I have mostly learnt to avoid this:
* (let ((list-of-items (list 10 9 8 7 6 5 4 3 2 1))) (sort list-of-items #'<) (print (length list-of-items))) 2
SBCL's compiler does warn us:
; caught STYLE-WARNING: ; The return value of STABLE-SORT-LIST should not be discarded.
The new head of the list is in the return value:
* (let ((list-of-items (list 10 9 8 7 6 5 4 3 2 1))) (setf list-of-items (sort list-of-items #'<)) (print (length list-of-items))) 10
What keeps catching me out though is something like this:
(let ((list-of-items (list 10 9 8 7 6 5 4 3 2 1))) (process-list list-of-items) (do-some-more list-of-items))
If I put a sort within the process-list
call, then the original list-of-items
may be
changed. So, copy-seq
is needed when passing lists which we expect to be able to use
later.
(Hence in Rust, you cannot reuse a variable after passing its value to a mut ref
!)