A simple Ragel example for parsing a markdown styled todo list.

lists.txt

## Tasks
- Go to Whole Foods
    - Go to produce section   
        - get oranges
          maybe Mandarine and Valencia
        - get avocados
        - get squash
          maybe buttercup if they have it
    - Go to bakery section
        - get bagels
        - get 12 cupcakes 
    - Go to Dairy
    - get milk
     	  should be organic 2% if they have it
- Pay for items 
   
## Tasks
- Write up a Ragel example for blog
    - Create simple example for parsing lists   
        - Ragel code for a parser
          Should provide support for parsing multiple task lists.
          It should also support hierarchical task lists
    - Create a simple ruby class that uses the parser 
    - post code as gists
    - Write up a blog post describing the use of ragel in the example
- Post to blog

mdlist.rb

require 'rubygems'
require './mdlist_parser.rb' 

class MDList
  
  def initialize(filename) 
      contents = File.open(filename, 'r') { |f| f.read }   
      lexer_lists = MDListParser.new(contents.to_str.gsub('\n',"\n"))
      puts lexer_lists
      lexer_lists.lists.each do |list| 
        	puts "Tasks:"
      		list[:items].each do |item|
      		  puts  "-".rjust(4*item[:level]) + item[:title] + " : (" + item[:level].to_s + ")"
      		  item[:description].split(/\r?\n/).each  do |l| 
      		     puts " ".rjust(4*item[:level]) + l.strip 
      		  end  
      		end 
        end

  end 
   
end
  

mdlist_parser.rl

class MDListParser  

  attr_accessor :lists

	%%{

	  machine test_lexer;

	  action MarkTaskStart { 
	    task_start = fpc  
	    lists_index += 1 
	    @lists[lists_index] = {:items => []}
	    item_index=-1    
	  }

	  action MarkTaskTitleStart { 
	    task_start = fpc  
	  }

	  action MarkTaskDescriptionStart { 
	    task_start = fpc
	    item_index=-1    
	  }

	  action IncrementTaskLevel { 
	    task_level += 1  
	  }

	  action TaskText {     
		if data[p]          
		    item_index += 1
			@lists[lists_index][:items] <<  { :type => task_item_type, :level => task_level, :title => data[task_start...p].pack('c*').strip, :description => ""}         
			task_level = 1
		end
	  } 

	  action TaskDescriptionText {     
		if data[p]          
			@lists[lists_index][:items][item_index][:description] = data[task_start...p].pack('c*').strip           
			task_level = 1
		end
	  }     
  
	  space_or_tab = " " | [\t];
	  indent_or_tab = "    " | [\t];  

	  task_header = "##" space_or_tab* "Tasks" space_or_tab* [\n];               
	  task_char = (digit+ '.' >{task_item_type = :ordered}) | ('-' >{task_item_type = :unordered}); 
	  task_title =  [^\n]+ [\n]; 
	  task_starter = indent_or_tab* @IncrementTaskLevel task_char;  
	  task_description_line =  ([^\n]+ - ^[##]) [\n]; 
	  task_description =  (task_description_line - task_header)+; 
	  #task_description =  (task_description_line)+; 
	  task_item =  task_starter space_or_tab* (task_title >MarkTaskTitleStart  %TaskText) (task_description*  >MarkTaskDescriptionStart %TaskDescriptionText);
	  task = (task_header >MarkTaskStart) . task_item*;      
                  
	  main := |*          
	    task+; 
	   *|;              

	}%%  
               
	def initialize(data) 
	  %% write data;  
	  data = data.unpack("c*") if(data.is_a?(String))
	  eof = data.length
	  @lists = []  
	  token_array = [] 
	  task_item_type = "" 
	  lists_index=-1 
	  task_level = 1
	  fpc = 0
	  fc = ""
	  %% write init;  
	  %% write exec;
	end     
                         
end