From: "Einar Magnús Boson" <einarmagnus@...>
Date: 2008-11-20T00:19:44+09:00
Subject: Qs on RegExps

Now that we are on the topic of Regular Expressions I have a question  
about the ruby implementation. Like I posted earlier I needed to parse  
something that looks like this:

- activity
     + name		
     + picture	

- area
     + name
     + picture

- activities_in_area
     + activity_id
     + area_id	

etc...


Last time I did complicated regexps seems to have been C# or possibly  
java. So I tried to match the whole thing with
	/(\- (\w*)\s*?\n([\t ]+\+ (\w+)\s*(\:\s*(\w*))?\s*?\n)+\s*)+/
and then I was gonna extract the captured data but it isn't available.  
All nested groups have only captured their latest match. Is there no  
regexp lib for ruby that can handle nested groups and save the  
captures? I solved it with nested scans instead and I have to admin  
that it is more readable, so I'm not sure what, exactly, I want with  
this message, except ask about the design choices involved. Why don't  
we want proper captures?

		table_name = /\- (\w*)\s*?\n/
		field_name = /(\s+\+ (\w+)\s*(\:\s*(\w*))?\n)/
		doc.scan /#{table_name}(#{field_name}+)/ do |tablename, fields|
			fields.scan field_name do |junk, fieldname, junk2, type|
				# here I can do what I want
			end
		end


And on the topic of pattern matching, can you recommend any good  
library for parser generation in ruby? I want to write a grammar and  
get an AST.

einarmagnus