April 2006 - Haskell-Cafe

Creating static libraries using GHC
by Tom Hawkins 16 Mar '07

16 Mar '07

I have a chunk of Haskell code I would like wrap up and distribute as a library. Is there a way to build a static library (*.a) that includes my code plus the Haskell runtime, which C programs can easily link against? Here is what I have tried so far... ghc --make -fffi MyLib # Builds MyLib.o and MyLib_stub.o. gcc -c -I/usr/local/lib/ghc-6.4.1/include MyLibWrapper.c ar -r libMyLib.a MyLib.o MyLib_stub.o MyLibWrapper.o This works fine when I use ghc to compile and link a C program... ghc main.c libMyLib.a But if I use gcc, it throws a lot of unresolved references. I have no problem compiling with ghc, but the folks using my library probably won't have it installed. I added -v to ghc to see how it calls gcc; it seems to link in different libraries based on what Haskell libraries are being used, and it undefines a bunch is symbol references. Are there any switches to have ghc return a single archive with everything included? Please excuse my ignorance of the linking process. Thanks for any help! -Tom

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Porting GHC to OSX86?
by Deling Ren 10 May '06

10 May '06

Hi there, Has anyone made any attempt to port GHC to Mac OS X on x86? Wolfgang Thaller’s binary package runs over Rosetta but slow (not surprising). It can not be used to compile a native version either (I got some errors related to machine registers). I tried to do a bootstrap but can't find the ".HC" files mentioned in the manual. They don't seem to be on the download page of GHC. Any ideas? Thanks. Deling

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Haddock seems to generate wrong types in newtype deriving
by Brian Hulley 06 May '06

06 May '06

Hi - I have the following code: data MState = MState -- details omitted type MonadStateMState = MonadState MState -- necessary for Haddock newtype ManagerM a = ManagerM (StateT MState IO a) deriving (Monad, MonadIO, MonadStateMState) which means that ManagerM is an instance of Monad, MonadIO, and MonadState MState. However, the Haddock docs look like: data ManagerM a Instances ??? a => Monad (ManagerM a) ??? a => MonadIO (ManagerM a) ??? a => MonadStateMState (ManagerM a) which doesn't seem at all right to me. I'd have thought it should say: data ManagerM a Instances Monad ManagerM MonadIO ManagerM MonadStateMState ManagerM Is this just a bug in Haddock or am I misunderstanding something about Haskell? Thanks, Brian.

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need help please [HOpenGL]
by enache alex 06 May '06

06 May '06

hello ; I am writing to ask you a thing ; I am writing a little game on Haskell's HOpenGL ; the game isn't much , but I want to make look a little better ; and for that I want to use bitmaps (or textures) ; I don't know very much about this subject ; I've tried to use de bitmap function from Graphics.Rendering.OpenGL.GL.Bitmap , but i gives me an error ; I've used the function like this ; bmp <- bitmap (Size (100,100)) (Vertex2 0 0 ) (Vector2 0 0 ) (Ptr "C:\1.bmp") end it tells me that he doesn't find the Ptr constructor ; if you can supply an full example on this matter it would great ; many thanks ; hope to hear from you soon ; thanks for your time in reading my letter ; PS : the example doesn't have to be big , it just has to contain all the things , in order for me not to miss something --------------------------------- Yahoo! Messenger with Voice. Make PC-to-Phone Calls to the US (and 30+ countries) for 2¢/min or less.

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The case of the missing module
by ihope 06 May '06

06 May '06

In the Haddock source, there's the following line: import Paths_haddock ( getDataDir ) Paths_haddock doesn't seem to be anywhere inside the Haddock distribution, and a Google search doesn't turn up any useful results. Where can I find this thing?

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Re: [Haskell-cafe] #if and #endif
by ihope 06 May '06

06 May '06

On 4/13/06, Jason Dagit <dagit(a)codersbase.com> wrote: > Try using passing -cpp to ghc when you compile. > > Jason Thanks. Will do.

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Is it possible to export module aliases?
by Brian Hulley 04 May '06

04 May '06

Hi - Given some large list of modules which need to be used qualified, I'd like to be able to make a convenience module that I could use instead, and which would export all these modules also qualified by an alias, ie: module Top ( module qualified Top.First as First , module qualified Top.Second as Second ) where ... import qualified Top.First so that I could then say: import Top main = do a <- First.create ... b <- Second.create ... instead of having to always write: import qualified Top.First as First import qualified Top.Second as Second -- this may be a *very* long list in every module that uses the "Top" API. The current "workaround" for this problem in the standard libraries seems to be to always append the module name to the name of the function or type or constructor (which is unfortunately, like record field names, not local to the type but that's another story) eg by using createFirst, createSecond etc, which seems a bit messy to me. An alternative is to use the C preprocessor and #include a file containing all the import declarations, but although "ok", I'd prefer to be able to express the code organization purely in Haskell itself. This must be a very common issue so I'm wondering if anyone else has some better ideas on how to solve it? Thanks, Brian.

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GetOpt
by Anton Kulchitsky 02 May '06

02 May '06

Hi all, I just started to study Haskell and it is my almost first big experience with functional languages (except Emacs Lisp and Python). I enjoyed all small exercises and started a bigger business writing a general utility. However, I have a problem from the beginning. The utility get some file and convert it to another format. It is a kind of small compiler. It also accepts many parameters and behaves depending on them. The problem is how to do this neat! How should I write my program to accept and neatly work with options???? Please, could you suggest an example of code how to do this properly in Haskell. No book or tutorial discuss this topic. It is really sad because the problem is very unclear. Indeed, what I do in C. I make a struct settings and set its fields. Then, the program uses this parameters easily. However, what can I do in Haskell? I imagine the program as a composite function that take some input and produce the output. I decided that now I should consider my program options as an additional variable(s) of the input. Well, it is still hard to implement. Below is an example of what I did first. However, it is just not enough and looks ugly for me. Please, HELP!!!: -------------------------CODE IS BELOW------------------------- module Main where -- std import System.IO import System.Console.GetOpt import System.Environment ( getArgs ) import System.Exit import Char -- data import Data.Maybe ( fromMaybe ) -- local -- main program: options, maybe in file >> out file main :: IO () main = do -- program info genInfo -- options processing args <- getArgs case check_filter args of (WrongOpts,strLst) -> usage ("Error: Wrong option list\n" ++ (concat strLst)) >> exitWith (ExitFailure 1) (ForHelp,strLst) -> usage [] >> exitWith ExitSuccess (ForVersion,strLst) -> version >> exitWith ExitSuccess --strLst contains 3 strings: input file name, output, and parameters (OK,strLst) -> do inputstr <- readFile infile --get the content writeFile outfile (pgnjs inputstr params) --write the result exitWith ExitSuccess --exit where infile = (strLst !! 0) outfile = (strLst !! 1) params = (strLst !! 2) --(_,_) -> version >> exitWith (ExitFailure (-1)) ---------------- OPTIONS DESCRIPTION ---------------- -- OptionFlag is data OptionFlag = Version | Help | Output String | Input String deriving (Show, Eq) -- description of all options options :: [OptDescr OptionFlag] options = [ Option ['h', '?'] ["help"] (NoArg Help) ("show this help"), Option ['V'] ["version"] (NoArg Version) ("show version number"), Option ['i'] ["input"] (ReqArg Input "file") ("input file name"), Option ['o'] ["output"] (ReqArg Output "file") ("output file name") ] ------------------------------------------------------ -- this data describes the result of program work data ErrKey = OK | ForHelp | ForVersion | WrongOpts deriving (Show, Eq) ----------------------------------------------------------------------- -- input is a string of options and output is the result of the -- program. Actually, this is only a filter which filter all -- exceptional situation in option lists and then call a real function -- if list is good check_filter :: [String] -> ( ErrKey, [String] ) check_filter args = case (getOpt Permute options args) of (os, [], []) -> if (elem Help os) then (ForHelp,[]) else if (elem Version os) then (ForVersion, []) else if (not ((elem "-i" args) && (elem "-o" args)) ) then (WrongOpts, ["both -i and -o must be specified\n"]) -- we filtered now all exceptional situation else (OK, ["in.tmp","out.tmp",[]]) (os, fs, ers) -> (WrongOpts, []) -------------- OPTIONS EXCEPTIONAL FUNCTIONS ----------------- -- Version info version :: IO () version = putStrLn $ "Version 0.1.1a of October-November 2005" -- Usage short info: Output error line and usage usage :: String -> IO () usage errLine = putStr $ errLine ++ (usageInfo "Usage: shipgnjs [option...]" options) -- General info string genInfo :: IO () genInfo = putStrLn "shipgnjs (c) 2005 Anton Kulchitsky" {- This is the main function that operates on correct string: input: the first element is input pgn, the second line are parameters the output is html text for the result file -} pgnjs :: String -> String -> String pgnjs pgnstr params = map toUpper pgnstr ---- Thank you in advance, Anton Kulchitsky (a.k.a. atoku)

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database access recommendation
by Brock Peabody 02 May '06

02 May '06

I'm teaching myself Haskell, and was wondering if anyone could recommend a library for accessing databases, PostgreSQL in particular. I looked at http://www.haskell.org/haskellwiki/Libraries_and_tools, and HSQL looked promising, but I can't get it to install on Windows or FreeBSD, with Hugs or GHC. According to the FreeBSD ports system, it is marked as broken. It fails with Hugs on both platforms on the "runhugs Setup.lhs configure" step in the base HSQL library with: FreeBSD: ERROR "/usr/local/lib/hugs/libraries/Text/ParserCombinators/ReadP.hs":133 - Syntax error in type expression (unexpected `.') Windows: ERROR "C:\Program Files\WinHugs\libraries\Text\ParserCombinators\ReadP.hs":156 - Syntax error in type expression (unexpected `.') GHC crashes with no error on the "runghc Setup.lhs build" step in the base HSQL library in Windows. In FreeBSD I can completely build and install the base library, but in any of the database specific directories, "runghc Setup.lhs configure" yields: "Setup.lhs:17:71: Couldn't match `PackageDescription' against `LocalBuildInfo' Expected type: Args -> ConfigFlags -> LocalBuildInfo -> IO ExitCode Inferred type: [String] -> ConfigFlags -> PackageDescription -> LocalBuildInfo -> IO ExitCode In the `postConf' field of a record In the record update: defaultUserHooks {preConf = preConf, postConf = postConf} <interactive>:1:87: Failed to load interface for `Main': Bad interface file: Setup.hi Setup.hi: openBinaryFile: does not exist (No such file or directory)" Thanks, Brock

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Newbie: Haskell Sine Oddities
by Aditya Siram 01 May '06

01 May '06

The Sine function in the prelude is not behaving as I expected. In the following Hugs session I tested sin on 0, 90,180 & 360 degrees. Prelude> sin 0 0.0 --correct Prelude> sin (pi/2) 1.0 --correct Prelude> sin pi 1.22460635382238e-16 --WRONG! Prelude> sin (2*pi) -2.44921270764475e-16 --WRONG! Is this normal behaviour? Or am I using the trig functions in an unexpected way? Thanks... Deech

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