[Haskell-cafe] Summer of Code idea: Haskell Web Toolkit
Hi, Alejandro Serrano Mena wrote: My idea is to make a client-side Haskell Web Toolkit, in the spirit of Google Web Toolkit, which would allow to program in Haskell the client part of a web application, and would complement the web frameworks already existing for Haskell (such as Yesod and Snap). http://www.haskell.org/haskellwiki/Haskell_web_toolkit - In memoriam ;) Feel free to use these ideas. It would be nice if you could pick it up and complete - I never did... -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] cpphs is missing from new Haskell.org server
Hi, One more thing is missing after migration. The link found on the cpphs package page at Hackage, http://haskell.org/cpphs/ points to non-existing page. Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Rendering of hask in new wiki (MSIE6)
Hi, In MSIE6, hask tags are rendered like this (from the Monad_Transformers page): transformers: provides the classes MonadTrans and MonadIO , as well as concrete monad transformers such as StateT ... etc. The Wiki source: [http://hackage.haskell.org/package/transformers transformers]: provides the classes haskMonadTrans/hask and haskMonadIO/hask, as well as concrete monad transformers such as haskStateT/hask. HTML (a small piece of it): provides the classes div class=inline-codediv dir=ltr style=text-align: left;div class=source-haskell style=font-family: monospace;MonadTrans/div/div/div Words MonadTrans, MonadIO, StateT etc are enclosed in hask tags. They show up in monospace, each starting a new line. Is this only MSIE6, or this is how it is supposed to render? Thanks. PS I am not attaching a screenshot to the mailing list; if anyone needs to see it I'll send via personal e-mail. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Cabal and using a throw-away package database during distro package building
Magnus, You might try Capri which operates Cabal-related stuff privately on a local-to-project package database not touching global or user databases. http://hackage.haskell.org/package/capri http://www.haskell.org/haskellwiki/Capri -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Is it possible to easily connect Haskell to JavaScript/JavaFX in the browser and use a browser as a Windows GUI? :)
Hi, Atze Dijkstra wrote: [skip] but to provide a proper interface to XML/HTML DOM (see http://www.haskell.org/haskellwiki/Haskell_in_web_browser), or a GUI abstraction around it (perhaps a subset of wxHaskell?) will take more work time. I hope this can be done as part of a studentproject, or maybe picked up during a Hackathon. I think a big portion of this task might be done using this package: http://hackage.haskell.org/package/webidl or its newer (not published on Hackage, but recommended) version split into two (you need both): http://code.haskell.org/yc2js/webidl/ -- lexer (FFI based), parser, and a test program.* http://code.haskell.org/yc2js/webidlsyn/-- just AST and pretty-printer I must admit: I haven't touched this project for more than a year, and have little plans to do so: it is up for grabs by anyone interested. But if it can parse something like this: http://es-operating-system.googlecode.com/svn/trunk/include/w3c/html5.idl or http://es-operating-system.googlecode.com/svn/trunk/include/w3c/svg.idl it's likely still intact. Back in those days it could. A WebIDL converter helps derive type signatures for DOM methods and attributes (just like HSFFIG does this for C function prototypes). Have fun ;) and don't hesitate to ask questions. PS I'm glad that the idea lives on. With more GHC flrxibility on backends than it was in 2006-2007, and with faster Javascript engines in browsers, this can get a second life... -- * the whole repo has to be downloaded: darcs get http://code.haskell.org/yc2js/ -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to catch exception within the Get monad (the Binary package)
Hi, Thanks to everybody who replied. I see another solution: are there any hidden problems? I found an interesting package, ChasingBottoms which contains a function testing a value to be bottom and returning a Boolean (of course it cannot be done without unsafePerformIO). I borrowed the idea from that package, and wrote two functions: unThrow :: (Exception e) = a - Either e a unThrow a = unsafePerformIO $ (E.evaluate a = return . Right) `E.catch` (\e - return $ Left e) -- or perhaps the right argument of catch could be just (return . Left)? bm2mb :: a - Maybe a bm2mb a = case unThrow a of Left (e::SomeException) - Nothing Right a - Just a So, if there is a value inside the lazy list which is a bottom (binary parse failure of the last received object in this case, catching any possible exception) then the value can be converted to Nothing within pure code, and then excluded from the result using catMaybes. This solution seems to be working for me. PS Maybe the way I am using the serialized data needs to be changed by implementing some kind of an iterator over the binary stream, and then by taking one object at a time and consuming it right there the problem might be eliminated entirely... Thanks again. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to catch exception within the Get monad (the Binary package)
Henning, On Tue, Sep 7, 2010 at 12:51 PM, Henning Thielemann schlepp...@henning-thielemann.de wrote: This solution looks very ugly to me. Catching 'error's is debugging, but parser failure is kind of exception handling. I guess, the errors you want to catch are caused by non-supported fail method, right? Can't you use a monad transformer like explicit-exception:Synchronous.Exception or transformers:ErrorT around the Binary parser? Alexey already replied, but after looking at the way Binary processes parser errors I came to the same conclusion: it is by design that it falls hard when data cannot be deserialized (btw makes sense in many cases, but not in mine). I am beginning to realize that probably (de)serializing lazy structures is not a good idea at all since such structure may be consumed in pure code, and such parser errors are hidden inside, and may fire at any moment. Any complications to the binary parser will bring performance penalty. Or weird solutions like mine are needed. Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to catch exception within the Get monad (the Binary package)
Hi, The following function* is supposed to decode a list of some serialized objects following each other in a lazy Bytestring: many :: Get a - Get [a] many prs = many' [] where many' a = do s - prs r - isEmpty case r of True - return (reverse a) False - many' (s:a) prs is a parser to decode a single object. If however something goes wrong, and prs fails, the whole function fails (error is thrown). Since [a] (result of decoding) is a lazy list, actual exception may be thrown at any moment the list is being processed, and exception handler may not be properly set. Is there any way to catch/detect failures inside the Get monad? It is not an instance of MonadError, so catchError does not work. Ideally, the function would keep decoding as long as it is possible, and upon the first failure of the parser, return whatever has been decoded. Thanks. --- * there is one intentional inaccuracy in this function: isEmpty is called _after_ decoding is tried, so an empty ByteString would cause parser failure and exception right away; this is used as a test case. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell SVG path parser?
Hi, Does there exist any Haskell package/library to parse the syntax of SVG elements, esp. PATH? That is, the syntax of the d attribute (e. g. M 100 100 L 300 100 L 200 300 z)? Hackage doesn't seem to have any, and Google search yields very broad results. Thanks. PS It should not be hard to write such parser, I just don't want to reivent the wheel ;) -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell SVG path parser?
Henning, Thanks, I'll try to use your code. BTW does it handle the syntax where repeated operation is omitted, per SVG spec 8.3.1? -- The command letter can be eliminated on subsequent commands if the same command is used multiple times in a row (e.g., you can drop the second L in M 100 200 L 200 100 L -100 -200 and use M 100 200 L 200 100 -100 -200 instead). -- see http://www.w3.org/TR/SVG11/paths.html#PathDataGeneralInformation On Mon, May 24, 2010 at 10:43 AM, Henning Thielemann lemm...@henning-thielemann.de wrote: [skip] Once I wrote such a function in order to convert an SVG path to PDF. See parsePath in http://code.haskell.org/~thielema/internetmarke/src/Main.hs -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell SVG path parser?
Tillmann, OK, I see: your code parses the glyph element which contains the same kind of path definition that the path element does. I think your code would be helpful for me as well. And I think I'll use the same xml package to read in the SVG file (I was thinking about this package earlier, and your code has a good example of using it). Thank you. On Mon, May 24, 2010 at 12:20 PM, Tillmann Vogt tillmann.v...@rwth-aachen.de wrote: [skip] more fully. I have spent quite some time on a tricky function commandsToPoints in ReadFont.hs which is about parsing the d field and translating it into outline points. Are you looking for something like that? That is, the syntax of the d attribute (e. g. M 100 100 L 300 100 L 200 300 z)? -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Number of CPUs/cores?
Hi, Does there exist a Haskell library function that returns the number of CPUs/cores (in portable way) on a computer where the program calling it runs? Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Number of CPUs/cores?
OK, makes sense. Thank you. On Tue, Apr 27, 2010 at 10:58 AM, Michael Lesniak mlesn...@uni-kassel.de wrote: [skip] numCapabilities, I think. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC core packages: same core?
Max, Thanks for the explanation. So, the extcore library is expected to match the spec in http://www.haskell.org/ghc/docs/6.10.4/html/ext-core/core.pdf and the core itself can be produced with -fext-core, correct? I think it might be interesting for people working on alternative backends (inlcuding myself). On Tue, Oct 13, 2009 at 4:53 PM, Max Bolingbroke batterseapo...@hotmail.com wrote: [skip] extcore is a library that parses external Core, which is an alternative format intended to be stable and hence a suitable target for consumption by non-GHC tooling. You can have GHC output external core instead of machine code / C. I don't believe this is widely used yet. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Any working example of using genericserialize?
Hi, I am trying to use the genericserialize package (http://hackage.haskell.org/package/genericserialize) but cannot get things working. While buildList (sexpSerialize [1, 2, 3]) yields (1 2 3) as it might be expected, I cannot deserialize it back: *Main (withList sexpDeserialize $ buildList (sexpSerialize [1, 2, 3])) :: Maybe [Integer] Nothing or *Main (withList sexpDeserialize $ buildList (sexpSerialize [1, 2, 3])) :: Maybe [Int] Nothing while I would expect at least one of these cases result in Just [1, 2, 3] What am I missing? Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Any generic serializer to String? was: Any working example of using genericserialize?
Hi, On 9/30/09, Jason Dagit da...@codersbase.com wrote: [skip] Seems like using withList is wrong or the deserializer is simply buggy. It certainly doesn't work the way I would expect SExp reading to work. I also notice from reading the source on hackage that there may not be any tests for this package and it is a 0.1 release. I'd contact the author, as it seems there is a deficiency in the documentation or a bug in the implementation. Thanks Jason for trying this. The genericserialize package is probably not finished yet. What else exists that could be used to serialize in generic way (i. e., anything that is an instance of Data and Typeable) into a string? It does not need to be very efficient as structures to be serialized are not huge (but may be pretty complex), and serialization is a part of an utility not to be used frequently. It only needs to just work. One thing I thought of was to serialize to JSON (there is a generic serializer in one of packages although I did not test it other way) which has higher overhead than S-expressions though. Any other thoughts? Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re[2]: [Haskell-cafe] Any generic serializer to String? was: Any working example of using genericserialize?
Bulat, OK, gread/gshow seem to be like the basis primitives. If they work properly, then it is what is needed. Thanks. On 9/30/09, Bulat Ziganshin bulat.zigans...@gmail.com wrote: Hello Max, Wednesday, September 30, 2009, 5:53:37 PM, you wrote: afaik, SYB just provides gshow/gread functions what serialize any Data instance to String FWIW, writing your own is not hard. I wrote a serializer for GHC using Data in less than 150 (simple) LOC. It produces [Word8], but producing strings instead would be easy. You can check out the code here: http://darcs.haskell.org/ghc/compiler/utils/Serialized.hs Cheers, Max [skip] -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re[2]: [Haskell-cafe] Any generic serializer to String? was: Any working example of using genericserialize?
OK, I got it to work with gread/gshow. However I have noticed this: *Main (gread $ gshow $ FuncExpr 0 [] (EmptyStmt 0)) :: [(Expression Int, String)] [(FuncExpr 0 [] (EmptyStmt 0),)] vs. *Main (gread $ gshow $ FuncExpr () [] (EmptyStmt ())) :: [(Expression (), String)] [] Or even narrower: *Main (gread $ gshow 1)::[(Int, String)] [(1,)] vs. *Main (gread $ gshow ())::[((), String)] [] that is, the unit type does not work well with gread/gshow, likely because inner parentheses are not parsed as a constructor. *Main gshow () (()) Is this a known bug? Thanks. On Wed, Sep 30, 2009 at 10:19 AM, Dimitry Golubovsky golubov...@gmail.com wrote: Bulat, OK, gread/gshow seem to be like the basis primitives. If they work properly, then it is what is needed. Thanks. On 9/30/09, Bulat Ziganshin bulat.zigans...@gmail.com wrote: Hello Max, Wednesday, September 30, 2009, 5:53:37 PM, you wrote: afaik, SYB just provides gshow/gread functions what serialize any Data instance to String -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Externally derive instance of Data?
Hi, Given a datatype defined somewhere in a third-party package, without deriving (Data) specified. Is it possible, in my module which is importing that datatype from that package, to auto-derive instance of Data for the said datatype? The goal is not to recompile the package just because an auto-derived instance is needed. Or no way other than to recompile the package? Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: HSH and IO ()
John, Thanks for the reply. In this case, would the body of my function run in a separate thread via forkProcess (that's what is needed, maybe I didn't make it clear)? In my previous project, I had to do like this (probably not very portable, at least requires System.Posix): (fd1, fd2) - createPipe hscfd - fileToFd hscFile hscpid - forkProcess $ redirFd fd1 0 $ redirFd fd2 (-1) $ redirFd hscfd 1 $ hsffigMain (fromJust $ gccPath dopt) (inclDirs dopt) minusD gccpid - forkProcess $ redirFd fd2 1 $ executeFile (fromJust $ gccPath dopt) False ([-E, -dD] ++ minusI ++ minusD ++ [incFile]) Nothing closeFd hscfd closeFd fd1 closeFd fd2 gccrt - getProcessStatus True False gccpid hscrt - getProcessStatus True False hscpid where hscpid corresponds to a process that runs a Haskell function (hsffigMain :: a - b - c - IO ()) defined within the same program, and gccpid runs an external program (gcc), and they are piped together. I am trying to avoid writing this mess using HSH. I'm just trying to find out whether this was already done. If not, what is the best way to write the above to be integrated into HSH (I'd be glad to contribute). Thank you. On Sat, Jun 13, 2009 at 12:46 AM, John Goerzenjgoer...@complete.org wrote: You can replace it with a function that can take any Channel, and produce a result as a Channel of one particular sort. In particular, this instance: instance ShellCommand (Channel - IO Channel) where -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: HSH and IO ()
John, On Sat, Jun 13, 2009 at 7:01 PM, John Goerzenjgoer...@complete.org wrote: where hscpid corresponds to a process that runs a Haskell function (hsffigMain :: a - b - c - IO ()) defined within the same program, and gccpid runs an external program (gcc), and they are piped together. I am trying to avoid writing this mess using HSH. OK, so I should have read more before starting to reply. But why are you writing to me about HSH if you're trying to *avoid* HSH? I'm confused. Sorry, I should have written by using; Jason made the right correction. I thought that forkProcess-based shell commands existed in HSH thus I could avoid all these low-level manipulations with handles that are usually done in C programming. Integraing hsffigMain into HSH directly will be difficult because it apparently already has its notions about where its input and output come from; the fact that its return type is IO () implies that its output I'll try to write a wrapper for a forked process inside a Channel - IO Channel typed function. Your best bet is to make this a separate executable. That's not what was intended, but now I see the situation more clearly. Thanks for the explanation. If I get any working code, I'll post a link on the list. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] HSH and IO ()
John all, I use HSH in my project where several external programs and Haskell functions need to be piped together: HSH is of great help here. I however came across the situation when one of pipe-connected functions has signature IO (), yet it reads from stdin* and writes to stdout. The documentation mentions instance ShellCommand (Handle - Handle - IO ()) which could be of some help, but in the latest version of HSH on Hackage this instance is commented out. What was the reason of doing that? Is this to be expected in the upcoming versions? Thank you. * I modelled that by calling getContents, but the actual program will call a foreign library that contains a C function that reads from stdin (that is, FILE *), and that cannot be changed easily. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] hsffig and duplicate typedef declarations
Dean, I am not sure how HSFFIG would deal with duplicate typedefs (I'm afraid you get error from gcc when processing hsc2hs output). In case you haven't seen this, I put a repo for HSFFIG here recently: http://code.haskell.org/hsffig/ Before running cabal install run make at the toplevel of the repo first. I have fixed some glitches recently, and adjusted both hsffig and ffipkg to work with contemporary GHC and Cabal (at least 1.6.0.x). I'd be glad to get any feedback on HSFFIG. E-mail me to golubovsky at gmail dot com. Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Few Alex questions
Hi,
Q1: I am trying to create an Alex equivalent of the following flex file:
http://code.haskell.org/yc2js/es-idl/lexer.ll (lexer for Web IDL which
is a dialect of OMG IDL)
I haven't been able to find Alex equivalent for the following line:
PoundSign ^{WhiteSpace}*#
that is any amount of whitespace at the beginning of line followed by '#'
I defined a @WhiteSpace macro some place earlier, but Alex gives me
parser error on the line I created:
@PoundSign = ^...@whitespace*#
in the position 28 that is position of '@', next to caret, that is,
caret is not recognized by Alex.
Can beginning of line (caret) be recognized by Alex?
Q2: The original line says:
MultiLineComment\/\*(([^*])|(\*[^/]))*\*\/
basically same as comments in C or Java.
I had to prefix star and slash even within square brackets with
backslashes to make it compile.
So I got:
@MultiLineComment = \/\*(([^\*])|(\*[^\/]))*\*\/
Is this correct understanding that if we want to match any character
except for an asterisk, then Alex would like to see [^\*] rather than
[^*]? And [^\/] rather than [^/]?
Or would it be better to use a hex code for the asterisk and slash?
Thanks.
--
Dimitry Golubovsky
Anywhere on the Web
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[Haskell-cafe] Haskell/JS -- better through typeclasses?
Jason and everybody interested, Please check out a package I recently (just by coincidence: I haven't seen this topic on the list until after I uploaded it) uploaded to Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/jsmw-0.1 This is a basic monadic interface to Javascript code generator (based on WebBits), providing sort of a macro (like in macro-assembler) facility. HJScript was used as a (sort of) prototype, but I chose slightly different notation for EDSL. From here, I think two directions may be taken: 1. Some techniques are described in the GRIN thesis [1] how to convert a Haskell core to monadic form. These may be explored for this case. 2. Similarly to how the Web Consortium defined interfaces to its components using IDL *, Haskell modules converted to Javascript may expose their interfaces same way, thus providing a basis for a reusable component-based approach. Any discussions and suggestions are welcome. From my own impressions, EDSL approach is better for interactive/AJAX parts of a Javascript application, as translation of non-strict evaluation (like it was done in the Yhc/Javascript project) just causes a lot of code generated, and does not improve the user interaction performance at all. For other (internal) components, translation from Haskell may be more appropriate, just to be able to reuse the existing libraries. One of experiments with Yhc involved a user-exposed form, and a parser to validate user's input. With this hybrid approach, the user interface part might be coded using an EDSL, and the parser could be translated from Haskell core. An IDL might be generated for the parser interface, thus making the parser module a reusable component. These are of course just thoughts and ideas for now. * See the DOM package: this is an auto-generated Haskel approximation of IDL specs provided for the basic DOM components. [1] http://www.cs.chalmers.se/~boquist/phd/index.html [2] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/DOM-2.0.1 -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell/JS -- better through typeclasses?
John wrote: I can't speak for Jason, but for me, this is not very useful. I don't want to write in a Haskell DSL, I want to write in Haskell. And not the whole program, either, just the parts that really lend themselves to functional programming (parsers, numeric computations, code generators, various algorithms). What I presented is of course not a complete solution; this is just a tool to construct Javascript expressions in haskellized type-safe form. What I also mentioned: this monadic form may be an end-point for some other conversion, like GRIN. This answers the question how to translate a true Haskell program (like a parser) into Javascript (or a similar language). There are some experimental compilers with GRIN backends, plus I did my own experiments with GRIN that gave me some ideas. So I would just look at it as a starting point of some new family of tools which hopefully will end up opening possibility to translate Haskell things to Javascript. PS For now I am more concerned with the IDL part of it, but any suggestions on GRIN are welcome. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to get program command line arguments in Unicode-aware way (Unix/Linux)?
Hi, I am trying to process command line arguments that may contain Unicode (cyrillic in this example) characters. The standard GHC's getArgs seems to pass whatever was obtained from the underlying C library without any regard to encoding, e. g the following program (testarg.hs): module Main where import System.Environment main = do x - getArgs mapM (putStrLn . show) x being invoked (ghc 6.10.1) runghc testarg -T 'привет' prints the following: -T \208\191\209\128\208\184\208\178\208\181\209\130 (not correct, all bytes were passed without proper encoding) Is there any way to get program arguments in GHC Unicode-aware? Or at least assuming that they are always in UTF-8? Something like System.IO.UTF8, but for command line arguments? Thanks. PS: BTW runhugs testarg -T 'привет' prints: -T \1087\1088\1080\1074\1077\1090 which is correct. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Automatic instance constraints derivation: how?
Hi, I am trying to understand, why do I need to place constraints with class instance declaration while all the information seems to be already available to the compiler. I have placed the code in question here: http://codepad.org/Akew0p2t so anybody can play with it. The code tries to model evaluation of GRIN-style thunks using Haskell type classes instead of tag-based pattern matching, as in the GRIN papers. That is, a thunk is represented as a datatype like data Ffun a b c = Ffun a b c, and there is some eval function which being applied to such data results in the call fun a b c. Such eval function is a method of class Eval: class Eval a b | a - b where eval :: (Monad m) = a - m b which means that thunks of some type (a) evaluate to values of some dependent type (b). The code is monadic because GRIN is a monad, so the code looks similar to GRIN. The ultimate goal is to make GRIN code understandable by Haskell compiler. Everything is fine with simple types like Int, that is instance Eval Int Int means that Int (and Char, and Bool) do not need in fact evaluation at all. instance Eval Int Int where eval = return Everything is fine with thunks encoding calls to primitives. See instances for FADD and FSUB. All type information for primitives (primPlusInt, primMinusInt) is specified in the code. Then, a function fun is defined that calls the primitives. The main function illustrates its use, and everything works as expected, as output shows. But when I tried to define a thunk for fun (instance for Ffun) I was only able to do that with all constraints on its parameters explicitly set. OTOH, even if I comment out the instance Eval for Ffun, and load the code in Hugs (or GHCi, doesn't matter) then type signature of fun is correctly derived by the compiler. If I try to define instance for Ffun like this: instance (Eval x x) = Eval (Ffun a b c) x where eval (Ffun a b c) = fun a b c meaning only the fact that result of the function fun will be like Int or Bool - evaluates to itself, and we don't care about the types of arguments, I cannot use forall x. with instance declaration, so I have to say something about x. I get the error (Hugs): Error occurred ERROR line 51 - Instance is more general than a dependency allows *** Instance : Eval (Ffun a b c) d *** For class: Eval a b *** Under dependency : a - b So, is there a way to define such an instance for a thunk without any constraints? Wouldn't it be reasonable to expect that eval (Ffun a b c) = fun a b c would allow the compiler to retrieve constraints on a, b, c from those already known for the called function? Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] CouchDB module in Yhc source tree: clarification, and small problems with other packages
Don All, On 8/21/08, Don Stewart [EMAIL PROTECTED] wrote: I think the best result here would be to put a CouchDB binding on hackage. Is anyone in a position to do this? As for myself, honestly, I did not plan to do this at this time as I am busy with other stuff (Yhc Core conversion). I'd be glad to help anyone who is willing to put CouchDB interface on Hackage. I'd like to note though that this may be a bit premature at the moment. CouchDB has been going through significant redevelopment within Apache Incubator (I am not a developer, but just watch silently), and what is available within the Yhc source tree may not work properly with the current CouchDB: it was for 0.7.x while they have 0.8.x in the incubator. So I would wait for graduation of CouchDB from the incubator, or at least checked with its core developers regarding API stability. Besides, the CouchDB interface in question was written only to satisfy the needs of the Yhc Web Service and may be missing some pieces, although it may be good for a starting point. Thank you. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Lines of code metrics
Hi, Greg Fitzgerald wrote: Does anyone know of a good case study comparing a project written in C versus one written in Haskell? I'm mostly looking for a comparison of lines of code, but any other metric, such as time to market and code quality metrics could also be Just curious, has anybody tried to apply Halstead's code metrics (see e. g. http://www.sei.cmu.edu/str/descriptions/halstead_body.html), but there is a 70s' book titled Elements of Software Science to Haskell and other functional languages vs. C and other imperative languages? I myself played with these calculations in late 80s trying to estimate code quality of Pascal programs on PDP-11, but that was a pain to count functions' operands properly as they might come from global variables. Application of these formulas to functional languages might be mich cleaner, so has anybody tried? Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] External query interface to HackageDB?
Hi, Is there any way to query the latest version of a particular package stored on Hackage, that was successfully built? I mean, not _how_ to do that (I have some ideas that I have to download directory listings, looking for failure logs, etc.), but is there any tool or interface already available that does similar things? Unfortunately, tarfiles provided on Hackage (like 00-index.tar.gz) do not help, e. g. BerkeleyDB failed to build in all three versions, yet its all cabal files are included in the tarball: tar tvf 00-index.tar.gz ... -rw-r--r-- www-data/www-data 1055 2007-04-06 13:03 ./BerkeleyDB/0.1/BerkeleyDB.cabal -rw-r--r-- www-data/www-data 1061 2007-04-06 16:59 ./BerkeleyDB/0.2/BerkeleyDB.cabal -rw-rw-r-- www-data/www-data 1236 2008-01-11 14:42 ./BerkeleyDB/0.3/BerkeleyDB.cabal I remember, in the past, HackageDB was expected to become a database of some sort: is there any database-like backend that would accept queries, other than just parsing Apache dir listings? My final goal, given some master-list of package names, to be able to retrieve latest succesfully built (not just uploaded) releases from Hackage Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Parsec, updateState, and failure
Hi, If a parser which updated user state fails, will such update be reverted? Suppose we have two parsers combined with | p = p1 | p2 p1 has the following: p1 = try $ do ... -- getting something from the input stream updateState (\st - ...) -- updated state based on what gotten from the input x - p3 -- p3 should see updated state and return something updateState (\st - ...) -- updated state again (if p3 succeeded) return x If p3 fails, p1 fails too (second updateState will not be reached). But what will p2 (tried next) see in the user state? Will it be state after the first updateState, or will failure of p1 roll the update back? Is there any bracket- or try-catch-finally-like mechanism for Parsec? Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Upd: Parsec, updateState, and failure
Hi, So far, I figured it out like this: updateState ... mbx - (p3 = return . Just) | (return Nothing) updateState ... case mbx of Just x - return x Nothing - pzero but this seems a bit clumsy - is there a more elegant solution? -- Forwarded message -- From: Dimitry Golubovsky [EMAIL PROTECTED] Date: Sat, May 31, 2008 at 10:12 AM Subject: Parsec, updateState, and failure To: haskell haskell-cafe@haskell.org Hi, If a parser which updated user state fails, will such update be reverted? Suppose we have two parsers combined with | p = p1 | p2 p1 has the following: p1 = try $ do ... -- getting something from the input stream updateState (\st - ...) -- updated state based on what gotten from the input x - p3 -- p3 should see updated state and return something updateState (\st - ...) -- updated state again (if p3 succeeded) return x If p3 fails, p1 fails too (second updateState will not be reached). But what will p2 (tried next) see in the user state? Will it be state after the first updateState, or will failure of p1 roll the update back? Is there any bracket- or try-catch-finally-like mechanism for Parsec? Thanks. -- Dimitry Golubovsky Anywhere on the Web -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Experimental compilation of Haskell to Erlang
Hi, Some time ago I became interested in compilation of Haskell programs (via Yhc Core) to Erlang to be able to run Haskell code in Erlang environment. This experiment seems to have been successful, so I'd like to publish its results for everyone to read and criticize. Results of the experiment are described in this Haskell Wiki article: http://www.haskell.org/haskellwiki/Yhc/Erlang/Proof_of_concept Any feedback is appreciated. Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell in Web Browser: draft tutorial
Hi, I have written a draft of the tutorial on Haskell programming for client side of Web applications (related to Yhc/Javascript backend): http://www.haskell.org/haskellwiki/Haskell_in_web_browser Any feedback, suggestions, and additions (like your own code examples) are welcome. Thanks. PS This part of the Tutorial does not cover XMLHTTP programming; this is yet to be written, but there is Haddock documentation under http://www.golubovsky.org:5984/_utils/yhcws/index.html Yhc web service online (where you may experiment with your code): http://www.golubovsky.org:5984/static/yhcws/MainGUI.html Users guide: http://www.haskell.org/haskellwiki/Yhc_web_service -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Hello World in Haskell for web browser
Hi, I have noticed that some people tried to compile a traditional Haskell program using IO monad to show Hello World using Yhc Web Service. Thanks for your interest, and here are some clues. The programming paradigm chosen for Haskell Web programming is not based on monads. It is based on CPS-style calls to DOM functions by Haskell code compiled to Javascript. Further on, additional layers may stack up (such as Haskell Web Toolkit) to provide more convenient APIs, but DOM is the basis. So here is an example of Hello World program written this way: -- begin pasteable code -- module HelloWorldDOM where import CPS import UnsafeJS import CDOM.Level2.DomUtils import DOM.Level2.Dom import DOM.Level2.Html2 import DOM.Level2.HTMLElement import DOM.Level2.HTMLDivElement main = getHTMLDocument $ \doc - documentBody doc $ \body - mkText doc Hello World $ \txt - mkDiv doc $ \dv - addChild txt dv $ \_ - addChild dv body $ id -- end pasteable code -- The meaning of this: * get reference to the HTML document node first (it is the parent of everything), * extract the BODY tag node, create at text element with Hello World, * create a DIV tag node, * insert the text node into div, * insert div into body Or, same in HTML: html body div Hello World /div /body /html but filled in dynamically. Using Haskell Web Toolkit API, the same may be expressed in more compact fashion: -- begin pasteable code -- module HelloWorldHsWTK where import DOM.Level2.HTMLDivElement import Graphics.UI.HsWTK main = docBodyC (mkDiv | textP Hello World) -- end pasteable code -- Here, docBodyC is roughly equivalent of the first two DOM calls, mkDiv is same as above, | means insert into container, and textP is a wrapper around mkText. Earlier, I posted the link to Haddock-generated documentation which also includes the Haskell DOM API. Here it is again: http://www.golubovsky.org:5984/_utils/yhcws/index.html Hopefully this example along with the documentation provided helps shed some light on Haskell Web programming techniques. Feel free to ask questions. Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: [Yhc] Yhc Web Service quietly opened for public testing
Justin, On 3/5/08, Justin Bailey [EMAIL PROTECTED] wrote: Does this take a Haskell program and compile it to JavaScript? That's pretty amazing. Yes, exactly. The two user interface programs, MainGUI and NewEntry were written in Haskell and compiled into Javascript by the same tools. With minimal changes they are pasteable/compilable by this service as well. See http://haskell.org/pipermail/yhc/2008-March/001194.html - anybody wants to try? I suggested this relatively simple program as a test example just to make sure results would be similar for everybody. More complex issues may arise e. g. with CSS interpreted differently by FF vs MSIE; this needs to work on in the future. Thanks for your interest. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haddock Documentation for Yhc Web Service available online
Hi, I have regenerated Haddock documentation for Haskell modules included into the Yhc Web Service. http://www.golubovsky.org:5984/_utils/yhcws/index.html Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] CouchDB module in Yhc source tree: clarification, and small problems with other packages
Hi, Don asked: Are we likely to see the couchdb bindings released as a standalone library for the wider community? Let me explain a little bit why the CouchDB module appears in the Yhc repo. As the next stage of the Yhc/Javascript project, I am trying to set up a web service where people might upload some Haskell code (or reference to such code, these details haven't been clarified yet), and get it compiled by background Yhc/ycr2js batch job, returning a HTML page with Javascript in response. CouchDB was picked* as intermediate storage for this project. Therefore an interface module was needed, so I wrote one. This module, `Database.CouchDB' is not 100% finished; it was coded up to satisfy the needs of the first utility I wrote, `cdbup' which is currently capable of uploading a text (utf-8 expected) or a binary file as a document attachment to CouchDB. So some functionality hasn't been coded yet, although it will definitely be, as the project develops. Regarding packaging, I hope I will eventually put it on Hackage, but there are some problems with another packages which I'll try to explain here, so maybe those packages' developers suggest something. 1. Text.JSON. This module was picked from Jun Mukai's haskellnet package (http://darcs.haskell.org/SoC/haskellnet/). One problem with this package, it needs too many dependencies (while JSON module relies only on Packrat parser). I had to extract the JSON module into Yhc tree; can the haskellnet package be split somehow into orthogonal sub-packages, and maybe one toplevel package which would pull all parts together if used? 2. Text.JSON again. I had to change the pNumber function (parser for numeric nodes) replacing the '1'..'9' digits range with '0' .. '9'. Otherwise it did not handle JSON-encoded numbers equal to zero. I am not sure I was 100% right, so perhaps some JSON experts here might correct me. 3. Packrat parser does not seem to be packaged anywhere else, does it? 4. The dataenc package (http://code.haskell.org/dataenc/devo/) from which I pulled the Codec.Binary.Base64 module. The package may need some adjustment to GHC 6.8.x packages structure as only base listed in build-depends does not seem to be enough: when building it, Cabal complains for hidden packages such as collections (which I had to add manually to the cabal file), etc. Is it some problem with my GHC setup, or does just the dataenc.cabal need to be updated? So, in order to get things done quicker, I pulled the said pieces from their packages into Yhc tree. For packaging the CouchDB interface, definitely these duplicates need to be removed. Other packages that CouchDB relies upon, are**: base, network, HTTP, filepath, base64-string, utf8-string Thanks for the interest in CouchDB interface, and feel free to ask any questions. --- * before support form IBM/Apache was announced, but this recent development definitely increases interest to CouchDB ** Just from the -package options I used to compile it; I may have something omitted here. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] problems building ycr2js
Hi, This is my stuff, and I am of course willing to fix this to make more compatible. I am not really deep into this shell hell (that is, used anything that worked for me not seeing much difference between shells in e. g. Archlinux vs. Ubuntu), but if there are any suggestions what could be fixed (if at all) please let me know. Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] problems building ycr2js
Hi again,
I'm thinking: if this all is about a small file, addtags.idl which is
generated in some unusual way, I might just add it to the
distributable source tree, and then nobody would have had problems
with ${var:m:n} substitution.
Thanks.
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[Haskell-cafe] problems building ycr2js (hopefully fixed)
Hi, I have made the file `addtags.idl' part of the repo. Please do scons update and see if it compiles. PS If there are any other problems with Yhc/Javascript backend, please CC me, [EMAIL PROTECTED] Thanks -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: problems building ycr2js (hopefully fixed)
Thomas, On Nov 25, 2007 5:50 PM, Thomas Hartman [EMAIL PROTECTED] wrote: Thanks Dmitri, I also had to fix an issue with System.FilePath, there's a message about this on haskell cafe. In fact, takeDirectory is the right replacement for getDirectory in older FilePath. I have pushed this change too. Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to abort a computation within Continuation Monad?
Hi, I finally was able to write a function which grabs the remainder of the computation in Cont monad and passes it to some function, in the same time forcing the whole computation to finish by returning a final value. I am not sure what kind of wheel I have reinvented, but here it is: -- Home-grown continuation delimiter function. Passes remainder of the -- whole computation to a given function and forces the whole computation -- to complete by returning a final value. Something similar to returning -- a final value in plain CPS instead of invoking the continuation. -- f: function which the remainder of the program will be passed to. -- Remainder will not be evaluated. -- r: final value of the whole computation that the latter will be -- terminated with. delimit f r = Cont $ \c - runCont (return 0) $ \a - f (runCont (return a) c) r I have created a simple (pseudo) concurrency demo that runs in a web browser, see the wiki page: http://haskell.org/haskellwiki/Concurrency_demos/Haskell-Javascript_concurrency Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to abort a computation within Continuation Monad?
Hi, I have been using plain non-monadic CPS for a while in my web-browser related stuff. Now I am tempted to switch from plain CPS to syntactically sweetened monadic style based on Continuation Monad, but I feel stuck with one important issue that I need an advice on. In plain CPS, I may write: type CPS x y = (y - x) - x a :: x a = f1 x $ \r - case r of foo1 - bar -- of type x foo2 - f2 r $ \p - ... -- something finally evaluating to a value of type x So, if at any time I return a value of a final type (x) instead of doing something with given continuation, I abort/suspend the whole computation. This can happen at any function call depth. I can also save the continuation reference in some persistent place, to resume the remainder of computation later. Now, I am trying to do the same with a Continuation Monad. But does anything similar exist in this monad? callCC is not exactly what I need because it only helps abort the inner computation, and what is returned, is a monadic value, not a final value. Besides, callCC defines a name of the function corresponding to the current continuation, and in order to use it, this name should be visible. If I have callCC $ \exit - do foo ... I cannot jump to `exit' from within foo unless `exit' is given to foo as an argument. Any suggestions? Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] New demo/test program for Yhc Javascript backend
Bit,
On Nov 18, 2007 8:41 AM, Bit Connor [EMAIL PROTECTED] wrote:
Safari 3.0.2 for windows gives an error though:
Maximum call stack size exceeded.
http://darcs.haskell.org/yhc/web/jsdemos/HsWTKDemo.html Line: 87
This is in fact a huge progress for Safari ;) Year ago, Safari on Mac
gave some weird error message Type Error line 1.
See http://osdir.com/ml/lang.haskell.yhc/2006-11/msg00033.html
The problem is, I am not sure how it enumerates lines.
Lines around 87 (ran with pr -n):
83 var consStr = function (s) {
84 if (s.length == 0) {
85 return new HSEOL ();
86 } else {
87 var hdc = mkChar (s.charCodeAt (0));
88 return new HSCons (hdc, s.length 1 ? s.substring (1) :
consStr ());
89 };
90 };
Nothing suspicious because mkChar is a wrapper around the Number constructor.
Line 314:
312 function NEG_D(a) {
313 return -(exprEval(a));
314 }
and so on.
Sometimes it gives the same error but instead of line 87 with line
314, and other times line 224 or 422
But does it at least display the widgets? Or do these errors appear as
you press buttons/type anything?
Are you aware of this issue?
Now I am ;) But to me not being an expert in Safari, these error
messages do little help (or if at least I knew what actual lines they
meant)...
Thanks.
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[Haskell-cafe] New demo/test program for Yhc Javascript backend
Hi, For those of you who are interested in using Haskell in client-side web application programming: I have added a new demo/test program to this Wiki page (Does it leak?): http://haskell.org/haskellwiki/Yhc/Javascript This demo program shows some progress made since the first announcement of Yhc Javascript backend (Core to Javascript converter) was made about a year ago. Please test the demo for functionality and memory leaks in various browsers. Your feedback is appreciated. The demo program is self-contained (does not require any Haskell libraries beyond those included with Yhc). There is a darcs repo: http://www.golubovsky.org/repos/wsptest/ from which this demo program along with Makefile can be obtained if anybody wants to play with the code. Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] placing modules in the module hierarchy
Hi, Long ago (back in 2001), there was a message in the Haskell mailing list, archived e. g. here: http://www.mail-archive.com/[EMAIL PROTECTED]/msg08187.html and what it refers to is here: http://www.cs.york.ac.uk/fp/libraries/layout.html which goes for Graphics.UI. etc I used this approach in my script to cabalize Fudgets: everything was placed below Graphics.UI.Fudgets (original Fudgets library used plain module space). I am currently working on another stuff related to Haskell GUI for web browser, and us the same approach: everything goes under Graphics.UI.library name So, I think, despite this creates longer paths in the hierarchy, the more specialized the stuff is, the deeper in the hierarchy it should be pushed. Slightly off topic, this is IMHO the same problem that we have in Linux packages/filesystem layout: every package containing binaries, places them into say /usr/bin. Then, if the two packages have a binary with the same name, this leads to conflict (HSSFFIG has a program named splitter. Another package in Debian also had a binary with the same name. they conflicted. To resolve it' I'd have to rename my binary to say hsffig-splitter. Should every package be installed into its own subtree, such conflicts wouldn't arise). So, to my personal opinion (which is in agreement with the proposal mentioned) each package has to have its own tree not crossing with other packages' tree. So, I'd suggest for the Grapefruit library: whatever is specific to this library, goes under Graphics.UI.Grapefruit. Whatever may be commonly used elsewhere (say some useful data structures) might go under Data. So, if FRP signals are usable outside the Grapefruit, they might go to Control. Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell-cafe] Haskell and a new web developement mailinglist?
Marco Weber wrote: I've been talking to Chris Eidhof the last days and we'd like to suggest adding another specialized haskell mailinglist: Haskell and web developement. I support the idea to have such a mailing list. Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell source transformer?
Hi, In order to automatize the creation of W3C DOM typesafe wrapper (this is needed for my Haskell-Javascript stuff) I am processing the OMG IDL files that contain interface definitions for DOM methods and attributes with HDirect. It works in general (for some reason it didn't like boolean type, so I used a preprocessor to redefine it as Boolean), and outputs some Haskell code full of foreign calls, yet it contains what I need: type signatures. For example, for the method appendChild it outputs: appendChild :: Node a1 - Node a0 - Prelude.IO (Node ()) appendChild newChild iptr = do o_appendChild - Com.invokeIt (\ methPtr iptr - Foreign.ForeignPtr.withForeignPtr newChild (\ new unmarshallNode o_appendChild (above lines of code may be truncated, they are just for illustration) This is almost it, but I need to replace the return type (using the JS monad instead of IO), and replace the method implementation with something else, based on unsafeJS. In some other cases I may need to modify type declarations, etc. I know there is a Haskell syntax parser around (maybe, more than one). Does anybody know of any utility based on such parser that does things I need, or rather a library on top of the parser? I just would like to avoid reinventing the wheel. Last thing I want to do is to change sources of HDirect. Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] YCR2JS Programmers Guide Draft available
Hi, I have finished typing in the draft of low-level programming guide for Yhc Core to Javascript converter. Everyone interested in future use of this tool is encouraged to read and review the Guide. Its purpose is to give some ideas about interaction of Haskell programs converted into Javascript with a web browser on the lowest possible level, without application frameworks and support libraries (just because these haven't been developed). Any feedback and ideas are appreciated. The document is located at: http://haskell.org/haskellwiki/Yhc/Javascript/Programmers_guide Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] A possible use for HSFFIG (FFIPKG) was USB Drivers in Haskell
Bjorn Bringert wrote: For cross-platform USB drivers, you may want to have a look at libusb [1]. I have only used it under Linux, but it seems to support Linux, *BSD and OS X. There also seems to be a win32 port [2]. A Haskell binding to libusb would be very welcome. I'm just wondering, would FFIPKG or HSFFIG help out? I just looked at usb.h, and it does not seem to contain anything that would break HSFFIG (mainly C functions that take/return structures rather than pointers to structures, do). I am not very much interested personally in interfacing USB, but if anybody is, feel free to try FFIPKG out and ask questions. PS Sorry for such self-advertising, but I believe that this tool could be helpful at least for prototyping bindings, so I'd appreciate any feedback. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [Haskell] AJAX applications in Haskell
Looks like the discussion is continuing in the Cafe, so I am reposting it here. Hi, Pasqualino 'Titto' Assini wrote: === Assuming that the balance is positive, this naturally raises the question: why not doing the same generate Javascript/Ajax application code to run in browser - DMG with our favourite language? This would require to: - Retarget one of the existing Haskell compilers to generate JavaScript (other possible targets would be Flash or higher level UI languages such as OpenLaszlo that in turn compiles down to either Flash or JavaScript/HTML) === Joel Björnson wrote: === I am currently working on a Google Summer of Code project relating to some of this... The project is more or less bound to Haskell Server Pages ( http://www.cs.chalmers.se/~d00nibro/hsp/), enabling JavaScript code generation. The main difference compared to the Google Web Toolkit approach is that there are no special compiler magic added for compiling directly into JavaScript. === Looks like the idea is picked up by more and more people ;) I saw some notes on this (generation of Javascript from Haskell source) in Jared Updike's blog, and I got this idea myself independently from Jared in about the same time. I am trying to add some code to nhc98 (contrary to GHC its code is much smaller and better observable) to generate Javascript at the same time when STG tree is converted into bytecodes*. I am in the very beginning though, so I cannot show any results. OTOH I do not feel like I have a lot of time to dedicate to this, so if someone else is working on this, could we team up (possibly for a different (if shown better) approach because one I chose is still questionable optimization-wise, but generation of Javascript from bytecodes does not seem better to me at the time)? -- * Work in progress may be observed at http://www.golubovsky.org/repos/nhc98/ in particular in http://www.golubovsky.org/repos/nhc98/src/compiler98/STGJcode.hs but at the moment there is virtually nothing done. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] FFI Wiki Page (was: FFI question)
Bulat wrote: we need to establish FFI page on the wiki and give at least links to all this packages and small info about using FFI with ghc/hugs There is such a page (to be more precise, a section of a page): http://haskell.org/hawiki/LibrariesAndTools section FFI Preprocessors Also there are http://haskell.org/hawiki/FfiCookbook and http://haskell.org/hawiki/FfiTutorial pages. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to redirect a handle...
Thanks everybody who answered. Indeed, forkProcess is something I completely overlooked... -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] XML Schema for Haskell parsing?
GCCXML defines some XML schema for the results of a C(++) program parsing. Does there exist any agreed-upon XML schema to represent the results of Haskell program parsing? Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell GUI on top of Xlib?
Einar, Are you talking about packet handling level only (i. e. same as I have now), or do you also have any of their transport algorithms (lazy request sending/response retrieval) implemented? Einar Karttunen wrote: I managed to parse the XCB XML protocol descriptions to Haskell data structures, next I'll try to emit some nice code from that. If it works well the end result should be a pure Haskell X library. Dimitry ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Lazier I/O?
This may be a stupud question, but how to make I/O in Haskell really lazy? Here is a simple program: module Main where import System.IO import Foreign import Data.Word import Data.Char s2c :: String - [Word8] s2c s = map (fromIntegral . ord) s sendstr :: Handle - String - IO Int sendstr h s = do let c = s2c s ln = length c allocaBytes ln $ \buf - do pokeArray buf c hPutBuf h buf ln return ln main = do hSetBuffering stdout NoBuffering l1 - sendstr stdout abcde\n l2 - sendstr stdout defghij\n putStrLn $ sent ++ (show l2) ++ bytes putStrLn $ sent ++ (show l1) ++ bytes It prints: abcde defghij sent 8 bytes sent 6 bytes i. e. the first string is output first although the result from that output (how many bytes sent) is needed second. What is desired is to have the IO actions perform as their results are needed. I am assuming some knowledge that those actions have only limited scope of side effects (e. g. order of outputs within a window is significant, but order of appearance of those windows on the screen may not be). I see some way to do this by writing regular non-monadic Haskell stuff, representing each side effects scope (i. e. where ordering of actions is necessary) with its own instance of an I/O like monad (but runnable from an outside non-monadic code), and then using unsafePerformIO as needed. But there may be some framework already developed (albeit with unsafePerformIO, but hiding it from application developers). Any ideas, pointers? Thanks Dimitry ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell GUI on top of Xlib?
Thanks Duncan for this link: a very interesting reading. Duncan Coutts wrote: Are you aware of the XCB library: http://xcb.freedesktop.org/ Indeed they mention that Haskell would be an obvious target for this: http://xcb.freedesktop.org/wiki/XCBToDo I haven't looked at their API closely, but it would not be a problem to generate bindings using HSFFIG unless there are functions taking/returning whole structures, or things like arrays of function pointers which are not yet handled by HSFFIG reliably. It might be worth trying to model their algorithms in Haskell though. They send requests to server semi-lazily (i. e. when request's result is needed, or eventually when the queue is flushed), and retrieve server replies lazily (i. e. on demand). But I am not ready to tell yet, would Haskell's natural laziness be sufficient to implement that, or something involving mutable objects needs to be built on top of the standard I/O stuff. Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell GUI on top of Xlib?
Do there exist Haskell graphics/UI toolkits implemented on top of the X11 library (Xlib) without any intermediate C/C++ libraries (i. e. not WxHaskell for example)? I have a very low level client-side interface to the X11 protocol implemented in pure Haskell (layout of protocol packets obtained from Xlib header files preprocessed by HSFFIG). As of now, I can open a display, build request packets manually and parse server responses (some of, but this is just a matter of writing more parsers), so this is more like a toolset for X11 protocol packets manipulations. I do not intend to implement a full analog of Xlib in Haskell. Instead, it might be interesting to create a fully functional GUI toolkit based on some already existing high-level interface. Any ideas will be appreciated. Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] records proposals list
David Roundy wrote:
4. Getters for multiple data types with a common field.
[skip]
4. Getters for multiple data types with a common field.
This basically comes down to deriving a class for each named field, or
something equivalent to it, as far as I can tell. This also works with the
namespace issue, since if we are going to define getters and setters as
functions, we either need unique field labels or we need one class per
field label--or something equivalent to a class for each field label.
This is a problem similar to one I had to solve for HSFFIG to design a
syntax to access fields of C structures (where different structures may
have fields of same name but of different types).
I ended up with a multiparameter class parameterized by a C structure
name, field name, field type, and for each occurrence of these in C
header file I autogenerated an instance of this class.
See
http://hsffig.sourceforge.net/repos/hsffig-1.0/_darcs/current/HSFFIG/FieldAccess.hs
for the class itself, and a typical instance (autogenerated of course)
looked like
instance HSFFIG.FieldAccess.FieldAccess S_362 ((CUChar)) V_byteOrder where
z -- V_byteOrder = ((\hsc_ptr - peekByteOff hsc_ptr 0)) z
{-# LINE 5700 XPROTO_H.hsc #-}
(z, V_byteOrder) -- v = ((\hsc_ptr - pokeByteOff hsc_ptr 0)) z v
{-# LINE 5701 XPROTO_H.hsc #-}
for a field `byteOrder' of type `unsigned char'.
This might work in general for what is proposed in the item 4 quoted
above. A class with 3 parameters will be needed, and perhaps some
syntactic sugar to autogenerate it and its instances. The only downside
is GHC needs too much memory to compile all this: I had to add a
splitter utility to HSFFIG otherwise GHC failed short of memory on even
several tens of C structures.
Dimitry Golubovsky
Middletown, CT
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[Haskell-cafe] Darcs and the Google Base
This may be just funny, but... As the Google Base went live yesterday (11/16/2005), I tried to add the information about my HSFFIG project to the Base. As the Base allows to define arbitrary attributes (labels) for each item, I added the two of Web URL type: CABAL and DARCS holding urls for the project Cabal file and the Darcs repo respectively. I was turned down on excessive capitalization of these labels. I made them into Cabal and Darcs. The former was accepted. the latter was turned down again as misspelled. I wrote an exemption request explaining that Darcs is not a misspelling. However, it's been more than a whole day since my attempt, it hasn't been resolved. Interestingly, my item was published after I removed the Darcs label, but shortly after I resubmitted the exemption request for Darcs the item disappeared. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Records (was Re: [Haskell] Improvements to GHC)
Sebastian Sylvan wrote: Personally I think that the dot is way to good of a symbol to be wasted on function composition. I mean, how often do you really use function composition in a way which doesn't obfuscate your code? I use ($) way more often than (.). Some people do use it more often than I I found it useful to use (mainly for debugging purposes) mapM (putStrLn . show) some list if I want to print its elements each on a new line. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-Cafe] DARCS and case of file name letters
I have a file in my repo (HSX11/Xauthority.hs) and I want to rename it changing just case of one letter: bash$ darcs mv HSX11/Xauthority.hs HSX11/XAuthority.hs darcs failed: A file or dir named HSX11/XAuthority.hs already exists in working directory. bash$ ls HSX11/X[aA]*.hs HSX11/Xauthority.hs bash$ darcs --version 1.0.3 (release) DARCS was compiled by GHC 6.2.2. bash$ uname -a Linux dmghome 2.2.16 #9 Mon Sep 16 22:43:25 EDT 2002 i686 unknown Is it DARCS that ignores the case of letters in filenames, or the Haskell runtime? Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Papers from the 2005 Haskell Workshop (Tallinn)?
The papers presented at the Workshop are already available in the ACM library which requires membership/subscription to read full text PDFs. Are there any plans to make those papers available anywhere else on the Web without subscription? -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Papers from the 2005 Haskell Workshop (Tallinn)?
Nils Anders Danielsson wrote: Most authors do put their papers on their web pages nowadays. In particular, I would like to read the paper on halfs (haskell filesystem). Googling for halfs haskell filesystem gave nothing but the Workshop's schedule and ACM Library TOC. Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [Announce] CabalFind 0.1
Some time ago, I expressed an idea that certain search engines may be used to collect information about existing .cabal packages whose developers made them indexable by those engines. Finally, I have written an experimental library, CabalFind. The library provides a generalized interface to search engines, and also sample implementations for Google and Yahoo* I haven't set it up as a separate project, say, on SourceForge because I am not sure whether it is feasible to do so. Instead, I am suggesting that the developers of Haskell Library Infrastructure decide whether this library may serve as a basis for library infrastructure maintenance utilities. The library may be downloaded at darcs get http://www.golubovsky.org/repos/cabalfind/ or http://www.golubovsky.org/repos/cabalfind/cabalfind.tar.gz The .cabal file for the package is tailored for GHC 6.2.2. For use with 6.4, changes may be necessary, as the XML Toolbox for 6.4 no longer includes the HTTP module, so HTTP.cabal needs to be included in build-depends. More information provided at http://haskell.org/hawiki/CabalFind Any feedback is appreciated. Dimitry Golubovsky Middletown, CT -- * Only these two search engines are found to be able to search by URI suffix (.cabal in our case); without this feature package search becomes very inefficient. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] XML Toolbox Question
Hi, How can I obtain a list of all a tags from the result of parseHtmlContent? Unfortunately, the Haddock documentation coming with the package is not rich on examples. Any suggestions will be appreciated. Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Announce: HSFFIG 1.0 Stable Release
Dear List Subscribers, I am pleased to announce the first stable release of HSFFIG, yet another tool for autogeneration of FFI bindings from C include files. The project is now hosted at Sourceforge: http://hsffig.sourceforge.net Downloads page: http://www.sourceforge.net/projects/hsffig Darcs repo: darcs get http://hsffig.sourceforge.net/repos/hsffig-1.0 Tutorial: http://www.haskell.org/hawiki/HsffigTutorial The wiki page HsffigExamples has been separated from the Tutorial. If anybody has an interesting example of using HSFFIG please update the page with code samples. Brief summary of changes: - The distribution is now cabalized. Please read the INSTALL file. - The multiparameter class and combinators to access members of structures/unions are moved to separate library. It is necessary to specify -package HSFFIG when compiling applications. Thanks to everybody who participated in discussions related to HSFFIG on this list, and privately. This helped me with implelentation of some features and gave some ideas for future improvement. Debian, RPM, and other packagers: if you create a HSFFIG package please let me know the package URL so I can update the Freshmeat project information page, and the project homepage. For any problems related to this project feel free to contact me. -- Dimitry Golubovsky ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] hssfig: Unresolved symbols when importing a foreign library: what is the preferred way of handling?
I would like to collect opinions from interested people on this matter. Background: Hsffig parses include files (.h) and generates FFI import declarations for every function/external variable it encounters a prototype declaration for. The result is a .hsc file which is converted into a Haskell source and compiled into an object file and linked into an executable along with other application source files using ghc as frontend (so far, hsffig is targeted to ghc users only). This object file will contain references to all foreign functions to be imported. Problem: In some cases, a include file may contain prototypes of functions not existing in the library it corresponds to. In my case, unistd.h (Linux, glibc2) contains prototypes for __ftruncate and pthread_atfork which come up unresolved when linking the executable without additional libraries specified. pthread_atfork is resolved when linking with -lpthread. Where is __ftruncate defined, I don't know, and I do not really want ot know unless I need to use this function. Possible solutions, sorted by expected amount of work necessary to implement (please pick one you would prefer, or suggest yours): - leave everything as is: the executable will not be linked until the developer finds all the libraries to resolve all the missing symbols. That's how it works (or doesn't work) now. - tell ld only to warn about unresolved symbols: the executable will be built anyway, but if the unresolved function is called from under the hood it most likely results in segfault hard to explain (which function caused it). Only special linker option is required. - for each foreign function imported, generate a stub which, when called, complains loudly and aborts the program. These stubs are placed in a separate object file and linked after all possible libraries, so library-defined symbols always take precedence. The disadvantage is: the developer would not know which symbols remained unresolved when the executable was linked, only will he know when the application crashes. I am trying to implement this now, using the hsc2hs' #def macro to define those stub functions. - analyze the linker output and make auto-correction in the generated .hsc file just by excluding FFI declarations for unresolved functions. Non-elegant, requires second pass and highly platform and tool dependent. - instead of generation of a single object file referencing all the functions, create one per funciton import and place them all in an archive (.a). Then, when linking, only actually used functions will be picked from the archive. I am not sure how would this interact with ghc --make: I got an impression that a .hi file is necessary for all modules (.hs/.hi/.o triple) imported unless they are gotten from a package. If I have in my program: import FOO_H and there is no FOO_H.hi nor FOO_H.hs, only libFOO_H.a: how ghc would live with this? The latter approach does not take much to implement in hsffig itself (I already have a splitter which splits into one object file per a structure/union). I am more concerned how to make ghc live with this. Creation of a package for each imported include file seems like overkill. PS I believe that hsffig will be an useful utility. I noticed several people downloaded nightly tarballs or checked out from the DARCS repo. If these persons have found this program useful, would they please suggest something on the matter I described. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Suggestions for #defines with FFI
John, Could you please give an example of such constant definitions? Is it possible to look at the include file? -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] hsffig issues (was: Suggestions for #defines with FFI)
John Goerzen wrote: Incidentally, I looked at hsffig. There were a couple issues with using it for this: 1) It didn't declare types for the imported constants, so Haddock wouldn't generate a list over it. I never tried to make hsffig output documentable: the whole idea is just to write import FOO_H in Haskell as one would write #include foo.h in C. 2) It included all sorts of other #defined items, from other headers (stdio.h maybe), making it unsuitable to re-export directly to the user. (I'd have to re-key everything anyway) I mentioned this in the Tutorial: hsffig gives the Haskell compiler the same look at information about the library to import as the C compiler would have. It is hard to separate such things: your header file that you include may include ten other headers, five of them related to the library, and the rest from /usr/include And you do not need to reexport because wherever you need the bindings, you just import them there. You still have to have some library interface layer in your application, but you do not focus on type signatures of foreign functions. 3) It tried to list some of the GCC internal conditionals as constants, making the .hsc not compile unless I manually removed some of them. Can you provide an example of that? With (almost antique) egcs-2.91.66 I never had anything like this. What was in the .hsc file and what was the compilation error? I really like the idea, though. Autodetecting these is great, since they could vary somewhat from implementation to implementation. Exactly: the Haskell compiler gets the same information (e. g. from features.h) as the C compiler got when compiling the library. Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Arbitrary files in a Cabal package: how to install
I am trying to use Cabal for buiding HSFFIG as a package. Among other files to install I have the special template for hsc2hs which is a C include file. If I specify it in the Includes: clause nothing happens: it is not copied anywhere during installation. I need this file to be placed somewhere in the package instalation location, so when programs are compiled with my package could include that file. Of course I may specify additional step in the Makefile, but it would be more consistent to do this in Cabal. How can arbitrary files be declared parts of a package, and destination directories for them be specified? I am using the simplified (?) version of Cabal that Ross suggested whrn I asked in this list whether it would be possible to use it with older GHC. Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Unicode in GHC 6.2.2 and 6.4.x (was: Re: [Haskell-cafe] Unicode.hs)
Dear List Subscribers, Simon Marlow wrote: On 30 June 2005 14:36, Dimitry Golubovsky wrote: It is in CVS now, and I believe will be in 6.4.1 Not planned for 6.4.1, but definitely in 6.6. I have put those files that work for me in GHC 6.2.2 (Unicode support) for download. Please read the Wiki page: http://haskell.org/hawiki/GhcUnicode for instructions. Any feedback will be appreciated. I believe, the code will work with GHC 6.4.x as well. Please let me know if there are any problems. Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Unicode.hs (was: RE: Re[2]: ANNOUNCE: GHC survey results)
Hi, Vadim Konovalov wrote: === that file reads: -- Based on the GHC.Unicode library, Copyright 2005, Dimitry Golubovsky. -- See GHC's LICENSE file for the full license text. That said, it is part of GHC? === Clarifying on Unicode stuff in GHC I contributed: It is in CVS now, and I believe will be in 6.4.1 At least it shows up at: http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/libraries/base/GHC/Unicode.hs?rev=1.14 (MAIN branch) But this module is just an interface to another module, WCsubst.c: http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/libraries/base/cbits/WCsubst.c?rev=1.3 which in turn was produced from UnicodeData.txt (? I believe this is correct name of the file from www.unicode.org) by the shell script: http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/libraries/base/cbits/ubconfc?rev=1.2 This API handles simple case conversions (Char - Char), and categorization of characters according to what is in the UnicodeData.txt file. Before (i. e. up to and including 6.4), Unicode stuff was handled through wc* locale based functions for wide chars conversion. Since not every installation of Unix (or some other OS) has this set up properly (mine was not: personal itch), this code was proposed for GHC and finally made it there. Hope this explains everything. In fact, Unicode.hs itself is not completely mine ;) PS: Autrijus (the guy who develops Pugs) included those files on his own because 6.4 was just out, and Unicode stuff was not there yet. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Announce: Yet Another Tool to Generate FFI Bindings: hsffig
I am pleased to announce the very first alpha release of the (yet another) FFI binding autogeneration tool. Some time ago, I asked the list subscribers about available bindings to Berkeley DB. Several people kindly shared their code with me. One thing I noticed in all bindings: they required manually-written wrappers to accomodate for Berkeley DB indirect style of calling functions. Considering large number of such functions in BDB, I attempted to write a tool which would automatically parse the BDB include file, and extract function prototypes to generate FFI declarations. Soon it became clear that an almost full C syntax parser would be necessary. Finally it resulted in what I am presenting to the Haskell community with hope that this utility will be useful to many developers. Of course there are many omissions and shortcuts, but before I move forward, I would like to get some feedback from potential users of this tool. There is no detailed documentation. I have written a brief README file. More detailed documentation will follow. I haven't created a homepage for this project yet: the only way to get it so far is the darcs repo: darcs get http://www.golubovsky.org/repos/hsffig Files in the repository may be browsed at: http://www.golubovsky.org/repos/hsffig/ I will appreciate any feedback. Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Generalized version of `words'?
Does there exist a generalized version of the `words' function i. e. one that breaks an arbitrary list into parts by an arbitrary predicate? splitAt is not what I need. I had to write my own: -- A version of words, but works with any lists on any predicate. parts pred s = case dropWhile pred s of [] - [] s' - w : parts pred s'' where (w, s'') = break pred s' (just by parameterizing `words' found in Data.List with a predicate passed as a parameter). In case such a function already exists, what is its name? In the opposite case, can such a function be added to the standard library? (or why didn't it exist?) Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] OT: http://www.cse.unsw.edu.au host name does not resolve
Sorry for this OT, but the server seems to be unaccessible. And so is the Haskell-related stuff on it (like the FFI Addendum). The requested URL could not be retrieved Here's what the proxy says: (possibly a DNS problem) While trying to retrieve the URL: http://www.cse.unsw.edu.au/~chak/haskell/ffi/ The following error was encountered: Unable to determine IP address from host name for unknown server name This means that: The cache was not able to resolve the hostname presented in the URL. Check if the address is correct. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Infix operators naming conflicts (was: class Ref)
Gracjan Polak wrote: val = readIORef a=:b = writeIORef a b Pretty shame := is already reserver :(. There is something alike Graphics.Rendering.OpenGL.GL.StateVar. The use $= for assignment. Generalizing variables (in respect to some monad) seems to be often reinvented idea :) Indeed, has anyone tried to summarize possible conflicts between infix operators as they are defined in many places to serve different purpose? e. g. (!) :: Ix i = Array i e - i - e The value at the given index in an array. (Data.Array) (!) :: a - [HtmlAttr] - a (Text.Html) so if a module imports both modules mentioned above simultaneously, will the compiler complain about (!) and ask to use a qualified name? I had the following experience: when trying to create a convenient syntax to access fields of foreign C structures using appropriate Ptr and field label, I tried to define a combinator for that, and to name it (.) (dot, same as dot-composition defined in Prelude, to look similarly to Java notation) Type signature for my (.) was totally different than Prelude's (.), and semantically it is not composition of functions. However the compiler (GHC) asked to use qualified name. Finally I ended up with the name (--) which looks like C notation. But who knows, whether someone wishes to use (--) for other purposes? -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] G machine in FORTH
Andrew Harris wrote: I've been thinking about writing a G-machine interpreter in FORTH so that one could write Haskell like programs that would compile down and run graph-reduction style on the FORTH machine. Many developers think FORTH is nice, but the language is so, shall we say, terse. I'm curious about what people think about this; having the expressiveness of a Haskell-like language that compiles to this environment might provide the best of both worlds, simple hardware architecture and an advanced programming language. IMHO Koopman's TIGRE (http://www.ece.cmu.edu/~koopman/tigre/) might be a close approximation of what you want. I had some (rather non-serious) experience with Forth, and I had great pleasure reading Koopman's paper on TIGRE. Unfortunately I couldn't find any further development on this topic (although I saw some later Koopman's publications on Forth itself). I guess, only someone thinking Forth (as in the Brodie's book) might develop such a thing. Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] RFE: Extensible algebraic user-defined data types?
Hi, Is it possible to have such a feature in the future versions of the Haskell language? For example, there is an Either datatype which is Left a| Right b. Suppose I want to extend this datatype to the one including possibility of neither Left or Right (i. e. None). Currently I have to use Maybe Either, so my options are: Just (Left a) Just (Right b) Nothing If I could extend the Either datatype I might have (syntax may be different, this is just an example) data NEither a b = Either a b | None where datatype in angles is a parent datatype, and all its possible data constructors are included, and their list is extended with None. which gave me possibilities: Left a | Right b | None Probably I wouldn't expect to be able to reuse Nothing here (although I might want to) because Nothing already has been defined to be of the type Maybe. This is just a suggestion, that's why it is posted in the Cafe. PS Or is there a similar feature in the language already? Regarding reusing constructor names across several datatypes: is it possible to qualify them with their enclosing datatype name, like Maybe.Nothing where there is a name conflict? Then I might reuse Nothing in my hypothetical data type, and it would be NEither.Nothing if conflicting with Maybe.Nothing PPS I may be missing something again, as always ;) -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] FFI and pointers to pointers
Hi, I am trying to generalize my knowledge about FFI declarations when dealing with pointers to pointers (import from C to Haskell). Maybe these are silly questions, but It seems to me, I am missing some understanding. Per the FFI Addendum: For a variable, we use import: int bar; foreign import ccall bar :: Ptr CInt If we have int *pbar;, will Ptr (Ptr CInt) be correct? For arbitrary level of pointer nesting, will nesting of the same number of Ptr's be correct? For a function, we use static import: int system (char *str); foreign import ccall static stdlib.h system :: Ptr CChar - IO CInt but for a pointer to a function (i. e. a variable) we use: int (*psystem) (char *str); foreign import ccall dynamic mkFun :: FunPtr (CInt - IO ()) - (CInt - IO ()) and then psystem should be declared as a variable with import, I believe. Or as a FunPtr? And then (mkFun psystem) returns something to be called as a function. Then (talking to myself) pointer to pointer to a function may be imported as shown in the very beginning, i. e. by nesting Ptr's? So indeed my question is: would nesting of Ptr's work if nested pointers are imported? I haven't experimented with this yet, but maybe someone has? Thanks for any advice. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Closest analog to popen()
Peter Simons wrote: Dimitry Golubovsky writes: Does there exist any analog of popen in the standard Haskell libraries? Maybe System.Process.runInteractiveCommand is what you need? http://haskell.org/ghc/docs/latest/html/libraries/base/System.Process.html Is this available only in 6.4? In 6.2.2 I've got only System.Posix.Process, and this is just binding to Unix functions dealing with processes. Thanks for pointing me out. Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Haskell] URLs in haskell module namespace
Dear list members, I'd like to share some sketchy ideas I have on the subject to address some of the issues raised. At 12:14 22/03/05 +, Malcolm Wallace wrote: I cannot see any of the Haskell compilers ever implementing this idea as presented. It would introduce an enormous raft of requirements (networking client, database mapping, caching, etc) that do not belong in a compiler - they belong in separate (preprocessing/packaging) tools. Furthermore, these tools already exist, albeit they are young and have a long maturation process still ahead of them. An external program acting as an URI streamer might be the solution. Such a program (identified via an environment variable or a compiler's command line option, just like Hugs external editor) would take an URI as its command line argument, and respond with a streamed contents of that URI on its stdout. Like e. g. curl/wget -O -. All the compiler has to do is popen() that program if an import statement contains an URI. Using curl/wget helps get around various issues with proxies/encryption/etc. as those programs are specifically designed for that. I do not believe this would result in significant overhead comparing to regular fopen() used by the compiler for opening source files. On a non-networked system, such a program would be a not so complicated shell script pretending it downloads from an URI, but reading from local disk (flash, any other kind of storage) instead. To address the problem of module/package URI changes over time, the following may be suggested. Either purl.org is used (and then it is responsibility of a package maintainer to keep its URL pointer valid). Or, some kind of a purl server may be set up somewhere (at haskell.org for example) which also supports mirroring. This means that for each package/module registered with this server, multiple locations are known (well, probably willing people might allocate their computer resources for that, at least I would not object as long as I have my own web server). The hypothetical purl server serves redirects as usual, but shifting randomly to another mirroring location for each new request for a module/package. So, if an attempt to retrieve a module/package fails, it may be repeated, and other mirror location will be tried. Mirrors will be synchronized behind the scenes. Will such a centralized purl server a bottleneck or a single point of failure? Probably not more than a centralized Hackage database (or is it planned to be distributed?) Also, some resolver might be part of the URI streamer which maps module names to URIs. For example, the Prelude will most likely be stored locally, but some other module will not. This means that the resolver consults the local package database (cabal), and its own cache, and either streams a local file or popens curl with some URI constructed specifically based on the desired module name. Once downloaded, a module may be cached with some TTL, so further recompilations do not result in curl involvement (until the TTL expires). PS This all is written in the assumption that Haskell source files are served. Binary distributions, of course would require different techniques. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Parsec question: how to access parser state
Hi, I am trying to develop a parser with the Parsec library. At some point I need to do something with parser state, say, convert it to a string. I declared the type for the parser: type TParser a = GenParser Token (FiniteMap String Declaration) a The FiniteMap (which is the user state) is expected to be updated during parsing whus building some internal lookup table. and in one of the parsing functions I want to call show getState assuming it will apply show to the FiniteMap and return some string of characters. During compliation, I get: No instance for (Show (GenParser tok st st)) arising from use of `show' at (file location) In the first argument of `', namely `(show getState)' But GenParser is a newtype, not a data constructor, so attempt to write instance Show (GenParser tok st t) results in error message about missing constructor GenParser. How could I extract actual user state from the result of getState? The parser itself works as needed, but dealing with user state gets me in trouble. Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] invalid character encoding
Glynn Clements wrote: To get a better idea, you would need to consult users whose language doesn't use the roman alphabet, e.g. CJK or cyrillic. Unfortunately, you don't usually find too many of them on lists such as this. In Russia, we still have multiple one byte encodings for Cyrillic: KOI-8 (Unix), CP1251 (Windows), and getting more and more obsolete CP866 (MSDOS, OS/2). Regarding filenames, I am sure Windows stores them in Unicode regarding of locale (I tried various chcp numbers in a console window, printing directory containing filenames in Russian and in German altogether, and it showed non-characters as question marks when locale-based codepage was set, and showed everything with chcp 65001 which is Unicode). AFAIK Unix users do not create files named in Russian very often, and Windows users do this frequently. Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-Cafe] FFI and foreign function returning a structure
Hi, If I have a C function returning a structure (not a pointer, but structure itself), can this be accomodated via FFI? I re-read the FFI Addendum, and my conclusion is most likely No. I am asking just to make sure this is not only my finding. Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell binding to Berkeley DB?
Thanks everybody who answered. Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell binding to Berkeley DB?
Hi, Has anyone tried/been successful on developing such a binding? Google returns reference to a message written 2 years ago (on the gtkhs mailing list) that someone developed it partially: http://www.haskell.org/pipermail/gtkhs/2003-January/000317.html and a description of a student's assignment: http://www.cse.unsw.edu.au/db/thesis/topicinfo/MMTC13.html The rest of links that Google returns are of little relevance. Any ideas? Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Convert to unboxed value? How?
Hi, What function should be used to convert an integer value to Int#? A character to Char#? Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Hugs vs GHC (again)
Ketil, Ketil Malde wrote: Dimitry Golubovsky [EMAIL PROTECTED] writes: (Did you intend this for the list?) Yes, and I re-posted similar message on the list. I think perhaps the answer is all of the above. The functions could be defined in multiple modules, so that 'ASCII.isSpace' would match the normal space character only, while 'Unicode.isSpace' could match all the weird and wonderful stuff in the standard. And then there might be a bunch of (perhaps autogenerated) locale-matching modules like ISO8859_1, KOI_8 etc. Well - maybe. Another option is for these to require conversion from to Unicode. Right, because input of encoding-specific functions will be Unicode anyway. And AFAIK conversion from/to unicode may be also contained in localedef files (or for instance in Java CharTo, XXXToChar classes) - I mean that there must be enough information around to build those modules automatically. Except for Unicode itself which would be autogenerated from the Unicode database files like multiple examples of doing this (including mine) that were posted on this list. Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Unicode: Hugs vs GHC (again) was: Re: Some random newbie questions
Hi, Lennart Augustsson wrote: Simon Marlow wrote: Here's a summary of the state of Unicode support in GHC and other compilers. There are several aspects: - Can the Char type hold the full range of Unicode characters? This has been true in GHC for some time, and is now true in Hugs. I don't think it's true in nhc98 (please correct me if I'm wrong). I remember, it was in GHC. But any attempt to output Unicode characters using standard I/O functions always ended up outputting only low 8 bits. Has anything changed since then? - Do the character class functions (isUpper, isAlpha etc.) work correctly on the full range of Unicode characters? This is true in Hugs. It's true with GHC on some systems (basically we were lazy and used the underlying C library's support here, which is patchy). Which basically means that one with older or underconfigured system where they do not have permissions/technical possibilities to configure locales in the C library properly is out of luck... - Can you use (some encoding of) Unicode for your Haskell source files? I don't think this is true in any Haskell compiler right now. Well, Hugs from CVS accepts source code in UTF-8 (I am not sure about locale-based conversion) - at least on my computer. Another thing, string literals may be in UTF-8 encoding, but Hugs would not accept function/type identifiers in Unicode (i. e. one could not name a type or a function in Russian for instance - their names muct be ASCII). I put an example of such a file in UTF-8 on my web-server: http://www.golubovsky.org/software/hugs-patch/testutf.hs Well, even if hbc is mostly dead I must point out that it has supported this since Unicode was first added to Haskell. As well as the point above, of course. If the GHC implementors feel lazy they can always borrow the Unicode (plane 0) description table from HBC. It is a 64k file. Or in Hugs, there is a shell script (awk indeed, just wrapped in a shell script) which parses the Unicode data file and produces a C file (also about 64k), and compact set of primitive functions independent from C library - src/unix/mkunitable and part of src/char.c in the Hugs source tree respectively. The reason I asked this question was: I am trying to understand, where is internationalization of Haskell compilers on their developers' list of priorities, and also how high is demand from users to have at least basic internationalization. Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Hugs vs GHC (again) was: Re: Some random newbie questions
Hi, Looks like Hugs and GHC are being compared again ;) I am just interested to know, what is the current status of Unicode support in GHC? Hugs has had it for about a year (or more, in CVS) at least at the level of recognizing character categories and simple case conversions based on the Unicode database files. Also UTF-8 or locale-based I/O encoding conversion to internal Unicode is available. Does GHC has similar support? Some time ago (about 1.5 years) I tried to play with Unicode I/O in GHC, and it looked like it did not have much Unicode support back then (at least on I/O level). Has anything progressed in this regard since then? Most of this list subscribers seem to be GHC users, so can anybody answer? BTW when answering the original post (brief quote below) different aspects were mentioned, but not internationalization ones. Is it really not that important? Dimitry Golubovsky Middletown, CT Benjamin Pierce wrote: * What are the relative advantages of Hugs and GHC, beyond the obvious (Hugs is smaller and easier for people not named Simon to modify, while GHC is a real compiler and has the most up-to-date hacks to the type checker)? Do people generally use one or the other for everything, or are they similar enough to use Hugs at some moments and GHC at others? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell as data manipulation language?
Graham All, Graham Klyne wrote: 1. The lack of variables in Haskell isn't a problem so much as an opportunity to think in new and interesting ways. What I was trying to say: where in imperative languages there is a boundary between in-memory computations and I/O, equivalent semantic boundary in functional languages is between stateful and stateless. I. e. functional programming is a stateless way to control stateful world (remember state-of-the-world-p? :) 2. I think that when you talk about versioning, you come close to a useful way of thinking about mutable data in Haskell. My understanding is that the classical way (i.e. pre-monads) to think of mutable values in functional languages was to model them as a time-sequence of intermediate values, where a function to update a state returns the next value in that sequence. Expressed this way, a practical problem arises that the intermediate values don't (necessarily) go away, creating a potential for exploding storage requirements. (If, as with document versioning, you want to keep the intermediate values, then you need to figure a way to live with this; value sharing in pure functional languages is a big help here.) But often one is only interested in the latest or current value in the time-sequence. Monads provide a way of capturing this: the state is implicitly threaded through a sequence of computations (e.g. the expressions in a do-list), with old versions thrown away as new ones are created (unless the state is explicitly saved, which is not always possible). I was writing about the same, but applied to persistent storage. I meant that to store a new version, it is sufficient just to store a seralized compiled expression which being applied to version N of an object evaluates to its version N+1. In other words, store updates lazily. If there are too many stored versions (or lazy evaluation takes too much time), then at some moment of time the whole expression (spanning down to the oldest stored version) may be deserialized, forced to evaluate, serialized, and stored. Older versions may be discarded after that (unless any other objects refer to them directly). P.S. A question to those who needs mutable variables: has anybody tried Manuel Chakravarty's Haskell Ports Library? http://www.cse.unsw.edu.au/~chak/haskell/ports/ I spotted it today, but had no time to look at the code and/or try it. According to its (rather sketchy) documentation, this library provides some mechanisms to simulate varying values as time-sequences (lazy streams?) Can anyone tell wether it is more/less functional/efficient than IORefs? Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell as data manipulation language?
Hi, I am probably not the first to think about this, yet I was unable to find any signs of activities in this direction, so maybe I will be able to know something from this list. First of all, reading multiple messages about global and mutable variables desired in Haskell, I was thinking: isn't the root of the problem in the fact that there are no variables in Haskell at all? Indeed (and my experience of digging in Hugs sources confirms) Haskell program (function) is just a description of some memory structure which being completed by the bindings of its arguments, is further transformed by the evaluator into some other data structure, etc. Now imagine a data storage with structure similar to one of a Haskell program. I. e. a storage having metadata-objects like data constructor functions, data types which are parents to data constructors (like in data X = Foo Int | Bar Float), classes, instances, modules, etc. Also data objects themselves, i. e. precompiled and serialized functions along with their type information. Data objects do not differ from functions i. e. they are stored the same way. Now quoting Graham Klyne Subject was: [HAskell-Cafe] Mutable and persistent values (was: Top Level TWI's again) posted 2004-11-23 05:11:25 PST: (I tried to post reply via Google Groups, but it did not make it back to the list): It is my view that use a functional language effectively, it is necessary to think differently about its structure than one would for a conventional imperative program. Global values become parameters and return values; mutable values become input values and new (separate) return values. If you're used to writing imperative programs that do not use global state, but rather use parameters to pass values, the difference isn't always quite as great as might be imagined. For complex values, this sounds horribly inefficient, but because values are pure (not mutable), very high levels of sharing can (sometimes, with good design!) be extensively shared. Thus, a return value may well consist mostly of a copy of the input value, with differences, rather than actually being a complete new copy. (Chris Okasaki's book shows well how to design to obtain these benefits.) Also, because Haskell is lazy, complex structures passed between functions don't necessarily ever exist in their entirety. Sometimes, I think of a data structure as describing a computational traversal through some data, rathert than something that actually exists. (This leads to very elegant expression of things like Prolog search-and-backtrack algorithms.) So, if there is a data object (say, a list) stored with version number N, and another value is cons'ed to the list, then version N+1 will be stored as an application of cons to the value added, and the version N. Thus, via versioning, some kind of mutability may be achieved (and of course these check-in and check-out must belong to IO monad). These stored functions must be visible to the compiler, and when compiling some function f which calls g (compiled earlier and stored as version N), the code of this version of f (say, M) is built to call version N of g further on. So, all the type checks are done during compilation, and are not necessary during runtime, and yet the functions are compiled and stored separately (trying to address the issue with too large monolithic programs). Newer version of f (say M+1) may be compiled against newer (at that time) version of g (N+1). So different versions of the same function may demonstrate different behaviors, but the history of development is preserved. Put together, this gives some conceptual image of a programmable data storage with queries being calls to stored functions (with externally supplied agruments). All good things of Haskell like static type safety are preserved. I am thinking of implementation of something like this using Hugs runtime as the basis. I realize, this may be very time consuming, so I am wondering, maybe someone already is developing something like this? Or someone already tried, and found this inefficient or in some other way not feasible to implement? Dimitry Golubovsky Middletown, CT ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
