Here it is in Ruby. LISP_METH = /^c[ad]+r$/ def method_missing(name, *args) meth = name.to_s raise NoMethodError, "undefined method '#{name}'" u

Here it is in Ruby. LISP_METH = /^c[ad]+r$/ def method_missing(name, *args) meth = name.to_s raise NoMethodError, "undefined method '#{name}'" unless meth =~ LISP_METH list = args.first calls = meth.split('')[1..-2].reverse calls.each {|call| list = (call == 'a' ? list.first : list[1..-1]) } list end cadr [1,2,3] # => 2 caaddddr [1,2,3,4,[9,8,7]] # => 9 cadadr [1,[9,[100],8,7],3,4] # => 100