Re: [Haskell-cafe] subversion with haskell
Hi, Try the next: % env EXTRA_CPPFLAGS=-I/usr/local/include/subversion-1 \ EXTRA_LDFLAGS=-L/usr/local/lib \ runhaskell Setup.hs configure % runhaskell Setup.hs build % runhaskell Setup.hs install (and read the installation instructions included into the tarball :) ) 2010/8/5 Andrew U. Frank fran...@geoinfo.tuwien.ac.at: i found the file in usr/include/subversion-1 (i use an ubuntu (debian) installation form). but the cabal installer (i.e. the configure script) does not find the file. can you give me a hint where it could search and where i could copy the file to. i tried to read the configure script, but cannot see, where it searches. i am not familiar with cpp and do not understand what the hint 'extra cpp flags' could mean. thanks for your help! andrew ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] what's the best environment for haskell work?
On Fri, Aug 6, 2010 at 6:11 AM, Hamish Mackenzie hamish.k.macken...@googlemail.com wrote: On 5 Aug 2010, at 21:12, David Virebayre wrote: Can you try out this... ~/haskell/test$ cat ~/bin/cabal_quick_init #!/bin/sh SOURCE_FILE=$1 CABAL_NAME=`basename -s .lhs $SOURCE_FILE` CABAL_NAME=`basename -s .hs $CABAL_NAME` echo Creating Cabal Package $CABAL_NAME echo For file $SOURCE_FILE mkdir $CABAL_NAME.package || exit cd $CABAL_NAME.package || exit cabal init -n -p $CABAL_NAME --is-executable --source-dir=.. || exit sed -e s/-- *[mM]ain-[iI]s *\:/Main-is:$SOURCE_FILE/ -i $CABAL_NAME.cabal || exit This script doesn't word as-is for me. basename doesn't have a -s option, but that's easily corrected. Then, I couldn't get the sed command to work, so I edited manually the cabal file to modify and uncomment the Main-is line. This will make a Euler/Euler.cabal file. You can then simply add that .cabal file to your workspace (right click in the Workspace pane). Actually it makes a Euler.package/Euler.cabal file. Minor detail :) I'll try to fix leksah Euler.hs so it does the following * if the file belongs to an package in the workspace open the file and activate the package * if not ask the user if they want to simply open it or cabalize it That would be great. We do plan to fix this in the same way we resolve missing imports. I had a look to see if I could do it when a user cabalizes the source, but ghc --make -v does not include the packages automatically loaded in its output. Instead we will need to wait for the error then resolve it when the user presses Ctrl+R. Continuing on my Euler.hs example, I then created the cabal package with your script. Added the package, then tried to build. ../Euler.hs:1:0: Failed to load interface for `Prelude': It is a member of the hidden package `base'. Perhaps you need to add `base' to the build-depends in your .cabal file. It is a member of the hidden package `base-3.0.3.2'. Perhaps you need to add `base' to the build-depends in your .cabal file. Use -v to see a list of the files searched for. I didn't find a way to automatically fill the dependencies, Ctrl-R doesn't seem to do something. I added base = 4 using the package editor, then it build. By the way, did I mention you guys are doing an awesome job with leksah ? David. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] what's the best environment for haskell work?
On 6 Aug 2010, at 19:33, David Virebayre wrote: Continuing on my Euler.hs example, I then created the cabal package with your script. Added the package, then tried to build. ../Euler.hs:1:0: Failed to load interface for `Prelude': It is a member of the hidden package `base'. Perhaps you need to add `base' to the build-depends in your .cabal file. It is a member of the hidden package `base-3.0.3.2'. Perhaps you need to add `base' to the build-depends in your .cabal file. Use -v to see a list of the files searched for. I didn't find a way to automatically fill the dependencies, Ctrl-R doesn't seem to do something. I added base = 4 using the package editor, then it build. Yes Ctrl+R currently only fixes missing import errors where you called a function in a package you are using. It does this by adding import X ( f ) to your source. We have had plans for a while to extend this so it can handle these hidden package errors too by updating the .cabal file. By the way, did I mention you guys are doing an awesome job with leksah ? Thanks Hamish___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lambdacats
Tony Morris wrote: Hello, does anyone happen to have the lambdacats page cached? The domain (arcanux.org http://arcanux.org) and server have disappeared and the wayback machine doesn't have the images. Somebody else noticed, eh? Good thing I grabbed most of the actually amusing images before it vanished. Still, that site was hardly ever updated anyway. And it's not like you need a special website just to stick broken English on pictures of cats... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: using Network.CGI
dear anders indeed, the example on your page works perfectly and mine now too! i did misunderstand something basic on how to use network.cgi. my wrong approach: 1. i copied the program from the web page (commented out the getinput:: line, which seems to be in error). 2. i run it with runghc and pasted the result into a web page; this page opens in the browser, but does not have actions. correct is to compile with ghc and copy the executable into the cgi-bin folder. then it works... i will put this hint somewhere in the web wiki. i think this limits what network.cgi can be used for: it will work only on systems, where the output from the ghc can execute. specifically, this means, i cannot move the executable to an android mobile phone and use it there (assuming that there is a web server, e.g. i-jetty, which understands cgi (does it?)). is this correct? i appreciated your quick reply - thank you for your help! andrew On Thu, 2010-08-05 at 18:31 -0400, Anders Kaseorg wrote: On Thu, 5 Aug 2010, Andrew U. Frank wrote: which is clearly not producing the second part of the code, namely output a greeting. That’s what it’s supposed to output. Have you considered typing in a name and submitting the form? It works fine for me: http://andersk.mit.edu/greet.cgi. i try to use the Network.CGI package from darcs. (Note also that the current version is maintained in Git, not Darcs, but that’s a minor detail. See http://hackage.haskell.org/package/cgi .) Anders ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lambdacats
On 6 Aug 2010, at 09:48, Andrew Coppin wrote: Hello, does anyone happen to have the lambdacats page cached? The domain (arcanux.org http://arcanux.org) and server have disappeared and the wayback machine doesn't have the images. Somebody else noticed, eh? Good thing I grabbed most of the actually amusing images before it vanished. Still, that site was hardly ever updated anyway. And it's not like you need a special website just to stick broken English on pictures of cats... Search by an actual image can be done at http://www.tineye.com/. This is useful if one wants to find an original, or see its original context. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: [web-devel] statically compiled css
On Thu, Aug 5, 2010 at 3:41 PM, Tim Matthews tim.matthe...@gmail.comwrote: On Thu, Aug 5, 2010 at 11:33 PM, Mark Bradley barkmad...@gmail.comwrote: but CSS type checking might be possible within hamlet. I have often wondered OK haml implemented now what about sass. Michael Snoyman what is your opinions on sass? Would a sass inspired syntax like you did with the haml-hamlet fit in well and if so, as it often best to keep styles separate, could a quasi quoted language live in in a separate haskell module and then at run time it recreates the separate css files on first launch? After looking into sass a little bit, I've decided I like it ;). I see the following benefits of implementing something sass-like in Haskell via quasi-quotation: * Compile-time guarantee of well-formedness. * The speed benefits of blaze-builder. Of course, this will still be slower than serving a static file. * Ability to use the same Haskell variables for both Hamlet and CSS. I've started a new repo on Github[1]; I'm tentatively calling the project stylish. So far, I've gotten a quasi-quoter that handles nesting working, and it's all built on top of blaze-builder. Here's some design decisions that are up for grabs: * I think the older sass syntax (whitespace sensitive) is a better call than the newer scss syntax (a superset of CSS). It fits in better with Hamlet and looks more like Haskell code. * I'm not planning on implementing variable declarations within a Stylish template; instead, it will use Haskell variables like Hamlet. * I think mixins could be an awesome feature, but I think they'll be implemented much closer to how embedding of templates works in Hamlet. I'm thinking there will be a separate stylishMixin quasi-quoter. * Sass has special support for colors and unit measurements. I think we could provide the same thing with Haskell datatypes. Another thing to consider is just throwing this in with Hamlet; once blaze-html 0.2 is released and is based on blaze-builder, Stylish won't be adding any extra dependencies to Hamlet. I also think that the three forms of interpolation in Hamlet ($$, @@ and ^^) make equals sense in Stylish: just imagine using url(@myUrl@) and not having to guess how many parent directories to ascend. Michael [1] http://github.com/snoyberg/stylish ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] what's the best environment for haskell work?
For another programs (that compile fine with ghc --make), I didn't bother making the package. But I had to find out the package dependencies by building, checking where it fails, and trying to add a package to the dependency list. Maybe there's a better way, didn't find it. We do plan to fix this in the same way we resolve missing imports. I had a look to see if I could do it when a user cabalizes the source, but ghc --make -v does not include the packages automatically loaded in its output. Instead we will need to wait for the error then resolve it when the user presses Ctrl+R. I looked into this for Vim's haskellmode (would also be nice for cabal itself), never got the time to implement more than ':show packages', but perhaps this info helps you along: - 'ghc -v -e ..' instead of 'ghc -v --make ..' avoids the temporary files (assuming the file can be loaded by GHCi). - GHCi's ':show packages' was intended to provide package info, but seems to have bitrotted (you could try the undocumented internal ':show linker' and please file a ticket for ':show packages'). - to force loading without running the code, one might have to resort to ugly things like: ghc -v -e 'snd(main,1)' -e ':show linker' tst.hs - at which stage, we might as well use something like $ ghc -v -e 'snd(main,1)' tst.hs 21 | grep Load Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... *** Parser: Loading package ffi-1.0 ... linking ... done. Loading package ghc-paths-0.1.0.6 ... linking ... done. Loading package array-0.3.0.1 ... linking ... done. Loading package containers-0.3.0.0 ... linking ... done. - for automatic package generation, one would also need the language extensions in use (among other things); unfortunately, the code for that in GHC stops at the first missing extension and is not yet written in a way that makes it easy to identify all such cases. - ideally, one would have ghc --show-languages and ghc --show-packages, or ghc --mk-cabal, or implement them via GHC API. Hth, Claus PS. if someone started a haskell-tools list (for cross-tool interests in haskellmodes, ides, ghc-api clients, etc., I would subscribe, though I can't afford the time to do much Haskell hacking at the moment) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: DSTM 0.1.1
Paul, Yes, I use Read and Show to serialize. I thought of switching to Binary myself but could not find the time yet ;-) Now, a student here is going to work on that. Also, as TCP communication involves a lot of overhead, the library makes some efforts to reduce the amount of messages and makes message exchange itself quite efficient which resulted in a significant efficiency gain. But, there is definitely more optimization potential buried... Frank Am 06.08.2010 um 00:49 schrieb Paul Johnson: Looks interesting. One point: you seem to be using Read and Show typeclasses for serialisation. I think you would be better off using Binary, which is much more efficient. Paul. On 03/08/10 09:35, Frank Kupke wrote: Hi, DSTM is an implementation of a robust distributed Software Transactional Memory (STM) library for Haskell. Many real-life applications are distributed by nature. Concurrent applications may profit from robustness added by re-implementation as distributed applications. DSTM extends the STM abstraction to distributed systems and presents an implementation efficient enough to be used in soft real-time applications. Further, the implemented library is robust in itself, offering the application developer a high abstraction level to realize robustness, hence, significantly simplifying this, in general, complex task. The DSTM package consists of the DSTM library, a name server application, and three sample distributed programs using the library. Provided are a simple Dining Philosophers, a Chat, and a soft real-time Bomberman game application. Distributed communication is transparent to the application programmer. The application designer uses a very simple name server mechanism to set up the system. The DSTM library includes the management of unavailable process nodes and provides the application with abstract error information thus facilitating the implementation of robust distributed application programs. For usage please look into the documentation file: DSTMManual.pdf. The package including the documentation can be found on: http://hackage.haskell.org/package/DSTM-0.1.1 Best regards, Frank Kupke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: [web-devel] statically compiled css
On 6 August 2010 09:19, Michael Snoyman mich...@snoyman.com wrote: After looking into sass a little bit, I've decided I like it ;). I see the following benefits of implementing something sass-like in Haskell via quasi-quotation: * Compile-time guarantee of well-formedness. * The speed benefits of blaze-builder. Of course, this will still be slower than serving a static file. * Ability to use the same Haskell variables for both Hamlet and CSS. I've started a new repo on Github[1]; I'm tentatively calling the project stylish. This sounds pretty interesting. I wrote a Ruby tool called Stylish [1] a couple of years ago to solve a similar set of problems, and have occasionally wondered about rewriting it in Haskell. I look forward to seeing what you come up with. One potentially useful feature is generating code that requires browser prefixes (-webkit-border-radius etc.). There's also potential for generating minified versions of the code, concatenating multiple stylesheets etc.—it's a lot easier to do this stuff if you can programmatically manipulate the stylesheet at run-time. Embedding assets (graphics) as data URIs is another thing; have a look at how something like Jammit [3] does this. There's also a Firefox and Thunderbird extension [2] called Stylish. Obviously you're free to call your project whatever you wish; I just thought I should let you know. Benedict. [1] http://ionfish.github.com/stylish [2] http://userstyles.org/stylish [3] http://documentcloud.github.com/jammit/#embedding ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: DSTM 0.1.1
Am 04.08.2010 um 23:16 schrieb Andrew Coppin: Frank Kupke wrote: Andrew, Thanks for pointing your finger at it Am 04.08.2010 um 17:48 schrieb Andrew Coppin: In that case, is there a way to determine whether or not the rest of the transaction completed? Because it looks like you can the same exception either way, regardless of whether a commit happened or not. Ah, now I see. Excellent point. I was always focussing the commit case which is well designed, I am certain. OK, so there's design work to do here. (Or at least, things to think about.) But that's OK. It's new and exciting. :-) Andrew, oops. Your question was sure pointing me to an issue I had to rethink twice. My last reply to you was shot a bit too quickly. The implemented design throws an exception to the application in two cases: - if the app reads a TVar, calling readTVar, and the TVar is not accessible - if a transaction, a call of atomic, is validated and one or more of the to be validated TVars are not accessible (that I said also before) However, *no* exception is thrown if the transaction *has been* validated and the failure occurs afterwards during the commit phase (here my reply was incorrect). In this case the transaction silently commits all remaining (i.e. non failing) TVars. Failing TVars are simply ignored besides internal cleanup work which is transparent to the app. Back to your original question then: A transaction throwing the distribution exception (other exceptions are possible, too, but are orthogonal to this one) signals to the app that the transaction did not commit because of a TVar failure (Btw, reading a TVar also occurs in a transaction and in case of such an exception the app knows also that the transaction did not finish, it did not even try to validate, though). What about a transaction that committed in spite of unavailable TVars? Answer: The app would not know until the next time it tries to access the failing TVar. Then it definitely gets an exception, either because of reading it or validating the transaction. A committed (i.e. returning) transaction tells the app that whatever it wanted to synchronize with other parts of the system succeeded and it can continue its work. It does not guarantee, though, that the other parts are still alive. This failure semantics, of course, can be discussed. Any input is welcome. Frank PS: I have uploaded DSTM 0.1.2 with minor changes based on the discussion here. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: [web-devel] statically compiled css
On Fri, Aug 6, 2010 at 12:28 PM, Benedict Eastaugh ionf...@gmail.comwrote: On 6 August 2010 09:19, Michael Snoyman mich...@snoyman.com wrote: After looking into sass a little bit, I've decided I like it ;). I see the following benefits of implementing something sass-like in Haskell via quasi-quotation: * Compile-time guarantee of well-formedness. * The speed benefits of blaze-builder. Of course, this will still be slower than serving a static file. * Ability to use the same Haskell variables for both Hamlet and CSS. I've started a new repo on Github[1]; I'm tentatively calling the project stylish. This sounds pretty interesting. I wrote a Ruby tool called Stylish [1] a couple of years ago to solve a similar set of problems, and have occasionally wondered about rewriting it in Haskell. I look forward to seeing what you come up with. One potentially useful feature is generating code that requires browser prefixes (-webkit-border-radius etc.). There's also potential for generating minified versions of the code, concatenating multiple stylesheets etc.—it's a lot easier to do this stuff if you can programmatically manipulate the stylesheet at run-time. Embedding assets (graphics) as data URIs is another thing; have a look at how something like Jammit [3] does this. As far as the border-radius kind of stuff: the approach I'm taking to mixins should make it possible to write a plain old Haskell function to output multiple border-radius statements. I might even include such a mixin in the main package. Regarding concatenating stylesheets: I believe that would have to be handled at the level *above* Stylish; Yesod, for example, automatically concatenates all style statements added via the addStyle function. There's also a Firefox and Thunderbird extension [2] called Stylish. Obviously you're free to call your project whatever you wish; I just thought I should let you know. I'm open to naming suggestions. Here's a few other ideas I'd had: * sasslet: I don't really like too much, but makes clear the connection to Hamlet and Sass. * csser/cssar: pronounced Caesar, might give Shakespeare fans something to chuckle at. As it stands, I'm leaning fairly strongly towards including Stylish in the Hamlet package. Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Question about rpc design
Hi, I'm tinkering with making a DHT im my spare time this summer. For this i need to do some unusual rpc calls. You see in a dht a query (rpc) is first sent from you (node a) to a node b which probably doesn't know the answer. If it still does know the answer it returns the value of the query to node a. This gives the latency: 2*latency(a,b) On the other hand, if i t doesn't it sends a new rpc to a node c more probable to know the ansver. Then the latency is: latency(a,b) + 2*latency(b,c) + latency(b,a) While what I would like is this: latency(a,b) + latency(b,c) + latency(c,a) you see that for many forwards this adds considerable latency and also many more calls than nessesary. Is this way of sending messages already known? Does it have a name? And if not, how hard do you think it would be to hack some rpc library to implement this? -- View this message in context: http://old.nabble.com/Question-about-rpc-design-tp29356441p29356441.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wildly off-topic: de Boor's algorithm
On Aug 5, 2010, at 4:31 PM, Andrew Coppin wrote: mo...@deepbondi.net wrote: Andrew Coppin wrote: Given a suitable definition for Vector2 (i.e., a 2D vector with the appropriate classes), it is delightfully trivial to implement de Casteljau's algorithm: de_Casteljau :: Scalar - [Vector2] - [[Vector2]] de_Casteljau t [p] = [[p]] de_Casteljau t ps = ps : de_Casteljau t (zipWith (line t) ps (tail ps)) line :: Scalar - Vector2 - Vector2 - Vector2 line t a b = (1-t) *| a + t *| b Now, de Boor's algorithm is a generalisation of de Casteljau's algorithm. It draws B-splines instead of Bezier-splines (since B-splines generalise Bezier-splines). But I think I may have ACTUALLY MELTED MY BRAIN attempting to comprehend it. Can anybody supply a straightforward Haskell implementation? It took me a while to get around to it, and another while to work it out, but here's what I've come up with. OK, cool. First, here's a restatement of your code with a concrete choice of types (using Data.VectorSpace from the vector-space package) My types *are* concrete. They're from AC-Vector. ;-) Nope, they were abstract until you told me where I can get an implementation ;) To generalize to De Boor's algorithm, the primary change is the interpolation operation. In De Casteljau's algorithm, every interpolation is over the same fixed interval 0 = x = 1. For De Boor's algorithm we need a more general linear interpolation on the arbitrary interval [x0,x1], because all the interpolations in De Boor's recurrence are between pairs of knots, which have arbitrary values instead of just 0 or 1. Right. That's basically what I figured. I'm having trouble wrapping my brain about the exact relationship between the number of control points, the number of knots, the degree of the spline, which knots and control points are active at a given parameter value, etc. There seems to be an utterly *huge* avenue for off-by-one errors here. It took me a while to get the intuition right on those, but here's a quick sketch. Let n = number of control points, m = number of knots, and p = degree. For p = 0 (constant segments), each control point corresponds to one span of the knot vector, so n = m - 1. Each time you move up a degree, the basis functions span one more segment of the knot vector. Thus, to keep the same number of control points you have to add a knot when you add a degree, so n = m - 1 + p. Equivalently, n - p = m - 1, which incidentally makes an appearance in the deBoor function below when we zip spans p us with spans 1 ds. This is just the property that ensures that the length of these lists is equal. As for off-by-one errors, I agree. I am reasonably sure that I at least don't have any major ones, but I would only be slightly surprised if there are corner cases I have handled incorrectly. After quite a bit of plotting and deliberately introducing errors in the implementation I found that in most of the obvious places for off-by-one type errors (such as getting the wrong pair of knots for the pair of control points) the results were spectacularly sensitive to those errors, so at least those ones I think are hard to get wrong if you're actually looking at the splines the implementation draws. Computing the table is now nearly as straightforward as in De Casteljau's algorithm: deBoor p _ [] x = [] deBoor p (_:us) ds x = ds : deBoor (p-1) us ds' x where ds' = zipWith (interp x) (spans p us) (spans 1 ds) Making use of a simple list function to select the spans: spans n xs = zip xs (drop n xs) Don't you need an uncurry in there? Or am I missing something? Not unless I pasted the wrong version of the code. I'm not sure where you mean - perhaps you're thinking of the arity of interp? The interp function takes 3 arguments, 2 of which are pairs - those pairs are the ones being supplied by zipWith above, and are the results of this function. I had a version that used zipWith4 (interp t) us (drop p us) ds (tail ps) instead but I felt it was overly complicated, so I abstracted out the spans function. Note that the algorithm does not make use of @us!!0@ at all. Yeah, that's the killer, isn't it? Figuring out exactly which combination of list function you need to pipe the correct values to the right places. (You might remember be asking about expression dye for this exact reason...) I believe this is correct, based both on the Wikipedia description of the algorithm and the implementations I've seen. Heh, prove it. ;-) (I guess just go draw some splines and see if they look... spliney.) Oh, believe me, I've done a lot of the informal stuff like that to check my sanity. The next few paragraphs that were apparently confusing (probably due to my habit of rambling at times) were a gesture in the direction I believe a proof is to be found. If I feel ambitious I'll probably revisit that line of
Re: [Haskell-cafe] Preview the new haddock look and take a short survey
On Thu, Aug 5, 2010 at 2:35 PM, Dino Morelli d...@ui3.info wrote: One thing I haven't seen anyone else comment on is the width of the new docs. I have a large (26) monitor and use the browser full-screen (with xmonad, so even more screen space). When I load these pages, particularly the non-frame one, something like 50% of my screen real-estate is empty whitespace on either side of the doc content. There is also wasted space in the frames version, just a little less of it. I wish the docs were using that space like the current Haddock does. Is the plan to use a fixed width like this? Please say no, it's a disappointing trend that you see everywhere. Like Twitter's web interface, for instance, very narrow. Yeah, I wrote about this in my survey response. It seems to me that if I find text in a narrow page more readable, I can easily just resize my browser window, this doesn't need to be enforced by the webpage itself. I'm also not so enthusiastic about tabbed synposis. I'm not convinced you can easily use the synopsis and doc text simultaneously, so I don't see any reason for it to be apart from the text body. Simplicity is a virtue :) I do think that in terms of colours, fonts etc. it's prettier, but the fixed max width and kind of gimmicky synopsis tab are steps backward in my opinion. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wildly off-topic: de Boor's algorithm
mo...@deepbondi.net wrote: It took me a while to get the intuition right on those, but here's a quick sketch. Let n = number of control points, m = number of knots, and p = degree. For p = 0 (constant segments), each control point corresponds to one span of the knot vector, so n = m - 1. Each time you move up a degree, the basis functions span one more segment of the knot vector. Thus, to keep the same number of control points you have to add a knot when you add a degree, so n = m - 1 + p. Equivalently, n - p = m - 1, which incidentally makes an appearance in the deBoor function below when we zip spans p us with spans 1 ds. This is just the property that ensures that the length of these lists is equal. How embarrassing, I managed to get this simple math wrong. That's what I get for trying to think in the morning without either my notes or my coffee, I suppose. At least, I have that standard excuse to fall back on, so I'll take advantage of it. n = m - 1 + p should read n + p = m - 1 - I added p to the wrong side. It is indeed the property that makes the zip line up, but not by the math I gave. Instantiating n and m as the respective length expressions makes the equation: length ds + p = length us - 1 With subsequent derivation in light of the fact that the 1st control point is being ignored (which introduces a - 1 on the RHS, if I'm not mistaken again), as mentioned earlier, and the fact that the expression in question is supposed to return a list one shorter than ds: length ds + p - 1 = length us - 1 = length (tail us) length ds - 1 = length (tail us) - p length (spans 1 ds) = length (spans p (tail us)) (Under the assumption that all the lists involved are long enough for the tail and drop operations) And all is (hopefully) right again. -- James ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wildly off-topic: de Boor's algorithm
mo...@deepbondi.net wrote: How embarrassing, I managed to get this simple math wrong. That's what I get for trying to think in the morning without either my notes or my coffee, I suppose. I _said_ it was tricky, didn't I? ;-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Question about rpc design
snip Is this way of sending messages already known? Does it have a name? And if not, how hard do you think it would be to hack some rpc library to implement this? I think you are describing telescopic routing. Of sorts. The easiest way to achieve your goal is by making the communications asynchronous and the party which has an answer to send it directly to the originator. It won't necessarily reduce the latency though, and you would probably get multiple answers, unless you have no redundant data in the network. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Suggestions For An Intro To Monads Talk.
Thanks all for you suggestions! Upon further reflection I realized that my audience is more pragmatic than theoretical. Instead of emphasizing how monads are constructed and the monad laws I think I want to dive right into the most common and useful monads. From my vantage point they are (in no particular order) : Reader, Writer, State, IO, ST, STM, Parsec (have I missed any?) and of course the transformer versions. I am debating whether or not to add [] to the bunch. To explain monads (now that I have Timothy's awesome blog post to reference) I'll be drawing the parallel between monads and interfaces in Java. And thanks to Tillman for showing me where the analogy breaks down. Are there any such parallels in other languages like Perl and Python? I'm still a little iffy on why the monad concept isn't used in other languages. From where I sit it seems as though monads really let you play with the order of evaluation - just because one statement is executed after another doesn't mean they are executed in that order. I think other languages don't make this easy. -deech On Wed, Aug 4, 2010 at 6:21 PM, Daniel van den Eijkel d...@gmx.net wrote: For me, the following two things did the magic, so I'll suggest them: 1. Writing a recursive function that takes a binary tree and returns the same tree, but with its leaves enumerated. Each function call takes the tree and the counter and returns the resulting tree and the new counter value. The pattern that emerges is similar to the state monad. The pattern shows that the order of the recursive calls is not ambiguous, unlike in a function that just counts the leaves, for example. Changing the order of the recursive calls changes the result. (code below) 2. Putting the above pattern into a datatype and rewriting the apply-funtion for this datatype (=) allows only to apply funtions in a non-ambiguous way. Not giving a deconstructor for the IO monad forces the programmer to decide in which order calls to IO functions have to be done. I hope this is clear enough; I was able to use the IO monad at the moment I realized that Haskell uses this kind of trick to ensure that the order of execution of function arguments is always well-defined and never ambiguous. Of course, there is much more about monads, but this was my entry point. Best regards Daniel code (tree enumeration): data Tree a = Leaf a | Node (Tree a) (Tree a) deriving Show enumTree n (Node a b) = let (n', a') = enumTree n a in let (n'', b') = enumTree n' b in (n'', Node a' b') enumTree n (Leaf x) = (n+1, Leaf n) aditya siram schrieb: Hi all, I am doing an Intro To Monads talk in September [1]. The audience consists of experienced non-Haskell developers but they will be familiar with basic functional concepts (closures, first-class functions etc.). I am looking for suggestions on how to introduce the concept and its implications. I'd also like to include a section on why monads exist and why we don't really see them outside of Haskell. Has anyone here done a talk like this? And if so what parts of your presentation were successful and what would you stay away from. Thanks for the feedback. -deech [1] It's in St.Louis, Missouri at the St.Louis Perl Mongers meetinghttp://St.Louis%20Perl%20Mongers%20meetingso come on by if you're around! -- ___ Haskell-Cafe mailing listhaskell-c...@haskell.orghttp://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: DSTM 0.1.1
Another interesting direction would be to use Matt Morrow's vaccum infrastructure to make a neat, almost completely general, serialization mechanism. It's not safe, and can traverse any value that doesn't contain functions or unevaluated thunks, but would be very helpful for sending values like `cycle [1,2,3]` over the network. He and I were talking about writing such a library before he disappeared, but it doesn't seem terribly difficult if you have a good use for it. Dan On Fri, Aug 6, 2010 at 11:14 AM, Frank Kupke f...@informatik.uni-kiel.dewrote: Paul, Yes, I use Read and Show to serialize. I thought of switching to Binary myself but could not find the time yet ;-) Now, a student here is going to work on that. Also, as TCP communication involves a lot of overhead, the library makes some efforts to reduce the amount of messages and makes message exchange itself quite efficient which resulted in a significant efficiency gain. But, there is definitely more optimization potential buried... Frank Am 06.08.2010 um 00:49 schrieb Paul Johnson: Looks interesting. One point: you seem to be using Read and Show typeclasses for serialisation. I think you would be better off using Binary, which is much more efficient. Paul. On 03/08/10 09:35, Frank Kupke wrote: Hi, DSTM is an implementation of a robust distributed Software Transactional Memory (STM) library for Haskell. Many real-life applications are distributed by nature. Concurrent applications may profit from robustness added by re-implementation as distributed applications. DSTM extends the STM abstraction to distributed systems and presents an implementation efficient enough to be used in soft real-time applications. Further, the implemented library is robust in itself, offering the application developer a high abstraction level to realize robustness, hence, significantly simplifying this, in general, complex task. The DSTM package consists of the DSTM library, a name server application, and three sample distributed programs using the library. Provided are a simple Dining Philosophers, a Chat, and a soft real-time Bomberman game application. Distributed communication is transparent to the application programmer. The application designer uses a very simple name server mechanism to set up the system. The DSTM library includes the management of unavailable process nodes and provides the application with abstract error information thus facilitating the implementation of robust distributed application programs. For usage please look into the documentation file: DSTMManual.pdf. The package including the documentation can be found on:http://hackage.haskell.org/package/DSTM-0.1.1 Best regards, Frank Kupke ___ Haskell-Cafe mailing listhaskell-c...@haskell.orghttp://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] real-time audio processing [Was: can Haskell do everyting as we want?]
Hey John, The language you are working on - is it a EDSL in Haskell? If not, had you considered such an option? On Thu, Aug 5, 2010 at 8:11 PM, Job Vranish job.vran...@gmail.com wrote: Yeah Atom is pretty slick, though unfortunately it's not quite powerful enough for much of the stuff that we do. John Van Enk and I are actually working on a language that's similar to C (and compiles to C), but has polymorphism, type inference and other goodies. The goal is to make working on embedded systems a bit less painful, while still being able to do anything that C can do (like run on an 8 bit micro). Hopfully, if things go as planned, we'll have a working beta out by the end of the month :) - Job On Wed, Aug 4, 2010 at 5:58 PM, Don Stewart d...@galois.com wrote: job.vranish: + 1 This is probably the biggest obstacle to using Haskell where I work. (Aviation industry, software for flight management systems for airplanes) We often need to perform some computations with hard deadlines, say every 20ms, with very little jitter. Major GC's spoil the fun; It's quite easy to have a major GC take longer than 20ms, and currently they are not pauseable (nor is it trivial to make them so). It would be very nice to have some annotation/DSL/compiler-flag that would let me run a small block of mostly regular haskell code under hard, real-time constraints. Hmm, it looks like the HASP project is working on some of this, though I'm not sure how portable their work is back to GHC: http://hasp.cs.pdx.edu/ Or look at EDSLs, like Atom: http://hackage.haskell.org/package/atom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Regards, Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Suggestions For An Intro To Monads Talk.
On Fri, Aug 06, 2010 at 10:17:26AM -0500, aditya siram wrote: From my vantage point they are (in no particular order) : Reader, Writer, State, IO, ST, STM, Parsec (have I missed any?) and of course the transformer versions. I am debating whether or not to add [] to the bunch. Not sure how much time you have budgeted, but I'd start with a simple one like Maybe, actually show how to implement it, then move on to list, and then finally talk about Reader, Writer, State, etc. from a more high level perspective. Hopefully people would grok the monad concept by that point, and should realize how useful it is to add logging, or state, etc. Then they may wonder about mixing in more than 1, so that could lead to transformers. To explain monads (now that I have Timothy's awesome blog post to reference) I'll be drawing the parallel between monads and interfaces in Java. And thanks to Tillman for showing me where the analogy breaks down. Are there any such parallels in other languages like Perl and Python? I get the type class / Java interface analogy, but trying to draw a parallel between Java interface and monads seems likely to just create confusion IMHO. I'm still a little iffy on why the monad concept isn't used in other languages. From where I sit it seems as though monads really let you play with the order of evaluation - just because one statement is executed after another doesn't mean they are executed in that order. I think other languages don't make this easy. I first encountered monads in OCaml. And the concept exists in other languages, although maybe not always explicitly by that name. Good luck, should be a good talk, Alex ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Suggestions For An Intro To Monads Talk.
At version 2 Parsec was an amalgamation of a state and error monad - by amalgamation I mean the data types and Monad instance encoded the combination directly, it wasn't made from transformers. Version 3 of Parsec complicates things a quite a bit. If you're addressing Perl programmers, you could try and encode the monads in Perl and see what it looks like. Maybe Mark Jason Dominus the author of Higher Order Perl has done this already? On 6 August 2010 16:17, aditya siram aditya.si...@gmail.com wrote: [SNIP] I think I want to dive right into the most common and useful monads. From my vantage point they are (in no particular order) : Reader, Writer, State, IO, ST, STM, Parsec (have I missed any?) and of course the transformer versions. I am debating whether or not to add [] to the bunch. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lambdacats
I happened to download them all (i think all) a while ago to torment my coworkers: http://sw17ch.com/dump/lambdacats.zip Enjoy. On Fri, Aug 6, 2010 at 12:12 AM, Tony Morris tonymor...@gmail.com wrote: Hello, does anyone happen to have the lambdacats page cached? The domain ( arcanux.org) and server have disappeared and the wayback machine doesn't have the images. -- Tony Morris http://tmorris.net/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] real-time audio processing [Was: can Haskell do everyting as we want?]
It's not an EDSL (though I'm a huge fan of the concept) because we wan't to pitch the language to programmers who currently use C/Ada. As much as I love EDSL's, they are particularly hard to sell to entrenched engineers without substantial effort or mandate. Dangling a few neat features on top of a comfortable tool set hopefully will stimulate some curiosity and help sell Haskell/EDSL's in the future... On Fri, Aug 6, 2010 at 11:34 AM, C K Kashyap ckkash...@gmail.com wrote: Hey John, The language you are working on - is it a EDSL in Haskell? If not, had you considered such an option? On Thu, Aug 5, 2010 at 8:11 PM, Job Vranish job.vran...@gmail.com wrote: Yeah Atom is pretty slick, though unfortunately it's not quite powerful enough for much of the stuff that we do. John Van Enk and I are actually working on a language that's similar to C (and compiles to C), but has polymorphism, type inference and other goodies. The goal is to make working on embedded systems a bit less painful, while still being able to do anything that C can do (like run on an 8 bit micro). Hopfully, if things go as planned, we'll have a working beta out by the end of the month :) - Job On Wed, Aug 4, 2010 at 5:58 PM, Don Stewart d...@galois.com wrote: job.vranish: + 1 This is probably the biggest obstacle to using Haskell where I work. (Aviation industry, software for flight management systems for airplanes) We often need to perform some computations with hard deadlines, say every 20ms, with very little jitter. Major GC's spoil the fun; It's quite easy to have a major GC take longer than 20ms, and currently they are not pauseable (nor is it trivial to make them so). It would be very nice to have some annotation/DSL/compiler-flag that would let me run a small block of mostly regular haskell code under hard, real-time constraints. Hmm, it looks like the HASP project is working on some of this, though I'm not sure how portable their work is back to GHC: http://hasp.cs.pdx.edu/ Or look at EDSLs, like Atom: http://hackage.haskell.org/package/atom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Regards, Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lambdacats
On Fri, Aug 6, 2010 at 12:12 AM, Tony Morris wrote: Hello, does anyone happen to have the lambdacats page cached? The domain ( arcanux.org) and server have disappeared and the wayback machine doesn't have the images. On Fri, Aug 6, 2010 at 18:43, John Van Enk wrote: I happened to download them all (i think all) a while ago to torment my coworkers: http://sw17ch.com/dump/lambdacats.zip And from that to this: http://spl.smugmug.com/Humor/Lambdacats/13227630_eKt46 Sean ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] finding out which gcc is hard-coded into a ghc?
Hello, how can I find out which gcc a ghc is hard-coded to use and is it possible to override it? Günther ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] finding out which gcc is hard-coded into a ghc?
If you're on Windows, I believe you can find the gcc.exe at the following location: C:\Program Files\Haskell Platform\2009.2.0.2\gcc.exe See this link for how to pick which C compiler to use: http://www.haskell.org/ghc/docs/6.12.2/html/users_guide/options-phases.html#replacing-phases 2010/8/6 Günther Schmidt gue.schm...@web.de Hello, how can I find out which gcc a ghc is hard-coded to use and is it possible to override it? Günther ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Preview the new haddock look and take a short survey
On Fri, 6 Aug 2010, Ben Millwood wrote: On Thu, Aug 5, 2010 at 2:35 PM, Dino Morelli d...@ui3.info wrote: One thing I haven't seen anyone else comment on is the width of the new docs. I have a large (26) monitor and use the browser full-screen (with xmonad, so even more screen space). When I load these pages, particularly the non-frame one, something like 50% of my screen real-estate is empty whitespace on either side of the doc content. There is also wasted space in the frames version, just a little less of it. I wish the docs were using that space like the current Haddock does. Is the plan to use a fixed width like this? Please say no, it's a disappointing trend that you see everywhere. Like Twitter's web interface, for instance, very narrow. Yeah, I wrote about this in my survey response. It seems to me that if I find text in a narrow page more readable, I can easily just resize my browser window, this doesn't need to be enforced by the webpage itself. Agreed, it's like a premature optimization for the Haddock page build to decide and enforce width without knowing my needs, hardware or windowing situation. I'm also not so enthusiastic about tabbed synposis. I'm not convinced you can easily use the synopsis and doc text simultaneously, so I don't see any reason for it to be apart from the text body. Simplicity is a virtue :) The more I play with it, the more I'm not that thrilled with the sliding synopsys thing as well. I think moving away from static pages is making the docs less usable. There was a period of time when the simple static alphabetic function index was replaced with some dynamic JavaScript filtering that responded to keystrokes in the edit control. It performed really terribly on even my very modern systems with Firefox. I was happy when it went away. I appreciate the idea, but it pays to be very very conservative with reference material. I do think that in terms of colours, fonts etc. it's prettier, but the fixed max width and kind of gimmicky synopsis tab are steps backward in my opinion. I can agree with this too. I like the existing higher-contrast coloring more, which was also mentioned by a couple of the other responses in this thread. -- Dino Morelli email: d...@ui3.info web: http://ui3.info/d/ irc: dino- pubkey: http://ui3.info/d/dino-4AA4F02D-pub.gpg twitter: dino8352 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lambdacats
Sean Leather wrote: On Fri, Aug 6, 2010 at 12:12 AM, Tony Morris wrote: Hello, does anyone happen to have the lambdacats page cached? The domain (arcanux.org http://arcanux.org) and server have disappeared and the wayback machine doesn't have the images. On Fri, Aug 6, 2010 at 18:43, John Van Enk wrote: I happened to download them all (i think all) a while ago to torment my coworkers: http://sw17ch.com/dump/lambdacats.zip And from that to this: http://spl.smugmug.com/Humor/Lambdacats/13227630_eKt46 Heh. unsafePerformDoggeh# still amuses me... Sadly, I lack the 31337 skills required to think of original ideas myself. Just laugh at what other people have thought up. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Does Hackage have a connection to some SFT package (Significant FFT coefficients) ...
Does Hackage have a connection to some SFT package (Significant FFT coefficients) and/or can one get the SFT from FFTW without generating all the coefficients? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lambdacats
Sean Leather schrieb: On Fri, Aug 6, 2010 at 12:12 AM, Tony Morris wrote: Hello, does anyone happen to have the lambdacats page cached? The domain (arcanux.org http://arcanux.org) and server have disappeared and the wayback machine doesn't have the images. On Fri, Aug 6, 2010 at 18:43, John Van Enk wrote: I happened to download them all (i think all) a while ago to torment my coworkers: http://sw17ch.com/dump/lambdacats.zip And from that to this: http://spl.smugmug.com/Humor/Lambdacats/13227630_eKt46 I remember the first lambdacat said something like why can't u curry this funkshun. I don't see it in this list. :-( ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lambdacats
I apologize if I missed any. :( On Fri, Aug 6, 2010 at 3:03 PM, Henning Thielemann schlepp...@henning-thielemann.de wrote: Sean Leather schrieb: On Fri, Aug 6, 2010 at 12:12 AM, Tony Morris wrote: Hello, does anyone happen to have the lambdacats page cached? The domain (arcanux.org http://arcanux.org) and server have disappeared and the wayback machine doesn't have the images. On Fri, Aug 6, 2010 at 18:43, John Van Enk wrote: I happened to download them all (i think all) a while ago to torment my coworkers: http://sw17ch.com/dump/lambdacats.zip And from that to this: http://spl.smugmug.com/Humor/Lambdacats/13227630_eKt46 I remember the first lambdacat said something like why can't u curry this funkshun. I don't see it in this list. :-( ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lambdacats
I remember the first lambdacat said something like why can't u curry this funkshun. I don't see it in this list. :-( Simon cat and Oleg cat are also missing, unfortunately. Also the 'catamorphism' picture with the banana peel (there may be others I can't recall, too). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] finding out which gcc is hard-coded into a ghc?
On 6 Aug 2010, at 18:05, Günther Schmidt wrote: Hello, how can I find out which gcc a ghc is hard-coded to use and is it possible to override it? See this page: http://www.haskell.org/ghc/docs/6.12.2/html/users_guide/options-phases.html Cheers, G ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Suggestions For An Intro To Monads Talk.
On Fri, Aug 6, 2010 at 9:17 AM, aditya siram aditya.si...@gmail.com wrote: Upon further reflection I realized that my audience is more pragmatic than theoretical. Instead of emphasizing how monads are constructed and the monad laws I think I want to dive right into the most common and useful monads. From my vantage point they are (in no particular order) : Reader, Writer, State, IO, ST, STM, Parsec (have I missed any?) and of course the transformer versions. I am debating whether or not to add [] to the bunch. If your audience is indeed a pragmatic lot then they will not be interested in the same things as a more theoretical crowd (obviously). So they might not be interested in Monads at all. You've got your work cut out for you! With that said, I would suggest starting with the advantages of purity. I would guess that 95% of bugs in imperative code are related to some erroneous state. Pure code, on the other hand is immune to this huge class of bugs. Sometimes state is useful or even necessary (stateful computations, IO, in-place algorithms, etc), so you really can't forgo state entirely. The cool thing about Monads is they allow us to have our cake and eat it too! We can model stateful computations in pure code. You might also mention the separation of pure and impure code and how this helps us to reason about a program. I'm still a little iffy on why the monad concept isn't used in other languages. From where I sit it seems as though monads really let you play with the order of evaluation - just because one statement is executed after another doesn't mean they are executed in that order. I think other languages don't make this easy. My guess would be that other languages have much less commitment to purity. You don't need Monads in other languages because state is implicit, everything is in the IO monad, in a sense. While Monads are still an excellent abstraction in other languages they're often more awkward than just using implicit state/IO/whatever operations. Haskell has some sweet built-in syntax for monads. Also related to advantages of purity: http://www.haskell.org/haskellwiki/Why_Haskell_just_works I think this approach (stating benefits of purity and maybe laziness) would be more interesting to a pragmatic crowd. Just a guess though. Good luck with your presentation! --Jonathan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Suggestions For An Intro To Monads Talk.
On Fri, Aug 6, 2010 at 11:17 AM, aditya siram aditya.si...@gmail.comwrote: I'm still a little iffy on why the monad concept isn't used in other languages. The greatest feat that monads have accomplished, in my opinion, is providing the right mathematical abstraction for declaring side-effect and stateful computation in a pure functional language. For the first time it was now possible for a pure functional programming language to be a general purpose programming language. That's was quite an accomplishment! The second most important feat of monads was their close offspring, the monad transformers. These guys gave pure functional programmers the ability to maintain invariants on which side-effect/stateful computations their end users are going to use. This enhanced verifiability by a measured mix of pure and impure. The other languages that you mention are impure. So feat #1 is pointless since they were already general purpose without monads, and feat #2 is not realistically achievable since impure languages generally don't have a way of restricting a function from having arbitrary side-effects. There have been some clever things done with monads aside from #1 and #2. Parsec is one, but it seems applicative functors are a better match for the parsing domain. Other things are neat, but not killer features that would turn the head of a pragmatist of the impure type in my opinion. So, that is why I think the monad concept isn't generally used in other languages. David -- David Sankel Sankel Software www.sankelsoftware.com 585 617 4748 (Office) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Suggestions For An Intro To Monads Talk.
It might be a little late at this point, but here's my take on monads: In most imperative languages sequencing of statements is a feature that is hard-coded into the language to act in a certain way, e.g. to have a particular implicit state (the global state plus possibly the fields available from a class, if the code is in a method). In Haskell, sequencing of statements is a first-class feature of the language that we can define to work however we want. For example, the Maybe monad allows us to define the sequencing operation to abort whenever we access a Maybe value that is Nothing. In most languages they have to introduce a special keyword return to get this kind of early-exit functionality, but in Haskell we don't need such a keyword because Monads allow us to extend the sequencing operation to *add* this kind of functionality. Similarly, in most languages you cannot completely change the implicit state available to code; the most that you can do is to use Object-Oriented programming, which is an additional feature to the language, to add additional implicit state that is available to code (when it is inside a method) that stacks on top of the global state. By contrast, in Haskell defining an implicit state for code is trivial, and furthermore we can do additional things like forcing this state to be read-only, all without having to add new features to the language itself. Not only is sequencing is a first-class operation that we can define at will, but it is also possible to compose the functionality of multiple sequencing operations so that, for example, we can get access to both a read-only state, a global mutable state, *and* have the ability to perform an early exit from our code, all (again) within the language. This technique is known as stacking Monad transformers, and there are multiple libraries for doing it. Finally, here is something that is trivial to do in Haskell: create a sequencing operation based on continuations that allows code to perform operations asynchronously while writing code in a synchronous style. That is, you can define a monad that lets you write code that looks like do result - request x case result of A - request y B - request z which has the feature that rather than blocking a thread while we wait for a request, we instead actually implicitly creates a callback that runs the rest of the code as soon as the result as ready. In most other languages you'd have to invent a special language features such as continuations in order to allow for a coding style like this, but in Haskell we don't need them because *overriding the sequence operation itself* is a first-class feature of the language that allows us to do this. So again, the moral of this story is that just like having access to continuations as a first-class object allows one to do powerful things, so too does having access to the sequencing operation as a first-class object let us do stuff that makes our job as programmers easier. Cheers, Greg On 08/06/10 08:17, aditya siram wrote: Thanks all for you suggestions! Upon further reflection I realized that my audience is more pragmatic than theoretical. Instead of emphasizing how monads are constructed and the monad laws I think I want to dive right into the most common and useful monads. From my vantage point they are (in no particular order) : Reader, Writer, State, IO, ST, STM, Parsec (have I missed any?) and of course the transformer versions. I am debating whether or not to add [] to the bunch. To explain monads (now that I have Timothy's awesome blog post to reference) I'll be drawing the parallel between monads and interfaces in Java. And thanks to Tillman for showing me where the analogy breaks down. Are there any such parallels in other languages like Perl and Python? I'm still a little iffy on why the monad concept isn't used in other languages. From where I sit it seems as though monads really let you play with the order of evaluation - just because one statement is executed after another doesn't mean they are executed in that order. I think other languages don't make this easy. -deech On Wed, Aug 4, 2010 at 6:21 PM, Daniel van den Eijkel d...@gmx.net mailto:d...@gmx.net wrote: For me, the following two things did the magic, so I'll suggest them: 1. Writing a recursive function that takes a binary tree and returns the same tree, but with its leaves enumerated. Each function call takes the tree and the counter and returns the resulting tree and the new counter value. The pattern that emerges is similar to the state monad. The pattern shows that the order of the recursive calls is not ambiguous, unlike in a function that just counts the leaves, for example. Changing the order of the recursive calls changes the result. (code below) 2. Putting the above pattern into a datatype and rewriting the
Re: [Haskell-cafe] Suggestions For An Intro To Monads Talk.
On 6 August 2010 20:47, David Sankel cam...@gmail.com wrote: There have been some clever things done with monads aside from #1 and #2. Parsec is one, but it seems applicative functors are a better match for the parsing domain. Monadic bind is very, very handy for parsing, giving you context sensitive parsing if you need it. If you have a grammar that is LL1 plus helpers (i.e. the extended Kleene operators - many1, sepBy etc.) then applicative formalism is nice and as Doaitse Swierstra has shown provides good opportunities for optimization; but I'd hasten to call it a better match in general. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lambdacats
Henning Thielemann wrote: I remember the first lambdacat said something like why can't u curry this funkshun. I don't see it in this list. :-( Actually, I believe it said why u not curry that funkshun?! In other news, I probably need to get a life... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: using Network.CGI
On Fri, 6 Aug 2010, Andrew U. Frank wrote: i think this limits what network.cgi can be used for: it will work only on systems, where the output from the ghc can execute. That’s not a limitation of Network.CGI; it’s just the way CGI always works, no matter what language you use. http://en.wikipedia.org/wiki/Server-side_scripting specifically, this means, i cannot move the executable to an android mobile phone and use it there (assuming that there is a web server, e.g. i-jetty, which understands cgi (does it?)). is this correct? You’d need a Haskell compiler that targets Android; I don’t know whether such a thing exists yet. (Of course, keep in mind that if the CGI script is running on another computer, such as http://andersk.mit.edu/greet.cgi , you will still be able to visit it and use it from a browser running on Android. That’s the point of CGI; only the server needs to know how to run the code.) Anders ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haddock New Look Survey results
Thank you to all who took the Haddock New Look Survey. We got a 161 responses. Some graphs of the results can be found here: http://www.ozonehouse.com/mark/snap-xhtml/Haddock-Survey-Summary.pdf I've read through all of the comments, and I'd like to share some initial thoughts with you: • Source links are indeed still supported in Haddock, I just happened to generate those sample pages with it turned off. Sorry for any confusion. The functionality remains exactly like it is in Haddock today. • I also failed to turn off all the alternate style bits on the index page, and many of you found it, explored the other styles, and then wondered why it failed on the module pages. I had intended for the survey to just give pages in the new style, and missed updating the index page. In the new Haddock, you can specify which themes you want to render your documentation with. If you include more than one, the pages have a style switcher menu added. The default themes that will come with Haddock include Classic which is a pretty faithful recreation of the current look. • Many great suggestions were made about ways to improve the UI experience of Synopsis drawer. Of course, the web is hardly a full featured UI framework, and to implement many of them we would have to decide to move to a much larger JavaScript framework. At present, Haddock attempts to use JavaScript very lightly, and only needs one small .js file. I think we are planning on keeping it that way for now. • Several people mentioned that perhaps we should have user preferences for things like where the Synopsis section goes. This is possible (the style switcher menu above uses such a preference), but know that a page can only set a cookie for a site. So if we do such things, they will stick per site, and users will have to choose their preference for each new site of Haddock docs they browse to. Fortunately, all of Hackage would count as one site, as does your local machine, and those two settings probably cover the bulk one's use. There were many many good suggestions, reported problems, and observations among the comments. I'm pulling together a short of list with the Haddock team of high priority changes based on these to be completed before the first release. To be sure, this will include: - fixing the layout issues on Firefox Chrome - improving the expanding/collapsing behavior in module lists The most difficult issue is how to handle the Synopsis. As evident both from the multiple choice question in the survey, and from the comments, there is no clear consensus. While 2/3rds of you like the Synopsis drawer, there is a wide range of how it should look and operate. Another 1/5th want it back where it was, in-line with the page. There were many other suggestions as well. I'm going to go have to spend some time mulling what to do. Finally, thanks for the huge amount of positive feedback. When working on open source, often on speculation that it is what the community will want, it is really great to hear that you've done good! I realize that there is no way that such a change as this can please everyone 100%, but I'm glad to see that we are, on the whole, people are really happy with the work. - Mark Mark Lentczner http://www.ozonehouse.com/mark/ m...@glyphic.com irc: mtnviewmark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lambdacats
Simon cat and Oleg cat are also missing, unfortunately. Also the 'catamorphism' picture with the banana peel (there may be others I can't recall, too). Well, I found what I could... http://spl.smugmug.com/Humor/Lambdacats/13227630_eKt46#960831913_rhDdG http://spl.smugmug.com/Humor/Lambdacats/13227630_eKt46#960824968_hNkLy I welcome any others you want to share or create. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Preview the new haddock look and take a short survey
I prefer the new look. That being said, I'd rather like haddock handling unicode characters in comments, at the moment it's unusable if I want to write comments in French. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Haskell in Industry
On Thu, 5 Aug 2010 21:58:15 -0500 Tom Hawkins tomahawk...@gmail.com wrote: Good, we need more functional programmers actually solving real problems. But please put your skills to work in an industry other than investment banking. +1000 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Preview the new haddock look and take a short survey
On Sat, Aug 7, 2010 at 01:00, David Virebayre dav.vire+hask...@gmail.com wrote: I prefer the new look. That being said, I'd rather like haddock handling unicode characters in comments, at the moment it's unusable if I want to write comments in French. jokeWouldn't the docs be unusable if it were in French even if Haddock handled unicode characters correctly?/joke Seriously though, it would be useful for Haddock to handle unicode, if for nothing else just to allow developers to have their names showing properly. /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
