March 2001 - Haskell - Haskell.org

modules and re-export
by Peter Thiemann 20 Mar '01

20 Mar '01

I have a little question about the following two modules. Suppose you want to write your own variant of the prelude that redefines a couple of names but leaves all the rest unchanged. The Haskell report says that the following should work: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ module BUG2A (module BUG2A, module Prelude) where import Prelude hiding (head) head = "HEAD" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ This overrides the definition of head and should reexport head along with everything imported from the Prelude. Hugs98/feb2001 loads it happily and says head :: [Char] Now, I want to use this module as an alternative prelude: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ module BUG2B where import qualified Prelude import BUG2A ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Unfortunately, this does not behave as (I think) it should: Reading file "BUG2B.hs": Parsing........................................................................ ERROR "BUG2B.hs": Entity "head" imported from module "BUG2A" already defined in module "Prelude" However, this should be legal from my reading of the report. Any help appreciated. -Peter

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ANNOUNCE: HasChorus - some modules for Haskore
by Martin Schwenke 20 Mar '01

20 Mar '01

HasChorus: A set of Haskell (http://haskell.org/) modules written on top of Haskore (http://haskell.org/haskore/) to make it easier to sequence simple, repetitive music. HasChorus is available via: http://meltin.net/hacks/haskell/ ---------------------------------------------------------------------- HasChorus *has* a bunch of useful modules: HasChords.lhs: Build (diatonic) chords from scales and scale degrees. HasDrums.lhs: Sequence drums in a similar manner to a drum machine. HasEasyMusic.lhs: Allow simple specification of simple music sequences. HasGroove.lhs: Modify Haskore performances via normal distributions. HasPatterns.lhs: Sequence patterns by playing chords in different ways. HasScales.lhs: Build scales and pick notes by scale degree. HasSounds.lhs: Some boring ways of playing some instruments. HaskoreExtras.lhs: Some useful functions that aren't in Haskore. BubbleSort.lhs: An implementation of bubble sort. Used by HasGroove.lhs. Normal.lhs: Generate normal distributions. Used by HasGroove.lhs. TwelveBar.lhs: An example song. Many of the modules can be used without requiring all of the others. The dependencies look something like: HasEasyMusic -> HasChords -> HasScales HasDrums -> HaskoreExtras HasSounds -> HasPatterns HasGroove -> BubbleSort, Normal TwelveBar -> HasChorus -> *EVERTHING ELSE* ---------------------------------------------------------------------- HasChorus has been tested under: * Hugs: Currently I use Hugs 98, February 2000. I use -h1000000 so that HasGroove doesn't melt down... :-) * GHC: 4.08 (previously under 4.07) under x86 Linux. ---------------------------------------------------------------------- I use HasChorus to sequence up simple backing tracks for my own compositions. Enjoy... peace & happiness, martin Martin Schwenke <martin(a)meltin.net> p.s. Several people who have expressed interest in this project during the last few years have received this announcement via a BCC. They haven't been secretly subscribed to the Haskell mailing list. :-)

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knight's tour - please help
by The Ghost 19 Mar '01

19 Mar '01

Hello everyone, I have a little problem with implementing the knight's tour in haskell. My goal is to print out all possible solutions for the knight's tour. Allthough finding one path (with given startinposition (x,y) of the horse and dimension of the bord M*N) is not enough. I have to find all of them. (the printing out may be very simpel) I've wrote this problem is several other languages and there they work perfect. But I'm searching for an implementation in Haskell. The implementation may also be simpel (I think it can be solved only by using lists and backtracking). If I have the implementation I can go one with my project, I should use it to explain the differences between a functional language and the others (effiency, speed,..) Is ther someone who has such an implementation (that is not too complicated and not too lang). Would you be so kind to send it to me? I should be very thankfull. Greetings, The White Ghost. _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.

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question does haskell have a something like a wild character
by john xxx 19 Mar '01

19 Mar '01

i want to know if HAskell has an inbuilt function in the prelude a function that allows me to use wild character like so: ie. if a list of strings contains a word or a combination of words that do not necessarily have to be side by side. someting that works like so [.. "hello" ..] == ["my", "tie" , "egg", "hello", "good"] would return True. where .. represents other elements of the list it counld be 1element or a hundred elements. please reply urgently to johnjohnjohn64(a)hotmail.com if haskell does not provide such a function can you please give me information on how to create one that would do such a thing that i need. THANKYOU FOR YOUR TIME. please reply! i need this function for an assignment for university. p.s if you're interested in the question visit. http://www.cse.unsw.edu.au/~cs1711/ass1/spec-ass1.html _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.

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Re: Greencard, GHC and FFI.
by Sigbjorn Finne 17 Mar '01

17 Mar '01

Mike Thomas mthomas(a)gil.com.au writes: > > I'm having trouble with using green-card 2 on Windows > with GHC-4.08.2. As the default output for -target ghc seems > to be for the C back-end rather than native code, I thought I would > try the FFI target. > .... example code deleted > > I get > > $ ghc main.hs -o main.exe GCTest.o StdDIS.o -package lang -package greencard > --------------------------------------------- > Compilation IS NOT required > GCTest.o(.text+0x7f):fake: undefined reference to `prim_my_sin' > .... Hi, Greencard lets you write C and Haskell in one source file. When using GHC's C back end, it is possible to combine the two in one source file (via GHC's _casm_s.) The FFI doesn't let you do this, but requires you to provide the C bits separately, and link the Haskell code to it via 'foreign' declarations. So, when using GC's FFI backend, it generates two source files for you (and some header files) - in your case, GCTest.hs and GCTest_stub.c. To achieve linker happiness, you need to compile up the latter and include it on the link line *and* drop StdDIS.o from that link line. hth --sigbjorn

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Greencard, GHC and FFI.
by Mike Thomas 17 Mar '01

17 Mar '01

Hi all. I'm having trouble with using green-card 2 on Windows with GHC-4.08.2. As the default output for -target ghc seems to be for the C back-end rather than native code, I thought I would try the FFI target. Using the example from the green-card doc: --------------------------------------------- module GCTest where import StdDIS %fun my_sin :: Double -> Double %code res1=sin(arg1); --------------------------------------------- Compiling for target FFI: --------------------------------------------- green-card -c GCTest.gc -o GCTest.hs --target ffi ghc -c GCTest.hs -fglasgow-exts --------------------------------------------- Linking with this main module: --------------------------------------------- module Main(main) where import GCTest main :: IO() main = putStrLn (show (my_sin (20.0))) --------------------------------------------- I get: --------------------------------------------- $ ghc main.hs -o main.exe GCTest.o StdDIS.o -package lang -package greencard Compilation IS NOT required GCTest.o(.text+0x7f):fake: undefined reference to `prim_my_sin' StdDIS.o(.text+0x549):fake: undefined reference to `prim_free' StdDIS.o(.text+0x600):fake: undefined reference to `prim_allocCharStar' StdDIS.o(.text+0x731):fake: undefined reference to `prim_readCharAddr' StdDIS.o(.text+0xc84):fake: undefined reference to `prim_malloc' StdDIS.o(.text+0xd38):fake: undefined reference to `access_prim_malloc_res1' StdDIS.o(.text+0xdec):fake: undefined reference to `access_prim_malloc_gc_failed ' StdDIS.o(.text+0xea0):fake: undefined reference to `access_prim_malloc_gc_failst ring' StdDIS.o(.text+0x1206):fake: undefined reference to `prim_writeCharAddr' collect2: ld returned 1 exit status --------------------------------------------- Where have I gone wrong? Cheers Mike Thomas.

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PPDP'01 deadline extension to 23 March
by Harald Sondergaard 16 Mar '01

16 Mar '01

PPDP'01 Principles and Practice of Declarative Programming Florence, Italy, 5-7 September 2001 http://music.dsi.unifi.it/pli01/ppdp/ EXTENSION OF DEADLINE FOR SUBMISSIONS The deadline for paper submissions has been extended to 23 March 2001. Harald Sondergaard PPDP'01 Program Chair

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TACS 2001 call for papers (deadline April 1)
by Benjamin C. Pierce 16 Mar '01

16 Mar '01

Call For Papers Fourth International Symposium on Theoretical Aspects of Computer Science (TACS 2001) October 29-31, 2001 Tohoku University, Sendai, Japan http://tacs2001.ito.ecei.tohoku.ac.jp/tacs2001/ The TACS Symposium will focus on the theoretical foundations of programming and their applications. The topics of interest include... Theoretical aspects of the design, semantics, analysis, and implementation of programming languages and systems; logics of programs; calculi and models of concurrency and parallel computation; theories of mobile computation and system security; categories and types in computer science; formalisms, methods, and systems for program specification, verification, synthesis, and optimization; constructive, linear, and modal logics in computer science. The scientific program will consist of invited lectures, contributed talks, and demo sessions. A proceedings containing the full papers of the invited and contributed talks will be published by Springer-Verlag as a volume of Lecture Notes in Computer Science. IMPORTANT DATES Submission deadline: April 1, 2001 Notification to authors: June 15, 2001 Deadline for final versions: July 20, 2001 INVITED SPEAKERS Luca Cardelli Microsoft Research Daniel Jackson Massachusetts Institute of Technology Christine Paulin-Mohring Universite Paris Sud & INRIA Andrew Pitts University of Cambridge Jon Riecke Lucent Technologies Kazunori Ueda Waseda University CONFERENCE CHAIR: Takayasu Ito Tohoku University PROGRAM CO-CHAIRS: Naoki Kobayashi Tokyo Institute of Technology kobayasi(a)cs.titech.ac.jp Benjamin Pierce University of Pennsylvania bcpierce(a)cis.upenn.edu PROGRAM COMMITTEE: Zena Ariola University of Oregon Cedric Fournet Microsoft Research Jacques Garrigue Kyoto University Masami Hagiya University of Tokyo Robert Harper Carnegie Mellon University Masahito Hasegawa Kyoto University Nevin Heintze Lucent Technologies Martin Hofmann Edinburgh University Zhenjiang Hu University of Tokyo Naoki Kobayashi Tokyo Institute of Technology Martin Odersky Ecole Polytechnique Federale de Lausanne Catuscia Palamidessi Pennsylvania State University Benjamin Pierce University of Pennsylvania Francois Pottier INRIA Andre Scedrov University of Pennsylvania Natarajan Shankar SRI International Ian Stark Edinburgh University Makoto Tatsuta Kyoto University SUBMISSION INFORMATION Authors are invited to submit full papers (up to 6000 words, including figures and bibliographies). Papers must be unpublished and not submitted for publication elsewhere. Submissions should be in Postscript or PDF format, on A4 or US letter pages. They must be printable on common printers and viewable with ghostview or acroread. The first page of each submission should include the email address, telephone, and fax numbers of the corresponding author. Accepted papers must be presented at the symposium, and the final manuscript must be prepared in the LNCS format. All submissions should be done electronically through the TACS submission page http://saul.cis.upenn.edu:8086/.

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Please help us with our research....
by Mini Haskell 16 Mar '01

16 Mar '01

Hi We are a small group of undergraduate computer science students from the University of Nottingham. As part of our second year we have been assigned to do a software engineering group project. The project put us together as a group and we were told what we had to do, our instructions were as follows: Mini Haskell ------------ The aim of this project is to build an interpreter for a small functional programming language called Mini Haskell. For simplicity, the only values in the language will be integers, lists, and functions. As well as allowing expressions to be evaluated to a final result, the interpreter should also allow the individual steps in the evaluation process to be seen. ------------ AS part of our research we have developed an on-line questionnaire which looks at the importance of some of the ideas we have had for the project. The questionnaire is found on our website and asks some very simple multiple choice questions which should take no longer than 2 minutes to complete. Please help us by looking at the site and by filling in our questionnaire in the feedback section. Please go to questionnaire: http://quest.minihaskell.com website: http://www.minihaskell.com thankyou for your time Dave - minihaskell _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.

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Ghc / Hugs inconsistencty.
by Grace Trigue White 15 Mar '01

15 Mar '01

The following program compiles under ghc, but hugs complains that there is an unexpected keyword "forall" on the line defining the type X. The type used is the type of the primitive runST, so it is a valid type. It seems that one should be able to create a type synonym for it. The situation is unchanged if the type X is given a parameter a, i.e. "type X a = (forall s. ST s a) -> a". module Main where import ST type Module s a = ST s a type X = (forall s. ST s a) -> a f :: (forall s. ST s a) -> a f x = undefined --type ModuleConnect = forall s. (forall t. ST (s, t) a) -> ST s a main :: IO () main = do { putStrLn "Hello World!!!" }

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