Prevent Ragel from calling actions multiple times while matching the same string

Question

I have this parser:

class Parser
  %%{
    machine test_lexer;

    action s { s = p; puts "s#{p}" }
    action e { e = p; puts "e#{p}" }
    action captured {
      puts "captured #{s} #{e}"
    }
    key_value = "a" %s ("b" | "x" "c")+ %e %captured;
    tags = ("x"+)? key_value;

    main := tags*;
  }%%

  def initialize(data)
    data = data
    eof = data.length
    %% write data;
    %% write init;
    %% write exec;
  end
end


Parser.new(ARGV.first)

And I hit it with abxc then why does it call the captured twice / the e twice, and how can I prevent this ?

ragel -R simple.rl && ruby simple.rb "abxc"
s1
e2
captured 1 2
e4
captured 1 4

on github: https://github.com/grosser/ragel_example

Answer 1

Here is the diagram for your machine, BTW: http://bit.do/stackoverflow-19621544 (created with Erdos).

With "abxc" the ("b" | "x" "c")+ machine first matches the "b" and then the "xc". When transitioning from "b" (to "x") it calls the leaving actions (e and captured) for the first time, and when transitioning from "xc" (to EOF) it calls the leaving actions (e and captured) for the second time.

I guess the e action is supposed to set the end pointer in order to capture the string between start s and end e. If so, then Ragel calling the e action multiple times isn't really a problem, you just advance the end pointer like you already do.