Checking that Ragel matched the entire input

Question

Are there better ways to require that Ragel consume all of the input? Here is what I'm using now:

=begin
%%{
  machine my_lexer;
  # ...
  # extract tokens and store into `tokens`
  # ...
}%%
=end

class MyLexer

  %% write data;

  def self.run(string)
    data = string.unpack("c*")
    eof = data.length
    tokens = []
    %% write init;
    %% write exec;
    data.length == p ? tokens : nil
  end

end

Most of the above is boilerplate, except for the data.length == p test. It works -- except that it doesn't verify that the lexer ended in a final state. So, I have test cases that give me tokens back even if the entire input was not successfully parsed.

Is there a better way?

(Testing for the final state directly might work better. I'm looking into how to do that. Ideas?)

Answer 1

I'm only starting out with ragel, but it's possible you want to look at EOF actions or Error actions, executed respectively when the input ends or when the next character satisfies no transition from the current state.

Answer 2

You can handle errors using either global or local error actions.

For global error actions you can use this syntax:

$!action

For local error actions, which are local to your machine definition, you can use this syntax:

$^action

If you put a flag on your action, you can check the flag to detect an error.