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Anomalous Class Fundep Inference
by Ashley Yakeley 08 Apr '01

08 Apr '01

In Hugs 98 Feb2001 (as hugs -98), this piece of code gives an error: -- class X a b | a -> b where x :: a; class (X a b) => Y a b | a -> b where y :: a; instance (X a b) => Y a b where y = x; instance (Num a) => X a a where x = 0; -- line A --instance X Int Int where x = 0; -- line B -- Reading file "Bug.hs": Type checking ERROR Bug.hs:3 - Inferred type is not general enough *** Expression : y *** Expected type : Y a b => a *** Inferred type : Y a a => a However, if I replace line A with line B, it compiles. Is this correct, or is it a bug in Hugs? Sooner or later I should install GHC for Mac OS X... -- Ashley Yakeley, Seattle WA

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IO recursion
by mapple apple 06 Apr '01

06 Apr '01

Hi everyone, I'm not sure this is the place to ask, coz I hvn't join your mailing list. But anyway .. Here's the case .. does anybody know 'bout IO recursion? ie. We've a file and we want to put a numberline 1: 'first line' 2: 'second line' until n, where n is the last line I know how to convert a file into a huge string using 'readFile' and I'm using the 'lines function' in the prelude. That means i have a huge string like "\nHi mate\nHow r u?" using the helper function 'lines' i can do that by saying : main :: IO () main = do putStr "Filename plz: " file <- getLine content <- readFile file putStr ("1: " ++ read (show (head (lines content)))) and so on that's not recursive function and will not work for all cases. So please .. if anyone knows how to do those things, let me know. one more thing, does anybody know how to join the mailing list?? mapple apple mapple_83(a)hotmail.com _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.

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Revised Haskell Report
by Simon Peyton-Jones 06 Apr '01

06 Apr '01

The Revised Haskell 98 Report I'm happy to say that at long last I have worked through my immense heap of Haskell-98 typos, and have revised the Language and Library Reports. You can find a draft of the revised reports at http://research.microsoft.com/~simonpj/haskell98-revised Please take a look at these drafts, and tell me if there are any remaining errors. I'd be glad to hear from you by May 12; I plan to freeze both documents at the end of May. Simon

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Profiling burn-rate
by Sengan 06 Apr '01

06 Apr '01

Is there any way to profile the "burn-rate" of a Haskell program? Profiling as I understand it tells you what the "live" information on the heap is. It doesn't tell you what garbage collector has just freed. So, if a function were generating tons of intermediate values which it then immediately consumed, you wouldn't see it on the profile. Yet this is a place where rewriting the code or adding strictness could help reduce time spent garbage collecting. I liken this to cash-flow: you're not just interested in the amount of cash you have, but also where it's going. Profiling currently gives us only the first dimension not the second, if I understand it correctly. Sengan

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FFI - some comments
by Ronald Legere 06 Apr '01

06 Apr '01

This is just some notes about my experiences with the various FFI tools, and my opinions. Maybe I am missing something but...... Let me just say that I like the 'new' FFI. The approach is much better then the usual approach to 'native' interfaces that you see with Tcl, java, python, whatever. In those cases you have to do the marshalling by hand, except where you can use SWIG, which is a pretty cool tool. Overall, I think there is not a perfect solution. Someone correct me if I am wrong. The ideal solution should take advantage of the fact that we are using Haskell: 1) Use the new FFI, for hugs and ghc. 2) Do Marshalling on the haskell side only. 3) Be a high level marshaling combinator library (written in haskell). 4) OPTIONALLY support some sort of IDL for automatically finding invoking the correct marshalling combinators. How do the existing tools stack up? I am not sure, because they are all in various states of support/etc. Here are my impressions... they may be wrong! Please take this with a grain of salt, I have not spent a lot of time with the tools below, just played with them a bit. Most of time was spent trying to build them L:) Greencard: Seems to work pretty well overall.. I dont beleive it supports hugs/ffi, but it does support hugs. It does the marshalling in haskell, but with a lot of _casm_ so I am not sure what that means. I got some simple examples to work, but not the Gdbm. The makefile didnt seem to make sense.. HC not defined, etc. Probably could with abit of work. I cant tell if callbacks are supported. HDirect: This one is still pretty beta, and so I had some trouble getting it to compile on my solaris machine. Probably not intended for solaris. I had to by hand prune some of the makefiles, ( in lib, there was some mysterious error about 'test' haveing no arguments when deciding whether to create a 'hugs' subdirectory, and In the end I commented out the all :: dlls line. but I did finally get it to go, at least the ghc parts. This one does its marshalling in haskell. It uses an IDL that is fairly common, although I dont know how much longer COM is going to be important. Anyway, when ready for prime time it might work pretty well, although like I said I would rather have a nice library. As for examples, I got the string example to work (you have to set FOR_WIN32 to no, even if you set FOR_HUGS to no. The makefile is a bit misleading). The gd example doesnt work, it assumes an old libgd that used to support GIFs. They arent suppored anymore, for legal reasons. KDirect: Looked at it abit. Pretty sparsely documented. I could not figure out how it fits in with the latest tools. How does QForeign relate to Foreign? What is an hsc file? Also it is pretty limitted in the marshalling. No callbacks etc. Others: I know there are a couple of others, but I lost interest. I Just wanted to report my findings for others, and then I am going into wait and see mode :) I dont have a dire need for this stuff at the moment, I can get my tasks done a different way. (Dont ask, it aint pretty).... Cheers to all! __________________________________________________ Do You Yahoo!? Get email at your own domain with Yahoo! Mail. http://personal.mail.yahoo.com/

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floor(Inf), floor (NaN)
by Simon Peyton-Jones 06 Apr '01

06 Apr '01

Further to my mail re the Haskell 98 report, there is one loose end. | 2. George Russell pointed out that floor(Inf) and floor(NaN) are not | defined in Standard Haskell; indeed GHC and Hugs have | different behaviour. This point led to an inconclusive discussion back in March 2000. Fergus Henderson and George Russell were the main protagonists. I'm too ignorant to have an opinion, but given the lack of conclusion I have taken no action. If anyone wants to revive the discussion, go ahead, but remember the extremely conservative nature of this revision! Simon

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RE: FFI - some comments
by Simon Marlow 06 Apr '01

06 Apr '01

> Thu, 5 Apr 2001 07:45:44 -0700 (PDT), Ronald Legere > <rjljr2(a)yahoo.com> pisze: > > > KDirect: Looked at it abit. Pretty sparsely documented. I could not > > figure out how it fits in with the latest tools. How does QForeign > > relate to Foreign? What is an hsc file? Also it is pretty limitted > > in the marshalling. No callbacks etc. > > Here is the story of QForeign, hsc and KDirect. [ long story deleted... thanks Marcin. ] To summarise GHC's FFI support: in the upcoming GHC 5.00 (not long now!) we have the latest FFI libraries, and we've bundled Marcin's hsc2hs tool. This means writing bindings to C libraries is fairly well supported out of the box; if you want something more sophisticated then the other tools mentioned in this thread are available. Cheers, Simon

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13 vacant positions at the IT University of Copenhagen
by Mads Tofte 05 Apr '01

05 Apr '01

[This job announcement is being sent to mailing lists that are read by researchers who work on aspects of information technology relevant to the IT University of Copenhagen. Feel free to circulate it! Apologies if you receive multiple copies. I'll be very happy to provide further information. Sincerely, Mads Tofte (tofte(a)it-c.dk) ] The IT University of Copenhagen was established by the Danish Ministry of Research in 1999. It is a graduate scool for research and research-based teaching in Information Technology. During its less that two years of existence, the IT University of Copenhagen has grown to employ 20 scientific staff at the level of assistant professor or higher, 20 ph.d.-students, some 700 students, and a teaching network of a further 90 teachers who are either part-time staff at the ITU or permanent staff of four nearby universities, namely the University of Copenhagen, Copenhagen Business School, The Technical University of Denmark (Lyngby), and Roskilde University. The four research departments of the IT University of Copenhagen currently have 13 vacant positions as assistant professor or associate professor. We welcome applications within the following areas: mobility, media and communication, software technology, software applications, theoretical computer science and virtual reality. The four research departments are: * The Department of Design and Use of IT * The Department of Digital Aesthetics and Communication * The Department of Innovation * The Theory Department The full job announcement may be found at www.it-c.dk/eng (look under Vacancies). At www.it-c.dk/eng one may also register on an electronic news service which provides information about future job announcements and scholarships. Sincerely, Mads Tofte Director of the IT University of Copenhagen

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RE: help wanted with type error message
by Simon Peyton-Jones 05 Apr '01

05 Apr '01

| A third extension which is ocasionally useful is not present | in any Haskell implementation. I would like to say | instance (forall a. Seq (s a) a) => Foo (Bar s) | It would allow to e.g. wrap my collections in Edison's | interfaces, not only vice versa. Yes, indeed. See Section 7 of http://research.microsoft.com/~simonpj/Papers/derive.htm We havn't implemented it yet, I fear. Simon

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RE: GHC non-standard interface file location problem
by Simon Peyton-Jones 05 Apr '01

05 Apr '01

Add "-package concurrent" to your command line. In general, GHC-usage messages should go to glasgow-haskell-users(a)haskell.org Simon | -----Original Message----- | From: Bernd Holzmüller [mailto:holzmueller@ics-ag.de] | Sent: 05 April 2001 08:50 | To: haskell(a)haskell.org | Subject: GHC non-standard interface file location problem | | | Hi all, | | while compiling a file select.hs ghc said: | | select.hs:1: | Could not find interface file for `Concurrent' | in the directories ./*.hi | | c:/programme/haskell/ghc-4.08/lib/imports/std/*.hi | | can someone tell me why ghc does not find the interface files | for the concurrency library (or any of the other non-standard | libraries) or how to tell ghc, where this library sits? Is | there any GHC INCLUDE path to be set? I am using ghc 4.08 on | a Windows NT machine. | | Thanks, | Bernd Holzmüller | | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell |

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