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Re: Coding Problems!! Please help
by John Hughes 17 Apr '02

17 Apr '02

I am currently working on an assignment with requires us to write in Haskell. I am having trouble with "pipeline". The required textbook called, "The Craft of Functional Programming" 2nd Edition. There is a pipeline example, which I find it useful in my assignment, but for some reason, there may be a typo in the pipeline syntax, which is ">.>". Coz it doesn't compile. Your problem is that that book defines and uses a non-standard composition operator. The standard Haskell function composition is written just ".", defined by (f . g) x = f (g x) Notice that in f . g, it is *g* which is applied first to the argument, and f which is applied to the result of that. That is, composition is "backwards" in some sense. Here's an example: sqrt . abs takes the absolute value of its argument first, and then the square root of that, not the absolute value of the square root (which would fail for negative arguments). Many people (including mathematicians) prefer to write the arguments of compose in the other order, so that the first function to be applied is the first one you write. To make that possible, Simon Thompson defines (f >.> g) x = g (f x) So now you would write the example above as abs >.> sqrt You take the absolute value first, so you write it first. Regardless of which you prefer, the important thing to understand is that >.> IS NOT PART OF THE HASKELL STANDARD. So if you want to use it, you have to include the definition above in your own program. John Hughes

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Coding Problems!! Please help
by Jack Tsai 17 Apr '02

17 Apr '02

Dear staff, I am currently working on an assignment with requires us to write in Haskell. I am having trouble with "pipeline". The required textbook called, "The Craft of Functional Programming" 2nd Edition. There is a pipeline example, which I find it useful in my assignment, but for some reason, there may be a typo in the pipeline syntax, which is ">.>". Coz it doesn't compile @_@ I have attached a file of the example, I found from the book. There is a website where I could download the entire book. It's got the same stuff as in my textbook. Please help me, coz i've tried even Unix's pipeline syntax which is obviously wrong... I'm not desperate, please reply, thank you very much. Sincerely, Jack This is the output of the compilor... /*********************************************************************/ Haskell 98 mode: Restart with command line option -98 to enable Reading file "C:\PROGRAM FILES\HUGS98\lib\Prelude.hs": Parsing........................................................ Dependency analysis............................................ Type checking.................................................. Compiling...................................................... Reading file "E:\433\CHAPTE~1.LHS": Parsing........................................................ Dependency analysis ERROR "E:\433\CHAPTE~1.LHS" (line 22): Undefined variable ">.>" Prelude> /**********************************************************************/ _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com

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Coding Problems!! Please help
by Jack Tsai 17 Apr '02

17 Apr '02

Dear staff, I am currently working on an assignment with requires us to write in Haskell. I am having trouble with "pipeline". The required textbook called, "The Craft of Functional Programming" 2nd Edition. There is a pipeline example, which I find it useful in my assignment, but for some reason, there may be a typo in the pipeline syntax, which is ">.>". Coz it doesn't compile @_@ I have attached a file of the example, I found from the book. There is a website where I could download the entire book. It's got the same stuff as in my textbook. Please help me, coz i've tried even Unix's pipeline syntax which is obviously wrong... I'm not desperate, please reply, thank you very much. Sincerely, Jack This is the output of the compilor... /*********************************************************************/ Haskell 98 mode: Restart with command line option -98 to enable Reading file "C:\PROGRAM FILES\HUGS98\lib\Prelude.hs": Parsing........................................................ Dependency analysis............................................ Type checking.................................................. Compiling...................................................... Reading file "E:\433\CHAPTE~1.LHS": Parsing........................................................ Dependency analysis ERROR "E:\433\CHAPTE~1.LHS" (line 22): Undefined variable ">.>" Prelude> /**********************************************************************/ _________________________________________________________________ Send and receive Hotmail on your mobile device: http://mobile.msn.com

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Feeling Old? We Can Help!
by unknown＠example.com 15 Apr '02

15 Apr '02

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HC&AR (May edition) - call for contacts and contributions
by C.Reinke 15 Apr '02

15 Apr '02

Dear fellow Haskeller, it is time again - for contributions to the second edition of the Haskell Communities and Activities Report http://www.haskell.org/communities/ The current plan is to get contributions in by the end of April, and to get the collective report out early next month (*). The general idea is to update all existing summaries, to drop any topics that didn't have any activity for two consecutive 6-month periods, and to add any new developments or topics for which no-one contributed summaries to the first edition, while trying to keep the whole under 25 pages. As you can see on the report's home page, many of last time's contributors have already volunteered to provide updates of their reports, including coverage of the major Haskell implementations and Report Addenda. But where you don't yet see contacts listed for your own subject of interest, you are welcome to volunteer, or to remind your local community/project team/mailing list/research group/etc. that they really ought to get their act together and let the Haskell community as a whole know about what they've been doing!-) A typical summary report would be between 1 and 3 paragraphs (what's it about? major topics and results since the last report? current hot topics? major goals for the next six months?) plus pointers to material for further reading (typically to a home page, or to mailing list archives, specifications and drafts, implementations, meetings, minutes,..). New suggestions for current hot topics, activities, projects, .. are welcome - especially with names and addresses of potential contacts. Two particular new suggestions I'd like to try this time are appended below. Thanks, Claus (*) Last time's experience showed that it takes an arbitrary number of weeks to write a nice summary in the last hour, so I hope that 2 weeks give enough flexibility to find a spare hour, or to coordinate the summary with any planned releases. ---------------------------------------------- Two new suggestions: 1 Applications: "what are you using Haskell for?" The implementation mailing lists are full of people sending in bug reports and feature suggestions, stretching the implementations to their limits. Judging from the "reduced" examples sent in to demonstrate problems, there must be quite a few Haskell applications out there that haven't been announced anywhere (probably because Haskell is "just" the tool, not the focus of those projects). If you're one of those serious Haskell users, why not write a sentence or two about your application? We'd be particularly interested in your experience with the existing tools (e.g., that all-time-favourite: how difficult was it to tune the resource usage to your needs, after you got your application working? Which tools/libraries where useful to you? What is missing?). 2 Project pings: "anyone still working on this?" There are numerous projects out there that don't add new features to their software releases every week, but are steadily working towards longer-term goals while keeping their software releases maintained and up-to-date. The people involved often say "We don't really have to report anything new, so we won't report anything.". However, most of you out there know that there is a *huge* difference between projects and software in silent maintenance mode (i.e., actively being worked on) and those that die the silent death of "been there, published that, let's move on". If you are the contact person for a project/software of the former kind, and you just want to reassure Haskellers that your stuff is still alive and kicking, send me a brief "ping", and I'll try to include a list of those pings, with contact addresses (as proofs of liveness), in the upcoming report.

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help need
by Benny 15 Apr '02

15 Apr '02

type Poly = [Float] addPoly::Poly->Poly->Poly addPoly x y = zipWith (+) x y instance (Float a) => Num (Poly a) where x + y = addPoly x y I got the "Cannot use type synonym in instance head" error message when I was trying to compile the above code. Can you tell me why and how to solve it? Cheers Benny

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"do" notation and ">>"
by Simon Peyton-Jones 15 Apr '02

15 Apr '02

Folks Following a good deal of email I now propose to DO NOTHING to the rules defining do-notation in the Haskell 98 Report. That means that GHC and Hugs, and nhc perhaps, should change so that they actually implement the do-notation translation rule do {e ; stmts} = e >> do {stmts} using (>>) and not (>>=). >From my reading of the email, some people will agree strongly, and no one will disagree strongly. I suppose I could be wrong about this, though. Simon

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about downloading
by walter blanchard 14 Apr '02

14 Apr '02

please,where can I download a version of Haskell? Thank you --------------------------------- Yahoo! Mail -- Une adresse @yahoo.fr gratuite et en français !

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about downloading
by julie madec 14 Apr '02

14 Apr '02

where can I download a version of Haskell? Thank you

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Lexing character literals in H98
by Sven Panne 14 Apr '02

14 Apr '02

Yet another H98 question, this time regarding the module Char: Is it a deliberate design decision that readLitChar handles decimal, octal, and hex escapes, but lexLitChar handles only decimal ones? It looks more like an oversight to me... Another question is if the uppercase variants '\O...' and '\X...' should be forbidden explicitly. Current implementations seem to differ in this aspect. Cheers, S.

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