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Re: Why no exceptions in Haskell?
by Marcin 'Qrczak' Kowalczyk 23 Nov '01

23 Nov '01

Fri, 23 Nov 2001 07:12:10 +1100, Fergus Henderson <fjh(a)cs.mu.oz.au> pisze: > ... and the main reason why Haskell 98 didn't incorporate this is because, > well, 98 was before 99 ;-). In order for exceptions to be practical, one should be able to throw other types than the builtin IOError which roughly corresponds to errno in C. In GHC Dynamic is used for this. IMHO exceptions should not be standarized without such capability. I don't like Dynamic much but no other solution has been designed for Haskell. Maybe some kind of extensible datatypes would be better, preferably not limited to exceptions. It has other problems though, for example how to define functions like (==) for extensible datatypes? A static type system sometimes do get in the way! Python people have some right in saying this. (But IMHO they are wrong in saying that very small amount of errors is catched by static typing.) -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ QRCZAK

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VIRUS ALERT Read this first. (Was Fwd: Re some MP3s here hehe ;-) )
by Theodore Norvell 23 Nov '01

23 Nov '01

The message entitled Fwd: Re some MP3s here hehe ;-) not only doesn't belong on the list, but also contains a virus. Happy Haskelling, Theodore Norvell

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Fw: Re: some mp3s here hehe ;-)
by daan＠cs.uu.nl 22 Nov '01

22 Nov '01

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Why no exceptions in Haskell?
by Michael Marte 22 Nov '01

22 Nov '01

Hello *, I am just curious: Why does Haskell not provide exceptions a la SML? Why does only the IO monad allow for exceptions? Michael

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Haskell and ASN.1
by Dmitry Astapov 21 Nov '01

21 Nov '01

Two keywords mentioned in 'Subject' - does it ring the bell for someone? Any usefull links? I'm interested in something like Erlang's "asn1" compiler or snacc/C++ -- that is, I'm looking for translator from ASN.1 layout into native Haskell data type, along with I/O functions. Seems like pretty easy thing to write myself, though, but I dont want to reinvent the wheel, if there is any. -- Dmitry Astapov //ADEpt E-mail: adept(a)umc.com.ua GPG KeyID/fprint: F5D7639D/CA36 E6C4 815D 434D 0498 2B08 7867 4860 F5D7 639D

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Re: Haskell and ASN.1
by Steinitz, Dominic J 19 Nov '01

19 Nov '01

I have done some work on this with colleagues at Kingston University. Nothing automatic though. There is a translation scheme but you have to define an encode and decode function for each ASN.1 type. I assume you want to use to BER and all that is handled for you. I'm tied up at the moment but I'll try and send you something by the end of the week. I don't think parsing ASN.1 is trivial but if you were thinking of doing an automatic translator I'd be very interested. Dominic. adept(a)umc.com.ua on 19/11/2001 08:55:00 To: haskell-cafe cc: bcc: Dominic Steinitz Subject: Haskell and ASN.1 Two keywords mentioned in 'Subject' - does it ring the bell for someone? Any usefull links? I'm interested in something like Erlang's "asn1" compiler or snacc/C++ -- that is, I'm looking for translator from ASN.1 layout into native Haskell data type, along with I/O functions. Seems like pretty easy thing to write myself, though, but I dont want to reinvent the wheel, if there is any. -- Dmitry Astapov //ADEpt E-mail: adept(a)umc.com.ua GPG KeyID/fprint: F5D7639D/CA36 E6C4 815D 434D 0498 2B08 7867 4860 F5D7 639D _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ------------------------------------------------------------------------------------------------- To receive our special fares directly by email, register at http://www.britishairways.com/registration

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(no subject)
by Ciaran Dunn 16 Nov '01

16 Nov '01

__________________________________________________________________ Get your free Australian email account at http://www.start.com.au

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Re: Closure
by Juan Carlos Arevalo-Baeza 14 Nov '01

14 Nov '01

On Wed, 14 Nov 2001 12:05:44 +0000, Keith Wansbrough wrote: >> >Yeap, that's exactly what I thought (I think - what exactly is a 'closure'? >> >> :) I'll try to tackle this one. I have always had trouble understanding this concept, and I haven't been able to find a good definition or description on the web. It's always assumed you know what's being talked about, for some reason. > >Please submit your explanation to FOLDOC or the Haskell Wiki (or both): > > http://wombat.doc.ic.ac.uk/foldoc/index.html > http://haskell.org/wiki/wiki > >Otherwise your carefully-crafted explanation will end up lost deep in a mail archive somewhere and never be seen. :) I'll be happy to. I just don't know how accurate my explanation was. I do not claim to know what a closure is. Never read a single definition of it. This whole explanation is, at best, an educated guess built from all the contexts where I've heard it mentioned. I'll wait for some confirmation from somebody who knows. >Thanks! No problem. There's nothing like trying to explain something to be able to understand it more fully :) Salutaciones, JCAB email: jcab(a)roningames.com ICQ: 101728263 The Rumblings are back: http://www.JCABs-Rumblings.com

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Hugs 1.4 sourcecode availability?
by Christopher Milton 13 Nov '01

13 Nov '01

Does anyone here still have a tarball of Hugs 1.4 (any release)? I seem to have lost my copies somewhere along the line. I like to make comparisons between different releases sometimes. (I still play with Gofer, too.) -- Christopher Milton cmiltonperl(a)yahoo.com Colorado Springs, Colorado, USA http://www.geocities.com/cmiltonperl itinerant programmer __________________________________________________ Do You Yahoo!? Find the one for you at Yahoo! Personals http://personals.yahoo.com

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Re: Counting recursive calls
by John Hughes 13 Nov '01

13 Nov '01

Hi all, got some questions on recursive functions. I got a simple recursive function (f3) In *some* situations I'll want to know how many recursive calls did it make. I came up with two simple implementations to do that (f1) and (f2) f [] w = (w,0) f (x:xs) w = (nextw, steps+1) where (nextw, steps) = f xs (g x w) f2 [] k w = (w,k) f2 (x:xs) k w = f2 xs (k+1) (g x w) f3 [] w = w f3 (x:xs) w = f3 xs (g x w) ... Anyway like I said I don't *always* want to know the n. of steps, so I could chose either to: - use 2 different functions, one when I want the n. of steps (f or f2) another one when I don't need it (f3) - use just one function (f or f2) if I don't need the n. of steps, use fst. The second choice seemed to make more sense to me. Lazy evaluation should do the trick, and the n. of steps would not have to be evaluated, so efficiency-wise it would be the same as calling f3. Oh oh --- lazy evaluation isn't what you want here! Certainly it will avoid *computing* the number of steps, but it will do so by building up a gigantic unevaluated closure of the form (((((((((0+1)+1)+1)+1)+1)+1)+1)+1)+1). So you'll be using memory linear in the running time -- not good. Moreover, when you finally come to evaluate that closure, you'll need a *huge* stack to do it on. ... [2] Any tips on which function(s) should I choose, or any way to make them more efficient. Most efficient will be to force strict evaluation of the count. In GHC you can do that by using an unboxed integer. ----- (**) would I get a different behavior if I had compiled the program. I've had some problems when trying to compile and use getCPUTime. Some stack overflows for big values of w, and for smaller values 0 in the execution time... I'll try to figure out what I'm doing wrong here... What did I say about the stack? If you compile your code, and especially if you use an unboxed integer as I suggest, then the cost for counting steps should be very low. In particular, it will certainly be cheaper to *compute* k+1 (single unboxed addition) than to build a suspension for it (memory allocation). You might get a different result in the interpreter, because of all the interpretation overhead, but in compiled code there should be no question about it. John

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