- Haskell-Cafe - Haskell.org

class method name scope
by Jason Dusek 05 Dec '08

05 Dec '08

What proposals are out there to address the issue of scoping class methods? I always feel I must be careful, when exposing a class definition that I want clients to be able to extend, that I mustn't step on the namespace with semantically appropriate but overly general names (e.g. 'run'). It'd be nice if class method names were module scoped and could be qualified. -- _jsn

2 4

Re: [Haskell-cafe] detecting socket closure in haskell
by Donn Cave 05 Dec '08

05 Dec '08

Quoth "Tim Docker" <timd(a)macquarie.com.au>: | Hence I seem to need a means of detecting that a socket has been closed | remotely, without actually reading from it. . Does anyone know how to do | this? One reference I've found is this: | | http://stefan.buettcher.org/cs/conn_closed.html | | Apparently recv() with appropriate flags can detect this - though I'm | not convinced that the code as shown on that page doesn't busy wait when | there is unread data from the client. Right - poll() will still find data there, after the "peek", so you'll be running that loop as fast as you can make the 2 system calls, and what I think might be worse, it should keep reading the same 32 bytes at the head of the buffer ... and never notice the connection close. Well, I haven't tried it, but this solution doesn't make sense to me. | Any tips or pointers? Perhaps what I'm trying to do is not currently | possible in haskell, without using the FFI (which would be ok). Or | perhaps it's not possible in linux at all. I don't know of a way to do it in C. I think it's very likely that the kernel finds out only after all the data has been delivered through the network interface, so by the time you can even in principle know that the connection closed, all the data will either have been processed by the client or reside in memory somewhere on the computer. I guess you might try your buffering thread, and if you're really worried about undue amounts of buffered data, set some maximum size, where you either stop trying to notice end-of-file, or switch to another storage medium (e.g., disk file.) Donn

1 0

detecting socket closure in haskell
by Tim Docker 04 Dec '08

04 Dec '08

This is a haskell + networking question... I have a multi threaded haskell server, which accepts client connections, processes their requests, and returns results. It currently works as desired, except where a client drops a connection whilst the server is processing a request. In this circumstance, the server currently doesn't notice that the client has gone until it finishes the processing and attempt to read the next request. I'd like to change it so that the request is aborted as soon as the client disconnects. One way of doing this would would be to maintain a separate thread that is always reading from the client, and buffers until the main thread needs the information. Whilst this would detect the remote close, it also would potentially consume large amounts of memory to maintain this buffer. Hence I seem to need a means of detecting that a socket has been closed remotely, without actually reading from it. . Does anyone know how to do this? One reference I've found is this: http://stefan.buettcher.org/cs/conn_closed.html Apparently recv() with appropriate flags can detect this - though I'm not convinced that the code as shown on that page doesn't busy wait when there is unread data from the client. Any tips or pointers? Perhaps what I'm trying to do is not currently possible in haskell, without using the FFI (which would be ok). Or perhaps it's not possible in linux at all. Thanks, Tim

2 1

ANN: "Real World Haskell", now shipping
by Bryan O'Sullivan 04 Dec '08

04 Dec '08

Good evening - John Goerzen, Don Stewart and I are delighted to announce the availability of our book, "Real World Haskell". It is 710 pages long, and published by O'Reilly Media. This is the first book to comprehensively cover modern Haskell programming. From an introduction to functional programming, it focuses on teaching through many worked examples. We discuss the "awkward squad" of I/O, concurrency, and exceptions. We cover network programming, databases, and system hacking. We motivate and work with monoids, applicative functors, monads, and monad transformers. We show you how to debug code, and how to ship well-tested software. Better yet, the book is available under a Creative Commons license, so you can read as much of it as you please before you buy: http://book.realworldhaskell.org/ We developed this book with the enthusiastic and voluble support of the Haskell community, and we are proud to share our work in a fashion that will help newcomers to our field. And best of all, if you order now (at least in North America), you can have a copy of the book in your hands in a matter of days. Thank you from all of us to our friends in the Haskell world who have been so generous with their feedback and kind words!

17 34

gmp license == no commercial/closed source haskell software ??
by Lionel Barret De Nazaris 04 Dec '08

04 Dec '08

I've just discovered the GMP license problem. (see http://hackage.haskell.org/trac/ghc/wiki/ReplacingGMPNotes) From my understanding, the gmp is GPL, GHC statically links it on windows. As a consequence, any program compiled using GHC must be distributed under a GPL compatible license. In the threads I've read, some workarounds are proposed on linux and OsX, but I didn't see anything on windows. Is the situation still the same ? Does anybody know a work-around to make a closed-source programm in haskell without violating the GPL ? ( Note this could block Haskell in our company. ) -- Best Regards, lionel Barret de Nazaris, ========================= Gamr7 : Cities for Games http://www.gamr7.com

6 5

GHC on Fedora 10 - getMBlock: mmap: Permission denied
by Fraser Wilson 04 Dec '08

04 Dec '08

Hi all, Has anybody seen this? I thought it might be an SELinux thing, but then I wouldn't expect GHC or darcs to run. Audley is a fairly simple program in operating system feature terms, but I get the same error with anything I build myself. [fraser@astroboy audley]$ ./dist/build/audley/audley audley: internal error: getMBlock: mmap: Permission denied (GHC version 6.8.3 for i386_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Aborted [fraser@astroboy audley]$ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.8.3 [fraser@astroboy audley]$ cat /proc/version Linux version 2.6.27-0.352.rc7.git1.fc10.i686 ( mockbuild(a)x86-5.fedora.phx.redhat.com) (gcc version 4.3.2 20080917 (Red Hat 4.3.2-4) (GCC) ) #1 SMP Tue Sep 23 21:26:04 EDT 2008 [fraser@astroboy audley]$ cheers, Fraser. -- http://thewhitelion.org/mysister

4 5

is there something special about the Num instance?
by Anatoly Yakovenko 04 Dec '08

04 Dec '08

module Test where --why does this work: data Test = Test class Foo t where foo :: Num v => t -> v -> IO () instance Foo Test where foo _ 1 = print $ "one" foo _ _ = print $ "not one" --but this doesn't? class Bar t where bar :: Foo v => t -> v -> IO () instance Bar Test where bar _ Test = print $ "test" bar _ _ = print $ "not test"

3 3

Re: [Haskell-cafe] is there something special about the Num instance?
by Yuriy 03 Dec '08

03 Dec '08

Numeric literals are special. Their type is (Num t) => t, so it can belong to any type that is instance of Num. Whereas Test belongs to Test type only so you cannot call bar on any instance of Foo. So your pattern constrains type signature of bar more then it is constrained by class declaration. On Wed, Dec 03, 2008 at 03:05:37PM -0800, Anatoly Yakovenko wrote: > module Test where > --why does this work: > data Test = Test > > class Foo t where > foo :: Num v => t -> v -> IO () > > instance Foo Test where > foo _ 1 = print $ "one" > foo _ _ = print $ "not one" > > --but this doesn't? > > class Bar t where > bar :: Foo v => t -> v -> IO () > > instance Bar Test where > bar _ Test = print $ "test" > bar _ _ = print $ "not test" > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

1 0

Re: [Haskell-cafe] library to process zip files
by Yuriy 03 Dec '08

03 Dec '08

Almost as fast as typing "proper" google query :) Thanks. On Wed, Dec 03, 2008 at 06:01:59PM -0500, Jeff Heard wrote: > http://hackage.haskell.org/cgi-bin/hackage-scripts/package/zip-archive > > On Wed, Dec 3, 2008 at 5:59 PM, Yuriy <yuriy.halytskyy(a)gmail.com> wrote: > > On Thu, Dec 04, 2008 at 11:56:10AM +1300, Yuriy wrote: > > Hi, > > > > Is there any haskell library to work with ZIP file format? > > > > Thanks, > > Yuriy > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

1 0

library to process zip files
by Yuriy 03 Dec '08

03 Dec '08

On Thu, Dec 04, 2008 at 11:56:10AM +1300, Yuriy wrote: Hi, Is there any haskell library to work with ZIP file format? Thanks, Yuriy

2 1