February 2001 - Haskell-Cafe

RE: GHC Core Language
by Andrew Tolmach 07 Feb '01

07 Feb '01

[moving to haskell-cafe] > From: matt hellige [mailto:matt@immute.net] > a quick question re: ghc's Core language... is it still very similar > to the abstract syntax given in, for example, santos' "compilation by > transformation..." (i think it was his dissertation?) and > elsewhere, or > has it changed significantly in the last couple of years? i only ask > because i know the language used in that paper is somewhat > different from > the Core language given in peyton jones and lester's > "implementing functional > languages" from 92, and includes type annotations and so on. > > m > The current Core language is still quite similar to what is described in Santos' work; see SL Peyton Jones and A Santos, "A transformation-based optimiser for Haskell," Science of Computer Programming 32(1-3), pp3-47, September 1998. http://research.microsoft.com/Users/simonpj/papers/comp-by-trans-scp.ps.gz But there have been some noticeable changes; for example, function arguments are no longer required to be atomic. A more recent version of Core is partially described (omitting types) in SL Peyton Jones & S Marlowe, "Secrets of the Glasgow Haskell Compiler Inliner," IDL'99. http://research.microsoft.com/Users/simonpj/papers/inline.ps.gz

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Re: Revamping the numeric classes
by Ch. A. Herrmann 07 Feb '01

07 Feb '01

moved to haskell-cafe Ketil> E.g. way back, I wrote a simple differential equation solver. Ketil> Now, the same function *could* have been applied to vector Ketil> functions, except that I'd have to decide on how to implement Ketil> all the "Num" stuff that really didn't fit well. Ideally, a Ketil> nice class design would infer, or at least allow me to Ketil> specify, the mathematical constraints inherent in an Ketil> algorithm, and let my implementation work with any data Ketil> satisfying those constraints. the problem is that the --majority, I suppose?-- of mathematicians tend to overload operators. They use "*" for matrix-matrix multiplication as well as for matrix-vector multiplication etc. Therefore, a quick solution that implements groups, monoids, Abelian groups, rings, Euclidean rings, fields, etc. will not be sufficient. I don't think that it is acceptable for a language like Haskell to permit the user to overload predefined operators, like "*". A cheap solution could be to define a type MathObject and operators like :*: MathObject -> MathObject -> MathObject Then, the user can implement: a :*: b = case (a,b) of (Matrix x, Matrix y) -> foo (Matrix x, Vector y) -> bar -- Christoph Herrmann E-mail: herrmann(a)fmi.uni-passau.de WWW: http://brahms.fmi.uni-passau.de/cl/staff/herrmann.html

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RE: binary files in haskell
by Simon Marlow 06 Feb '01

06 Feb '01

> > How about this slightly more general interface, which works > with the new > > FFI libraries, and is trivial to implement on top of the > primitives in > > GHC's IOExts: > > > > hPut :: Storable a => Handle -> a -> IO () > > hGet :: Storable a => Handle -> IO a > > What about endianess? In which format are Floats or even just Bools > stored? For a file which probably shall be read from > different machines > this is not clear at all. The behaviour is defined by the Storable instances for each type. The endianness for writing say an Int32 would be the same as the host architecture, for instance. If you want to work with just bytes, you can always just use hPut and hGet at type Word8. Overloading with Storable gives you more flexibility, since if you have a way to serialise an object in memory for passing to a foreign function, you also have a way to store it in binary format in a file (modulo problems with pointers, of course). In the long term, we'll want to be able to serialise more than just Storable objects (c.f. the other overloaded binary I/O libraries out there), and possibly make the output endian-independent - but after all there's no requirement that Haskell's Int has the same size on all implementations, so there's no guarantee that binary files written on one machine will be readable on another, unless they only use explicitly sized types or Integer. Perhaps these should be called hPutStorable and hGetStorable so as not to prematurely steal the best names. > I think John is right that there needs to be a primitive interface for > just writing bytes. You can then build anything more > complicated on top > (probably different high-level ones for different purposes). > > I just see one problem with John's proposal: the type Byte. It is > completely useless if you don't have operations that go with it; > bit-operations and conversions to and from Int. The FFI > already defines > such a type: Word8. So I suggest that the binary IO library > explicitely > reads and writes Word8's. yup, that's what I had in mind. Cheers, Simon

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Re: binary files in haskell
by malcolm-haskell＠cs.york.ac.uk 06 Feb '01

06 Feb '01

John Meacham wrote: > I wrote up a proposal for a binary file IO mechanism to be added > as a 'blessed addendum' to the standard at best and as a commonly > implmented extension (in hslibs) at least.. I have looked at your proposal. If you would like it to be widely available, you will need to write an implementation of the library, or find someone who can write it for you. Type signatures are great as documentation, but they are not directly executable. :-) Regards, Malcolm

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Haskell Implemetors Meeting
by Timothy Docker 05 Feb '01

05 Feb '01

> We agreed that it would be a Jolly Good Thing if GHC could > be persuaded to produce GHC-independent Core output, > ready to feed into some other compiler. For example, > Karl-Filip might be able to use it. > ANDREW will write a specification, and implement it. A quick question. What is meant by "Core output"? Subsequent posts seem to suggest this is some "reduced Haskell", in which full Haskell 98 can be expressed. Am I completely off beam here? Tim Docker

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Knight
by Christoph M. 04 Feb '01

04 Feb '01

Hi ! Yes, I meant the Knight's Tour problem. Could anybody post me a solve of this problem in haskell ? Thanks a lot, Christoph

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Provider / Haskell-CGI's
by Claudius Heitz 03 Feb '01

03 Feb '01

Hello! Does anybody know a provider, where I can run Haskell-CGI's? I mean, in standard webhosting package? And are there any in Germany? TIA! Claudius _______________________________________________________________________________ Alles unter einem Dach: Informationen, Fun, E-Mails. Bei WEB.DE: http://web.de Die große Welt der Kommunikation: E-Mail, Fax, SMS, WAP: http://freemail.web.de

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Fundeps and quantified constructors
by Tom Pledger 02 Feb '01

02 Feb '01

nubie nubie writes: | So I want to have a polymorphic Collection type, just because. | | > class Collection c e | c -> e where | > empty :: c | > put :: c -> e -> c | | > data SomeCollection e = forall c . Collection c e => MakeSomeCollection c | | Hugs (February 2000) doesn't like it. It says | Variable "e" in constraint is not locally bound | | I feel that e *is* bound, sort of, because c is bound and there's a | fundep c->e. That line of reasoning establishes that e is constrained on the right hand side of the "=". However, it's still bound (by an implicit "forall e") on the left hand side of the "=". The problem is that e can leak details about c to parts of the program outside the "forall c". It's still a problem if you remove the "| c -> e" fundep. A more common use of a "Collection c e | c -> e" class is: data SomeCollection e = --some data structure involving e instance SomeContext e => Collection (SomeCollection e) e where --implementations of empty and put, for the aforementioned --data structure, and entitled to assume SomeContext Is that collection type polymorphic enough for your purposes? : | The following things work as expected: | | > data IntCollection = forall c . Collection c Int => MakeIntCollection c | > data AnyCollection = forall c e . Collection c e => MakeAnyCollection c Neither of them has a type variable tunnelling through the local quantifier. HTH. Tom

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Various software and a question
by Ian Lynagh 02 Feb '01

02 Feb '01

Hi all First a brief question - is there a nicer way to do something like #ifdef __GLASGOW_HASKELL__ #include "GHCCode.hs" #else > import HugsCode #endif than that (i.e. code that needs to be different depending on if you are using GHC or HUGS)? Secondly, I don't know if this sort of thing is of interest to anyone, but inspired by the number of people who looked at the MD5 stuff I thought I might as well mention it. I've put all the Haskell stuff I've written at http://c93.keble.ox.ac.uk/~ian/haskell/ (although I'm new at this game so it may not be the best code in the world). At the moment this consists of a (very nearly complete) clone of GNU ls, and MD5 module and test program and the smae for SHA1 and DES. The ls clone needs a ptch to GHC for things like isLink (incidentally, would it be sensible to try and get this included with GHC? It is basically a simple set of changes to the PosixFiles module, but needs __USE_BSD defined (which I guess is the reason it is not in there, but it could have it's own file?)). Have fun Ian, wondering how this message got to be so long

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Source tar ball for Simon Marlow's Haskell Web Server??
by Bill Halchin 01 Feb '01

01 Feb '01

Hello, I looked on www.haskell.org for the Simon Marlow's Web Server, but couldn't find. Did I overlook it? Regards, Bill Halchin _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com

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