- Haskell-Cafe - Haskell.org

State Monad
by Georg Martius 04 Mar '04

04 Mar '04

Hi folks, I have a question to the State Monad or Monads in general - I'am not sure. Lets assume I have functions to transform strings. I can use the State Monad as follows: strTrans :: String -> String strTrans s = s ++ s f :: State String () f = do put "hallo" modify strTrans modify strTrans' ... Up to this point everything is clear. Now I have also functions to map from (a, String) -> (a,String). I could write: modifyT :: ((a, String) -> (a, String)) -> a -> State String a modifyT trans a = do str <- get let (a', str') = trans (a, str) put str' return a' f :: State String () f = do put "hallo" modify strTrans i <- modifyT strIntTrans 4 -- strIntTrans :: (Int, String) -> (Int, String) i' <- modifyT strIntTrans i ... But this is obviously awkward. How can I stick two Monads in each other? I could't figure out how to use StateT. Any help would be appreciated. Thanks! Georg

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a rant from a stoned suicidal person
by Chris Moline 04 Mar '04

04 Mar '04

i want to start off by apologizing. im lonely. i dont know anyone. anyone at all who is liek me. im different. everyone else is content to just watch tv all the time and then on weekends go and get drunk. im not. i am not threatening anything here when i say waht i am about to say. i know that waht i am about to say is not appropriate for haskell-cafe. i know this. but this needs to be said. im going to kill myself not right now. no you dont need to do anything. this is a plea. im begging you. ok see here im on my knees. my not-stoned self is going to hate me for this. but he needs the help and i know hes going to forgive me. because im him:) isnt that funny? i have no friends. none at all. im surrounded by motherfucking idiots *IDIOTS* i dont hate them. ok, im lying i hate them. i hate you. i hate this mothierfucking list. all i want is a goddamned friend who is *like me* i like thinking about shit. i like philosophy and math and all that stuff. dont suggest going to college. im sorry but ive found this out the hard way. im a loser. im a motherfucking loser. im too lazy. i have difficulty speling nad pronoundni big words. i do drugs. i know everyone says drugs are bad, but i like them. deal with it however you wnat. sned me to jail if you feel the need to. because i dont care anymroe do you hera that? I DONT FUCKING GIvE A ShIT ANYMORE im going to kill myself. i must. do you why i must? because im going insane. im surrounded by people but im completey alone. I HAVE NO IONE TO TAlK TO I AM LOSER I MUST DIE because im a loser so i am sendign this mesage to this list even though none of you care. none of you wnat ot deal with my problems. thats fine. i respect that. but i have noone and i cant find anyone and so i am begging PLEASE PUT ME OUT OF MY FUCKI*NG MISERY SHOOT ME * chris is crying * so anyways i am sorry for bothering you with this incoherent message but hers your mesage for the day FUCK YOU!

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Re: [Haskell-cafe] State Monad
by Wolfgang Jeltsch 04 Mar '04

04 Mar '04

Am Mittwoch, 3. März 2004 18:15 schrieb Georg Martius: > Thanks for your answer. I got it now. > It works with lift instead of liftM. Yes, of course. > Georg Wolfgang

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Trouble with [in,string]char* with hdirect
by Vincenzo aka Nick Name 03 Mar '04

03 Mar '04

Hi all, I am experimenting with hdirect for the first time, and I can't figure out how to call an haskell function of type String -> IO Int from C. I already can compile and use a function of type Char -> IO Int, so I assume to be using the right command line arguments. I have, in Math.idl ---- module Math { int munlink([in,string]char *s); }; ---- in Math.hs ---- module Math where munlink :: String -> IO Int munlink s = putStr ("Hey!" ++ s ++ "\n") >> return (-1) ---- This is the generated .hs file: module MathProxy where import Prelude (fromEnum, toEnum) import qualified Prelude import qualified Foreign.Ptr (Ptr) import qualified HDirect (unmarshallString) import qualified Math (munlink) munlink_proxy :: Prelude.String -> Prelude.IO Prelude.Int munlink_proxy = wrap_munlink Math.munlink foreign export ccall "munlink" munlink_proxy :: Foreign.Ptr.Ptr Prelude.String -> Prelude.IO Prelude.Int wrap_munlink :: (Prelude.String -> Prelude.IO Prelude.Int) -> Foreign.Ptr.Ptr Prelude.String -> Prelude.IO Prelude.Int wrap_munlink munlink_meth s = do s <- HDirect.unmarshallString s munlink_meth s I get a type error when compiling MathProxy.hs, and the strange thing is that commenting out the type declaration for "munlink_proxy" makes my program work like a charm. Errors from the compiler follow, any help will be highly appreciated. Vincenzo Ciancia ghc -O2 -fglasgow-exts Math.hs -c ihc -fshow-idl-in-comments -s -fhs-to-c --gen-headers -fuse-ints-everywhere -c Math.idl ghc -O2 -c main.c -o main.o ghc -O2 -fglasgow-exts -package hdirect MathProxy.hs -c MathProxy.hs:15: Couldn't match `GHC.Ptr.Ptr GHC.Base.String' against `GHC.Base.String' Expected type: GHC.Base.String -> GHC.IOBase.IO GHC.Base.Int Inferred type: GHC.Ptr.Ptr GHC.Base.String -> GHC.IOBase.IO GHC.Base.Int In the application `wrap_munlink Math.munlink' In the definition of `munlink_proxy': munlink_proxy = wrap_munlink Math.munlink MathProxy.hs:17: Couldn't match `GHC.Base.String' against `GHC.Ptr.Ptr GHC.Base.String' Expected type: GHC.Ptr.Ptr GHC.Base.String -> GHC.IOBase.IO GHC.Base.Int Inferred type: GHC.Base.String -> GHC.IOBase.IO GHC.Base.Int When checking declaration: foreign export ccall "munlink" munlink_proxy :: GHC.Ptr.Ptr GHC.Base.String -> GHC.IOBase.IO GHC.Base.Int

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[Haskell-cafe] ITCC 2004, April 5 -7 2004 - Call For Participation, Las Vegas, USA
by jolly＠egr.unlv.edu 29 Feb '04

29 Feb '04

My apologies if this is a duplicate email. CALL FOR PARTICIPATION - ITCC 2004 http://www.itcc.info International Conference on Information Technology- ITCC 2004 is going to be held in Las vegas, NV USA.ITCC is an international forum which brings together researchers and practitioners working on different aspects of Information Technology. It is a technical congregation where the latest theoretical and technological advances on Information Technology are presented and discussed. This year's conference will bring together the world's most respected authorities on Information Retrieval, Operating Systems, Networks,Image/Video Processing, Digital Library, Coding & Data Compression,Watermarking, Simulation, Computer Graphics, Information Technology: Education, Curriculum & Accreditation, Information/Website Security, Data Mining and plethora of IT related technologies.(Pls check the advanced Program at our website). Whether you are a speaker, tutorial presenter, and/or sponsor, you will find ITCC 2004 as the best forum to share and demonstrate your knowledge with the depth and breadth of Information Technology.For registration details,Visit our Website http://www.itcc.info/ Any questions/Comments may be forwarded to it(a)egr.unlv.edu We look forward to your participation and hope to see you in Las Vegas! If you do not wish to be included in this list, and/or do not wish to receive further announcements regarding ITCC, please reply at jolly(a)egr.unlv.edu Your email address will be removed immediately from the distribution list. With Best Regards Vasu Jolly The ITCC 2004 Conference Secretary

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Outstanding context : (Num b, Random b)
by "horsh 27 Feb '04

27 Feb '04

Hi, I am very new to haskell. Could anyone please explain why these two things are not equivalent: m2 = do a <- (drawInt 1 10) print a drawInt :: Int -> Int -> IO Int drawInt x y = getStdRandom (randomR (x,y)) m1 = do b <- getStdRandom (randomR (1,10)) print b the second one produces *** Binding : m1 *** Outstanding context : (Num b, Random b) in Hugs. thanks horsh

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Perl-ish =~ operator
by ozone＠algorithm.com.au 24 Feb '04

24 Feb '04

In my effort to turn Haskell into a language more like Perl (muahaha)[1], I got a bit fed up and implemented something like Perl 5's =~ binding operator (a.k.a. "regex" operator); I thought maybe somebody else here might find it useful. Perl has the concept of 'contexts': a function does something different depending on what type its caller expects back from the function. Sounds like a perfect abuse of type classes, to me :). Code follows: --- {-# OPTIONS -fglasgow-exts #-} {- Need this for "instance Foo [String]" declarations -} module PLRE where -- Perl-Like Regular Expressions import Text.Regex -- Perl-Like =~ operator, which changes behaviour depending on its calling -- context class RegExContext a where (=~) :: String -> String -> a instance RegExContext Bool where s =~ re = case matchRegex (mkRegex re) s of Nothing -> False Just x -> True instance RegExContext [String] where s =~ re = case matchRegex (mkRegex re) s of Nothing -> [] Just x -> x boolContextTest string regEx = case string =~ regEx of True -> print True False -> print False stringListContextTest string regEx = case string =~ regEx of (a:x) -> print ("First match: " ++ a) _ -> error "No subexpression matches" --- Some test output for you: *PLRE> boolContextTest "foo" "^f" True *PLRE> boolContextTest "foo" "^g" False *PLRE> stringListContextTest "foo" "^(.)" "First match: f" *PLRE> stringListContextTest "goo" "^(.)" "First match: g" *PLRE> stringListContextTest "" "^(.)" *** Exception: No subexpression matches Note that you have a fairly severe restriction if you want to use =~ in your code: the Haskell compiler must be able to determine a concrete type for the context that =~ is used in. i.e. if stringListContextTest was defined as: stringListContextTest string regEx = case string =~ regEx of (a:x) -> print a _ -> error "No subexpression matches" The compiler can't concretise a type for 'a', and it'll complain about not having an instance for RegExContext [a] (which is fair enough). Even with this restriction, I'm sure it'll still be useful. It shouldn't be a bit leap to define other Perl-ish operators in this fashion, such as !~, or even s/.../. Have the appropriate amount of fun! 1. Actually, I wanted to turn Haskell into a language more suitable for text processing, but that doesn't sound as evil. -- % Andre Pang : trust.in.love.to.save

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RE: [Haskell-cafe] More help for the newb
by Matthew Morvant 22 Feb '04

22 Feb '04

Thanks for the catching the typo. However, I keep getting type errors. The error that I get seems self-explanaotry, by telling me what to change the type to. But when I change it I get another error that seems to tell me to change it back. -----Original Message----- From: Philippa Cowderoy [mailto:flippa@flippac.org] Sent: Saturday, February 21, 2004 10:02 AM To: Matthew Morvant Subject: Re: [Haskell-cafe] More help for the newb On Sat, 21 Feb 2004, Matthew Morvant wrote: > 36 code3 :: [b] -> [Char] > > 37 code3 = do{char '!'; digit; char 's'; many (do char 's'); return "Suc"} > +++ do{char '%'; char 's'; digit; many (do digit): return "Suc"} > You appear to have a colon instead of a semicolon, which isn't good. Consider "many digit" rather than "many (do digit)", too. -- flippa(a)flippac.org

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Thinner secure email?
by Justin Walsh 22 Feb '04

22 Feb '04

Re: my last goof up Hi, I know, being a totally ignorant Haskell newbie, that I should soon get to know my pecking order. But this e-paper shuffle is so damned annoying. i.e. "Hello World" In .txt mode is 11 bytes. In NoteTab Lite .txt (with url; say "Ripose.com.au") is 28 bytes In WordPad .doc 4,603 kbytes In MS Word .doc 19,456 kbytes. I would have though that the first project might have been the email itself. X does not seem to have been considered here. Why is so much rubbish data going down the line? Am I asking too many question? On the squeak-dev list I would be getting; Well $#1*? stop winging and fix it. I would, if I knew that Haskell is the right tool to use, if a tool is really needed at all. Does anybody get my reasoning? At my age 64.5 I'm too old to start another language, then find out that it's another dead end. I'm not trolling (I forgot to mention, I hate trolls too). With respect Justin walsh --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com) Version: 6.0.585 / Virus Database: 370 - Release Date: 2/11/04

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5 Kb limit with notetab lite attachment
by Justin Walsh 21 Feb '04

21 Feb '04

Is this better? Please note that the entire email I first sent is 7,153 bytes and in attachment This one plus attachment is under 5 kb. I am using notetab lite. How does that rank with security i.e. I don't want to scare people with attachments. Note: I am not good at this sort of thing. Subject: Your message to Haskell-Cafe awaits moderator approval > Your mail to 'Haskell-Cafe' with the subject > > Rational Haskell? > > Is being held until the list moderator can review it for approval. > > The reason it is being held: > > Message body is too big: 6180 bytes with a limit of 5 KB >

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