# File lib/rack/builder.rb, line 70
70:     def to_app
71:       @ins[-1] = Rack::URLMap.new(@ins.last)  if Hash === @ins.last
72:       inner_app = @ins.last
73:       @ins[0...-1].reverse.inject(inner_app) { |a, e| e.call(a) }
74:     end