- Haskell - Haskell.org

Re: Efficient way to perform independent processing of list from IO?
by Marcin 'Qrczak' Kowalczyk 29 Aug '01

29 Aug '01

Wed, 29 Aug 2001 12:07:47 -0600, mctague(a)one.net <mctague(a)one.net> pisze: > return (read string) > but with this approach, all the data are read before they are written, read is the problem. It wants to see if the whole string can be parsed before deciding whether to deliver a result or signal error. It can be solved by manually splitting the input (e.g. on commas, stripping also initial '[' and final ']') and reading each part separately. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK

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Re: Prefix negation
by Pixel 29 Aug '01

29 Aug '01

"Marcin 'Qrczak' Kowalczyk" <qrczak(a)knm.org.pl> writes: > Wed, 29 Aug 2001 16:34:52 +0200, Rijk-Jan van Haaften <rjchaaft(a)cs.uu.nl> pisze: > > > -3 ^ 2 = -9 > > > > In most programming languages as well as in mathematics > > it is quite unusual to have infix operators with a higher > > priority than prefix operators. > > I agree that many languages got it wrong :-) many languages have it the haskell way: -9: perl, ruby, python, haskell 9: ocaml > In mathematics the prefix negation is handled like in Haskell: > > 2 > -3 = -9 -3^2 = -9 doesn't bother me -3 ^ 2 = -9 do bother me :-(

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Prefix negation
by Rijk-Jan van Haaften 29 Aug '01

29 Aug '01

Section 3.4 (Expressions.Operator applications) of the language report, says this about prefix negation: Prefix negation has the same precedence as the infix operator - defined in the Prelude (see Table 1). This is not what I expected (and not what other languages mostly do). One of the consequences is that -3 ^ 2 = -9 In most programming languages as well as in mathematics it is quite unusual to have infix operators with a higher priority than prefix operators. Why is this rule chosen in Haskell? Thanks in advance, Rijk-Jan

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Re: ANN: C->Haskell 0.9.9 "Blue Ginger"
by Marcin 'Qrczak' Kowalczyk 29 Aug '01

29 Aug '01

Wed, 29 Aug 2001 15:20:55 +1000, Manuel M. T. Chakravarty <chak(a)cse.unsw.edu.au> pisze: > Thanks for pointing it out. It is, however, strictly a Gtk+HS > problem. C->Haskell already deals with GHC's new convention. They were both in a gtk+hs's own .hs file and in foreign calls produced from .chs by c2hs-0.9.9. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK

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Re: ANN: ports 0.3.3 "Autumn Sun"
by Marcin 'Qrczak' Kowalczyk 29 Aug '01

29 Aug '01

Wed, 29 Aug 2001 15:21:22 +1000, Manuel M. T. Chakravarty <chak(a)cse.unsw.edu.au> pisze: > Hmm, I had an application where I absolutely wanted to kill > it (ie, prevent it from surviving by registering a signal > handler). But I agree, in general you probably want a > sigTERM. So, I guess we need an additional argument here. I still think that it's enough to have sigTERM here (would be some other default method of killing on non-POSIX systems) *and* the ability to reach pids of processes for direct manipulation. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK

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Re: ANN: ports 0.3.3 "Autumn Sun"
by Marcin 'Qrczak' Kowalczyk 29 Aug '01

29 Aug '01

Tue, 28 Aug 2001 18:30:21 +1000, Manuel M. T. Chakravarty <chak(a)cse.unsw.edu.au> pisze: > It now has experiemental support for process management. IMHO processes should not be killed using killProcess (sigKILL). Better use softwareTermination (sigTERM). -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK

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Re: ANN: C->Haskell 0.9.9 "Blue Ginger"
by Marcin 'Qrczak' Kowalczyk 29 Aug '01

29 Aug '01

Tue, 28 Aug 2001 00:39:13 +1000, Manuel M. T. Chakravarty <chak(a)cse.unsw.edu.au> pisze: > I am pleased to announce version 0.9.9 "Blue Ginger" of the > C interface generator C->Haskell. gtk+hs doesn't compile under ghc-5.01 because of "library" "function" pairs in foreign imports which are no longer supported. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK

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RE: Numeric literals: Haskell 98
by Simon Peyton-Jones 28 Aug '01

28 Aug '01

Mark Caroll points out that the Haskell 98 Numeric library should be able to read the numbers "Infinity" and "NaN", which can be printed by formatRealFloat. So I propose the following ammendment to the Numeric library: Page 16, Section 4, Numeric library. In the definition of readFloat, after "... (k,t) <- readExpr s]" add ++ [ (0/0, t) | ("NaN",t) <- lex r] ++ [ (1/0, t) | ("Infinity",t) <- lex r] However, the Haskell language report seems to say that it's optional for a Haskell implementation to actually support NaNs and Inifinity. I don't propose to change this, though it's a bit unsatisfactory because one can't rely on it. I'm proposing the above change to the Numeric library just for consistency: if 'show' can print "Infinitity" (and it can), then 'read' should be able to read it. Thanks, Mark. Simon | -----Original Message----- | From: Mark Carroll [mailto:mark@chaos.x-philes.com] | Sent: 27 August 2001 20:40 | To: haskell-cafe(a)haskell.org | Subject: Numeric literals | | | Today's other question has to do with numeric literals. How | do I write literals for interesting IEEE values, e.g. | | Prelude> x | Infinity | Prelude> :type x | Double | Prelude> (read "Infinity") :: Double | *** Exception: Ratio.%: zero denominator | Prelude> | | ...? | | If I'm just missing something obvious in the standard | documentation, please feel free to just give me a citation. | I've already tried sections 2.5 and 6.4.1 of the Haskell | Report, etc. though. | | Thanks. | | -- Mark | | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe |

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ANN: ports 0.3.3 "Autumn Sun"
by Manuel M. T. Chakravarty 28 Aug '01

28 Aug '01

There is a new version of the Haskell Ports Library available at http://www.cse.unsw.edu.au/~chak/haskell/ports/ It now has experiemental support for process management. You can create a process that gets its stdin from a lazy string and pumps its stdout and stderr into two ports. There are a couple of combinators that facilitate Unix-pipe-like behaviour and you can wait for the exit code of a subprocess in a single Haskell thread without blocking all the others. It's all quite a hackery and still pretty experimental, but as the subprocess management question did come up a couple of times recently, I thought I share what I have at the moment with the rest of you. Cheers, Manuel PS: This requires GHC as it relies on preemptive concurrency, exceptions, and the POSIX libs.

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ANN: C->Haskell 0.9.9 "Blue Ginger"
by Manuel M. T. Chakravarty 27 Aug '01

27 Aug '01

I am pleased to announce version 0.9.9 "Blue Ginger" of the C interface generator C->Haskell. Among bug fixes, the system includes the following features wrt to the previous release: * Sizeof hooks (to compute the size of C types in Haskell) * Local prefix for enum hooks * Pointer hooks (abstract pointers, foreign pointers, and stable pointer) * Support for parametrised pointers * Extended documentation including a description of all binding hooks * Deriving option for enum hooks * Adapted to GHC 5.0 This release greatly benefitted from code contributions by Armin Sander and Axel Simon. Moreover, a number of people have been very helpful in reporting and, in some cases, fixing bugs. Thanks guys! More information as well as source and binary packages are available from http://www.cse.unsw.edu.au/~chak/haskell/c2hs/ Happy Hacking! Manuel

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