pub fn duplicate_top(&mut self) {
        let value = self.pop();
        self.push(value);
        self.push(value);
    }
// duplicate_top takes the top most item on the stack (or 0) or pushes it on the stack
duplicate_top takes the top most item on the stack (or 0) or pushes it on the stack
duplicate_top takes the top most item on the stack ( or 0 ) or pushes it on the stack
pub fn duplicate_top(&mut self) {
        let value = self.pop();
        self.push(value);
        self.push(value);
    }
pub fn duplicate_top ( & mut self ) { let value = self . pop ( ) ; self . push ( value ) ; self . push ( value ) ; }
duplicate_top takes the top most item on the stack (or 0) or pushes it on the stack
duplicate_top takes the top most item on the stack ( or 0 ) or pushes it on the stack
&mut self
&mut self