Deprecate reduce and accumulate?

[okamsn]

set-accum is the more general version of both. The reduce command has a sligtly different argument order compared to the function anyway.

(accumulate n #'-)
(set-accum (- n loopy-result))

(reduce n #'-)
(set-accum (- loopy-result n))

[okamsn]

To replace reduce, which has a different behavior depending on whether an
initial value is provided, we should add multiple values to set-accum so that
it works more like set.

Currently, we need to do something like this:

;; => 24
;; Note that this example `reduce` doesn't currently work because `loopy-result'
;; is initialized to `nil'.
(loopy (list i '(1 2 3 4))
       (reduce i #'*))

(loopy (list i '(1 2 3 4))
       (set first-time t nil)
       (set-accum (if first-time
                      i
                    (* i loopy-result))))

It would be better if we did something like this:

(loopy (list i '(1 2 3 4))
       (set-accum i (* i loopy-result)))

;; Same as above:
(loopy (list i '(1 2 3 4))
       (set loopy-result i (* i loopy-result))
       (finally-return loopy-result))

[okamsn]

It would be better if we did something like this:

(loopy (list i '(1 2 3 4))
       (set-accum i (* i loopy-result)))

;; Same as above:
(loopy (list i '(1 2 3 4))
       (set loopy-result i (* i loopy-result))
       (finally-return loopy-result))

However, we can't, because it's impossible to distinguish between
(cmd VAR VAL1) and (cmd VAL1 VAL2).