Function references in Scala October 17, 2011
Posted by CK in Software.Tags: Languages, Programming, Scala
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I’m starting to learn Scala, and have some trouble coming to terms with its syntax. Maybe I’m spoiled by Python. In any case, here’s an example of things that I find annoying:
scala> def f(x:Int):Int = x
f: (x: Int)Int
scala> def g(f:Int=>Int, y:Int, b:Boolean):Int = if (b) g(f, y, false) else y
g: (f: (Int) => Int,y: Int,b: Boolean)Int
scala> def h=f
:6: error: missing arguments for method f in object $iw;
follow this method with `_' if you want to treat it as a partially applied function
def h=f
^
scala> def h=f _
h: (Int) => Int
So basically, although it is fine to use just f when defining function g, in the definition of function h it is necessary to postfix f with an underscore.
I haven’t read the language reference yet, and there may be good reasons to do it like this (although I can’t think of any right now), but the inconsistency is quite confusing.
My personal little “cloud” May 24, 2011
Posted by CK in Internet, Productivity, Software.Tags: Archiving, PIM data, Synchronization
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Here it is, and it works perfect:
- You will need a VPS or a home server. I’m using the wonderful, fan-less Shuttle XS35GT with a small SSD, as it is also my HTPC
- A Linux distribution. I very highly recommend Mint 10 if you’re using the XS35GT so that you get a working audio + wireless and a stable XBMC, otherwise you may wish to use an LTS release like Ubuntu 10.04 or Mint 9.
- An installation of eGroupware, to use its addressbook and calendar modules with its GroupDAV and SyncML synchronization facilities. You can easily install eGroupware using the deb repository provided on the project’s site.
- Thunderbird, Lightning and the SOGo connector to support GroupDAV. Make sure you don’t use the “SOGo Lightning” extension; at least for me it didn’t work. Then subscribe Lightning to the eGroupware calendar and addressbook. Don’t bother with TODO items, unless a flat list is your thing.
- A SyncML application to synchronize your phones. My Nokia E71 comes installed with one, while on an Android you can use the wonderful Synthesis client. Synthesis offers clients for additional platforms, but I only tried the one for Android.
- The amazing Tracks application for GTD. It takes some effort to install, but it is totally worth it. You can also subscribe Lightning to various views of Tracks exported calendars. I’ve subscribed only to the one for due items, so that they appear with deadlines in my calendar. There are also two mobile applications to sync with Tracks, one for the iOS and one for the Android. Unfortunately the latter doesn’t work yet with Tracks 2.0, but it looks like it’s only a matter of time before it does.
- …and, finally, Mindtouch Core (DekiWiki) as my data sink. There’s also a for-pay version, but I’m using the free/open-source one, which is fine. It’s also installed via a deb repository. I guess others may prefer some other platform, but for me Deki is perfect.
Then, your router set to post its address to DynDNS/No-IP or a similar service, and some CNAMEs in your domain to point to the hostname you have chosen (or simply the address of your VPS). All three services (Mindtouch, Tracks, eGroupware) are powered by Apache2, on virtual servers over HTTPS.
The data is yours!
PS: Special thanks to Yannis for suggesting to use eGroupware instead of SOGo+Funambol. A great improvement, indeed.
PPS: I only accept IaaS to fall under the term “cloud computing”, hence the quotes in the title.
Suspending a Dell 6410 w/ Mint 11RC May 20, 2011
Posted by CK in Software.Tags: Dell Latitude 6410, Linux, Mint, suspend, wpa_supplicant
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If you just installed Linux Mind 11 RC on a Dell Latitude 6410 and, while on wireless, your system crashes when trying to suspend it, try this:
sudo mkdir /var/run/wpa_supplicant
This should fix it.
Blogilo January 15, 2011
Posted by CK in Software.Tags: Blogillo
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BTW, the previous post was the first one I wrote with Blogilo, and I like this tool quite a lot. Simple, and it just works.
Steve, I won January 15, 2011
Posted by CK in Mobility, Productivity, Software.Tags: Citadel, Funambol, Kontact, PIM, Synchronization
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After spending a considerable amount of time (yes, George, I know) looking at my options and trying various ways to synchronize desktop PIM data with my Nokia E71 phone, I eventually managed to make it work. It wasn’t piece of cake, and it requires running on my laptop some additional services, which I would not otherwise run. But it works. The main problem to deal with, is understanding your options. I tried many different setups with various combinations of Kontact / Evolution / Thunderbird+Lightning / Funambol / SOGo / OpenSync / SyncEvolution. Some of them appear to work for some people, but none worked for me in complete. Some that worked partially were
- Evolution + SyncEvolution + Funambol, but unfortunately Evolution was giving me so much pain re: my IMAP severs, that I just couldn’t stay with it;
- Thunderbird + SOGo connector + Funambol, but after creating TODOs and events I could not edit them anymore (this is a known bug, which remains unresolved).
Eventually, what worked for me was a combination of Kontact, Citadel, Groupware Sync server (customized Funambol release) and the Funambol SyncML client on the phone (although Nokia’s native client is used underneath and would apparently work directly if I tried it). This setup works almost out of the box (well that’s sort of a euphemism, admittedly); if you want to reproduce it, here’s how to do it:
First, install Citadel. This acts as a bridge between Kontact and Funambol, using GroupDAV on one side, and a Funambol connector on the other. Kontact is a full GroupDAV implementation, and so is Citadel. The alternative is eGroupware, but Citadel’s being fully open with no "upgraded" versions was the key factor to try it first. I never tried eGroupware eventually. The installation of Citadel (from source, as I could not find a Fedora package) was smooth and just happened. Configuration was, more or less, painless.
Then, I created a new KDE standard calendar resource from within System Settings, using GroupDAV and connecting to the local Citadel server. This bypasses akonadi, which has plenty of problems to solve, and is used immediately within Kontact (KOrganizer). Works like a charm. Following that, there was the biggest challenge: Going through akonadi for contacts. Unfortunately, KAddressbook cannot bypass akonadi; using a GroupDAV-based contact store must necessarily go through it. Until I managed to get it right, I had to fight with data store inconsistencies and delayed synchronization, disappearing contacts, and the like. Eventually it worked, when I created the new akonadi addressbook resource via KAddressbook and, before inserting any contacts, I set (via "Folder properties") an "Interval check time" of 2 min, "Local cache timeout" of 5 min. Apparently the exact values are semi-random and don’t play an important role, but it is (I guess) important to deactivate ""Inherit cache policy from parent". Based on the set up described above, contacts are always synchronized without problems, albeit with a delay of up to 5 minutes.
Having completed all that, it was time to install the Groupware Sync server, which was as easy as it gets. It knows where to find the local Citadel installation, and the built-in users are created automatically based on Citadel accounts. So not much more to do on this side either.
The last step was to install the Funambol SyncML client on the phone, and set it up. After some trial-and-error, I got it working. One of the things I had to do was to change the Funambol server’s port from 8080 to 80. As I am not running any other services on that port, it’s ok for me. I guess that eventually it would also work with 8080, if I would commit some more time to figure out the correct settings on the phone.
To make sure there’s a clean start, I removed all contacts and calendar entries from the phone — they were outdated anyway. The Funambol client has an option to do that very easily. Then I chose to synchronize everything, and, voila! My Kontact addressbook and calendar entries made it on the phone.
While using it I found out that addressbook entries are not synchronized when the default phone of the contact is a cell phone number (apparently a bug, it’s ok if it’s declared as a land line), and also that contact photos are not sync’ed (who cares). Perhaps these would be ok with eGroupware, but I’m not interested to change only because of that. Citadel’s appalling web interface? Yes, that could make me switch.
The result is much more important for me than simply synchronizing my PIM data. It means that, to a large extent, I am now safe from lock-in. I am running my PIM using an open integrated solution (Kontact) on an open desktop (KDE) and an open platform (Linux), so I’m safe enough on this side. Citadel is GPL as well, and Funambol is also open source (not sure about the exact license). All are running on my own infrastructure, and the data remains with me. On the phone side, I can use anything with a SyncML client available — and apparently, there’s one for most of the interesting phones/platforms out there. So I could simply switch to a different phone & OS, without caring too much about PIM synchronization. Which is, honestly, a blessing.
I’d love to hear if this article solved similar problems for you, so just leave a comment if you find it useful!
The story so far November 3, 2010
Posted by CK in IT, Productivity, Software.Tags: Chrome, Crossover, Evolution, Fedora, Firefox, GNOME, KDE, Konqueror, Kontact, Kubuntu, Linux
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So here’s the summary of my linux@laptop adventures so far:
I started with Kubuntu, which as it turned out, after some kernel upgrade would not suspend to RAM/disk correctly. For a laptop, this is a no-go apparently, so after I realized that others also had the problem and that it would not be solved any time soon, I decided to give other distributions a chance.
I tried OpenSUSE, but after installation it wouldn’t even start. Without wasting too much time on this, I moved to Fedora 13; and it worked. It installed without problems, booted without problems, suspended without problems. After upgrading to the latest packages, I faced a common issue with newer Nouveau drivers, which wouldn’t work any more. By then, I had already found out about rpmfusion, which includes Nvidia drivers to install at the click of a mouse. Smooth.
Having solved the basics, I started using the system on a day-to-day basis. I thought I’d give a try to Gnome after a few years of faithfully discarding it, only to realize I was very much correct in doing so. Maybe Ubuntu has done a good job in its customizations, I don’t know, but the vanilla flavour in Fedora is ugly and unintuitive. Whoever disagrees, I would like them to walk into the shoes of a gnome-illiterate user and try to make changes such as setting date format to DD/MM/YYYY (instead of MM/DD/YYYY). I’m not interested in changing the whole system locale for that (and let’s forget about the fact that a linux apprentice knows nothing about locales). KDE, on the other hand, just works, and makes full sense when configuring and using it.
Where Gnome shines, is certain applications such as Evolution. It just rocks, especially when compared with Kmail. With the latter I had plenty of problems while using it with IMAP, but moving to disconnected IMAP was a game changer and Kmail now works quite well. In addition, Kmail failed to notify me while one of my IMAP accounts would not authenticate due to a server-side problem. The result was that for 4 days I would not get email there, thinking I was just not the recipient of any. This could have very bad consequences, for reasons irrelevant with this post. In any case, I would have already switched to Thunderbird or Evolution, but I want to have a desktop-wide addressbook that I can sync with a phone in the future, so I’m giving Kmail some more time and one more chance. In addition, Kontact is really nice in its entirety.
One more thing to mention in the “email” category, is spam detection. The default with Fedora/KDE/Kmail, is using SpamBayes, which would leave quite some spam in my mailbox even after some (admittedly, not too much) training. I then installed/tried SpamAssassin, but integration with Kmail was poor and spam would not be moved out of the mailbox even if marked as such. Eventually I went with Bogofilter and am happy to have done so, it works like a charm and improves a lot with training.
The, browser wars commenced. The default of Konqueror is slow and outdated in comparison to other browsers. I tried switching to the webkit kpart, which improved things a lot but didn’t solve many of the various problems such as random crashes. I really insisted, due to desktop integration, but at some point I just gave up. I made Firefox my default browser, and I’m very happy to have done so. Yesterday, I decided I can’t rely on Konqueror even as a second browser (I always keep 2 around). So for the first time, I decided to give Chrome a chance. So far I was resisting, mostly due to my concerns about Google. I must admit, the thing is *fast*. Although I haven’t switched to it as a main/default browser, I have been tempted to do so. In any case, it now serves as my alternative browser, should I need to test something without cleaning up cookies, or if Firefox does not work properly with some site.
Finally, when it comes to every-day usage, Office applications deserve a mention. Being realistic, I had to be able to run MS Office. I’m not interested in booting up virtual machines for this purpose, so I tried CrossOver for Linux. It works beautifully, and did not have a single problem so far. Well done.
PS: The Ubuntu font is amazing. It is my main desktop font.
Python memory management 101 July 12, 2010
Posted by CK in Software.Tags: Memory management, Python
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>>> a = 1
>>> b = a
>>> b += 1
>>> b
2
>>> a
1
>>>
…but:
>>> a = []
>>> b = a
>>> b.append(1)
>>> b
[1]
>>> a
[1]
>>>
Same for custom classes/objects.
Technically it makes sense, of course, to avoid deep-copying. On the other hand, it may be counter-intuitive in cases like this:
>>> a = 2 * [[]]
>>> a
[[], []]
>>> a[0].append(1)
>>> a
[[1], [1]]
>>>
It took me a minute to recover and realize, that statement a = 2 * [[]] does not create 2 different lists within “a”, but rather 2 references to the same list.
PuLP modeler June 12, 2010
Posted by CK in Research, Software.Tags: CBC, COIN-OR, CPLEX, GLPK, Gurobi, MILP, Optimization, PuLP, Pyomo, Python, SCIP
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I have to solve some optimization models, and looked out there for relevant tools. Solvers is one thing, and there’s a number of options depending on the money you can(not) spend, your requirements, etc. Modelers is another game though, and it took me some time to decipher the various options. What output (i.e. solver input) they can produce, by which solvers this input can be used, if there are converters, etc.
Eventually I went with PuLP, and do not regret it so far. It supports GLPK, COIN-OR, Gurobi and CPLEX. That’s basically all the solvers I wanted to test my models with (except for SCIP, which however I had terrible problems installing and I skipped it).
PuLP installation on the MacOS was as easy as “easy_install pulp”, and then it just worked. From a modeling perspective, I don’t find it to be very intuitive, but it does the work nevertheless, so I can’t complain. The fact that modeling is done in Python code is of course the greatest advantage. As a PuLP rookie, I had the first model ready and running in less than two hours today (including fixing a nasty bug in my code). There’s one more open-source, python-based modeler, Pyomo, but it supports less solvers (although I understand they’re working on it).
Finally, since we’re at the topic of optimization problems and solvers, maybe you’re interested in some recent benchmarks I came across. I was mostly interested in COIN-OR’s CBC, Gurobi and CPLEX, all for (mixed) integer linear problems. You can find them here and here.
Clojure November 6, 2009
Posted by CK in IT, Software.Tags: Clojure, Jython, Languages, Programming, Python, Scala
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Even before I actually study it in detail, Clojure becomes my latest fixation. A Lisp-based functional, general-purpose language, which produces JVM bytecode and has access to Java libraries? Sounds like a dream come true. I never liked Java, and as a matter of fact, I consider myself a Java-dyslexic. No matter how much I tried in the past, I never got around learning enough of it to use further than “Hello, world”s. Its syntactic resemblance to C, with which I am (was?) quite proficient, didn’t help much. Nevertheless, the breadth and depth of libraries that exist in Java are mind-boggling, and the ability to use them with a different language is just great. I know there are other JVM-based languages, e.g. Scala, but somehow after reading introductory material they never enticed me enough. Also, I really don’t know how come, although a big fan of Python I never tried Jython. I assume I just preferred the real thing — Python also has an extensive and compelling set of libraries.
In any case, I’ll try to get a closer look at Clojure and come back with a more complete opinion.
Mendeley 0.9.4 with LaTeX support September 30, 2009
Posted by CK in Productivity, Software.Tags: Bibliography management, BibTeX, LaTeX
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After a long a tiring day, my RSS reader brought me some great news. Mendeley‘s latest release now supports LaTeX. One more interesting new feature: Automatic library backups and easier restoration of backups.
