docs/7.0-latest/html/users_guide/separate-compilation.html#source-files
[3] - http://www.python.org/dev/peps/pep-0263/
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Re: [Haskell-cafe] darcs repo browser
Nice work! The view file part seems to have problems with utf-8 encoded files: http://handra.rampa.sk/dawb/view?repoVURL=http%3A%2F%2Fcode.haskell.org%2Fnumerals&repoVFile=test%2FText%2FNumeral%2FLanguage%2FZH%2FTestData.hs It is unreadable even when explicitly asking my browser to decode the document as UTF-8. This makes me suspect the problem is in the code that processes files to produce the HTML. I have no solution ready for this problem. Each file could potentially use a different encoding. Apart from this inconvenience your tool looks very useful. Regards, Roel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [ghci] unknown symbol in base-unicode-symbols-0.2.1.2 ...
I can reproduce the problem on my system with GHC-7.0.3. The flag old-base is meant for base libraries before 3.0.3.1 which didn't export a Control.Category module. It looks like I accidentally inverted the logic of the flag. What is weird is that is still builds okay on my system. I would expect that, given the inverted flag logic, Control.Category.Unicode would be missing from the installed package's exposed module list. I fixed the logic of the flag and the bug appears to be gone. I uploaded the fixed version 0.2.1.3. Thanks for the bug report! On 31 March 2011 00:05, John Obbele wrote: > On Wed, Mar 30, 2011 at 10:37:47PM +0200, John Obbele wrote: >> I'm having a problem in GHCi when loading modules relying on the >> base-unicode-symbols package. My prompt gives me the following >> message: >> >> >> ghci $ >> Loading package base-unicode-symbols-0.2.1.2 ... linking ... : >> /home/john/.cabal/lib/base-unicode-symbols-0.2.1.2/ghc-7.0.2/HSbase-unicode-symbols-0.2.1.2.o: >> unknown symbol >> `__stginit_basezmunicodezmsymbolszm0zi2zi1zi2_ControlziCategoryziUnicode_' >> ghc: unable to load package `base-unicode-symbols-0.2.1.2' > > > Oki, so I'm answering to myself: the base-unicode-symbols cabal > file introduces a quirk concerning 'base' version which hides the > symbols in Control.Category.Unicode. > >>> base-unicode-symbols.cabal -- line 42-46 > if !flag(old-base) > build-depends: base >= 3.0 && < 4.4 > else > build-depends: base >= 3.0.3.1 && < 4.4 > exposed-modules: Control.Category.Unicode > > I should contact the maintainer about this … ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data constructor synonyms
Remember that constructors are functions, except that you can't pattern match against them. > data MyType = GeneralConstructor [Double] > -- GeneralConstructor :: [Double] -> MyType Note the lower case character, just a plain function: > specialConstructor :: Double -> MyType > specialConstructor a = GeneralConstructor (a:[]) > zero :: MyType > zero = GeneralConstructor [0] The downside is that you can't pattern-match against these functions. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] order of arguments matters
I checked out the GHC documentation on the GADTs extension [1]: "The key point about GADTs is that pattern matching causes type refinement." So in tr2 (Tree Int) (Node _ (t:_)) = Node 1 [t] the 'a' in 'Type a' is refined to 'Type (Tree a)'. But in tr1 (Node _ (t:_)) (Tree Int) = Node 1 [t] you want to "generalise" the type 'Tree a' to 'Type (Tree a)', which is not possible. 1 - http://www.haskell.org/ghc/docs/7.0-latest/html/users_guide/data-type-extensions.html#gadt ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] order of arguments matters
I believe this is caused by type equalities that are introduced by the Type a argument. In tr2 you get something like a ~ Int or a ~ String, allowing the function to type check. In tr1 that equality is never introduced so the type checker thinks a and Int are distinct types. But I'm sure someone else can provide a better (more correct) explanation. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Tagless interpreter, expression problem and zipper
Both your replies where very helpful. I combined both approaches to
get nearer to what I want.
> class Lit α where lit ∷ Integer → α
> class Add α where add ∷ α → α → α
> instance Lit Integer where lit = fromInteger
> instance Add Integer where add = (+)
This time I require TypeSynonymInstances:
> instance Lit String where lit = show
> instance Add String where add x y = "(" ++ x ++ " + " ++ y ++ ")"
Felipe's generalized context type:
> data AddCtx α = Empty
> | AddL α (AddCtx α)
> | AddR α (AddCtx α)
Combination of Oleg's tagless transformer and Felipe's CtxInterpB:
> instance (Add α, Add β) ⇒ Add (AddCtx β → α, β) where
> add (xa, xb) (ya, yb) = ( \c → add (xa (AddL yb c))
>(ya (AddR xb c))
> , add xb yb
> )
The previous instance allows me to construct Strings while having
Integers in the context.
Silly interpreter, version 2.0
> instance Lit (AddCtx Integer → String, Integer) where
> lit n = ( \c → case c of
> AddL 3 _ → "Foo!"
> _ → lit n
> , lit n
> )
Simple term:
> t1 ∷ (Lit α, Add α) ⇒ α
> t1 = lit 2 `add` lit 3
Interpret as a String:
> bar = let (f, x) = t1 ∷ (AddCtx Integer → String, Integer)
> in f Empty
>> "(Foo! + 3)"
This is already an improvement to my current code. But I am not
entirely satisfied. I can pick and choose which structures to use in
my terms but the context type is still an ordinary data type. Each
module which extends the expression language with new structures needs
to define a complicated context type.
My plan is to define the context as a type class. Obviously I can't
perform case analysis on a polymorphic type so I'll have to add that
functionality to each context class in some way.
Thank you for your helpful replies!
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[Haskell-cafe] Tagless interpreter, expression problem and zipper
Hello everyone,
I am stuck rewriting some code in the tagless style. My problem can be
thought of as an interpreter for a very simple language:
> data Exp = Lit Integer
> | Add Exp Exp
> | Mul Exp Exp
>deriving (Show)
But some complexity is added by the fact that my interpreter also
needs to know the context in which literals appear in an
expression. So given the example
> t1 :: Exp
> t1 = (Lit 3 `Add` Lit 4) `Mul` Lit 2
I want to have access to the fact that the literal 3 appears on
the left side of an addition. Therefore I created a type:
> data Ctx = Empty
> | AddL Exp Ctx
> | AddR Exp Ctx
> | MulL Exp Ctx
> | MulR Exp Ctx
>deriving (Show)
This is almost a zipper over the Exp type. I left out a context for
literals themselves because it wasn't necessary. Now I can create a
simple evaluation function:
> eval :: (a -> a -> a)
> -> (a -> a -> a)
> -> (Integer -> Ctx -> a)
> -> Exp
> -> a
> eval add mul lit = go Empty
> where
> go ctx (Lit n) = lit n ctx
> go ctx (Add x y) = let x' = go (AddL y ctx) x
> y' = go (AddR x ctx) y
> in x' `add` y'
> go ctx (Mul x y) = let x' = go (MulL y ctx) x
> y' = go (MulR x ctx) y
> in x' `mul` y'
This function can evaluate an expression to any type 'a', but it needs
some additional functions to accomplish that: add, mul and lit. Notice
how the 'lit' function has access to a literal's context. To interpret
an Exp as an Integer I use:
> evalInt :: Exp -> Integer
> evalInt = eval (+) (*) const
Or as a String:
> evalStr1 :: Exp -> String
> evalStr1 = eval addStr mulStr (const . show)
> addStr x y = "(" ++ x ++ " + " ++ y ++ ")"
> mulStr x y = "(" ++ x ++ " * " ++ y ++ ")"
Or a silly example which uses the context:
> evalStr2 :: Exp -> String
> evalStr2 = eval addStr mulStr lit
> where
> lit _ (AddL (Lit 4) (MulL _ _)) = "Foo!"
> lit n _ = show n
The silly example replaces a literal with "Foo!" if it appears on the
left side of an addition with 4, and the whole addition is the left
side of a multiplication, like in (x + 4) * ?.
All of this works. But I want to be able to add additional
constructors to the Exp language without changing existing code. This
looks like the expression problem.
Ignoring the zipper-like context I came up with the following:
First define the language:
> class Lit a where lit :: Integer -> a
> class Add a where add :: a -> a -> a
> class Mul a where mul :: a -> a -> a
Integer interpreter:
> instance Lit Integer where lit = fromInteger
> instance Add Integer where add = (+)
> instance Mul Integer where mul = (*)
String interpreter, using a newtype so I don't need
TypeSynonymInstances:
> newtype Str = Str {unS :: String}
> instance Show Str where show = show . unS
> instance Lit Str where lit = Str . show
> instance Add Str where add x y = Str $ addStr (unS x) (unS y)
> instance Mul Str where mul x y = Str $ mulStr (unS x) (unS y)
Same example expression, now polymorphic:
> t1 :: (Lit a, Add a, Mul a) => a
> t1 = (lit 3 `add` lit 4) `mul` lit 2
This expression can now be interpreted in multiple ways:
> t1 :: Integer
>> 14
> t1 :: Str
>> "((3 + 4) * 2)"
This solves the expression problem. I can add new structures to my
language in other modules without having to change existing code. The
necessary parts are mentioned in the type constraint (Lit a, Add a,
Mul a).
But I lost the power of the context! How do I get it back?
Attached are the two approaches, WithTags.hs and Tagless.hs (but
without context).
Any help would be greatly appreciated!
module WithTags where
data Exp = Lit Integer
| Add Exp Exp
| Mul Exp Exp
deriving (Show)
data Ctx = Empty
| AddL Exp Ctx
| AddR Exp Ctx
| MulL Exp Ctx
| MulR Exp Ctx
deriving (Show)
eval :: (a -> a -> a)
-> (a -> a -> a)
-> (Integer -> Ctx -> a)
-> Exp
-> a
eval add mul lit = go Empty
where
go ctx (Lit n) = lit n ctx
go ctx (Add x y) = let x' = go (AddL y ctx) x
y' = go (AddR x ctx) y
in x' `add` y'
go ctx (Mul x y) = let x' = go (MulL y ctx) x
y' = go (MulR x ctx) y
in x' `mul` y'
evalInt :: Exp -> Integer
evalInt = eval (+) (*) const
addStr x y = "(" ++ x ++ " + " ++ y ++ ")"
mulStr x y = "(" ++ x ++ " * " ++ y ++ ")"
evalStr1 :: Exp -> String
evalStr1 = eval addStr mulStr (const . show)
evalStr2 :: Exp -> String
evalStr2 = eval addStr mulStr lit
where
lit _ (AddL (Lit 4) (MulL _ _)) = "Foo!"
lit n _ = show n
t1 :: Exp
t1 = (Lit 3 `Add` Lit 4) `Mul` Lit 2
module Tagless where
class Lit a where lit :: Integer -> a
class Add a where add :: a -> a -> a
class Mul a where mul :: a -> a -> a
instance Lit In
Re: [Haskell-cafe] Performance difference between ghc and ghci
In general code compiled with GHC will be a lot faster than code interpreted by GHCI. You can also call compiled code from within GHCI, in which case you would hardly see a performance difference. On 22 February 2011 08:26, C K Kashyap wrote: > Hi, > Is there a runtime performance difference between a haskell program running > under GHCI vs in its compiled form? > Especially for a long running program - as in, ignoring the initial setup > time. > If I understand right, in both case tree reduction is what is happening and > performance should be similar. > Regards, > Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Status update on {code, trac, projects, planet, community}.haskell.org
I believe code.haskell.org has moved to a new machine. Its IP address also changed, which causes your ssh to issue a warning. You can fix it by deleting the code.haskell.org entry from your local ~/.ssh/known_hosts file. On 16 February 2011 18:58, Henning Thielemann wrote: > > Thank you a lot for bringing code.haskell.org back! I missed it a lot! > However, I still get > > $ ssh code.haskell.org > @@@ > @ WARNING: POSSIBLE DNS SPOOFING DETECTED! @ > @@@ > The RSA host key for code.haskell.org has changed, > and the key for the according IP address 178.63.91.44 > is unknown. This could either mean that > DNS SPOOFING is happening or the IP address for the host > and its host key have changed at the same time. > @@@ > @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ > @@@ > IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! > Someone could be eavesdropping on you right now (man-in-the-middle attack)! > It is also possible that the RSA host key has just been changed. > ... > > > How can I verify that it is safe to continue logging in? > Could you restore the old host key? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Byte Histogram
On 7 February 2011 22:00, Andrew Coppin wrote: > I clearly have my languages mixed up. > > The language I'm thinking of required all variables (even top-level ones) to > be declared with "let" - unless the definition is recursive, in which case > you have to say "letrec" (i.e., the compiler it too stupid to deduce this > automatically). Apparently that isn't Clean... You are not necessarily wrong. Clean, like Haskell, is a moving target. To quote the paper "Exchanging Sources Between Clean and Haskell" [1]: The year of 1987 was a founding one for two pure, lazy, and strongly typed functional programming languages. Clean (Brus et al., 1987) was presented to the public for the first time and the first steps towards a common functional language, later named Haskell, were taken (Hudak et al., 2007). Clean was conceived at the Radboud University Nijmegen as a core language that is directly based on the computational model of functional term graph rewriting to generate efficient code. It also serves as an intermediate language for the compilation of other functional languages (Koopman and Nöcker, 1988; Plasmeijer and van Eekelen, 1993). For these reasons, it deliberately used a sparse syntax (van Eekelen et al., 1990): “... at some points one can clearly recognize that [..] Clean is a compromise between a functional programming language and an intermediate language used to produce efficient code. For instance, a minimal amount of syntactic sugar is added in [..] Clean.”. Later, the core language was sugared. The Clean of 1987—1994 sounds a lot like the language you are talking about. 1 - http://www.cs.ru.nl/~thomas/publications/groj10-exchanging-sources-between.pdf ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Byte Histogram
On 5 February 2011 16:21, Andrew Coppin wrote: > I didn't think Clean supported laziness at all? I thought it was a strict > language. "CLEAN is a practical applicable general-purpose lazy pure functional programming language suited for the development of real world applications." [1] Haskell en Clean are very much alike. You can even compile Haskell 98 code with the latest (experimental) Clean compiler and having it interact with Clean code and vice-versa [2]. The main difference is Clean's use of uniqueness typing. 1 - http://clean.cs.ru.nl/download/Clean20/doc/CleanLangRep.2.1.pdf 2 - http://www.cs.ru.nl/~thomas/publications/groj10-exchanging-sources-between.pdf ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] hmatrix's fitModel function crashes ghc(i)
Thank you for your reply. I will follow progress on the ticket. On Mon, Nov 8, 2010 at 3:57 AM, Vivian McPhail wrote: > Here's the ticket: > > http://hackage.haskell.org/trac/ghc/ticket/781 > > They aim to fix the problem (with fPIC) by ghc 7.2. > > Cheers, > > Vivian ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: hmatrix's fitModel function crashes ghc(i)
Cool, this means hmatrix is still an option for my fitting problem. The problem is a bit annoying but I can work with it. My assumption about the cause of the problem (wrong number of arguments) made me miss the real problem. Thanks for the explanation. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] hmatrix's fitModel function crashes ghc(i)
Hello, I would like to use hmatrix to do some function fitting with the Levenberg Marquardt algorithm. As an example I would like to fit the very simple function "f x = a*x + b" on some data points. The problem is that executing the 'fitModel' function crashes GHC(i) with a segmentation fault. This makes debugging difficult. Can anyone spot what I am doing wrong? Given all the lists of Double's it seems very easy to make an error regarding the number of arguments with the model function or the derivative. Try to evaluate the 'test' function in the small program listed below. I would expect an output of [1, 0] (y = 1*x + 0) instead of a segmentation fault. Relevant versions: - hmatrix-0.10.0.0 - gsl-1.14 - ghc-6.12.3 (64 bit) Small program: module Test where -- from base: import Control.Arrow ( second ) import Control.Applicative ( pure ) -- from hmatrix: import Data.Packed.Matrix( Matrix ) import Numeric.GSL.Fitting ( FittingMethod(LevenbergMarquardt), fitModel ) -- input list of (x, y) pairs, output coefficients of "f x = a x * b" fitLinear :: [(Double, Double)] -> ([Double], Matrix Double) fitLinear samples = fitModel 1 1 10 (linearModel, linearDer) (map (second pure) samples) [0, 0] linearModel :: [Double] -> Double -> [Double] linearModel [a, b] x = [a*x + b, 0] linearModel _ x = error "wrong arguments" linearDer :: [Double] -> Double -> [[Double]] linearDer [_, _] x = [[x, 0]] linearDer _ _ = error "wrong arguments" test = fitLinear [(0,0), (1,1), (2,2)] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] commutativity
Yes, that would prevent the shadowing. But now you are ignoring the argument op1. Choosing a name that is more different from 'op' might be helpful. You can even invent your own operator as an argument to your commutative function: commutative (⊕) = \a b -> (a ⊕ b) == (b ⊕ a) On Mon, Nov 1, 2010 at 11:15 AM, Patrick Browne wrote: > Does the following avoid the shadowing? > > infixl 5 `op` > op :: Int -> Int -> Int > x `op` y = (x + y) > commutative op1 = \a b -> (a `op` b) == (b `op` a) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Bulletproof resource management
> I think somebody else already mentioned region-based management, which is > also completely safe AFAIK. Ben Franksen mentioned my brother's regions package [1]. He's about to release a new version with simpler type machinery. The list of packages that make use of the regions package [2] can serve as an example how to use these lightweight monadic regions [3]. Regards, Roel 1 - http://hackage.haskell.org/package/regions 2 - http://bifunctor.homelinux.net/~roel/cgi-bin/hackage-scripts/revdeps/regions#direct 3 - http://okmij.org/ftp/Haskell/regions.html#light-weight ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Make your Darcs repositories hashed?
The darcs installed on code.haskell.org is still version 2.02. It doesn't know about 'optimize --upgrade'. How do I upgrade those repositories? On Sat, Oct 9, 2010 at 2:30 PM, Christopher Done wrote: > Every Darcs repository I've pulled this year has always showed me this > message: > > *** > Fetching a hashed repository would be faster. Perhaps you could persuade > the maintainer to run darcs optimize --upgrade with darcs 2.4.0 or higher? > *** > > Maintainers! Please run darcs optimize --upgrade ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Lambda-case / lambda-if
I really like the lambda-case. There are dozens of places in my code where I could use it. Not so sure about the lambda-if. It is just as easily done using an ordinary function. lambda-case: +1 lambda-if: neutral ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Coding conventions for Haskell?
Here is a list of fonts that support that particular character: http://www.fileformat.info/info/unicode/char/2237/fontsupport.htm I think I'll add a little font overview to my unicode-symbols wiki page. Most Unicode symbols that are useful in Haskell are not terribly obscure and supported by a wide range of fonts. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Coding conventions for Haskell?
I align my imports by hand, but your Emacs scripts look useful. I think I'm going to use them too. Another extremely useful function for aligning is align-regexp. On the subject of coding style, I can work with almost any style as long as it is used somewhat consistently. Personally I try to optimize my code for ease of reading because I spend much more time reading code than writing. Aligning stuff vertically makes it easier to spot differences. On Thu, Sep 30, 2010 at 4:02 PM, Christopher Done wrote: > FWIW, I align all my module imports up, as seen here: > http://github.com/chrisdone/amelie/raw/master/src/Web/Codepad.hs and > here http://github.com/chrisdone/amelie/raw/master/src/Amelie/HTML.hs > etc. > > I use the following Emacs library to do it for me: > http://github.com/chrisdone/haskell-mode-exts/raw/master//haskell-align-imports.el > > I also sort them with this: > http://github.com/chrisdone/haskell-mode-exts/blob/master//haskell-sort-imports.el > but it only works for one-line imports, which I advocate anyway. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haltavista - look for functions by example
Impressive! I didn't think you could implement it so quickly. Now someone needs to add this functionality to Leksah or hack something up for Emacs. Regards, Roel On Sun, Sep 19, 2010 at 8:27 PM, Paul Brauner wrote: > It works: > > brau...@worf:/tmp$ cat test.hs > import Test.QuickCheck > import Test.QuickCheck.Arbitrary > import Control.Monad(forM_) > > intMul :: Integer -> Integer -> Integer > intMul x n | n < 0 = -(intMul x $ abs n) > | n == 0 = 0 > | n > 0 = x + intMul x (n - 1) > > main = do xs <- sample' arbitrary > ys <- sample' arbitrary > zip xs ys `forM_` \(x,y) -> > putStrLn (show x ++ " " ++ show y ++ " " ++ (show $ intMul x y)) > > > brau...@worf:/tmp$ runghc test.hs | haltavista > Prelude (*) > > I will include this functionality in the next version. Thank you for > this nice idea. > > Paul ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haltavista - look for functions by example
In my haste to reply I made an error in my 'newby' multiplication function. Pesky negative numbers... intMul ∷ Integer → Integer → Integer intMul x n | n < 0 = -(intMul x $ abs n) | n == 0 = 0 | n > 0 = x + intMul x (n - 1) I do wonder what happens when haltavista encounters a function that diverges. Like my original intMul applied to a negative number: "intMul 2 (-1)". ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haltavista - look for functions by example
Very interesting! It got me thinking: if you combine this with the Arbitrary class [1] of QuickCheck you can use it check if you have defined a function that is "equal" to an already defined function. Let's say I write the following function: intMul ∷ Integer → Integer → Integer intMul x 0 = 0 intMul x n = x + intMul x (n - 1) No you can automatically apply this function to a list of 100 generated inputs to get a list of input output pairs. Feed this into haltavista and it should tell you that you can replace your definition with Prelude (*). While such an observation is certainly not a proof it is still useful. It would be a nice addition to a Haskell editor. Especially for those new to the language. Regards, Roel 1 - http://hackage.haskell.org/packages/archive/QuickCheck/2.3/doc/html/Test-QuickCheck-Arbitrary.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] feasability of implementing an awk interpreter.
On Mon, Aug 23, 2010 at 8:07 AM, Richard O'Keefe wrote:
> But what _is_ "the core functionality".
> The Single Unix Specification can be browsed on-line.
> There is no part of it labelled "core"; it's all required
> or it isn't AWK. There are weird little gotchas like
> File "foo" = '{ prin'
> File "bar" = 't 2 }'
> awk -f foo -f bar
> is legal and is required to act the same as
> awk '{ print 2 }'
> mawk fails this, and I don't blame it, and I don't really _care_.
> Is that "core"? Who knows?
I say that that behaviour is not part of the language but of the runtime.
> Whatever the "core functionality" might be, YOU will have to define
> what that "core" is. There's no standard, or even common, sublanguage.
One approach to find the core of a language is to find which parts can
be implemented in terms of other parts. If part B can be expressed in
terms of part A then B doesn't belong in the core.
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Re: [Haskell-cafe] Question about memory usage
On Tue, Aug 17, 2010 at 3:53 AM, Richard O'Keefe wrote: > On Aug 17, 2010, at 12:37 AM, Roel van Dijk wrote: >> >> phi = (1 + sqrt 5) / 2 >> fib n = ((phi ** n) - (1 - phi) ** n) / sqrt 5 >> >> The use of (**) should make the complexity at least O(n). Please >> correct me if I'm wrong (or sloppy). > > Using the classic > x**0 = 1 > x**1 = x > x**(2k+0) = (x**2)**k k > 0 > x**(2k+1) = (x**2)**k + x k > 1 > powers of smallish numbers or matrices can be computed in logarithmic > time. That is an interesting trick. So there exists an algorithm that calculates Fibonacci numbers in O(log n) time. > Using x**n = exp(n*log(x)) and floating point arithmetic, > the whole thing can be done in O(1) time, and the price of > some inaccuracy. It will calculate a subset of the Fibonacci numbers in O(1) time. Thinking about it I think you can easily calculate subsets of any function in O(1) time, as long as the function is guaranteed to terminate. Simply precompute the answers and store them in an array. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Question about memory usage
On Sat, Aug 14, 2010 at 5:41 PM, Andrew Coppin wrote: > (Then again, the Fibonacci numbers can be computed > in O(1) time, and nobody ever needs Fibonacci numbers in the first place, so > this is obviously example code.) A bit off-topic, but I don't think there exists a function that computes fibonacci numbers in O(1) time. There exists a closed-form expression to calculate the nth Fibonacci number, but the complexity of that expression is not O(1): phi = (1 + sqrt 5) / 2 fib n = ((phi ** n) - (1 - phi) ** n) / sqrt 5 The use of (**) should make the complexity at least O(n). Please correct me if I'm wrong (or sloppy). Regards, Roel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] expression problem
Have you read Wouter Swierstra's "Data Types A La Carte" [1]? Whether it uses basic and easy parts of Haskell depends on your mindset. You need to wrap your head around the fixpoint. It requires at least the MultiParamTypeClasses language extension. Regards, Roel 1 - http://www.cs.nott.ac.uk/~wss/Publications/DataTypesALaCarte.pdf On Mon, Aug 16, 2010 at 12:17 PM, Patrick Browne wrote: > Hi, > The expression problem [1] can be described as the ability to add new > variants (either constructors or methods) to a data type without > changing the existing code. The Haskell and OO language issues are well > described at [1] > It seems that the expression problem does not exist in Maude[2]. > > My question is: > Using basic and easy parts of the Haskell, does Haskell currently handle > the expression problem. In other words I would like to avoid demanding > and sophisticated coding techniques or non-standard Haskell extensions > (i.e. it should be easy for the average programmer to use). > If there is a simple solution could you please point me to an example. > > Thanks, > Pat > > > > [1] Dr. Ralf Laemmel > http://channel9.msdn.com/shows/Going+Deep/C9-Lectures-Dr-Ralf-Laemmel-Advanced-Functional-Programming-The-Expression-Problem/ > [2]http://lists.cs.uiuc.edu/pipermail/maude-help/2010-January/000336.html > > > This message has been scanned for content and viruses by the DIT Information > Services E-Mail Scanning Service, and is believed to be clean. > http://www.dit.ie > ___ > 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] xemacs newbie question - haskell mode
Note the following line from the haskell-mode project page: "If it works on XEmacs, consider yourself lucky." [1] Regards, Roel 1 - http://projects.haskell.org/haskellmode-emacs/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Недвижимость во Ф ранции, аренда и продажа вилл
Google translation: > The office of our company is located in Nice - the heart of the > Riviera, that gives us an immediate opportunity to offer villas > for rent and sale in all their diversity, as well as guidance to > our clients on the most interesting and important events in the > rich cultural and social life Cote d'Azur. We offer our customers > a wide choice of luxury villas on the entire length of the Côte > d'Azur of France - from St Tropez to Monaco, visa support and > arrange visits to your vending facility at the conclusion of > contracts for lease or purchase of houses and other real estate > Mediterranean coast. Dear partners, we offer you our cooperation > in the acquisition of your clients property in France, Cote > d'Azur, which has always valued art lovers, connoisseurs of > history, lovers of fine cuisine and beautiful scenery. So spam for luxury villa's? I guess Haskell really failed in avoiding success... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wait forever in main thread
Use our threads package [1]. import Control.Concurrent.Thread ( forkIO, wait_ ) myDBusThingie :: IO () myDBusThingie = error "TODO" main :: IO () main = do tid <- forkIO myDBusThingie wait_ tid But like David said, this is only usefull if you plan on multiple concurrent waits or doing some other work during the wait. Otherwise you can simply replace the contents of main with myDBusThingie. Regards, Roel 1 - http://hackage.haskell.org/package/threads (new, backwards compatible, version will be released soon) On Mon, May 17, 2010 at 7:04 PM, DPX-Infinity wrote: > Hi, > I'm writing a program which listens to some D-Bus signals using > DBus.Client.onSignal function from dbus-client package. This function > runs IO action in separate haskell thread when signal is received. My > program does nothing except signal handling, so after setting up > signals it has to wait indefinitely. Now I'm using not very clean (I > think so) forever $ threadDelay 1000 . Is there another (I mean, > correct) method to do this thing? > ___ > 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] ANN: precis-0.3.1 - Cabal package diff tool
On Thu, May 13, 2010 at 5:23 PM, Stephen Tetley wrote: > Hi Bas > > I'm not entirely surprised... > > Do you know if haskell-src-exts can parse files with Unicode syntax > (and I'm not using enough extensions)? > > Thanks > > Stephen Last time I checked it had problems with the ∷ and ∀ characters. I reported it to Neil Mitchell (it showed up in hlint) who in turn reported it to Niklas Broberg. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Shorthand method of enumerating a list a gotcha ... or is it just me?
>From the Haskell 98 report (section 6.3.4): > For Float and Double, the semantics of the enumFrom family is given by the > rules for Int above, except that the list terminates when the elements become > greater than e3+i/2 for positive increment i, or > when they become less > than e3+i/2 for negative i. So yes, it is surprising, but according to the specification. But then again the very concept of a type like Float having an Enum instance is a bit weird. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] nun.haskell.org http services down?
I think it would be nice in general to be able to mirror at least hackage.haskell.org. Something like rsync would be close to ideal for this purpose. Reasons I would like to mirror hackage: 1 - Provide alternative when the main hackage is down 2 - Access to the sources of all uploaded packages for analysis purposes ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Learning about Programming Languages (specifically Haskell)
Here is my attempt. I tried to avoid higher concepts like folds and
things like the ($) operator. Most recursions are written explicitly.
{ BEGIN CODE }
module Main where
-- Data type representing a door which is either Open or Closed.
data Door = Open | Closed deriving Show
toggle :: Door -> Door
toggle Open = Closed
toggle Closed = Open
-- Applies the function f to every n'th element of a list.
skipMap :: (a -> a) -> Int -> [a] -> [a]
skipMap f n | n < 1 = error "skipMap: step < 1"
| otherwise = go (n - 1)
where
-- Apply the function 'f' to an element of the list when the
-- counter reaches 0, otherwise leave the element untouched.
go _ [] = []
go 0 (x:xs) = f x : go (n - 1) xs
go c (x:xs) = x : go (c - 1) xs
-- Calculate the final answer.
run :: Int -> [Door]
run n = go 1 initialDoors -- Start by toggling every door.
where
-- Initial list of closed doors
initialDoors :: [Door]
initialDoors = replicate n Closed
-- Toggle every c doors, then proceed by toggling every c+1 doors
-- of the result, etcetera... Stops after toggling the n'th door.
go :: Int -> [Door] -> [Door]
go c doors
| c > n = doors
| otherwise = go (c + 1) (skipMap toggle c doors)
-- Print information about a single door.
printDoor :: (Int, Door) -> IO ()
printDoor (n, door) = putStrLn ("Door #" ++ show n ++ " is " ++ show door)
printRun :: Int -> IO ()
printRun n = mapM_ printDoor (zip [1..n] (run n))
-- The program entry point.
main :: IO ()
main = printRun 100
{ END CODE }
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Re: [Haskell-cafe] Strict type system allows for a maximum number of programming errors to be caught at compile time.
In my opinion code is 'right' when it conforms to the specification. Haskell's type system allows the programmer to express a part of the specification in the types, which then get checked by the compiler/type-checker. This is where I see the biggest benefit of a very expressive statically checked type system. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Threads freezing
The problem could be in your use of forkIO. To quote the documentation of forkOS [1]: >Like forkIO, this sparks off a new thread to run the IO computation passed as >the first argument, and returns the ThreadId of the newly created thread. >However, forkOS creates a bound thread, which is necessary if you need to call >foreign (non-Haskell) libraries that make use of thread-local state, such as >OpenGL (see Control.Concurrent). So you have to make sure that all calls to OpenGL originate from a bound thread and furthermore that all calls to OpenGL originate from _the same_ thread. Regards, Roel 1 - http://hackage.haskell.org/packages/archive/base/4.2.0.1/doc/html/Control-Concurrent.html#v%3AforkOS ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] a way to convert partial functions to functions with Maybe's
On Wed, Apr 14, 2010 at 2:32 AM, Ivan Miljenovic wrote: > Why not use Maybe for func1 in the first place? Or are you wanting to > automagically make all uses of head, tail, etc. safe? In which case there is already the 'safe' package: http://hackage.haskell.org/package/safe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is the consensus about -fwarn-unused-do-bind ?
Can anyone provide an example of an error that is prevented by this warning? When exactly is it dangerous to ignore a monadic function's return value? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Hackage accounts and real names
On Tue, Apr 6, 2010 at 1:08 PM, Serguey Zefirov wrote: > http://lambda-the-ultimate.org is one lovely community that has that > restriction: http://lambda-the-ultimate.org/policies#Policies LtU has no restriction on user names. From LtU's policy: > Anonymity and the use of pseudonyms is discouraged. I'm against *requiring* the use of a "real name" for hackage accounts. I have no problems with encouraging the use of given/everyday names. Regards, Roel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Are there any gay haskelleres?
Programming in Haskell certainly makes me feel gay. define gay cheery: bright and pleasant; promoting a feeling of cheer; "a cheery hello"; "a gay sunny room"; "a sunny smile" ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Timeouts that don't cause data growth.
I tried a few things. First I added another timeout to main, so the
program kills itself after a few seconds.
doit :: IO (Maybe ())
doit = timeout 1200 $ {- yield >> -} return ()
main :: IO ()
main = do _ <- timeout 500 $ forever doit
return ()
This program failed to terminate. But when I compiled -with threaded
and added a yield to doit, it worked (kinda). If the timeout in doit
is not too long, like 200 milliseconds, the program has constant space
usage. But when I increased the timeout in doit to 12 seconds I got a
stack overflow.
I'll investigate further when I have more time.
Regards,
Roel
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Re: [Haskell-cafe] developing against privately patched libraries, and cabal
The documentation for Data.Version might be insightful:
http://haskell.org/ghc/docs/latest/html/libraries/base-4.2.0.0/Data-Version.html
If Cabal uses the parseVersion function to parse versions then the
following version is valid: "1.2.3-a-b-c". If should result in this
value:
Version {versionBranch = [1,2,3], versionTags = ["a", "b", "c"]}
But I don't know if Cabal allows you to depend on such a version.
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Re: [Haskell-cafe] Re: Has "Try Haskell! An interactive tutorial in your browser" been announced yet?
I think these reddit posts are relevant: First announcement: http://www.reddit.com/r/haskell/comments/b58rk/try_haskell/ Second announcement: http://www.reddit.com/r/haskell/comments/b7dil/try_haskell_now_with_t_and_wip_interactive/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Testing and module export lists
What I usually do in such a case is create a separate internal module. The internal module exports everything. Then create a module which defines the public interface. This module simple reexports symbols from the internal module. Now you can create a Test module which has full access to all internal symbols. module Internal where a = 1 b = 2 secret = 42 module Public ( a, b ) where import Internal ( a, b ) module Test where import Internal ( secret ) test = assert $ isUltimateAnswer secret On Wed, Feb 24, 2010 at 10:17 AM, Magnus Therning wrote: > How do people who like unit testing / property testing deal with export lists? > > I often find that I do want an export list to reduce clutter in the > finished code, but for testing I'd like to expose everything in a > module. Is there a nice way to deal with this (using the C > pre-processor would not qualify as "nice" ;-)? > Maybe there's a switch that causes GHC to simply ignore the export > list of a module and export everything? > > /M ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: concurrent-extra-0.2
Hello, We would like to announce an update of concurrent-extra [1]. Bug fixes: - A bug in RLock.acquire (thanks to Felipe Lessa). New features: - Broadcast: Wake multiple threads by broadcasting a value. This is a generalisation of Event. - Thread: Threads extended with the ability to wait for their termination. - delay: Arbitrarily long thread delays. - timeout: Wait arbitrarily long for an IO computation to finish. The lightweight thread wrapper was inspired by the threadmanager package [2]. The main advantage of our implementation is that we don't maintain an internal mapping from ThreadId to ThreadStatus. Instead we rely on the forked thread to broadcast its status to interested listeners. This should result in better performance (no lookup required). Every exported symbol is now documented. Regards, Roel & Bas van Dijk [1] http://hackage.haskell.org/package/concurrent-extra-0.2 [2] http://hackage.haskell.org/package/threadmanager-0.1.3 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: concurrent-extra-0.1
On Wed, Feb 17, 2010 at 3:27 PM, Felipe Lessa wrote: > In acquire (l. 111), if the lock was already acquired it goes by > > | otherwise → do putMVar mv mb > Lock.acquire lock > > So it puts back the information about the owner of the RLock and > waits for its release in the normal Lock. And then... nothing? > Shouldn't it need to put into mv information about itself? Well spotted! In order to fix this we changed the structure of an RLock a bit. The inner lock isn't contained in a Maybe anymore but directly in the MVar. So now there is only 1 Lock associated with an RLock. This makes reasoning about the control flow a bit simpler. We also added a test case which fails on the original code but succeeds with the new version. > In release (l. 142) Nothing is put into mv > > then do Lock.release lock > putMVar mv Nothing I'm not sure if that was a bug in the original. In the new version we put the lock back inside the MVar. Current version: http://hackage.haskell.org/package/concurrent-extra-0.1.0.1 Thanks, Roel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: concurrent-extra-0.1
Hello, We would like to announce the release of concurrent-extra [1]. A library which offers a few extra synchronization primitives. These primitives are found in the standard libraries of languages like Java and Python, but not in Haskell. Quick overview: * Lock: Enforce exclusive access to a resource. Also known as a mutex or a binary semaphore. * RLock: A lock which can be acquired multiple times by the same thread. Also known as a reentrant mutex. * Event: Wake multiple threads by signaling an event. Includes both pessimistic and optimistic versions. * ReadWriteLock: Multiple-reader, single-writer locks. Used to protect shared resources which may be concurrently read, but only sequentially written. * ReadWriteVar: Concurrent read, sequential write variables. Plug & Play: cabal install concurrent-extra Darcs: darcs get http://code.haskell.org/~roelvandijk/code/concurrent-extra/ Thanks to Neil Brown and Simon Marlow for an initial review. Comments are still more than welcome! Regards, Roel & Bas van Dijk [1] http://hackage.haskell.org/package/concurrent-extra ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] RFC: concurrent-extra
2010/2/17 Neil Brown : > You don't need to do use ThreadId: MVar has an Eq instance, so you could > make your Lock type derive an Eq instance, and then you can just compare the > Locks to remove it after the timeout occurs (e.g. using delete to take it > out of the list; it should be quite near the head of the list anyway). In > fact, you may as well make most of your types derive an Eq instance where > possible, as this can be useful sometimes. Now I am wondering why I didn't think of that before. It's an elegant solution. Thanks! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: RFC: concurrent-extra
2010/2/16 Simon Marlow : > You might want to take a look at the concurrency part of the GHC test suite: > > http://darcs.haskell.org/testsuite/tests/ghc-regress/concurrent/should_run/ > > Not that we've really solved the problem you're talking about, but you might > get some ideas. The method of testing appears to be similar to what I do now using unit tests. But the contents of the tests are interesting. I'll see if they are applicable to our primitives. Thanks, Roel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] RFC: concurrent-extra
2010/2/16 Neil Brown : > I had a look at the code for Event (both versions) and Lock (but not the > others just yet) and it seemed fine. If you do lots of calls to waitTimeout > before a set you will accumulate old locks in the list, but that won't cause > any error that I can see, so it would only be a problem in pathological > cases. I think I can fix the garbage locks on waitTimeout by tupling each lock with the ThreadId of the thread that created it. When a timeout occurs I can then simply remove the unnecessary lock from the list. The extra overhead would be the construction of a tuple and acquiring a ThreadId each time you wait for an event. > I'm not sure there is a good way to test MVar algorithms. One way to do it > (which the Concurrent Haskell Debugger did online, IIRC: > http://www.informatik.uni-kiel.de/~fhu/chd/) is to reimplement IO to explore > different interleavings of the various MVar calls to look for deadlocks. If > you're testing STM, generally you can look to capture invariants of your > transactions and check that they hold after each transaction (e.g. that if > the state is Set, there shouldn't be any locks waiting with an event). Interesting. It reminds me of Wouter Swierstra's recent paper "Beauty in the Beast": http://www.cs.nott.ac.uk/~txa/publ/beast.pdf Thanks, Roel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] RFC: concurrent-extra
Hello, We wrote a small library (1) which offers a few extra synchronization primitives. These primitives are found in the standard libraries of languages like Java and Python, but not in Haskell. Before releasing concurrent-extra on hackage, we would like some comments on its name, design, implementation, documentation (2) and general usefulness. All primitives are implemented with MVars and IORefs, except for Control.Concurrent.STM.Event. There is a small test suite which tests some properties: cabal configure -ftest cabal build cabal test The test suite still needs to be expanded a great deal. We found that testing concurrent algorithms is really hard. Now we test things like "this shouldn't deadlock" by checking if it doesn't take too long. But that doesn't feel very formal. Is there a more principled approach to testing concurrent algorithms in Haskell? After writing our version of a read-write lock we noticed the package rwlock (3) on hackage. But there is a difference: rwlock is implemented with STM while our version is implemented entirely with MVars. Regards, Roel & Bas van Dijk 1 - http://code.haskell.org/~roelvandijk/code/concurrent-extra/ 2 - http://code.haskell.org/~roelvandijk/code/concurrent-extra/doc/html/concurrent-extra/index.html 3 - http://hackage.haskell.org/package/rwlock ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: ftdi-0.1
Hello, I just released a very early version of my 'ftdi' library [1]. It is a small layer on top of the usb package [2] that enables you to communicate with FTDI [3] devices. Its design is based on the C-library libftdi [4], but it implemented completely in Haskell. Most functionality is untested. I only have access to an FT2232C chip, so testing other chips is not possible at the moment. Furthermore, the only thing I do with that chip is perform bulk reads and the occasional small (1 byte) bulk write. The good news is that it is quite good a bulk reads. It outperformed both libftdi-0.16 and the official driver [5] by about 40% for my use case. Although to be fair, both C libraries used the old libusb-0.1 library. This library is ultimately linked with libusb-1.0.* which is a complete rewrite. To play with the library either cabal install ftdi or darcs get http://code.haskell.org/~roelvandijk/code/ftdi Regards, Roel van Dijk 1 - http://hackage.haskell.org/package/ftdi 2 - http://ftdichip.com/ 3 - http://hackage.haskell.org/package/usb 4 - http://www.intra2net.com/en/developer/libftdi/ 5 - http://www.ftdichip.com/Drivers/D2XX.htm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haddock - 'could not find link destination"
On Thu, Jan 21, 2010 at 3:06 PM, Daniel Fischer wrote: > But I find it easier to let Cabal deal with haddock, make a Cabal package, > > runghc ./Setup.hs configure --user --prefix=$HOME > runghc ./Setup.hs haddock --hyperlink-source If you use a Cabal package in conjunction with cabal-install it saves you even more typing: cabal configure cabal haddock --hyperlink-source ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Conditional code for Haddock
On Wed, Jan 20, 2010 at 12:57 PM, Sean Leather wrote: > I did some conditional Haddocking in EMGM. See, for example: > http://hackage.haskell.org/packages/archive/emgm/0.3.1/doc/html/src/Generics-EMGM-Data-Bool.html At first I didn't see what you did differently. Until I checked your Setup.lhs. It does exactly what I want! Plus a few other things which I am going to borrow (runtests hook, nolib flag and hpc program coverage). Thank you. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Conditional code for Haddock
> Doesn't haddock define __HADDOCK__ by itself? That appears to be a common misconception. The discussion on this ticket [1] indicates that haddock does *not* define __HADDOCK__. So I can not rely on it being defined. Therefore I would like to define it myself, but only in the case that haddock is being run on my code. 1 - http://trac.haskell.org/haddock/ticket/76 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Conditional code for Haddock
I want to generate documentation for the following code snippet: > import qualified Data.ByteString as BS ( ByteString, length ) > > -- | Foo 'BS.empty' equals 0 > foo ∷ BS.ByteString → Int > foo = BS.length Because I do not explicitly import BS.empty haddock will not generate a nice link. I can fix it by adding: > import qualified Data.ByteString as BS ( empty ) But now the compiler rightly warns me: > Warning: Imported from `Data.ByteString' but not used: `BS.empty' There is a ticket related to this problem [1], but I do not think making haddock 'magically' find BS.empty is the right answer. What I would like to do is: > #ifdef __DOC__ > import qualified Data.ByteString as BS ( empty ) > #endif Because I use additional symbols in my comments it feels natural to also have special imports for them. I know that cabal used to define the __HADDOCK__ macro. Is it possible to manually define a preprocessor macro when haddock is run? Perhaps an equivalent to ghc-options: haddock-options? Ideally I want only have to add the following to my .cabal file: > haddock-options: -D__DOC__ Regards, Roel van Dijk 1 - http://trac.haskell.org/haddock/ticket/78 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: AlternativePrelude extension
On Sun, Jan 17, 2010 at 12:27 PM, Ketil Malde wrote: > I think there might be justification for doing it multiple places. The > cabal file tells you what is required to build the package, the pragmas > what is required to build each source file. > > Perhaps cabal should complain when source files use pragmas not > declared in the cabal file, and perhaps also warn about options in the > cabal file not used in any source file. The "extensions" field in a cabal package description is a bit tricky. The documentation states "A list of Haskell extensions used by every module". This might give the impression that it documents the various extensions used in a package. What it actually does is enable those extensions for every module. Duncan's comments on this ticket are enlightening: http://hackage.haskell.org/trac/hackage/ticket/370 I think the idea of adding a new field "used-extensions" warrants a separate ticket. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hackage strangeness
> It's in the process of moving to a new (and hopefully more reliable) host. That is good news. Nice work! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Hackage strangeness
I wrote a small cronjob to update my hackage reverse-deps. When checking if it worked I noticed that my hackage appears to be more up-to-date than the real thing! Compare the "What's new" of both: Real hackage: http://hackage.haskell.org/packages/archive/recent.html Play thing: http://bifunctor.homelinux.net/~roel/hackage/packages/archive/recent.html At the time of writing this message the newest package on Hackage is dated Tue Jan 12 16:24:18 UTC 2010. The newest on my mirror is Thu Jan 14 20:07:04 UTC 2010. I thought that possibly the recent.html page wasn't being built, but when I follow an actual package, like vacuum-opengl the most recent version on hackage is 0.0.2 while on my mirror it is 0.0.3. Is this a case of data loss or something else? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Language simplicity
On Thu, Jan 14, 2010 at 12:47 PM, Colin Paul Adams wrote: >>>>>> "Roel" == Roel van Dijk writes: > > Roel> I think it is time for an Obfuscated Haskell Contest :-) > > Are you allowed to use obsolete scripts for your identifiers? :-) Sure, I'll consider bonus points if you write your program entirely in cuneiform. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Language simplicity
> Thus speaketh the report (http://haskell.org/onlinereport/lexemes.html): > > symbol -> ascSymbol | uniSymbol > ascSymbol -> ! | # | $ | % | & | * | + | . | / | < | = | > | ? | @ > | \ | ^ | | | - | ~ > uniSymbol -> any Unicode symbol or punctuation > > Punctuation characters are legitimate for operators. Aha, didn't know that (or forgot it). Also kind of obvious when you consider that '.' and ':' are punctuation characters. I think it is time for an Obfuscated Haskell Contest :-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Language simplicity
2010/1/14 Evan Laforge :
> Wow, that's kind of cute:
>
> {-# LANGUAGE UnicodeSyntax #-}
> (＊) = (*)
> (／) = (/)
> 公式 高 中 低 = 高 ＊ 中 ＊ 低 ／ 整數
> 整數 = 123
That code snippet is also perfectly legal Haskell without the
UnicodeSyntax language extension. You use UnicodeSyntax if you want to
write code like this:
{-# LANGUAGE UnicodeSyntax, ScopedTypeVariables #-}
swap ∷ ∀ α β. (α, β) → (β, α)
swap = uncurry $ flip (,)
> Oddly, if I change the order of these definitions I get syntax
> errors. Very mysterious. Nice how it knows that ＊ is a symbol,
> but I'm not sure how I'm supposed to name a type.
I was a bit surprised that you could use ＊ as an operator since it is
a punctuation character. Maybe there are some corner cases with
fullwidth characters or with composition of characters.
> Unicode identifiers are fun but this is a good point. The line has
> to be somewhere, so it might as well be in the historical position
> unless there are widely agreed on benefits to moving it.
I have already crossed that line:
http://hackage.haskell.org/package/base-unicode-symbols
http://hackage.haskell.org/package/containers-unicode-symbols
But I am aware that there is a point beyond which unicode symbols only
make your code harder to understand. So I try to be conservative in my
use of them. Still, there are a lot of useful and acceptable symbols
which are not part of the historic ASCII set: ∈, ≤, ∪, ∧, ¬, ∘ to name
a few.
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Re: [Haskell-cafe] Hackage down
I have downloaded the torrent with the hackage archive from 19 oktober 2009 and put it on my server. This means you can now download all the packages contained in that archive (only the latest versions at that date). Happy hacking, Roel On Wed, Jan 6, 2010 at 11:57 AM, Roel van Dijk wrote: > If you are desperate for some hackage you can at least browse packages > on my reverse dependencies thingie: > > http://bifunctor.homelinux.net/~roel/hackage/packages/hackage.html > > The last update was the 4th of january. But it doesn't have the actual > packages, so it is probably not so useful in this case. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hackage down
If you are desperate for some hackage you can at least browse packages on my reverse dependencies thingie: http://bifunctor.homelinux.net/~roel/hackage/packages/hackage.html The last update was the 4th of january. But it doesn't have the actual packages, so it is probably not so useful in this case. On Wed, Jan 6, 2010 at 11:50 AM, Daniel Fischer wrote: > Just a heads up, hackage is down, doesn't respond to ping even, cabal update > says > > cabal: : resource vanished ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Mysterious factorial
I can't offer much insight but could the answer lie in the Integer type? I suspect that with a sufficiently large fixed Int type (2^14 bits?) the performance of the two functions would be almost equal. Could it be that the second function delays the multiplication of large numbers as long as possible? The divide-and-conquer approach? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: unicode-symbols-0.1.1
2009/12/10 Richard O'Keefe : > On Dec 10, 2009, at 2:58 AM, Roel van Dijk wrote: >> I tried to be conservative with the choice of unicode symbols. I have >> defined the division sign (÷) to be (/). But it could just as well be >> defined as 'div'. > > No it couldn't. One expects 3÷2 to be 1½, not 1. > You will, for example, find this text on the web: > "Mathematically, the division sign is equivalent to the forward slash. > Thus, for example, 4 ÷ 5 = 4/5 = 0.8" > This is actually historically backwards. When I was a nipper, > 1/6 meant "one and six" or "eighteen pence" or at least three > loaves of good bread. As far as I'm aware, the use of "/" > instead of "÷" is a computerism introduced in the days of 6 bit > character sets. Ok, this makes me happy I choose (/) instead of 'div'. >> Another choice that could lead to some discussion is the definition of >> (⊂) to be 'Data.Set.isProperSubsetOf' and (⊆) to be >> 'Data.Set.isSubsetOf'. An alternative choice would be to have (⊊) for >> 'isProperSubsetOf' and (⊂) for 'isSubsetOf'. > > Mathematicians may use the plain horseshoe for either subset or > proper subset, depending on the author. But I've never ever seen > anyone use the horseshoe with an equals bar for proper subset; > that would really make no sense. As James Hall pointed out there is actually a tiny slash trough the equal bar underneath the horseshoe. The fact that this is hard to see is another reason why I choose the first option. > I suggest that you take the Z formal specification language as your > guide (plain horseshoe is proper subset, horseshoe with equal bar is > subset-or-equal). If you don't like Z, try B: same thing. Yes, this is how I have defined things in the current version. Thank you for your comments, Roel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: usb-0.3
On Wed, Dec 9, 2009 at 4:20 PM, stefan kersten wrote: > looks great, thanks! do you happen to have some example code for working with > HID devices (mice, keyboards, etc.)? The usb package does not support the various device classes directly. You won't find a function like "isKeyPressed ∷ Device → KeyCode → IO Bool". But you could write it based solely on functions from the usb package. Enumerate the devices connected to your system, find your HID device, open a handle (or enter a safe region), choose an interface and an alternative and finally send some sort of control request encoded in a ByteString. The actual bytes you need to send in order to discover if some key on your USB keyboard is pressed is defined somewhere in the USB HID device class specification. If you really need that kind of functionality then you could create a package "usb-hid" that offers an abstraction over the HID device class. But if you just want to know if some key is pressed then a much simpler solution would be to use a library like SDL or GLUT. Keep in mind that all functions in the usb package run in *client side*. To actually use a device (communication) you need the proper permissions, which in practice implies super-user privileges. Libraries like SDL interface with the kernel drivers and do not need such permissions (correct me if I'm wrong). Regards, Roel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANNOUNCE: unicode-symbols-0.1.1
Hello, I would like the announce the release of my package unicode-symbols: http://hackage.haskell.org/package/unicode-symbols It offers alternative symbols for a number of common functions and operators from the base and containers packages. When used in combination with the language extension UnicodeSyntax you can write really nice code. The only thing missing is a nice λ symbol. The documentation on hackage should be pretty self explanatory. For each symbol the documentation gives its exact definition. The source code however, probably due to a bug in hscolour, is totally unreadable. To view the sources simply download the package and use a text editor. I tried to be conservative with the choice of unicode symbols. I have defined the division sign (÷) to be (/). But it could just as well be defined as 'div'. I do not know what would be the logical choice. Another choice that could lead to some discussion is the definition of (⊂) to be 'Data.Set.isProperSubsetOf' and (⊆) to be 'Data.Set.isSubsetOf'. An alternative choice would be to have (⊊) for 'isProperSubsetOf' and (⊂) for 'isSubsetOf'. I choose the former because it is more symmetrical with (<) and (≤). This package was inspired by unicode-prelude from Péter Diviánszky: http://hackage.haskell.org/package/unicode-prelude Regards, Roel van Dijk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANNOUNCE: ls-usb-0.1.0.2
Hello everyone, I have released a minor update of my ls-usb program: http://hackage.haskell.org/package/ls-usb This small utility lists USB devices connected to your system. It can also show you the device descriptors, interface descriptors, vendor and product identifiers and various other things. All in wonderful colours of course. The only major change is that it now depends on usb-0.3.* Regards, Roel van Dijk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hayoo and Hoogle (beginner question)
On Mon, Dec 7, 2009 at 10:24 AM, Lyndon Maydwell wrote: > I had heard that Hoogle actually compiled any type-signatures, where > as Hayoo just did a text comparison. > > I'm not actually sure if this is true or not though. > > If it is, it would mean that "[q] -> [r] -> [(q,r)]" would return zip > in Hoogle, but not Hayoo. > > Am I right about this? You are right: http://haskell.org/hoogle/?hoogle=[q]%20-%3E%20[r]%20-%3E%20[%28q%2Cr%29] But Hayoo searches all of hackage while Hoogle also searches a lot, but not all. If I'm searching for a function that is probably in base or containers, I use hoogle. Otherwise I use hayoo. In short: They are both very useful. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
