Value of SETF

[Fahlman at CMU-20C]

Just for the record, I am also persuaded by Masinter's arguments for
having SETF return the value that it stores, assuming that RPLACA and
RPLACD are the only forms that want to do something else.  It would
cause no particular problems in the Spice implementation to add two new
primitives that are like RPLACA and RPLACD but return the values, and
the additional uniformity would be well worth it.

-- Scott
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