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    Date: 19 Sep 1983 0331-PDT
    From: Dave Dyer       <DDYER@USC-ISIB.ARPA>
     There should be only ONE implementation of the mapping functions,
    written in unambiguous primitives, shared by all common lisp
    implementations.  Likewise for the largest possible subset of
    the core language.  This is the best way to make sure that
    the zillion+1 small implementation choices one has to make,
    even working from the tightest specification, are made the same 
    way by all the implementations.
I disagree with this view fairly strongly.  Different implementations
have different instruction sets and primitives, and what appears to
be an optimal macro expansion for one implementation is often not so
for another.  It is best to specify the contracts of one of these goddamn
things by documentation, driven from need of what problem the function
or form at hand was supposed to solve, not by code that nails its implementation
so that you can find delightful and challenging ways to undercut
its intended purpose.