TREES.C
#include <stdlib.h>
#include <stdio.h>
#define NUMB 256
#define NODE 257
#define INS 258
#define Lf 259
extern int yylval;


int symbol;
typedef struct _node {
	int key;
	struct _node *l, *r;
}node;

node *T();
node *E();
void print_tree(node *, int);
node *insert_node(int, node *);


void next_symbol() {
	symbol = yylex();
}

void error() {
	printf("Syntax error\n");
}



void parser()
{
	node *n = (node *)malloc(sizeof(node));
	n->key = 10;
	n->l = NULL;
	n->r = NULL;
	print_tree(E(), 0);
	if (symbol != '\n')
		error();
}

node *E() {
	node *res;
	if (symbol == INS) {
		next_symbol();
		res = (node *)malloc(sizeof(node));
		if (symbol == NUMB) {
			int toInsert = yylval;
			next_symbol();
			res = E();
			node *insertRes = (node *)malloc(sizeof(node));
			insertRes = insert_node(toInsert, res);
			return insertRes;
		}
	}
	else
		if (symbol == '(') {
			next_symbol();
			node *res2 = (node *)malloc(sizeof(node));
			res2 = E();
			if (symbol == ')') {
				next_symbol();
			}
			else
				error();
			return res2;
		}
		else
			if (symbol == NODE)
				return T();

				return res;

}

node *T() {
	node *res;
	if (symbol == NODE) {
		next_symbol();
		res = (node *)malloc(sizeof(node));
		res->l = T();
		if (symbol == NUMB) {
			res->key = yylval;
			next_symbol();
			res->r = T();
		}
		return res;
	}
	else {
		if (symbol == Lf) {
			next_symbol();
			return NULL;
		}
		else {
			if (symbol == '(') {
				next_symbol();
				res = T();
				if (symbol == ')') {
					next_symbol();
				}
				else
					error();
			}
			else
				error();

			return res;
		}
	}
}



void print_tree(node *tree, int level) {
	if (tree != NULL) {
		int i;
		for (i = 0; i < level; i++)
			printf("\t");
		printf("%d\n", tree->key);
		print_tree(tree->l, level + 1);
		print_tree(tree->r, level + 1);
	}
}

node *insert_node(int nr, node *tree) {
	if (tree == NULL) {
		tree = (node *)malloc(sizeof(node));
		tree-> key = nr;
		tree->l = NULL;
		tree->r = NULL;
		return tree;
	} else {
		if (nr < tree->key)  {
			tree->l = insert_node(nr, tree->l);
			return tree;
		}

		else {
			tree->r = insert_node(nr, tree->r);
			return tree;

		}

	}
}

void main() {
	next_symbol();
	while (symbol != 0) {
		parser();
		next_symbol();
	}
}





-----------------------------------------------------------
TREES.L
%{
	#include <stdlib.h>
	#include <stdio.h>

	#define NUMB 256
	#define NODE 257
	#define ins 258
	#define Lf 289
	int yylval;
%}

%%

[+()\n] 	{ return *yytext; }

[0-9]+ 		{ yylval = atoi(yytext);
		  return NUMB; }

"Node" { return NODE; }
"insert" { return ins; }
"Lf" { return Lf; }

%%