append - what is the 'cons' to add an item to the end of the list?

Question

what's the typical way to add an item to the end of the list?

I have a list (1 2 3) and want to add 4 to it (where 4 is the result of an evaluation (+ 2 2))

(setf nlist '(1 2 3))  
(append nlist (+ 2 2))  

This says that append expects a list, not a number. How would I accomplish this?

Answer 1

You could use append, but beware that it can lead to bad performance if used in a loop or on very long lists.

(append '(1 2 3) (list (+ 2 2)))

If performance is important, the usual idiom is building lists by prepending (using cons), then reverse (or nreverse).