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Re: Simulating client server communication with recursive monads
by apfelmus 16 Jan '08

16 Jan '08

[redirected to haskell-cafe] Jan Stranik wrote: > Do you know what is the theoretical foundation for having mfix process > side-effects in the lexical order as opposed to execution order? > Could you point me to some papers, if you know of any off top your head? http://www.cse.ogi.edu/pacsoft/projects/rmb/ Regards, apfelmus

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hmp3 1.4: ncurses mp3 player in Haskell
by Don Stewart 16 Jan '08

16 Jan '08

4 years after its original release, and with almost daily use, I'm pleased to announce a new release of hmp3, the Haskell mp3 player. The goal of this project was a more stable, resize-friendly mp3 player for the console, that didn't compromise on efficiency or the user interface. This release, version 1.4, introduces pcre support for searching for tracks and albums, and improves support for ghc 6.8. Install: $ cabal install hmp3 Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hmp3 Homepage: http://www.cse.unsw.edu.au/~dons/hmp3.html Repos: http://code.haskell.org/~dons/code/hmp3 Cheers, Don --- Take direct action against bad code: program Haskell!

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High-readibility version of "CONS should not evaluate its arguments?"
by Benjamin L. Russell 16 Jan '08

16 Jan '08

While reading the paper "A History of Haskell: Being Lazy With Class" (Paul Hudak, John Hughes, Simon Peyton Jones, Philip Wadler: The Third ACM SIGPLAN History of Programming Languages Conference (HOPL-III) San Diego, California, June 9-10, 2007) (http://research.microsoft.com/~simonpj/papers/history-of-haskell/history.pdf) I came across a reference (in Part I, Section 2.1: The Call of Laziness) to the paper ""CONS should not evaluate its arguments" (D. P. Friedman and D. S. Wise, in Automata, Languages, and Programming, S. Michaelson and R. Milner, Eds. Edinburgh: Edinburgh University Press, 1976, pp. 257-284), and looked for a highly readable version. However, all I could come across was Technical Report TR44 at the Indiana Department of Computer Science, at http://www.cs.indiana.edu/cgi-bin/techreports/TRNNN.cgi?trnum=TR44. This version appears as small, light typewritten type on horizontally placed double pages, and is very hard to read. Does anybody know where I can find a version of this paper with higher readability?

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ErrorT and catchError question
by Adam Smyczek 16 Jan '08

16 Jan '08

Hi, I'm trying to use ErrorT transformer based on Don Stewart's Shell example: http://cgi.cse.unsw.edu.au/~dons/blog/2007/03/10#programmable-semicolons It's probably a trivial question, but I cannot figure out how to implement the catchError function in: instance MonadError String Shell where throwError = error . ("Shell failed: "++) catchError l h = ??? Thanks for help, Adam

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jumping to code every and anywhere : what about installing tagfile and source ?
by Marc Weber 15 Jan '08

15 Jan '08

I feel this is the right place to think about this? (I'll crosspost a small announcement on ghc as well pointing to this thread) Copied from http://hackage.haskell.org/trac/hackage/ticket/207#preview: == Introduction == I personally depend on tags because the source code only tells what is really going on. So it would be incredible useful to not only get information using ghci after loading libs but also beeing able to jump to all functions you might be using anywhere (The only solution providing this in all cases is uning tags, right? Because cpp defines can introduce new functions.. To be able to jump to the code source must be installed along with libs (the way you can optionally install haddock docs) == Use case: == setup configure --with-tags --install-source (or something like that) setup build && setup install do this for each dependency given in the .cabal file (VIM:) let tags+=system('ghc-pkg --query-tagfile-location haskell98-1.0.0.0') == Issues: == * Which tool to generate tag files? * ghc(i) when targeting ghc * the hasktags program shipping with ghc * some others? * Tagfile path type relative or absolute? * absolute: After moving/ installing the sources the tagfile must be patched * relative: Do editors take the right base directory to find source files? * When to invoke the tagfile generating program? * Perfect case would be after all preprocessing has been done (Thus the tagging program should understand line number changing comments!) * Template Haskell? ( This is really tricky I think ) * Hmm sorted tagfiles would be useful as well :) == alternatives ? == If you do not think this is useful (mandatory?) how do you lookup code? (Yes I know hoogle :) perhaps using Eclipse or Visual Studio? I'd like to start implementing this somehow the next weeks. So don't hesitate and start discussing Marc Weber

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fast fractional part of floating point number - modf?
by Henning Thielemann 15 Jan '08

15 Jan '08

Is there a fast and reliable way to compute the fraction of a floating point number? I can implement fraction x = snd (properFraction x :: (Int, Double)) or fraction x = x - fromIntegral (truncate x :: Int) (actually I need 'floor' not 'truncate' but this is another issue) but these need considerably more time than fraction x = x - GHC.Float.int2Double (GHC.Float.double2Int x) Is there a fast 'fraction' built-in function? Or do I have to use FFI to modf ?

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\_ -> not equivalent to const $
by Luke Palmer 15 Jan '08

15 Jan '08

In attempting to devise a variant of cycle which did not keep its argument alive (for the purpose of cycle [1::Int..]), I came across this peculiar behavior: import Debug.Trace cycle' :: (a -> [b]) -> [b] cycle' xs = xs undefined ++ cycle' xs > take 20 $ cycle' (const $ 1:2:3:4:trace "x" 5:[]) [1,2,3,4,x 5,1,2,3,4,5,1,2,3,4,5,1,2,3,4,5] Nuts. Oh, but wait: > take 20 $ cycle' (\_ -> 1:2:3:4:trace "x" 5:[]) [1,2,3,4,x 5,1,2,3,4,x 5,1,2,3,4,x 5,1,2,3,4,x 5] Hey, it worked! Can someone explain what the heck is going on here? Luke

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Computer Science Books using Haskell
by PR Stanley 15 Jan '08

15 Jan '08

Hi Can the list recommend books that use Haskell - or any FP language but preferably Haskell - to illustrate the principles of compilers and/or algorithms? I think most of you would understand if I said that I'd prefer FP code instead of funny math symbols that don't translate into ANSI characters with the current OCR technology, unless, of course, you know of a book available in latex code. Rather than rushing straight to Google I thought I'd first draw on the wealth of knowledge that exists on this list. Cheers Paul

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QuickCheck properties: export or not?
by Paul Johnson 15 Jan '08

15 Jan '08

I was recently sent a patch for my Ranged Sets library which exported all the QuickCheck properties. I'd left them unexported on the grounds that they clutter up the documentation (although simplified versions are included in the documentation) and you can easily run them with the standard "quickcheck" script. The contributor, gwern0(a)gmail.com suggested an explicit test harness instead. I'm not unduly bothered one way or the other, but I thought I'd ask the community: what is the best practice here? Paul.

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Displaying # of reductions after each computation in ghci?
by Fernando Rodriguez 15 Jan '08

15 Jan '08

Hi, Is there a way to configure ghci to display the number of reuctions after each compution (as in winhugs)? Thanks!

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