Metacircular semantics for common Lisp special forms

McCarthy's metacircular interpreter for Lisp has been criticized by Reynolds and others for not providing precise semantics. Unfortunately, the alternative of English prose currently favored by the ANSI X3J13 and ISO committees for the definition of Common Lisp is even less precise than a metacircular interpreter. Thus, while a system of denotational semantics á la Scheme or ML could be developed for Common Lisp, we believe that a carefully fashioned system of metacircular definitions can achieve most of the precision of denotational semantics. Furthermore, a metacircular definition is also more readable and understandable by the average Common Lisp programmer, since it is written in terms he mostly understands. Finally, a metacircular definition for Common Lisp special forms enables us to transparently customize the representation of certain "built-in" mechanisms such as function closures, to enable sophisticated systems like "Portable Common Loops" to become truly portable.