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Calling ghc dll's with MSVC++ code
by Mauricio Carvalho 03 Dec '02

03 Dec '02

Hey! I need to call haskell DLL's from a c++ program, and this C++ is written in Microsoft's Visual C++ 6.0 I created the DLL sing the directives given at ghc user's guide (11.3 and 11.4) and created the dll. To create a .lib import file, I linked with the option -optdll--output-lib -optdllMyDll.lib I can compile and link my C++ problem, but when I run it, it crashes. I tried even to create a DLL from a C source I'm sure it works (as I created the DLL before with MSVC++ environment, and I could make it work out), and even this DLL crashes whe its functions are accessed. I'm using GHC 5.0.4.1 Is there some special command lines that must be used to create DLLs to be used with windows? Or is there some known difficulty doing it? Someone that succeded can please tell me exactly how was it done? If more info is needed, I can send the sources and command lines I used to compile. ps: I'm not using cygwin (i don't have it installed in my computer actually), but as far as I understood, it shouldn't be a problem ´Thanks for help! Mauricio

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The Haskell 98 Report
by Simon Peyton-Jones 01 Dec '02

01 Dec '02

Folks, As you know, Cambridge University Press are doing us the huge service of publishing the Haskell 98 report, both as a special issue of the Journal of Functional Programming (Jan 2003) and as a hardback book (it'll cost around £35). I'm very, very, very happy to say that, following discussion with CUP, the copyright and reproduction arrangements for the report will remain unchanged; i.e. exactly as they are at: http://research.microsoft.com/~simonpj/haskell98-revised/haskell98-report-h… I'm signing a letter that grants CUP a *non-exclusive* license to publish the Report, but it places no limitations on what else may be done with it. The copyright will still be (c) Simon Peyton Jones (as it has for some while; it has to be attached to someone or some thing), and the existing notice that says "you can do what you like with this Report" will stay unchanged. No "non-commercial only" caveats. In my view this is extremely generous of CUP, and I am particularly grateful to Conrad Guettler for making it happen. As a thank-you to CUP, perhaps you can all go out and buy a copy! Simon

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Re: Running out of memory in a simple monad
by Zdenek Dvorak 29 Nov '02

29 Nov '02

Hello, I hope I understand what's going on; if not please someone correct me. >I have problems with monads and memory. I have a monad through which >I thread output. If I do the concatenation of the output-strings in >one way Hugs runs out of memory, but if I do it in another way >everything works. I can't see why the first way doesn't work but the >second is OK. I woudl appreciate if someone could tell me what I am >doing wrong. > Here is the non-working monad: -} The problem is not directly connected to monads; what is the problem: [] ++ x = x (h:t) ++ x = h : (t++x), i.e. time complexity of ++ is proportional to the length of first list. first way: >putCharM c = M $ \o -> ((), o ++ [c]) -- Is this stupid in some way? this takes list (looong) of everything produced before this putCharM and concatenates c as last member; this takes time linear in the length of the list, summing over all putCharMs it is quadratic (and of course, due to laziness a lot of memory is consumed; seq does not help, as it only evaluates first cell of the list so that it sees it is not empty; deepSeq would solve this, but the time consumption would still stay long). the second way: > M f >>= k = M $ > let (x, o) = f > M f2 = k x > (x', o') = f2 > in (x', o ++ o') this is done reverse way (because >>= is bracketed to the right); we concatenate output of f (short) with output of f2 (the rest of computation, i.e. looong); but the time is proportional to the length of first list, so it is constant in our case; summing it over all putCharMs, we get linear time and we are happy :-) If you want to do it the first way, define putCharM c = M $ \o -> ((), c : o) and then reverse the list in runM. Zdenek Dvorak _________________________________________________________________ Add photos to your messages with MSN 8. Get 2 months FREE*. http://join.msn.com/?page=features/featuredemail

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ANNOUNCE: HaXml-1.08
by Malcolm Wallace 29 Nov '02

29 Nov '02

HaXml-1.08 ---------- http://www.haskell.org/HaXml/ We announce a fresh release of HaXml, a collection of libraries and tools for using XML from Haskell. This is mainly a bug-fix release. What is new in 1.08? * A new and highly useful function, Text.XML.HaXml.Validate.partialValidate, does validation except for checking whether the root element type matches that of the DTD's root element. This is just what you need in order to validate any partial document or sub-document. * The function Text.XML.HaXml.Html.Generate.htmlprint had a little bug which caused it to loop infinitely if some text was longer than 60 characters without a space. * The Xtract parser and combinators are now included in the HaXml library package, rather than existing solely for the Xtract command-line tool. * HaXml now works nicely with ghc-5.04.x as well as ghc-5.02.x and nhc98. Regards, Malcolm

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Re: nub
by Jan-Willem Maessen 29 Nov '02

29 Nov '02

I find that nub is nearly always the wrong tool for the job (unless the job is trivial quickie coding). I'll point out that: > map head . group . sort has O(n lg n) asymptotic complexity, whereas nub or (sort . nub) both are O(n^2). This fact seems all too frequently forgotten. For short lists it doesn't matter much---but I find I like to use set union a lot, and "merge" is quite a bit better than List.union for this, so I tend to keep even short sets sorted. (For bigger sets, of course, one should import a nice set implementation.) Richard Braakman <dark(a)xs4all.nl> writes: > uniq = map head . group and later: > I think both functions are useful. If I understand it right, uniq > can evaluate its argument list lazily, while nub cannot. There's no > real need to put uniq in the standard library, though. Here's a little experiment for folks with big Haskell programs: Look for uses of "group" in your code. I suggest: find -name '*.hs' | xargs grep -n '[^a-zA-Z]group[^a-zA-Z]' Now, look at two divisions of these calls: 1) What proportion are *not* performed in conjunction with a call to sort? 2) What proportion are *not* preceded by "map head"? In the case of the Eager Haskell compiler, the answer to (1) was "none", and the answer to (2) was "several". I suspect I'm not uniq in this finding. Providing "uniq" and/or "uniqSort" as prelude functions could in fact be a great service. Of course, if I only got to add one function to List, it would be some variant of "merge". -Jan-Willem Maessen

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Research Grants at UPM
by clip-small＠clip.dia.fi.upm.es 29 Nov '02

29 Nov '02

[Apologies for multiple copies] [Please, post as you deemed appropriate] The CLIP Group, Technical University of Madrid (UPM), offers 2 pre-doctoral, 4-year scholarships (research assistant level) available within the area of programming language technology: program analysis, transformation, and compilation. The work, intended to lead to a Ph.D., is to be done as a member of the CLIP Group http://www.clip.dia.fi.upm.es, within a nationally funded research project. The scholarships are funded by the Ministry of Science and Technology http://www.mcyt.es. Requirements for candidates are detailed in the CLIP group's job openings page: http://www.clip.dia.fi.upm.es/Job_Openings/jobs.html Application deadline is December 6th, 2002 (strict). Please, send a short CV, including previous research work and publications, and 1 to 3 references in electronic form in reply to this message. The main theme of the work envisioned within the scholarships is to advance the state of the art of automatic program manipulation techniques. The objective is to increase the power of such techniques and integrate them in practical tools within the Ciao multi-paradigm programming system, including logic, functional, constraint, and object-oriented programming. One additional objective is to target program optimizations to the needs of the computational elements of pervasive computing environments. One of the main lines of work implies extending the program compilation and development tools so that they can be used in such an environment to reduce program resource consumption and to instrument programs to perform dynamic control of such consumption during execution. The final aim is to develop an environment that would be an ideal candidate for programming ambient intelligence in mobile and pervasive computing environments.

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nub
by Christian Maeder 29 Nov '02

29 Nov '02

> > What does "nub" stand for? (This is the first I've heard of it.) > Hmm, maybe that's not such a great explanation. I wonder who can come up > with the best acronym? My contribution is > > "Note Unique Bits" "no duplicates" (or "no doubles") although that's no acronym Christian

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question about haskell report terminology
by Bernard James POPE 29 Nov '02

29 Nov '02

Hi All, In section 4.4.3 "Function and Pattern Bindings" of the Haskell 98 Report, it gives the following translation: ---- (The general binding form of a function is): x p_11 ... p_1k match_1 ... x p_n1 ... p_nk match_n Translation: The general binding form for functions is semantically equivalent to the equation (ie simple pattern binding): x = \x_1 ... x_k -> case (x_1, ..., x_k) of (p_11, ..., p_1k) match_1 ... (p_n1, ..., p_nk) match_n where x_i are new identifiers ---- What does it mean by "semantically equivalent". A rough approximation is "has the same meaning", but that depends on how you define the "meaning". For example: foo x = show x versus foo = \x -> show x I think the answer to the question is something like: this rule is intended to translate Haskell into the kernel, but it is not an equivalence that the programmer may (always) use in their own program (ie it is applicable only after type checking). I'm not sure where this rule fits into the definition of the language. Cheers, Bernie.

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RE: Implementing forward refs in monadic assembler and interprete r
by Erkok, Levent 29 Nov '02

29 Nov '02

Hi, As Ross pointed out, forward labels can easily be implemented using recursive monadic bindings. There're a number of alternatives as to which underlying monad you want to use. Continuations are problematic, but this problem can be solved by using a simple state monad: please see the attached file for one possible implementation. The variables test1-test4 (see the end of the file) are bound to the compiled and interpreted versions of your examples compute112 and compute12. Note: I had to add a "return ()" to the end of your compute12 example, since mdo-notation requires the last generator to be an expression, just like an ordinary do-expression. You need a fairly recent version of Hugs to run this example, November 2002 release would do (try with -98). For ghc, you need the CVS version, or wait till the next release. As far as I know, no other implementation supports mdo, nor there are any plans for it. -Levent. > -----Original Message----- > From: Mike Gunter [mailto:m@ryangunter.com] > Sent: Friday, November 15, 2002 1:38 AM > To: haskell(a)haskell.org > Subject: Implementing forward refs in monadic assembler and interpreter > > > I need to implement an assembler and interpreter for a simple > instruction set. For example, this code > > \begin{code} > compute112 = do > { zero r1 > ; zero r2 > ; addi r2 3 -- loop three times > ;topLoop <- label > ; addi r1 4 > ; addi r2 (-1) -- decrement loop counter > ; brPositive r2 topLoop > ; add r1 100 > } > \end{code} > > would result in register r1 having a value 112. Without forward > branches, the implementation is reasonably straightforward. The > assembler can use a Monad with state and writer capabilities. The > interpreter can use a continuation monad to implement branches and a > state monad for the machine state. > > However, forward branches make things harder. I'd like to be able to > write something along the lines of: > > \begin{code} > compute12 = mdo > { zero r1 > ; zero r2 > ; addi r2 3 -- loop three times > ;topLoop <- label > ; addi r1 4 > ; addi r2 (-1) -- decrement loop counter > ; brPositive r2 topLoop > ; mov r3 r1 > ; addi r3 (-10) > -- !!! Forward branch: > ; brPositive r3 out -- if r1 > 10 don't add 100 > ; add r1 100 > ;out <- label > } > \end{code} > > but it's not clear to me how to implement it. I'd be willing to > accept a somewhat less clean version (for instance, with more > cumbersome forward references.) > > Any help would be greatly appreciated. > > thanks, > mike > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell

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You can finally run your Chameleon programs!
by Martin Sulzmann 28 Nov '02

28 Nov '02

The latest Chamleon release includes a compiler. Chameleon programs are translated into plain Haskell (= Hindley/Milner subset plus polymorphic recursion). Note that Chameleon comes also with a type debugger. Check out http://www.comp.nus.edu.sg/~sulzmann/chameleon/ for the latest release including a number of examples. Martin

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