- Haskell - Haskell.org

RE: FFI and ODBC connectivity
by Simon Peyton-Jones 05 Jun '02

05 Jun '02

HaskellDirect (or HDirect for short) is very much alive and being actively maintained by Sigbjorn Finne. http://www.haskell.org/hdirect/ It's built on top of the Haskell FFI, but it is much higher level. Simon | -----Original Message----- | From: Jamie Love [mailto:jlove@eservglobal.co.nz] | Sent: 05 June 2002 06:30 | To: Haskell Mailing List | Subject: FFI and ODBC connectivity | | | Hello all, | | Currently I am investigating the availability of haskell to | ODBC connectivity and have been excited by the possibilities. | Downloading the HaskellDB package | (http://haskell.cs.yale.edu/haskellDB/) | and having it run was fantastic. | | In the interests of continuing the work of HaskellDB, I wish | to have this system work under Linux. Before attempting to | extend HaskellDB to support ODBC (and work through unixODBC - http://www.unixodbc.org) I wish to ensure that my efforts are not misdirected. My questions include: Is HaskellDB dead? Is it worth extending? (I very much wish to keep the type safety HaskellDB has). Is HaskellDirect dead or superseeded by the Haskell FFI? I am having difficulty discovering which FFI technology/package is still useful, viable and alive, the same applies to ODBC connectivity packages. The second set of libraries I am interested in is HTML/CGI libraries. I have yet to investigate those available, so any direction on which library package is currently live and well would also be useful. The reason for these queries is that I wish to write pure Haskell software based heavily around both a database backend and HTML frontend. Thankyou, -- Jamie Love Phone: +64 4 9393425 "If possible, try to find a way to come downstairs that doesn't involve going bump, bump, bump, on the back of your head. - " Pooh in Winnie the Pooh _______________________________________________ Haskell mailing list Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell

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FW: cvs commit: hugs98/lib IO.hs Prelude.hs
by Simon Peyton-Jones 05 Jun '02

05 Jun '02

Folks I plan to push out a new draft H98 report this week. Here is one suggested clarification from Sigbjorn, arising from recent uncertainty about the true meaning of getLine. I'll incorporate it unless anyone yells. Simon -----Original Message----- From: Simon Marlow Sent: 05 June 2002 10:27 To: Sigbjorn Finne; Simon Peyton-Jones Subject: RE: cvs commit: hugs98/lib IO.hs Prelude.hs Agree with everything Sigbjorn says below. Also: change the definition of getLine (section A.3) to be getLine = hGetLine stdin Cheers, Simon -----Original Message----- From: Sigbjorn Finne [mailto:sof@galois.com] Sent: 04 June 2002 16:17 To: Simon Peyton-Jones Cc: Simon Marlow Subject: Re: cvs commit: hugs98/lib IO.hs Prelude.hs How about the following: * change the Report (7.1) to say something along the lines of: getChar raises an exception (Section <http://research.microsoft.com/Users/simonpj/haskell98-revised/haskell98 -report-html/io-13.html#io-exceptions> 7.3) on end-of-file; a predicate isEOFError that identifies this exception is defined in the IO library. getLine raises an end-of-file exception under the same conditions as hGetLine in the IO library. * in the Library Report, say when hGetLine raises an exception: Computation hGetLine hdl reads a line from the file or channel managed by hdl. The Prelude's getLine is a shorthand for hGetLine stdin. Error reporting: the hWaitForInput, hReady and hGetChar computations may fail with: isEOFError if the end of file has been reached. hGetLine will also fail with isEOFError if end-of-file is encountered when reading the first character of the line. If hGetLine encounters end-of-file at any other point while reading in a line, it is treated as a line terminator and the (partial) line is returned. Actually, I'd prefer if 11.7.1 only dealt with hWaitForInput and hReady (as they're the "checking for input" operations). A second section, named "Reading input", would then be concerned with hGetChar and hGetLine. --sigbjorn ----- Original Message ----- From: "Simon Peyton-Jones" < <mailto:simonpj@microsoft.com> simonpj(a)microsoft.com> To: "Sigbjorn Finne" < <mailto:sof@glass.cse.ogi.edu> sof(a)glass.cse.ogi.edu>; < <mailto:simonmar@microsoft.com> simonmar(a)microsoft.com> Sent: Tuesday, June 04, 2002 04:03 Subject: RE: cvs commit: hugs98/lib IO.hs Prelude.hs > Should I change the Report wording to be clearer? > > Simon > > | -----Original Message----- > | From: Sigbjorn Finne [mailto:sof@glass.cse.ogi.edu] > | Sent: 03 June 2002 15:49 > | To: <mailto:cvs-hugs@haskell.org> cvs-hugs(a)haskell.org > | Subject: cvs commit: hugs98/lib IO.hs Prelude.hs > | > | > | sof 2002/06/03 07:49:12 PDT > | > | Modified files: > | lib IO.hs Prelude.hs > | Log: > | Interpret Report wording for Prelude.getLine and IO.hGetLine > | to mean the Right Thing. If EOF is encountered for a partial > | line (>= 1 chars), interpret this as '\n'. > | > | Revision Changes Path > | 1.4 +25 -8 hugs98/lib/IO.hs > | 1.25 +23 -5 hugs98/lib/Prelude.hs > | _______________________________________________ > | Cvs-hugs mailing list > | <mailto:Cvs-hugs@haskell.org> Cvs-hugs(a)haskell.org <http://www.haskell.org/mailman/listinfo/cvs-hugs> http://www.haskell.org/mailman/listinfo/cvs-hugs > |

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Beginner's question: Memo functions in Haskell
by Matthias Heiler 05 Jun '02

05 Jun '02

Hello, In a machine learning application I am currently playing with string kernels which are recursively defined functions operating on strings. In Haskell the implementation of these functions is very pleasing as it is a one-to-one translation of the mathematical definition (see code below [2] and reference [1], p.424). However, the runtime performance is less pleasing as certain subexpressions are computed over and over again (profiling with ghc showed that the function k' (see code below) is called 1425291 times in a toy example). In a non-functional implementation I would now set up an auxillary data structure (e.g. a hash table) for caching/memorizing some intermediate results. How would this be done (elegantly, efficiently, by a Haskell-beginner) in Haskell? So far, I have seen code using lists to speed up fib(n). In my case the arguments of k' are Int -> String -> String, and I don't expect a simple list of tuples (Int, String, String, RESULT) to be efficient. Thank you very much for you help, Matthias [1] Huma Lodhi, Craig Saunders, John Shawe-Taylor, Nello Cristianini, Chris Watkins: "Text Classification using String Kernels", Journal of Machine Learning Research, 2(Feb):419-444, 2002. Available online at http://www.ai.mit.edu/projects/jmlr/papers/volume2.html [2] My code (actually the first 'real' piece of code I wrote in Haskell) is the following: ------------------------------------------------------------ module SKernel where k' :: Double -> Int -> String -> String -> Double k' lambda 0 s t = 1 k' lambda i s t = if min (length s) (length t) < i then 0 else (lambda * (k' lambda i s' t)) + sum [ lambda^((length t) - j + 2) * (k' lambda (i-1) s' t') | j <- [1..length t], t!!(j-1) == last s, t' <- [take (j-1) t] ] where s' = take ((length s) - 1) s k :: Double -> Int -> String -> String -> Double k lambda i s t = if min (length s) (length t) < i then 0 else k lambda i s' t + sum [ lambda^2 * (k' lambda (i-1) s' t') | j <- [1..length t], t!!(j-1) == last s, t' <- [take (j-1) t] ] where s' = take ((length s) - 1) s nk :: Double -> Int -> String -> String -> Double nk lambda n s t = (k lambda n s t) / sqrt ((k lambda n s s) * (k lambda n t t)) -- a toy example would be the call nk 0.5 5 "This is a string." "Here we have another string." ------------------------------------------------------------

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Bilgisayar Egitiminde Bir Numara
by Sertifikam.Com 05 Jun '02

05 Jun '02

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Bilgisayar Egitiminde Bir Numara
by Sertifikam.Com 05 Jun '02

05 Jun '02

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Type extensions
by Ronald Legere 04 Jun '02

04 Jun '02

Greetings. I have decided to try and understand the type system of haskell with extensions. As far as I can tell, the following set of extensions has been included, for example in ghc: multiparameter type classes constructor classes existential types explicit universal quantification scoped type signatures funtional dep?? Etc There is probably some overlap, and probably missed a few, as i do not understand what all these things do! ! My question: How do you get started learning all this? which of these is the most important? Is there a paper out there that explains most or all of these extensions and why you would want them and HOW the heck they work together? Ron Legere __________________________________________________ Do You Yahoo!? Yahoo! Greetings - send holiday greetings for Easter, Passover http://greetings.yahoo.com/

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RE: readFloat
by Simon Peyton-Jones 04 Jun '02

04 Jun '02

| Especially converting rationals to a string and back should | always be the identity. It would be better to print rationals in the | form | numerator % denominator | | and read them in the same form. Oh yes, that is absolutely what Haskell does for Rationals. The 'read' and 'show' for Rational uses the % notation. No proposed change here. The point is instead this: if you specifically want to read a Rational from a string like "3.24", which is perfectly reasonable (324 % 100), then the same function (readFloat) should do it as read a Float from the string in that format. That's what type-class overloading is for. Simon

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GreenCard: list marshalling
by Ferenc Wagner 03 Jun '02

03 Jun '02

Hi, I'd like to call LaPack routines from Haskell. Having read the GreenCard documentation it's still not obvious to me how I could marshall a list of numbers to C. Surely it's possible to create a ForeignObj, then fill it in element-by- element. But isn't there a more straightforward way? Even without monads? Cheers: Feri.

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Haskell HBLAS Library
by Hal Daume III 03 Jun '02

03 Jun '02

Hi All, I've just finished porting the BLAS linear algebra library to Haskell and am about to begin porting the LAPACK lin alg extensions. Currently the "package" looks very flat: HBlas.Types -- basic type HBlas.Convert -- basic conversion routines HBlas.Level1 -- BLAS level1 routines HBlas.Level2 -- BLAS level2 routines HBlas.Level3 -- BLAS level3 routines since I intend to share types between the HBlas system and the HLapack system, I intend to (shortly) make it something like: LinAlg.Types -- basic types LinAlg.Convert -- conversion LinAlg.HBlas.Level1 .Level2 .Level3 LinAlg.HLapack.and-so-on Before I do this, since changing module names is nontrivial, I was looking for some input whether this would be sufficient, or if I should make it Math.LinAlg... or something else. or Contrib.LinAlg or whatever. I don't mean to start a huge discussion; if there's a correct thing to do, and someone would tell me that, that's sufficient. Also, I'm looking for someone to help me out packaging it all up; I know very little about making makefiles, etc. The whole package is fairly complicated, since it requries BLAS to be installed, greencard to be run, the haskell to be compiled, and haddock to generate the documentation. Hopefully someone will volunteer. Finally, I've been trying to make myself document the library; you can find a somewhat recent version of the haddock docs at: http://www.isi.edu/~hdaume/HBlas but this will probably move shortly. - 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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Re: arrows
by Ashley Yakeley 03 Jun '02

03 Jun '02

At 2002-05-25 01:32, Koen Claessen wrote: >Might I remind you that an arrow (as defined in category >theory) only requires identy and composition to be defined >and satisfying some laws? > >In particular, an arrow does not have to have the operations >"arr" and "first". Well either "arrow" is being used in two different senses or the "Arrow" class should be renamed. If you can't define "arr" and "first", it may be an arrow but it's not an Arrow. -- Ashley Yakeley, Seattle WA

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