teaching machines

CS 330 Lecture 4 – State Machines and Regular Expressions

January 30, 2013 by Chris Johnson. Filed under cs330, lectures, spring 2013.

Agenda

• State machines: states, transitions, accepting states
• A machine to recognize parenthesized words
• A machine to recognize numbers
• A possible implementation
• Regular expressions as state machine encoding
• Not much Ruby
• Composing a string of email addresses
• Removing all HTML
• Instantiating states (geographic ones)

TODO

• If we want more on regex, read pages 257-269 of Read Ruby. (There’s a better site for this book, but it appears to be down.)
• If we want to start assembly, read chapters 1-3 of Programming From the Ground Up, stopping before the Finding a Maximum Value section (page 21 in the letter-size edition.)

Program This

Code

email_list.rb

#!/usr/bin/env ruby

text = IO.read(ARGV[0])
list = ""

text.scan(/[A-Z]{2,}/) do |match|
  list += $& + "@uwec.edu,"
end

puts list

strip_html.rb

#!/usr/bin/env ruby

text = IO.read(ARGV[0])
text = text.gsub(/<.*?>/, '')
puts text

Haiku