variable vs. identifier

[Jonathan A Rees <JAR@AI.AI.MIT.EDU>]

>From the messages I've recieved, it apparently wasn't clear why two
distinct words are needed.  I want to make sure that the grammar
reflects the decision that we will leave it up to implementations
(i.e.  leave it "unspecified") just what things like (let ((if ...))
...)  would mean.  So at the very least these expressions have to be
excluded from the grammar.  Therefore one word is needed for things
that are lexically like symbols (and can appear inside of QUOTE
expressions), and another is needed for those things that can be bound
and referred to.  I chose "identifier" for the first and "variable"
for the second.  Thus IF is an identifier but not a variable.  I like
the way this turned out, and can't think of anything else that would
work as well.