Lexeme pollFirst(){
		if(this.size == 1){
			Lexeme first = this.head.lexeme;
			this.head = null;
			this.tail = null;
			this.size--;
			return first;
		}else if(this.size > 1){
			Lexeme first = this.head.lexeme;
			this.head = this.head.next;
			this.size --;
			return first;
		}else{
			return null;
		}
	}