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From: HenHanna <HenHanna@devnull.tb>
Newsgroups: comp.lang.lisp
Subject: Re: Finding Average without using Recusrion only using Prog
Date: Sun, 16 Jun 2024 12:48:24 -0700
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On 6/16/2024 11:28 AM, HenHanna wrote:
> On 6/15/2024 9:39 PM, B. Pym wrote:
>>>      (defun avg (args)
>>>        (loop for x in args
>>>            for l upfrom 1
>>>            summing x into tot
>>>            finally (return (/ tot l))))
>>
>> Gauche Scheme
>>
>> (use gauche.collection) ;; fold2
>>
>> (define (add&count n sum cnt) (values (+ sum n) (+ cnt 1)))
>>
>> (define (avg nums)
>>    (apply /
>>      (values->list
>>        (fold2
>>          add&count
>>          0 0
>>          nums))))
>>
>> (avg '(20 30 40 50 60 70 80))     ===>   50
> 
> 
> Nice...    Here's a more boring version:
> 
> 
> (define (ave x)
>    (let ((L (length x)))
>      (if (> L 0)
>        (/ (fold + 0 x) L))))
> 
> (define (Pave x)   (format #t "~%    ~S  ~S  ~%" x (ave x)))
> 
> (Pave  '(1 2 3))
> (Pave  '(1 2 3 4))
> (Pave  '(1))
> (Pave  '())
> 


(define-macro (ave x)
   `(/ (+ ,@ (map (lambda (n) `(+ ,@ (make-list n 1))) (cadr x)))
       (+ ,@ (map (lambda (n) 1) (cadr x)))))

(print (ave  '(1)))
(print (ave  '(1 2 3)))

gosh> (macroexpand '(ave '(1 2 3)))
          ==>        (/ (+ (+ 1) (+ 1 1) (+ 1 1 1)) (+ 1 1 1))