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asking for a favor
by garroyo＠dsic.upv.es 23 Mar '04

23 Mar '04

Hi, Does someone has the Haskell XML Toolbox, lets say working in Windows environment?. I have tried install them in Hugs 98 for Windows but there are Hexadecimal characters escape out of range. One choice, I know, is go to LINUX. I am working in CNC programming and I am in the begining of the a research. Thanks in advace. Gustavo. ------------------------------------------------- This mail sent through IMP: http://horde.org/imp/

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haskell idiom for reversible computations
by S. Alexander Jacobson 23 Mar '04

23 Mar '04

If I am writing a rener/parser for e.g. HTTP Requests and Responses, I would like to be able to guarantee that the parser really is the inverse of the generator. I assume that if I define a pair of computations as reversible then I can put those computations in some monad such that I can do: parse = inverse generate and parse2 = inverse do {generate;generate2} Actually, I assume this is an arrow rather than a monad because a render is a computation that takes a value and produces a value rather than simply a computation that produces a value. Whether its an arrow or not, I also assume this problem is sufficiently common that there is a well worked out idiom for this such that I don't have to hand-code and prove inverse functions for all my data structures. I just don't know what it is. -Alex- _________________________________________________________________ S. Alexander Jacobson mailto:me@alexjacobson.com tel:917-770-6565 http://alexjacobson.com

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Seen in ACM technews...
by Graham Klyne 22 Mar '04

22 Mar '04

[[ # "Learning Functional Programming Through Multimedia" Slashdot (03/16/04); Jones, Isaac Haskell is a purely functional programming language and the book, "The Haskell School of Expression: Learning Functional Programming Through Multimedia," is a great introduction to the platform now being used for cutting-edge programming language research. The Haskell community is still rather small, but working on tremendously innovative research such as the meta-programming environment Template Haskell implemented by the Glasgow Haskell Compiler, while Haskell can also be extended with Embedded Domain-Specific Languages for Web authoring, parsing, and controlling humanoid robots without changing the language itself. Paul Hudak's book prepares the reader to begin writing tools or participate in ongoing programming language research. Haskell prepares readers for new developments such as the arrows concept used by the Yale Haskell group; Yale-developed Yampa, a "Functional Reactive Programming" framework, shares concepts with the animation described in "The Haskell School of Expression." The book is written in a tutorial style with alternating conceptual and application chapters. The provided code examples may be insufficient for those who want to jump ahead, but the Web site provides fill-in code. Readers completing the examples given in the book will also need the "November 2002" version of the Hugs interpreter and the User's Guide. "The Haskell School of Expression" eases programmers who are unfamiliar with functional programming into complex components such as recursion; falling back on non-functional style is not allowed with Haskell. The book also tackles the difficult issue of monads by getting readers to use them very early on and explaining the concepts behind them later in the book. Although there is a lot of drawing and music involved in "The Haskell School of Expression," the author includes mathematical background such as the algebraic reasoning for shapes and music, as well as a chapter on proof by induction. Click Here to View Full Article http://books.slashdot.org/books/04/03/12/221232.shtml?tid=126&tid=156&tid=1… ]] -- http://www.acm.org/technews/articles/2004-6/0322m.html#item12 ------------ Graham Klyne For email: http://www.ninebynine.org/#Contact

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????Pattern match(es) are overlapped???
by S. Alexander Jacobson 22 Mar '04

22 Mar '04

I am implementing HTTP and I have something like: newtype Method = Method String getMethod = Method "GET" putMethod = Method "PUT" [...] doMeth getMethod = ... doMeth putMethod = ... GHC gives me a patter matches are overlapped warning. And when I run, I discover that pattern matching is not actually happening. getMethod is always executed even though the method passed is putMethod.... What am I doing wrong? -Alex- _________________________________________________________________ S. Alexander Jacobson mailto:me@alexjacobson.com tel:917-770-6565 http://alexjacobson.com

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Dividing integers?
by Matias Hernandez 18 Mar '04

18 Mar '04

Hello there! Although you might not believe it since I'm going to ask a very very very basic question, I have been using Haskell for educational purposes for a couple semesters now. Nevertheless, I don't think I have ever worked with non-Int number types! :) I don't understand why I get this error. I mean, apparently "/" is not defined for integers but I don't know how to "cast" the result of the length function into a Double... Prelude> (length [1,2]) / 3 <interactive>:1: No instance for (Fractional Int) arising from use of `/' at <interactive>:1 In the definition of `it': it = (length [1, 2]) / 3 Besides, a simple integer division works: Prelude> 2 / 3 0.6666666666666666 But I would guess that's because '2' and '3' are parsed as Floats because they are used in a divide function. Any help will be appreciated! Best regards, - Matías

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RE: [Haskell-cafe] Building Haddock on Windows
by Simon Marlow 17 Mar '04

17 Mar '04

> Has anyone recently built Haddock on Windows? I'm invoking > configure and > make from Cygwin bash. Configure takes a couple of hours, and > then make produces a load of errors (see below). I'm ashamed to say that Haddock, like Alex and Happy don't really support native Windows too well. You can use them in a Cygwin (and possibly MSYS) environment, by doing the usual ./configure && make install, which will install the tool by default in /usr/local/bin. Cheers, Simon

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RE: [Haskell-cafe] Building Haddock on Windows
by Simon Marlow 17 Mar '04

17 Mar '04

> Got it built after realising that my PATH didn't include ghc > (thanks Andy > Moran). I renamed haddock.bin to haddock.exe and copied to > into ghc's bin > for convenience (ghc's bin is already in my path). Now I just > have to figure out how to invoke it... > > Where can I find instructions for use? I see haddock.sgml in > haddock-0.6/haddock/doc but reading sgml hurts. Is there an > html version of this somewhere? HTML docs are on the web: http://www.haskell.org/haddock/docs/haddock.html Haddock is designed to be installed via 'make install', and then run using the script named 'haddock' in $prefix/bin. You *can* run the binary directly, but you'll need to pass it some extra arguments so that it can find its files. > I have a few questions: > - can you invoke it on a folder and have it generate docs > for all of the > source files in it (and sub-folders)? > - does it work on .lhs source containing bird-track style > code? It would > appear not, as I get a parse error. These Qs are answered in the docs. > - why doesn't it know what Int, String, Float, IO, Monad, > Show, etc are? > What invocation option do I need to ensure it links to > Prelude/hierarchical-library stuff? (I think it's > --read-interface; must I > generate interface files for the Prelude and libraries though?) You get the interfaces for the libraries with a GHC installation. Just use the --read-interface flag to tell Haddock about them. Cheers, Simon

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RE: [Haskell-cafe] Building Haddock on Windows
by Bayley, Alistair 17 Mar '04

17 Mar '04

http://www.haskell.org/haddock/docs/haddock.html Ahh, sorry, somehow I missed that. Yes, that is the html generated from the sqml. > -----Original Message----- > From: Arjan van IJzendoorn [mailto:afie@cs.uu.nl] > Sent: 17 March 2004 14:00 > To: Bayley, Alistair > Cc: haskell-cafe(a)haskell.org > Subject: Re: [Haskell-cafe] Building Haddock on Windows > > > Hello Alistair, > > > Where can I find instructions for use? I see haddock.sgml in > > haddock-0.6/haddock/doc but reading sgml hurts. Is there an > html version > of > > this somewhere? > > Haddock is very well documented at http://www.haskell.org/haddock/ > > Greetings, Arjan ----------------------------------------- ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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RE: [Haskell-cafe] Building Haddock on Windows
by Bayley, Alistair 17 Mar '04

17 Mar '04

Got it built after realising that my PATH didn't include ghc (thanks Andy Moran). I renamed haddock.bin to haddock.exe and copied to into ghc's bin for convenience (ghc's bin is already in my path). Now I just have to figure out how to invoke it... Where can I find instructions for use? I see haddock.sgml in haddock-0.6/haddock/doc but reading sgml hurts. Is there an html version of this somewhere? I have a few questions: - can you invoke it on a folder and have it generate docs for all of the source files in it (and sub-folders)? - does it work on .lhs source containing bird-track style code? It would appear not, as I get a parse error. - why doesn't it know what Int, String, Float, IO, Monad, Show, etc are? What invocation option do I need to ensure it links to Prelude/hierarchical-library stuff? (I think it's --read-interface; must I generate interface files for the Prelude and libraries though?) Thanks, Alistair. > -----Original Message----- > From: Simon Marlow [mailto:simonmar@microsoft.com] > Sent: 17 March 2004 13:22 > To: Bayley, Alistair; haskell-cafe(a)haskell.org > Subject: RE: [Haskell-cafe] Building Haddock on Windows > > > > > Has anyone recently built Haddock on Windows? I'm invoking > > configure and > > make from Cygwin bash. Configure takes a couple of hours, and > > then make produces a load of errors (see below). > > I'm ashamed to say that Haddock, like Alex and Happy don't really > support native Windows too well. > > You can use them in a Cygwin (and possibly MSYS) environment, by doing > the usual ./configure && make install, which will install the tool by > default in /usr/local/bin. > > Cheers, > Simon ----------------------------------------- ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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infix naming
by David Roundy 17 Mar '04

17 Mar '04

[moving to haskell-cafe due to an extreme shift in topic] On Wed, Mar 17, 2004 at 08:55:22AM +0100, Ketil Malde wrote: > > So it is agreed: we use "isXXXX" :-) > > Hmm... > > s1 `isSubsetOf` s2 vs s1 `isSubset` s2 > isSubsetOf s1 s2 isSubset s1 s2 > > I'm not sure I have any clear preference. ..Of reads slightly clearer > in infix notation, but is arguably a bit more confusing in prefix. This seems to be a common problem: a name that makes sense (i.e. it is obvious what it does) in prefix notation very often is completely wrong in infix notation, particularly when partially applied. "e `isElementOf` list" makes perfect sense, while "isElementOf e list" seems a bit wrong, and "isElementOf e" (of type [a] -> Bool) reads completely wrong. I guess "`isElementOf` list" (which is of type a -> Bool) does make sense. I guess perhaps names just have be chosen to either make sense in infix notation, or in prefix notation, but not both? Is this a general principle, and if so, that seems bad, since the choice of infix vs prefix notation seems like it shouldn't have to be made at the API level. Does anyone know why it was originally decided to make infix notation work as it does? To me it seems like it would make sense for (`f` x) to be the same as (f x) rather than the opposite. e.g. (`is_less_than` 2) and (is_less_than 2) sound the same way when I pronounce them, and it's not entirely pleasant that the second one is in fact the same as (>= 2). On the other hand, if you don't think of it as (is_less_than a) b, one might naturally think that (is_less_than a b) should be (a < b). -- David Roundy http://www.abridgegame.org

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