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RE: [Haskell-cafe] Set of reals...?
by Brian Beckman 30 Oct '04

30 Oct '04

Very pretty, Keean, though to get it to work in Hugs Nov 2002 I had to type the following uglier but equivalent syntax > myInterval = Interval { > isin = (\r -> > if r == 0.6 then True else > if r > 0.7 && r < 1.0 then True else > False ) > } -----Original Message----- From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Keean Schupke Sent: Wednesday, October 27, 2004 3:53 AM To: Stijn De Saeger Cc: haskell-cafe(a)haskell.org Subject: Re: [Haskell-cafe] Set of reals...? I think someone else mentioned using functions earlier, rather than a datatype why not define: data Interval = Interval { isin :: Float -> Bool } Then each range becomes a function definition, for example: myInterval = Interval { isin r | r == 0.6 = True | r > 0.7 && r < 1.0 = True | otherwise = False } Then you can test with: (isin myInterval 0.6) Keean _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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hugs segmentation fault
by Andrej Bauer 30 Oct '04

30 Oct '04

Hi, I am new to haskell, but otherwise experienced in programming languages. My first attempt at Haskell was this (on a Linux Debian) session with hugs: Type :? for help Prelude> :version -- Hugs Version November 2003 Prelude> let p = 1 : [2 * x | x <- p, x < 1] in p [1Segmentation fault Is it the norm for hugs to dump core like this? Or was I just very lucky to discover a bug? Best regards, Andrej

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Re: [Haskell-cafe] Set of reals...?
by MR K P SCHUPKE 29 Oct '04

29 Oct '04

>Keith Wansbrough wrote: >>Which brings me to a question: is there a better way to write -inf and >>+inf in Haskell than "-1/0" and "1/0"? Why not do it with types: data InfDbl = Dbl Double | PositiveInfinity | NegativeInfinity Keean.

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Re: [Haskell-cafe] Set of reals...?
by MR K P SCHUPKE 29 Oct '04

29 Oct '04

> | otherwise = contractSet (contract x0 y0:xs) ys I think you'll find the original is correct. The first two cases deal with non-overlapping ranges. The only remaining case is overlapping ranges, (partial and full overlap) both these cases are dealt with by contract, and as a result use up both the ranges at the head of both lists, sdo the merged range is prepended to the output list and the tail is calculated by passing the unused tails of both lists to contactSet... Keean.

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Re: [Haskell-cafe] Set of reals...?
by Keith Wansbrough 29 Oct '04

29 Oct '04

I forgot to mention: With regard to the dangerous practice of using "==" (as in your `elem` example) on Double, every computer scientist or programmer should read the following paper at some point in their training: David Goldberg, "What every computer scientist should know about floating-point arithmetic". ACM Computing Survey Volume 23 , Issue 1 (March 1991) Pages: 5 - 48. http://portal.acm.org/citation.cfm?id=103163 --KW 8-) -- Keith Wansbrough <kw217(a)cl.cam.ac.uk> http://www.cl.cam.ac.uk/users/kw217/ University of Cambridge Computer Laboratory.

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Calling Haskell from .Net Environment
by David Lo 29 Oct '04

29 Oct '04

Dear all, I'm new in Haskell. I need to port a haskell application written by someone else to be called by a .Net C# application. Please kindly advise on which option to pursue. Any helps will really be appreciated. Best Regards, David

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Are handles garbage-collected?
by Peter Simons 29 Oct '04

29 Oct '04

What happens when a System.IO.Handle falls out of scope without being explicitly hClosed? Is that a resource leak? Or will the RTS close the handle for me? Peter

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intToWord32
by John Velman 29 Oct '04

29 Oct '04

I'm trying to test TclHaskell under Hugs98-Nov2003, compiled from source. My current problem with getting it to work seems to be a failure to load the function intToWord32. Well, here is a partial transcript of a session run from within the TclHaskell src directory (after compiling TclPrim.so): ------------- bash-2.05b$ hugs __ __ __ __ ____ ___ _________________________________________ || || || || || || ||__ Hugs 98: Based on the Haskell 98 standard ||___|| ||__|| ||__|| __|| Copyright (c) 1994-2003 ||---|| ___|| World Wide Web: http://haskell.org/hugs || || Report bugs to: hugs-bugs(a)haskell.org || || Version: November 2003 _________________________________________ Haskell 98 mode: Restart with command line option -98 to enable extensions Type :? for help Prelude> :load "../demo/Demo.hs" ERROR "./TclPrim.hs":49 - Undefined variable "intToWord32" Word> :names Hugs.Array.! Hugs.Prelude.!! Hugs.Prelude.$ Hugs.Prelude.$! Hugs.Prelude.% Hugs.Prelude.&& Hugs.Prelude.() Hugs.Prelude.* Hugs.Prelude.** Hugs.Prelude.+ ....[snipped many lines] Hugs.Int.intToInt16 Hugs.Int.intToInt32 Hugs.Int.intToInt8 Hugs.Prelude.intToRatio Hugs.Word.intToWord16 Hugs.Word.intToWord32 ... [snipped the rest] ---------------------- So ':names' thinks there is such a thing, but the loader doesn't? I see that intToWord32 is declared with the keyword "primitive" -- i.e., specifically, from Word.hs in the library: primitive intToWord32 "intToWord32" :: Int -> Word32 I'm having trouble finding this syntax in the documentation, but, as I recall -- perhaps incorrectly -- I ran across some gopher documentation that indicated that the "intToWord32" in quotation marks was supposed to be the file name where the foreign primitive could be found. Using "locate" I can't find any files by the name of "intToWord32" in my system. Perhaps this is the Undefined variable in question. Finally, I'm running on a Linux system, Slackware 9, 400Mhz pentium II, 128 mb memory. Any advice or references to documentation will be appreciated. (By the way -- I decided to try TclHaskell because it seemed to be the simplest way to get a graphical interface to an application going! Any advice here will be appreciated as well.) Thanks, John Velman

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exitFailure under forkProcess
by John Goerzen 28 Oct '04

28 Oct '04

Hello, I'm having a little weird situation here. Whenever I call exitFailure under forkProcess, I get: (progname): forkProcess: uncaught exception Test program: import System.Exit import System.Posix.Process main = forkProcess exitFailure If you remove the forkProcess call, the program properly silently exits with exit code 1. I have no idea why it is displaying this message to stderr when called under forkProcess. I argue that it shouldn't. It is perfectly valid to return with an error code from a child process, and absolutely necessary in some cases when your later waitpid() call needs to know what happened. (Or, in Haskell, getProcessStatus()). Thoughts?

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Text.XML.HaXML.HaskellToXml DRIFT example
by S. Alexander Jacobson 28 Oct '04

28 Oct '04

Does someone have an example of how to use DRIFT to convert a Haskell type into XML? The documentation appears rather sparse... -Alex- ______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com

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