That's the sentence terminator. No ;, no braces. The parser needs the dot to know you're done. Miss it and you get expected '.'.
list with 0 for a number?Inside a define, set x to 3 is local. To keep a number across calls, store it as list with 3 and mutate via x[0] or add_to. See spec §5.
with then?Zero-arg calls still need with: foo with. and define f with as. Also check you didn't use is greater than or equal to — use >=.
ketiwe needs X11 (:0). On a server use Xvfb :99 & and DISPLAY=:99 sb file.sb.
sb build file.sb makes a native binary, sb pack deb makes a .deb. Std is bundled.