From Newsgroup: comp.lang.lisp

B. Pym wrote:

Kenny Tilton wrote:

What if the sequence is empty?

(defun average (sequence)
(let ((len 0)
(sum 0))
(map nil #'(lambda (elt)
(incf len)
(incf sum elt))
sequence)
(if (zerop len)
0
(/ sum len))))

(defun average (sequence &key (key #'identity) &aux (len 1))
(/ (reduce (lambda (x y)
(incf len)
(+ x y))
sequence :key key :initial-value 0)
len))

Testing:

* (average '(2 3 4))

9/4

Incorrect.

Gauche Scheme

(define (average seq)
(let1 len 0
(if (null? seq)
0
(/ (fold (lambda (x sum) (inc! len) (+ x sum))
0
seq)
len))))

(defun average (seq)
(if seq
(do ((sum 0 (+ sum (pop seq)))
(i 0 (+ 1 i)))
((not seq) (/ sum i)))
0))

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