March 2003 - Haskell - Haskell.org

Re: URI handling code in Haskell available
by Graham Klyne 06 Mar '03

06 Mar '03

At 08:25 06/03/2003 +0100, Johannes Waldmann wrote: >On Wed, 5 Mar 2003, Graham Klyne wrote: > > > I've released a first version of some URI parsing and handling code at: > > http://www.ninebynine.org./Software/HaskellURI.zip > >but this library is already in ghc: >http://www.haskell.org/ghc/docs/latest/html/network/Network.URI.html Oops. I didn't find that. Thanks for the pointer. (Thinks: does it work with HUGS?) A significant amount of my work went into the test cases and matching the parsing code against the (revised work-in-progress) URI spec, so maybe there's some residual value there...? #g ------------------- Graham Klyne <GK(a)NineByNine.org> PGP: 0FAA 69FF C083 000B A2E9 A131 01B9 1C7A DBCA CB5E

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URI handling code in Haskell available
by Graham Klyne 06 Mar '03

06 Mar '03

I've released a first version of some URI parsing and handling code at: http://www.ninebynine.org./Software/HaskellURI.zip With a (very) few words of write-up at: http://www.ninebynine.org./Software/ReadMe-URI-Haskell.txt The URI parser code is based very closely on the syntax specification given in Roy Fielding's current revision of the URI specification [1]. The unit tests are based substantially on Dan Connolly's Python code [2]. The code is a bit scrappy, as I'm new to Haskell, but it does pass a fairly comprehensive array of unit tests (also included with the software). Error handling is in the range of weak-to-non-existent. #g -- [1] http://www.apache.org/~fielding/uri/rev-2002/rfc2396bis.html [2] http://www.w3.org/2000/10/swap/uripath.py ------------------- Graham Klyne <GK(a)NineByNine.org> PGP: 0FAA 69FF C083 000B A2E9 A131 01B9 1C7A DBCA CB5E

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Re: fundeps for extended Monad definition
by oleg＠pobox.com 06 Mar '03

06 Mar '03

Ashley Yakeley wrote: > If this were allowed, it would effectively allow type-lambda > class C a b | a -> b > instance C Int Bool > instance C Bool Char > newtype T a = MkT (forall b.(C a b) => b) > helperIn :: (forall b.(C a b) => b) -> T a > helperIn b = MkT b; -- currently won't work > helperOut :: T a -> (forall b.(C a b) => b) > helperOut (MkT b) = b And it does work (based on the code shown here previously): > class C a b | a -> b > instance C Int Bool > instance C Bool Char > instance C Char Float > instance C Float (Int->()) > instance (C a b) => C (a->()) (b->()) > newtype T a = T (forall b.(C a b) => b) > data T1 a = T1 a (T a) > xx b = case (T1 b (T undefined)) of T1 _ (T x) -> x Ok, modules loaded: Main. *Main> :type xx$(1::Int) Bool *Main> :type xx$ xx$ (1::Int) Char *Main> :type xx$ xx$ xx$ (1::Int) Float *Main> :type xx$ xx$ xx$ xx$ (1::Int) Int -> () *Main> :type xx$ xx$ xx$ xx$ xx$ (1::Int) Bool -> () *Main> :type xx$ xx$ xx$ xx$ xx$ xx$ (1::Int) Char -> () *Main> :type xx$ xx$ xx$ xx$ xx$ xx$ xx$ (1::Int) Float -> () *Main> :type xx$ xx$ xx$ xx$ xx$ xx$ xx$ xx$ (1::Int) (Int -> ()) -> () *Main> :type xx$ xx$ xx$ xx$ xx$ xx$ xx$ xx$ xx$ (1::Int) (Bool -> ()) -> () *Main> :type xx$ xx$ xx$ xx$ xx$ xx$ xx$ xx$ xx$ xx$ (1::Int) (Char -> ()) -> () It seems it does compute.... The principle was to use constraints to force the "evaluation" of the type "lambda". Obtaining the type "lambda" was the thrust behind the exercise with existential and useless types. Perhaps I neglected to mention that point. We can use the Coerce type function (aka class) mentioned in the thread on first-class types to convert from the types computed by 'xx' to values. Incidentally, the class D was already a type function: the function 'meet'.

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Function wows
by Robert Perren 06 Mar '03

06 Mar '03

As part of a larger program I have created the following functions to convert a list of bits into the integer represents, also to simplify things the order of the bits is reversed [1,1,0,1] represents 1011 (or 13). At the moment the frombin function below works fine. type Bit = Int frombin :: [Bit] -> Int frombin xs = sum (tonum xs) tonum :: [Bit] -> [Bit] tonum [] = [] tonum (n:ns) = (n:(tonum (map (*2) ns))) However why when I try the function below does it not work in Hugs? frombin :: [Bit] -> Int frombin [] = 0 frombin (n:ns) = sum (n:( frombin (map (*2) ns))) Is this surely not just a combination of the two? Any help would be much appreciated Thanks, Rob --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com) Version: 6.0.456 / Virus Database: 256 - Release Date: 18/02/2003

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(no subject)
by b.i.mills＠massey.ac.nz 06 Mar '03

06 Mar '03

To <haskell(a)haskell.org> Subject: Re: int to float problem In-Reply-To: <200303031210.AA617087468(a)snip.net> Yo, > Haskell Integers are not a proper subset of Haskell Floats or > Doubles. Haskell does not support real numbers. I'd just like to add ... Real numbers are not implementable on a digital computer. This is not a "practical" matter of resources, or a design decision in by the language designer, but the fact that any data type each of whose elements are represented in a finite number of bytes can't have more than a countable number of data elements. Integers, and Rationals can be represented. Even the so-called computable-real-numbers, (still countable) don't work as well as you would want, since things such as "is this number bigger than that one" can't always be computed. Add to this the fact that the generic float type does not satisfy algebraic constraints such as associativity, and so can't, from the axiomatic point of view, be considered to be a representation of rational numbers (let alone reals). Basically, from the algebraic perspective, the float type is a messy fudge, and does not fit in nicely with any of the "pure" types. In general the containment Complex ---> Real --> Rational ---> integer ---> whatever. Does not apply in this simple way to numerical types on a computer, because data types are often constructed on the basis of not just what they represent, but also how they represent these things. The computable world (constructive mathematics) is a lot more complicated and open ended than the existential approach. Regards, Bruce. ps: I've made previous comments about this sort of thing: ``Algebraic Conversions'', A mathematical paper introducing a generalisation of homomorphism of universal algebras. In Research Letters in the Information and Mathematical Sciences Vol 2, May 2001. (pub by Massey University New Zealand). see also, \verb|http://www.massey.ac.nz/~wwiims/rlims|

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RE: HTTP protocol libraries
by Bayley, Alistair 05 Mar '03

05 Mar '03

On a related note, what happened to the source code for the Haskell Web Server? http://research.microsoft.com/~simonmar/hws.tar.gz Is it no longer suitable for public consumption? (I have a copy at home somewhere, though). -----Original Message----- From: Johannes Waldmann [mailto:joe@isun.informatik.uni-leipzig.de] Sent: 05 March 2003 13:42 To: haskell(a)haskell.org Subject: HTTP protocol libraries Dear all, I am looking for a Haskell library for the HTTP/1.1 protocol, i. e. data types for Requests and Responses, and functions to read chunked bodies etc. Is there such a thing? -- -- Johannes Waldmann ---- http://www.informatik.uni-leipzig.de/~joe/ -- -- joe(a)informatik.uni-leipzig.de -- phone/fax (+49) 341 9732 204/207 -- ***************************************************************** The information in this email and in any attachments is confidential and intended solely for the attention and use of the named addressee(s). This information may be subject to legal professional or other privilege or may otherwise be protected by work product immunity or other legal rules. It must not be disclosed to any person without our authority. If you are not the intended recipient, or a person responsible for delivering it to the intended recipient, you are not authorised to and must not disclose, copy, distribute, or retain this message or any part of it. *****************************************************************

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RE: HTTP protocol libraries
by Simon Marlow 05 Mar '03

05 Mar '03

> From: Bayley, Alistair [mailto:Alistair_Bayley@ldn.invesco.com] > > On a related note, what happened to the source code for the > Haskell Web > Server? > > http://research.microsoft.com/~simonmar/hws.tar.gz > > Is it no longer suitable for public consumption? (I have a > copy at home somewhere, though). It's in GHC's CVS repository, under fptools/hws. Cheers, Simon

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AW: Parsec: GHC /= Hugs?
by Markus.Schnell＠infineon.com 05 Mar '03

05 Mar '03

> Try the November release of Hugs with the +N option. Well, now Hugs and ghc show the same behaviour for my program: they don't parse my doc, even with the same error. But the +N does not work: it says "New hierarchical libraries not found along search path; ignoring +N toggle." I tried adding {Hugs}\libraries to the Options, but after a restart, it is missing again. How can I change that?

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Parsec: GHC /= Hugs?
by Markus.Schnell＠infineon.com 05 Mar '03

05 Mar '03

My program has a different behaviour under hugs and ghc. I wrote a very simple parser with Parsec and it parses a file quite easily - as long as I use hugs to run it. But when I compile it with ghc, the parse fails. (I'm currently working on WinNT with cygwin). Something else, but related: how do I avoid writing different Code for Hugs and ghc? For example, I had to hide "Word" in Hugs with > import Prelude hiding (Word) but was not allowed to do that with ghc. I ended up using "Wort". Why the difference? Markus

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RE: GUI for Windows
by Guest, Simon 05 Mar '03

05 Mar '03

Hi Markus, I use FranTk with ghc 5.04.2 on windows, and it works just fine. It provides a high level of abstraction, which is what I find particularly compelling. To build it with ghc 5.04 I had to patch it a little. Only trivial things like: in src/FRPSrc/StaticTypes/Compatibility.ghc.hs, you have to define fromInt and toInt in terms of fromIntegral. in src/FranTkSrc/FranTkConc.lhs and src/TclHaskellSrc/ConcTcl.hs, you have to import CVar (I think that's all.) I could send you my patches if you like. cheers, Simon > -----Original Message----- > From: Markus.Schnell(a)infineon.com [mailto:Markus.Schnell@infineon.com] > Sent: 03 March 2003 15:21 > To: haskell(a)haskell.org > Subject: GUI for Windows > > > What User Interface Library would you recommend for use under Windows? > I tried FranTk but it crashes as soon as I run the display > function (under > hugs) > and with ghc it won't even compile (I already tinkered with > the makefiles, > so > finally I could make the package, but then the demos won't compile). > > Any ideas, suggestions? > > Markus > > > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell >

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