9. Convert the BNF rules into YACC form and write code to generate abstract

 syntax tree.

Certainly, I can help you with that. To convert BNF rules into YACC form and generate an abstract syntax tree (AST), let's consider a simple arithmetic expression grammar. Here's the BNF grammar for reference:

```

<expr> ::= <term> '+' <expr>

         | <term> '-' <expr>

         | <term>

<term> ::= <factor> '*' <term>

         | <factor> '/' <term>

         | <factor>

<factor> ::= '(' <expr> ')'

          | <number>

```

Now, let's convert these BNF rules into YACC form and include code to generate an abstract syntax tree. The abstract syntax tree can be represented using a struct in C.

```yacc

%{

#include <stdio.h>

#include <stdlib.h>

// Define the structure for the abstract syntax tree nodes

typedef struct ASTNode {

    char operation;         // '+' for addition, '-' for subtraction, '*' for multiplication, '/' for division

    int value;              // For terminals (numbers)

    struct ASTNode* left;   // Left child

    struct ASTNode* right;  // Right child

} ASTNode;

// Function to create a new node for the abstract syntax tree

ASTNode* createNode(char op, int val, ASTNode* left, ASTNode* right) {

    ASTNode* newNode = (ASTNode*)malloc(sizeof(ASTNode));

    newNode->operation = op;

    newNode->value = val;

    newNode->left = left;

    newNode->right = right;

    return newNode;

}

%}

%token NUMBER

%%

expr    : term '+' expr   { $$ = createNode('+', 0, $1, $3); }

        | term '-' expr   { $$ = createNode('-', 0, $1, $3); }

        | term            { $$ = $1; }

        ;

term    : factor '*' term { $$ = createNode('*', 0, $1, $3); }

        | factor '/' term { $$ = createNode('/', 0, $1, $3); }

        | factor          { $$ = $1; }

        ;

factor  : '(' expr ')'    { $$ = $2; }

        | NUMBER          { $$ = createNode('N', $1, NULL, NULL); }

        ;

%%

int main() {

    yyparse();

    // Further processing of the abstract syntax tree can be done here

    return 0;

}

int yylex() {

    // Your lexer code to recognize tokens and return them

}

void yyerror(const char* msg) {

    fprintf(stderr, "Error: %s\n", msg);

}

```

Explanation of key parts:

- `%{ ... %}`: This is the C code block that you can include at the beginning of your YACC file. It defines the abstract syntax tree structure and a function to create nodes.

- `%token NUMBER`: This defines a token named `NUMBER` which is used to represent numeric values.

- `expr`, `term`, `factor`: These are non-terminal rules in the YACC grammar that correspond to the BNF rules. The code following each rule constructs the abstract syntax tree nodes using the `createNode` function.

- `$$`, `$1`, `$2`, `$3`: These variables represent the value associated with different parts of the rule. For example, `$$` represents the value of the entire rule, `$1` represents the value of the first part of the rule, and so on.

- `yyparse()`: This function starts the parsing process.

- `yylex()`: You need to provide your lexer code here to return tokens.

- `yyerror()`: This function is called when an error occurs during parsing.

Remember that this example focuses on demonstrating the conversion of BNF to YACC and the creation of an abstract syntax tree. You would need to integrate this YACC code with your lexer and further process the generated AST for actual use.