[plt-scheme] Adding a list

I'm very new to Scheme and need some help.  I'm trying to write a function
that accepts an accumulating function(summation, product) and a list of
numbers and returns the accumulation of the operation on each element of the
list.  So, if '(1 2 3 4) was supplied to the function and an operation 'sum'
that adds two elements the function would return the sum of the list. 

This is what I have started with and I keep getting an error:

(define (doall fn l)
  (if (null? (cdr l)
          (list (fn(car l)))
          (append (process_all fn(cdr l))(list fn(car l))))))
 
The error is this:

if: bad syntax (has 1 part after keyword) in: (if (null? (cdr l) (list (fn
(car l))) (append (process_all fn (cdr l)) (list fn (car l)))))

I am trying to define the list with this function.  I suppose after I can
get it to work, next I will work on the summation, product function.  First
I need to get this list function to work.  Any ideas?

Trista
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