Whenever you run a Ruby program, Ruby’s parser processes the code and turns it into an “abstract syntax tree” (an AST) which can then be either turned into bytecode for YARV (on Ruby 1.9) or be interpreted immediately (as with Ruby 1.8).

While a programming language allows programmers to represent the logic of a program in a way that’s both suitable for developers and computers to easily understand, abstract syntax trees act as a low-level tree representation of the program’s mechanics. Given that ASTs are typically simple data structures, it’s possible to use them to convert one language to another, to semantically analyze what a program is going to do, to detect repetition, or to optimize how the final program will run. Read More

HappyMapper is John Nunemaker’s attempt at “making XML fun again” for Rubyists by providing an object to XML mapping library with a succinct syntax. Essentially, you can use HappyMapper to rapidly turn XML into Ruby objects – even nesting them inside and referring to each other. This is powerful stuff. To install, just gem install happymapper

John’s own examples are powerful demonstrations of how it works, so check them out. The first is parsing the XML returned from Twitter. The statues and associated users in that XML can be processed (with the relationship maintained) with the following code:

class User
include HappyMapper

element :id, Integer
element :name, String
element :screen_name, String
element :location, String
element :description, String
element :profile_image_url, String
element :url, String
element :protected, Boolean
element :followers_count, Integer
end

class Status
include HappyMapper

element :id, Integer
element :text, String
element :created_at, Time
element :source, String
element :truncated, Boolean
element :in_reply_to_status_id, Integer
element :in_reply_to_user_id, Integer
element :favorited, Boolean
has_one :user, User
end

statuses = Status.parse(xml_string)
statuses.each do |status|
puts status.user.name, status.user.screen_name, status.text, status.source, ”
end

Added: Or.. Read More