- Haskell - Haskell.org

penalty for proper tail recursion
by Richard Uhtenwoldt 07 Nov '01

07 Nov '01

What is the penalty that compilers pay these days for allowing "proper" tail-recursion (that does not grow the stack)? It used to be that implementations targetting C would use the while (1) {cont=(*cont)();} trick, which would lose a factor of 2 or so in speed IIRC. If the compiler generates native code, then the penalty I believe consists mainly of the "opportunity cost" of not targetting C and thus not being able to piggyback on GCC development efforts, but there may be costs which I'm failing to visualize from the fact that the hardware is specialized to handle the conventional way of iterating (ie, structured looping constructs). Please share answers for other languages like Mercury, even though some might think it slightly off-topic...

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ANN: tagsh 0.1
by Jonas Svensson 06 Nov '01

06 Nov '01

Hello, I've written a version of the tags program for Haskell, tagsh. It does things differently compared to the hasktags program but the main reason I wrote this is that I didn't knew hasktags existed. It uses the hssource and posix library from hslibs, works with GHC 5.02.1. tags file has been checked to work with vim and nedit. Features: Run files trough cpp (optional) Only write tags for things which are exported (optional) Download: http://www.dtek.chalmers.se/~d99josve/tagsh.tar.gz Run with "-h" for list of options. /jonas

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PLI 2002-Second call for workshop proposals
by Carsten Schuermann 06 Nov '01

06 Nov '01

SECOND CALL FOR WORKSHOP PROPOSALS Principles, Logics, and Implementations of high-level programming languages (PLI 2002) Pittsburgh, USA October 3 - 8, 2002 Carsten Schuermann http://www.cs.yale.edu/~carsten/pli02 PLI 2002, a federation of colloquia which includes ICFP 2002 (ACM-SIGPLAN International Conference on Functional Programming), PPDP 2002 (ACM-SIGPLAN International Conference on Principles and Practice of Declarative Programming), and GC 2002 (ACM-SIGPLAN Conference on Generative Component-based Software Engineering (GCSE), and the Semantics, Applications, and Implementation of Program Generators (SAIG) Generators and Components). PLI 2002 will be held in Pittsburgh, USA, October 3 - 8 2002. Affiliated workshops will be scheduled from October 3 through October 8. Researchers and practitioners are invited to submit workshop proposals, that may be sent to the PLI 2002 Workshop Chair Carsten Schuermann, carsten(a)cs.yale.edu by e-mail (Postscript, Pdf, ASCII) with "PLI02 Workshop Submission" in the subject header. Following SIGPLAN's sponsorship procedures, proposals should include: 1. Name of the workshop and the sponsoring conference (ICFP/PPDP/GC). Workshops associated with ICFP may be scheduled during PPDP/GC, workshops associated with PPDP may be scheduled during ICFP, workshops associated with GC may be scheduled during ICFP. 2. The goals of the workshop. 3. Names and addresses of organizers. 4. Names of potential participants, such as program committee members. 5. Plans for call for participation (e.g., call for papers). 6. Expected number of attendees. 7. Plans for publicity. 8. Plans for a proceedings. 9. Description of past versions of the workshop including date, organizers, paper submission/acceptance counts, attendance, site, registration fees and summary budget information. 10. Url address of the workshop description. Proposals will be evaluated by the PLI 2002 Workshop Chair, the ICFP, PPDP, and GC Program and Conference Chairs, and by the SIGPLAN Executive Committee. Be advised that workshops must be sponsored by SIGPLAN and require therefore SIGPLAN approval (see http://www.acm.org/sigplan/sigplan_workshop_proposal.htm for more information.) THE DEADLINE FOR RECEIPT OF PROPOSALS IS DECEMBER 7, 2001. Notification of acceptance will be made by February 1, 2002. Workshop selection committee: Don Batory : Program Co-Chair of GC 2002 Charles Consel : Program Co-Chair of GC 2002 Claude Kirchner : Program Chair of PPDP 2002 Simon Peyton Jones : Program Chair of ICFP 2002 Frank Pfenning : General Chair of PPDP 2002 Carsten Schuermann : Workshop Chair of PLI 2002 Walid Taha : General Chair of GC 2002 Mitch Wand : General Chair of ICFP 2002

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Haskell Wiki Upgraded
by John Heron 06 Nov '01

06 Nov '01

Hi All, As you may know, I've had to fix the Haskell wiki quite a number of times due to a bug, probably a bombing CGI script. I did a trial upgrade to a new version of pywiki a couple of weeks ago and didn't find problems or get any complaints so tonight (Nov 5, 2001) I went ahead and updated the wiki to a new version. There hasn't been anything like what I usually like in the way of testing, but you can't wait forever, and I'm comforted by a backup, and the fact that RCS lies underneath all. In any case, please let me know right away if you've any problems with it. Cheers, John Heron

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using haskell as a shell language
by Hal Daume 06 Nov '01

06 Nov '01

Hi, As we all know well, we can write scripts like: #!/usr/bin/perl -w print "foo" and whatnot. i'd like to be able to write something like: #!/usr/local/ghc/bin/ghc main = do putStrLn "foo" and whatnot, even if I have to explicitely say something like: #!/usr/local/ghc/bin/ghc module Main(main) where main = do putStrLn "foo" it doesn't really matter. but i'd like to be able to write something like this, chmod +x it and be able to execute it, interpreted. i have *no* idea what the semantics of #!... is in shell scripts, so i don't know if it's easy or hard to hack something like this together, but if anyone has any pointer (or if anyone's done something like this before), please please please let me know. thanks! - hal -- Hal Daume III "Computer science is no more about computers | hdaume(a)isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume

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URGENT: File exists
by bracaman＠box.sk 06 Nov '01

06 Nov '01

I need to create a function that checks if a file exists. My intention is to do something like: teste :: String -> Bool (Beeing the String the FilePath) I've tried to use openFile and catch functions, but i couldn't put it working. The purpose of this function is to test a file before trying to read it. Example: if (test "filepath") then readfile else fail Thank you very much for your help, Joao ------------------------------------ geek code inside :: powered by linux

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Re: Non-monolithic version of 'sequence' for IO monad?
by Marcin 'Qrczak' Kowalczyk 06 Nov '01

06 Nov '01

Mon, 05 Nov 2001 14:23:18 -0800, Joe English <jenglish(a)flightlab.com> pisze: > Is there any way, short of using unsafePerformIO, > to implement a combinator > > f :: [IO a] -> IO [a] > > in a way that the the result is produced lazily? No. If evaluation of list elements causes IO, then it's unsafe. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ QRCZAK

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GHC version 5.02.1 is released
by Julian Seward (Intl Vendor) 05 Nov '01

05 Nov '01

GHC 5.02.1 is available. Currently the source, x86-linux and sparc-solaris tarballs are available. We hope to add binary builds for Win32 and Alpha early next week. -- J The (Interactive) Glasgow Haskell Compiler -- version 5.02.1 ============================================================== We are pleased to announce a new patchlevel release of the Glasgow Haskell Compiler (GHC), version 5.02.1. The source distribution is freely available via the World-Wide Web, under a BSD-style license. See below for download details. Pre-built packages for Linux, FreeBSD, Solaris and Win32 are also available. Haskell is a standard lazy functional programming language; the current language version is Haskell 98, agreed in December 1998. 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, C++, whatever). 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 at http://www.haskell.org/ GHC's Web page lives at http://www.haskell.org/ghc/ What's new in 5.02.1 ====================== Fixed various bugs, some of which caused GHCi to crash or misbehave. Some documentation fixes. Nothing major. What's new in 5.02 ==================== 5.02 incorporates many small refinements and bug fixes over the previous stable release (5.00.2). There are no major changes. - Much improved support for Windows platforms. Binary builds are now entirely freestanding. There's no need to install Cygwin or Mingwin to use it. It's a one-click-install-and-off-you-go story now. - Several small changes to bring GHC into line with the newest Haskell 98 report. - GHCi (the interactive system) now works on Windows. - Partial FFI support in GHCi. At the moment, foreign import (both static and dynamic) is supported on x86 and sparc platforms. - A compacting garbage collector, to try and reduce space use. - Experimental: partial support for hierarchical module names. - Experimental: following heroic hacking by Ken Shan, 5.02 now works on Alpha (Tru64 only). Many 64-bit bugs have been shaken out. At the moment only the batch-mode compiler works -- no GHCi or native code generator yet. We've found and fixed more bugs than you could possibly imagine. A big thank-you to all those who reported bugs in the 5.00.X series. We claim to have fixed almost all reported bugs. In general we've spent a large amount of effort trying to improve the stability of the system relative to 5.00.X. (Famous last words ...) For full details see the release notes: http://www.haskell.org/ghc/docs/5.02/set/release-5-02.html 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 InstallShield form for Windows folks. Everybody else gets a .tar.gz which can be installed where you want. Once you have the distribution, please follow the pointers in the README file to find all of the documentation about this release. 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, GNU C and perl. This release is known to work on the following platforms: * i386-unknown-{linux,freebsd,mingw32} * sparc-sun-solaris2 * alpha-dec-osf3 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 included in distribution gives a complete run-down of what ports work; an on-line version can be found at http://www.haskell.org/ghc/docs/5.02/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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Haskell 98 Revised
by Simon Peyton-Jones 05 Nov '01

05 Nov '01

Haskellers! It's that time of the month. I'm putting out the November release of the Revised Haskell 98 Report. As ever, I earnestly seek your feedback. Especially I'd like to know whether I have stumbled in rewriting the section about Enum in the light of recent email. http://research.microsoft.com/~simonpj/haskell98-revised My plan is to iterate just once more (early Dec), and then freeze the report at Christmas. I'm getting tired! Simon

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Re: Haskell 98 Revised
by Ian Lynagh 05 Nov '01

05 Nov '01

On Mon, Nov 05, 2001 at 06:47:17AM -0800, Simon Peyton-Jones wrote: > indeed, it's a stream of lexemes that gets passed to L, so > there's no whitespace anyway The report says: The input to L is: * A stream of tokens as specified by the lexical syntax in the Haskell report, with the following additional tokens: immediately before where I suggested "token" be changed to "lexeme". I think I prefer this for a descriptive algorithm as it means you can do things like the figures in section 2.7 (Layout). > | L (t:ts) ms = L ts ms if t is whitespace Bah, I *really* meant L (t:ts) ms = t : L ts ms if t is whitespace :-) Also, the line L (}:ts) (0:ms) = } : (L ts ms) should be L (}:ts) (m:ms) = } : (L ts ms) if m == 0 = error "Implicit block explicitly closed" otherwise or the } will get allowed through by L (t:ts) ms = t : (L ts ms) So my complete suggested function is: L (t:ts) [] = t : L ts [] if t is whitespace = error "lexeme outside of module contents" otherwise L ({n}:ts) (m:ms) = { : (L ts (n:m:ms)) if n > m = { : } : (L ts (m:ms)) otherwise L (<n>:ts) (m:ms) = ; : (L ts (m:ms)) if m = n = } : (L (<n>:ts) ms) if n < m = L ts (m:ms) otherwise L (t:ts) (m:ms) = } : (L (t:ts) ms) if m /= 0 and parse-error(t) L (}:ts) (m:ms) = } : (L ts ms) if m == 0 = error "Implicit block explicitly closed" otherwise L ({:ts) ms = { : (L ts (0:ms)) L (t:ts) ms = t : (L ts ms) L [] [0] = [] L [] (m:ms) = } : L [] ms if m /= 0 Thanks Ian

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