An imperative-style function that flattens a list of integers and adds all of them.
val flatsumimp(xs) =
let val ys = new() in
let val s = new() in
ys := xs;
s := 0;
while !ys <> nil do (
if integer(head(!ys))
then (
s := !s + head(!ys);
ys := tail(!ys)
)
else ys := append(head(!ys), tail(!ys))
);
!s;;