webapp.rb

require 'rubygems'
require 'rack'

class Object
    def webapp
        class << self
            define_method :call do |env|
                func, *attrs = env['PATH_INFO'].split('/').reject(&:empty?)
                if !func.nil? &&
                   !func.empty? &&
                   !Kernel.methods.include?(func.to_sym) &&
                   self.class.instance_methods.include?(func.to_sym) then
                    [200, {}, send(func, *attrs)]
                else
                    [404, {}, "Not Found"]
                end
            end
        end

        self
    end
end

Rack::Handler::Mongrel.run [].webapp, :Port => 9292

# http://localhost:9292/push/1  -> 1
# http://localhost:9292/push/2  -> 12
# http://localhost:9292/push/3  -> 123

# http://localhost:9292/to_a    -> 123

# http://localhost:9292/pop     -> 3
# http://localhost:9292/shift   -> 1