.code

emacs keybinding for chrome in gnome

2011-01-31T20:49:00.000+05:30

Type this in the terminal

gconftool-2 --set /desktop/gnome/interface/gtk_key_theme Emacs --type string

and below shortcuts work. Thanks to http://kb.mozillazine.org/Emacs_Keybindings_-_Firefox

Ctrl+A	Go to beginning of line
Ctrl+E	Go to end of line
Ctrl+F	Go right one character
Ctrl+B	Go left one character
Ctrl+P	Go to previous line ("up") (only works in multiline text areas)
Ctrl+N	Go to next line ("down") (only works in multiline text areas)
Ctrl+K	Delete to end of line (if cursor is at the end of the line, deletes the following newline)
Ctrl+U	Delete entire line (different from readline, in which Ctrl+U deletes to the beginning of the line)
Ctrl+W	Delete word, left
Ctrl+H	Delete character, left (backspace)
Ctrl+D	Delete character, right

PDF viewer in Google Chrome

2010-12-04T15:53:00.000+05:30

Google Chrome has enabled PDF rendering in their latest beta. It's fast as expected and the rendering seems good compared to evince. See the screenshots below.

private members

2010-12-01T19:08:00.005+05:30

In languages like java/c# private members of an object are not accessible by objects of other classes. But they are accessible by other objects in the same class.

for e.g.


class A {
  private int secret;

  A(int secret) {
      this.secret = secret;
  }

  void printSecret(A otherObject) {
      Console.WriteLine(otherObject.secret);
  }
}

And then


var x = new A(42);
var y = new A(43);

x.printSecret(y);

You see that x is able to access the secret of y. The protection mechanism in these languages are class oriented and not object oriented.

In JavaScript using functional style classes we get access restriction across objects


function A(secret) {
  var self = {};

  self.printSecret = function(otherObject) {
      //Won't work as secret is a closed variable within A and not part of self
      alert(otherObject.secret);
  };

  return self;
}

var x = A(42);
var y = B(43);
x.printSecret(y); //x cannot access y's secret

disclaimer: expect compiler errors as I am writing this directly into the blog editor.

xmonad

2009-11-03T21:04:00.002+05:30

There were many reasons i switched to emacs. I do hate emacs also, but all those are for another post. One of the reasons i found hooked to emacs was the window management (or panes as you call it in normal world). Many times i wondered how it would be like to have something like that for normal windows.
Enter XMonad. It's an automatic tiling window manager. If you are in an old microsoft windows (i don't have access to a newer one right now), try clicking the taskbar and do tile all windows. If i can remember correctly, all the windows will align itself in the screen so that no screen space is wasted and you can see all of them. XMonad is something like that except whenever you open any window, you automatically tile the window.
This is really cool while working. When working you don't want interference from anything. Usually i'll open my editor (emacs), documentation, browsers etc. XMonad automatically fills all these in my screens so that i don't have to worry about resize/maximize/minimize the windows as you do in an ordinary window manager. I got all the power to view all the window, or view only a window. The keyboard shortcuts to learn are minimal.
Another reason to switch was the second monitor i got. I realized that i was not using the second monitor all the time unlike i should have had. Now i put my emacs in the main screen and all the others in the second.
Try it out. I do use gnome/kde while not working as i'm used to normal window managers

dict bites

2009-07-24T12:56:00.002+05:30

Python dict has a nice method called setdefault which sets a value if key is missing, and finally returns the value for the key


   >>> d = {}
   >>> d.setdefault('x', []).append(42)
   >>> d
   {'x': [42]}

which is almost similar to


   >>> d = {}
   >>> if 'x' not in d:
   ...     d['x'] = []
   >>> d['x'].append(42)
   >>> d
   {'x': [42]}

The setdefault is really handy when you have many nested dicts. But today it bit me. I didn't take into account that parameter you pass to a function will be evaluated first. So that second parameter you pass to setdefault will be evaluated even though the dict already
contains the key. Let me give you an example

Say i have a Value class which maintains no of instances created


   >>> class Value(object):
   ...     count = 0
   ...     def __init__(self):
   ...         Value.count += 1

and i use this in setdefault


   >>> v = Value()
   >>> v
   <Value object at 0x884d56c>
   >>> d = {'x': v}
   >>> d['x']
   <Value object at 0x884d56c>
   >>> d.setdefault('x', Value())
   <Value object at 0x884d56c>

Everything seems fine till now. The setdefault correctly returned existing Value object for the key 'x'. But if you check the no of instances created


   >>> Value.count
   2

So that's right. The second parameter passed to setdefault in the last step got evaluated and it had side effect. It's obvious now but easy to overlook.

Another interesting thing in python is defaultdict. It returns a default value if key is not present. Again there's a catch there that a lookup will actually insert the value.


   >>> from collections import defaultdict
   >>> d = defaultdict(lambda: 42)
   >>> d['x'] = 100
   >>> d
   defaultdict(<function <lambda> at 0xb7dfb8ec>, {'x': 100})
   >>> d['y']
   42
   >>> d
   defaultdict(<function <lambda> at 0xb7dfb8ec>, {'y': 42, 'x': 100})

As you see i did a lookup of 'y' and it correctly returned the default value 42. But it also inserted that in the dict. Easy to miss this side effect.

A new keyboard

2009-07-23T22:18:00.004+05:30

I got myself a Microsoft Ergonomic keyboard 4000 today. Actually my mouse middle button stopped working sometime back, so i thought i'll get a new keyboard as well apart from the mouse. Two main things i don't like about the keyboard are

The 'b' key is on the left. I had learned typing for a month or so during my school days. They taught me to use the right hand for the b key. Now i have to relearn that. I am wondering why they made me use my right hand :?
The space key. It's bad. There's a big friction between the space key and the plastic that surrounds it. I have put some lubricant, but not so much help.

The keys are not so much better compared to my previous one (it cost around 5 times more than a normal keyboard). The leathery arm rest is nice and i hope to get adjusted to this one soon hopefully. The control key is big and will help me in emacs. Interestingly most of the extra keys work right out of the box for ubuntu. The volume keys, search, calc etc works properly. The zoom thing right in the middle of the keyboard doesn't work. I have to checkout keytouch.

A problem statement

2008-06-25T15:34:00.002+05:30

Try to implement this in your language and tell me how it goes.

Problem Statement

There is a class/struct/record Node which is something like

Node {
Node next;
string value;
}

It has a default constructor, so you can call new Node().

Implement a function (or something similar) with which it should be possible to say

safeAssign(node.next.next.next.next.value, "dragon")

and it should create any next objects if not present and finally assign the value to dragon. It should not cause any null pointer exception. You should not modify the Node class.

Introscope

2008-06-10T14:35:00.004+05:30

At work i'm trying to use wily introscope for checking out application performance. As a starting point, i want to know how much time each method takes for a request and also the memory consumption for each request.

My experience with the tool has been really bad so far. All the configurations are done through property files. You need to specify the classes you need to analyze in some property files. Suppose you want to analyze a class and all the subclass of it, well there is no way decent way to do that prior to java 5 (i don't know what they've done with java 5 which makes this possible). As far as i know, they inject their code in the bytecode at interesting points.
I spent some time in figuring out how to analyze all the classes in a particular package and failed. And whereever i read, anything which touches many class files are not recommended by introscope. If i know the classes which are taking time, they why would i need to analyze anyway?

Turned out there was an option to do that. It's something like

SetFlag: X
TurnOn: X
IdentifyMatchingClassesAs: "com.example*" X
TraceAllMethodsIfFlagged: X BlamePointTracer "Perf|{packagename}|{classname}|{method}"

The viewer (which requires a j2ee server of it's own) is so sluggish. I am not sure if it's because of turning on all the classes.

I was able to trace a single soap request. But turns out certain classes are not traced part of the request, and they come as separate trace. Sometime back i read about a single request tracing tool somewhere. They inject some metadata into the request and whereever code is touched, the metadata is transferred. I wonder introscope uses such mechanism?

Today i tried to change the config file and restart the app server. Well, introscope stopped working. A look at log file suggested that the problem was in the line

introscope.autoprobe.directivesFile=perf.pbd, leakhunter.pbd

it failed because of the space after the ',' ! It tried to load ' leakhunter.pbd' and failed. Now i want to know who in the world codes without stripping extraneous spaces in a config file. sigh!

Regarding memory analysis. I was excited to see something called LeakHunter. Well reading at docs suggests that it can only check if any java.util collections classes are growing over a period of time (by checking it's size() method). Nothing good.

I really really hope they still have something good and i'm not wasting my time.

windows console

2008-05-30T11:48:00.005+05:30

One of the major things that's missing in windows is a decent command window. The command interpreter in windows is not as good as bash, but it's decent enough for many things. If you think interpreter is bad, you can use cygwin. And now there is powershell. I am yet to try out powershell (which reminds me of the book i have to read )

The pain is in managing multiple command prompts. In gnome or kde, you can open multiple tabs and navigate easily. When you are working with vim, you would want to code in one tab, execute in another. I used emacs in windows just for this reason. Emacs can have multiple buffers and multiple windows. It has a shell command which emulates the command prompt. But it's not that great and the mysql command prompt don't work over there.
Another pain is the font. For a long time i didn't know that anything existed beyond the default raster fonts. There is an option btw, the Lucida Console font. It will look crappy if you don't enable cleartype. If i get an option, i would love to use consolas.

Well, here comes Console. It has both the features which i longed for. You have configurable keyboard shortcuts, transparancy (if you're into that sort of things), configurable command interpreters. Download the beta and try it out.

books i picked

2008-05-09T19:06:00.003+05:30

I picked up three books today

RESTful Web Services

I've been hearing enough about resource oriented architecture, APP etc. Though i don't plan to publish any web related apis in near future, it would be good to know about this. At work I've been using only SOAP web services and been quite ignorant about everything. Last i tried reading J2EE web services and quit somewhere in between and only to be told by the author that it's complex over engineered thing. Maybe reading this book help me in designing simple web services. I've read some parts of it this afternoon and it looks promising.

Building Scalable Web Sites

This one is by the lead engineer from flickr. Can't wait to read it

Beautiful Code

I've been reading some chapters of this book sometime back. This book didn't get through that much attention i think. (read Bryan Cantrill's entry).
There is a companion website to this book where people discuss beautiful code.

Rounded Corners

2008-05-06T17:22:00.004+05:30

Rounded corners adds nice touch to user interface. Read this macintosh story.

Quoting from the aritcle

Steve suddenly got more intense. "Rectangles with rounded corners are everywhere! Just look around this room!". And sure enough, there were lots of them, like the whiteboard and some of the desks and tables. Then he pointed out the window. "And look outside, there's even more, practically everywhere you look!". He even persuaded Bill to take a quick walk around the block with him, pointing out every rectangle with rounded corners that he could find.

And of course i want rounded corners in my UI. I searched around how to add rounded corners and got lots of way involving css, javascript and images. Most of the ones which i looked involved some complexity be it by wrapping content in four or five divs, adding a javascript library, adding external image etc. I almost decided to create a custom GWT panel by wrapping the techniques used by one of libraries.

Then i thought of seeing how google's UI implemented rounded corners. I fired up my firebug and started searching. It was a little disappointing to see both GMail and Google Reader using background images to rounded corners. Then i looked at Google Mashup Editor and i found some simple CSS properties that they've used.But they looked mozilla specific. So i opened the editor in IE and sure enough, rounded corners are not there. It's interesting that they've decided not to have this style in IE. Maybe mashups are only created by people using firefox :)

I've decided to add the same thing to my UI as it's the simplest of the approaches i've seen. These are the properties

-moz-border-radius-topleft
-moz-border-radius-topright
-moz-border-radius-bottomleft
-moz-border-radius-bottomright

And here is the example. If you are viewing this blog in firefox, you will see this text in rounded corners.

Compiler fix in eclipse

2008-04-29T17:21:00.000+05:30

Eclipse uses its own compiler called ecj. You can download is as a standalone jar file. It is an incremental compiler . I guess they had to write that because at the time sun's javac was a batch compiler. JSR 199 now provides programmatic apis to the compiler, and probably we can build eclipse kindof editors with these apis. I haven't read the apis though.
Anyway, sometime back while i was reading the Java Puzzlers book, while checking out puzzle 37, i found that eclipse compiler didn't work as it was expected. So i filed a bug. You can read the puzzler there. The example is kindof weird and i can't think of a usecase for that right now. The bug is fixed now and i just verified it in the I20080429-0100 build.

GWT updates

2008-04-29T02:11:00.000+05:30

I came home today and started the layout design fresh. I used DockPanel everywhere and used the setCellHeight/setCellWidth api with percentages. To my surprise everything worked as i expected it to be. I was in joy. Sadly it was shortlived one. When i started testing it in firefox, the ScrollPanel no longer scrolled. It increased the page height with the size of the inner contents instead of giving a scroll bar. A little bit searching found that this was a bug (GWT issue 316). I tried modifying different style options in firebug, but was unable to do anything useful. The interesting thing here was it worked in IE as well as in the hosted mode (i think the hosted mode uses some old firefox).
I gave up. I had options to hardcode the size in pixels (that worked, but percentages doesn't) and somehow listen to browser resize events to dynamically modify the size. I guess the mashup editor is doing that.

All is not lost yet!
I remembered that once when i used a SplitPanel, it put a scrollbar inside. Why not use SplitPanel instead of ScrollPanel? And it perfectly suits my needs in this particular UI. I tried it and it works like a charm, even in firefox. So my main layout tools now in GWT are DockPanel and Vertical/Horizontal SplitPanels. I bet there are tons of other glitches as well. Patiently waiting for other surprises.

While compiling from the shell, i got weird OutOfMemoryException in compiler while checking some permutation. Wonder what they are doing to cause this :(

p.s I couldn't find any scroll related panel in dojo.

Layout woes

2008-04-28T15:04:00.000+05:30

I've been trying out GWT for my project from last week. Everything looks wonderful except layout. It doesn't do as what i want. The DockPanel for example doesn't dock things like it ought to do. So i checked the generated html in firebug and found that they actually use tables for panels. Setting the cell's horizontal and vertical alignments helped me most of the times.
Interestingly the UI which i designed first in dojo looks similar to the Google Mashup Editor. I would have given up on GWT if not for the mashup editor. It is written in GWT and works like charm. I love its simplicity. If you have seen some of the dojo examples (the beta bloglines comes to mind), you would appreciate the simplicity of google designers.
So anyway, i am checking out mashup editor through firebug and found one class called gwt-VerticalExpander to be doing what i wants. The only css knowledge i have is from last two days when i tried reading the CSS book (btw i found this book to be much readable from others)
Once all these are resolved, i will try to post the quirks in GWT.

My requirements are - the application should fit the viewport. No hardcoding of pixels (i am ready to use em units at some places). The application UI is very similar to mashup editor, but i would love if the sidebar was a draggable split panel.