filter.rb

class Filter
  class << self
    def filters
      @filters ||= {}
    end

    def add(name, &code)
      filters[name] = code
    end
  end

  def initialize(obj)
    @methods = []
    @obj = obj
  end

  def |(method)
    @methods << method
    self
  end

  def run
    @methods.inject(@obj) do |mem, method|
      if method.is_a?(Array)
        method, *args = method
      else
        args = []
      end
      
      if custom = Filter.filters[method]
        custom.call(mem, *args)
      else
        mem.send method, *args
      end
    end
  end

  def to_s
    run.to_s
  end
end

module CoreExt
  [Fixnum, Float, String].each do |klass|
    refine klass do
      def |(other)
        return super unless other.is_a?(Symbol) || (other.is_a?(Array) && other[0].is_a?(Symbol))
        Filter.new(self) | other
      end
    end
  end
end

filter_usage.rb

require './filter'
using CoreExt

puts 'hello' | :upcase
# >> HELLO

puts 123 | :next
# >> 124

puts 'Mississippi' | :upcase | :squeeze | :chars | :reverse
# >> ["I", "P", "I", "S", "I", "S", "I", "M"]

puts 123 | :next | :even?
# >> true

Filter.add :currency do |int, sign = "$"|
  raise ArgumentError unless int.is_a?(Numeric)
  "#{sign}%.2f" % int
end

puts 123.45 * 3 | :currency
# >> $370.35

puts 123.45 | [:*, 3] | [:currency, "￡"]
# >> ￡370.35

Filter.add :titleize do |str|
  str.scan(/\w+/).map(&:capitalize)*' '
end

puts 'ruby on rails' | :titleize
# >> Ruby On Rails