[clisp-list] question about creating a first-class function

[david <dav...@ac...>]

I created this function using recursion:

(defun sigma-sum (lower upper step)
  "Sum numbers from lower to upper 
incrementing the lower by step"
  (cond ( (> lower upper) 0)
 (t (+ lower 
       (sigma-sum 
        (+ step lower) 
        upper step)))))
 
it works fine, but I am trying to create a function that can be used for any
problem expressed in sigma notation. Here is that attempt:
(defun sigma (opr lower upper step)
  "Operate on numbers using process defined
by sigma notation."
  (cond ( (> lower upper) 0)
 (t ((apply opr lower 
        (sigma 
         (apply opr step lower) 
         upper step))))))

and here is how I call the function:
(sigma '+ 1 4 1)
 
but it does not work. Any advice?