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Newbied question on IO Monad
by Sara Kenedy 12 Sep '06

12 Sep '06

Hello all, update :: String -> String update sss = ... main = do writeFile "myFile.txt" sss x <- callSystem "myFile.txt" y <- openFile "result.txt" ReadMode zzz <- hGetContents y return zzz I know that function main returns IO String, function update returns String. And my purpose is to get the string zzz from main for the value return of function update. But I do not know which way I can do. Sorry if the question seems ridiculous. Thanks for any help. S.

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RE: [Haskell] Re: H/Direct (HaskellDirect) still maintained?
by Simon Marlow 12 Sep '06

12 Sep '06

On 08 September 2006 17:35, Andreas Marth wrote: > Now that I used a more recent ghc (6.4.2 which has cabal-1.1.4 > installed) I did install comlib with it. > But I am a bit surprised because it did not generate a ihc. So how do > I get a Proxy from an idl-file now? > > If I look at the files in vsHaskell they state "Automatically > generated by HaskellDirect (ihc.exe) ....". > Does anybody know how to generate ihc.exe? comlib is just the COM interface library, it doesn't include ihc (the IDL compiler, which is part of H/Direct). Some of the the Visual Haskell sources were originally generated by ihc, but since then we have modified the sources by hand, and we're no longer using ihc. You should be able to use these files as example code to see how to write your COM interface code. It's a lot of tedious boilerplate, unfortunately. Maybe someone will resurrect or write a replacement for ihc someday. Cheers, Simon

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Heap profiling
by Mark Goldman 12 Sep '06

12 Sep '06

Does anyone know if there is a way around the 20 charachter identifier limitation when heap profiling? I have a number of identifiers that indistinguishably break that limit. -mdg -- Our problems are mostly behind us, now all we have to do is fight the solutions.

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Re[2]: [Haskell] Proposal: unification of style of function/data/type/class definitions
by Bulat Ziganshin 11 Sep '06

11 Sep '06

Hello Taral, Sunday, September 10, 2006, 9:45:33 PM, you wrote: >> data Expr t = If (Expr Bool) (Expr t) (Expr t) >> Expr Int = Lit Int >> Expr Bool | Eq t = Eq (Expr t) (Expr t) > I find this somewhat unreadable due to the implicit "t" parameter not > showing up on the left-hand side... if you mean last line, i tend to agree. i was just a little impulsive and don't mentioned that we define existential here :) it may look as Expr Bool = Eq (Expr t) (Expr t) | Eq t Brian Hulley developed here an idea about implicit "forall" declaration just before class restrictions involving this variable, so it will be equivalent to: Expr Bool = Eq (Expr t) (Expr t) | forall t . Eq t -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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HaXml and ghci unresolved symbol
by Andrea Rossato 11 Sep '06

11 Sep '06

Hello! probably it's me, but I cannot understand what I'm doing wrong. I'm trying to learn HaXml. I've never used it before and I never did xml processing in Haskell. So I'm a total newbie!! I downloaded and compiled. Everything seems fine. I'm also able to run some examples in the related directory of the source tree. Then I try doing something myself. Very simply, a document with just one element: module Xml where import Text.XML.HaXml xml = "<a>test</a>" doc = xmlParse "test" xml elemName (Document prolog _ (Elem name _ _) _) = name When I try it: *Xml> elemName doc I get a message I've never got before (I'm a newbie!) and I don't know whether the problem is in my code (this would be my first guess), in HaXml or in GHCi. And so I cannot even start understanding out to solve it: During interactive linking, GHCi couldn't find the following symbol: TextziXMLziHaXmlziParse_xmlParse_closure This may be due to you not asking GHCi to load extra object files, archives or DLLs needed by your current session. Restart GHCi, specifying the missing library using the -L/path/to/object/dir and -lmissinglibname flags, or simply by naming the relevant files on the GHCi command line. Alternatively, this link failure might indicate a bug in GHCi. If you suspect the latter, please send a bug report to: glasgow-haskell-bugs(a)haskell.org *Xml> xmlParse is defined in Text.Xml.HaXml (xmlParse :: String -> String -> Document) and it should be imported by Text.XML.HaXml. Can you give me please some directions? Thanks for your kind attention.

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Nice cygwin application to be used with ghci
by Maurício 11 Sep '06

11 Sep '06

Hi, I've just uploaded a package ('rlwrap') to cygwin that I like to use with ghci. You can use it like this: rlwrap ghcii.sh and then you will use ghci as if it were readline aware (i.e., you can press up arrow to get last typed lines etc.). 'rlwrap' is very stable and I never had unexpected results while using it. Since the issue of ghci integration with terminals has been raised here sometimes, I thought some guys here would be interested (actually, I found rlwrap looking for a better way to use ghci). Best, Maurício

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Re: [Haskell] Re: Proposal: unification of style of function/data/type/class definitions
by Neil Mitchell 10 Sep '06

10 Sep '06

Hi > I don't see the problem. You can read all of Bulat's > examples as "'thing being declared' 'relationship' 'value' > given that 'context'", so this one is ""sequence" has type > "[m a] -> m [a]" given that "m" is a "Monad"". So viewed > that way, they're all consistent with each other. How about name, context, value as the three elements: class <name> | <context> where <value> data <name> | <context> = <value> type <name> | <context> = <value> <name> | <context> :: <value> For class and data, you can argue that it isn't really a <value>, its <inner> or something. But type definately has a <value>. And if you want data and type consistent, you need to put them like that. And then, if you want functions consistent with types, you have to do the above. Or at least thats what my brain interprets as logical, and on the plus side it changes data/type/class which I personally don't like, but doesn't change function declarations, which I am not aware of anyone having issue with. Thanks Neil

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Re: [Haskell-cafe] HaXml and ghci unresolved symbol
by Andrea Rossato 10 Sep '06

10 Sep '06

Il Sat, Sep 09, 2006 at 05:20:55PM -0400, Mark T.B. Carroll ebbe a scrivere: > FWIW I have the same problem - I can't use HaXml with ghci. > So it's not just you. (-: Indeed! So I found my first bug in ghc... And now I'll dig into ghc bug reports to see if someone is working on the problem... This is going to be hard, but it's the way you start learning something....;-) Thanks for your kind attention. Below the full error messages with the code producing them. Andrea The code below works fine with Hugs: Main> :load xml.hs Main> main prova Main> If I try to compile it with ghc I get this: [11:16:06][andrea@laptop:~/devel/haskell/xml]$ ghc --make xml.hs -package HaXml -package hxml -o prova Chasing modules from: xml.hs Compiling Main ( xml.hs, xml.o ) Linking ... /usr/local/lib/hxml-0.2/lib/libhxml.a(HaXmlAdapter.o)(.text+0x12c1): In function `spZc_dflt': : undefined reference to `TextziXMLziHaXmlziPretty_zdwelement_infó /usr/local/lib/hxml-0.2/lib/libhxml.a(HaXmlAdapter.o)(.text+0x1435): In function `spZy_dflt': : undefined reference to `TextziXMLziHaXmlziPretty_zdwelement_infó /usr/local/lib/hxml-0.2/lib/libhxml.a(HaXmlAdapter.o)(.rodata+0xa4): undefined reference to `TextziXMLziHaXmlziPretty_zdwelement_closure` /usr/local/lib/hxml-0.2/lib/libhxml.a(HaXmlAdapter.o)(.rodata+0xc4): undefined reference to `TextziXMLziHaXmlziPretty_zdwelement_closure` collect2: ld returned 1 exit status Loading HaXml and hxml in ghci will produce: [11:15:39][andrea@laptop:~/devel/haskell/xml]$ ghci -package HaXml -package hxml ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 6.4.2, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Loading package base-1.0 ... linking ... done. Loading package Cabal-1.1.4 ... linking ... done. Loading package haskell98-1.0 ... linking ... done. Loading package haskell-src-1.0 ... linking ... done. Loading package HaXml-1.13.1 ... linking ... done. Loading package hxml-0.2 ... linking ... ghc-6.4.2: /usr/local/lib/hxml-0.2/lib/hxml.o: unknown symbol `TextziXMLziHaXmlziTypes_AttValue_con_info` ghc-6.4.2: unable to load package `hxml-0.2' This is the code: module Main where import Text.XML.HaXml import HaXmlAdapter -- from hxml xml = "<a>prova</a>" doc = xmlParse "tmp" xml getContent (Document prolog _ (Elem name _ content) _) = content cont = getContent doc showDoc :: [Content] -> IO () showDoc [] = return () showDoc (x:xs) = do putStrLn $ showContent x showDoc xs main = showDoc cont

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nondet function
by Ashley Yakeley 10 Sep '06

10 Sep '06

Is it possible to write nondet? nondet :: a -> a -> a nondet _|_ _|_ = _|_ nondet _|_ q = q nondet p _|_ = p nondet p q = p or q nondet evaluates its arguments in parallel, and returns the first one of them to evaluate. It's thus a bit different from the "par" of GPH. This isn't referentially transparent, of course, but maybe it could be written in the IO monad: nondet p q = unsafePerformIO (getnondet p q) getnondet :: a -> a -> IO a -- Ashley Yakeley, Seattle WA

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Re[2]: [Haskell] Proposal: unification of style of function/data/type/class definitions
by Bulat Ziganshin 10 Sep '06

10 Sep '06

Hello Neil, Sunday, September 10, 2006, 2:21:50 PM, you wrote: >> class Monad m | Functor m, Monoid m where ... > It also makes grep'ing easier. yes, i also had problems finding class declarations in base package >> sequence :: [m a] -> m [a] | Monad m > I don't like this. In the other two instances you are moving the most > important information (the name of the thing) to the front. In this > the name is at the front, but the instances move to the end, which > isn't really where they should be. And following the function | rule > function | predicates = body > I would have said that logically, you want: > sequence | Monad m :: [m a] -> m [a] > (of course, this might present a problem for parsing...) > Note this also makes sense compared to your: > data Data | Classes = Alternatives you have omitted "patterns, or parameters shape" part: function shapes_of_parameters | guards_for_parameters = result so, in my proposal: data T a b | Eq a, Monad b = .... and function signature obey the same rule - first write shape of function type, then narrow type variables used to some classes: addEncoding :: Encoding m -> h -> m (WithEncoding m h) | Monad m, ByteStream m h Of course, that's more important is readability. it's discussible whether we need to know that m is monad and h is stream before reading shape of function type btw, the following is anyway most readable: sequence :: [Monad a] -> Monad [a] ;) -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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