pub trait ExecutionStack<BuiltinTok, SeqTok>{
// Required methods
fn push(&mut self, data: RuntimeWord<BuiltinTok, SeqTok>);
fn pop(&mut self) -> Result<RuntimeWord<BuiltinTok, SeqTok>, Error>;
fn last_mut(
&mut self,
) -> Result<&mut RuntimeWord<BuiltinTok, SeqTok>, Error>;
}