September 2009 - Haskell-Cafe

FFMpeg, SDL and Haskell
by Vasyl Pasternak 23 Sep '09

23 Sep '09

Hi all, Last few days I was playing with FFI, FFMpeg and Haskell. Currently I am trying to make this tutorial http://www.dranger.com/ffmpeg/ on Haskell. Now I have done tutorial 01 and tutorial 02 (show video stream in SDL window). The third tutorial is about audio, and I found that audio doesn't supported in SDL bindings completely. So I'd like to fill this gap, but I don't know where to get latest version and to whom I have to send SDL patches. Anyway, does anybody interested in FFMpeg bindings ? Should I put it on Hackage ? The preliminary version I've put on google code: http://hs-ffmpeg.googlecode.com/files/hs-ffmpeg-0.2.0.tar.gz, but this is "work on my PC" version. Vasyl

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ANNOUNCE: Darcs Hacking Sprint - 14-15 November Vienna
by Eric Kow 23 Sep '09

23 Sep '09

Dear Haskellers, The Darcs Team will soon be hosting its third hacking sprint. Details ------- When : 14-15 November 2009 Where: University of Technology, Vienna, Austria Who : Anybody who wants to hack on Darcs (or Camp, Focal, SO6, etc) Beginners especially welcome! Why : Darcs aims to have bi-annual hacking sprints so that we can get together on a regular basis, hold design discussions, hack up a storm and have a lot fun. What : We plan to put some finishing touches on Darcs-2.4. Darcs 2.4 is a pretty exciting release because we expect it to offer nice performance enhancements from Petr's Google Summer of Code Project, and also a nice new 'hunk splitting' feature. We also intend to set aside at least one Darcs hacker for mentoring beginners, so if you're new to Haskell or to Darcs hacking, here's a good chance to plunge in and start working on a real world project. How: Add yourself to http://wiki.darcs.net/Sprints/2009-11 or email me to let me know you're interested! Thanks ------ Thanks to our local team David Markvica and Benedikt Huber for generously offering to host this event! Thanks also to donors from the last fundraising drive. We'll be using that money to help Darcs hackers get to Vienna. Supporting Darcs ---------------- Darcs is a very happy member of the Software Freedom Conservancy. Among other things, the Software Freedom Conservancy makes it easy for open source projects to raise funds and hold assets (as part of a legal entity). For more information on supporting Darcs, see http://darcs.net/donations.html See you there! -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

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accessible layout proposal?
by Jimmy Hartzell 23 Sep '09

23 Sep '09

I am in love with this proposal: http://www.haskell.org/haskellwiki/Accessible_layout_proposal However, after some Google searching and contacting its original author, I have still not found any implementation or project to implement it. Are there any I'm missing? And, if not, who would be willing to help undertake a project to patch ghc to support it? Alternatively, you can try to talk me out of liking the proposal so much, but that is much less likely to work. Jimmy Hartzell

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Re: [Haskell-cafe] Problem with Text.XHtml.Strict.Formlets.file on Mac OSX
by Chris Eidhof 23 Sep '09

23 Sep '09

OK, the trick is to set the attribute enctype="multipart/form-data" on the form whenever your form contains a file upload item. Using the third parameter you can detect if this is the case. This is typical of using file-upload fields in web programming and independent of the formlets. It's also covered in the Happstack tutorial [1] and in the HTML form spec [2]. Good luck, -chris [1] http://tutorial.happstack.com/tutorial/file-uploads [2] http://www.w3.org/TR/html401/interact/forms.html#h-17.13.4 On 23 sep 2009, at 15:35, Colin Adams wrote: > I'm not sure, but the other components of the form work (before I > added the file bit, that is), so they will all be using the same > method. > > I'm using a generic form-handling function named withForm that I got > from one of the examples - this code appears to ignore the third > component of the tuple. > > Note that I don't really understand all of this yet. > > 2009/9/23 Chris Eidhof <chris(a)eidhof.nl>: >> Hey Colin, >> >> The code looks OK to me. Are you sure you are setting the right >> method for >> your form? It's the third component of the tuple returned by the >> runFormState. >> >> Thanks, >> >> -chris >> >> On 22 sep 2009, at 08:56, Colin Adams wrote: >> >>> I'm writing a form that involves picking a file to upload, and so >>> uses >>> Text.XHtml.Strict.Formlets.file. The form displays OK, but when I >>> click the Browse button, and select a file from the dialog (no >>> matter >>> what the file type), and then click on the Submit button, I get an >>> error: >>> >>> "fval[2] is not a file" >>> >>> I haven't added any validation yet. >>> >>> The generated html looks ok to me: >>> >>> <input type="file" name="fval[2]" id="fval[2]"> >>> >>> This is on my laptop running Mac OSX. I can't test it on Linux >>> until I >>> get home at the weekend, so I don't know if I've made a silly >>> error in >>> my coding, but it is very simple: >>> >>> imageInputForm = F.plug (\xhtml -> X.p << (X.label << "Image file:") >>> +++ xhtml) F.file >>> >>> Are there any known problems with the file formlet? Might it be OSX >>> specific? >>> -- >>> Colin Adams >>> Preston, >>> Lancashire, >>> ENGLAND >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> Haskell-Cafe(a)haskell.org >>> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> > > > > -- > Colin Adams > Preston, > Lancashire, > ENGLAND

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Problem with Text.XHtml.Strict.Formlets.file on Mac OSX
by Colin Adams 23 Sep '09

23 Sep '09

I'm writing a form that involves picking a file to upload, and so uses Text.XHtml.Strict.Formlets.file. The form displays OK, but when I click the Browse button, and select a file from the dialog (no matter what the file type), and then click on the Submit button, I get an error: "fval[2] is not a file" I haven't added any validation yet. The generated html looks ok to me: <input type="file" name="fval[2]" id="fval[2]"> This is on my laptop running Mac OSX. I can't test it on Linux until I get home at the weekend, so I don't know if I've made a silly error in my coding, but it is very simple: imageInputForm = F.plug (\xhtml -> X.p << (X.label << "Image file:") +++ xhtml) F.file Are there any known problems with the file formlet? Might it be OSX specific? -- Colin Adams Preston, Lancashire, ENGLAND

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Re: Multiple-selection formlet?
by Chris Eidhof 23 Sep '09

23 Sep '09

Hey Colin, Currently, I don't think this is supported. It would help a lot if you could send me a dumbed-down version of your code, I'll file an issue for it on github. Thanks, -chris On 23 sep 2009, at 14:35, Colin Adams wrote: > Just in case you missed it on the cafe. > > ---------- Forwarded message ---------- > From: Colin Adams <colinpauladams(a)googlemail.com> > Date: 2009/9/21 > Subject: Multiple-selection formlet? > To: Haskell Cafe <haskell-cafe(a)haskell.org> > > > I can't work out how to get multiple selections delivered from a > formlet. I can add the multiple attribute to get the formlet to allow > the user to make multiple selections, but I only get a single answer > back. This seems inevitable from the type of rawSelect (or select) - > since the list of values to select from is of type [(a, h)] and the > result type is a. > > Am I missing something? > > -- > Colin Adams > Preston, > Lancashire, > ENGLAND > > > > -- > Colin Adams > Preston, > Lancashire, > ENGLAND

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Got it working, now trying to abstract it
by Günther Schmidt 23 Sep '09

23 Sep '09

Hi all, I'm finished with my implementation, an app that analyses financial data for budgeting. But there are no abstractions in my code whatsoever, everything is coded exactly to the point. So now that I'm done I'd like to start it over, this time using far more abstractions than I have, I was thinking along the lines of creating a DSL for it first. The aspects I have to consider are two-fold: ETL-ish - I need to assemble the "records" from a set of csv files BI-ish - I need then to group, filter and aggregate the data. I've come across "How to write a financial contract" S. Peyton Jones in the "fun of programming" and it gives me some ideas on how to go about the BI-ish part of the application. Does anyone know of a DSL example which could fit the bill? Günther

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How to install GD library on Mac OSX?
by Colin Adams 23 Sep '09

23 Sep '09

It needs some missing C libraries - gd, png, jpeg, fontconfig and freetype. Does anyone know what to do to install these on OSX? -- Colin Adams Preston, Lancashire, ENGLAND

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Re: [Haskell-cafe] accessible layout proposal?
by Jimmy Hartzell 23 Sep '09

23 Sep '09

> On Sep 23, 2009, at 3:04 PM, Evan Laforge wrote: > Let's not forget what the proposal actually _is_. > It is that "#(" "#[" "#$" and "#" should become magic > tokens such that > > #( {a;b;c} is read as (a,b,c) > #[ {a;b;c} is read as [a,b,c] > f #$ {a;b;c} is read as f (a) (b) (c) > # {a;b;c} is read as {a,b,c} > > [http://www.haskell.org/haskellwiki/Accessible_layout_proposal] > > Are you not troubled by the inconsistencies here? I am indeed. I concede that the proposal in its present form is completely unacceptable. How about this (which I believe to be backwards compatible): * For data-type declarations, simple indentation may be used: data Tree a Leaf a Branch (Tree a) (Tree a) deriving Show -- this bit may be overkill Read * For records, simple indentation is extended: data Tree a = Branch left::a right::a Leaf a * Export lists are similarly without extra symbols: module Foo Zap Con1 Con2 Con3 mkZap count where * [~] and (~) introduce newline-separated lists and tuples, respectively: wrapWithParens str = concat [~] "(" str ")" Ideally, I'd want something even more light-weight, but I can't think of anything backwards-compatible that satisfies the bracket-matching requirement (which I also care about, as I don't particularly want to hack my editor for this layout proposal either). * For the magic uncurried-function operator, I don't want to have the monstrosity of $$(~). A simple ~ should do here: main = between_ ~ enter a exit a body a This is also allowable in data declarations: data Tree a = Branch ~ Tree a Tree a Leaf a I'd also be interested in knowing if any of these seem interesting separately. I would personally use this new layout for virtually all datatypes, records, and long (where long = (> 2) . length) lists and tuples. I would probably use the '~' notation heavily in writing parsec parsers (the following based loosely off of code from a compiler for a toy programming language): classDeclaration = LiftM4 ClassDeclaration ~ scopeDesignator >>~ keyword "class" typeNameDeclaration option rootClass $ parens qualifiedConstantName -- look, no parens list fieldVariable >>~ operator ";" I like how this version allows me to plainly list the components of a ClassDeclaration. Certainly, if I was actually designing a programming language for writing parsers in, I wouldn't require a bunch of parentheses for productions like this. The fact that, with this proposal, Haskell would no longer require them I take as a good sign. (>>~) is defined as per an article I can't seem to find right now: a >>~ b = do res <- a b return res Furthermore, a function 'if_ a b c = if a then b else c' would be a lot more natural to use. I prefer programming languages where an if-function is as natural to use as the programming language's native 'if', especially those that have a function to implement the functionality of 'if', as those languages are usually the most flexible in their control structures (in Haskell, the only awkwardness with 'if_' at present is syntactic): if_ $ a < 3 ~ errorResult "insufficient allocations" Right $ f b c I feel that with the existence of ($), do notation, the significant whitespace for both do-notation and case statements, Haskell already leans in the direction of allowing for minor awkwardness and inconsistency to eliminate parentheses and to make the structure of the program easily visibly accessible. Jimmy Hartzell

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Re: [Haskell-cafe] accessible layout proposal?
by Jimmy Hartzell 23 Sep '09

23 Sep '09

> Am Mittwoch 23 September 2009 04:06:11 schrieb Jimmy Hartzell: >> Daniel Fischer wrote: >> > Or, what I do: >> > >> > concat >> > [ "(" >> > , str >> > , ")" >> > ] You're right: my objections to this seem mostly to be matters of taste -- as I think about it, I find fewer and fewer practical reasons for disliking it. I still would prefer it if the proposal were implemented (and I would modify it so brackets weren't mismatched), and I'm still interested in implementing it, if only so I (and others) can do programming projects both ways and see if it actually makes a big difference.

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