require 'facets/functor'

module Kernel

  # Yield self -or- return self.
  #
  #   "a".ergo.upcase #=> "A"
  #   nil.ergo.foobar #=> nil
  #
  #   "a".ergo{ |o| o.upcase } #=> "A"
  #   nil.ergo{ |o| o.foobar } #=> nil
  #
  # This is like #tap, but tap yields self -and- returns self.
  #
  #   CREDIT: Daniel DeLorme

  def ergo &b
    if block_given?
      b.arity == 1 ? yield(self) : instance_eval(&b)
    else
      self
    end
  end

end

class NilClass

  # Compliments Kernel#ergo.
  #
  #   "a".ergo{ |o| o.upcase } #=> "A"
  #   nil.ergo{ |o| o.bar } #=> nil
  #
  #   CREDIT: Daniel DeLorme

  def ergo
    @_ergo ||= Functor.new{ nil }
    @_ergo unless block_given?
  end
end