- Haskell-Cafe - Haskell.org

Organising code in FRP
by luc taesch 31 Mar '13

31 Mar '13

I am just learning FRP ( via reactive-banana) . so possibly opening a topic already mentionned , apologises in advance, and pointers welcomed. I am wondering about "code structuration" ? ie spagetti code for the network 1/ in a non trivial FRP applicaiton, how to manage "modulatity" or structuration of the Network ? ( most of the example I scanned are toy-size). I ca imagine it may not be trvial to find its way around in a large setup ... 2/ what about the separation of "layers". I mean fine, we extract the reactive ness from the GUI, and separate the layout of widgets from the behaviors of these great, but is it to then mingle the UI with the "business part" ( say in banking), and the infrastructure side ( say persistence, comms, transactionnality, etc) in other words, how tdoes the nice abstraction developped ( module/ interface / categoty patterns, monad, etc) coexsit with a netork of FRP event and behaviors ? Any prior art on this ? ( and which place si best to discuss this ?)

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Specialized Computer Architecture - A Question
by OWP 31 Mar '13

31 Mar '13

Hi, I was reading the paper "A History of Haskell: being lazy with class" ( http://www.haskell.org/haskellwiki/History_of_Haskel) and came on a section (I 2.1) which briefly explained the work people did on making non-von Neumann architectures. It concluded by saying "Much (but not all) of this architecturally oriented work turned out to be a dead end, when it was later dis- covered that good compilers for stock architecture could outper- form specialised architecture. But at the time it was all radical and exciting." These "stock architectures", were they really so good that they out performed the specialized ones on it's own merits or was this mainly due to Moore's Law on transistors? In other words, suppose we separate Moore's Law from the stock architecture, would it still outperform the specialized ones? Thank you for any response

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Threadscope 0.2.2 goes in segmentation fault on Mac Os X 10.8.3
by Alfredo Di Napoli 31 Mar '13

31 Mar '13

Hi Cafè, I've tried installing threadscope, but when I run it from console with "threadscope" I get a laconic segmentation fault. Some info to help the debugging: * Installed gtk via brew * gtk-demo runs correctly * I'm using Mac Os X 10.8.3 * Running gtk and threadscope through a virtual environment (provided by hsenv) * Using XQuartz 2.7.4 I know it's a bit difficult to debug this way, I can try debugging with gdb if it can help. Cheers, A.

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[ANN] hoodle-0.2
by Ian-Woo Kim 30 Mar '13

30 Mar '13

Hi, all, Pen note-taking program hoodle, which is being developed entirely in haskell, is updated to version 0.2. The previous version was 0.1.1. About what is hoodle, please refer to http://ianwookim.org/hoodle The changes in this version are - hoodle data format updated. now hoodle document has a unique id. - linking between documents implemented - vertical space inserting tool implemented - a widget introduced for panning and zooming - drag and drop linking implemented - drag and drop image embedding implemented - poppler pdf support is mandatory - pdf can be embedded in a file - toolbox ui reflects current hoodle state more correctly - slimmer select box design - several rendering glitches fixed Note that poppler is mandatory for hoodle (in the previous versions, poppler support was optional). One needs to install poppler-glib before installing hoodle. After gtk2hs and poppler installed, installing hoodle should be simply > cabal install hoodle As for the detail information about wacom tablet support, please read installation page on the webpage. If you were using the previous versions of hoodle, you will find this version gives you much smoother experience and many interesting improvements. (especially adding vertical space tool and pan-zoom widget ) Enjoy~ best, Ian-Woo Kim

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Idea: Source maps for GHC's -pgmF
by Christopher Done 30 Mar '13

30 Mar '13

Here's an idea. For the -pgmF flag, because compile errors become really obscure and line numbers rendered unhelpful, why don't we use source maps as recently done for JavaScript in the browser? Info: https://wiki.mozilla.org/DevTools/Features/SourceMap https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0… Here is an example I experimented with the Fay (Haskell→JS compiler): https://dl.dropbox.com/u/62227452/Screenshots/Screenshot%20from%202012-09-2… This shows the original source code and a backtrace of an exception thrown in JavaScript. We can use Mozilla/Google's format: http://hackage.haskell.org/package/sourcemap Though it's kind of an obscure format because it's aimed at being small, but if it's already been done, why not? Otherwise a simple JSON format is probably sufficient. It could be used both in GHC's compilation, pattern match exceptions, and even in debugger stepping, if desired. Provided with, e.g. -pgmFsm foo.map. This would make things like the XML mode or other syntactical extensions feel quite natural and not awkward in GHC's error messages. What say you, -pgmF users and GHC hackers? Ciao!

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Monad.Reader #22 call for copy
by Edward Z. Yang 29 Mar '13

29 Mar '13

Call for Copy: The Monad.Reader - Issue 22 -------------------------------------------- Another ICFP submission deadline has come and gone: why not celebrate by submitting something to The Monad.Reader? Whether you're an established academic or have only just started learning Haskell, if you have something to say, please consider writing an article for The Monad.Reader! The submission deadline for Issue 22 will be: **Saturday, June 1** The Monad.Reader ~~~~~~~~~~~~~~~~ The Monad.Reader is a electronic magazine about all things Haskell. It is less formal than journal, but somehow more enduring than a wiki- page. There have been a wide variety of articles: exciting code fragments, intriguing puzzles, book reviews, tutorials, and even half-baked research ideas. Submission Details ~~~~~~~~~~~~~~~~~~ Get in touch with me if you intend to submit something -- the sooner you let me know what you're up to, the better. Please submit articles for the next issue to me by e-mail (ezyang(a)mit.edu) Articles should be written according to the guidelines available from http://themonadreader.wordpress.com/contributing/ Please submit your article in PDF, together with any source files you used. The sources will be released together with the magazine under a BSD license. If you would like to submit an article, but have trouble with LaTeX please let me know and we'll work something out.

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my knucleotide fast on 64 bit but extremely slow on 32 bit?
by Branimir Maksimovic 29 Mar '13

29 Mar '13

I have posted previous knucleotide program, it is fast on 64 bit butvery slow on 32 bit.I cannot install 32 bit ghc to test it so I can only guess is thatcause is use of Int64 for hash and HashMap array indexing.What bothers me is that it that much slower , and I guessthat array indexing of 64 bit int where native index is 32 bitis culprit.Am I right? If I make Int index of array it will be fast on32 bit platform too?I cannot imagine that hashing to 64 bit int is culprit ratherarray indexing as I guess that every array accessrequires indirect access on 32 bit platform? 64 bit :http://benchmarksgame.alioth.debian.org/u64q/program.php?test=knucleotide&lang=ghc&id=119.80 secs32 bit:http://benchmarksgame.alioth.debian.org/u32q/program.php?test=knucleoti… secs ;( I really like Haskell, but Im frustrated as how inpredictable it is.Im programming from 1983' but found Haskell as much more difficultto program efficiently than C++.In C++ whatever lousy program I write it performs decently,but not so in Haskell. It requires much deeper knowledge thanc++.

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introducing Maybe at managing level
by luc taesch 29 Mar '13

29 Mar '13

I was looking for some link introducing the way FP/ Haskell handles errors and Exceptions. This is for a non FP Guy, and ideally withought scaring them with Monads and category theory :-). for the background : the guy said : As I mentioned in another thread in banking (in particular) it is the exception processing that often dominates the functionality of a system - as the core concept is generally very straightforward. Developing for "exception handling" (not in a Java/C++ sense) is a tricky thing - as the exception don't necessarily shout themselves out - and are often why we have large misunderstood legacy systems which are hard to replace.

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Re: [Haskell-cafe] warp and http-conduit on concurrent threads on windows
by Lars Kuhtz 29 Mar '13

29 Mar '13

That resolved the issue. Thanks for the hint. Lars On 2013-03-28 18:17, Joey Adams wrote: > Try upgrading to the latest network package. There's a bug prior to > version 2.4.1.0 where 'connect' blocks other threads from running, > because the underlying FFI call was marked "unsafe". > > Somewhat unrelated, but if your program needs to run for long periods > of time (e.g. a server), you're in for a nasty surprise: GHC > currently > doesn't support interrupting network I/O on Windows. After about a > thousand hung connections, the program will run out of address space > and hang. A partial workaround is to use socket timeouts; see > setHandleTimeouts in the network-socket-options package.

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Remove redundancy with Template Haskell
by Corentin Dupont 29 Mar '13

29 Mar '13

Hi Café, I have a function that looks like this: call :: SomeFunction -> String -> SomeState The string is actually the representation of the function passed in parameter. It is stored in the state for documentation. So a call looks like that: call (\a -> putStrLn a) "\a -> putStrLn a" There is a clear redundancy here, how could I remove it with Template Haskell? I cannot figure out... Thanks! Corentin

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