Motivation for PARSE-BODY

[Guy Steele <gls@Think.COM>]

Some of us, at least, use Lisp for the inventing of new embedded languages, and
one of the great things about Lisp is that is lets you get at various tools that
are used within the Lisp implementation itself (or were, at a time when a
particular paradigm was standard).  Examples of these are READ, PRINT, PROGV,
ASSOC, and PAIRLIS.  (You might not think of READ and PRINT as peculiarly part
of the interpreter, but consider how many language implementations have a very
complicated routine for reading and parsing programs but don't let the user get
at it?  Consider APL, for example, whose program editor is not invocable by user
programs.)

If I want to invent my own interpreter (and I often do), having PARSE-BODY around
would be very convenient.
--Guy