November 2001 - Haskell-Cafe

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

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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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RE: Here is a tiny idea for a QT based GUI library
by Simon Marlow 13 Nov '01

13 Nov '01

> -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > On Tuesday 13 November 2001 06:18, Manuel M. T. Chakravarty wrote: > > The time consuming part in creating such a system are the C > > bindings, not the XML stuff. In fact, similar functionality > > is available for GTK+ already for a long while. The cool > > point about it is that the graphical interface builder Glade > > > > http://glade.gnome.org/ > > > > can generate these XML files, which you just load into your > > application using a library called libglade (that > > corresponds to the QWidgetFactory that you mention above). > > I guess, KDE's interface builder can do the same. > > > > Yes, I know. I used to be a poor GTK+ coder myself. :) I'm a konvert. > > The C bindings are already available, so you can just use > them it seems. The point Manuel was making is that it takes a lot of time & effort to code up the Haskell binding to the C libraries. Just having a way to load up the interface from the XML spec isn't enough - you need a complete enough binding to be able to manipulate the interface from Haskell at run time. This is not a GTK vs. Qt argument. We *have* most of a GTK+ binding and it would be a shame to divide our efforts when said efforts are in short supply. When we have one complete GUI binding, then let's think about making another one. Cheers, Simon

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Having contraints like 'Fractional Int => IO ()'
by Jesper Louis Andersen 13 Nov '01

13 Nov '01

This problem has had my attention for a while now. I hope someone would like to help me out on the problem. I have a simple average function defined as: mean :: (Fractional a) => [a] -> a mean l = (sum l)/ fromIntegral (length l) Which imposes a type constraint (of course). My problem is, that i cannot ``let go'' of this constraint. The constraint travels through the call tree of my functions and ends at the top-level function, which is defined as a Monad (I need some IO operations on some files). Now, I have tried to solve the problem, but the closest I have got is to make my main function be of type: main :: Fractional Int => IO () But that is not something that Hugs likes as it tells me that I have a ``unresolved overloading'' at the expression ``main'' on the type. So... Is there a way to get rid of the constraint by converting the function to something more sensible. I seem to have missed a point here, as I have migrated from Standard ML to Haskell (the latter being a far more complicated language it seems). As SML doesn't have type classes, they seem to have bitten me hard. If anyone could point to the relevant information, it would be very nice. Thanks in advance -- Jesper

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Re: Having contraints like 'Fractional Int => IO ()'
by Ashley Yakeley 13 Nov '01

13 Nov '01

At 2001-11-12 18:06, Jesper Louis Andersen wrote: >mean :: (Fractional a) => [a] -> a >mean l = (sum l)/ fromIntegral (length l) > >Which imposes a type constraint (of course). My problem is, that i >cannot ``let go'' of this constraint. ... >main :: Fractional Int => IO () It sounds like you're trying to use your 'mean' function on Ints. Int is not a Fractional type (unless you make it one), and so '/' isn't defined on it. What's "mean [3::Int,4::Int]"? It can't be "3.5::Int" because 3.5 is not an integer and so not an Int. -- Ashley Yakeley, Seattle WA

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Haskell coding environment for windows users?
by Srineet 13 Nov '01

13 Nov '01

Hi, I am not sure whether this is the right place to ask this question. I want to know what's the Haskell coding environment used by GHC users on windows? What 's the preferred editor? Is there any Haskell tags for vim? Also, is there any program which will convert Haskell modules to HTML with cross-links so that one can use the HTML files to browse the source? Please let me know. Thanks. Bye. - Srineet.

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