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Stupid questions...
by Sarah Thompson 23 Jan '03

23 Jan '03

Sorry about such lame questions. I'm currently using Haskell 'in anger' for the first time, so differences with other functional languages are biting me occasionally. I need to convert Ints to Strings and vice-versa. What's the best way to do this? I've not found library functions for this. Second question: Using division over integers. I appreciate that a division operator with integers as arguments can not be guaranteed to return an exact integer result. However, if I *do* want to do integer division, how should I do it? Is floor(a/b) appropriate? TIA Sarah Thompson

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RE: Arrays and arrays
by Simon Marlow 23 Jan '03

23 Jan '03

> Since you're on the line, could you confirm or deny that the (//) > operator is something equivalent to (roughly): > > a // ps = runST (thaw a >>= \u -> update ps >> unsafeFreeze u) > > I.e. that the list of updates are treated as an atomic operation? > Because doing it that way explicitly sure didn't seem to help. Yes, it is. > OTOH, doing lots of small (//) seems to be faster than doing a few > large ones (containing the same updates). Go figure. That's bizarre. Perhaps the results are obscured by some other optimisations which are happening. Cheers, Simon

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RE: Arrays and arrays
by Simon Marlow 22 Jan '03

22 Jan '03

> Hal Daume III <hdaume(a)ISI.EDU> writes: > > [snip my functions that use the ST monad to do (//)] > > > You shouldn't try to write these functions. You should do all array > > modifications within the ST monad, rather than looking for a pure > > solution. > > All right, but why? It seems an obvious trick, take some pieces that > benefit from imperative processing, and wrap them in ST, leaving the > rest of the program as it were. > > Can you (or anybody else) explain the memory behaviour I see (using > hundreds of megabytes, but only tens of K visible in the profiling > output)? That's because currently large objects aren't included in the profile. There's no really good reason for this, except that threads (including their stacks) count as large objects, and seeing them in the profile might be confusing. On the other hand, it might also be enlightening if you have a program that uses a lot of stack space. I'll look into fixing this. Cheers, Simon

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Arrays and arrays
by ketil＠ii.uib.no 22 Jan '03

22 Jan '03

Hi Having written a suffix-array based program using lists, I thought I'd speed it up a bit, and perhaps more importantly, save space, using arrays. Basically, the problem is to sort all suffixes of a string, represented as an array of offsets, alphabetically. (Does anybody have such code? Efficient?) The good news is that space consumption is reduced -- except for a few weird spikes (which makes me suspect there are many of them, living for very short durations), memory use is low. But speed is another issue -- the list based version is a lot faster. Okay, I use UArrays and permute them by (//), and this operation is totally dominant in the profile. Is it correct that GHC is very naive about updating them, and even small updates cost O(n)? Is it better to (//) over few large lists than over many small ones? I'll try a IOUArray next; however, is there anything else I could/should try? I know there has been array sorts implemented previously, are anybody aware of recent results? -kzm -- If I haven't seen further, it is by standing in the footprints of giants

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RE: Trying to get a copy of HaskellDirect urgently...
by Simon Peyton-Jones 21 Jan '03

21 Jan '03

I've just grabbed it ok, so I'll send it to you in a separate message. It says that it's built for GHC 4.08.1 which is pretty old. I wonder if you've made a more recent release somewhere, Sigbjorn? Sarah: you can always get the sources from the CVS tree Simon | -----Original Message----- | From: sarah(a)telergy.com [mailto:sarah@telergy.com] | Sent: 21 January 2003 13:26 | To: haskell-cafe(a)haskell.org | Subject: Trying to get a copy of HaskellDirect urgently... | | Hi Folks, | | I'm currently trying to urgently get a copy of the HaskellDirect release, but I'm | finding it impossible to get to the ftp server at Glasgow (it seems to be | refusing connections - it's not a firewall problem). | | If anyone has a copy they could email me, or knows of somewhere else I can get | the release, I would be extremely grateful. | | TIA, | Sarah Thompson | | PS: Are there any known issues using HaskellDirect with the latest GHC release | (GHC 5.04.2)? | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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IORefs, MVars und CVars
by Martin Huschenbett 21 Jan '03

21 Jan '03

I just started some multithreaded programming and as I am a newbie, I've gat a question. 1.) What are the differences between IORefs and MVars? 2.) What are CVars for? Thanks, Martin.

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Trying to get a copy of HaskellDirect urgently...
by sarah＠telergy.com 21 Jan '03

21 Jan '03

Hi Folks, I'm currently trying to urgently get a copy of the HaskellDirect release, but I'm finding it impossible to get to the ftp server at Glasgow (it seems to be refusing connections - it's not a firewall problem). If anyone has a copy they could email me, or knows of somewhere else I can get the release, I would be extremely grateful. TIA, Sarah Thompson PS: Are there any known issues using HaskellDirect with the latest GHC release (GHC 5.04.2)?

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RE: Evaluation Question
by Simon Marlow 20 Jan '03

20 Jan '03

[ moved to haskell-café ] > Simon Marlow wrote: > > The original version should also evaluate the expression > 'cis wn' only > > once: [...] > > Nice theory, but GHC's interpreter and compiler behave differently: > > -- Main.hs ----------------------------------------------------------- > module Main where > > import Data.Complex ( Complex ) > import qualified Data.Complex ( cis ) > import Debug.Trace > > cis :: (RealFloat a) => a -> Complex a > cis x = trace "cis" $ Data.Complex.cis x > > nco1, nco2 :: RealFloat a => a -> [ Complex a ] > nco1 wn = 1 : map ((*) (cis wn)) (nco1 wn) > nco2 wn = iterate (cis wn *) 1 > > main :: IO () > main = do > let test f = print . take 5 . f $ (pi/2 :: Double) > test nco1 > test nco2 > ---------------------------------------------------------------------- Oops, I didn't notice that nco1 was recursive. I should have said the expression (cis wn) is evaluated once for each call to nco1. It is not evaluated once for each element of the list in map's second argument, which is what I thought was being asked. > panne@jeanluc:~> ghci Main.hs > ___ ___ _ > / _ \ /\ /\/ __(_) > / /_\// /_/ / / | | GHC Interactive, version 5.05, > for Haskell 98. > / /_\\/ __ / /___| | http://www.haskell.org/ghc/ > \____/\/ /_/\____/|_| Type :? for help. > > Loading package base ... linking ... done. > Compiling Main ( Main.hs, interpreted ) > Ok, modules loaded: Main. > *Main> main > [1.0 :+ 0.0,cis > 6.123031769111886e-17 :+ 1.0,cis > (-1.0) :+ 1.2246063538223773e-16,cis > (-1.836909530733566e-16) :+ (-1.0),cis > 1.0 :+ (-2.4492127076447545e-16)] > [1.0 :+ 0.0,cis > 6.123031769111886e-17 :+ 1.0,(-1.0) :+ > 1.2246063538223773e-16,(-1.836909530733566e-16) :+ (-1.0),1.0 > :+ (-2.4492127076447545e-16)] > *Main> :quit > Leaving GHCi. > panne@jeanluc:~> ghc -Wall -O Main.hs && ./a.out > cis > cis > cis > cis > [1.0 :+ 0.0,6.123031769111886e-17 :+ 1.0,(-1.0) :+ > 1.2246063538223773e-16,(-1.836909530733566e-16) :+ (-1.0),1.0 > :+ (-2.4492127076447545e-16)] > cis > [1.0 :+ 0.0,6.123031769111886e-17 :+ 1.0,(-1.0) :+ > 1.2246063538223773e-16,(-1.836909530733566e-16) :+ (-1.0),1.0 > :+ (-2.4492127076447545e-16)] > ---------------------------------------------------------------------- This difference is due to the different buffering behaviour on stdout/stderr between compiled and interpreted programs. GHCi sets these handles to unbuffered by default, which tends to be more useful for an interpreter. Cheers, Simon

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Re: A question about dynamic typing
by Jon Cast 19 Jan '03

19 Jan '03

Nick Name <nick.name(a)inwind.it> wrote: > On Sun, 19 Jan 2003 16:02:41 -0600 > Jon Cast <jcast(a)ou.edu> wrote: > > So, I would attach a list of named operations of type (Dynamic -> > > Result) to each type, and offer the operations for a given type to > > the user. > Thanks for your answer, it's interesting. > What do you mean with "named operations"? Something like operations > labeled with string, to be able to compare it? Yes: (String, Dynamic -> Result). > Vincenzo Jon Cast

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Question about lists
by cris cris 19 Jan '03

19 Jan '03

hello there, To be honest I'm not very familiar with haskell and stuff so don't laugh with my question... here it goes.. We can represent a matrix as a list of lists... which means that 1 2 3 4 7 6 2 5 1 could be written as follows: [[1,2,3],[4,7,6],[2,5,1]] The question is how can I reverse the matrix (each row becomes a column) Thanx a lot ______________________________________________________________________________________ http://mobile.pathfinder.gr - Pathfinder Mobile logos & Ringtones! http://www.pathfinder.gr - Δωρεάν mail από τον Pathfinder!

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