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The above examples can thus be written in terms of foldr, by simply supplying the appropriate accumulator generating function and the accumulator base value:

(define (sum lon)
    (foldr + 0 lon))

(define (get_largest_pos lon)
   (foldr (lambda (x rr)
              (if (> x rr) x rr))
          0
          lon))  

 "Forward Accumulation"

A general mantra that we have about moving data during an algorithm's execution is to say that we are "moving data from where it is, to where it can be processed".   

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All the "outer" function, "sum_fwd", does is to set up the initial value of the accumulator.  It is is not a recursive function.   Only the helper is recursive.

We can write a template for forward accumulation, once again based on the template for a list-of-any:

(define (f_fwd loa)
    (cond
        [(empty? loa) base]
        [(cons? loa)
            (local
                 [(define (helper acc loa)
                      (cond
                          [(empty? loa) acc]
                          [(cons? loa) (helper (... (first loa)...acc...) (rest loa))]))]
                 (helper (...first...) (rest loa)))]))