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on the issue of the "ATOMness" of hunks

I have a small quarrel with Alan Bawden's statement that "hunks never
being atoms in Maclisp" is a universally-agreed bug.  There are indeed
useful structures that one would like to build in Lisp that act as CONS
cells (i.e., CAR and CDR are applicable), but that can have further
structure.  I have sorely missed such objects in Lisp Machine Lisp and
NIL, where flavor-instances are always atomic, when I wanted to build
Brand X (interned "list structure" and universal property lists).  In
Maclisp, I could do this using hunks, though even that was not
completely right because I wanted to be able to disallow RPLACA and
RPLACD while allowing CAR and CDR, and this was hard, given the hunk
abstraction.  I would, however, love to have non-atomic flavor-instances