collections define: #Stack &parents: {ExtensibleArray}.
"An abstraction over ExtensibleArray implementations to follow the stack
protocol. The convention is that the Sequence indices run least-to-greatest
from bottom to top."

s@(Stack traits) push: obj
[s addLast: obj].

s@(Stack traits) pop
[s removeLast].

s@(Stack traits) pop: n
[s removeLast: n].

s@(Stack traits) top
[s last].

s@(Stack traits) top: n
[s last: n].

s@(Stack traits) bottom
[s first].