A basic 4 operator LISP implemented in ruby.

lispo.rb

module LISPO
  module ArrayCallable
    refine Array do
      def call
        inject &shift
      end
    end
  end

  class Parser
    def self.call(string)
      string.gsub! '(', '[:'
      string.gsub! ' ', ', '
      string.gsub! ')', '].call'
    end
  end

  module VM
    using ArrayCallable
    def self.call(string)
      module_eval Parser.call(string)
    end
  end
end

puts LISPO::VM.call <<-LISP
(+ 1 2 (* 2 9) 4 6 7)
LISP