Sunday, May 13, 2007

Colorless green ideas sleep furiously: Fun with a Ruby ChomskyBot

I recently fell over the concept of a Chomsky bot. A funny little thing which generates random paragraphs of text from a set sentence building blocks. It combines four kinds of phrases (introduction phrases, subject phrases, verb phrases and object phrases) into a sentence. The sentences this simple construction can create are amazing. They are syntactically correct and "hovers on the edge on understandability".

By the way, the title of this post "Colorless green ideas sleep furiously" is a syntactically correct but nonsensical sentence devised by Noam Chomsky. Noam Chomsky pioneered the field of generative grammars. The ChomskyBot implements a simple generative grammar.

The sentences generated by the bot are similar to the language of Noam Chomsky's works, and I guess the pun is intended.

Of course, I couldn't resist the temptation to write a Ruby version of the Chomsky bot:

class ChomskyBot
@@phrase_elems = [ "intro", "subject", "verb", "object" ]

def initialize(intro_file, subject_file, verb_file, object_file)
@@phrase_elems.each do |e|
instance_eval("@#{e}s = []")
instance_eval("{e}_file).each_line" +
"{ |l| @#{e}s.push l.chop }")

def generate_lines(n)
lines = []
n.times do
@@phrase_elems.each do |e|
eval("lines << @#{e}s.slice!(rand(@#{e}s.size-1)) << ' '")

def paragraph

I tried to make it as simple as I could get away with. I shaved quite a few lines using eval, hope it doesn't hurt readability to much.

You'll need some phrase files to play with it. You can find those here:

Introduction phrases
Subject phrases
Verb phrases
Object sentences

You can try the original version of the ChomskyBot online. It's written in Perl (source) by Kevin McGovan. For more information, pay a visit to Chomsky bot inventor John Lawlers website.

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