Monthly Archives: April 2013

Hedstrom’s Desires-Believes-Acts model in Emacs lisp

Emacs-lisp is a pretty functional language for managing Emacs and automating complex tasks within it, particularly to do with text processing. It’s probably not wise to use it for more general programming or analytical tasks, but every now and then (when I need to procrastinate, mostly) I get carried away.

A few years ago I was reading Peter Hedstrom’s book, Dissecting the Social, and realised his Desires-Believes-Acts model (a kind of cellular automaton) would be easy enough to implement. More recently, I noticed that Emacs’ tools for displaying simple games like Tetris (do “M-x tetris”) would permit a clean display.

In Hedstrom’s model, every cell in a grid may desire an outcome, and may believe they are able to achieve it. If they do both, they act. Belief and desire depend on the beliefs and desires of your neighbours. Generally, even starting from random and low distributions of belief and desire, within a number of iterations stable configurations emerge, with systematic segregation; often everyone acts in the end but sometime stable oscillating systems emerge.

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