こういうふうに文字列チェックしたい

moji_chekku_suru.rb

module Nyan

  class BaseValidator

    def initialize(*values)
      @values = values
      @result = false
      @or = false
      @not = false
    end

    def and
      @or = false
      self
    end

    def or
      @or = true
      self
    end

    def not
      @not = true
      self
    end

    def to_b
      !! @result
    end

    def method_missing(method, *args)
      super unless /\?$/ =~ method.to_s

      _method = method.to_s.sub(/\?$/, '').to_sym

      if self.respond_to? _method
        self.send(_method, *args).to_b
      else
        super
      end
    end

    class << self
      alias_method :is, :new
      alias_method :does, :new
      alias_method :are, :new
      alias_method :do, :new
    end

    protected

    def evaluate
      return self if @or && @result || !@or && !@result

      @result = @values.all? do |value|
        (yield value) ^ @not
      end

      @or = false
      @not = false

      self
    end
  end

  class StringValidator < BaseValidator

    def initialize(*values)
      super
      @is_string = values.all? {|value| value.is_a? String}
      @result = @is_string
    end

    def match(regexp)
      evaluate {|value| (regexp =~ value) != nil}
    end

    def integer
      match /^(?:-|\+)?[0-9]*$/
    end

    def float
      match /^(?:-|\+)?[0-9]+\.[0-9]+$/
    end

    def yes
      match /^(?:1|true|TRUE|True|T|t|yes|YES|Yes|Y|y)$/
    end

    protected

    def evaluate
      return self if !@is_string
      super
    end
  end

  module Validator
    def is(*values)
      values = values.length == 0 ? [self] : values
      StringValidator.new(*values)
    end

    alias_method :does, :is
    alias_method :are, :is
    alias_method :do, :is
  end

end

moji_chekku_suru_example.rb

include Nyan::Validator

p is('nyan').not.yes? # => true
p is('y').not.yes? # => false
p is('999').integer? # => true
p does('nya', 'nyannya').match(/nyan/).and.match?(/nya$/) # => false
p does('nya', 'nyannya').match(/^nya/).and.match?(/nya$/) # => true

class String
  include Nyan::Validator
end

p 'nyan'.is.yes? # => false
p 'y'.is.yes? # => true
p 'opopo'.is.not.integer? # => true
p '12345'.is.integer? # => true