The Magic Trackpad is, sadly, a bluetooth device which means a certain amount of messing around with hidd. The missing link for me was that there needs to be a bluetooth PIN agent running to prompt you for the PIN you want to connect with: hidd --connect won’t do that for you. There are all sorts of gnomic things, but the simplest one is the simple-agent which comes as part of the bluez distro … run this in another terminal, now when hidd tries to connect it’ll contact the simple-agent, you can enter the proper PIN (0000, of course …), and it’ll connect.

Alternatively, the gnome bluetooth applet seems to work, although it has some odd UI bugs. See also this post on broken bluetooth support in ubuntu / bluez 4 which explains where hcid.conf has gone …

It also helps to know that the trackpad is a bit fussy about when it is discoverable … the easiest thing is to hold the button down until the light starts flashing a slowish double-blink, and keep holding it down until the connection is made. Otherwise it seems to time out. If the light goes out instead of starting to flash, you’ve turned the trackpad off instead of on.

Now, that’s enough to get you basic mouse function … move the pointer, button one on tap or click. But that’s not all that useful, especially in X windows.

The file /usr/share/X11/xorg.conf.d/60-magictrackpad.conf (created by package xserver-xorg-input-evdev) overrides the trackpad to use the “evdev” driver. If you don’t already have a custom xorg.conf as in these instructions, the easiest way to override it back again is to create:

/usr/share/X11/xorg.conf.d/99-magictrackpad.conf
Section "InputClass"
Identifier "Magic Trackpad"
MatchUSBID "05ac:030e"
Driver "synaptics"
Option "SHMConfig" "True"
EndSection


Which defines it right back to what you’d like it to be. Apparently many more sophisticated gestures are available with the multitouch driver, but I’m kind of used to synaptics so I’ll stick with it for the moment.

So this is what the input part of the desk looks like right now:

This puts the halves of the kinesis keyboard about the right distance apart for me, and the trackpad is well positioned to get to without much wrist movement. The synaptics driver uses the right hand edge of the trackpad for vertical scrolling … this is particularly easy to do with my right thumb.

photos


device_classes = (FooDevice, BarDevice, BazDevice)

for device_class in device_classes:
device_class.probe()


See? The classes are being treated just like any other variable, because they are, they’re just instances of type ‘classobj’ . But the equivalent doesn’t work in C# — doing this:


Type[] DeviceClasses = {
FooDevice,
BarDevice,
BazDevice
};


… complains that “‘FooDevice’ is a ‘type’ but is used like a ‘variable’”. At first it seemed that C# didn’t have first class classes, and indeed a few web searches came up empty handed.

Thankfully after a bit more exploration it turns out that all that is needed is some syntactic nastiness … namely, typeof(), GetMethod() and Invoke() (Passing “null” to Invoke works for static methods).


Type[] DeviceClasses = {
typeof(FooDevice),
typeof(BarDevice),
typeof(BazDevice)
};

foreach (Type dct in DeviceClasses) {
dct.GetMethod("Probe").Invoke(null, new object[] {} );
}


Now, quite why a shiny new programming language has to get saddled with such godawful syntax is a bit beyond me, but so it goes.

As always, this is lovingly documented in MSDN, in such a way that the answer is clear so long as you already know what you’re looking for.

(As a bonus, yes, you can use reflection to find the list of Devices in the first place. It just wasn’t all that relevant to this example)

I stumbled across this problem because I was reading a protocol document for a device connected by RS-232. The document described what bytes to put in a text file, and how to use Hyperterminal’s “send text file” to send them. That all worked great. But as soon as I tried to get it working in C#, nothing nada zip. Unfortunately, “Line Feed” (ASCII LF, 0x0A) was one of those bytes.

This problem is mostly suffered by people trying to use Hyperterminal to send files to, eg: a microcontroller. But it looks like I’m not the only one to have stumbled upon this one:
“11 0d 0a 44 4d”

The document specifies it, hyperterminal eats it, and when my code actually sent it the device just ignores the whole message … Leave it out and bingo! The message, no longer corrupt, produces a response. What’s really odd is this: the device, when it replies, uses CRLF as its line separator. This raises the horrible suspicion that the alleged developers of this protocol wanted to send CRLF, found themselves stumped by Hyperterminal, and just gave in and changed the implementation instead of changing the protocol or using an non-broken client …

(if only it was a blood-pressure meter, that’d come in handy about now …)

[whatever]
host = whatever.example.com
port = 1433
instance = foo

This isn’t really documented anywhere, and seems very counterintuitive, but if you look in the FreeTDS source, there it is in src/tds/login.c:

if (!IS_TDS50(tds) && !tds_dstr_isempty(&connection->instance_name))
connection->port = tds7_get_instance_port(tds_dstr_cstr(&connection->ip_addr), tds_dstr_cstr(&connection->instance_name));

So now you know. If you don’t specify the instance name, it notices that you’ve specified the port and just goes there directly. Filed it as a bug on FreeTDS, just for fun.


s/fi?b/i/
s/fii(i*)b/f$1bfi$1b/


For those unfamiliar with Perlish regexes: that first one says “replace the string ‘fb’ or ‘fib’ with the string ‘i’”. The second one says “replace a string ‘fiiXb’ with ‘fXbfiXb’, where X is zero or more ‘i’s.”

We can repeatedly apply these rules to a string until the string stops changing. So for example, our string might mutate as follows:

* fiiiiib
* fiiibfiiiib
* fibfiibfiibfiiib
* ifiibfiibfiiib
* ifbfibfbfibfibfiib
* iiiiiifbfib
* iiiiiiii

Expanding the path of fiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiib is left as an exercise to the reader .

What on earth is this all this substituion doing? Well, it is calculating Fibonacci numbers of course!

Regexes don’t handle arithmetic well, so we represent numbers in unary … a string of n ‘i’s represents the number n. When dealing with unary, you can add numbers by simply appending them. ‘f’ and ‘b’ are like parens around the number we’re calculating the Fibonacci number of. So “iiiii” represents the number 5, and “fiiiiib” represents the fifth Fibonacci number.

So the sequence of strings above could also be written:

* fib(5)
* fib(3)+fib(4)
* fib(1)+fib(2)+fib(2)+fib(3)
* 1+fib(0)+fib(1)+fib(0)+fib(1)+fib(1)+fib(2)
* 6+fib(0)+fib(1)
* 8

So really, any language
that allows a sufficiently powerful regex mechanism is able to calculate Fibonacci numbers.

And it is pretty easy to see how to implement a Turing machine by representing each state transition as a regex substitution, so these languages are bound to be Turing complete as well, even if they do turn out to be Turing tarpits.

I’m quite interested in substitution as a kind of pure functional programming. More on that later.

It is called NonTemplate. Let me know what you think!

UPDATE: Some vague performance figures, using the same very simple benchmark as the previous template language performance comparison posts.

These figures are running on Python 2.6.5, on a linux laptop (x64) with output to /dev/null …

print: 1.612
Mako: 1.756
Jinja: 10.803
nontemplate: 18.198
django: 42.212
SimpleTAL: 59.024
genshi: 81.460


… mako is very very clearly the winner here … its code generation is head-and-shoulders above the rest, producing pretty much
exactly the same code as you’d get if you wrote a whole lot of “print” statements yourself. Nontemplate is stuck in the middle … unfortunately, all the ‘with’ shenanigans turns out to be pretty slow. On the other hand, it is still a lot quicker than Django templates, SimpleTAL or Genshi, and a lot smaller than any of them, so I guess it is not all bad news.