Rust language:

fill in the code:

// Fill in the enum with variants that represent the following / symbols: '+', '-', *1 # [derive (Debug) ] enum Token t // Add two fields to the following struct. One for holding // a vector of characters, and another that is an index (usize) //into the vector # [derive (Debug) ] struct Scanner [ // Implement the following methods for the Scanner struct: // (1) A "new" method that creates a scanner from a String /7 (2) A "get_next_token" method that returns an Option representing the next symbol in the vector (or None when appropriate). impl Scanner // The main function should do the following: // (1) Read the contents of a file into a String. The name of the file is given as a program argument // (2) Create a scanner object with the String / (3) Use a "while let" loop to print all Tokens found in the String fn main)