In C#, implement the Recursive Descent Parser (RDP) for the Grammar

Details:

1. Create a class called Lexer that takes an input expression as a string and outputs its token stream.

2. The Lexer needs to catch any unidentified characters that don't belong to the grammar.

3. The RCP should then proceed to parse the input expression.

4. Please provide comments to explain what you have done with each line of code, and how the code compiles.

The output should appear as shown below.

Enter your expression:

num1 + num2 / (7 + total)

-----------------------------------

Calling Lexer:

num1: IDENT

+: ADD_OP

num2: IDENT

/: DIV_OP

(: LEFT_PAREN

7: INT_LIT

+: ADD_OP

total: IDENT

): RIGHT_PAREN

----------------------------------

Calling the Recursive Descent Parser:

NextToken: IDENT

Enter

Enter

Enter

NextToken: ADD_OP

Exit

Exit

NextToken: IDENT

Enter

Enter

NextToken: DIV_OP

Exit

NextToken: LEFT_PAREN

Enter

NextToken: INT_LIT

Enter

Enter

Enter

NextToken: ADD_OP

Exit

Exit

NextToken: IDENT

Enter

Enter

NextToken: RIGHT_PAREN

Exit

Exit

Exit

NextToken: EOF

Exit

Exit

Exit

Press any key to continue . . .

--------------------------

Here's my code in progress.

using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks;

namespace RecursiveDescentParser {

class MainClass {

public static void Main(string[] args) { // Function expr parses strings in the language // Generated by the rule: -> { (+ | -) } void expr() { Console.WriteLine("Enter your expression: ");

// Parse the first term term();

while (nextToken == ADD_OP || nextToken == SUB_OP) { lex(); term(); }

Console.WriteLine("Exit "); }

void term() { Console.WriteLine("Enter ");

//Parse the first term factor();

// As long as the net token is * or /, call lex to get the // next token and parse the next factor

while (nextToken == MUL_OP || nextToken == DIV_OP) { lex(); factor(); }

Console.WriteLine("Exit "); }

void factor() { Console.WriteLine("Enter ");

//Determine which RHS

if (nextToken == ApplicationIdentity || nextToken == INT_LIT) lex(); //Get the next token

//If the RHS is (), call lex to pass over '(', call expr, and check for ')' else { if (nextToken == LEFT_PAREN){ lex(); expr();

if(nextToken == RIGHT_PAREN) { TypeLoadException(); }

else { error(); } } //End of if (next Token ==

else{ error(); }

}

Console.WriteLine("Exit "); } } }

term> ((* factor-) id l int-constant l ( ((* factor-) id l int-constant l (