I love Emacs GDB mode, but I always found it annoying that there is no given key binding (or function which could be directly mapped into a key binding) for switching between the different views given by gdb-many-windows. The usual window and buffer switching functions are insufficient because the GDB windows are flagged as dedicated (so switch-buffer refuses to swap them in place), and in the case of the Locals/Registers and Breakpoints/Threads windows, the buffer you want to visit doesn’t necessarily even exist until you click that button.

This went from mildly annoying to a major headache when I needed to run the debugger in a remote Emacs session, over SSH from Mac OS X’s Terminal.app which does not support xterm mouse emulation. So I wrote this gdb-select-window function and corresponding key bindings to finally get the desired behavior…

;; For the consistency of gdb-select-window's calling convention...
(defun gdb-comint-buffer-name ()
  (buffer-name gud-comint-buffer))
(defun gdb-source-buffer-name ()
  (buffer-name (window-buffer gdb-source-window)))

(defun gdb-select-window (header)
  "Switch directly to the specified GDB window.
Moves the cursor to the requested window, switching between
`gdb-many-windows' \"tabs\" if necessary in order to get there.

Recognized window header names are: 'comint, 'locals, 'registers,
'stack, 'breakpoints, 'threads …

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Additional discussion: Hacker News, Reddit

I ran into a really fun bug at work yesterday, where I discovered that my C program was branching down logically inconsistent code paths. After drinking another cup of coffee and firing up GDB I realized that somehow, a boolean variable in my code was simultaneously testing as both true and not true.

While I cannot reproduce the actual source code here, the effect was that code like

bool p;

/* ... */

if ( p )
    puts("p is true");

if ( ! p )
    puts("p is false");

would produce the output:

p is true
p is false

So what’s going on here?

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Additional discussion: Hacker News

I’ve been getting back into Python lately… I just wrote a small module that provides support for pointfree style programming with a combination of automatic partial function/method application and operator overloading for function composition:

from pointfree import *
from operator import add

fn = pfmap(len) \
  >> pfmap(lambda n: n**2) \
  >> pfreduce(add, initial=0)

fn(["foo", "barr", "bazzz"]) # == 50

See the overview for a lengthier introduction. You can install the pointfree module from the Python Package Index:

$ pip install pointfree

Links:

• Module documentation
• Github project page
• Python Package Index page

I just found a great blog post by Martin Kleppmann titled Accounting for Computer Scientists, a succinct introduction to double-entry accounting (although he doesn’t refer to it as such) in terms of basic graph theory:

Eventually I figured it out: basic accounting is just graph theory. The traditional ways of representing financial information hide that structure astonishingly well, but once I had figured out that it was just a graph, it suddenly all made sense.

He goes on to illustrate how a profit-and-loss statement and a balance sheet can be visualized on a simple DAG.  Good stuff…

I’ve been using OpenBSD as a NAT router for a few years now. Here’s a guide showing how I got it up and running, in case anyone is interested in doing the same.

I’ve been banging my head against the wall on account of different music players which can’t play the subset of songs I have encoded as either Vorbis or AAC. So I’m slowly converting my entire music library over to MP3, which works everywhere, even if it’s less efficient.

But before I go digging through my old CDs I need to identify which albums I have to re-encode. My music is organized in folders by artist and then album, e.g.:

~\Music\Library\Pixies\Surfer Rosa\Where Is My Mind.mp3

So this means I effectively have to list the names of folders containing non-MP3 music files. Fortunately Windows PowerShell makes this a one-liner (though admittedly it’s a pretty long line; the backtick is PowerShell’s line continuation syntax):

ls -r Music\Library `
| ?{ $_.PSIsContainer -And ( $_.GetFiles() `
| ?{ $_.Name -Match "\.(m4[ap]|ogg|wma)$" } ) } `
| %{ New-Object PSObject -Property `
@{ Artist = (gi $_.PSParentPath).Name; Album = $_.Name } }

This will give you a nice list of non-MP3 albums, like:

Album              Artist
-----              ------
That's Your Fire   Aloha
Noble Beast        Andrew Bird
Believe It Mammals Bats & Mice
Charm School       Bishop Allen
[...]

And thanks to PowerShell’s object-oriented pipes, this …

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