This works:
(+ 1 2 3)
6
This doesn't work:
(+ '(1 2 3))
This works if 'cl-*' is loaded:
(reduce '+ '(1 2 3))
6
If reduce were always available I could write:
(defun sum (L)
(reduce '+ L))
(sum '(1 2 3))
6
What is the best practice for defining functions such as sum?
If you manipulate lists and write functional code in Emacs, install dash.el library. Then you could use its -sum function:
(-sum '(1 2 3 4 5)) ; => 15
Linearly recursive function (sum L)
;;
;; sum
;;
(defun sum(list)
(if (null list)
0
(+
(first list)
(sum (rest list))
)
)
)
You can define your custom function to calculate the sum of a list passed to it.
(defun sum (lst) (format t "The sum is ~s~%" (write-to-string (apply '+ lst)))
EVAL: (sum '(1 4 6 4))
-> The sum is "15"
This ought to do the trick:
(defun sum-list (list)
(if list
(+ (car list) (sum-list (cdr list)))
0))
Edit: Here is another good link that explains car and cdr - basically they are functions that allow you to grab the first element of a list and retrieve a new list sans the first item.
(insert (number-to-string (apply '+ '(1 2 3))))
(eval (cons '+ '(1 2 3))) -- though not as good as 'reduce'
