March 2004 - Glasgow-haskell-users

ANNOUNCE: GHC version 6.2.1
by Simon Marlow 26 Apr '04

26 Apr '04

============================================================ The (Interactive) Glasgow Haskell Compiler -- version 6.2.1 ============================================================ We are pleased to announce a new patchlevel release of the Glasgow Haskell Compiler (GHC), version 6.2.1. As usual for patchlevel releases, this is mainly a bugfix release and should not break any code that was working with the previous major release (6.2). We did sneak a couple of new features into the compiler: - The "threaded runtime system" is included by default. To link a program with this variant of the RTS, add the -threaded option when linking. The main advantage of the threaded RTS is that it allows calls to foreign functions which block, while allowing other concurrent Haskell threads to continue running. - A debugging variant of the RTS is also included. Use -debug when linking to get it. The debugging RTS includes lots of sanity checking and has some extra options for producing debugging output while your Haskell program is running. How to get it ~~~~~~~~~~~~~ The easy way is to go to the WWW page, which should be self-explanatory: http://www.haskell.org/ghc/ We supply binary builds in the native package format for various flavours of Linux and BSD, and in Windows Installer (MSI) form for Windows folks. Binary builds for other platforms are available as a .tar.gz which can be installed wherever you want. The source distribution is also available from the same place. Packages will appear as they are built - if the package for your system isn't available yet, please try again later. Background ~~~~~~~~~~ Haskell is a standard lazy functional programming language; the current language version is Haskell 98, agreed in December 1998 and revised December 2002. GHC is a state-of-the-art programming suite for Haskell. Included is an optimising compiler generating good code for a variety of platforms, together with an interactive system for convenient, quick development. The distribution includes space and time profiling facilities, a large collection of libraries, and support for various language extensions, including concurrency, exceptions, and foreign language interfaces (C, whatever). GHC is distributed under a BSD-style open source license. A wide variety of Haskell related resources (tutorials, libraries, specifications, documentation, compilers, interpreters, references, contact information, links to research groups) are available from the Haskell home page (see below). On-line GHC-related resources ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Relevant URLs on the World-Wide Web: GHC home page http://www.haskell.org/ghc/ Haskell home page http://www.haskell.org/ comp.lang.functional FAQ http://www.cs.nott.ac.uk/~gmh/faq.html System requirements ~~~~~~~~~~~~~~~~~~~ To compile programs with GHC, you need a machine with 64+MB memory, GCC and perl. This release is known to work on the following platforms: * i386-unknown-{linux,*bsd,mingw32} * sparc-sun-solaris2 * alpha-dec-osf3 * powerpc-apple-darwin (MacOS/X) Ports to the following platforms should be relatively easy (for a wunderhacker), but haven't been tested due to lack of time/hardware: * hppa1.1-hp-hpux{9,10} * i386-unknown-solaris2 * mips-sgi-irix{5,6} * {rs6000,powerpc}-ibm-aix The builder's guide on the web site gives a complete run-down of what ports work; it can be found at http://www.haskell.org/ghc/docs/latest/html/building/building-guide.html Mailing lists ~~~~~~~~~~~~~ We run mailing lists for GHC users and bug reports; to subscribe, use the web interfaces at http://www.haskell.org/mailman/listinfo/glasgow-haskell-users http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs There are several other haskell and ghc-related mailing lists on www.haskell.org; for the full list, see http://www.haskell.org/mailman/listinfo/ Please report bugs using our SourceForge page at http://sourceforge.net/projects/ghc/ or send them to glasgow-haskell-bugs(a)haskell.org. GHC users hang out on glasgow-haskell-users(a)haskell.org. Bleeding edge CVS users party on cvs-ghc(a)haskell.org.

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RE: Haskell performance
by Simon Marlow 07 Apr '04

07 Apr '04

> Okay. What's really bothering me is that I can't find any good > indication of what to do to get IO faster. Do I need to FFI the whole > thing and have a C library give me large chunks? Or can I get by with > hGet/PutArray? If so, what sizes should they be? Should I use memory > mapped files? hGet/PutArray should be pretty quick. For small requests, they get the usual buffering treatment that other Handle operations have, and for large requests the buffer is bypassed. For reading a file in one go, hGetArray (or hGetBuf) is the way to go. GHC itself uses hGetBuf for reading source files, hGetArray for reading interface files, and hPutBuf for writing output. Memory mapped files (mmap) should be even quicker. But then you'll have to use peek & co from Foreign to access the bytes. Cheers, Simon

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FAQ: How to Use Extensible Records in GHCi
by S. Alexander Jacobson 30 Mar '04

30 Mar '04

I feel like I have way too much code of the form: changeGpart (C a b c d e f g h i) g' = C a b c d e f g' h i So, I got excited reading Simon and Mark's "Lightweight Extensible Records For Haskell" paper as a way to get rid of this cruft. I immediately started GHCi, typed {a="Hello world"}, and got an error. Is the feature described in the paper just a proposal or is there a switch somethere to enable it? Alternatively, perhaps this code is a common beginner mistake due to ignorance of the proper idiom... -Alex- _________________________________________________________________ S. Alexander Jacobson mailto:me@alexjacobson.com tel:917-770-6565 http://alexjacobson.com

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RE: How to Use Extensible Records in GHCi
by Simon Peyton-Jones 30 Mar '04

30 Mar '04

No, extensible records are not implemented in GHC. Hugs (or some variant of it) implements TRex, another extensible record variant. The problem is that the record design space is large, and seems to lack local optima. And all reasonable variants break backward compatibility. As a result, nothing much happens. But for the particular code you write, H98 does the job fine: data C = C { a :: Int, b:: Bool, c::Int, ... i::String} Then if there's an expression e::C, you can write e { b=True } to change the b component to True. Check the H98 report SImon | -----Original Message----- | From: glasgow-haskell-users-bounces(a)haskell.org [mailto:glasgow-haskell-users- | bounces(a)haskell.org] On Behalf Of S. Alexander Jacobson | Sent: 30 March 2004 00:14 | To: GHC users | Subject: FAQ: How to Use Extensible Records in GHCi | | I feel like I have way too much code of the form: | | changeGpart (C a b c d e f g h i) g' = | C a b c d e f g' h i | | So, I got excited reading Simon and Mark's | "Lightweight Extensible Records For Haskell" paper | as a way to get rid of this cruft. I immediately | started GHCi, typed {a="Hello world"}, and got an | error. | | Is the feature described in the paper just a | proposal or is there a switch somethere to enable | it? | | Alternatively, perhaps this code is a common | beginner mistake due to ignorance of the proper | idiom... | | -Alex- | | | _________________________________________________________________ | S. Alexander Jacobson mailto:me@alexjacobson.com | tel:917-770-6565 http://alexjacobson.com | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users(a)haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users

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Re: :kind feature request in ghci
by Benjamin Franksen 28 Mar '04

28 Mar '04

On Saturday 27 March 2004 16:33, S. Alexander Jacobson wrote: > Alternatively, is there another way to > figure out how to create an instance of > a class like this? > > class MyClass a b where emptyVal::a b > > Here are one of the thing that don't work: > > type MyType a = [a] > instance MyClass (MyType a) a where emptyVal=[] > > And I have no idea why... Well, you've been told why. Anyway, why do you insist on using a two parameter type class? The more general class MyClass a where emptyVal::a would do exactly the same. To make type constructor B applied to type C an instance you just write instance MyClass (B C) where ... for instance instance MyClass [a] where emptyVal=[] If you enable overlapping instances you could even add instance MyClass [Int] where emptyVal=[0] The only difference to your 2-parameter class is that now you can declare instances for simple types like Integer too. Is that a problem? Ben

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:kind feature request in ghci
by S. Alexander Jacobson 27 Mar '04

27 Mar '04

I keep running into kind errors (see my most recent post on Haskell cafe). Would it be possible for ghci to expose a :kind function that operates on types the way :type operates on values? Alternatively, is there another way to figure out how to create an instance of a class like this? class MyClass a b where emptyVal::a b Here are one of the thing that don't work: type MyType a = [a] instance MyClass (MyType a) a where emptyVal=[] And I have no idea why... -Alex- _________________________________________________________________ S. Alexander Jacobson mailto:me@alexjacobson.com tel:917-770-6565 http://alexjacobson.com

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GHC 6.2.1 under darwinports
by Gregory Wright 25 Mar '04

25 Mar '04

Hi, The Glasgow Haskell Compiler supported under darwinports has been bumped to version 6.2.1. By default, GHC now builds with OpenGL support. The build should work for both OS X 10.2.x and 10.3.x. This lets Mac OS X jaguar users to get the latest version of GHC, as Wolfgang Thaller's binary release is only tested with panther. It can also provide amusement for those who just like to build from source. For information on getting darwinports, see http://darwinports.opendarwin.org. Best Wishes, Greg Wright Gregory Wright Antiope Associates LLC gwright(a)antiope.com

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RE: [Haskell] deriving with newtypes
by Simon Peyton-Jones 25 Mar '04

25 Mar '04

[Redirecting to GHC users.] This seems like a very reasonable point. Not possible today, but it should be. It'll go on my to-do list. Meanwhile, I guess you can always do it by steam. Simon | -----Original Message----- | From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] On Behalf Of Wolfgang | Jeltsch | Sent: 21 March 2004 17:55 | To: The Haskell Mailing List | Subject: [Haskell] deriving with newtypes | | Hello, | | I'm trying to use GHC's deriving mechanism for newtypes in the following way: | class C a b | instance C [a] Char | newtype T = T Char deriving C [a] | Unfortunately, this isn't possible. Is there a reason for this? Can I | circumvent this restriction? | | Wolfgang | | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell

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RE: Bug report.
by Simon Marlow 25 Mar '04

25 Mar '04

> Started getting: > > ghc-6.2.1.20040313: panic! (the `impossible' happened, GHC > version 6.2.1.20040313): > mkTyVar a1 {- tv a75q -} > > Please report it as a compiler bug to > glasgow-haskell-bugs(a)haskell.org, > or http://sourceforge.net/projects/ghc/. > > today... definitely a but to do with class inference, as it > started appearing > aftyer changing some instance constraints and fundeps on classes. > > Can't really be a lot more specific as code is big. Let me > know if you want > me to produce a small code extract which triggers it. Could you send us enough code to reproduce the bug? The smaller the better, but don't worry if you can't reduce it. Cheers, Simon

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RE: ANNOUNCE: GHC version 6.2.1
by Simon Marlow 25 Mar '04

25 Mar '04

> > ============================================================ > > The (Interactive) Glasgow Haskell Compiler -- version 6.2.1 > > ============================================================ > > A Mac OS X 10.3 (Panther) binary installer package is now > available at: > http://www.uni-graz.at/imawww/haskell/GHC.6.2.1.dmg Thanks! 6.2.1 packages are now available for: Windows, RedHat 9, FreeBSD, and MacOS X. Cheers, Simon

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