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Date: Fri, 13 May 88 01:56:30 PDT
From: Jon L White <firstname.lastname@example.org>
In a more general sense, a user would want to be able to tell the
compiler that a certain named function has no internal state and that:
(1) it has no side effects, and
(2) its value is completely determined by its arguments.
Thus RANDOM is not side-effect-free, since it updates *random-state*; and
while FIND-SYMBOL is side-effect-free, it is not stateless since it is
sensitive to the setting of the global variable *package* as well as to
the entries in the package database. AREF is both side-effect-free and
Be careful here. Lisp has various ideas of equality, so whether a
"value is completely determined by its arguments" has to be qualified
by the type of equality you are talking about. For example
(eq (aref some-array 3)
(progn (some-function some-array)
(aref some-array 3)))
is NOT guaranteed to return T, even though AREF is being given EQL
arguments in both cases.
I think you partially addressed this in the later portion of your
message, but I was uncomfortable with this AREF example you gave.