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AW: Tree insert, lookup with keys
by Ingo Wechsung 20 Dec '02

20 Dec '02

Ketil wrote: >But it isn't obvious what b is supposed to be. Sure, it must be an instance of Ord. In a way, I promise the compiler not to use anything but compare on b's. Of course, when I define n instances, there will be n different b-Types that must not be confused. >(Requires -fglasgow-exts) Thanks for the tip. Since I am obviously still learning, I prefer not to use the extensions until I know exactly what they are about. (As it seems, I am just experiencing one case where the extensions are useful. I'm sure there are many other cases.) Meanwhile, I see 2 possibilities to solve the problem in standard Haskell: (a) Stick with String keys key :: a -> String; or, (b) forget class Keyed and for every type s in Tree s derive an instance from Ord that defines compare accordingly. Solution (b) seems not so good to me since we might need the standard Ord behaviour elsewhere. Solution (a) is practical and should perform fairly well, except when we must write something like key (Baz x s y) = show x; Are there any other solutions in standard Haskell? Ingo

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Parsing date and time specifications
by Peter Simons 20 Dec '02

20 Dec '02

Hi, I have written a parser that turns an RFC2822 date and time specification into a datatype usable in Haskell. While the parser is working just fine so far, I have a problem with the CalendarTime datatype. It appears that in order to construct one of those, I need _all_ the information it contains, including the weekday (Day) and the number of the day in the year. The problem now is that I do not have this information! Of course I could calculate these values by hand, but this is immensely complicated. I thought about using a TimeDiff instead, but apparently the functions provided in the Prelude do not handle TimeDiff for anything except for "maths" -- what doesn't really help me for what I am trying to do. I briefly looked at the Posix module that comes with GHC as well, and which seems to provide CTime. But then, the Posix module appears to be non-standard. *sigh* Any suggestions what I could do? -peter

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Re: Library for concurrent threads running
by Kevin Hammond 18 Dec '02

18 Dec '02

I am also not quite sure of your motivation! The current version of GpH is (or can be with very little difficulty) implemented using library calls. There is really no language extension per se, rather there are calls to tightly-coupled C code, plus a set of high level libraries to provide structure (evaluation strategies). There are, of course, modifications to the RTS to support proper scheduling, communications etc. , but these are necessary for a properly integrated high-level approach. If you want a low-level approach, one of the MPI libraries for Haskell may suit you better? Kevin At 7:16 pm +0100 16/12/02, Christian Sievers wrote: Dusan Kolar asked: > My question/wish is maybe naive, but anyway: > Is there a library (not a language extension, like > Concurrent Haskell, Glasgow Parallel Haskell, ...) enabling > to run two functions in parallel, possibly in cascade? I think the best you can get without language extensions is what is described in Koen Claessen's Functional Pearl "A Poor Man's Concurrency Monad". It's really nice, but not exactly what you seem to want. You can get that article from http://www.cs.chalmers.se/~koen/publications.html All the best Christian Sievers _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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Random
by Filipe Santos 18 Dec '02

18 Dec '02

I need some help to do a function so that I cant get 4 numbers between 1 and 6, i tried to use random but i can't make it work well.

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(no subject)
by Olga Lucia Quintero Fonseca 17 Dec '02

17 Dec '02

Por favor, estoy aprendiendo el lenguaje y no se como usar Complex aqui, el prompt siempre esta como Prelude y no se como incluir ese package module. Podrian ayudarme ? De antemano gracias !!!

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FW: Random
by Simon Peyton-Jones 17 Dec '02

17 Dec '02

I'm behind the times... Thanks Volker Simon -----Original Message----- From: Simon Marlow Sent: 17 December 2002 15:51 To: Simon Peyton-Jones Subject: RE: Random Volker Stolz already did this (and for a bunch of other H98 libraries), but I didn't merge it into the branch, sorry. Cheers, Simon > -----Original Message----- > From: Simon Peyton-Jones [mailto:simonpj@microsoft.com] > Sent: 17 December 2002 15:08 > To: Mark Carroll; haskell-cafe(a)haskell.org > Subject: RE: Random > > > | Ah - I was never sure what to make of that - I normally just use the > GHC > | online Haddockised stuff which tells me no more than the type > signatures, > | but I suppose "split" must be more than (\x->(x,x))! (-: (I'll be > happy to > | help with adding documentation once I'm sure of the > semantics myself.) > > The Random library is carefully documented in the Haskell Report. It > would be an excellent and wonderful thing if someone could Haddock-ise > the Haskell Report documentation and put it in the library > documentation. > > Volunteers get CVS write access! > > Simon > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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RE: Random
by Simon Peyton-Jones 17 Dec '02

17 Dec '02

| Ah - I was never sure what to make of that - I normally just use the GHC | online Haddockised stuff which tells me no more than the type signatures, | but I suppose "split" must be more than (\x->(x,x))! (-: (I'll be happy to | help with adding documentation once I'm sure of the semantics myself.) The Random library is carefully documented in the Haskell Report. It would be an excellent and wonderful thing if someone could Haddock-ise the Haskell Report documentation and put it in the library documentation. Volunteers get CVS write access! Simon

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Library for concurrent threads running
by Dusan Kolar 16 Dec '02

16 Dec '02

Hello, My question/wish is maybe naive, but anyway: Is there a library (not a language extension, like Concurrent Haskell, Glasgow Parallel Haskell, ...) enabling to run two functions in parallel, possibly in cascade? Something like: > testAll (threadStart f1 (threadStart f2 f3)) > > where threadStart :: a -> b -> (WillBe a, WillBe b) > where type WillBe is something like Maybe, but > changing within a time (mutable values) ~ Processing, Just a, Nothing > > testAll (Nothing,p) = putStr "No result for f1" >> testPair p > testAll (l,(Nothing,r)) = putStr "Noresult for f2" >> testPair (l,r) > testAll (l,(ll,Nothing)) = putStr "No result for f3" >> testPair (l,ll) > testAll (Just a,p) = putStr ("res of f1: " ++ show a) >> testPair p > ... > > testPair ~ about the same like testAll Probably the explanation is not too clear and what I wish is out of the language scope (not really functional), but I would appreciate something like that. Is there something like that for Haskell/Hugs? Thx for any ref. Dusan

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Re: Haskell run-time tutorial
by Jonathan Holt 16 Dec '02

16 Dec '02

Matt Hellige wrote: > I found the book: > > Simon Peyton-Jones and David Lester > "Implementing Functional Languages: A Tutorial" > Prentice Hall, 1992 Thanks for the detailed and helpful reply. I've already downloaded the book, and from what I've seen thus far, it seems to be exactly what I need! Thanks! -Jony __________________________________________________ Do you Yahoo!? Yahoo! Mail Plus - Powerful. Affordable. Sign up now. http://mailplus.yahoo.com

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Haskell run-time tutorial
by Jonathan Holt 14 Dec '02

14 Dec '02

Hi guys, Having completed a simple parser project using Haskell, I'm getting more and more "hooked" on functional-programming in general and Haskell in particular. And learning the language has been a real treat as well, using the tutorial with occasional peeks at the report. However, when I'm considering undertaking more complex projects, I realize that there is one important erea of the Haskell language that is still pretty much a "black-hole" for me: the run-time environment. I honestly can't say that I completely understand how the actual control and data flows work when a Haskel program is executed, and I seem to be constantly surprised by the garbage-collection, which sometimes seems as if it doesn't work at all, and at other times seems to do magic. I've tried reading some of the articles related to the design of GHC's run-time. But they don't seem to be much help. They either assume that the reader has prior knowledge of functional-programming run-time environments, or get into very low-level details. And at the end of the day, this is very confusing, and I find terms like thunks, entries, partial-function-applications, etc. floating in my head hoplessly seeking anchor. So, where can one find a good introductory book / article on the subject? Thanks, -Jony __________________________________________________ Do you Yahoo!? Yahoo! Mail Plus - Powerful. Affordable. Sign up now. http://mailplus.yahoo.com

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