Infocom's games of 1979–88, such as "Zork", were written using a 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 only had to be ported to a computer once, rather than once each 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 the hall". With the Z-machine, Infocom was able to release most of their games for most popular home computers of the time simultaneously, including Apple II family, Atari 800, IBM PC compatibles, Amstrad CPC/PCW (one disc worked on both machines), Commodore 64, Commodore Plus/4, Commodore 128, Kaypro CP/M, Texas Instruments TI-99/4A, the Mac, Atari ST, the Commodore Amiga and the Radio Shack TRS-80. Infocom was also known for shipping creative props, or "feelies" (and even "smellies"), with its games.