Infocom games were written using a roughly LISP-like programming language called "ZIL" (Zork Implementation Language or Zork Interactive Language—it was referred to as both) that compiled into a byte code able to run on a standardized virtual machine called the Z-machine. As the games were text based and used variants of the same Z-machine interpreter, the interpreter had to be ported to new computer architectures only once per architecture, rather than once per game. Each game file included a sophisticated parser which allowed the user to type complex instructions to the game. Unlike earlier works of interactive fiction which only understood commands of the form 'verb noun', Infocom's parser could understand a wider variety of sentences. For instance one might type "open the large door, then go west", or "go to festeron".