- Haskell - Haskell.org

Re: Minimal definitions proposal
by Marcin 'Qrczak' Kowalczyk 18 Aug '01

18 Aug '01

Fri, 17 Aug 2001 23:45:55 -0400, Dylan Thurston <dpt(a)math.harvard.edu> pisze: > Here's one cheap proposal: > > Add a "MINDEFINITION" pragma which takes a boolean expression whose > variables are the class functions. Since it's a pragma, this should > only produce warnings if violated. You mean an expression using && and || and method names? They are indeed enough almost always. In my experience they are not enough only if the default definitions are correct for some uses and incorrect for others, e.g. "foo and bar, and also baz if this is a set rather than a bag" or "succ and pred, and also enumFrom* functions if the type doesn't fit in Int". Since these side conditions are hard to express at all, in these cases the programmer would simply not be warned. I like it, except the name MINDEFINITION, although I tend to call it "minimal definition". REQUIRED? Although "Minimal definition: nothing, all default definitions will make a correct instance" could be spelled by omitting the pragma, an explicit "True" should be allowed too, so one reading the class definition can distinguish between this case and "I didn't bother with specifying what is required". I don't feel a need of having a special shortcut for "all methods must be specified, despite some having default definitions" - just name the methods. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK

1 0

Re: How do you stop functions being inlined?
by Marcin 'Qrczak' Kowalczyk 18 Aug '01

18 Aug '01

Fri, 17 Aug 2001 10:32:05 -0700, Simon Peyton-Jones <simonpj(a)microsoft.com> pisze: > OK. For the Haskell 98 report I propose > > 1. Change "notInline" to "NOINLINE". > 2. Change "specialize" to "SPECIALIZE" > 3. Delete E.3 (optimize pragma) altogether I like it. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK

1 0

Minor problem with "Floating" class in Prelude
by Dylan Thurston 18 Aug '01

18 Aug '01

The 'Floating' class in the standard prelude reads: > class (Fractional a) => Floating a where > pi :: a > exp, log, sqrt :: a -> a > (**), logBase :: a -> a -> a > sin, cos, tan :: a -> a > asin, acos, atan :: a -> a > sinh, cosh, tanh :: a -> a > asinh, acosh, atanh :: a -> a > > -- Minimal complete definition: > -- pi, exp, log, sin, cos, sinh, cosh > -- asinh, acosh, atanh > x ** y = exp (log x * y) > logBase x y = log y / log x > sqrt x = x ** 0.5 > tan x = sin x / cos x > tanh x = sinh x / cosh x Please add asin, acos, and atan to the minimal complete definition list. [Incidentally, I find these minimal definition lists very useful; I'd love to see them become more than just comments.] --Dylan

1 1

Enforcing Strict Evaluation
by Bernd Holzmüller 17 Aug '01

17 Aug '01

Hi all, I wrote an application that successively reads the contents of several (big) files, building an intermediate data structure, pretty printing their contents into one accumulated output file and extracting some information from the data structure for further processing. To avoid needing huge heap space the program reads one input file, pretty prints a representation of its contents (big) to the output file (via appendFile), extracts the necessary information (small) and proceeds with that information, so that the data structure representing the file contents can be released. To achieve the latter, however, I need to force strict evaluation of the extraction. My first approach was using $! as follows: ... info <- mapM (apply outfile) files ... apply outfile infile = do result <- read infile -- parses infile and generates data structure of its contents appendFile outfile (show result) return $! (extractInfos result) -- extractInfos returns a list of some sort of information but that did not work. I tried then printing the length of the extracted list because this would require the strict evaluation, and this works: ... info <- mapM (apply outfile) files ... apply outfile infile = do result <- read infile -- parses infile and generates data structure of its contents appendFile outfile (show result) let result' = extractInfos result -- extracts necessary information from result putStrLnFlushed (show (length result')) -- forces evaluation of result'! return result' Why does the first solution not work? How can I achieve the effects of the latter solution without printing something? Thanks, Bernd

2 1

RE: lexical description problem in language report?
by Simon Peyton-Jones 17 Aug '01

17 Aug '01

1 0

RE: foldl'
by Simon Peyton-Jones 17 Aug '01

17 Aug '01

No good reason -- but it's too late for H98. Adding it to the Prelude would break some existing programs (ones which define their own foldl'), and it's an unforced change. Alas. Simon | -----Original Message----- | From: Jon Fairbairn [mailto:Jon.Fairbairn@cl.cam.ac.uk] | Sent: 28 July 2001 11:28 | To: haskell(a)haskell.org | Subject: foldl' | | | Unless I'm mistaken, foldl' (the strict version of foldl) | doesn't appear in (the export list of) the standard prelude | or the list library. | | Is there a good reason for this? New users quite quickly | find that they need it. | | Jón | | | -- | Jón Fairbairn | Jon.Fairbairn(a)cl.cam.ac.uk | 31 Chalmers Road | jf(a)cl.cam.ac.uk | Cambridge CB1 3SZ +44 1223 570179 (after 14:00 | only, please!) | | | | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell |

1 0

Mathematics of Program Construction, 1st CFP
by mpc02 17 Aug '01

17 Aug '01

[Apologies for multiple copies] MPC 2002 6th International Conference on MATHEMATICS OF PROGRAM CONSTRUCTION ----------------------------------- http://www.cs.ukc.ac.uk/conf/mpc2002/ Organised in conjunction with WCGP '02 8--10 July, 2002 Dagstuhl, Germany CALL FOR PAPERS This conference aims to promote the development of mathematical principles and techniques that are demonstrably useful and usable in the process of constructing computer programs (whether implemented in hardware or software). The focus of the conference is on techniques that combine precision with conciseness, enabling programs to be constructed by formal calculation. Within this theme, the scope of the conference is very diverse. We welcome contributions to programming methodology (for example, formal methods for program specification and transformation), to programming paradigms (for example, generic programming techniques and type systems) and to language design (for example, programming calculi and programming language semantics). Theoretical contributions are welcome provided their relevance to program construction is evident; discussion of applications is welcome provided the mathematical basis is evident. The conference will be organised in conjunction with the IFIP TC2 Working Conference on Generic Programming, WCGP '02. There will also be a number of co-located workshops, including CMPP. IMPORTANT DATES Deadline for submission of papers: 6th January, 2002 Notification of acceptance/rejection: 4th March, 2002 Final papers due: 25th April, 2002 Full papers should be submitted in Postscript or pdf format by e-mail to mpc02(a)ukc.ac.uk by 6th January, 2002. PROGRAMME COMMITTEE Roland Backhouse (UK) Eerke Boiten (UK, co-chair) Michael Butler (UK) Ernie Cohen (USA) Jules Desharnais (Canada) Jeremy Gibbons (UK, GP liaison) David Gries (USA) Lindsay Groves (New Zealand) Ian Hayes (Australia) Eric Hehner (Canada) Zhenjiang Hu (Japan) John Hughes (Sweden) Bart Jacobs (The Netherlands) Johan Jeuring (The Netherlands, GP liaison) Dick Kieburtz (USA) Dexter Kozen (USA) K. Rustan M. Leino (USA) Christian Lengauer (Germany, CMPP liaison) Erik Meijer (The Netherlands/USA) Bernhard Moeller (Germany, co-chair) David Naumann (USA) J.N. Oliveira (Portugal) Alberto Pardo (Uruguay) Peter Pepper (Germany) Kaisa Sere (Finland) Mark Utting (New Zealand) FURTHER INFORMATION Please refer to the web page for further details. http://www.cs.ukc.ac.uk/conf/mpc2002/ -- Mathematics of Program Construction '02 at Dagstuhl Eerke Boiten, Computing Laboratory, University of Kent at Canterbury, UK +44.1227.827615 (fax 762811)

1 0

ANN: linkchk-0.00 - a gtk based network link heartbeat monitor
by Jens-Ulrik Petersen 17 Aug '01

17 Aug '01

Hello, I am happy to announce the first release of linkchk, a small program whose sole job is simply to monitor a ping heartbeat between its host and a gateway (router) on a local network link. Sounds simple? Well it is really, except for some first hurdles of pipes, lazy fileRead'ing, etc. Source code and a Linux binary are available from <http://www.01.246.ne.jp/~juhp/haskell/linkchk/>. ghc and gtk+hs are required to build linkchk. This is the first Haskell program I am releasing on the net, so I would appreciate any feedback I can get whether it be in the form of comments on the code, questions, or patches. Happy pinging! Jens

1 0

series
by Luis Pablo Michelena 16 Aug '01

16 Aug '01

hello, i just want to ask a simple question: does somebody have or know where to find a haskell program that calculates the number e, that is the list of infinite digits? Because i think it may be possible to do it, but i haven´t find the way to do it. what i am looking for is something like the ertostenes sifts, that prints every prime number until it run out of memory... thank you, Luis

4 3

How do I export Haskell-functions to C under Linux or Unix?
by Robbert de Haan 15 Aug '01

15 Aug '01

Hi, I'm currently working on a project where it would save me a lot of time if I could use the FFI's 'foreign export'-statement, enabling me to call Haskell-functions from C. Unfortunately, I can't get it to work... After reading about various tools and compilers and experimenting with some, I came to the conclusion that the most (and perhaps only) viable option would be to use HDirect in combination with the Glasgow Haskell Compiler. But even the most simple example, exporting Int -> Int-functions, (which doesn't even appear to use the HDirect library) just won't work. When using ghc-4.08.2 everything compiles and links just fine, but when running the result I get an 'Illegal instruction' error (RedHat Linux 7.1) or a 'Segmentation Fault' under Solaris 8. When using ghc-5.00.2 the object files are created, but I get the following error when linking (using ghc-5.00.2 -fglasgow-exts -static -no-hs-main -i../../lib -L../../lse -lhdirect -o tst tst.o libHStst.a, see the HDirect server-example): Undefined first referenced symbol in file Main_main_closure /home/rdehaan/ghc/lib/ghc-5.00.2/libHSstd.a(PrelMain__2.o) __init_Main /home/rdehaan/ghc/lib/ghc-5.00.2/libHSstd.a(PrelMain__1.o) ld: fatal: Symbol referencing errors. No output written to tst Has anyone else succeeded in exporting Haskell-functions and using them in C-modules under Linux or Unix? Any help would be appreciated! Robbert.

1 0