[wplug] [wplug-announce] Popular Demand: Regular Expressions Sat 6/11/2005 10am-2pm CMU NSH

James O'Kane jo2y at midnightlinux.com
Thu Jun 9 23:41:48 EDT 2005


On Thu, 9 Jun 2005, Rob Prowel wrote:

>> Popular Demand Meeting
>> featuring Regular Expressions.
>
> interesting...is there an irregular expression?

No, the regular in that phrase is a linguistics term, there's a whole set 
of features and algrebra that can be used to decide if a language is 
regular, one of which is it can be accepted [generated/matched] by a 
deterministic finite state machine. It's probably not interesting to most 
users, so I'll just link to something: 
http://en.wikipedia.org/wiki/Regular_languages

Chomsky, a linguist, defined 4 different types of languages or grammars. 
Recursive, Context-sensitive, Context-free and Regular. Two of them turned 
out to be good for linguistist to play with, and the other two were good 
for Computer Scientists. I think there's some overlap and not a strict 
division, so I'm not going to say which are which, since I can't find my 
text book on this.
Again, from memory, some example languages:
Recurisve: Haskell
Context-senstive: English
Context-free: C, C++, Java
Regular: Regular Expressions

As you can see, REs are a language in and of themselves. But since that 
type is the more restrictive of the group, it's easy to pick up once you 
start learning some of the basic symbols (.?+) and rules (greediness).

-james



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