Common Lisp has succeeded. Since publication of the first edition of this book in 1984, many implementors have used it as a de facto standard for Lisp implementation. As a result, it is now much easier to port large Lisp programs from one implementation to another. Common Lisp has proved to be a useful and stable platform for rapid prototyping and systems delivery in artificial intelligence and other areas. WIth experience gained in using Common Lisp for so many applications, implementors found no shortage of opportunities for innovation. One of the important characteristics of Lisp is its good support for experimental extension of the language; while Common Lisp has been stable, it has not stagnated.

The 1984 definition of Common Lisp was imperfect and incomplete. In some cases this was inadvertent: some odd boundary situation was overlooked and its consequences not specified, or different passages in were conflict, or some property of Lisp was so well-known and traditionally relied upon that I forgot to write it down. In other cases the informal committee that was defining Common Lisp could not settle on a solution, and therefore agreed to leave some important aspect of the language unspecified rather than choose a less than satisfactory definition. An example is error handling; 1984 Common Lisp had plenty of ways to signal errors but no way for a program to trap or process them.

Over the next year I collected reports of errors in the book and gaps in the language. In December 1985, a group of implementors and users met in Boston to discuss the state of Common Lisp. I prepared two lists for this meeting, one of errata and clarifications that I thought would be relatively uncontroversial (boy, was I wrong!) and one of more substantial changes I thought should be considered and perhaps voted upon. Others also brought proposals to discuss. It became clear to everyone that there was now enough interest in Common Lisp, and dependence on its stability, that a more formal mechanism was needed for managing changes to the language.

This realization led to the formation of X3J13, a subcommittee of ANSI committee X3, to produce a formal American National Standard for Common Lisp. That process is nearing completion. X3J13 has completed the bulk of its technical work in rectifying the 1984 definition and codifying extensions to that definition that have received widespread use and approval. A draft standard is now being prepared; it will probably be available in 1990. There will then be a period (required by ANSI) for public review. X3J13 must then consider the comments it receives and respond appropriately. If the comments result in substantial changes to the draft standard, multiple public review periods may be required before the draft can be approved as an American National Standard.

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