title: Do we have a criterion class or gem in ruby? Could I use RSpec::Matchers?
body: <p>I want to read filters from a yaml file that will reject or accept data. The criteria are something like: greater_than, in_list, smaller_than, not_in_list, etc.</p>
  
  <p>We already have a great set of matchers in RSpec and I was thinking to use those. </p>
  
  <pre><code>require 'rspec/expectations'
  include RSpec::Matchers
  [1].should have(2).entries
    # raises: RSpec::Expectations::ExpectationNotMetError: expected 2 entries, got 1
  [1,3].should have(2).entries
    # returns true
  </code></pre>
  
  <p>I don't like though the fact that every object will have the should method in it and the fact that it's raising exceptions when expectation is not met. </p>
  
  <p>DO you have suggestions of other libraries or classes from other open source projects that can be reused? </p>