push(x)=v=concat(v,[x]);;
pop()={
  if(#v,
    my(x=v[#v]);
    v=vecextract(v,1<<(#v-1)-1);
    x
  ,
    error("Stack underflow")
  )
};
empty()=v==[];
peek()={
  if(#v,
    v[#v]
  ,
    error("Stack underflow")
  )
};