REDUCE function re-proposed

[Guy.Steele at CMU-10A]

I would like to mildly re-propose the REDUCE function for Common
LISP, now that adding it would require only one new function, not ten
or fifteen:


REDUCE function sequence &KEY :START :END :FROM-END :INITIAL-VALUE
    The specified subsequence of "sequence" is reduced, using the "function"
    of two arguments.  The reduction is left-associative, unless
    :FROM-END is not false, in which case it is right-associative.
    If the an :INITIAL-VALUE is given, it is logically placed before the
    "sequence" (after it if :FROM-END is true) and included in the
    reduction operation.  If no :INITIAL-VALUE is given, then the "sequence"
    must not be empty.  (An alternative specification: if no :INITIAL-VALUE
    is given, and "sequence" is empty, then "function" is called with
    zero arguments and the result returned.  How about that?  This idea
    courtesy of Dave Touretzky.)

    (REDUCE #'+ '(1 2 3 4)) => 10
    (REDUCE #'- '(1 2 3 4)) => -8
    (REDUCE #'- '(1 2 3 4) :FROM-END T) => -2   ;APL-style
    (REDUCE #'LIST '(1 2 3 4)) => (((1 2) 3) 4)
    (REDUCE #'LIST '(1 2 3 4) :FROM-END T) => (1 (2 (3 4)))
    (REDUCE #'LIST '(1 2 3 4) :INITIAL-VALUE 'FOO) => ((((FOO 1) 2) 3) 4)
    (REDUCE #'LIST '(1 2 3 4) :FROM-END T :INITIAL-VALUE 'FOO)
				 => (1 (2 (3 (4 FOO))))

--Guy