How do I do this?

magical_mr_mistoffelees.rb

# Premise: a chainable DSL where evaluating a section in an if statement calls valid? 
# Example: Each item changes the current synonym, it tests it against 

class Moggy
  SYNONYMS = [:cat, :moggy, :pussycat, :feline]
  def set(syn)
    @synonym = syn
    self
  end

  def valid?
    SYNONYMS.include? @synonym
  end
end

m = Moggy.new
m.set(:pussycat).set(:dog).valid? #=> false

if(m)
  raise "Fail" # is there any way of preventing this result?
else
  "Correct!"
end
  

In case you were expecting a real-world example, I would like to be able to do this

foo.matches?(/some regex/).and_also(:foo => /bar/).exactly(1).times #=> true
foo.matches?(/some regex/).and_also(:foo => /bar/) #=> Want this to evaluate to true in an if statement